Species-selective Aerobic Degradation of Dinoflagellate Cysts - Results of a Natural Exposure Experiment
Organic-walled dinoflagellate cysts undergo species-selective decomposition in oxic environments but are preserved under anoxic conditions. The relative degradation rate of individual species has been assessed during exposure experiments under oxic and anoxic conditions at two sites in the Eastern Mediterranean, namely the Urania and Bannock Basins areas. These areas contain anoxic brine waters and are overlain by oxic intermediate and surface waters. The exposed material consisted of sediments collected from (a) the Namibian shelf, (b) the S1 sapropel and (c) modern eastern Mediterranean. After 15 months of exposure to oxic conditions, sub-samples from the Namibian shelf and the sapropel showed a considerable reduction in cysts concentration compared to their original abundance. Exposure to anoxic conditions did not lead to detectable differences in relation to the initial composition. Our experimental results indicate that Brigantedinium spp. and Echinidinium granulatum are very sensitive to oxygen exposure, whereas Spiniferites spp., Lingulodinium machaerophorum and Echinidinium spp. appear to be moderately sensitive. Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum, and Impagidinium aculeatum are extremely resistant against aerobic decay. The observed changes in the dinocysts assemblages provide clear and straightforward argument that species- selective degradation of dinocysts takes place rapidly under oxic conditions independently from dinocyst production and transport processes. Our results imply that diagenetically induced composition changes have to be taken into account not only during interpretations of fossil records but also (sub) recent dinocyst assemblages.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 4952 Palynology