Abstract
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.
Highlights
Today, Arctic sea ice plays an important role in both regional and global climate due to its effect on Earth’s albedo, ocean-atmosphere exchange and primary productivity[1,2]
While the current consensus is that the Central American Seaway (CAS) closure/shoaling was not a direct trigger for the glaciation in the Northern Hemisphere around 2.7 Ma, the proposed mechanism predicts the formation of sea ice in the Pliocene Arctic Ocean following enhanced northward heat and moisture supply in the North Atlantic region
We present the first Early Pliocene (~4.9–3.5 Ma) sea ice reconstructions based on the sea ice proxy IP25, sterols and palynology from the Iceland Sea Ocean Drilling Program (ODP) Site 907 and Yermak Plateau ODP Hole 911A (Fig. 1) to determine and understand the underlying causes of sea ice presence in the Early Pliocene Arctic
Summary
Our reconstructions reveal sea ice-free conditions and relatively high marine productivity in the Iceland Sea between 5.0 and 4.6 Ma, evidenced by the absence of IP25 and relatively high concentrations of the open water biomarker brassicasterol (Fig. 2B). With a sub-aerially exposed Barents Sea[20], the heat advection through the West Spitsbergen Current towards the Yermak Plateau is increased[32,33] (Fig. 3A), thereby inhibiting a long-term sea ice cover but allowing occasional local sea ice formation or sea ice export from the Arctic. It is, very likely that the different paleoceanographic interpretations for ODP holes 910C and 911A are best explained by the different ages of the investigated samples at both sites and that sea ice appeared in the region only sporadically
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