Uni Research Climate, Bjerknes Centre for Climate Research, Jahnebakken 5, 5007, Bergen, Norway.
Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568, Bremerhaven, Germany.
Sci Rep. 2019 Jan 30;9(1):989. doi: 10.1038/s41598-018-37047-y.
Scattered and indirect evidence suggests that sea ice occurred as far south as the Iceland Sea during the Early Pliocene, when the global climate was warmer than present. However, conclusive evidence as well as potential mechanisms governing sea ice occurrence outside the Arctic Ocean during a time with elevated greenhouse gas concentrations are still elusive. Here we present a suite of organic biomarkers and palynological records from the Iceland Sea and Yermak Plateau. We show that sea ice appeared as early as ~4.5 Ma in the Iceland Sea. The sea ice either occurred seasonally or was transported southward with the East Greenland Current. The Yermak Plateau mostly remained free of sea ice and was influenced dominantly by Atlantic water. From ~4.0 Ma, occurrence of extended sea ice conditions at both the Yermak Plateau and Iceland Sea document a substantial expansion of sea ice in the Arctic. The expansion occurred contemporaneous with increased northward heat and moisture transport in the North Atlantic region, which likely led to a fresher Arctic Ocean that favors sea ice formation. This extensive sea ice cover along the pathway of the East Greenland Current gradually isolated Greenland from warmer Atlantic water in the Late Pliocene, providing a positive feedback for ice sheet expansion in Greenland.
零星且间接的证据表明，在早中新世时期，全球气候比现在温暖，当时海冰曾出现在冰岛海以南地区。然而，在温室气体浓度升高的时期，仍难以确定北极圈以外是否存在海冰以及潜在的控制机制。在这里，我们展示了来自冰岛海和叶尔马克高原的一系列有机生物标志物和孢粉记录。研究表明，早在约 450 万年前，冰岛海就出现了海冰。海冰要么季节性出现，要么随东格陵兰洋流向南移动。叶尔马克高原大部分时间没有海冰，主要受大西洋水影响。从大约 400 万年前开始，叶尔马克高原和冰岛海出现长时间的海冰条件，这表明北极的海冰范围大幅扩大。这种扩张发生在北大西洋地区向北热量和水分输送增加的同时，这可能导致了更凉爽的北冰洋，有利于海冰形成。沿着东格陵兰洋流的这条广泛的海冰覆盖带逐渐将格陵兰岛与温暖的大西洋水隔离开来，这为格陵兰冰盖的扩张提供了正反馈。
