Quantitative estimation of aerobic diagenetic overprint of palaeoproductivity signals


Organic-walled dinoflagellate cysts, oxidation, degradation, organic matter. - Species-selective aerobic decomposition affects fossil organic-walled dinoflagellate cyst (dinocyst) records and hence dinocyst-based interpretations of primary productivity and oceanographic conditions. However, since the recognition of dinocyst species sensitive and resistant to oxic degradation (S- and R-cysts, respectively) it has become apparent that R-cysts may still serve as reliable productivity and oceanographic conditions proxies. On the other hand S-cysts provide a way to quantify aerobic degradation of organic matter (OM) and past bottom-water O2 concentrations. OM degradation plays a key role in global carbon cycling and is important for global climate change. Therefore dinocysts are a valuable tool for estimating the rate of diagenetic process. Questions concerning species-selective aerobic degradation still remain and will be adressed here. To obtain information on the rate of S-cyst decomposition, the relationship between S-cyst degradation and O2 concentrations, and the aerobic degradation of extinct dinocyst species, a natural exposure experiment has been conducted and studies of both Quaternary and pre-Quaternary material from sediment cores were executed. The exposure experiment was conducted in the natural setting of the Eastern Mediterranean. During a 15 month exposure period to oxic water masses, concentrations of S-cysts (Brigantedinium spp. and Echinidinium granulatum) decreased by 24 to 57%. However, taxa such as Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum and Impagidinium aculeatum demonstrated a slight increase in concentration, indicating resistance to aerobic degradation. These results show that even short-term exposure to oxygen may cause considerable changes in the dinocyst assemblage ...
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