Biogeosciences, 11, 7009–7023, 2014
www.biogeosciences.net/11/7009/2014/
doi:10.5194/bg-11-7009-2014
© Author(s) 2014. CC Attribution 3.0 License.
Biomarkers in the stratified water column of the
Landsort Deep (Baltic Sea)
C. Berndmeyer1, V. Thiel1, O. Schmale2, N. Wasmund2, and M. Blumenberg1,*
1Geobiology Group, Geoscience Center, Georg August University Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany
2Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Seestr. 15, 18199 Rostock-Warnemünde, Germany
*now at: Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655 Hanover, Germany
Correspondence to: C. Berndmeyer (christine.berndmeyer@geo.uni-goettingen.de)
Received: 28 May 2014 – Published in Biogeosciences Discuss.: 25 June 2014
Revised: 28 October 2014 – Accepted: 29 October 2014 – Published: 11 December 2014
Abstract. The water column of the Landsort Deep, central
Baltic Sea, is stratified into an oxic, suboxic, and anoxic
zone. This stratification controls the distributions of individ-
ual microbial communities and biogeochemical processes.
In summer 2011, particulate organic matter was filtered
from these zones using an in situ pump. Lipid biomark-
ers were extracted from the filters to establish water-column
profiles of individual hydrocarbons, alcohols, phospholipid
fatty acids, and bacteriohopanepolyols (BHPs). As a ref-
erence, a cyanobacterial bloom sampled in summer 2012
in the central Baltic Sea Gotland Deep was analyzed for
BHPs. The biomarker data from the surface layer of the oxic
zone showed major inputs from cyanobacteria, dinoflagel-
lates, and ciliates, while the underlying cold winter water
layer was characterized by a low diversity and abundance
of organisms, with copepods as a major group. The suboxic
zone supported bacterivorous ciliates, type I aerobic methan-
otrophic bacteria, sulfate-reducing bacteria, and, most likely,
methanogenic archaea. In the anoxic zone, sulfate reducers
and archaea were the dominating microorganisms as indi-
cated by the presence of distinctive branched fatty acids:
archaeol and pentamethylicosane (PMI) derivatives, respec-
tively. Our study of in situ biomarkers in the Landsort Deep
thus provided an integrated insight into the distribution of rel-
evant compounds and describes useful tracers to reconstruct
stratified water columns in the geological record.
1 Introduction
The Baltic Sea is a brackish marine marginal sea with a max-
imum depth of 459 m in the Landsort Deep (western central
Baltic Sea; Matthäus and Schinke, 1999; Reissmann et al.,
2009; Fig. 1). A positive freshwater budget and saltwater in-
flows from the North Sea through Skagerrak and Kattegat
lead to a permanent halocline that stratifies the water column
of the central Baltic Sea at about 60 m water depth (Reiss-
mann et al., 2009). Major saltwater inflows, as detected in
1993 and 2003, sporadically disturb the stratification in the
eastern central Baltic Sea and oxygenate the suboxic zone
and deep water. These inflows, however, rarely reach the
western central Baltic Sea. Even the strong inflow from 1993
had only minor effects on Landsort Deep, where stagnating
conditions prevailed throughout (Bergström and Matthäus,
1996). Therefore, the Landsort Deep offers stable environ-
ments for microbial life within the oxic, suboxic, and anoxic
zones and provides an excellent study site for the investi-
gation of biomarker inventories that specify stratified water
columns.
The Black Sea, although much larger in size, is compara-
ble with the Landsort Deep with respect to the existence of a
permanently anoxic deep-water body. Two comprehensive in
situ biomarker reports gave a wide-ranging overview of var-
ious biomarkers and their producers in the Black Sea water
column and identified a close coupling of microorganisms
to biogeochemically defined water layers (Wakeham et al.,
2007, 2012). Several other in situ biomarker water-column
studies exist, but they were usually focused on certain as-
pects, for example anaerobic and aerobic methanotrophy
Published by Copernicus Publications on behalf of the European Geosciences Union.
7010 C. Berndmeyer et al.: Biomarkers in the stratified water column
Figure 1. Map showing the sampling locations in the central Baltic
Sea.
(Schouten et al., 2001; Schubert et al., 2006; Blumenberg et
al., 2007; Sáenz et al., 2011; Xie et al., 2014, and others).
For the Baltic Sea water column, biomarker knowledge
is limited as most studies so far were focused on pollution-
related compounds (e.g., Beliaeff and Burgeot, 2001; Lehto-
nen et al., 2006; Hanson et al., 2009). Recently, we reported
the water-column distributions and 13C-content of individual
bacteriohopanepolyols (BHPs) and phospholipid fatty acids
(PLFA) from the Gotland Deep, located about 150 km SE of
the Landsort Deep in the eastern central Baltic Sea. These
studies were aimed at microbial methane turnover and con-
firmed the importance of the Baltic Sea suboxic zone for bac-
terial methane oxidation (Schmale et al., 2012; Berndmeyer
et al., 2013; Jakobs et al., 2014). The theoretical possibility
of sulfate-dependent methane oxidation in the anoxic zone
was also stated (Jakobs et al., 2014) but still remains to be
proven for the central Baltic Sea water column.
Because the eastern central Baltic Sea is regularly dis-
turbed by lateral intrusions in intermediate water depths
(Jakobs et al., 2013), we chose the more stable Landsort
Deep in the western central Baltic Sea as a sampling site for
this biomarker study. Furthermore, published genetic studies
reporting on prokaryotes and the related metabolisms in the
water column of the Landsort Deep (Labrenz et al., 2007;
Thureborn et al., 2013) provide a background to which the
organic geochemical results can be advantageously related.
The depth profiles of biomarkers from this setting not only
reveal how actual biogeochemical processes are reflected by
lipid abundances, distributions, and stable carbon isotope sig-
natures, they also provide reference data for the reconstruc-
tion of past water columns using biomarkers from the sedi-
mentary record.
2 Materials and methods
2.1 Samples
Samples were taken during cruise 06EZ/11/05 of R/V Elisa-
beth Mann Borghese in summer 2011. The Landsort Deep is
located north of Gotland (58◦35.0′ N, 18◦14.0′ E; Fig. 1). A
Seabird sbe911+ CTD (conductivity, temperature, density)
system and a turbidity sensor ECO FLNTU (WET Labs)
were used for continuous water-column profiling. Oxygen
and hydrogen sulfide concentrations were measured colomet-
rically with Winkler’s method, respectively (Grasshoff et al.,
1983). Filter samples of 65 to 195 L obtained from 10, 65,
70, 80, 90, 95, and 420 m water depth were taken with an in
situ pump, and particulate material was filtered onto precom-
busted glass microfiber filters (∅ 30 cm; 0.7 µm pore size;
Munktell & Filtrak GmbH, Germany). Filters were freeze-
dried and kept frozen at −20 ◦C until analysis.
