Sea ice variability in the North Atlantic subpolar gyre throughout the last interglacial

Abstract

The Last Interglacial period, Marine Isotope Stage 5e (MIS 5e ∼116–128 ka), is thought to have had a warmer, but less stable climate than the present interglacial. One key factor that has the potential to influence the ocean and climate is sea ice, but its presence and extent throughout MIS 5e is poorly constrained. Here we reconstruct the sea surface hydrography and sea ice variability in the Labrador Sea, a region influenced by the subpolar gyre (SPG) and where deep water formation occurs, in order to evaluate the potential of sea ice to drive or amplify ocean variability. We analysed biomarkers (highly branched isoprenoids, HBIs, and sterols), dinoflagellate cyst assemblages and stable oxygen isotopes from the late stages of MIS 6, throughout MIS 5e, into MIS 5d. Our results show that the late glacial MIS 6 was likely characterised by a thick multiyear sea ice cover. During the first phase of MIS 5e, the hydrography was highly variable. The initial 1500 years (128–126.5 ka) were characterised by the presence of a seasonal Marginal Ice Zone (MIZ) accompanied by subsurface warmth. As the sea ice retreated, cool, likely polar-sourced water dominated the surface and subsurface ocean (126.5–124 ka), until an abrupt surge of sea ice marked the final pulse of the remnants of the deglaciation. The second half of MIS 5e (124–116 ka) was characterised by a persistent inflow of warm water, only interrupted by incursions of cold water as summer insolation declined. Seasonal sea ice returned to the Eirik Drift during MIS 5d. We infer that sea ice variability throughout MIS 5e was coupled with the variability of the SPG. Especially the location of a proximal MIZ to the Labrador Sea convection region could have been important for SPG dynamics. In addition, the presence of sea ice at the transitions into and out of MIS 5e could point to its important role in modulating and enhancing the magnitude and coherence of climate signals at major climatic transitions.