Selective preservation of organic-walled dinoflagellate cysts in Quaternary marine sediments: An oxygen effect and its application to paleoceanography

Abstract

Twenty years after the discovery of major glacial-interglacial cycles in atmospheric CO2, one of the hottest topics in paleoceanographic research is the global carbon cycle. Motivated by public concerns considerable progress has been made in pinning down the ocean's role as a source and sink for atmospheric CO2. Yet, we remain ignorant of several key issues. To answer some questions we critically depend on methods that can separate productivity from preservation and enable to estimate deep-ocean ventilation.The ultimate goal of this work is to develop and evaluate methods that enable to transform the paleoenvironmental signal of organic-walled dinoflagellate cysts (dinocysts) into estimates of export production, organic matter preservation, and oxygen contents of the ocean's deepest water. Dinocyst assemblages in marine sediments not only bear important information on ocean productivity, sea surface temperature, salinity, and nutrient availability, but after being buried to surface sediment certain dinocysts (S-cysts) exhibit lower degradation rates under anoxic as compared with oxic conditions. As a result, S-cysts are less efficiently preserved when oxygen is present than dinocysts that can protect themselves against decay (R-cysts). The results of this work suggest that these attributes together might be an ideal tool to link export production, organic matter preservation, and oxygenation of bottom water to the fossil record. This provides important new insights into the use dinocysts as indicators for marine export production, organic matter preservation, and deep-ocean ventilation. Moreover, the perspective that is generated draws attention to the potential of degradation models for estimating the diagenetic status of geological records, which is difficult to accomplish using conventional criteria but crucial to avoid spurious interpretations on past changes in marine bioproduction, biogeochemical cycles, ocean circulation, and, ultimately, the marine carbon cycle.