A cyanobacterial bloom was sampled in summer 2012
on cruise M87/4 of R/V Meteor at the Gotland Deep
(57◦19.2′ N, 20◦03.0′ E; Fig. 1), east of Gotland. Water sam-
ples of 10 L were taken at 1 m water depth and filtered with
a 20 µm net. The samples were centrifuged and the residue
freeze-dried. Samples were kept frozen at −20 ◦C until anal-
ysis.
2.2 Bulk CNS analysis
Three pieces (∅ 1.2 cm) from different zones of the filters
were combusted together with V2O5 in a EuroVector Eu-
roEA Elemental Analyzer. Particulate matter in the Baltic
Sea was reported to be free of carbonate (Schneider et al.,
2002), and, thus, the filters were not acidified prior to analy-
sis. C, N, and S contents were calculated by comparison with
peak areas from standards. Standard deviations were ±2 %
for C and ±5 % for N and S.
2.3 Lipid analysis
Three quarters of each filter were extracted (3× 20 min) with
dichloromethane (DCM) /methanol (MeOH) (40 mL; 3 : 1,
v : v) in a CEM Mars 5 microwave (Matthews, NC, USA) at
60 ◦C and 800 W. The freeze-dried residue of the cyanobac-
terial bloom was extracted (3× 10 min) with DCM /MeOH
(10 mL; 3 : 1, v : v) and ultrasonication. All extracts were
combined.
An aliquot of each filter extract and the bloom extract was
acetylated using Ac2O and pyridine (1 : 1, v : v) for 1 h at
50 ◦C and then overnight at room temperature. The mixture
was dried under vacuum and analyzed for BHPs using liquid-
chromatography–mass-spectrometry (LC-MS).
Another aliquot of each filter extract was separated into a
hydrocarbon (F1), an alcohol and ketone (F2), and a polar
fraction (F3) using column chromatography. The column (∅
ca. 1 cm) was filled with 7.5 g silica gel 60; samples were
dried on ca. 500 mg silica gel 60 and placed on the column.
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C. Berndmeyer et al.: Biomarkers in the stratified water column 7011
The fractions were eluted with 30 mL n-hexane /DCM 8 :
2 (v : v, F1), 30 mL DCM /EtOAC 9 : 1 (v : v, F2), and
100 mL DCM /MeOH 1 : 1, (v : v) followed by an additional
100 mL MeOH (F3). F2 was dried and derivatized using a
BSTFA / pyridine 3 : 2 (v : v) mixture for 1 h at 40 ◦C. A to-
tal of 50 % of the polar fraction F3 was further fractionated to
obtain PLFA (F3.3) according to Sturt et al. (2004). Briefly,
this entails filling the column with 2 g silica gel 60 and stor-
ing it at 200 ◦C until use. The F3 aliquot was dried on ca.
500 mg silica gel 60 and placed on the column. After suc-
cessive elution of the column with 15 mL DCM and 15 mL
acetone, the PLFA fraction was eluted with 15 mL MeOH
(F3.3). F3.3 was transesterified using trimethylchlorosilane
(TMCS) in MeOH (1 : 9; v : v) for 1 h at 80 ◦C. In the re-
sulting fatty acid methyl ester (FAME) fractions, double-
bond positions in monounsaturated compounds were deter-
mined using dimethyldisulfide (DMDS; Carlson et al., 1989;
Gatellier et al., 1993). The samples were dissolved in 200 µL
DMDS, 100 µL n-hexane, and 30 µL I2 solution (60 mg I2 in
1 mL Et2O) and derivatized at 50 ◦C for 48 h. Subsequently,
1 mL of n-hexane and 200 µL of NaHSO4 (5 % in water)
were added and the n-hexane extract was pipetted off. The
procedure was repeated 3 times, and the n-hexane extracts
were combined, dried on ca. 500 mg silica gel 60 and put
onto a small column (ca. 1 g silica gel 60). For cleaning, the
n-hexane extract was eluted with 10 dead volumes of DCM.
F1, F2, F3.3, and the samples treated with DMDS were an-
alyzed using gas-chromatography–mass-spectrometry (GC-
MS).
2.4 Gas-chromatography–mass-spectrometry (GC-MS)
and GC-combustion isotope ratio mass
spectrometry (GC-C-IRMS)
GC-MS was performed using a Varian CP-3800 chromato-
graph equipped with a Phenomenex Zebron ZB-5MS fused
silica column (30 m× 0.32 mm; film thickness 0.25 µm) cou-
pled to a Varian 1200L mass spectrometer. Helium was
used as a carrier gas. The temperature program started at
80 ◦C (3 min) and ramped up to 310 ◦C (held 25 min) with
4 ◦C min−1. Compounds were assigned by comparing mass
spectra and retention times to published data. Concentrations
were determined by comparison with peak areas of squalane
(F2 and F3) and n-eicosane-D42 (F1) as internal standards.
Compound-specific stable carbon isotope ratios of
biomarkers in F2 and F3.3 were measured (twice) using a
Thermo Trace gas chromatograph coupled to a Thermo Delta
Plus isotope ratio mass spectrometer. The GC was oper-
ated under the same conditions and with the same column
as for GC-MS. The combustion reactor contained CuO, Ni,
and Pt and was operated at 940 ◦C. Isotopic compositions
are reported in standard delta notation relative to the Vienna
PeeDee Belemnite (V-PDB) and were calculated by compar-
ison with an isotopically known CO2 reference gas. GC-C-
IRMS precision and linearity was checked daily using an ex-
ternal n-alkane isotopic standard (provided by A. Schimmel-
mann, Indiana University).
2.5 Liquid-chromatography–mass-spectrometry
(LC-MS)
LC-MS was performed using a Varian Prostar Dynamax
high-performance liquid chromatography (HPLC) system fit-
ted with a Merck Lichrocart (Lichrosphere 100; reversed
phase (RP) C18e) column (250× 4 mm) and a Merck Lichro-
sphere pre-column of the same material coupled to a Varian
1200L triple quadrupole mass spectrometer (both Varian).
The solvents used were MeOH /water 9 : 1 (v : v; solvent A)
and MeOH / propan-2-ol 1 : 1 (v : v; solvent B), and all sol-
vents were Fisher Scientific HPLC grade. The solvent gradi-
ent profile was 100 % A (0–1 min) to 100 % B at 35 min and
then isocratic to 60 min. The MS was equipped with an at-
mospheric pressure chemical ionization (APCI) source oper-
ated in positive/ion mode (capillary temperature 150 ◦C, va-
porizer temperature 400 ◦C, corona discharge current 8 µA,
nebulizing gas flow 70 psi, auxiliary gas 17 psi). In SIM
(single-ion monitoring) mode, ions obtained from acetylated
BHP peaks in the samples were compared to authentic BHP
standards with known concentrations (acetylated BHP and
aminotriol) to determine BHP concentrations (external cal-
ibration). Amino BHPs had a 7 times higher response fac-
tor than nonamino BHPs, and concentrations in the samples
were corrected accordingly. Comparisons with elution times
of previously identified compounds further aided in BHP as-
signment. The quantification error is estimated to be ±20 %.
