Southern Ocean frontal system changes precede Antarctic ice sheet growth during the middle Miocene
Southern Ocean frontal system changes precede Antarctic ice sheet growth during the middle Miocene
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中新世中期，南大洋锋面系统的变化先于南极冰盖的增长
DOI：
10.1016/j.epsl.2009.05.030
复制
发表时间：
2009
影响因子：
5.3
通讯作者：
Paulsen H.
中科院分区：
文献类型：
--
作者：
Kuhnert H;Bickert T;Paulsen H.
大约14 Ma前的中中新世气候的特征是南极洲的冰川作用、深海冷却和全球碳循环的变化。虽然南大洋经历了重大的海洋变化，但关于其空间范围和时间的信息有限。然而，这些知识对于了解南大洋和南极绕极流对南极冰川作用的作用以及海洋和大陆气候之间的耦合至关重要。利用有孔虫氧同位素（δ 18 O）和镁钙比值（Mg/Ca）重建了南大洋大西洋极锋区大洋钻探计划（ODP）1092站的表层温度和海水氧同位素。在13.8- 13.9Ma，南极冰盖增长的主要阶段之前，在14.2Ma，海水δ 18 O（δ 18 Osw）降低了约1‰，表明海面冷却约4 °C，海水淡化。这种模式定性地反映了以前的研究结果，从太平洋部门，我们解释的表面水文变化，以反映环南极北移的南大洋锋，特别是在站点1092次南极洲锋的通道。重建的δ 18 Osw变化幅度要求δ 18 Osw：盐度梯度显著高于现代值（~0.52‰），可能超过1.1‰。这意味着极锋区受到来自南极洲的淡水的影响，这反过来又证实了高于现代大陆的降水量。后者以前曾被认为有助于南极冰川。
The middle Miocene climate approximately 14 Ma ago was characterized by the glaciation of Antarctica, deep-ocean cooling and variations in the global carbon cycle. Although the Southern Ocean underwent significant oceanographic changes, there is limited information on their spatial extent and timing. However, such knowledge is crucial for understanding the role of the Southern Ocean and the Antarctic Circumpolar Current (ACC) for Antarctic glaciation and the coupling between the ocean and continental climate. We have reconstructed surface temperatures and seawater oxygen isotopes at Ocean Drilling Program (ODP) Site 1092 in the Polar Frontal Zone of the Atlantic sector of the Southern Ocean from foraminiferal oxygen isotopes (δ18O) and magnesium to calcium ratios (Mg/Ca). Sea surface cooling by ~4 °C and freshening indicated by the ~1‰ reduction of seawater δ18O (δ18Osw) at 14.2 Ma precede the major step in Antarctic ice sheet growth at 13.8–13.9 Ma. This pattern qualitatively mirrors previous findings from the Pacific sector, and we interpret the surface hydrographic changes to reflect the circum-Antarctic northward shift of the Southern Ocean fronts and specifically at Site 1092 the passage of the Subantarctic Front. The magnitude of change in reconstructed δ18Oswrequires a δ18Osw: salinity gradient significantly higher than the modern value (~0.52‰) and it possibly exceeded 1.1‰. This implies the Polar Frontal Zone was influenced by freshwater derived from Antarctica, which in turn confirms higher than modern continental precipitation. The latter has previously been suggested to have contributed to Antarctic glaciation.
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