Plio-pleistocene dinoflagellate cysts and paleoceanography of the North Atlantic region

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Described as an early failed attempt by the climate system to reach a full glacial state, marine isotope stage (MIS) M2 occurring 3.29 million years ago represents the first severely cold episode of the Pliocene. Yet it was followed immediately by an interval of exceptional and sustained warmth that has attracted intense interest owing to its relevance for modeling future climate. MIS M2 in contrast has been largely overlooked. Our research focuses on the cold event MIS M2, its inception, (in)stability, recovery, and transition to sustained warmth, and we are the first to have published specifically and in detail on it. Our results show an abrupt southward shift of the North Atlantic Current (NAC) that allowed the Greenland ice sheet to expand. Yet the causes of NAC instability remain uncertain, although they are critical to the modeling of future as well as past climates. The proposed research expands our spatial coverage by analyzing new sites in the North Atlantic at millennial-scale resolution. We use a novel combination of proxies (dinoflagellate cysts, geochemistry, ice-rafted debris) to reconstruct sea-surface temperature, salinity, evidence of ice melting, and NAC strength. MIS 16 at 0.65 million years ago saw the first major climatic deterioration of the Middle Pleistocene and first massive release of icebergs into the North Atlantic. Paradoxically, global atmospheric CO2 levels and geochemically-based paleotemperatures increased well before the termination of MIS 16, implying an unknown amplification mechanism. We propose the first millennial-scale study of dinoflagellate cysts through MIS 16 to assess NAC influence and quantify sea-surface temperatures and salinities from two strategically located sites in the North Atlantic. An expanding data set of Pliocene dinoflagellate cyst assemblages linked to geochemical paleotemperatures based on our novel same-sample method will uniquely allow us to determine numerical temperature requirements of extinct Pliocene taxa and to compare present-day with Pliocene temperature distributions of extant taxa, improving the utility of Pliocene dinoflagellate cysts for paleoenvironmental reconstructions.