2.6 Principle component analysis (PCA)
PCA was based on the relative abundance of individual com-
ponents in different water depths and was performed using
R (version 3.0.2, 25 September 2013) with the “princomp”
module (The R Foundation, 2014).
3 Results
3.1 Physicochemical parameters of the water column
In summer 2011, the Landsort Deep showed a strong vertical
stratification (Fig. 2). The oxic zone consisted of the upper-
most 80 m and was divided by a strong thermocline into a
warm surface layer (∼ 0–10 m) and a cold winter water layer
(∼ 10–60 m). The halocline was located between 60 and
80 m. O2 concentrations rapidly decreased from > 8 mL L−1
at ∼ 50 m to < 0.2 mL L−1 at ∼ 80 m, defining the upper
boundary of the suboxic zone (Tyson and Pearson, 1991).
H2S was first detected at 83 m. Because O2 concentrations
could methodologically only be measured in the complete
absence of H2S, oxygen could not be traced below this
depth. Therefore, the lower boundary of the suboxic zone
was defined to be at 90 m, where H2S concentrations sharply
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7012 C. Berndmeyer et al.: Biomarkers in the stratified water column
Figure 2. Physicochemical characteristics of the Landsort Deep wa-
ter column in summer 2011. The suboxic zone is shaded light grey.
Temperature and methane data were partially taken from Jakobs et
al. (2014).
increased. The upper suboxic zone also showed a sharp peak
in turbidity that is possibly caused by the precipitation of Fe
and Mn oxides (Dellwig et al., 2010) or zero-valent sulfur
(Kamyshny Jr. et al., 2013) and can be used as an indica-
tor of the O2-H2S transition (Kamyshny Jr. et al., 2013). The
anoxic zone extends from 90 m to the bottom and is charac-
terized by the complete absence of O2 and high concentra-
tions of H2S and CH4.
CH4 was highest in the deep anoxic zone and decreased
strongly towards the suboxic zone but was still present
in minor concentrations in the oxic zone. A small CH4
peak was detected at the suboxic–anoxic interface (Fig. 2).
Particulate organic carbon (POC) was highest at 10 m
(380 µg L−1), decreased to a minimum in the cold winter wa-
ter layer (48 µg L−1), and showed almost constant values of
∼ 70 µg L−1 in the suboxic and anoxic zones.
Generally, we follow the zonation of the Landsort Deep
water column as given in Jakobs et al. (2014). We regarded
the onset of H2S as the top of the anoxic zone, however, as
this is better supported by our biomarker data (see below).
3.2 Lipid analysis
The PCA analysis separated six groups of biomarkers ac-
cording to their distribution in the water column (Fig. 3,
Sect. 3.2.1-6). Out of these groups, 18 compounds were se-
lected as representative biomarkers, specifying inputs from
individual prokaryotes and eukaryotes (with phototrophic,
chemotrophic, and/or heterotrophic metabolisms). These
biomarkers and their distributions are discussed in detail in
Sect. 4.
The concentrations of these compounds are shown in
Fig. 4, and compound-specific δ13C values are given in Ta-
ble 1. Apart from the biomarker families revealed by PCA,
two compound classes – n-alkanes and n-alkenes in the sea
surface layer – and individual BHPs obtained from the water
Table 1. δ13C values of the compounds chosen from the PCA
groups. No δ13C values were available for Group 4. N.d. stands
for “not detectable”.
δ13C [‰]
Compound oxic zone suboxic zone anoxic zone
Group 1
7-Me-17 : 0 alkane n.d. n.d. n.d.
β-Sitosterol −29.9 n.d. −30.1
20 : 4ω6 PLFA −30.1 −31.7 −31.6
20 : 5ω3 PLFA −29.2 n.d. n.d.
16 : 1ω7c PLFA −30.6 −28.0 −28.3
Cholesterol −26.8 −28.9 −31.7
Group 2
Dinosterol −29.9 −30.9 −32.0
Tetrahymanol −28.7 −27.9 −25.9
Ai-15 : 0 PLFA −29.3 −32.5 −34.2
Diploptene n.d. n.d. n.d.
Group 3
16 : 0–18 : 1 Wax ester −28.1 −28.2 n.d.
Group 5
16 : 1ω8 PLFA n.d. −45.4 n.d.
Group 6
Cholestanol −27.8 −28.9 −30.1
10-Me-16 : 0 PLFA n.d. −32.5 −35.4
PMI+PMI 1 n.d. n.d. n.d.
Archaeol n.d. n.d. –
column and a cyanobacterial bloom are reported separately
(Fig. 5, Sect. 3.2.7; Fig. 6a, Sect. 3.2.8, respectively).
3.2.1 Group 1: surface maximum
The first group is defined by a strong maximum in the sur-
face layer and only minor concentrations in greater depths.
A subgroup of 14 compounds exclusively occurs at 10 m
water depth (Fig. 3). For the other compounds, abun-
dance in greater water depths increases towards the y axis.
7-methylheptadecane (52), 24-ethylcholest-5-en-3β-ol (β-
sitosterol; 48), 20 : 4ω6 PLFA (34), 20 : 5ω3 PLFA (33),
16 : 1ω7c PLFA (11), and cholest-5-en-3β-ol (cholesterol;
44) were taken as representative for Group 1. Among these
compounds, 16 : 1ω7 PLFA and cholesterol showed the high-
est concentrations (1154 and 594 ng L−1, respectively) and 7-
methylheptadecane the lowest (6 ng L−1, Fig. 4). Apart from
their maximum in the surface layer, the fate of these biomark-
ers in deeper water layers differed. 7-methylheptadecane ex-
clusively occurred in the surface layer, whereas 20 : 4ω6 was
traceable throughout the water column. β-sitosterol occurred
in the surface and the bottom layers. Unlike the other com-
pounds, cholesterol and 20 : 5ω3 PLFA did not show a linear
decrease with depth; rather, there are minor occurrences right
Biogeosciences, 11, 7009–7023, 2014 www.biogeosciences.net/11/7009/2014/
C. Berndmeyer et al.: Biomarkers in the stratified water column 7013
Table 2. Compounds sorted by number as shown in Fig. 3. Compounds chosen for further discussion are marked bold.
