Deciphering global cooling of the mid-latitude oceans and its implication for the ocean circulation and climate during the early Pliocene (~5-3.5 Ma)

我们将重点研究上新世早期（~5 ~ 3.5 Ma）中美洲海道（CAS）收缩对南北大西洋的古海洋学影响。在~4.8 ~4 Ma期间，加勒比-太平洋地表水交换明显受限，达到了CAS关闭历史上的一个临界阈值。这导致了赤道东太平洋的温跃层浅化，并增加了大西洋经向翻转环流，将温暖的咸水输送到北纬高纬度地区。最近的模拟研究首次量化了这种构造引起的海洋变化。他们预测北大西洋会明显变暖（高达7°C），而北半球的“热海盗”会使南半球明显变冷（~2°C）。为了验证上新世早期半球间跷跷板的假设，我们选择了北大西洋和南大西洋对北半球“热海盗”敏感的深海钻探项目（DSDP）和海洋钻探计划（ODP）的多个核心地点。我们将对表层和次表层浮游有孔虫进行δ18O和Mg/Ca测量，并对底栖有孔虫进行δ13C分析，重建上新世早期上层水体和深水水流的水文特征。

We will focus our studies on the paleoceanographic effects of the constriction of the Central American Seaway (CAS) on the North and South Atlantic Ocean during the early Pliocene epoch (~5-3.5 Ma). During ~4.8-4 Ma, a critical threshold in the closing history of the CAS was reached with a significantly restricted Caribbean-Pacific surface water exchange. This caused a thermocline shoaling in the equatorial east Pacific and increased the Atlantic Meridional Overturning Circulation transporting warm and more saline waters towards high northern latitudes. For the first time recent simulation studies quantified this tectonic induced oceanographic changes. They predicted a distinct warming of the North Atlantic (up to 7°C) and a pronounced cooling of the Southern Hemisphere (~2°C) through “heat piracy” of the Northern Hemisphere. To test this hypothesis of an interhemispheric seesaw during the early Pliocene we selected various Deep-Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) core sites in the North and South Atlantic Ocean sensitive to “heat piracy” from the Northern Hemisphere. We will conduct combined δ18O and Mg/Ca measurements of planktic foraminifera from surface and subsurface levels and δ13C analyses from benthic foraminifera to reconstruct the hydrography of the upper water column and deep water currents during the early Pliocene.