FACIES 27 71-104 PI. 18-24 19 Figs. 4 Tabs. ERLANGEN 1992 Facies Belts and Communities of the Arctic Vesterisbanken Seamount (Central Greenland Sea) DFG·Schwerpunkl • BIOGENE SEDIMENTATION Rüdiger Henrich, Kiel, Martin Hartmann, Kiel, Joachim Reitner, Berlin, Priska Schäfer, Kiel, Andre Freiwald, Kiel, • Stefan Steinmetz, Bremerhaven, Peter Dietrich, Freiberg, • • .' • • • • • • ••• . " and Jörn Thiede, Kiel I • KEYWORDS: GREENLAND SEA - SPONGE BRYOZOAN MOUND - SPICULITE DEVELOPMENT - MICROBIAL BINDING - ARCTIC FORAMOL FACIES - BENTHIC COMMUNITIES - HOLOCENE , n und CONTENT Summary 1 Introduction 1.1 Regional setting and previous studies 1.2 Oceanography 2 Methods 2.1 Hydrosweep survey 2.2 Surveys with Ocean Floor Observation System 2.3 Detection of hydrothermalism 2.4 Sampling of sediments and organisms 2.5 Methods of fixing biological material 3 Results 3.1 Bathymetry of the Vesterisbanken Seamount 3.1.1 General aspects 3.1.2 Crest morphology 3.1.3 Slope morphology 3.2. Facies belts 3.2.1 The Crest facies 3.2.2 The Shallow slope facies 3.2.3 The Deep slope facies 3.3 Indications for hydro thermal activity 4 Discussion 4.1 Sediment dynamics 4.2 FOllllation of spiculites 4.3 Bryozoan ecology ' . 4.3.1 Species composition 4.3.2 Depth zonation, growth forms and adaptation to seasonal food supply 4.3 4.4 5 The vagile epibenthos Arctic mixed siliceous and carbonaceous deposits: the modem end members of the ForAMoL facies? Conclusions References SUMMARY The Arctic Vesterisbanken Seamount, situated far offshore in the central Greenland Sea, provides a unique facility for studying modem cold watersiliceous carbonate deposits. A nearly year round sea ice cover, which retreats on average only during two months, and a rather constant temperature and salinity structure of the water column characterize the Arctic conditions of the area. Despite predominantly oligotrophie conditions with a pronounced food supply from the pelagic realm only during the ice-free season, the seamount is covered extensively by extended sponge-bryozoan constructions. Three distinct facies belts reveal a pronounced depth zonation which depends on variations in downslope food transfer and which is specifically effective due to the development of a TA YLOR current regime over the seamount: i) the crest facies from the summit at -133m 10 -260 m, ii) the shallow slope facies from -260 m to -400 m, üi) the deep slope facies from -400 m down 10 the abyssal plain at about - 3.000 m. Different biogenie structures and communities are found within these facies belts, including widely extended biogenie mats, sponge bryozoan-serpulid buildups with mounds, hedges, spurs and flatcake-like structures, bryozoan thickets and sponge-crinoid mounds. Depth zonation, internal structure and controlling parameters in the fOllnation of these biogenie structures are discussed in the context of their significance as a modem end member of the Foramol facies and their implication for the fossil record. In addition, the younger volcanic and hydrothyrmal history of the seamount is presented with special reference to its bearing on Holocene bio genie colonization patterns. 1 INTRODUCTION Benthic communities on shelves and in near coastal areas are determined by a large variety of natural and anthropogenie constraints that exaggerate strong environmental stress on the organisms and thus effect specific survival strategies. Due to Addresses: Dr. R. Henrich, Dipl. Geol. A. Freiwald und Prof. Dr. J. Thiede, GEOMAR - Forschungszentrum für marine Geowissenschaften, Wischhofstraße 1-3, D-2300 Kiel 14; Prof. Dr. P. Schäfer und Dr. M. Hartmann, Geologisch- Paläontologisches Institut der Universität Kiel, Olshausenstraße 40-60, D-23oo Kiel 1 ; Dr. J. Reitner, Institut für Paläontologie, Freie Universität Berlin, Schwendener Str. 8, D- 1000 B erlin 33; Dr. P. Dietrich, Bergakademie Freiberg - Sektion Geowissenschaften, WB Hydrogeologie, Postfach 47 , D-9200 Freiberg; Dr. S. Steinme tz, Alfred-Wegener-Institut für Polar- und Meeresforschung, Columbusstraße, D-28oo Bremerhaven. 72 I a 2 <;( / -J / / / / / / / / • • • • • • • • • • • • • • • • • • • • • • / • / • • • 2 UJ • 75°N UJ er CJ • ~ " ./ ~ ~ § (j ~ ~ . ~ .. ., 0; " ',' ':.: .' l'U ". cY . . • • . " : '. " • • • • •• • / " / • • • • • • • , • • • • • • • • • • • • • • • • • • • • • • • · -• • • • • • • • • • • • • • • • • • , • • • • • • • • • • • • • • • • • • the complexity of these environmental constraints it is often hard to deduce principle factors that control the internal structure ofbenthic communities. In contrast, offs hore open ocean conditions are more strictly confined, thus providing a better chance for investigating controlling parameters of benthic ecosystems. As a consequence, open ocean sea- mounts are uniquenaturallaboratories forconducting studies on benthic ecosystems. In particular they provide facilities for: -- the study of variations in settling strategies and structures of benthic ecosystems in response to open ocean water mass characteristics and pelagic food supply. -- the investigation of colonization patterns of benthic communities on various substrates, e.g. soft bottom, firm ground and volcanic hard ground. • • • • • ~ ~ § (j ~ ~ qj ~ ~ &} '-CI) ~ • • • • • • • • • · .' • • • • • • • • • . . . . : . • • • • • • • • • • • • • • • • • \l • • • • • • • • , 75°N • , Fig. 1. Location of the Vesteris- banken Seamotmt (triangle) in the central Greenland Sea. Cir- culation of recent surface waters in the Norwegian-Greenland Sea and in the northeastem North At- lantic are indicated by black ar- rows. Extension of sea ice is in- dicated for a) mild summersitu ation (dashed line), and b) severe winter situation (dotted line) . -- the evaluation of the principle parameters that control depth-related zonation of otganisms. -- the deciphering of sea level changes in response to glaciaV interglacial climatic shifts from compositional changes in the topmost Holocene benthic communities and sediments. We report observations from an Arctic seamount, the Vesterisbanken, central Greenland Sea, made during the Arctic (ARK) VIIl1 expedition with RV POLARSTERN in June/July 1990 (Fig. 1). This volcano has a variety of pecularities. It is the only known Arctic seamount with Holocene, and possibly still ongoing, volcanic activity. Due to its position close to the polar front it is characterized by a strong seasonality in surface water regimes. On average, the area is covered nearly year round with a dense ice pack, which retreats westward for two months, most commonly 7 73° N 13° 25 ' '---!-0 __ N \ D 73 o ( • G r-QoI5 ' QOOO ' -" 8°45 ' ---"=.:.. '-'-_"--_w ____ ---'::::::::::::::::~~ Y_W~_=__~ '--__ . --'---'-~--:.../_W_'_'" "-". '-" ____ I Fig. 2. Bathymetric map of the Vesterisbanken Seamount based on hydrosweep transects during ARK VII/1 expedition with RV POLARS1ERN. Data-processing facilities are provided by the Alfred-Wegener-Institute, Bremerhaven. r during August and September. Because of these strong environmental constraints, ecological studies on the Ves- terisbanken benthic communities may provide us with a much better knowledge of Arctic benthic communities with exceptionally high population densities, survival strategies and benthic organism adaptations to episodic or continous food supply from planktic primary producers. 1.1 Regional setting and previous studies Vesterisbanken Seamount is an intraplate volcano in the south-western area of the Greenland Basin at 73°30' N and 9°10' W, approximately 280 km north of Jan Mayen and 300 km east of the East Greenland Continental Margin (Fig. 2). It is positioned on magnetic anomaly no. 19, which corresponds to an crust age of 44 Ma (ELDHOLM & THIEDE 1980). Vesterisbanken was first shown in a bathymetric map published by EGGVIN (1963). A first combined bathymetric, geological and geophysical survey was carried out during ARK 11 Expedition ofRV POLARSTERN in 1984 (AUGSTEIN et al. 1984). Results from seven sea beam tracks were integrated in a more detailed bathymetric map of the seamount (HEMPEL et al. 1991). This map shows a slighüy SW-NE-elongated seamount rising up from -3.100 m. The summit reaches - o 10 20 30 < -0 .25 oe 40 ~ E 50 - oe -60 Cl. GI 'C 70 "-GI -.. 80 ~ 90 100 110 bottom (m) 3081 Isotherms > 1.5 oe 449 606 308 Oe -0 .25 0 . 00 0 . 25 0 .50 1700 0 .75 1.00 1.25 1.50 , 75 Fig. 4. Uplifted isothelllls over the V esteris banken SeanlOunt give evidence for a TAYLOR cWlent regime. The data were compiled from 5 CTD-stations following the crest line of the seamount (compare with Fig. 5). 120+---------.-------------------~------------------~-------- CTD-sites 21878-1 21879-1 21888-1 21880-4 21885-2 1.2 Oceanography The oceanography of the Norwegian-Greenland Sea depicts steep E-W gradients in surface waterregimes, On the eastern side, the Norwegian Current, the northern prolongation of the GulfStream, carries warm saline Atlantic water to the high north Arctic region, while on the western side the Greenland Current (EGC) transports cold, less saline Arctic water to the south. The EGC is covered by a seasonally variable sea ice pack (JOHANNESSEN 1986, SWIFI' 1986). A wideareain thecentreoftheNorwegian-Greenland Sea is occupied by a mixed water mass, the Arctic surface water, with slightly higher temperatures and salinities than the EGC. When warm and salty North Atlantic waters become exposed to the cold autumn and winter atmosphere in the Greenland and Iceland Seas, they are cooled by complex interactive processes. This cooled water becomes dense and ultimately convects and sinks to the bottom. The newly formed deep water is weIl oxygenated and ventilated because it has just been in contact wilh the atmosphere. It flows southward across lhe sills of the Greenland-Scolland Ridge and forms North Atlantic Deep Water. The cold EGC moving southward along the Greenland continental margin is responsible for sea ice coverage al the Vesterisbanken site for most time of the year. The positions of pack ice boundaries are displayed in Fig. 1. A lemperature/salinily profile laken with a CTD-probe at site 21878-1 (about 15 nautical miles to the south of the summit of Vesterisbanken Seamount) is shown in Fig. 3. It illustrates the principal structure of the water column in the Vesterisbanken area lo -3000 m. The profile shows a tongue of low salinity water only 20 m thick with downwards increasing salinily and decreasing temperature (+0.3°C to- 0.9°C). This configuration reflects a typical summer situation with an influence of freshwaler from melting sea ice fields. This low salinity surface water lens floats on a 100 m thick layer of colder water that gradually increases in salinity and temperature wilh depth to a temperature maximum of + 1.1 °C at -110 m. Below this layer the temperature decreases continuously with depth while a nearly constant salinity (34.88 and 34.94 ppt) is found throughout the entire lower profile seclion. The minimum temperature (-1.0°C) is observed near lhe bottom at -3071 m. In alm ost stable stratified water masses a seamount obstacle creales distinct current regimes that are known as TAYLOR columns (TAYLOR 1923). This current regime is expressed by an anticyclonal downwelling vortex. Although we have no direcl observations from current measurements, there is other independent evidence for a TA YLOR column above the Veslerisbanken Seamount: -- The water temperature structure along a transect of CTD- sites across the seamount depicts uplifted isothenns over the summit (Fig. 4). -- Sea ice charts reveallhe ice edge with a typical bump in the area ofthe Veslerisbanken during those periods ofthe year, when areas north and south ar:e already ice free (VINJE 1985). Average ice conditions over the top of the seamount are much heavier than in surrounding areas, possibly indicating a trapping of ice over the seamount. 2 METHODS 2.1 Hydrosweep survey The bathymelric mapping of the Vesterisbanken Seamount was perfOl med during ARK VII Expedition in 1990 (TlUEDE & HEMPEL 1991) with a hydrosweep multi- beam deep-sea echosounding system recording the topography along a profile strip of ± 45° width. In order to get complete coverage, overlapping profiles were run , starting at the top along a spiral-like course around the seamount edifice. The raw profiles were processed on board to exclude offsels along the transecL 76 1'\0 _ • Fig. 5. Enlarged section of the crest line. The sites of OFOS tracks (truck line). TV -grabs (tri angle ). box corer (asterisk). and CfD-probes (square) are included. 2.2 Surveys with Ocean Floor Observing System A first visual mapping ofbouom features and ecology at Vesterisbanken Seamount was carried out with an Ocean Roor Observing System (OFOS). The OFOS was equipped with a black and white video camera. 4 floodlights. and a photo camera combined with flash. Film lengths for up to 800 slides (24 x 36 mm size) could be loaded. Kodak- Ektachrome 200 ASA colour slide film material was used. More than 1 ()()(} photos were taken along 20 km totallength of 7 OFOS-profiles on Vesterisbanken Seamount. An independent control of the real depth position was possible by hydrostatic pressure readings from a CTD-probe (Conductivity - Temperature - Depth) unit attached to the OFOS-frame. The mean ship speedduring video observation was around 0.7 nautical miles/h (equivalenttoO.3 and 0.4 mf sec). Based on the hydrosweep map, four OFOS surveys were made along the seamount summit to investigate topo- graphy-related sea floor characteristics and volcanic structures (Fig. 5). Two OFOS-profiles were run along the crest line over the summit of the seamount. Both profiles were started at the northeastem peak almost at the same point. Profile 21880-0 is facing downslope towards NE, while profile 21880-7 is facing downslope towards SW. Additional tracks were perfonned in the upper section of the NW-flank (profile 21887-0) and downslope the SW-crest (21891-1 A) starting from the southwestem summit peak. ThreeOFOS surveys (21883-0, 21891-1B, 21891-1 C) cover flank areas deeper than -400 m (Fig. 5). 