Compounds:
1 13 : 0 PLFA 22 18 : 4 PLFA 43 26 : 0 PLFA 64 n-C22:1
2 i14 : 0 PLFA 23 18 : 2 PLFA 44 cholesterol 65 n-C22 : 0
3 14 : 0 PLFA 24 18 : 3 PLFA 45 cholestanol 66 n-C23 : 1
4 i15 : 0 PLFA 25 18 : 1ω9c PLFA 46 16 : 0-18.1 wax ester 67 n-C23 : 0
5 ai15 : 0 PLFA 26 18 : 1ω7c PLFA 47 18 : 0− 18 : 1 wax ester 68 n-C24 : 1
6 15 : 0 PLFA 27 18 : 1ω6c PLFA 48 β-Sitosterol 69 n-C24 : 0
7 16 : 4 PLFA 28 18 : 1ω5c PLFA 49 dinosterol 70 n-C25 : 1
8 i 16 : 0 PLFA 29 18 : 0 PLFA 50 tetrahymanol 71 n-C25 : 0
9 16 : 1ω9c PLFA 30 10-me-18 : 0 PLFA 51 archaeol 72 n-C26 : 1
10 16 : 1ω8c PLFA 31 iC19 : 0 PLFA 52 7-methylheptadecane 73 n-C26 : 0
11 16 : 1ω7c PLFA 32 19 : 0 PLFA 53 PMI +PMI D 74 n-C27 : 0
12 16 : 1ω7t PLFA 33 20 : 5ω3 PLFA 54 diploptene 75 n-C28 : 0
13 16 : 1ω5c PLFA 34 20 : 4ω6 PLFA 55 n-C17 : 1 76 n-C29 : 0
14 16 : 1ω5t PLFA 35 20 : 3 PLFA 56 n-C17 : 0 77 n-C30 : 0
15 16 : 0 PLFA 36 20 : 3 PLFA 57 n-C18 : 0 78 n-C31 : 0
16 10-me-16 : 0 PLFA 37 20 : 1 PLFA 58 n-C19 : 1 79 n-C32 : 0
17 iC17 : 0 PLFA 38 20 : 0 PLFA 59 n-C19 : 0 80 n-C33 : 0
18 ai C17 : 0 PLFA 39 22 : 6 PLFA 60 n-C20 : 1 81 n-C34 : 0
19 17 : 1 PLFA 40 22 : 4 PLFA 61 n-C20 : 0 82 n-C35 : 0
20 17 : 0 PLFA 41 22 : 0 PLFA 62 n-C21 : 1 83 n-C36 : 0
21 18 : 4 PLFA 42 24 : 0 PLFA 63 n-C21 : 0 84 total BHPs
above and at the bottom of the suboxic zone. δ13C values of
all compounds were between −32 and −26 ‰ (Table 1).
3.2.2 Group 2: surface and lower suboxic zone maxima
Like Group 1, Group 2 shows a surface maximum, but it
exhibits a stronger emphasis on the lower suboxic zone
(Fig. 4). With the exception of 16 : 7ω7t, all compounds
were chosen for further consideration. 4α, 23, 24-trimethyl-
5α-cholest-22E-en-3β-ol (dinosterol; 49), and gammacer-
3β-ol (tetrahymanol; 50) had their maximum concentration
in the surface water (dinosterol: 66 ng L−1; tetrahymanol:
42 ng L−1) and were not detectable in the layers below un-
til a sharp second maximum occurred at the bottom of the
suboxic zone. Concentrations decreased again below the sub-
oxic zone and remained constantly low in the bottom water.
Unlike these compounds, ai 15 : 0 PLFA (5), total bacteri-
ohopanepolyols (BHPs; 84), and the hopanoid hydrocarbon
hop-22(29)-ene (diploptene; 54) showed steadily increasing
concentrations throughout the suboxic zone and further in-
creasing concentrations in the anoxic zone. The δ13C values
of all compounds were between −35 and −25 ‰ (Table 1).
3.2.3 Group 3: cold winter water layer maximum
The third group showed compounds that peaked in the cold
winter water layer at 65 m water depth (Fig. 3). 17 : 1ω9
PLFA (19) only occurred at 70 m water depth, and n-C21 (61)
occurred from 10 to 70 m, with a strong peak at 70 m. The
16 : 0− 18 : 1 (46; Fig. 4) and 18 : 0− 18 : 1 (47) wax esters
Figure 3. PCA of the relative abundances of compounds in differ-
ent water depths. Group 1: surface maximum; a subgroup of com-
pounds exclusively occurring at the surface are listed in the box.
Group 2: surface and lower suboxic zone maxima. Group 3: cold
winter water layer maximum. Group 4: oxic-zone high concentra-
tions. Group 5: suboxic zone maximum. Group 6: absent in oxic
zone, bottom layer maximum. Compound names are given in Ta-
ble 2.
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7014 C. Berndmeyer et al.: Biomarkers in the stratified water column
Figure 4. Vertical distribution of biomarkers in the Landsort Deep
water column. The suboxic zone is shaded grey.
only occurred from 65 to 80 m, with a maximum at 65 m (287
and 228 ng L−1, respectively). Of Group 3, the 16 : 0−18 : 1
wax ester was included in the discussion. δ13C values of the
wax esters were ∼−28 ‰ (Table 1).
3.2.4 Group 4: oxic-zone maximum
Group 4 consisted exclusively of saturated n-alkanes from
n-C21 to n-C36 as well as 26 : 0 PLFA (43). 26 : 0 PLFA
only occurred at 80 m, whereas all other compounds were
abundant from the surface to the upper suboxic zone at 80 m
(data not shown). The homologues n-C27 (74), n-C29 (76),
and n-C31 (78) show maxima at the surface (21–30 ng L−1).
For the other compounds, maxima were either located at
65 or 70 m, with highest concentrations for n-C25− n-C36
(10–23 ng L−1). Below 80 m, concentrations dropped to con-
stantly low values. As an example, the depth profile of n-C25
(71) is shown in Fig. 4. δ13C values for these compounds
could not be obtained.
Figure 5. Concentrations of n-alkanes and n-alkenes in the Land-
sort Deep surface layer (oxic zone, 10 m water depth).
3.2.5 Group 5: suboxic-zone maximum
Group 5 contained only two compounds: 16 : 1ω8c PLFA
(10) and the n-C26 : 1 alkene (72). n-C26 : 1 occurred in very
low concentrations at 10 m and peaked at 80 and 95 m (7–
8 ng L−1). 16 : 1ω8c PLFA occurred only at 80 and 90 m wa-
ter depth, with highest values at 80 m (8 ng L−1; Fig. 4), and
was chosen for further discussion. δ13C values of this com-
pound were ∼−45 ‰ (Table 1).
