A global ocean GCM is coupled to a sea ice model and driven with output from an atmospheric GCM (GENESIS2) for modern conditions and paleoclimates warmer (6 ka BP) and colder (115 ka BP) than present in the high-latitude Northern Hemisphere. The simulations are used to examine the impact of ocean dynamics on the ice pack, as well as the effect of varied sea ice regimes on the robustness of the Arctic Ocean halocline and convective overturning in the Nordic Seas. The atmospheric paleoclimatic perturbations generate significant changes in SST, sea ice area, and ice volume. Mean annual surface salinity in the Central Arctic rises slightly (0.1 ppt) at 6 ka BP and dramatically at 115 ka BP (almost 3 ppt), sufficient to reduce the static stability of the polar ocean, particularly near the Nordic Sea boundary.
The interactive ocean causes important feedbacks which modify the locally forced response from the altered sea ice regimes. Two positive feedbacks include an increased (decreased) poleward oceanic heat transport north of the Arctic Circle at 6 ka (115 ka) BP and a corresponding poleward (equatorward) shift in the northern limit of convective overturning in the Greenland Sea. The latitudinal shift in convection is forced by the decreased (increased) ice volume at 6 ka (115 ka) BP causing anomalous discharge of fresh water from the Arctic basin, which causes the surface waters of the Greenland Sea to salinize (freshen). Two negative feedbacks involve recirculation of this Greenland Sea salinity anomaly into the Arctic Ocean in both scenarios and cooling of the ocean's upper kilometer at 115 ka BP due to enhanced convection on Arctic continental shelves. At 6 ka BP the salinization of central Arctic surface waters results from the recirculation feedback, which is large enough to completely counteract the freshening forced by the reduced ice volume in the Arctic basin. Although the strength of the halocline at 115 ka BP in the central Arctic is sharply reduced due to the increased surface salinity, the cooler sub-surface water mitigates the melting impact of above-freezing intermediate water reaching the ice base