2.3 Detection of hydrothermalism Physical parameters of water masses around a seamount may differ significantly from the surrounding areas. One of the scientific targets was the discovery of active hydro- thermalisms, indicated by anomalies in the water. Hydro- thermal activity is detectable by: - direct methods (visual observation) - indirect methods, a) recording of temperature anomalies and b) recording of geochemical anomalies in the water column. In order to study the principle water mass structure of the Vesterisbanken and to localize potential hydrothellJlal vents, CTD-profiles were run and water sampies were taken at 5 sites from the top region, flanks, and adjacent deep sea (Tab. 2, Fig. 5) with a rosette water sampier in combination with a CTD-device. A continous record of salinity, temperature, and hydrostatic pressure was received from each water column profile. A maximum of nine water sampies was able to be Laken at each hydrocast site. They were positioned mainly in the deepersections ofthe respective watercolumn . • The sites (Fig. 5) for hydrocast stations were chosen according to morphologic features and as near as possible to the OFOS-profile tracks. The water sampies were prepared on board for determination of manganese and methane in the shore-based lab. Manganese was measured by graphite- furnace atomic absorption after separation from saltcontent and enrichment by a factor of 40 (HruHMANN et al. 1989). For Tab. 2. Positions ofCfD-probe and hydrocast sites. Compare with Fig. 5. Station Bottom depth m 21878-1 3081 21879-1 449 21880-4 308 21885-2 1685 21888-1 606 Latltude N 73°15.00 73°28.68 73°31.10 73°35.70 73°30.00 Longltude W 9000.00 9°11.68 9°08.60 9°02.26 9°09.93 Station Latltude Longltude bottom N W depth (m) 21696-2 73°31.00 09°11 .1 235 21878-2 73°15.10 09°00.94 3.038 21878-3 73°15.33 09000.74 3.048 21880-3 73°32.80 09004.77 333 21882-1 73°35.52 08°23.80 3.169 21882-2 73°35.96 08°19.29 3.175 21886-3 73°32.29 09005.22 260 21892-1 73°44.05 09°37.52 3.125 21892-3 73°44.06 09°41.17 3.002 21885-3 73°35.86 09002.48 1.619 21891-4 73°27.43 09°16.34 727 analysing the methane concentrations, the gas-content was extracted from 1 I seawater on board using an ultrasonic degassing method (SCHMIIT et al. 1991). The extracted gas sampies were transferred to gas-tight glas vessels and measured after the expedition by M. SCHMITI" (Fa. "Geoche- mische Analysen", Lehrte) with a GC-system. 2.4 Sampling of sediments and organisms Sediments and organisms of soft-bottom and semi- stabilized rum ground were sampled with giant box corers (occasionally also grabs) and chain-dredges, which were mainly used to collect rock sampies from hard bottoms (e.g. pillow lavas). Some sampIes were made by using a large TV- grab. The adjacent deep-sea plain was sampled with a long gravity corer (Tab. 3). The determination of the benthos is based on underwater photographs, collected material from the seamount and from comparison with additional sampies from the Jan Mayen Ridge and the Greenland Fracture Zone. 2.5 Methods of fIXing biological material All collected organisms were registratedand immediately fixed. From large sponges (> IOcm) sm all pieces were cut off and fixed first with 4% glutaraldehyde solution in seawater buffered with sodium cacodylate and after 20 hours washed and preserved in increasing alcohol concentrations (30-50- 70%). Some sampies were post fixed with 2% osmium tetroxide for SEM and TEM studies. A large number of specimens were fixed in 10% fOIlualdehyde solution in seawater for two days and than preserved in 70% alcohol. Very big specimens were primarily fixed in 95% alcohol. The sponges are housed in the Institut für Paläontologie der Freien UniversitätBerlin, theremaining organisms are housed in the GEOMAR Institute in Kiel. 3 RESULTS 3.1 Bathymetry of the Vesterisbanken Seamount 3.l.1 General aspects The bathymetry of the Vesterisbanken area shows an isolated seamount clearly elongated in NE - SW direction (Fig. 2, 5). This prefered direction is underlined by the crest structure of the main edifice. About 15 to 20 side cones, elevating up to 500 m above their surroundings, cover the deeper flanks (e.g. at the -2.500 m to -3.000 m level) at sampllng devlce giant box corer giant box corer gravity corer giant box corer giant box corer gravity corer giant box corer giant box corer gravity corer TV-grab TV-grab recovery cm/kg 20 48 510 27 17 755 18 28 450 150kg 100kg • 77 Tab. 3. Listed sites and sampling device of the bottom sampling program on the seamount during ARK V/3a and ARK Vll/1 ex- pedition . . various places. The distribution pattern of side cones under- lines the general strike of the seamount, specifically in the southwestem region. The NE - SW striking morphologic features correspond to the lineation of magnetic anomalies in this area, suggesting a causal relationship between plate configuration and the pathways for ascending magmas. The main edifice of the Vesterisbanken (mean diameter about 28 km at the -2.800 m level) ascends from the 3.100- m-deep basin floor up to -133 m. No crater-like structures were found neither in the top area nor in the side cones. Slope steepness exceeding 240 is present over large areas of the seamount. Along the OFOS-profiles, vertical escarpments exceeding 10 m were found in several places. The volcanic material recovered from two dredge hauls during ARK II expedition consisted of basanite and trachyandesite (HÖRMANN & RAASE 1991). During ARK VIII 1 expedition 4 dredge hauls and 5 TV -grabs were run on the Vesterisbanken Seamount. The rock materi,d recovered represents fresh to slightly altered volcanics with a high proportion of phenocrysts in fine-grained matrix with rare glass. The volcanics can be grouped into a basanite-tephrite series and an alkalibasalte-trachybasalte-mugearite series following the classification ofLE BAS etal. (1986). The suite of rocks is typical of intraplate lavas, which are characterized by a high enrichment of incompatible elements (HAASE et al . in prep.). 3.l.2 Crest morphology The NE - SW elongated summit shows two morphologic highs with the topmost poin~ at the southwestem head -133 m (Fig. 5). They are separated by a 55-m-deep saddle. The summit reveals a relatively smooth morphology along the crest line, while steep inclined slopes occur perpendicular to the crest line. The rather smooth relief of the seamount top could have resulted from intensive tidal abrasion during maximum glaciation (e.g. isotope stage 2, FAl"RBANKS 1989) when sea level was lowered by -130 m, exposing the seamount proper in the intertidal zone. If this is correct, no major volcanic eruptions could have affected the top region of the Vesterisbanken later on during the Holocene. A general feature in all crestline OFOS tracks is the gently undulating morphology to the -300 m level. 3.1.3 Slope morphology The steepest inclinations occur on the SE as weil as on the NW flanks between -300 and -2.000 m. Nearly vertical 78 escarpments exceeding 10m were found atseverallocations. These escarpments consist of sharp-edged block lava or sheetflows; in some cases pillows may be seen. Except for these short escarpment sections, however, the hardrock basement is covered by volcanoclastic sediment (grey to black ash to cm-sized lapilli material) often mixed or altemating with ftne-grained pelagic sediments. A thin sediment cover is present along most sections of steep slope sections. Weak undulation and mini-escarpments of the basalt floor can often be traced under the faint sediment cover. Uncovered black basalt surfaces occur at several sections of the steep profiles, but only over short distances. Most of the outcropping basalts look relatively fresh. However, grey-olive weathering crusts frequently outcrop along profile 21887-0. 3.2 Facies beIls A pronounced faunal zonation exists at the present-day in the carbonate- and silica-producing organisms. The zonation is expressed by distinct benthic communities, growth forms, and population densities that are clearly alined along the seamount flanks: 1. The Crest facies, ranging from -133 m to around -260 m which arecomprised of extensive biogenic mats and mounds constructed by sponges, bryozoans, serpulids, and hydrozoans and occasionally semi-stabilized sandy mud areas. - -- -'- - - .. .. - - -,-- . . ". ... '" : . " . . . . . '. . . \(1/(1' ~ Firm ground Volcanoclastlc deposlts Carbonate sand BIogenie mats and hedges Sponge bryozoan mounds Cyclopecten NE Schaudlnnla Hyalonema Caulophacus Octocorals Ascldlans Crlnolds Actlnlans 2. The Shallow slope facies, ranging from -260 m to approximately -400 m is occupied by pectinid bivalves, echinodeI IIlS, and epibenthic polychaetes existing on a semi- stabilized sandy mud. Small sponge-bryozoan mounds are present on morphological highs. ' 3. The Deep slope facies, ranging from :.400 m to -3.000 m is characterized by soft-, ftrlll-, and volcanic hard grounds with different sponge and crinoid communities. The adjacent Abyssal plain facies is characterized by soft- bottom communities (benthic fpraminifera, sponges) and a large admixture from planktic organisms. 3.2.1 The Crest facies The top (-133 m to -260 m) of the Vesterisbanken Sea- mount is almost entirely covered by biogenic material. Over wide areas a dense biogenic mat composed of a close meshwork of large, mostl y long-shafted sponge spicules and branched bryozoan fragments forll1s an alm ost continous sheet on the sea floor (Figs. 6-8). Dark, ftne-grained, microbe- rich sediment is trapped within this network. Light-coloured sandy muds with abundant planktic and benthic foraminifers locally cover the biogenic mat and ftU small depressions on the sea floor. At the surface of the biogenic mat and on the sediment-covered areas, a close arrangement of chimney and/or crater -1 ike structures is visible on most photographs. These paired openings are related to filter-feeding endo- benthic ascidians. The stable spicule meshwork of the biogenic mat is an ideal substrate for ftxosessile benthic organisms. Because of heavy ice conditions only a single in-situ sam pie is available from the crest facies of the Vesterisbanken Seamount. At a ridge north of the western part of the Jan Mayen Fracture Zone a similar facies was sampled at -509 m (Box core GIK 21877). This spiculite mat exhibits a number of unique features most of which 100_21880-0 Geodia/Then ea/Sc haudin nla - small flat spange mounds 160- 22 -~ o m o 280- z r-- CI) 340- 400- depth (m) • r-- Shallow Siope Facies spongel bryozoan mounds and hedge. on elevated topography sandy mud bottom 3.000 2.400 sandy bollom Crest Facies 1 .800 1.200 t .pot-lIke hydrothermal Indlcatlons 600 profile length (m) , Fig. 6. Bathymetry and facies distribution along OFOS-track 21880-0, northem crest section. NE 110- 1 60 := "': !Iat cake sponge mounds ,... . o domlneted by Thenea, o ectinien. Crest Facies SW Shallow Siope Facies • := Il) -• '" o o '" o 79 Fig. 7. Bathymetry and facies distribution along OFOS-track 21880-7, southwestem crest sec- tion. For legend see Fig. 6. 2 1 - ~ Geodis, and Schsudinnis z Il) CD dense bryozoen thlckets on Thenea, z CD '" • o M o M ,... • 260- -M o M ,... end Schaudinn/a communities 290- depth (m) o • 21880-7 400 800 resemble many of the pecularities of the biogenic mat from the Vesterisbanken Seamount (pI. 23/1-2). The spiculite from the ridge top contains only small quantities of incorporated sediment. We suppose that sea water continously percolates through the spiculite pore space. The spicules are often completely covered by microbes (pI. 23/3-4). These microbes are capable of binding sediment particles within the spiculite meshwork. In addition, the spiculite mat has numerous small, several cm-sized cavities which are inhabited by a specific cryptic fauna with small sponges, bryozoans and benthic foraminifers (pI. 2313-6). Another irnportant observation is that sponge larvae settle on spicules, preferentially in the interior parts of the mat (pI. 23/5). As 200 400 S Crest Facies := ,... ... • ;- sendy mud bottom ~ wlth apongel bryozoan mound. z N CD • 0 M 0 Shallow Siope Facies aandy mud bottom with small blogenic mals 1 .200 bottom aandy bottom with onuphld worm • 1.600 profile length (m) these sponges grow, they push up the spiculite mat Because of the protection of the spiculite meshwork and the specific taphonomic conditions inside the mat, the sponges may be preserved alm ost in-situ after death. In summary, the pecularities of the spiculite mat provide us with an excellent example of how autochthonous spiculites can fOlm in-situ near the sediment surface. The only box core (GIK 21696-2) from the crest facies was taken during the ARK V13a expedition of RV POLAR- STERN in 1988. The box core was recovered from -235 m at 73°31'N and 09°11.1'W (Fig. 9), a position near the lower boundary of the crest facies. The vertical profile reveals three depositionl\l units: the surface layer with a 10 cm thick Deep Siope Facies Sponge bryozoan mounds Sponge - crinoid mounds , N := ,... .., - -o '" o z o o • M ,... acorillceou. bottom wlth pillow. end escarpment N M o M ,... 