The effect of dynamic–thermodynamic icebergs on the Southern Ocean climate in a three-dimensional model |
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| Authors: | Jochem I Jongma Emmanuelle Driesschaert Thierry Fichefet Hugues Goosse Hans Renssen |
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| Institution: | 1. Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield S10 2TN, UK;2. Department of Geography, University of Sheffield, Sheffield, S10 2TN, UK;3. School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield, MK43 0AL, UK;1. JMA Meteorological Research Institute, Tsukuba, Japan;2. National Center for Atmospheric Research (NCAR), Boulder, CO, USA;3. Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan;4. University of Bristol, Bristol, UK;5. Uni Research Climate, Bjerknes Centre for Climate Research, Bergen, Norway;6. GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany;7. Center for Ocean-Atmospheric Prediction Studies (COAPS), Florida State University, Tallahassee, FL, USA;8. Rutgers University, New Brunswick, NJ, USA;9. Institute for Marine and Antarctic Studies, University of Tasmania, Australia;10. Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Australia;11. ARC Centre of Excellence for Climate System Science, Australia;12. CSIRO Oceans and Atmosphere, Australia;13. Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, CA, USA;14. NOAA Geophysical Fluid Dynamics Laboratory (GFDL), Princeton, NJ, USA;15. Eurasia Institute of Earth Sciences, Istanbul Technical University, Istanbul, Turkey;p. National Oceanography Centre (NOC), Southampton, UK;q. Japan Meteorological Agency (JMA), Tokyo, Japan;r. Université Grenoble Alpes/CNRS/IRD/G-INP, IGE,, Grenoble, France;s. Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), Bologna, Italy;t. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Bologna, Italy;u. Institute for Space-Earth Environmental Research (ISEE), Nagoya University, Nagoya, Japan;v. University of Reading, Reading, UK |
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| Abstract: | Melting icebergs are a mobile source of fresh water as well as a sink of latent heat. In most global climate models, the spatio-temporal redistribution of fresh water and latent heat fluxes related to icebergs is parameterized by an instantaneous more or less arbitrary flux distribution over some parts of the oceans. It is uncertain if such a parameterization provides a realistic representation of the role of icebergs in the coupled climate system. However, icebergs could have a significant climate role, in particular during past abrupt climate change events which have been associated with armada’s of icebergs. We therefore present the interactive coupling of a global climate model to a dynamic thermodynamic iceberg model, leading to a more plausible spatio-temporal redistribution of fresh water and heat fluxes. We show first that our model is able to reproduce a reasonable iceberg distribution in both hemispheres when compared to recent data. Second, in a series of sensitivity experiments we explore cooling and freshening effects of dynamical icebergs on the upper Southern Ocean and we compare these dynamic iceberg results to the effects of an equivalent parameterized iceberg flux.In our model without interactive icebergs, the parameterized fluxes are distributed homogeneously South of 55°S, whereas dynamic icebergs are found to be concentrated closer to shore except for a plume of icebergs floating North–East from the tip of the Antarctic Peninsula. Compared to homogeneous fluxes, the dynamic icebergs lead to a 10% greater net production of Antarctic bottom water (AABW). This increased bottom water production involves open ocean convection, which is enhanced by a less efficient stratification of the ocean when comparing to a homogeneous flux distribution.Icebergs facilitate the formation of sea-ice. In the sensitivity experiments, both the fresh water and the cooling flux lead to a significant increase in sea-ice area of 12% and 6%, respectively, directly affecting the highly coupled and interactive air/sea/ice system. The consequences are most pronounced along the sea-ice edge, where this sea-ice facilitation has the greatest potential to affect ocean stratification, for example by heat insulation and wind shielding, which further amplifies the cooling and freshening of the surface waters. |
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