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Bipolar Atlantic deepwater circulation in the middle-late Eocene: Effects of Southern Ocean gateway openings

机译：中晚始新世的双极大西洋深水环流：南洋通道入口的影响

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We present evidence for Antarctic Circumpolar Current (ACC)-like effects on Atlantic deepwater circulation beginning in the late-middle Eocene. Modern ocean circulation is characterized by a thermal differentiation between Southern Ocean and North Atlantic deepwater formation regions. In order to better constrain the timing and nature of the initial thermal differentiation between Northern Component Water (NCW) and Southern Component Water (SCW), we analyze benthic foraminiferal stable isotope (δ~(18)O_(bf) and δ~(13)C_(bf)) records from Ocean Drilling Program Site 1053 (upper deep water, western North Atlantic). Our data, compared with published records and interpreted in the context of ocean circulation models, indicate that progressive opening of Southern Ocean gateways and initiation of a circum-Antarctic current caused a transition to a modern-like deep ocean circulation characterized by thermal differentiation between SCW and NCW beginning ~38.5 Ma, in the initial stages of Drake Passage opening. In addition, the relatively low δ~(18)O_(bf) values recorded at Site 1053 show that the cooling trend of the middle-late Eocene was not global, because it was not recorded in the North Atlantic. The timing of thermal differentiation shows that NCW contributed to ocean circulation by the late-middle Eocene, ~1–4 Myr earlier than previously thought. We propose that early NCW originated in the Labrador Sea, based on tectonic reconstructions and changes in foraminiferal assemblages in this basin. Finally, we link further development of meridional isotopic gradients in the Atlantic and Pacific in the late Eocene with the Tasman Gateway deepening (~34Ma) and the consequent development of a circumpolar proto-ACC.
机译：我们提供了始于中新世晚期的南极绕极水流（ACC）样效应对大西洋深水环流的证据。现代海洋环流的特征是南大洋与北大西洋深水形成区之间存在热差异。为了更好地限制北成分水（NCW）和南成分水（SCW）之间初始热分化的时间和性质，我们分析了底栖有孔虫的稳定同位素（δ〜（18）O_（bf）和δ〜（13 ）（C_（bf））记录来自海洋钻探计划第1053号站点（北大西洋西部深水区）。我们的数据与已发表的记录进行了比较，并在海洋环流模型的背景下进行了解释，这些数据表明，南大洋通道的逐步开放和南极洋流的启动导致了向现代样深海环流的过渡，其特征是SCW之间的热区别在德雷克海峡通道的初期，NCW的开始时间约为38.5 Ma。另外，在1053站记录的相对较低的δ〜（18）O_（bf）值表明，中晚期始新世的冷却趋势不是全球性的，因为它没有记录在北大西洋。热分化的时间表明，NCW导致中新世晚期晚了海洋环流，比以前认为的早了约1-4 Myr。我们建议早期NCW起源于拉布拉多海，基于该盆地的构造重建和有孔虫组合的变化。最后，我们将始新世晚期大西洋和太平洋的子午同位素梯度的进一步发展与塔斯曼海峡加深（〜34Ma）以及随之而来的绕极原ACC的发展联系起来。

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