3.2.6 Group 6: absent in oxic zone, bottom-layer
maximum
Group 6 consisted of compounds that only occurred in
the suboxic zone and below and increased in concentration
in the anoxic zone. An exception is 5α(H)-cholestan-3β-
ol (cholestanol; 45), which was also present in the surface
layer. 10-me-16 : 0 PLFA (16), the irregular C25 isoprenoid
2, 6, 10, 15, 19-pentamethylicosane (PMI) and three unsat-
urated derivatives thereof (PMI 1; 53), 2, 3-di-0-isopranyl
sn-glycerol diether (archaeol; 51), and cholestanol were con-
sidered for further discussion. For all compounds, maxima
were detected in the anoxic zone, with highest concentra-
tions observed for cholestanol (35 ng L−1) followed by 10-
me-16 : 0 PLFA (10 ng L−1), PMI and PMI 1 (8 ng L−1),
and archaeol (1 ng L−1). Compared to other compounds, 10-
me-16 : 0 PLFA shows a slight 13C depletion in the anoxic
zone (−35.4 ‰ ; Table 1). Concentrations of archaeol, PMI,
and PMI 1 were too low to determine δ13C.
3.2.7 n-Alkanes and n-alkenes in the sea surface layer
The concentrations of n-alkanes and n-alkenes in the surface
sample (10 m water depth) are given in Fig. 5. The longest
n-alkane chain was n-C36, and odd carbon numbers domi-
nated over even. Highest concentrations were found for n-
C27 (21 ng L−1), n-C29 (30 ng L−1), and n-C31 (26 ng L−1).
The longest n-alkene chain was n-C26 : 1, and highest n-
alkene concentrations were measured for n-C23 : 1 (3 ng L−1)
and n-C25 : 1 (3 ng L−1).
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C. Berndmeyer et al.: Biomarkers in the stratified water column 7015
3.2.8 Water-column profiles of BHPs
In the Landsort Deep, seven individual BHPs were identified
(Fig. 6a). In all samples, bacteriohopane-32, 33, 34, 35-tetrol
(BHT) accounted for the greatest portion of the total BHPs
(88–94 %). An as yet uncharacterized BHT isomer, BHT II,
was present only below 70 m and showed its highest rela-
tive abundance (∼ 2 %) between 70 and 90 m. BHT cycli-
tol ether, BHT glucosamine, and 35-aminobacteriohopane-
32, 33, 34-triol (aminotriol) were present throughout the wa-
ter column. BHT cyclitol ether and BHT glucosamine were
most abundant in the oxic zone (ca. 1–4 %) but showed
only minor abundances (< 1 %) below. Aminotriol was el-
evated at 65 and 420 m (∼ 7 and ∼ 5 %, respectively). 35-
Aminobacteriohopane-31, 32, 33, 34-tetrol (aminotetrol) oc-
curred throughout the suboxic and anoxic zones, whereas 35-
aminobacteriohopane-30, 31, 32, 33, 34-pentol (aminopen-
tol) was observed only at 90 m and below. Both aminotetrol
and aminopentol showed minor relative abundances of ∼ 2
and < 1 % of the total BHPs, respectively (Jakobs et al.,
2014).
For comparison, the major phytoplankton species from a
cyanobacterial bloom in the Gotland Deep (2012) were deter-
mined by microscopy (HELCOM manual, 2012) and the par-
ticulate organic matter (POM) was analyzed for BHPs. This
reference biomass contained mainly Aphanizonemon and, to
a smaller extent, Anabaena and Nodularia, which were ac-
companied by dinoflagellates. Three BHPs were observed
in the bloom POM (Fig. 6b). Among these compounds, the
most abundant was BHT (∼ 86 %), followed by BHT cyclitol
ether (∼ 10 %) and BHT glucosamine (∼ 4 %).
4 Discussion
In the following, we discuss several aspects of the biomarker
profiles with respect to their significance as tracers for the
relevant biota and biogeochemical processes in stratified wa-
ter columns.
4.1 Water-column redox zones as reflected by
cholestanol / cholesterol ratios
Different redox states of the Landsort Deep water column
and the associated microbial processes are reflected by the
profiles of cholesterol and its diagenetic product, cholestanol
(Fig. 4; Groups 1 and 6, respectively). Cholesterol is syn-
thesized by various eukaryotic phyto- and zooplankton and
higher plants (Parrish et al., 2000) and is abundant in wa-
ter columns and sediments. In sediments as well as in
stratified water columns, stanols are produced from sterols
by anaerobic bacterial hydrogenation (Gaskell and Eglin-
ton, 1975; Wakeham, 1989) and by the abiotic reduction
of double bonds by reduced inorganic species such as H2S
(Hebting et al., 2006; Wakeham et al., 2007). Therefore,
cholestanol / cholesterol ratios typically increase under more
Figure 6. Relative abundances of individual BHPs (as percent of the
total) of (a) the Landsort Deep water column and (b) the Gotland
Deep cyanobacterial bloom. Note that [%] axes start at 85 %. An
asterisk indicates data taken from Jakobs et al. (2014).
reducing conditions. In the Black Sea, low ratios of ∼ 0.1
were associated with oxygenated surface waters, and the sub-
oxic zone showed ratios between 0.1 and 1, whereas the
anoxic zone revealed values > 1 (Wakeham et al., 2007).
In the Landsort Deep, the cholestanol / cholesterol ratios
showed a slight increase with depth from the surface towards
the suboxic zone but always remained < 0.1 (Fig. 4). Below,
the values increased to ∼ 0.3 in the suboxic zone and further
to a maximum of 0.45 in the anoxic zone. Whereas the ra-
tios in the Landsort Deep are considerably lower than in the
Black Sea, the depth trend still clearly mirrors the changes
from oxic to suboxic, and further to anoxic conditions. It is
also interesting to note that total cholesterol and cholestanol
concentrations in the Landsort Deep were ten- and fourfold
higher, respectively, than in the Black Sea (Wakeham et al.,
2007).
4.2 Phototrophic primary production
As expected, in situ biomarkers for phototrophic organisms
were most abundant in the surface layer and are pooled in
PCA Group 1. 20 : 4ω6 PLFA is a biomarker traditionally
assigned to eukaryotic phytoplankton (Nanton and Castell,
1999; Lang et al., 2011) and organisms grazing thereon, such
as protozoa (Findlay and Dobbs, 1993; Pinkart et al., 2002;
Risse-Buhl et al., 2011). 20 : 5ω3 PLFA is known to be a ma-
jor compound in diatoms (Arao and Marada, 1994; Dunstan
et al., 1994), and high concentrations of these PLFAs, as ob-
served in the surface layer of the oxic zone, are in good agree-
ment with such an autochthonous plankton-based source.
7-Methylheptadecane is a characteristic marker for
cyanobacteria (Shiea et al., 1990; Köster et al., 1999). Its
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7016 C. Berndmeyer et al.: Biomarkers in the stratified water column
most likely source are members of the subclass Nosto-
cophyceae that were often reported to produce isomeric
midchain branched alkanes, including 7-methylheptadecane
(Shiea et al., 1990; Hajdu et al., 2007; Liu et al., 2013). Nos-
tocophyceae are key members of the photoautotrophic com-
munity in the Baltic Sea. Particularly the filamentous genera
Nodularia and Aphanizonemon (see Sect. 3.2.8) and the pic-
ocyanobacterium Synechococcus play a major role in blooms
during summer time (Stal et al., 2003; Labrenz et al., 2007).