600 depth (m) o 21887-0 -- 80 0 on pillowB sponge/crinoid communities, actinians on sandy, mud acoriaceous boUom bottom. with actlnlans _ 1 .600 2 . 400 profile length (m) Fig. 8. Bathymetry and facies distribution along OR>S-track21887-O,north- weste! 11 slope. For legend see Fig. 6. 80 biogenic mat; below it a thin volcanoclastic layer (thickness 0.5 to 2 cm); and a Cibicides-sand layer at the base at least 12 cm thick (pI. 22/2). The overall construction of the Uppellllost biogenic mat is similar to that found on the ridge north of the western J an Mayen Fracture Zone. Both mats show a dense meshwork of sponge spicules and branched bryozoan fragments. Never- theless, there are major differences in the specific composition of the biogenic mats. While the mat from the ridge north of the J an Mayen Fracture Zone is elearl y dominated by sponge spicules bound by microbial activity (see above), the living surface ofthe biogenic mat sampled from the Vesterisbanken Searnount is composedmainly ofliving hydrozoan-bryozoan thickets and a few serpulids that colonize the spiculite mat below. Hydrozoan colonies as weIl as surfaces and rootlets of branching, weakly calcified colonies ofbryozoans (Notoplites normanni, Tricellaria gracilis) are colonized by Cibicides lobatulus and other bryozoans. The living bryozoan fauna also ineludes species with a dendroid growth f01l11 such as Palmicellariaskenei, withreticulatecolonies such asSertella elongata , and encrnsting forms (Cribrilina watersi, Schizo- porella porifera, Smittina glaciata). In addition, species such as Hornera lichenoides, Tessaradoma gracile, Crisia sp .• Porellaplana,Porelia compressaand tubuliporid species occur as complete colonies and colony fragments within the biogenie mat. Another important observation is the high percentage of iron/manganese-stained bryozoan branches in the deeper meshwork below the living surface in the Vesterisbanken sampIe, possibly indicating a long period of exposure at or near the sea floor. However, because of the limited number of sampIes from both regions, the relevance of the com- positional differences of the Vesterisbanken mat and the mat , 0 E " . 20 v 21696-2 (-235 m) . ' .' .' • • ...... .- .:.;:.:: · ",' ',' .' .' .' · ..... . · . . .' .' . · .... .- :.',:,', .'. · . .- . .- :. : . .- .' .' . · .. .' .. : . · . . . . · .: .. : .. .' " : " .- · '. . ". . . ,..:.; · '. . . '. . . . · '. '. · ",' " . · " .". .' ;,'; . '; • • • • • • : .. .' .. : . ', . '. .. :.'::.': :. '; '.:';'.:'; · " .' " .- . .' . : . .- .' .' . · . .' .: .. " .- " .- .' .' .' '. '. :. : . .- .' .. . · . . . . · .. '. · '.' ' .. .. .. .. .' . .' . . Components / " Bryozoans ~ ~ Foraminllers ",""" Bivalves ~ Sponge spiculae V V v I Volcanoclastlcs Texture ~ Blogenie mal ;-:J"" •• '. o •• .;;; .......... .. ... .... oe. 0" ". :.'. :.",:," . .':. : -: . : ... ..- . ," . .'. :. .. . Gravel Sand .. ....... Mud -- , .. .. -. Fig. 9. Depositional uruts and sediment textures ofbox core 21696- 2, southwestelll slope, crest facies at -235m. on the ridge north of J an Mayen cannot be elearly detennined. It may be related to either local variability in composition of the matcaused by therelative proximity toa sponge buildup, or it may indicate fundamental differences in the fOllnation of the mats. The thin volcanoclastic layer is almost exelusively composed of rather fresh basaltic lapilli indicating a short period of volcanic activity. The basal unit is a bioclastic sand layer with a high proportion of the benthic foraminifer Cibicides lobatulus (27.3 wgt. %), bryozoan fragments (20 wgt. %) dominated by heavily corroded and iron/manganese-stained Palmi- PI a te 18 Vesterisbanken Seamount - Sponge bryozoan mounds and biogenie mats from the crest facies Fig. 1. A seetion of a flat sponge bryozoan mound from OFOS track 21880-0 at -185m. "Core" sponges, such as Thenea cf. muricata (TH) and Geodia (G) rest on and within a rigid biogenie mat constructed by branched bryozoan fragments and sponge spiculae. The large core sponge in the central part of the photo is laterally colonized by bryozoans, Schaudinnia (S), and brittle star. Core sponges living within the biogenie mat cause updoming effects of the mat during growth (compare with PI. 6/5). Additional faunal elements of the bio genie mat are endobenthic ascidians (ENDAS). whose paired openings are visible ~ small black dots on the mat surface. The surface itself provides habitat for lyssaeine hexactinellid Schaudinnia rosea (S) and for yeIlow poeciloselerid (P) ernsts (Mycale?). Furthermore, actinians (A), serpulids, brittle star and starfish complete the associated fauna. In the upper right corner a bryozoan fan is visible and a residual body (SR) of Schaudinnia is present in the upper left corner of the photo. The size of the photographed section is about 2 m2• Fig.2. A section of the biogenie mat with scattered sponges (poecilosclerid ernsts (P), geodüds (G» and bryozoan overgrowth from OFOS track 21880-0 at -155 m. The biogenie mat is densely colonized by endobenthic ascidians (ENDAS). The yellowish haloe in the upper central part is a hydrothelmal emanation. The size of the photographed section is about 1 m2 • Fig. 3. A section of a flatcake sponge mound from OFOS track 21880-7 at -172 m. In contrast to the sponge bryozoan mounds (see PI. 1/1) this mound type is fOllued by numerous, but flatcake-like Thenea (Th). In general, the flatcake sponge mounds cover areas of up to 10 m2., whereas sponge bryozoan mounds are smaller (1 - 3 m2). The mound surface is colonized by bryozoans, actinians (A), serpulids, small poecilosclerid ernsts, and Schaudinnia rosea (S). The size of the photographed section is about 2 m2 • Plate 18 81 • 82 cellaria skenei colonies, bivalve fragmenLs (10 wgt. %), planktic foraminifers (8.6 wgt. %), sponge spicules (3.8 wgt. %), and admixtures of radiolarian frustules, ptero- pods, ophiuroid ossic1es and serpulid remains. About one quarter of the partic1es are non-biogenic, predominantly of volcanoc1astic origin (21.2 wgt. %). According to its com- posiLional variability and the good sorting, this bioc1astic sand layer is c1early a currenL deposit with sediment input from varioussources(volcanoclastic, various benthic habitats and surface waters). A variety of autochthonous biogenic constructions have developed on the biogenic mal. Based on the information from the OFOS tracks, the following construction types of the biogenic buildups are evident: A) Sponge supported buidups -- small sponge-bryozoan-hydrozoan-serpulid mounds (\-3 m2 in size) -- Oatcake-like sponge-bryozoan mounds (about 10 m2 in size) --elongated sponge-bryozoan hedges and spurs (several meters to tens of meters in length) B) Bryozoan supported buildups -- extended bryozoan-sponge thickets C) Colonization of the semi-stabilized sandy mud -- Actinian-serpulid-poecilosc1erid sponge meadow. The remaining areas between the buildups are covered by calcareous sandy muds and sand with abundant planktic and benLhic foraminifers. A patchy concentration of foraminifers and other coarse particles indicates bottom currentactivity and winnowing offine-grained deposits. On these rather instable sandy botloms, a patchy colonization by actinians and serpulids is developed at severallocations. A high population density of starfish and brittle stars is characteristic in all buildup types of the crest facies. Small nat sponge-bryozoan-hydrozoan-serpulid mounds • Small Oat mounds of 1-3 m in diameter are very common within the uppermost benthic zone. They do not rise more than 0.5-1 m above the sedimenL surface. In mostcases, these mounds have a core of large domed demosponges of the Geodia-, Stelleta-, and/or Thenea-type (PI. 18/1, Fig. 10). These ball or ovate sponges secrete rigid organo-spicular skeletons. The tetraxone megascleres are long (> 1-2 cm) and occur within derll1al layers of large microscleres (sterraster) in geodiids. The size of these sponges varies between 5-50 cm; in some <;:ases, giant specimens of more than 1 m were observed. Within the Thenea specimens giant forms are a combination of genetically similar buds which are f used together and lose their individual shape (STEENSTRUP & TENDAL 1982). The most common sponge taxa in the mound core is Geodia barreui. Mature specimens are up to 50 cm diameter and approximately 30 cm height. Thenea cf. muricata with a maximum size of30-50 cm and long root-like protrusions at the base is also very common. The margins of these large domed sponge assemblages are inLensively overgrown by a diverse bryozoan fauna with a variety of different colony growth forms, long-shafted calcitic serpulid wonn tubes,and hydrozoans. Dredge sampIe GIK 21880-5 Laken from -180 m to -331 m reveals a predominantly fresh bryozoan fauna that is dominated by Diplosoien intricarius,ldmidronea atlantica var. gracillima, Palmicellaria skenei. Sertella beaniana, and the encrusting species Cribrilina watersi. All other species, such as diverse tubuliporid cyclostomes, Hornera lichenoides. Sertella elongata and others are of minor abundance. The associated sponge fauna ischaracterized by whitechimney-like Iyssacine rossellid hexactinellids ofthe taxon Schaudinnia (S . rosea). Very common in the vicinit)' of the core sponges are small (2-5 cm) yellow to grey ball-shaped Geodia specimens. P I a te 19 Vesterisbanken Seamount - Communities and sediments of the crest and shallow slope facies Fig. 1. A section of sponge bryozoan hedges and spurs in the crest facies (OFOS track 21880-0 at-152m). More than 10 m long spurs and hedges of dendroid, reticulate, and probably articulate bryozoan colonies (BRY) are alined perpendicular to the direction of slope inclination. The spurs rest on a biogenic mat which is colonized by small core sponges (CS), geodiids (G), actinians (A), and serpulids. The size of the photographed section is about 2 m2 • Fig. 2. A section of an actinian poccilosclerid sponge meadow in the crest facies (OFOS track 21880-7 at -182m). Patches ofcalcareous sand are colonized by actinians (A), branched poecilosclerid (P) Clathria, and serpulids. The size of the photographed section is about 3 m2 • Fig. 3. A section of a small sponge bryozoan mound in the shallow slope facies (OFOS track 21880-0 at -283m). The core sponge in the upper leh is intensively overgrown by a bryozoan colony (BRY), probably by Sertella elongata. The volcanoclastic sediment is colonized by Cyclopecten (CP), Thenea (TH), Geodia (G), poecilosclerid Clathria (PCL), and yellow poccilosclerid sponge crusts (Mycale?) (pY). The size of the photographed section is about 1.5 m2 • Fig.4. Dark volcanoclastic sediments in the shallow slope facies (OFOS track 21880-0 at -325m). The semi- stabilized substrate is densely colonized by Cyclopecten (CP), terebellomorph onuphid polychaetes (TBP), starfish (Solaster ),and brittlestar(Ophiopleura). Small bryozoancolonies (BRY) areattached to volcanoclastic pebbles. Not identified sponges (SP) and serpulid worm tubes are also presenl. The size of the pholographcd section is about 1 m2 . Plate 19 83 • • 84 Geodia - Thenea - Schaudinnia - Bryozoa community (sm all flal spange maun") A • . , ," ) • , - • • , ,. . .: (/ ' . ..... y . > :I' . \ -~ . ~, <\ ~-:,.: . I. . _ c·····. ;- ' ~l , .' :.', r ' .. ,~ .,. \' . . ' . • • • • • • • ~'~ .. ~ . . '" . [ ·',e . . ' .' ,-.". : ."' " . , . , . : \'. • ,;,~': :' .. i r .. -' .. , . .,.) , I " . " A: aclinlans BRYB : bryozoan bushes BRYF: bryozoan lans G: small Gaodia • - . . , ~, .. , ".""" , ~ ; \. " . ' . , .. ' ,. . 0 1 O. .. - •• 00': ' . ) , . '-i . .. " ••• . .::....- -' •• • ., , . . !, '. . '"" . • • ' • • ' '.Q~ SS - ' ''1, " ' • • • -0" u .. , ' . 0 o' .' . .. '- . S: Schaudlnnla (rosselld hexaclinellid s) SERP: serpulid worm lubes 55 : sea stars 0: brillie slars TH/G : Thenea, Gaodia "core"-sponges PY : poecllosclerld yellow spange crusts , "' . l u .. p ,. ~ ) d .,.' .... . ~ .':V . -- •• ' .. . . '. ' . G' ' . . " . 00 .' ••• • .. 