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

海洋同位素阶段（MIS） M2发生在329万年前，是上新世的第一个极冷时期，被描述为气候系统早期达到完全冰川状态的失败尝试。然而，紧随其后的是一段异常和持续的温暖期，由于它与未来气候模型的相关性，引起了人们的强烈兴趣。相比之下，MIS M2在很大程度上被忽视了。我们的研究重点是冷事件MIS M2，它的开始、稳定性、恢复和向持续温暖的过渡，我们是第一个专门和详细发表它的人。我们的研究结果显示，北大西洋洋流（NAC）突然向南移动，使得格陵兰冰盖扩张。然而，NAC不稳定的原因仍然不确定，尽管它们对未来和过去气候的建模至关重要。拟议的研究通过以千年尺度的分辨率分析北大西洋的新地点，扩大了我们的空间覆盖范围。我们使用一种新的代理组合（鞭毛藻囊、地球化学、冰筏碎片）来重建海面温度、盐度、冰融化的证据和NAC强度。

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.