Estimating the response of the sea ice-ocean-atmosphere system to paleoclimatic orbital variations using numerical models

A hierarchy of model simulations are used to investigate the response of sea ice and its interaction with the atmosphere and ocean under orbitally induced climatic perturbations. A one-dimensional, thermodynamic sea ice model with parameterized ice dynamics is coupled to a mixed-layer ocean and driven with prescribed atmospheric forcings for the central Arctic. This off-line model simulates the sensitivity of ice cover to traditionally neglected thermodynamic parameterizations under various atmospheric radiative anomalies. The results demonstrate that the meaning of "sea ice sensitivity" is not obvious. The response of ice volume and surface temperature to the same forcing anomaly can differ greatly, potentially leading to different types of climatic effects on the ocean compared with the atmosphere. Furthermore, the response of the ice pack to altered parameterizations often depends strongly on background atmospheric conditions.; A coupled atmosphere/mixed-layer ocean GCM (GENESIS2) is forced with altered orbital boundary conditions for paleoclimates warmer (6 ka BP) and colder (115 ka BP) than present in the Arctic. A pair of experiments is run for each paleoclimatic period, one with sea ice dynamics and one without, to determine the effect of ice motion. Contrary to previous simulations without atmospheric feedbacks, the sign of the dynamic sea ice feedback varies and depends on the climatic variable, the region, and the type of orbital perturbation. Comparisons with paleoenvironmental evidence suggest that the model underestimates the magnitude of climatic changes at these times.; An ocean GCM is coupled to the off-line sea ice model and driven with the atmospheric output from GENESIS2 for 6 ka and 115 ka BP to examine the effect of altered sea ice regimes on the robustness of the Arctic Ocean pycnocline and convective overturning in the Nordic Seas. The upper-ocean salinity increases and the pycnocline weakens in the Arctic in both simulations, due to local forcing from changes in sea ice volume and remote forcing from altered penetration of Atlantic surface water. The influence of the remote oceanic forcing is affected by the extent of the ice pack and the recirculation of fresh water from exported sea ice that melts in the Greenland Sea.