50 40 - 30 20+ 10 . . ' •• . ~ " " - ' Small flal sponge mound (21880-0) seelion: 2 sqm; n = 205 16 pairs 01 ascldian openings/0.5 sqm ---.: I liller leeders tentacle reeders Tli / G G S PY SERP A,llRYI'ßRYH 0 55 Fig. 10. Small flat sponge mound with statistical analysis of functional fecding groups for a representative sector in the crest facies (see PI. 18/1 ). Their grey colour resullS from finely grained organie "Ouff' which is baffled by protruding spicules, Smaller pale yellow ball-shaped sponges may be related to the taxon Tethya, In addition, scattered bright yeIlow, small sponges form irregular crusts on the top of the spicule meshwork and core mound sponges. These crusts are related to the poecilosclerid taxon Mycalidae. Specimens of Tetilla and Polymastia with the charactcristic papillae and white ball-shaped Suberites sp. with a single prominent oscular opening are present, but rare. Flatcake sponge-bryozoan mounds In contrast to the small flat mounds which exhibit one or two domed core sponges, the flatcake mounds exhibit PI a te 20 Fig.l Fig. 2, Fig. 3. Fig.4, Vesterisbanken Seamount - Crest and decp slope bryozoan sponge thickelS and sponge crinoid communities • A section of a bryozoan sponge thicket in the crest facies (OFOS track 21880-7 at -197m). Between -170 to -200 m, adense bryozoan thicketcovers the substratecompletely. Bryozoans (B~Y) aredominated by Serte/la elongata which forms erect reticulate fans. Poecilosclerid Clathria (PCL), actinians (A), and serpulids live in this thicket. The size of the photographed section is about 2 m2• A section of a sponge bryozoan mound in the deep slope facies (OFOS track 21891-IA at -450m), The core ofthese deep slope mounds are Thenea (TH) and Geodia (G) sponges. The mound surface iscolonized by large poecilosclerid Clathria (PCL), yeJlow poecilosclerid crusts (Mycale?) (PY), Schaudinnia (S), fan-type bryozoan colonies (BRY), and serpulids. The size of the photographcd section is about 2 m2• A section of a bryozoan thicket in the deep slope facies (OFOS track 2 1891-1 C at -1 ,OO8m). The deep slope bryozoan thickets (BRY) are dominated by slender, dichotomously branching and reticulate growth forms, probably Idmidronea atlantica var. gracillima and Serte/la elongata, The bryozoan thickets are associated with geodiid sponges (G), actinians (A), and large, blue ascidians (AS). The size ofthe photographed sec ti on is about 1.5 m2 , A decp slope sponge crinoid mound (OFOS track 21891-1C at -767m), Lava blocks provide hard grounds for settlement of Schaudinnia (S) aggregations. Thc chimney-like sponge is often used by f-1eliometra glacialis (HG) to get in elevated feeding position. The sizc of the photographcd sec ti on is about 1,5 m2• PI a t e 20 85 • • 86 numerousdomedcoresponges(Fig. 7,PI.18/3). Themounds are therefore larger (10 m diameter). The fixosessile benthic communities are similar in diversity and distribution to the smallflat mounds. Sponge-bryozoan hedges and spurs TotaIly different in morphology to the mound structures are long (more than 10 m) elongated spurs fOllned by ag- gregates of large domed core sponges that occur on the top plateau of the seamount (Fig. 6, PI. 19/1). These spurs are oriented longitudinally to the seamount slope. They are partly interrupted and resemble the overall morphology of ripple fields. The geometry of the elongated spurs reflects the predominant arrangement of domed sponges in long rows. The spur crests are densely covered of small bryozoan colonies. As can be judged from the photographs, the bryozoan fauna consists of a variety of dendroid, reticulate, and probably articulate taxa. As inferred from comparision with nearby bryozoan-hydrozoan communities, the spur crestcommunity mayaIso include hydrozoans. Conspicu- ous, however, are the low numbers oflyssacinehexactinellids in comparison to sponge-bryozoan mounds. Long-shafted serpulid worm tubes are also present. The initiation of these spurs is unclear. It might be related to earlier boltom current activity that caused the formation of ripple fields in the topmost region of the seamount, or it might retlect surface flow structures of lava sheet flows. Once created, the relief of the spur crests provided favorable conditions for filter- and tentacle-feeding fixosessile benthic communities. ßryozoan-sponge thickets An accumulation of den se bryozoan meadows was observed on a steep margin at -170 m to -200 m (OFOS track 21880-7, Fig. 7). The bryozoan colonies grow on large core sponges and on the flat seatloor, often covering the substrate completely (PI. 20/1). Judging from photographs, the bryozoan fauna seems to be dominated by Serte/la e/ongala forming prominent upright reticulate fans. Additional taxa are lyssaeine hexactinellids (Schaudinl']ia rosea), serpulids , branched white haplosclerid demosponges, and yellow irregular poecilosclerid demosponges (Mycale?) attached to bryozoan colonies. Actinians were rarely found in this subfacies. Endobentic activity, indicated by open tubes in the substrate, was observed only locally. Actinian-serpulid-poecilosclerid meadow OccasionaIly, an actinian cluster is seen on a thin cover of calcareous sand (Fig. 7, PI. 19/2). Actinians and serpulids dominate this facies. Additional faunal components are branched white, poecilosclerid Clalhria, rare geodiids and few lyssae ine hexactinellids (Schaudinnia sp.). 3.2.2 The Shallow slope facies The upper flanks of the Vesterisbanken Seamounl are covered by sediments and small biogenic buildups of lhe shallow slope facies from -260 m lo approximately -400 m. MOSl characleristic of this facies belt is a high abundance of thin-shelled valves of Cylclopeclen imbrifer and Cyclopeclen graui (PI. 19/3-4). The seatloor over wide areas is smooth and covered by semi-stabilized sandy mud bOllom and/or dark fine-grained volcanoclastic sediment. Small elevalions locally rise from the steeply inclined but smooth-struclured seatloor and are colonized by sponge-bryozoan buildups. In addition, small sponge-bryozoan mounds are randomly scallered on the sand and sandy mud bOlloms. The basaltic basemenl crops out only occasionally at lhe surface. From Lhe OFOS-underwaler TV records and colour slides there is Lhe overall impression thaL volcanic strucLures on the upper flanks ofLhe VesLerisbanken are more eXLensively buried by a volcanoclasLic-bioclastic sedimenL cover of variable Lhickness than allhe LOp. Vertical successions of Iithologic uniLs from Lwo box corers support Lhis assumpLion: (I) Box core GIK 21886-3 (Fig. 11), recovered al -260 m from the northeasLern flank of the seamounL contains lwo sedimentary units, both of which conLain brownish mixed • PI aLe 21 Vesterisbanken SeamounL - Deep slope sponge communiLies Fig.1. Hyalonema-Rosselidae-Cladorhiza-Thenea communily (OFOS track 21883-0 aL -1.684 m). The sponges (amphidiscophorid hexactinellid Hyalonema (HY), rosselid hexaclinellid SchclUdinnia (S), poecilosclerid Cladorhiza (CL), and Thenea (TH) core sponge) setLle on a pillow lava block. In the upper righL corner, a downslope volcanoclastic mass flow sediment is visible. The dislocaled pebbles are colonized by rapid growing actinians (A). The size of Lhe photographed seetion is abouL 1.5 m2• Fig.2. Hyalonema-Rosselidae-Cladorhiza-Thenea community (OFOS track 21883-0 aL -1.631 m). Only the steep inclined margins of the lava block are colonized (abbreviations sec PI. 4/1). The size of the phoLOgraphed seetion is about 1.5 m2 • Fig.3. Hyalonema-Rosselidae-Cladorhiza-Thenea community (OFOS track 21883-0 aL -1.715 m). The communily colonized an isolated lava block. The strange poecilosclerid Cladorhiza (CL) is weil visible in the center. Small depressions on the lava block are covered by a thin veneer of sand enriched with Pyrgo (PT) (abbreviaLions see PI. 4/1). The size of the phoLOgraphed section is abouL 1 m2 • Fig.4. Caulophacus-Hyalonema-Cladorhiza-Thenea community (OFOS track 21883-0 at -1.850 m). The lyssaeine hexactinellid Caulophacus arclicus grows on Thenea (TH). The basal parts of the funnel shafts are dark grey, resembling residual structures. Abbreviations see PI. 4/1. The size of the photographed section is about 2 m2 . Plate 21 , • > ::I: 87 88 21886-3 (·260 m) v E <> 2 6 1 0 21880-3 (-333 m) -.,...,~ ~":Z::: .. :. --'--' -'- ""-'-~ ' ... ' . V v "v v·· ..... :· v v . . ' . . : . '.' .' v v v v'" V v .... · vv v I/ v::- v v Vvvv/ ••• Fig. 11. Depositional units and sediment textures ofbox cores from the shallow slope facies. northeastem slope. Legend see Fig. 9. biogenic-lerrigenous sandy mud. The 6-cm-thick surface layeriscomposed predominantly ofbenthic (28 wgt. %)and planktic (27.7 wgt. %) foraminifers. Other important com- ponents are valves and shell debris (20.7 wgt. %) of Cy- clopecten, Limatula and branched bryozoan fragmenls (13.7 wgt. %). Among the lauer, Tubulipora cf. ventricosa is lhe mOSl common species, followed by Sertella elongata. Tessaradoma gracile./ dmidronea atlantica var. gracillima. Hornera sp., and Palmicellaria skene i. In addition, rare fragments of species such as Porella plana, Porella aperta. P seudoflustra sinuosa. Leieschara subgracilis, and lhe encrusting species Schizoporella thomsoni and Disporella sp. complete the bryozoan fauna. Minor amounls of sponge spicules (4.4 wgt. %) and volcanoc1astic componenls (5.5 wgt. %) also occur. The underlying biogenic layer shows a c1ear pre- dominance of branched bryozoan fragments (47.4 wgt. %). Shell debris (25.5 wgt. %), inc1uding Cylclopecten and Limatula, planktic (10.9 wgt. %) and benthic (7.9 wgt. %) foraminifers and sponge spicules (7.5 wgl. %) are found in considerably loweramounts, and volcanoc1astic components (0.8 wgt. %) occur only as admixtures. Both sedimentary units display about lhe same spectrum of parlicles, which are derived from various sources. Sponge spicules and branched bryozoan fragments can be relaled to sponge-bryozoan buildups. Planktic foraminifersare supplied from surface waters. Benthic foraminifers contain a high proportion of epibenthic species which are lypical of the sponge-bryozoan buildups. In addition, there is lhe volcano- clastic source from lhe seamounl itself. In conc1usion, most ofthe particles are nOl embedded in- si lu but are deri ved from downslope transport and/or bottom currenl activily. The composilional variabilily ofbolh units indicale variations in supply from differentsources. Because ofthe high percentageof coarse partic1es, both unitsrepresenl semi-stabilized sandy mud bottoms. A variable balance of processes explains the differenlial compositions, e.g . downslope transportof fine-grained partic1es (predominantl y lerrigenous mud), vs. partial infiltration of fine-grained sediment in the organic meshwork and winnowing of fine material al the surface by bouom currents. (2) The second box core (PIK 21880-3) was recovered al- 333 m from a more soulherly position on the northeastem flank of lhe seamount. Despile its proximily lo lhe firsl box core sampIe, il depicts a differenl lilhologic composition (Fig. 11). The vertical profile shows three depositional units from lOp LO bOllom: 1. Unil A, a surface layer a few millimelers thick with abundanl planklic and benthic foraminifers, valves of Cyclopecten, ophiuroids and agglutinating onuphid polychaeles in addition lo dark volcanoclastic grains. The dark sedimenl surface exhibilS biolurbation where while foraminifer sand was dislurbed by endobenthic organisms. About 90% of lhe isolated valves of Cyclopecten are agglulinated by an erranl onuphid polychaele. The valves are fixed on lhe organic worm lube wilh lhe convex side oUlside. Each single tube has not more lhan five isolated valves on the dorsal and ventral sides. Aparl from proleclive advantages, this agglutinating mode probably has lhe function of a ski to enlarge the contact-area to lhe semi-stabilized boltoms. 2. Unit B is a 6-cm-thick pyroclastic sand (61.2 wgt. %), which contains considerable amounts of planktic (22.8 wgt. %) and benthic foraminifers (12 wgt. %) and a small amounl of sponge spicules (3.9 wgt. %). 3. Unil Cis a mixed sandy biogenic and volcanoclaslic mud with 33.9 wgt. % of volcanoclastic components, 20.4 wgt. % bivalve debris (mostly Cylclopecten), 19.5 wgt. % sponge spicules, 13.2 wgt. % planktic foraminifers, and 13 wgt. % benthic foraminifers. In a comparison of both cores lhe presence of a 6-cm- lhick volcanoc1astic layer near lhe surface is striking. We infer, that during a relatively young eruption lhe seamount had been covered wilh volcanoclastic deposits. Later on, the volcanoc1astics were eroded in wide areas and dispersed by downslope transport. ' MOSl of the biogenic buildups in the shallow slope facies are similar lo lhe buildups of lhe cresl facies. Within OFOS track 21891-1A a sponge-bryozoan buildup wilh a typical Geodia-The nea-S c haudinnia-bryozoan comm uni ly is PI ale 22 Fig. 1. Veslerisbanken Seamounl - SedimenlS Fig. 2. Surficially cemented volcanoc1astic mass flow at -1.150m. The sizeofthe pholographed section is about 3 m2 • Cibicides sand underlying a biogenic mat in the crest facies (box core 21696-2 al-235 m). The peak of the sand fraction (250-500llm) isdominated by Cibicides lobatulus(C). FurtherconstituentsareNeogloboquadrina pachyderma tests (N), bivalve fragments (B V), bryozoans (B), and volcanoc1astic particles (V). The scale bar is 0.5 mm. PI a t e 22 89 90 developed on a morphological high on the seamounl slope (Fig. 12). Locally large bryozoan colonies of ldmidronea atlantica var. gracillima use larger sponges as a subSlrate for colonization. Cyclopecten was not observed within the sponge-bryozoan buildups. 