Jiayan Yang and J. David Neelin
Atmosphere-Ocean, 1997.
© Copyright 1997 by the Canadian Meteorological and Oceanographic Society.
Abstract. The role of sea ice in affecting the stability and long-term variability of the oceanic thermohaline circulation (THC) is studied in this paper. The emphasis is placed on studying how sea ice affects the stability and the long-term variability of the THC through its modulations on the surface heat and freshwater fluxes. A simple box model is analyzed to elucidate qualitatively the distinct physical meanings of these two processes. The analytical solution of this simple model indicates that the thermal insulation stabilizes the THC while the freshwater feedback increases the effective inertia of the coupled ice-ocean system. The sea-ice insulation lessens the negative feedback between heat flux and the SST, and therefore, allows the SST to play a greater role in counteracting changes of the THC and high latitude salinity field. The freshwater feedback effectively links the surface heat flux to a freshwater reservoir, and thus, increases the effective inertia of the coupled ocean-ice system. A two-dimensional ocean model coupled with a thermodynamic sea-ice model is used to estimate quantitatively the magnitudes of these two feedbacks. The numerical experiments involve the model's responses both to initial anomalies and to changes of forcing fields. For the free response cases (model responses to initial anomalies without changing the forcing fields), the model shows that the decay rate of an initial anomaly is greater when sea ice is included. For small perturbations the thermal insulation effect dominates over the freshwater feedback. The latter becomes increasingly more important for larger perturbations. In response to a change of external forcing, the presence of sea ice reduces the magnitude and the pace of the model's response. The numerical results are qualitatively consistent with the analytical solution of the box model.
Citation. Yang, J.-Y., and J. D. Neelin, 1997: Sea-ice interaction and the stability of the thermohaline circulation. Atmosphere-Ocean, 35, 433-469.
Acknowledgements This work was supported in part by NOAA through Grant GC95-054, an NSF Presidential Young Investigator Award, ATM-9158294, a grant from the National Institute for Global Environmental Change, and a Mellon Independent Study Award from the Woods Hole Oceanographic Institution.