Time-dependent response of a zonally averaged ocean–atmosphere–sea ice model to Milankovitch forcing |
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Authors: | Andrés Antico Olivier Marchal Lawrence A Mysak |
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Institution: | (1) Department of Atmospheric and Oceanic Sciences, McGill University, 805 Sherbrooke Street West, Montreal, QC, H3A 2K6, Canada;(2) Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA |
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Abstract: | An ocean–atmosphere–sea ice model is developed to explore the time-dependent response of climate to Milankovitch forcing for
the time interval 5–3 Myr BP. The ocean component is a zonally averaged model of the circulation in five basins (Arctic, Atlantic,
Indian, Pacific, and Southern Oceans). The atmospheric component is a one-dimensional (latitudinal) energy balance model,
and the sea-ice component is a thermodynamic model. Two numerical experiments are conducted. The first experiment does not
include sea ice and the Arctic Ocean; the second experiment does. Results from the two experiments are used to investigate
(1) the response of annual mean surface air and ocean temperatures to Milankovitch forcing, and (2) the role of sea ice in
this response. In both experiments, the response of air temperature is dominated by obliquity cycles at most latitudes. On
the other hand, the response of ocean temperature varies with latitude and depth. Deep water formed between 45°N and 65°N
in the Atlantic Ocean mainly responds to precession. In contrast, deep water formed south of 60°S responds to obliquity when
sea ice is not included. Sea ice acts as a time-integrator of summer insolation changes such that annual mean sea-ice conditions
mainly respond to obliquity. Thus, in the presence of sea ice, air temperature changes over the sea ice are amplified, and
temperature changes in deep water of southern origin are suppressed since water below sea ice is kept near the freezing point. |
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