3.2.3 The Deep slope facies The deeper flanks (below -400 m) of the seamount provide more different substrales than the crest and shallow slopes because oftheir morecomplex morphologic structure. Volcanic foundations crops out over long distances with steeply inclined slopes. Here, the seafloor is covered by lypical depth-related hard-substrale community zones. At other places, a thick cover of volcanoclastic sediments has acc um ulaled. Downslope sedimen l mass dislocation (debris flows, turbidites, volcanoclastic breccias (PI. 22/1)) indicates volcanoteclonic di slurbances or slope instabilily. Stab- ilization of the uppermost sediments is indicated by light- coloured surficial Iithified crusts, which appear just a few centimeters below the sediment surface within slide scars (PI. 22/1). Other extensive substrates are soft bottoms and unstable sand/sandy mud bOltoms. The large variety of seafloor substrates is reflected by a high variability of faunal assemblages and sedimentary facies. These deep slope communities can be grouped into: A) Hard rock related assemblages - deep slope sponge-bryozoan mounds - deep slope sponge-crinoid mounds - deep slope bryozoan thicke ts -deep slope sponge mounds and volcanoclastic sediments B) Soft botlom relaled assemblages - - deep slope soft bottom Bathycrinus community Deep slope sponge-bryozoan mounds (-300 m to -500 m) Near the lower boundary of the shallow slope facies on the upper seamount flanks slope inclinations increase drastically. Along OFOS track 21891-1A (Fig. 12), sponge- bryozoan mounds were observed almostcompletel y covering the deep southern slope. Huge bryozoan bushes and fan-type bryozoans have overgrown sponge mounds (PI. 20/2). The irregular surface of the mounds are fOlined by large core sponges, mainly large Geodia sp. and Thenea cf muricata. Lyssacine hexactinellids (Schaudinnia) are rare. The bryozoans are partly penetrated with yellow poecilosclerid sponges (Mycale sp.). Very common are bushes ofbranched, horn-shaped sponges which may be related to the poe- cilosclerid Clathria and LO a haplosclerid (Chalina ?). The large co re sponges are covered with dark grey fine-grained matter. Most large demosponges and hexactinellids exhibit adark grey baseand a white top thatindicates active growing tips du ring the Arctic summer, probably because ofincreased PI a te 23 Vesterisbanken Seamount - Sponge sp icu1es and microbial interaction Fig. 1. Ne twork of large parautochthonous tetractine llid and Iyssac ine hexac tinellid spicules [rom the uppeul10st sediment surface. The inner pore space ofthe spicule net work is still open and percolated by oxygenated water. SEM micrograph. This sam pIe was taken from a ridge north of Jan Mayen in the Greenland Sea ("Dorothee's Nose) at -600 m (also Figs. 3,4,6). Scale bar = I cm. Fig. 2. SEM micrograph from a network of large demosponge and hexactine llid spicules associated with bryozoans and serpulid worm tubes. Vesterisbanken Seamount at-400 m. Scale bar = 1 cm. Fig. 3. SEM micrograph of a critical point dried microbial enve lope attached on a I arge sponge spicule. The enve10pe exhibits a lot of coccoid bacteria (arrow). Scale bar = 25 ~m. Fig.4. Transmission light micrograph (TM) of methylenblue/ red fuchsine stained microbial colonies on a foraminifera test (arrows) . The test is surrounded by an organic fluff that is accumulated in deeper areas of the spicule network (approximate ly 20 cm below the surface) . In this area, the pore space is partly filled with degraded organic material. Scale bar = 50 ~m. Fig.5. Young spec imen of the tetraclinellid demosponge Craniella sp. growing on a spicule within the spicule network (approximate1y 20 cm below the surface). The sponge larvae moved in the open pore space of the spicule network and seU1e down on certain spicules that were probably enveloped by specific microbes that could stimulate metamorphosis of the larvae. Therefore, the sponges grow within the spicu1e network. This , behaviour explains the updomed structures of the biogenic mats which are shown in PI. 18/1 and 18/3. Additionally, thi s phenomenon explains the formation of autochthonous spicule enrichments (spiculites). SEM micrograph, scale bar = 200 ~m. Fig.6. TM mierograph of a very young demosponge Thenea sp. immediatcly after metamorphosis. The sponge settles on a large spicule with spec ial root structure linked lO a thin microbial envelope (arrow). Seale bar = 200 ~m. Fig. 7. Relies of the rigid spieular ske leton of the hexactine llid Chonelasma sp. 10 cm below the sediment surface. The axial filament canal s of the spiculcs are enlarged by bacterial activity (A) . The surfaces of the spicules are partly covered by bacteria-induced ferroan hydrox ides (B). The spaee between the spicule network is fi lled by an organic fluff and aggregated mostly by coceoid bacteria (e) . A young sponge is growing on a spicule (SP). Locality as in Fig. 1. Sea1e bar = 50 ~m Fig. 8. Surface of a large demosponge spiculeeomple tely covered by a sheet of filam entous bacte ria. The spicule was collected 2 cm below surface. The space between the spiculcs is open and in this part of the spieule ne twork run by surface water. Locality as in Fig. 1. Seale bar = 2 ~m PI at e 23 91 , • • , \. ~'" • · \ , • • • # , , • • • .. • • • • • • J , • • • , , , , " , • 'V , , • .. "T'" • J.~ '" .' , • . .,.. • , >1.,., • .. , je • , ~ . .. I • , • , ~ -:.. , I • • , . "- ~ - • ' r. , , .' :t' • .- • ." 'I t '" • • , , ., , , , , " ., 00\ 't=:'" • • , • ' ~ J • ., , • rq .. >. - -• • " 'f.. I " >, " .r , -1-,. , > t • ~ ......... ,. , ~~ ~ .. • I '.,'" ti ... l , , , ..... ', C· .. . ~ \ , .. ' , 1 I ' ' }"~ , • • . , 'SOi .~ . > • . ., , ~ , t • "; . 4 , '. .... .... " • • " ." • • • • , • )t\~ , ,;, • • :~ • • • • .. , ... • ~ .. 92 N S C rest Facies Shallow Siope Facies Deep Siope Facies 200-l 300 biogenic mats wit h rare Polymastia and Tetti- lid a e ~ .... 40 0- ~ 0> o , 0> o 500- z M Ol , " , Cyclopecten community on sandy mud bottom with rare sponges depth (m) o M o ~ 21891-1A - o 800 ~ ~ o Ol o '\) ,",r:.' ' , sponge bryozoan mounds biogenie mats and sponge bryozoan mounds ond hedges community on sandy mud bottom with blocks and brown gravel dominoted by Thenea, Geodia, and Schaudinnia 1 .600 dense bryo- zoon thickets 2.400 lapilli end osh , , M • • • • ~ • ~ 0 • 0> • • 0 Z 0> ~ • 0> N 0 M ,... Deep Siope Facies Sandy mud bOllom, locally lappi"; email sponge mounds on lava blocks domlnaled by ro .. elid hexacllnellide, lelraclinellid demosponges (Thenea, Geodis) and ceracllnomorph demosponges, a .. ociated with crinoids and blue alcldlans • • •• Legend see Fig. 6. ~ LI) ,... • 0 ~ 0 0> , 0. z 0 IX) • '" N 0 M • ,... 4.300 profile length (m) 4.100 3.700 3.900 The bryozoans are associated with thin and transparent blue ascidians (PI. 20/3). This deep water ascidian appears first at about -650 m but is relatively common throughout the entire deep slope facies. The associated sponge fauna is rather , " ( ' ..J .' ) , '. 1 scarce and smaIl-sized. However, bushes of Clathria and a few small geodiids as weil as residual bodies of the lyssaeine hexactinellid Schaudinnia are present. SmaIl actinians are relatively common. bP o ~. . . :,.) '~\" " ' I ,).;_ .... v b """" . ~, - ,:""" . \1.... e .. y I, .... q·l ' " . . . '" ,. 0 Ir' .' ." " ". . I ") I ' .. ~ . . .' '[ ' .... ~ I \. 0 .. .... .. =-: . ' .. '" , ' A . . '\ . . • .. ..... 1: _\ ':/" ~, 8 RY: bryazaans G: small Geodia LA.~(~~ \~ ___ r-~ I .- " , _~)' .. .I: > '-.. x " .... ~~ r: " .j...., . : .' '. ', . ~ '--~:~ ~7\ {t\' . , ! ~. ..... ) , , . . - ' , . ,. . ., . . " . · \t~f- • • • • ß--''''' " , • .' \: ) .::.J C . ' .J .0. . .- l'-I • ' . " .r- HG: HeJiometra glacialis PY: paecilasclerid yellow spange crusts S: Schaudinnia I rasselid hexactinellids SERP: serpulid warm tubes THJG: Thenea, Geodia "core"-spanges ~ '" 0'" '0 ß ERP 0 ~ J • " i) c' % 50 40 30 211 10 ~ " ') o () • • • • • .. • • • , , .' , . • • • ~ . . / ' .. ~., . ' .. -: . : . .-('-· /. • , • • • , · " I ' • I . , • I · ; . . • j: , Sponge crinold community (21880.0). n = 261 saction: 2 sqm I r--, ' filter fetiders tantacla reeders • • __ ,-- _,--_t=~~_ T1I /G G s rY II G IIR Y SEIU' Fig. 14. Deep slope sponge crinoid community with statistical analysis of functional feeding groups for a rcpresentative sector in the dcep slope facies (see PI. 20/4). 95 N S Fig. 15. Bathymetry and 21891-1C facies distribution along :t OFOS-track 21891-1C, 700 :t lower southern slope. co N N co • Legend see Fig. 6 . • co LI! - - 0 0 ." ." 0 0 sandy mud bottom with 825 z z amall aponge ...... LI! mounda M co • • LI! ...... N N 0 0 M • M ...... ...... • 950 - Deep Siope Facies 1.075- e.carpment depth (m) lava ground covered with sandy mud; aponge (rouelid hexactinellld) - crinoid (Hellometra) communities bryozoan thickets with blue ascidians 6.000 7.500 Small deep slope sponge mounds and volcanoclastic deposits (-1.532m to -2.063m) On the lower flanks of the seamount numerous small side-cones have been identified by hydrosweep mapping. This deeper zone displays acompletely different biozonation than that in the shallower areas of the deep slope facies . The morphology of the lower part of the northeastem flank undulates. In the OFOS survey 21883-0 between -1.650 m and -2.000 m, there may be an older sediment-buried crater. The seafloor between -1.600 m and -1 .650 m is covered with muds or sandy muds with abundant vertical WOIm tubes. Occasionally bottom current winnowing has fOIllled car- bonate-rich foraminiferal lag-deposits. Locally, volcano- clastic mass flows with coarse sharp-edged lava blocks and oxidized lava fragments and lapilli dissect the area. On small elevations, the volcanic foundation crops out S -- 9.000 1 0 .500 profile length (m) with a rough lava block or pillow surface. Within these areas small mound-shaped sponge buildups and hardrock-re la ted spongecommunities havedeveloped (Fig. 16). These sponge buildups displaya clear bathymetric zonation with a narrow ranged assem blage, the Hyalonema-Rosselidae-C ladorhiza- Thenea community at -1.600 m to -1.655 m, and a more broadly rangingCaulophacus-Hyalonema-Cladorhiza com- munity at -1 .655 m to -2.063 m. • a. Hyalonema-Rosselidae-Cladorhiza-Thenea community Small specimens grow on larger volcanic elasts of the black sediments in channels and debris flows. The sponge community is characterized by wine glass-shaped amphi- discophorid hexactinellids of Hyalonema (Fig. 17, PI. 21/1- 4). This taxon is charaterized by bundeIs of large root spicules and is therefore easy recognizable in underwater N 1.400- 21883-0 Deep Siope Facies • first occurrence of Hya/onema first occurrence of Caulophacus , :t 1 . 6 0 0 - ID octo- 1.800- ~ corala o o ." o ~ muddy to aandy mud bottom, locally "! volcanoclutlc debria flows In 0- M 2.00 0 ~ on lava blocks diverse depth (m) o .ponge/crinoid communitiea (hexactlnellids, C/adorhiza and div. demosponges) 800 1.600 eacarpment (platy or with pillowa); thin demoaponge/c ri no id overgrowth with thin sediment cover 2.400 3.200 :t .. N • N o o ." o z -N • ...... M o M ...... profile length (m) • Fig. 16. Bathymetry and facies distribution along OFOS-track 21883-0, distal north- em slope. Legend see Fig. 6. 96 H lonema - Rosselidae - Cladorhiza - Thenea community PCL 0 • 0 0 • ßa 0 o 0 0 0 0 <:> 0 0 ~ 0 0 , 0 HY • .... ' 0 ~oo '0 \ r. cE ~ • 0 \. , • • { 6 0 r.: :'- \-. .. . . - . \ l ' _,.I G \ 0 o 0 - 0 '::::' o % 50 + 30 20 Hys/onema eommunlty (21883·0); n = 116 seelion: 1.5 sqm IIlter leeders o . ' . o o o CL: C/adorhiza HY: Hya/onema , Cl \ \ .- .... , " , o I .'·' <:l 0 0., o I~' . " . " , ~ _ "" "': <." . , ' , - ~ • '. . . • ' , .···0· - ..... , -, ,,I, .' .. \. .• : ' .;.;;' I' 0 ',"', ", .~ .. . O . '\ o . ; • • . ', • • • • \ , . , • TH/G 10 T H/G HY CL PCL UNKSP PCL: poecilosclerid C/athria bushes TH/G: Thenea, Geodia "core"·sponges UNKSP: unknown sponges Fig. 17. Hyalonema-Rosselid-Cladorhiza-Thenea community with statisticaI analysis of functionaI feeding groups for a representative see tor in the deep slope facies (see PI. 21/2). photographs. Another new spange element is the strange poecilosclerid Cladorhiza, which grows as small tree-like sponges (pI. 21/1-4). The first sponge generation on this hard substrate is represented by large ball-shaped Thenea sp. and probably Geodia sp. All of these core sponges exhibit a dark grey colourresulting from fine sediment which is fixed between the protruding large dermal spicules. Some of them exhibit white areas indicating active growth. Rossellid hexactinellids are commonly represented by the taxa Schaudinnia and Scyphidium quite often combined with grey coloured residual skeletons. Some irregularly shaped big whitesponges areobserved, which demonstrate affinities to the rigid hexactinose hexactinellid Chonelasma. The poecilosclerid Clathria bushes are minor elements of the sponge comm unity. On hardrocks, many unidentified small white sponges are present which may be young hexactineUids. On some pillow surfaces blue grey coloured crnsts are visible which may be sponges, too, perhaps taxa of poecilosclerids (e.g. Hymedesmia) . Large volcanic bocks were sarnpled with a TV grab from -1.660 m to -1.668 m (GIK 21885-3). These lava bocks had been colonized by living ascidians, serpulids, Hyalonema. and bryozoans with solid arborescent colony growth fonns and sizes typical of Hornera lichenoides. Loose sediment is composed of bryozoan fragments which are heavily corroded and ironl manganese-stained, indicating a long time of exposure at the sedimentsurface. The bryozoan fauna includes Palmicellaria skene i and Sertella elongata as the most abundant species, followed in importance by Hornera lichenoides. Diplosolen intricarius. Tessaradoma gracile. I dmidronea atlantica var. gracillima. Porella compressa. Porella plana, Cribrilina watersi, Smittina glaciata. andSchizoporella porifera. Crisia sp .. Tubulipora sp .