Title: What Sets the Strength of the Middepth Stratification and Overturning Circulation in Eddying Ocean Models?

Abstract

The processes maintaining stratification in the oceanic middepth (between approximately 1000 and 3000 m) are explored using an eddy-resolving general circulation model composed of a two-hemisphere, semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain. The middepth region lies below the wind-driven main thermocline but above the diffusively driven abyssal ocean. Here, it is argued that middepth stratification is determined primarily in the model’s Antarctic Circumpolar Current. Competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel. Isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain, whereas isotherms that also outcrop in the Northern Hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport. A northern source of deep water (water with temperatures in the range of those in the channel) leads to the formation of a thick middepth thermostad. Changes in wind forcing over the channel influence the stratification throughout the domain. Since the middepth stratification is controlled by adiabatic dynamics in the channel, it becomes independent of the interior diffusivity κ as κ → 0. The meridionalmore » overturning circulation (MOC), as diagnosed by the mean meridional volume transport, also shows a tendency to become independent of κ as κ → 0, whereas the MOC diagnosed by water mass transport shows a continuing dependence on κ as κ → 0. A nonlocal scaling for MOC is created that relates the strength of the northern MOC to the depth of isotherms in the southern channel. Findings of this report compare favorably to observations of large-scale neutral density in the World Ocean.« less

Authors:

Wolfe, Christopher L. ^[1]; Cessi, Paola ^[1]

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+ Show Author Affiliations

1. Univ. of California, San Diego, CA (United States)

Publication Date:

Thu Jul 01 00:00:00 EDT 2010

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Univ. of California, San Diego, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1564725

Grant/Contract Number:  

FG02-01ER63252

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Oceanography

Additional Journal Information:

Journal Volume: 40; Journal Issue: 7; Journal ID: ISSN 0022-3670

Publisher:

American Meteorological Society

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; Eddies; Meridional overturning circulation; Antarctica; Currents; Channel flows; Wind effects