A model study of the Little Ice Age and beyond: changes in ocean heat content,hydrography and circulation since 1500 |
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Authors: | Jan Sedlá?ek Lawrence A Mysak |
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Institution: | 1.Earth System Modelling Group, Department of Atmospheric and Oceanic Sciences,McGill University,Montreal,Canada;2.Institute for Atmospheric and Climate Science,Swiss Federal Institute of Technology Zurich,Zurich,Switzerland |
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Abstract: | The Earth System Climate Model from the University of Victoria is used to investigate changes in ocean properties such as
heat content, temperature, salinity, density and circulation during 1500 to 2000, the time period which includes the Little
Ice Age (LIA) (1500–1850) and the industrial era (1850–2000). We force the model with two different wind-stress fields which
take into account the North Atlantic Oscillation. Furthermore, temporally varying radiative forcings due to volcanic activity,
insolation changes and greenhouse gas changes are also implemented. We find that changes in the upper ocean (0–300 m) heat
content are mainly driven by changes in radiative forcing, except in the polar regions where the varying wind-stress induces
changes in ocean heat content. In the full ocean (0–3,000 m) the wind-driven effects tend to reduce, prior to 1700, the downward
trend in the ocean heat content caused by the radiative forcing. Afterwards no dynamical effect is visible. The colder ocean
temperatures in the top 600 m during the LIA are caused by changes in radiative forcing, while the cooling at the bottom is
wind-driven. The changes in salinity are small except in the Arctic Ocean. The reduced salinity content in the subsurface
Arctic Ocean during the LIA is a result from reduced wind-driven inflow of saline water from the North Atlantic. At the surface
of the Arctic Ocean the changes in salinity are caused by changes in sea–ice thickness. The changes in density are a composite
picture of the temperature and salinity changes. Furthermore, changes in the meridional overturning circulation (MOC) are
caused mainly by a varying wind-stress forcing; the additional buoyancy driven changes due to the radiative forcings are small.
The simulated MOC is reduced during the LIA as compared to the industrial era. On the other hand, the ventilation rate in
the Southern Ocean is increased during the LIA. |
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Keywords: | Hydrography Ocean circulation Little Ice Age Radiative forcing Wind-stress forcing |
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