• and Tricellaria gracilis are considered to have been alive most recently. b. Caulophacus-Hyalonema-Cladorhiza community The deepest investigated area of the marginal cone mound between -1.800 m to -2.063 m is characterized by the lyssacine hexactinellid taxon Caulophacidae (Caulophacus arcticus). Caulophacus arcticus is a typical deep water hexactinellid with a depth range from -1.450 m to -4.379 m (KOLTUN 1967). The specim~ns observed exhibit charac- teristic mushroom shapes and arerelatively large (more than 20 cm high) (Fig. 18, PI. 21/4). They commonly grow on large ball-shaped sponges (Thenea). The long funnel shafts are dark grey at their bases, and this feature resembles the residual structures seen in various taxa of the Rosselidae (Schaudinnia) . The remaining sponge fauna is identical to those of the Hyalonema-Rosselidae-Cladorhiza-Thenea community. The vagile crinoid Heliometra glacialis is common and fixes its root arms on large hexactinellid sponges or within fissures of lava blocks. Deep slope soft bottom Bathycrinus communities ( -1.532m to -1.600m) Muddy soft bottoms containing sparse small rock fragments which have a low abundance fixosessile benthos (21883-0-83) are typical from wide areas on the deeper northeastem flank of the Vesterisbanken. Characteristic for 97 Deep slope Caulophacus community , .---------------' CAU , .9 .0 .. • PCL ;;: , '. . . . ..0 . . .. , . , . . . • • • • • • • • • • • • ;rH!G • • • • • • • , • • • • • • • • o • • • . . • , . ' . . . . . ' . - . ' ". . . .. .' '. " , ' , l Q :' ~ : '; . ' .: '. .: . .. .. .. . . t:).r:P: . '. . ." .. ' . . 50 Caulophacus communlty (21883-0), n = 114 secllon: 1.5 sqm . . . . . . . . " q " . .. .. . . o · ' . ... . _ .. . .. .. .. ... . . ..' . . • 00 • • • • • • • IIIler leaders ~ ____________ ..:....::o.= L_ 30 CAU: Cau/ophacus CL: C/adorhiza HY: Hya/onema PCL: poecilosclerid C/athria bushes S: Schaudinnia I rossellid hexactinellids TH/G: Thenea, Geodia "core"-sponges UNKSP: unknown sponges 20 10 CAU HY CL S PCL TIf UNlCSP Fig. 18, Caulophacus community with statistical analysis of functional feeding groups for a representative sector in the deep slope facies (compare to PI. 21/4). this facies are sessile crinoids (Bathycrinus carpentert) This typical deep water crinoid is closely associated with octocorals and actinians. 3.2.3 The Abyssal plain facies The abyssal plain surrounding of the Vesterisbanken Seamount is characterized by fme-grained sediments found in 3 deep water box corer sampies (GIK 21878-2, 21882-1, and 21892-1). Abundant benthic foraminifera (Pyrgo and several mm-sized agglutinated species) occur on the sediment surface. On these small "islands" , small sponges of the Calcarea are attached, mainly Grantia and Leucosolenia. Characteristic for this zone is the small tetractinellid Thenea abyssorum which is adapted to muddy sediments. Thenea abyssorum exhibits umbrella-like large deIlllal spicules which prevent the sponge from sinking into the soft bottom. This type of sponge is relatively common, a mean of 20-30 specimens were collected on the surface of each giant box core (area: 0.5 m2). 3.4 Indications for hydrothermal activity Indications for recent hydrothelllIal activities are scarce. In proflle 21878-1 (Fig. 3) a slight elevation of temperature (by 0.1 to 0.15°C) may be recognized between -740 to -840 m. It seems, however, improbable that this represents an indication of a hydrothermal "plume", as it would require a strong vent of sufficiently high temperature to create this anomaly in a l00-m-thick water mass more than 10 km remote from a possible vent Nevertheless, a slightly increased signal for Mn was found just at this depth, while Fe and methane are nearly unchanged compared to deeper and higher sections ofthe watercolumn. Ifthese slightly elevated temperature and Mn values were real indications for present hydrothellualism, active vents could probably be expected at water depths near 1.000 m on the southern flanks of the seamount. No sampies and CTD-proftles, however, are available from deeper flank 'sites to substantiate this vague • • SUsplclon. Visual indications of activ~ hydrothellnalism were not able to be detected from the black & white TV-recordings. From the color slides, however, yellow to orange coloured hues on the sediment surface were found along proftle 21880-0 at -ISO m to -170 m (pI. 18/2). These coloured spots extended no more than about 1 m2• No discharge openings or "smoker" edifices could be detected. The fresh hues and the lack of biogenic colonization, however, suggest that weak hydrothermal discharge is still active at these sites. These still active points probably mean that the northeastern part of the crest area was one of the last sites of volcanic activity on the Vesterisbanken. At 2 TV -grab sites (21885- 3 and 21891-4) yellowish to reddish brown oxide crnsts and stained scoriaceous material was found. Oxide encrnsted organisms found in TV-grab sampie 21885-3 indicate that 98 weak hydrothellnal emanations were still active recently at this site. Similar oxide crusts were dredged in 1984 on the southeastern slope. These observations document recent hydrothenllal activities at widely distributed areas of the seamount edifice. 4 DISCUSSION 4.1 Sediment dynamics The specific oceanographic conditions and the far- offshore position of the Vesterisbanken Seamount are important controlling parameters which define the major processes of sediment dynamics on the seamount. The nearly year round sea-ice cover and its short-tefln retreat (mostly during August and September) results in episodic peak sediment and nutient supply from surface waters. Ice edge blooms of phyto- and zooplankton organisms and melting of sea-ice deliver large quantities of particulate and suspendedorganic matter into the surface waters. In addition, fine-grained terrigenous sediments may be released from melting ice fols. Along the ice edge, the zooplankton, specifically the planktic foraminifer Neogloboquadrina pachyderma (sinistral) develops a high standing stockduring the ice-free season. Their calcareous tests are subsequently delivered as pelagic carbonate rain to the seafloor. As a result, organic matter, pelagic carbonate tests and terrigenous fine-grained particles show strong seasonal short-term sedimentation peaks, which arrive at the seafloor within a period of less than two months. Otherobservations of importance are frequentindications of bottom current activities at almost all depth levels of the seamount. These currents probably derive from a stream- lined downwelling anticyclonic vortex known as the TA YLOR column. As a result there is a rapid transfer of organic matter, planktic tests and terrigenous particles to the bottom. Within aT A YLOR column, the strongest bottom currents are expected over the top of the seamount. Such a configuration seems to be realized over the Vesterisbanken. This is indicated by the widecovemgeofbiogenic structures fOflned by filter-feeding organisms, mainly bryozoans and sponges, and serpulids. In addition, the overall construction of the widespread biogenic mat has characteristics which resemble lag-deposits (iron- stained byrozoan or serpulid skeletons). The overall impression is that the top of the seamount is continously current sweptand most fine-grained particles are transported downslope. Filter-feeding organisms preferentially colonize small elevations, where they reach above the near bottom laminar current regime (ALrENBACH et al. 1987, LUiZE & ALTENBACH 1987). As a result, all biogenic structures are initiated either on elevations ofthe volcanic foundation or on the crests of ripple fields. The close relationship between morphostructures of biogenic buildups and relief in the foundation indicates that local relief probably detennines changes in bottom current parameters, which, in turn, exaggerate a primary control in the shaping of biogenic structures. In particular, morphostructures such as hedges or spurs as weIl as flatcake mounds substantially support these assumptions. Two major sedimentological processes opemte on the flanks of the seamount, e.g. downslope sediment transport and deposition of fine-grained suspended particles in lee position. As a consequence, there is a downslope increase in overall sediment thickness and a geneml decrease in grain- size. Sea-floor characteristics change downslope in a predictable way. On the upper slopes, semi-stabilized sand or sandy mud bottoms dominate, while the deeper slopes are characterized by soft mud bottoms intersected by volcanoclastic flows (pIs. 21/1, 22/1). Again, all hard rock substrates are rapidly colonized by filter-feeding communities. Apart from more or less continous sedimentological processes, the seamount has been variously influenced by episodic volcanic events. In particular, a pyroclastic layer in the Holocene sediment cover of the seamount close to surface (see shallow slope facies) indicates a young volcanic event on the Vesterisbanken Seamount. The rapid colonisation of the pyroclastic substrate is important. It corresponds with similar observations of a rapid colonisation on young, shallow water lava surfaces at Jan Mayen (GULLIKSEN et al. 1980). The patchy distribution of buildups mayaiso point in this direction. That such volcanic events do not represent a single case during the younger history of the Vesterisbanken Seamount is evidenced by coring on the surrounding abyssal plain (GIK 21878-3, 21882-2, and 21892-3). Upto 17 discrete sandy/silty ash layersare present within 6 to 8-m-Iong sediment cores (yV ALLRABE-AnAMS in TmEDE & HEMPEL 1991). The uppenI1ost8 to 17-cm-thick ash layers are covered by 15 to 110 cm homogeneous brown pelagic silty clay. Considering the low sedimentation rates of the area, we estimate that this last major eruption took place near the PleistocenelHolocene boundary. These observations show that until modern times shorterperiods of volcanic activity are sepamted by longer time intervals of inactivity. The Vesterisbanken Seamount is at present a dormant volcano. 4.2 Formation of spiculites: actuopaleontological results from Arctic sponge communities The dense organic meshwork coverage of the seamount down to -260 m is unique and has not been described from the Arctic realm. BULLN ANT & DEARBORN (1967) sampled a similar spiculite-bryozoan mesh)Vork withLimatula bivalves from volcanic grounds of the Antarctic McMurdo Sound. The stable spicule meshwork is interpreted as an autochthonous spiculite. This type of organic-rich sediment is also present on a ridge northwest of Jan Mayen (pI. 23/1- 2) and is also described by VAN WAGONER et al. (1989) as occurring in shallow water of the northern Canadian Arctic Islands. The spicule networks are responsible for the dense cover with fixosessile benthos, because the open pore space of the spicule network and microbial cover of the spicules are an ideal biogenic substrate for settlement of larvae (pI. 23/3-6). The great stability ofthis sedimenttype on the steep slope of the Vesterisbanken Seamount results from an interaction of spicule networks and the settlement of fixosessile benthic organisms. The spicule mats are a result of relatively long-term stable ecological conditons, perhaps the entire Holocene, following re-establishment of nOllual marine conditions after glaciation or after the last volcanic eruption near the PleistoceneIHolocene boundary. Most of the sponges are long-lived k-strategislS (e.g."core" sponges, lyssacine hexactinellids), are adapted La oligotrophic stable conditions and survive in Arctic cold waters. They fOlln residual bodies in winter. These condensed skeletons may be reacti vated at the beginning of the Arctic summer coincident with increasing food supply from the surface waters. Most observed sponges exhibit numerous small, mostlyasexual, buds (Thenea and hexactinellids) whieh are probably also linked with increasing food supply. 4.3 Bryozoan ecology 4.3.1 Species composition Bryozoan sampies cover all facies beIlS at Vesterisbanken Seamount. The sampled material revealed at least 21 taxa (Tab. 4, PI. 24/1-15). Most bryozoan taxa found at Vesterisbanken Seamount are Arctic-boreal, Arctic-circumpolar or high Arctic species (KLUGE 1975). Despite the high geographie latitude of the seamount and its position within the Arctic water masses of the EGC, some species occur that are also known from the non-Arctic North Atlantic. This seems La be the case, es- pecially for Hornera lichenoides, for whieh a cosmopolitan occullence is presumed. 4.3.2 Depth zonation, growth fonus and adaptation to seasonal food supply Identification ofbryozoan taxa on the many photographs is based on colony growth fOllu and on comparison with a limited number of sampies laken from similar bathymetric settings. Our understanding of the depth-related occurrence of bryozoans remains therefore tentative. 