Mechanisms behind the temporary shutdown of deep convection in the Labrador Sea : lessons from the Great Salinity Anomaly years 1968–71
Katsman, Caroline A.
MetadataShow full item record
From 1969 to 1971 convection in the Labrador Sea shut down, thus interrupting the formation of the intermediate/dense water masses. The shutdown has been attributed to the surface freshening induced by the Great Salinity Anomaly (GSA), a freshwater anomaly in the subpolar North Atlantic. The abrupt resumption of convection in 1972, in contrast, is attributed to the extreme atmospheric forcing of that winter. Here oceanic and atmospheric data collected in the Labrador Sea at Ocean Weather Station Bravo and a one-dimensional mixed layer model are used to examine the causes of the shutdown and resumption of convection in detail. These results highlight the tight coupling of the ocean and atmosphere in convection regions and the need to resolve both components to correctly represent convective processes in the ocean. They are also relevant to present-day conditions given the increased ice melt in the Arctic Ocean and from the Greenland Ice Sheet. The analysis herein shows that the shutdown was initiated by the GSA-induced freshening as well as the mild 1968/69 winter. After the shutdown had begun, however, the continuing lateral freshwater flux as well as two positive feedbacks [both associated with the sea surface temperature (SST) decrease due to lack of convective mixing with warmer subsurface water] further inhibited convection. First, the SST decrease reduced the heat flux to the atmosphere by reducing the air–sea temperature gradient. Second, it further reduced the surface buoyancy loss by reducing the thermal expansion coefficient of the surface water. In 1972 convection resumed because of both the extreme atmospheric forcing and advection of saltier waters into the convection region.
Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 6743–6755, doi:10.1175/JCLI-D-11-00549.1.
Showing items related by title, author, creator and subject.
Air-sea CO2 fluxes and the controls on ocean surface pCO2 seasonal variability in the coastal and open-ocean southwestern Atlantic Ocean : a modeling study Arruda, R.; Calil, P. H. R.; Bianchi, A. A.; Doney, Scott C.; Gruber, Nicolas; Lima, Ivan D.; Turi, G. (Copernicus Publications on behalf of the European Geosciences Union, 2015-10-12)We use an eddy-resolving, regional ocean biogeochemical model to investigate the main variables and processes responsible for the climatological spatio-temporal variability of pCO2 and the air-sea CO2 fluxes in the ...
Understanding the ocean carbon and sulfur cycles in the context of a variable ocean : a study of anthropogenic carbon storage and dimethylsulfide production in the Atlantic Ocean Levine, Naomi M. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2010-02)Anthropogenic activity is rapidly changing the global climate through the emission of carbon dioxide. Ocean carbon and sulfur cycles have the potential to impact global climate directly and through feedback loops. Numerical ...