Plio-pleistocene marine paleoenvironments and dinoflagellate cyst paleoecology

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Numerical reconstructions of high-latitude environments in the North Atlantic and adjacent seas during the past 4.9 Myr are a major aim of this proposal.  Such reconstructions are critical for understanding the ocean-climate system and validating computer climate simulations. Organic-walled dinoflagellate cysts, or "dinocysts", are now used frequently in quantitative reconstructions of later Quaternary marine environments, especially at higher latitudes where calcareous microfossil assemblages decline in diversity.  The analysis of their fossil record allows us to reconstruct numerically both summer and winter sea-surface temperature and salinity, the duration of sea-ice cover, and levels of nutrient enrichment.  However, using dinocysts to reconstruct many earlier Quaternary and Pliocene environments is hindered by the increasing presence of extinct species and unusual species associations.  The challenge is to understand the environmental significance of these older assemblages, thereby extending backwards in time the utility of dinocysts for quantitative environmental analysis. The proposed research examines dinocysts at very high resolution across six time intervals (each about 100 kyr duration or less) of critical paleoclimatic interest for the Pliocene and Pleistocene.  Material will be examined from across the North Atlantic region, based on existing deep-sea core material.  Assemblages will be uniquely calibrated throughout by obtaining stable isotopes and Mg/Ca ratios to serve as fully independent proxies for climate change, and allow precise tuning to an orbital timescale.  The aim is to develop a quantitative understanding of Plio-Pleistocene dinocyst ecology, and to apply this to learn more about the time intervals in question.  Results address the dynamics of late Cenozoic climate, especially at higher latitudes where dinocyst reconstructions of sea-ice cover and seasonality will provide new insights into the timing and causes of Northern Hemisphere glaciations.  Results will be relevant to paleoclimate modeling and stratigraphy especially at high latitudes where mineralized microfossil groups are of low diversity.