99 Although most bryozoan species show a wide bathymetric range at Vesterisbanken Seamount, the facies belts seem to be dominated by distinct bryozoan taxa that produce specific biogenie structures (Fig. 19). Of striking significance is the volumetric dominance of taxa with erect growth fOBUS among the Cheilostomata and Cyclostomata in contrast to the eastem shelves of the Norwegian-Greenland Sea, where encrusting taxa prevail at all water depths. At Vesterisbanken, erect-growing taxa with arborescent colony growth forms are Hornera lichenoides, Palmicellaria skenei, Porella plana, Porella compressa, Leieschara subgracilis, Tessaradoma gracile, and ldmidronea atlantica var. gracillima. Species with reticulate growth fOllus are Sertella elongata, Sertella beaniana, and Diplosoien intricarius occur. In addition, species such as Notoplites normanni, Tricellaria gracilis and Crisia sp. grow as weakly calcified, articulate colonies. Less frequently than the erect-growing taxa, several species with encrusting zoarial growth fOBUS such as Cribrilina watersi, Schizoporella porifera, Smittina glaciata, ? Mega- pora rigens, Schizoporella thomsoni, and Disporella sp. occur as epibionlS on other bryozoan colonies, serpulid tubes and mollusc fragmenlS. Colonial growth fonus ofbryozoans have been related 10 different environmental settings and are frequently used for interpretations of waterenergy regimes (STACH 1936, SCHOPF 1969, HARMELIN 1975, NELSON et aI. 1988). Based on the volumetric dominanceofbryozoan species thateitherpossess weakly calcified, articulate colonies, or erect and non- articulate, but sometimes fenestrate, colonies, a medium current velocity above the sea floor is interpreted 10 occur at nearly all water depths at Vesterisbanken Seamounl. Thus, weakly calcified, but articulated colonies of No- toplites normanni and Tricellaria gracilis Lagether with hydrozoans, sponges and serpulids fOlm the living cover of the sponge-bryozoan malS that occur at the crest of the Cribrilina watersi ANOERSSON Crisia sp. arctic-atlantic DiplosoIen intricarius (SMITT) Disporella sp. Hornera lichenoides (LINNIO) Idmidronea atlantica var. gracillima (BUSK) Notoplites normanni (NORDGMRO) Leieschara subgracilis (O'ORBIGNV) Palmicellaria skenei (ELLIs & SOLANOER) Porella plana HINCKS Porella compressa (SOWERBV) Pseudoflustra sinuosa (ANOERSSON) Schizoporella porifera (SMITT) Schizoporella thomsoni KLUGE Sertella beaniana (KING) Sertella elongata (SMITT) SmiNina glaciata (WATERS) Stegohornera arctica (KLUGE) Tessaradoma gracile (SARS) Tricellaria gracilis (VAN BENEOEN) Tubulipora cf. T. ventricosa BUSK arctic arctic-boreal, atlantic boreal-atlantic; deepwater high arctic; deepwater arctic, circumpolar arctic-boreal, atlantic arctic-atlantic arctic-boreal, circumpolar high arctic; deepwater arctic arctic arctic-boreal, atlantic arctic, circumpolar high arctic boreal-atlantic; deepwater arctic-boreal, atlantic; deepwater arctic, circumpolar arctic, circumpolar • , Tab. 4. List of bryozoa identified from the Vesterisbanken Seamount. 100 Bryozoen auf dem Crest Shallow Vesterisbanken Facies Siope Seamount Facies Cribri/ina walersi Crisia sp. DiplosoIen inlricarius Disporells sp. Horners lichenoides Idmidrones slsnlics var. grscllis 1====1' Nolopliles normsnni Leieschsrs subrscilis Pslmlcellsrls skene! -+ Porells plana Porells compresss Pseudofluslrs slnuosa Schizoporella porifera Schizoporells Ihomsonl Serlells beanians Serlells elongsla -------I Smittina glacisla Stegohornera arclica Tesssrsdoms gracife Tricelfaris gracilis - Tubulipora cf. venlricosa seamount. The bryozoan-hydrozoan thickets form protected biotopes with more reduced water energies that are also occupied by a number of species with erect, but more fragile growth forms, such as Sertella elongata. ldmidronea atlantica. Tubulipora div. sp., species such as Palmicellaria skenei with stout, erect colonies, or encrusting species such as Cribrilina watersi. Schizoporella porijera. Smittina glaciata. and ?Megapora rigens. Stout colony fragments of Palmicellaria skenei are the most significant bryozoan constituents that contribute to the fOJ mation of carbonate sediment at all water depths. The sediment contains mainly dead and heavily corroded colony fragments of Palmicellaria skenei and other bryozoan species stained by iron/manganese, indicating aperiod of non- deposition or erosion on the sea floor caused by bottom currents. The physiography ofthe searnount, the limited terrigenous input and the transport of seasonally produced nutrients by TAYLOR current downwelling, enables the bryozoans to occur down to great water depth with high diversities and population densities. Competition for food seems to be the major factor causing the predominantly erect colony growth forms of bryozoan taxa. This has been assurned also for the benthic communities living on small drops tones in high latitude pelagic soft substrate environments such as the V 0ring Plateau in the Norwegian Greenland Sea (OSCHMANN 1990). In contrast, competition for space among bryozoan species is distinctly Iimited due to the preferred upward growth of the colonies that support the fOllnation of num- emus distinct bryozoan communities. Due to the highly seasonal production of organic matter in the subsurface water masses, variations in nutrient supply may cause various seasonal growth patterns in organisms at Vesterisbanken Seamount. An intense benthic/pelagic coupling as demonstrated by GRAF (1989) for deep-sea benthic communities on the V 0ring Plateau in theNorwegian Sea is also assumed to occur in benthic communities at Vesterisbanken. In bryozoans, reproductive cycIes stimu- lating the fonnation of brood chambers (cyclostomes) or Deep Siope Facies + I • Fig. 19. Occurrence ofbryozoan taxa in the 3 facies belts at Vesterisbanken Sea- mount (!hin lines). FOllnations ofprom- inent bryozoan aggregations are indicated with thick lines. • • ovicells (cheilostomes), as well as rhythmic growth ban ding that occurs in the extra-zooidal skeleton in species such as H ornera lic henoides, may berelated to such seasonal nutrient cycles. Most sectioned colonies of several species were found to be empty or to display degenerated polypides and soft tissues. Mostcolonies of Hornera lichenoides, especially, young polypides were found to have grown on top of several degenerated bodies within their zooecia. Such degeneration/ regeneration cycles in Arctic bryozoan species might be an adaptation to survive the Arctic winter. Bryozoans are known to feed on a variety of nutrients depending on their specific feeding behavior, the polypide and tentacle dimensions as well as the morphofunctional specializations of the digestive tract (WINSTON 1981). Thus, degenerated polypids in colonies of Diplosolen intricarius investigated in thin sections more frequently contain complete test~ of planktic foraminifers, whereas Hornera lichenoides may have a dietconsisting only of diatoms. FurtheIlllore, the strength and flow pattern of the actively produced feeding currents on colony surfaces is considered to be largely controlled by the zooecial budding pattern that causes the arrangement of zooecial apertures on colony surfaces (TA YLOR 1979, WINSTON 1981). , 4.3.3 The vagile epibenthos , The vagile epibenthos is present in every facies beIt of the Vesterisbanken Seamount. In general, abundance and diversity of the vagile organisms decreases downslope. The mostobvious epibenthic group are echinodeIIns, with starfish (Henricia. Solaster. Hymenaster) , brittle stars (Ophiopleura and more unidentified genera), and sea feathers (Heliometra glacialis). The latter is more abundant in the deep slope facies, whereas sea stars and brittle stars are present in the crest facies and shallow slope facies. No sea urchins or sea cucumbers are visible in the photos. MoIIuscs are the second major vagile epibenthic group. The bivalves are represented by pectinids (Cyclopecten imbrijer. Cyclopecten graui) and limiids (Limatula hyperborea). They inhabite the crest facies and are major elements ofthe shallow slope facies without being fixed by abyssus to the substrate. It should be stressed that these bivalves are able to float. Gastropods are rare and are representated by carnivore buccinid and naticid fonlls. The latter predates bivalves as is evidenced by numerous drilled holes in the valves. The semi-stabilized sandy muds of the shallow slope facies are occupied by onuphid polychaetes, building quivers ofbroken pectinid bivalve shells, suggesting a predator-prey relations hip between them. In summary, all identified members of the vagile epi- benthos are also elements atmany other Subarctic and Arctic localities (ÜCKELMANN 1958, RASMUSSEN 1965, BERNHARD 1979, LUBINSKY 1980, PIEPENBURG 1988, OsCHMANN 1991). 4.4 Arctic mixed siliceous and carbonaceous deposits: modern end members of the Foramol fades? Cold water siliceous and carbonaceous deposits fOllned by sponge-bryozoan constructions are regarded as low accumulating end members ofthe Foramol facies. This tenJl is widely used for non-tropical carbonate deposits fm lI1ed by foraminifers, moIluscs, balanids, echinodelllls, bryozoans, and coralline algae (LEES & BULLER 1972). Modem cold water, siliceous carbonate deposits are fOfllled under completely different environmental settings than their tropical counterparts. A good knowledge of principle controlling parameters in their formation will provide us with a different set of interpretations. Critically considered, they may serve as a non-tropical alternative formodels of similarly composed low diverse and low accumulating carbonate deposits in the fossil record. Physical parameters of the mixed biogenic siliceous and carbonaceous sediments on the Vesterisbanken Seamount represent the cold end member of modem carbonate deposition. Very low temperatures close to O°C and salinities around 34.5 ppt are recorded at nearly constant values over the entire water column, and thus seem to have no influence on the pronounced depth-related biogenic zonation on the seamount. All biogenic constructions are fOlllled in aphotic depths. Apart from the seasonal pulse of fine-grained sediments released from melting sea ice, the paucity of terrigenous sediment input favors concentration of biogenic skeletons on the seafloor. Due to harsh, nearly year-round pack ice covered Arctic conditions over the seamount, the food supply reveals a strong seasonality. The transfer of food to the seafloor communities is specifically effective due to an oceanographic configuration found over seamountobstacles - the TaYLOR column. An almost stable stratified water column in combination with current regime disturbances generated by seamount obstacles cause oceanographic com- plexities that strongly influence biological processes in the water column as weil as standing stocks and diversity of the benthic fauna (BOEI-U.ERT 1987). One possible result is the TAYLOR column (TAYLOR 1923), a closed stream-lined anticyclonic vortex that is trapped above isolated seamounts (HOGG 1973, HUPPERT 1975). Trapping of nu trients in shallow waters of the upper TA YLOR column may enhance primary 101 productivity. Such enhanced productivity or advection and concentration of food produced elsewhere may explain the high standing stock of benthic seamount communities, especially of filter-feeding organisms. The depth-related zonation of ecosystems may correspond to variations in quality and quantity of downslope food transfer as weIl as increasing hydrostatic pressure. Prevalent nu trient sources depending on water depth. The distribution and concentration of phyto- and zooplankton vs. particular organic matter may, in addition, control thedepth-dependent zonation and composition of the benthic seamount communities. Furthellllore, bacterial symbiosis and/or the take up of dissolved organic matter might support nutrition in spongesand enhance stabilization of spiculite frarneworks. We can only speculate about the fossilisation potential of the Arctic sponge-bryozoan-serpulid mounds and biogenic mats studied on the Vesterisbanken. At the low accumulation rates observed we would expect a considerable 10ss of biogenic silica during diagenesis. The resultant sediment after diagenesis could be a siliceous limestone-bearing abundant cool-adapted pelagic and benthic organism. Partial preservation of the in situ framework of sponge spicules within early chert nodules may refer to the process of in situ spiculite formation that is characteristic for the studied siliceous mats from the seamount. In summary, the different sponge-bryozoan-serpulid- echinodenIl biogenic structuresoftheArctic Vesterisbanken Seamount provide us with an example of one potential end member of the FORA MOL facies, in wh ich the primary control is exaggerated by a seasonally strong pelagic/benthic coupling of ecosystems and variations in downslope food transfer. Due to the Arctic conditions and its far offshore location such a system will develop at low accumulation rates. 