The importance of cyanobacteria in the surface layer of the
Landsort Deep is further reflected by the presence of C21 : 1,
C23 : 1, and C25 : 1 n-alkenes (Fig. 5). These compounds have
been reported from Anacystis (Gelpi et al., 1970) and Oscil-
latoria (Matsumoto et al., 1990). Oscillatoria vaucher is also
known to occur in the Baltic Sea but is of only minor abun-
dance (Kononen et al., 1996; Vahtera et al., 2007).
Unlike the n-alkenes that only occurred in the surface
layer, long-chain n-alkanes were present in the whole water
column, with high abundances in the oxic zone. Long-chain
n-alkanes with a strong predominance of the odd-numbered
n-C25 to n-C36 homologues (Eglinton and Hamilton, 1967;
Bi et al., 2005) and β-sitosterol (Volkman, 1986) are typical
components of higher-plant lipids, thus indicating continen-
tal runoff and/or aeolian input of terrigenous organic mat-
ter into the Landsort Deep. n-C27, n-C29, and n-C31 showed
surface maxima (not shown), indicating similar sources as
for β-sitosterol and a contribution of land plant leaf waxes.
Other than β-sitosterol, most n-alkanes peaked between 65
and 70 m (n-C25 for example; Fig. 4). Apart from the surface
peaks, this is also true for n-C27, n-C29, and n-C31. A pos-
sible explanation is the accumulation of terrigenous higher-
plant particles accumulating at the pycnocline, where density
differences were highest (MacIntyre et al., 1995)
4.3 Phototrophic vs. heterotrophic dinoflagellates,
and ciliates
The distribution of dinoflagellates and, most likely, ciliates in
the water column is reflected by two specific biomarkers: di-
nosterol and tetrahymanol (see Sect. 3.2.2, Fig. 4). Dinosterol
is mainly produced by dinoflagellates (Boon et al., 1979), al-
though it was also reported in minor abundance from a di-
atom (Navicula sp., Volkman et al., 1993). The dinosterol
concentrations in the Landsort Deep showed a bimodal dis-
tribution. The strong peak in the surface layer of the oxic
zone probably represents contributions from phototrophic di-
noflagellates. Plausible candidates are Peridiniella catenata
and Scrippsiella hangoei, both of which are involved in the
spring phytoplankton blooms in the central Baltic Sea (Was-
mund et al., 1998; Höglander et al., 2004). The latter species
was previously reported to produce dinosterol (Leblond et
al., 2007). However, P. catenata as well as S. hangoei are vir-
tually absent below 50 m water depth (Höglander et al., 2004)
and can thus not account for the second peak of dinosterol
at the suboxic–anoxic transition zone. An accumulation of
surface-derived dinosterol at the bottom of the suboxic zone
is unlikely, as the pycnocline, and thus the strongest density
discontinuity, is located at 60–70 m water depth, i.e., about
20 m further above. Dinosterol is absent in the pycnocline
and only occurs from the bottom of the suboxic zone down-
wards and below. Instead, a likely source of dinosterol at this
water depth is represented by heterotrophic dinoflagellates
that are abundant in the suboxic zones of the central Baltic
Sea (Anderson et al., 2012). Due to their enhanced produc-
tivity, these environments provide good conditions to sustain
communities of eukaryotic grazers (Detmer et al., 1993). A
possible candidate, Gymnodinium beii, was described from
the suboxic zones of the central Baltic Sea (Stock et al.,
2009). Indeed, several Gymnodinium species are known to
be heterotrophs (Strom and Morello, 1998) and some have
been reported to produce dinosterol (Mansour et al., 1999).
Like cholesterol and β-sitosterol, dinosterol was also found
in the anoxic zone at 400 m water depth. The production of
these compounds at this depth is unlikely, as the synthesis
of sterols requires oxygen (Summons et al., 2006). Hence,
the observed sterol occurrences probably reflect transport
through the water column.
A similar concentration distribution as for dinosterol was
observed for tetrahymanol. Tetrahymanol is known to be pro-
duced by ferns, fungi, and bacteria, such as the purple non-
sulfur bacterium Rhodopseudomonas palustris (Zander et al.,
1969; Kemp et al., 1984; Kleemann et al., 1990; Sinninghe
Damsté et al., 1995; Eickhoff et al., 2013). Moreover, cil-
iates ubiquitously produce tetrahymanol as a substitute for
cholesterol when grazing on prokaryotes instead of eukary-
otes, such as algae (Conner et al., 1968; Boschker and Mid-
delburg, 2002). This is also a feasible scenario for the Baltic
Sea, where the ciliate genera Metopus, Strombidium, Meta-
cystis, Mesodinium, and Coleps are abundant in the sub-
oxic zone and at the suboxic–anoxic interface (Detmer et al.,
1993; Anderson et al., 2012). Unidentified ciliates also oc-
curred in the anoxic waters of the Landsort Deep (Anderson
et al., 2012). Members of the genus Rhodopseudomonas, a
possible alternative source of tetrahymanol, have so far not
been identified in the suboxic zone (Labrenz et al., 2007;
Thureborn et al., 2013). We therefore regard bacterivorous
ciliates living under suboxic to anoxic conditions as the most
likely source of tetrahymanol in the suboxic zone and below.
Likewise, ciliates feeding on chemoautotrophic bacteria were
assumed as producers of tetrahymanol in the suboxic zone of
the Black Sea (Wakeham et al., 2007). The situation is some-
what different in the surface waters, where tetrahymanol
shows its maximum concentrations at 10 m water depth. Al-
though Rhodopseudomonas and other purple nonsulfur bac-
teria usually occur under oxygen-deficient conditions, they
have been genetically identified in the surface water of the
Landsort Deep (Farnelid et al., 2009) and thus have to be
considered as potential producers of tetrahymanol. Further-
more, cholesterol is abundant in the surface waters and could
be incorporated by ciliates instead of tetrahymanol. However,
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C. Berndmeyer et al.: Biomarkers in the stratified water column 7017
some ciliates seem to prefer prokaryotes as a prey. Sinking
agglomerates of cyanobacteria and other bacteria are known
to be covered by feeding ciliates (Gast and Gocke, 1988).
Hence, in addition to R. palustris, ciliates grazing selectively
on cyanobacteria would plausibly explain the abundance of
tetrahymanol in the shallow waters of the Landsort Deep.
