| Автор | Crowley, Thomas J. |
| Автор | Häkkinen, Sirpa |
| Дата выпуска | 1988 |
| dc.description | Geological data suggest that North Atlantic Deep Water (NADW) production rates decreased during the Pleistocene. We apply a coupled ice‐mixed layer model for vertical overturn in the marginal ice zone (Häkkinen, 1987a) to propose an explanation for such a decrease. The model predicts that prevailing wind direction is important in preconditioning of the water column along the marginal ice zone (MIZ) because it affects rates of upwelling and mixing of surface and subsurface waters, processes that result in deep ‐water formation. At present, prevailing wind directions during the winter in the Greenland Sea are northeasterly. Because ice has a larger drag coefficient than water, Ekman transport is greater under the ice than in open water. This configuration causes divergence along the MIZ, mixing of surface and subsurface waters, and vertical overturn. During the glacial maximum, however, the prevailing winds along the MIZ (polar front) were predominantly westerly. Modeling studies suggest that ice‐age changes in the prevailing winds would have significantly increased the depth of the mixed layer and decreased entrainment (equal to mixing) rates, in agreement with geological data. Mixing changes due to westerly winds are greater than mixing changes due to a lower ‐salinity layer under the present wind regime. Changes due to winds are so large that further changes in boundary conditions (low ‐salinity surface layer) result in only minor additional reductions in vertical mixing. Still, the maximum reduction occurs when the two processes are considered together, a situation that may be applicable to the Younger Dryas event during the last deglaciation, when a meltwater lid may have developed in the subpolar North Atlantic. Our study suggests that wind‐induced changes in mixed ‐layer depth along the MIZ represent a viable mechanism for decreasing past NADW production rates. |
| Формат | application.pdf |
| Копирайт | Copyright 1988 by the American Geophysical Union. |
| Тема | OCEANOGRAPHY: GENERAL |
| Тема | 4267 |
| Тема | Arctic and Antarctic oceanography |
| Тема | Water masses |
| Тема | OCEANOGRAPHY: PHYSICAL |
| Тема | Ice mechanics and air/sea/ice exchange processes |
| Название | A new mechanism for decreasing North Atlantic Deep Water production rates during the Pleistocene |
| Тип | article |
| DOI | 10.1029/PA003i003p00249 |
| Electronic ISSN | 1944-9186 |
| Print ISSN | 0883-8305 |
| Журнал | Paleoceanography |
| Том | 3 |
| Первая страница | 249 |
| Последняя страница | 258 |
| Выпуск | 3 |
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