5 CONCLUSIONS -The nearl y year -round sea ice cover over the Vesterisbanken Seamount and its ShOrt-tellIl retreat, mostly during August and September, results in episodic peak sediment and food supplies from surface waters. !ce edge blooms of phyto- (diatoms) and zooplankton (beside others the planktic foraminifer Neo globoquadrinapachyderma sin.) and melting sea ice deli ver huge quantities of particulate and suspended organic matter and fine-grained terrigenous sediments into surface waters. , - Due to the downwelling TAYLOR current regime over the seamount, a rapid and effective transfer of food is supplied to the benthic ecosystems reflecting an intensive pelagicl benthic coupling of ecosystems. - Facies belts and biogenic structures reveal a clear depth zonation depending on variations in food supply as weIl as on different substrates due to variable slope inclinations and roughness of the volcanic foundation. Major facies belts are the crest facies down to -260 m, the shallow slope facies from around -260 m to -400 m and the deep slope facies below 400 m. - Small sponge-bryozoan-serpulid mounds and hedges as weIl as flatcake-like structures fOllned by the same organisms 102 grow on a wide extended biogenic mat within the crest facies. On steeper margins extensive bryozoan thickets have developed on the volcanic foundation. The shallow slope facies is covered with semi-stabilized sandy mud bottoms and/or dark volcanoclastic sediments colonized by vast numbers of pectinid bivalves and onuphid polychates. Locally sponge-bryozoan-serpulid mounds are developed on elevations of the volcanic foundation. The deep slope facies comprises various kinds of sponge-bryozoan mounds, sponge mounds, and a typical sponge-crinoid assemblage on coarse volcanoclastics and lava surfaces. - The dense organic meshwork fonned by sponge spicules and bryozoan fragments on the upper sec tor of the seamount is unique in various ways. Most sponge spicu1es have a microbial cover, which is an ideal substrate for the settlement of larvae. The spiculite mat is predominantly fOllned by in situ decay of sponges revealing the actualistic formation of spiculites. The spiculite mat has various cryptic habitats, which are inhabited by bryozoans, ascidians, serpulids, and benthic foraminifers. - Most of the sponges are K- strategists adapted to stable oligotrophic conditions. They survive in cold Arctic waters by fOlming residual bodies in winter. Bacterial symbiosis and/or take up of dissolved organic matter might support the nutrition of sponges. - Prevalent nutrient sources depending on water depth, i.e. living phyto- and zooplankton versus particular organic maUer, control species distribution and growth fonns of bryozoans on the seamount. - The lag deposit character and frequent iron/manganese stainings on partic1es suggest low accumulation rates for the mixed siliceous, carbonaceous and terrigenous UppeI most sediment layers on the Vesterisbanken Seamount. -Weak hydrothennal activities (yellowish to reddish brown- ish oxide crusts and stained soriaceous material) were observed as being widely distributed on the seamountedifice. These weak and still active hydrothellJlal emanations do not show any prominent influence on the biotic zonation. Pyroclastic eruptions took place variously during the Holocene, providing new semi-stabilized substrates for biogenic overgrowths at wide areas of the seamount. - The different sponge-bryozoan-serpulid-echinodeIm biogenic structures of the Arctic Vesterisbanken Seamount can be regarded as one potential end member of the Foramol facies with c1early defined controlling parameters, e.g. a strictly seasonal pelagic/benthic coupling of ecosystems and variations in downslope food transfer. Beside serving as a modem case study for similar composed fossil counterparts, carbonate production reveals a set of controlling parameters whose significance has been traditionally underestimated in the tropical counterparts. ACKNOWLEDGEMENTS We thank Captain Jonas and his crew for exeellent support during the ARK V/I expedition of RV POLARS'IERN in Ju1y 1990. Jayne Welling kindly irnproved the language. Christian Reimers and Beate Baader assisted in photgraphie repro-techniques. Very constructive reviews by Prof. Noel James and an anonymous reviewer are gratefully acknowledged. REFERENCES ALlENBACH, A. V., UNSÖLD, G. & WALGER, E. (1987): The hydrodynamic environmult of Saccorhiza ranwsa. - Ber. Sonderforsehungsber. 313, 6, 47 -68, Kiel ARMAUERHANSEN, G. (1885): Spongiadae. -TheNorwegianNorth- Atlantie Expeditions 1876-1878, 13 (Zoology), 25 pp., Christiania (Leipzig) AUGs1EIN, E., HEMPEL, G., SCHWARZ, G., THIHDE, J. & WEIGEL, W. (1984): Die Expedition ARKTIS lIdes FS "POLARS11lRN" 1984. - Ber. Polarforschung, 20, 192 pp., Bremerhaven BERNHARD, F. R. (1979): Bivalve molluscs of the westu JI Beaufort Sea. - Contr. Sei., 313, 80 pp, Los Angeles BOEHI.ERT, G. W. (1987): A review of the effeets of seamounts on biological processes. - In: KEAUNG, B. H., FRYER, P., BA'IlZA, R. & BOEHI.ERT, G. W. (eds.): Seamounts, !slands and Atolls, Geophysieal Monographs, 43, 319-333, Washington BREJ'IFUSS, L. L. (1898): Die aretische Kalksehwammfauna. - ArehJ.Naturgeseh., 277-316, Berlin BRÖNSlEDT, H. V. (1914): Porifera - Conspectus Faunae Groen- landieae. - Meddl. om Gr~nland, 23, 459-544, Kopenhagen BULLlV ANT, 1 S. & DEARBoRN, J. H. (1967): The fauna of the Ross Sea, Pt. 5. - New Zealand Dept. Seient. Industr. Res. Bull., 176, 76 pp, Wellington BURTON, M. (1934): Zoological results of the Norwegian scientifie expeditions 10 East-Greenland. m. Report on the sponges of the Norwegian expeditons 10 East-Greenland (1930, 1931, and 1932). - Skrifter om Svalbard og Ishavet, 61, 33 pp., Oslo BURTON, M. (1959): Spongia. -TheZoology ofIsland, 2 (Part3-4), 71 pp., Kopenhagen & Reykjavik CLARK, A. H. (1970): Eehinodermata Crinoidea. - Marine Invertebrates of Seandinavia, 3, 55pp., Oslo EGGVIN, 1 (1963): Bathymetrie ehart of the Norwegian Sea and adjacent areas. Scale 1 :5.000.000. - Fiskeridir. Havforskings- inst., Bergen EIDHOLM, O. & THIEDE, J.(1980): Cenozoie continental separation between Europe andGreenland. - Palaeogeogr., Palaeoclimatol., Palaeoecol., 30, 243-259, Amsterdam FAtRBANKS, R. G. (1989): A 17.000 year glaeio-eustatic sea level reeord: influenee of glacial melting rates on the Younger Dryas event and deep ocean eireulation. - Nature, 143, 637-642, London FRISlEDT, K. (1885): Bidrag till Kännedomen om de vid Sveriges vestra kust lefvande Spongiae. - Kongl. Svenska Vetenskaps- Akad. Handl., 21/6, 56 pp., Stockholm GRAF, G. (1989): Benthic-pelagic eoupling in the deep-sea benthie community. - Nature, 341, 437-439, London GULLIKSEN, B., HAUG, T. & SANDNES, K. (1980): Benthicmacrofauna on new and old lava grounds at Jan Mayen. - Sarsia, 65, 137- 148, Bergen ' HARMEI.IN, 1-G. (1975): Relation entre la fOlIne zoariale etl' habitat ehez les bryozoaires eyclostomes et consequences taxonomique. , - Doeum. Lab. Geol. Fac. Sei. Lyon (hors Ser.) 3 (Bryozoa 1974),369-384, Lyon HARTMANN, M., LAss, H. & s, D. (1989): A new method for trace metal determination in seawater. - In: Wru,z, B. (ed.): 5. Colloquium Atomspektrometrische Spurenanalytik, 703-709 HAYWARD, P. 1 & RYLAND, J. S. (1979): British Aseophoran bryozoans. - In: KERMACK, D. M. & BARNES, R.S. K. (eds.), Synopsis of the British Fauna (n. s.), 14, 1-312, Aeademie Press, London HEMPEL, P., SCHREIBER, R., JOHNSON, L. & THlf.DE, J. (1991): The Vesterisbanken Seamount (Greenland Basin) - patterns of morphology and sediment distribution. - Marine Geology 96, 175-185, Arnsterdam HENTSCHEL, E. (1916): Die Spongien des Eisfjordes. -Zool. Ergebn. der Schwedischen Expedition nach Spitzbergen 1908, Teil ß (3), 18 pp., Stockholm Hooo, N. G. (1973): On the stratified TAYLOR colurnn. - 1. Fluid Mechanics, 58, 517-537, London HÖRMANN, P. K. & RAASE, P. (1991) Petrology ofbasalts from the Vesterisbanken (Greenland Sea). - Marine Geology (in press) HUPPl'.RT, H. E. (1975): Some remarks on the initiation of inertial TAYLOR colurnns. - J. Fluid Mechanics, 67, 397412, London JOHANNESSEN, O. M. (1986): Brief overview ofthe physical oceano- graphy. - In: HURDLE, B. G. (ed.): The Nordic Seas, 103-128, New York (Springer) KLUGE, G. A. (1975): Bryozoa of the northern seas of the USSR. - 711.pp., New Dehli (Amerind. Publishing Co.) KOLTIJN, V. M. (1959): Comeosiliceous sponges of the northern and far eastern seas of the USSR. - Keys for the identifications of the fauna of the USSR published by the Zoological Insitute of the . of Sciences of the USSR, (Akad. NAUK USSR) 67, 235 p., Moskow-Leningrad. (in Russian) -- (1964): Sponges from the Antarctic. 1. Tetraxonida and Cornacuspongida. In: Biological results of the Soviet Antarctic Expedition 1955/1958,2 Issled. Faunei Morei, 6-131, Moskow & Leningrad -- (1966): Four rayed sponges of the North and Far eastern Seas of the USSR (Order Tetraxonida). - Akad. NAUK USSR 90, 107 pp., Moskow & Leningrad. (in Russian) -- (1967): Glass sponges of the Northern and Far Eastem Seas of the USSR. - Akad. NAUK USSR 94, 124 pp., Moskow & Leningrad (in Russian) -- (1970): Sponges of the Arctic and the Antarctic: A faunistic review. - Sym. Zool. Soc. London, 25, 285-297, London LAMBE, L.M. (1896): Sponges from the Atlantic CoastofCanada. -Trans. Roy. Soc. Can., Sec. 6, 183-211, Montreal -- (1900): Catalogue of the recent marine sponges of Canada and Alaska. - OttawaNaturalist, 1419,153-172, Ottawa LE BAS, M. 1., LE MAlTRE, R. W., S1lrnCKEISEN, A. & ZANETI'IN, B. (1986): A chemical c1assification of vo1canic rocks based on the total alkali-silica diagram. - 1. Petrol., 27, 745-750, Oxford LEEs, A. & BULLER, A. T. (1972): Modem temperate-water and warm-water shelf carbonate sediments contras ted. - Marine Geology, 13, M67-M73, Amsterdam LUBINSKY, I. (1980): Marine bivalve molluscs of the Canadian central and eastern Arctic: Fauna! composition and zoogeo- graphy. - Can. J. Fish. Aquat. Sci. Bull., 207, 1-111, Ottawa LUNDBECK, W. (1902): Porifera. Homorrhaphidae and Hetero- rrhaphidae. - The Danish Ingolf-Expedition, 6/1, 105 pp., Hagerup (Kopenhagen) -- (1905): Porifera. Desmaeidonidae (pars.). -The Danishlngolf- Expedition, 6/2, 219 pp., Hagu up (Kopenhagen) -- (1909): The PoriferaofEast Greenland. - Meddr.om Gr0nland, 29, 423-464, Kopenhagen -- (1910): Desmacidonidae (pars.). - The Danish Ingolf-Expedi- tion, 6/3, 124 pp., (Kopenhagen) LUJ'IE, G. F. & ALTENBACH, A. V. (1987): Rupertina stabi/is (W ALLICH), eine hochangepaßte, filtrierende Benthos- Foraminifere. -Ber. Sonderforschungsber. 313, 6, 31-46, Kiel MARENMJ.ER, E. (1886): Poriferen, Anthozoen, Ctenophoren und WürInervon Jan Mayen. - Die Osterreichische Polarstation J an Mayen, Beobacht. Ergeb., 3, 9-14, Wien MEREJKOWSKY, C. (1878): Les Eponges de laMer Blanche. - Mem. Acad. Imper. Seienc. St. Petersbourg. - 26n, 7.Ser., 51 pp., St.Petersbourg NFJSON, C.S., HYDON. F.M., KEANE, S. L., LEASK, W. L. & GORDON, D. P. (1988): Application of bryozoan 1.oarial growth-fOlIIl studies in faeies analysis of non-tropical carbonate deposits in New Zealand. - Sed. Geology, 60, 301-322, Amsterdarn NORDGAARD, O. (1918): Bryozoafrom theArcticRegions. -Troms0 Museum Arshefter, 40/1, 1-99, TroffiS0 OcKFl.MANN, W. K. (1958): The zoology of east Greenland - marine Lamellibranchiata. - Meddr. om Gr0nland, 107n, 1- 256, Kopenhagen 103 OSCHMANN, W. (1990): Dropstones - rocky mini-islands in high- lati tude pelagic soft substrate environments. - Senckenbergiana marit., 21/14, 55-75, Frankfurt -- (1991): Ecology and bathymetryofthe LateQuaternary shelly macrobenthos from bathyal and abyssal areas ofthe Norwegian Sea. - Senckenbergiana marit., 21/5-6, Frankfurt PrnPENBURG, D. (1988): Zur Zusammensetzung der Bodenfauna in der westlichen Fram Straße. - Ber. Polarforschung, 52, 1-117, Bremerhaven POWELL, N.A. (1968): Bryozoa (Polyzoa) of Arctic Canada. - 1. Fish. Res. Bd. Canada, 25/11, 2269-2320, Toronto RASMUSSEN, B. N. (1965): On taxonomy and biology of the north Atlantic species of the as~eroid genus Henricia Gray. - Medd. Danm. Fiskeri. Havunders. N.S., 4n, 157-213, Kopenhagen RYLAND, J. S. (1963): Systematics and biological studies on Polyzoa (Bryozoa) from western Norway. - Sarsia, 14, I-59, Bergen SCHMfIT, M., BoTZ, R. & FABER, E. (1991): Ultrasonic vacuun degassing of water for methane extraction. - Analytical Chemistry (in press) SCHOPF, T. 1. M. (1969): Paleoecology of ectoprocts (bryozoans). - 1. Paleont. 43, 234-244, Tulsa SCHUl.ZE, F.E. (1900): Die Hexactinelliden. - Fauna Arctica, 1 (Lfg.1), 86-108, Fischer, Jena -- (1903): Cau/ophaeus aretieus (ARMAUER HANSEN) und Ca/y- eosoma graci/em F.E.SCH. nov.spec. - Abh. K. preuss. Akad. Wiss., 1903, 1-22, Berlin STACH, L. W. (1936): Correlation of zoarial growth fonn with habitat. - 1. Geol. 44, 60-66, Chicago STEENSTRUP, E. & TENDAL, O. S. (1982): The genus Thenea (Porifera, Demospongia, Choristida) in the Norwegian Sea and adjacent waters; an annotated key. - Sarsia: 67, 259-268, Bergen SWIFI', J. H. (1986): The Arctic waters. - In: HURDLE, B. G. (ed.), The Nordic Seas, 129-154, Springer Verlag, New York TAYLOR, G.I. (1923): Experiments on the motionof solid bodies in rotation fluids. - Proc. Roy. Soc. London, B., Biol. Sci.,104A, 213-218, London TAYLOR, P. D. (1979): The inference extrazooidal feeding currents in fossil bryozoan colonies. - Lethaia, 12, 47-56, Oslo TENDAL, O. S. (1970): Sponges from lörgen Brönlund Fjord, North Greenland. - Meddr. om Grönland, 184n, 1-14, Kopenhagen -- (1979): Sponges of lan Mayen. - Astarte, 12,53-55, Troms0 THIEDE, 1. & HEMPEL, G. (1991): Die Expedition ARKTIS-VIII 1 mit FS "POLARSlERN" 1990. - Ber. Polarforschung, 80, 1-137, Bremerhaven THORSON, G. (1958): The Godthaab expedition 1928: Scaphopoda, Placophora, Solenogastres, Gastropoda, Prosobranchia, Larn- ellibranchiata. - Medd. Gr0nland, 81/2, 117pp, Kopenhagen VANWAGONER, N. A., MUDIE, P. 1, COLE, F. E. & DABoRN, G. (1989): Siliceous spongecommunities, biological zonation, and Recent sea-level change on the Arctic margin: Ice Island results .. - Can.1. Earth Sci., 26, 2341-2355, Montreal VINJE, T. (1985): The physical environment ofthe western Barents Sea: Drift, composition, morphology anddistributionofthesea ice fields in the Barents Sea. -rNorsk. Polarinst. Skr., 179C, 1- 26,Osl0 VOSMAER, G. C. 1. (1885): The Sponges of the "Willern Barents" Expedition 1880and 1881. -Bijdr. Dierk., 12, 147, Amsterdarn W ALLRABE-ADAMS, H. 1. (1991): Submarine Aschelagen bei Vesterisbank (Grönlandsee). - IN: THIEDE, 1. & HEMPEL, G. (Hrsg.), Die Expedition ARKTIS-VIII 1 mit FS "POLARSlERN" 1990, Ber. Polarforschung, 80,82- 86, Bremerhaven WINSTON,1. E. (1981): Feeding Behavior of Modem Bryozoans.- IN: BROADHEAD, T. W. (ed.): Lophophorates, Notes for a short course. pp. 21, University ofTennessee, Cincinnati -- (1978): Polypide morphology and feeding behavior in marine ectoprocts. - BuH. Mar. Sci. 28, 1-31, Miarni Manuscript received lanuary 9, 1992 Revised manuscript accepted luly 14, 1992