The Influence of Distributed Sources and Upwelling on the Baroclinic Structure of the Abyssal Circulation

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  • 1 Department of Earth, Armospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts
  • | 2 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
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Abstract

The study of a simple, continuously stratified model of the abyssal ocean driven by upwelling out of the abyss into the main thermocline and by source fluid entering the basin through northern, western, and southern bound-aries is reported.

Our approach divides the deep mean into an inviscid interior and frictional boundary-layer regions. The interior circulation is fully determined by the horizontal distribution of upwelling and by the net, vertical distribution of sources entering the basin. Forcing by the local upwelling drives a barotropic velocity field, and remote forcing by both the upwelling and sources generates an underlying baroclinic flow, which can be considerably stronger and of opposite sign at some depths. The boundary current functions to redistribute around the perimeter fluid entering the boundary regions either through the basin walls or from the interior. In contrast to the interior flow, it depends also on the geographical location of sources. The boundary current is divided into three sublayers, one harotropic layer that is required to satisfy an overall mass balance and two baroclinic layers that close the baroclinic circulation. The outer baroclinic layer has a width that depends on the vertical scale of the flow and can extend far into the interior. Stratification induces the subdivision of both the interior and boundary layers into an upper region, dominantly driven by the upwelling, and a lower one, predominantly influenced by the sources.

Abstract

The study of a simple, continuously stratified model of the abyssal ocean driven by upwelling out of the abyss into the main thermocline and by source fluid entering the basin through northern, western, and southern bound-aries is reported.

Our approach divides the deep mean into an inviscid interior and frictional boundary-layer regions. The interior circulation is fully determined by the horizontal distribution of upwelling and by the net, vertical distribution of sources entering the basin. Forcing by the local upwelling drives a barotropic velocity field, and remote forcing by both the upwelling and sources generates an underlying baroclinic flow, which can be considerably stronger and of opposite sign at some depths. The boundary current functions to redistribute around the perimeter fluid entering the boundary regions either through the basin walls or from the interior. In contrast to the interior flow, it depends also on the geographical location of sources. The boundary current is divided into three sublayers, one harotropic layer that is required to satisfy an overall mass balance and two baroclinic layers that close the baroclinic circulation. The outer baroclinic layer has a width that depends on the vertical scale of the flow and can extend far into the interior. Stratification induces the subdivision of both the interior and boundary layers into an upper region, dominantly driven by the upwelling, and a lower one, predominantly influenced by the sources.

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