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Mechanisms of subantarctic mode water upwelling in a hybrid-coordinate global GCM

Mechanisms of subantarctic mode water upwelling in a hybrid-coordinate global GCM
Mechanisms of subantarctic mode water upwelling in a hybrid-coordinate global GCM
This article presents an investigation of the global circulation and upwelling of subantarctic mode water (SAMW), which is thought to be key in the supply of nutrients to support biological production over much of the world ocean excluding the North Pacific. The HYbrid isopycnic-cartesian Coordinate Ocean general circulation Model (HYCOM) is configured to simulate the global ocean circulation for time scales of up to centuries and a SAMW-tracking online tracer experiment is conducted. The tracer re-emergence fluxes across the mixed layer base effected by a range of physical mechanisms and by numerical mixing terms in HYCOM are diagnosed and discussed. For the global ocean north of 30°S, entrainment due to surface buoyancy loss and/or wind-induced mechanical stirring accounts for almost one third of the total tracer re-emergence. Ekman upwelling and shear-induced mixing are especially significant in the tropical oceans, and account for 19% and 18% of the total tracer re-emergence, respectively. There is substantial regional variation in the relative importance of the various upwelling mechanisms. Special attention is devoted to understanding the contrasting circulations of SAMW in the North Pacific and North Atlantic oceans. The modest penetration of SAMW into the North Pacific is found to arise from the comparatively light density level that the SAMW core resides at in the South Pacific Ocean, which results in its being captured by the Equatorial Undercurrent and prevents it from entering the western boundary current of the North Pacific. In the North Atlantic, a new conceptual model of SAMW circulation and re-emergence is proposed with application to nutrient supply to the regional upper ocean. The model formulates SAMW re-emergence as a sequence of distinct processes following the seasonal cycle of the thermocline as a water column circulates around the subtropical and subpolar gyres of the North Atlantic.
SAMW, HYCOM, Tracer upwelling, Numerical mixing, Nutrient circulation, Induction
1463-5003
59-80
Zuo, Hao
3d7fbe98-00e0-40da-a80c-120f88861e65
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
New, Adrian L.
69c2be8b-c6c2-408f-9612-6980b1a25802
Oschlies, Andreas
75e18f55-3134-44a2-82ba-71334397727f
Zuo, Hao
3d7fbe98-00e0-40da-a80c-120f88861e65
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
New, Adrian L.
69c2be8b-c6c2-408f-9612-6980b1a25802
Oschlies, Andreas
75e18f55-3134-44a2-82ba-71334397727f

Zuo, Hao, Naveira Garabato, Alberto C., New, Adrian L. and Oschlies, Andreas (2012) Mechanisms of subantarctic mode water upwelling in a hybrid-coordinate global GCM. Ocean Modelling, 45-46, 59-80.

Record type: Article

Abstract

This article presents an investigation of the global circulation and upwelling of subantarctic mode water (SAMW), which is thought to be key in the supply of nutrients to support biological production over much of the world ocean excluding the North Pacific. The HYbrid isopycnic-cartesian Coordinate Ocean general circulation Model (HYCOM) is configured to simulate the global ocean circulation for time scales of up to centuries and a SAMW-tracking online tracer experiment is conducted. The tracer re-emergence fluxes across the mixed layer base effected by a range of physical mechanisms and by numerical mixing terms in HYCOM are diagnosed and discussed. For the global ocean north of 30°S, entrainment due to surface buoyancy loss and/or wind-induced mechanical stirring accounts for almost one third of the total tracer re-emergence. Ekman upwelling and shear-induced mixing are especially significant in the tropical oceans, and account for 19% and 18% of the total tracer re-emergence, respectively. There is substantial regional variation in the relative importance of the various upwelling mechanisms. Special attention is devoted to understanding the contrasting circulations of SAMW in the North Pacific and North Atlantic oceans. The modest penetration of SAMW into the North Pacific is found to arise from the comparatively light density level that the SAMW core resides at in the South Pacific Ocean, which results in its being captured by the Equatorial Undercurrent and prevents it from entering the western boundary current of the North Pacific. In the North Atlantic, a new conceptual model of SAMW circulation and re-emergence is proposed with application to nutrient supply to the regional upper ocean. The model formulates SAMW re-emergence as a sequence of distinct processes following the seasonal cycle of the thermocline as a water column circulates around the subtropical and subpolar gyres of the North Atlantic.

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More information

Published date: 2012
Keywords: SAMW, HYCOM, Tracer upwelling, Numerical mixing, Nutrient circulation, Induction
Organisations: Marine Systems Modelling, Physical Oceanography

Identifiers

Local EPrints ID: 300222
URI: https://eprints.soton.ac.uk/id/eprint/300222
ISSN: 1463-5003
PURE UUID: e3fbc995-430d-45fd-ae05-3d04b41233f6

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Date deposited: 20 Feb 2012 10:34
Last modified: 18 Sep 2017 02:05

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