Articles | Volume 13, issue 9
Clim. Past, 13, 1153–1168, 2017
Clim. Past, 13, 1153–1168, 2017

Research article 11 Sep 2017

Research article | 11 Sep 2017

Highly variable Pliocene sea surface conditions in the Norwegian Sea

Paul E. Bachem1, Bjørg Risebrobakken1, Stijn De Schepper1, and Erin L. McClymont2 Paul E. Bachem et al.
  • 1Uni Research Climate, Bjerknes Centre for Climate Research, Jahnebakken 5, 5007 Bergen, Norway
  • 2Department of Geography, Durham University, Durham, DH1 3LE, UK

Abstract. The Pliocene was a time of global warmth with small sporadic glaciations, which transitioned towards the larger-scale Pleistocene glacial–interglacial variability. Here, we present high-resolution records of sea surface temperature (SST) and ice-rafted debris (IRD) in the Norwegian Sea from 5.32 to 3.14 Ma, providing evidence that the Pliocene surface conditions of the Norwegian Sea underwent a series of transitions in response to orbital forcing and gateway changes. Average SSTs are 2 °C above the regional Holocene mean, with notable variability on millennial to orbital timescales. Both gradual changes and threshold effects are proposed for the progression of regional climate towards the Late Pliocene intensification of Northern Hemisphere glaciation. Cooling from 4.5 to 4.3 Ma may be linked to the onset of poleward flow through the Bering Strait. This cooling was further intensified by a period of cool summers due to weak obliquity forcing. A 7 °C warming of the Norwegian Sea at 4.0 Ma suggests a major increase in northward heat transport from the North Atlantic, leading to an enhanced zonal SST gradient in the Nordic Seas, which may be linked to the expansion of sea ice in the Arctic and Nordic Seas. A warm Norwegian Sea and enhanced zonal temperature gradient between 4.0 and 3.6 Ma may have been a priming factor for increased glaciation around the Nordic Seas due to enhanced evaporation and precipitation at high northern latitudes.

Short summary
We present a high-resolution multi-proxy study of the Norwegian Sea, covering the 5.33 to 3.14 Ma time window within the Pliocene. We show that large-scale climate transitions took place during this warmer than modern time, most likely in response to ocean gateway transformations. Strong warming at 4.0 Ma in the Norwegian Sea, when regions closer to Greenland cooled, indicate that increased northward ocean heat transport may be compatible with expanding glaciation and Arctic sea ice growth.