The Pliocene Sea Ice Cover in the Arctic Ocean

Arctic sea ice coverage is shrinking in response to global climate change, and summer ice-free conditions in the Arctic Ocean are predicted by the end of the century. The validity of this prediction could potentially be tested through the reconstruction of the climate of the Pliocene epoch (5.33-2.58 million years ago), an analogue of a future warmer Earth. Here, we show that, in the Eurasian sector of the Arctic Ocean, ice-free conditions prevailed in the early Pliocene until sea ice expanded from the central Arctic Ocean for the first time ca. 4 million years ago as a response to preglacial, tectonically induced circum Arctic uplift and enhanced freshening of the Arctic Ocean. A rise in topography above a critical threshold for ice accumulation, and final establishment of circum-Arctic oceanic gateways during the early Pliocene preconditioned the northern landmasses to become recipients for glacial ice during the late Pliocene. As a consequence, sea ice expanded progressively in response to positive ice-albedo feedback mechanisms, which were amplified further by the freshening of the Arctic as a consequence of the closure of the Central American Seaways. Sea ice reached its modern winter maximum extension for the first time during culmination of the Northern Hemisphere glaciation, ca. 2.6 million years ago.