δ13C values of tetrahymanol revealed an opposite trend to
dinosterol. While dinosterol became isotopically more neg-
ative with depth (−29.9 to −32.0 ‰), tetrahymanol became
more positive (−28.7 to −25.9 ‰) and showed its highest
δ13C values in the anoxic zone. Although ciliates and di-
noflagellates are both grazers at the suboxic–anoxic inter-
face, they seem to occupy different ecological niches and
feed on different bacterial sources.
4.4 Heterotrophs in the cold winter water layer
The only biomarkers with enhanced concentrations in the
deep cold winter water layer are wax esters (e.g., 16 : 0−18 :
1 wax ester, Fig. 4) and, to a minor extent, cholesterol and
20 : 5ω3 PLFA. As the pycnocline, and thus a strong density
discontinuity, is also located at this depth, an accumulation of
settling organic debris containing these compounds has to be
considered (MacIntyre et al., 1995). Living organisms, how-
ever, may be also be plausible sources. Copepods are known
producers of wax esters and cholesterol (Lee et al., 1971;
Sargent et al., 1977; Kattner and Krause, 1989; Nanton and
Castell, 1999; Falk-Petersen et al., 2002), which are often
abundant in density layers, where they feed on accumulated
aggregates (MacIntyre et al., 1995). These organisms syn-
thesize wax esters with total chain lengths of between 28 and
44 carbon atoms (Lee et al., 1971; Kattner and Krause, 1989;
Falk-Petersen et al., 2002); several of wax esters were present
in the Landsort Deep (data not shown in Fig. 4), with roughly
the same distribution as the most prominent 16 : 0− 18 : 1.
Although copepods migrate through the water column, par-
ticularly those rich in wax esters prefer deep water or near-
surface cold water (Sargent et al., 1977), which is in full
agreement with the high amounts of these compounds in the
cold winter water layer. Copepods are abundant and diverse
in the Baltic Sea, with major species being Pseudocalanus
elongatus, Temora longicornis, and Acartia spp. (Möllmann
et al., 2000; Möllmann and Köster, 2002). Like the wax es-
ters, the 20 : 5ω3 PLFA shows higher concentrations in the
cold winter water layer, but it is also abundant in the surface
and at the suboxic–anoxic interface (Fig. 4). Copepods are
also known to feed on diatoms and incorporate their specific
fatty acids, such as 20 : 5ω3 PLFA, largely unchanged into
their own tissue (Kattner and Krause, 1989). Dinoflagellates
are also known producers of 20 : 5ω3 PLFA (Parrish et al.,
1994; Volkman et al., 1998) and may be an alternative source
in the surface layer and at the suboxic–anoxic interface; this
is supported by a good correlation with dinosterol at these
depths.
Unlike the abovementioned compounds, all other selected
biomarkers show particularly low concentrations in the cold
winter water layer. This is also true for widespread com-
pounds such as the 16 : 1ω7c PLFA, which is produced
by eukaryotes (Pugh, 1971; Shamsudin, 1992) as well as
prokaryotes (Parkes and Taylor, 1983; Vestal and White,
1989). While a mixed origin of 16 : 1ω7c PLFA has to be
assumed for the oxic zone, a bacterial source is more prob-
able in the suboxic zone and in the anoxic zone. Regardless
of the biological source, a very low amount of this ubiqui-
tous fatty acid (Fig. 4) indicates that the cold winter water
layer of the Landsort Deep does not support abundant plank-
tonic life. Based on microscopy, similar observations have
been made for the cold winter water layers of the Gotland,
Bornholm, and Gdansk basins (Gast and Gocke (1988) and
citations therein).
4.5 BHPs as indicators for aerobic and
anaerobic metabolisms
Bacteria are the only known source of BHPs (Kannenberg
and Poralla, 1999). Although the biosynthesis of BHPs and
their precursor, diploptene (both part of Group 2), does not
require oxygen, the production of hopanoids was long as-
sumed to be restricted to aerobic bacteria, as reports from
facultatively or strictly anaerobic bacteria were initially lack-
ing. More recently, however, planctomycetes (Sinninghe
Damsté et al., 2004), metal-reducing Geobacter (Fischer et
al., 2005), and sulfate-reducing Desulfovibrio (Blumenberg
et al., 2006, 2009, 2012) were identified as anaerobic produc-
ers of BHPs. In the Landsort Deep, cyanobacteria are abun-
dant in the surface water layer and may be considered as a
major source of BHPs (cf. Talbot et al., 2008; Welander et
al., 2010). Evidence for such cyanobacterial BHP contribu-
tions may come from our analysis of a Gotland Deep bloom
from summer 2012 (see Sect. 3.2.7). BHPs identified in this
bloom were BHT, BHT cyclitol ether, and BHT glucosamine
(Fig. 6b), which is in line with the BHP composition of the
Landsort Deep surface layer (Fig. 6a). These three cyanobac-
terial BHPs were present throughout the Landsort Deep wa-
ter column, although they were present in minor amounts in
the suboxic zone and below. In addition, the surface layer
contained aminotriol that was also present in the whole water
column. Aminotriol is an abundant BHP produced by various
bacteria (e.g., Talbot and Farrimond (2007) and references
therein), indicating that organisms other than cyanobacteria
may contribute BHP to the surface layer.
A further notable feature is the occurrence of BHT II
at 70 m and below. The source of BHT II is not fully re-
solved yet. It was recently related to planctomycetes, es-
pecially those performing anaerobic ammonium oxidation
(anammox) in sediments (Rush et al., 2014). Anammox bac-
teria can also be traced by 10-me16 : 0 PLFA and ladder-
ane PLFAs (not studied here; Sinninghe Damsté et al., 2005;
Schubert et al., 2006). 10-me16 : 0 PLFA does indeed show
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7018 C. Berndmeyer et al.: Biomarkers in the stratified water column
a peak in the lower suboxic zone, where BHT II is abun-
dant. However, 10-me16 : 0 PLFA may also be contributed
by sulfate-reducing bacteria (see Sect. 4.6), and no evidence
for anammox has been observed in the water column of the
Landsort Deep from molecular biological studies so far (Hi-
etanen et al., 2012; Thureborn et al., 2013). Regardless of the
biological source, BHT II was described in stratified water
columns of the Arabian Sea, Peru Margin and Cariaco Basin
(Sáenz et al., 2011), and the Gotland Deep (Berndmeyer et
al., 2013) and has therefore been proposed as a proxy for
stratified water columns. This hypothesis has been adopted
to reconstruct the development of water-column stratifica-
tion in the Baltic Sea during the Holocene (Blumenberg et
al., 2013).
Like BHT II, aminotetrol and aminopentol are absent from
the surface layer (Fig. 6a). Whereas both BHPs are biomark-
ers for methanotrophic bacteria, the latter typically occurs in
type I methanotrophs (Talbot et al., 2001). The presence of
type I methanotrophic bacteria is further supported by the
co-occurrence of the specific 16 : 1ω8c PLFA (Nichols et al.,
1985; Bowman et al., 1991, 1993) and its considerably de-
pleted δ13C value (−45.4 ‰).
