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| Titel |
Sea ice and its effect on mass transport between the atmosphere and the Southern Ocean interior |
| VerfasserIn |
Brice Loose, Peter Schlosser |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250044196
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| Zusammenfassung |
| We examine gas exchange in the presence of sea ice in the Southern Ocean using tracer data
and simple models of the oceanic surface layer. Convective cooling leads to sea ice formation
over much of the ocean surface, precisely when the water column is most turbulent and has
the greatest ability to exchange mass across the air-sea interface. It is this asynchrony of
sea ice advance and retreat, versus mixed-layer convection and stratification that
determines the net physical flux of gases between the atmosphere and the abyssal ocean
interior.
However, there is very little antecedent knowledge of the gas transfer velocity, k, through
ice-covered waters. The only known estimate, using the radon-deficit method in the Barents
Sea, yielded a value of k660 = 6 cm h-1 under ca. 90% ice cover. Here we attempt a second
estimate using an isopycnal inventory of three water column tracers measured during the
1992 Ice Station Weddell drift: 3He, CFC-11 and salinity. This effort produced a mean
value of 0.9 cm h-1 through ca. 92% ice cover, which is markedly reduced, despite
the apparent similarity in ice cover. However, it is difficult to assess the turbulent
forcing conditions in both estimates, and therefore we lack a complete basis for
comparison.
We use these disparate estimates to formulate alternative scenarios for gas ventilation
through the seasonal ice zone in the Southern Ocean, by applying them to the Robin
boundary condition on a reactive transport model for inorganic carbon. The results show that
CO2 flux through sea ice represents 13-34% of the net annual air-sea flux, depending on the
relationship between sea ice cover and k. However, the model also indicates that more
restriction of natural CO2 in winter produces greater ventilation in the springtime marginal
ice zone, with fluxes increasing by 200-700% over the winter value, despite photosynthetic
activity. These results highlight the importance of understanding the physical, as well as
biological, processes that regulate gas exchange in the marginal ice zone. These include
stratification, surface wave reflection/damping by ice floes, and turbulence production in the
ice-water boundary layer. |
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