Palaeoproductivity and post-depositional aerobic organic matter decay reflected by dinoflagellate cyst assemblages of the Eastern Mediterranean S1 sapropel

In the reconstruction of bioproductivity in surface waters the extent to wh ich a proxy has been diagenetically altered is often a matter of debate. He re we investigate how organic- and calcareous-walled dinoflagellate cysts c an be used for separately estimating bioproductivity and oxygen related dia genesis. This is achieved by studying the cyst content of the most recent E astern Mediterranean sapropel S1, that is thought to have been deposited Le nder conditions of increased primary production in surface waters and possi ble anoxia in the bottom waters. Based on chemical evidence, it has been sh own that the visible sapropelic layer represents only the residual lower pa rt of what was initially a much thicker sapropel. as a result of post depos itional decay of organic matter related to oxygen penetration into the sedi ments. The effect of aerobic organic matter decay on the cyst associations is studied through the comparison of the unaffected, lower part of the init ial sapropel and the 'oxidised' upper part. Comparing the unaffected saprop elic sediments with pre- and post-sapropelic material gives insight into th e relationship between fossil cysts assemblages and palaeoproductivity. Impagidinium aculeatum, Impagidinium patulum, Operculodinium israelianum, P olysphaeridium zoharyi and probably Impagidinium spp., Impagidinium paradox um and Nematosphaeropsis labyrinthus are very resistant against aerobic dec ay and their accumulation rates appear to be primarily related to productiv ity in surface waters. Protoperidinium and Echinidinium species, on the oth er hand, are shown to be very sensitive and can be used to recognise oxygen -related decay. The calcaerous-walled dinoflagellate cysts seem to be unaff ected by oxic organic matter decay in Mediterranean sediments. (C) 2001 Els evier Science B.V. All rights reserved.