Whereas a major in situ production of BHPs in the sub-
oxic zone is evident from our data, the sources of BHPs
in the anoxic zone are more difficult to establish. BHPs in
the anoxic zone may partly derive from sinking POM as
well as being newly produced by anaerobic bacteria. Sink-
ing POM as a source may apply to BHT cyclitol ether and
BHT glucosamine, which seem to derive from cyanobacte-
ria thriving in the oxic zone, as discussed above. Aminotriol,
aminotetrol, and aminopentol, however, are known products
of sulfate-reducing bacteria (Blumenberg et al., 2006, 2009,
2012) and may have their origin within the anoxic zone. This
interpretation is supported by the close correlation of the total
BHPs with the ai-15 : 0 PLFA, which is considered as indica-
tive of sulfate reducers (see Sect. 4.6; both compounds were
part of the same PCA Group 2). Thus, the anoxic zone of the
Landsort Deep is likely an active source for BHPs rather than
solely being a pool for transiting compounds.
4.6 Microbial processes in the anoxic zone
Sulfate-reducing bacteria were traced using ai-15 : 0 PLFA
and 10-me-16 : 0 PLFA (Parkes and Taylor, 1983; Taylor and
Parkes, 1983; Vainshtein et al., 1992). The high abundance
of ai-15 : 0 PLFA in the surface layer (Fig. 4) is surprising at
first glance, as sulfate reducers are not supposed to thrive in
oxic environments. However, these bacteria were previously
reported from oxygenated surface waters of the Gotland
Deep, where they were associated with sinking cyanobac-
terial agglomerates (Gast and Gocke, 1988). 10-Me-16 : 0
PLFA is otherwise absent from the oxic zone (Fig. 4). This
FA was reported to occur in Desulfobacter and Desulfobac-
ula (Taylor and Parkes, 1983; Kuever et al., 2001), both
strictly anaerobic organisms (Szewzyk and Pfennig, 1987;
Widdel, 1987; Kuever et al., 2001). Indeed, Desulfobacula
toluolica was genetically identified by Labrenz et al. (2007)
in suboxic and anoxic waters of the central Baltic Sea.
In addition to the bacterial FA, two archaeal in situ
biomarkers, archaeol and PMI, were identified. Archaeol is
the most common ether lipid in archaea but is especially
abundant in euryarchaeotes, including methanogens (Torn-
abene and Langworthy, 1979; Koga et al., 1993). Like-
wise, PMI and its unsaturated derivatives are diagnostic for
methanogenic euryarchaeotes (Tornabene et al., 1979; De
Rosa and Gambacorta, 1988; Schouten et al., 1997). In the
Landsort Deep, both compounds are virtually absent in the
oxic zone and increase in abundance with depth through the
suboxic zone (Fig. 3). The same trend has been described for
PMI in the Black Sea (Wakeham et al., 2007), and the pres-
ence of Euryarchaeota in Landsort Deep anoxic waters has
recently been proven by Thureborn et al. (2013).
Given the available sample resolution, it is impossible
to further elucidate the exact distribution of archaea in the
anoxic zone of the Landsort Deep. Likewise, δ13C values
could not be obtained for archaeol and PMI due to low com-
pound concentrations, which makes statements on inputs of
these lipids from archaea involved in the sulfate-dependent
anaerobic oxidation of methane (AOM) impossible (cf. Hin-
richs et al., 1999; Thiel et al., 2001). Whereas it has been
shown that AOM is theoretically possible in the anoxic zone
of the Landsort Deep and anaerobic methane consumption
has recently been demonstrated to occur (Jakobs et al., 2013),
clear evidence for abundant AOM is as yet lacking and re-
quires further investigations focused on the anoxic water
bodies of the Baltic Sea.
5 Conclusions
The Landsort Deep in the western central Baltic Sea is char-
acterized by a stratified water column. Marine microbial or-
ganisms have adapted to the vertical chemical limitations of
their ecosystems, and their distributions in the water column
can be reconstructed using diverse in situ biomarkers. Ac-
cording to their behavior in the water column, PCA analy-
sis revealed six groups of biomarkers for distinct groups of
(micro)organisms and the related biogeochemical processes.
Within the oxic zone, a clear preference for the surface layer
became obvious for distinctive biomarkers. Among these
compounds, 7-methylheptadecane, different alkenes, BHT
cyclitol ether, and BHT glucosamine were indicative of the
presence of bacterial primary producers, namely cyanobac-
teria. Dinosterol concentrations and −δ13C values revealed
a phototrophic dinoflagellate population in the surface wa-
ters and a second, heterotrophic community thriving at the
suboxic–anoxic interface. Similarly, abundant tetrahymanol
at the surface indicated ciliates feeding on cyanobacterial ag-
glomerates, but a second maximum at the suboxic–anoxic
interface suggested a further ciliate population that grazed
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C. Berndmeyer et al.: Biomarkers in the stratified water column 7019
on chemoautotrophic bacteria. The cold winter water layer
at the bottom of the oxic zone showed only low concentra-
tions of biomarkers and seemed to be avoided by most organ-
isms, except copepods. In contrast, biomarkers obtained from
the suboxic zone reflected a high abundance and diversity
of eukaryotes and prokaryotes. Whereas 16 : 1ω8 PLFA and
aminopentol revealed the presence of type I aerobic methane-
oxidizing bacteria, ai-15 : 0 PLFA, 10-me-16 : 0, and total
BHPs indicated the distribution of sulfate-reducing bacte-
ria in the Landsort Deep water column. The close coupling
of ai-15 : 0 PLFA with total BHPs suggests that these bac-
teria represent a major in situ source for hopanoids in the
anoxic zone. The anoxic zone was also inhabited by most
likely Euryarchaeota, as shown by the presence of archaeol
and PMI and its derivatives. Our study in the water column
of the Landsort Deep gives insights into the recent distribu-
tions and actual sources of organic matter as reflected by lipid
biomarkers. The results may also aid the interpretation of or-
ganic matter preserved in the sedimentary record and thus
help to better constrain changes in the geological history of
the Baltic Sea.
Acknowledgements. We thank the captains and crews of R/Vs
Elisabeth Mann Borghese and Meteor for assistance during the
cruises. We thank C. Conradt and L. Kammel for laboratory
assistance, T. Licha and K. Nödler for help with LC–MS, and
N. Cerveau for help with R. We thank S. Bühring and an anony-
mous reviewer for helpful comments on our manuscript. The
German Research Foundation (Deutsche Forschungsgemeinschaft,
DFG) is acknowledged for financial support (Grants BL 971/1-3
and 971/3-1).
This Open Access Publication is funded
by the University of Göttingen.
Edited by: J. Middelburg
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