The warm-water "Halo" around Maud Rise

Properties, dynamics and Impact

L. de Steur, D. M. Holland, R. D. Muench, M. G. McPhee

Research output: Contribution to journalArticle

Abstract

Regional hydrographic and current observations from the 2005 MaudNESS winter field campaign in the Maud Rise seamount region of the eastern Weddell Sea show that an annular Halo consisting largely of Warm Deep Water (WDW) encircled the Rise at depths just below the mixed layer. The Halo was associated with elevated isopycnals and, on the northern flank of the Rise, strong subsurface velocities up to 20 cm s-1. Intercomparison of these observations with winter 1986 and 1994 conditions confirms the presence of the Halo and suggests that it, and associated warm pools west of the Rise, are at least semipermanent features of the region. These observational results compare well with the output from an isopycnic ocean model for a variety of parameters including shape of the seamount, inflow conditions and vertical stratification. The model captures processes associated with a steady westward flow impinging on the isolated seamount and shows (1) that the dynamics of the warm-water Halo with a shallow mixed layer are related to the formation of a jet surrounding the Rise and the overlying Taylor column and (2) that eddies of alternating sign (cyclones and anticyclones) are formed from instability of the jet-like flow structure, and are subsequently shed from the western flanks of the Rise. The eddies closest to the rise are dominated by cyclones which tend to adhere to the flanks more strongly than anticyclones. The formation and passage of approximately 3-5 eddies per year is seen in the sea-surface-height anomalies over a 12-year period. Despite apparent spatial and temporal variability in the dynamics of the Halo and shedding of eddies, the time-mean picture is such that significantly elevated isopycnals with WDW below the mixed layer are always present on the flanks of Maud Rise. This mechanism likely contributes annually to earlier seasonal ice loss in the eastern Weddell Sea than farther west. For unusually strong inflow conditions, possibly due to large-scale interannual variability, the Halo becomes more intense and overlies a much larger part of Maud Rise, potentially preconditioning the area for deep ocean ventilation and a subsequent polynya event such as observed in the 1970s.

Original languageEnglish (US)
Pages (from-to)871-896
Number of pages26
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Volume54
Issue number6
DOIs
StatePublished - Jun 2007

Fingerprint

dynamic property
warm water
eddy
seamount
mixed layer
anticyclone
oceans
cyclone
steady flow
inflow
deep water
winter
water
polynya
warm pool
sea surface height
flow structure
ocean
ice
ventilation

Keywords

  • Eddies
  • Flow-topography interactions
  • Maud Rise seamount
  • Upper-ocean processes
  • Weddell Sea

ASJC Scopus subject areas

  • Aquatic Science
  • Geology
  • Oceanography

Cite this

The warm-water "Halo" around Maud Rise : Properties, dynamics and Impact. / de Steur, L.; Holland, D. M.; Muench, R. D.; McPhee, M. G.

In: Deep-Sea Research Part I: Oceanographic Research Papers, Vol. 54, No. 6, 06.2007, p. 871-896.

Research output: Contribution to journalArticle

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AU - Muench, R. D.

AU - McPhee, M. G.

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N2 - Regional hydrographic and current observations from the 2005 MaudNESS winter field campaign in the Maud Rise seamount region of the eastern Weddell Sea show that an annular Halo consisting largely of Warm Deep Water (WDW) encircled the Rise at depths just below the mixed layer. The Halo was associated with elevated isopycnals and, on the northern flank of the Rise, strong subsurface velocities up to 20 cm s-1. Intercomparison of these observations with winter 1986 and 1994 conditions confirms the presence of the Halo and suggests that it, and associated warm pools west of the Rise, are at least semipermanent features of the region. These observational results compare well with the output from an isopycnic ocean model for a variety of parameters including shape of the seamount, inflow conditions and vertical stratification. The model captures processes associated with a steady westward flow impinging on the isolated seamount and shows (1) that the dynamics of the warm-water Halo with a shallow mixed layer are related to the formation of a jet surrounding the Rise and the overlying Taylor column and (2) that eddies of alternating sign (cyclones and anticyclones) are formed from instability of the jet-like flow structure, and are subsequently shed from the western flanks of the Rise. The eddies closest to the rise are dominated by cyclones which tend to adhere to the flanks more strongly than anticyclones. The formation and passage of approximately 3-5 eddies per year is seen in the sea-surface-height anomalies over a 12-year period. Despite apparent spatial and temporal variability in the dynamics of the Halo and shedding of eddies, the time-mean picture is such that significantly elevated isopycnals with WDW below the mixed layer are always present on the flanks of Maud Rise. This mechanism likely contributes annually to earlier seasonal ice loss in the eastern Weddell Sea than farther west. For unusually strong inflow conditions, possibly due to large-scale interannual variability, the Halo becomes more intense and overlies a much larger part of Maud Rise, potentially preconditioning the area for deep ocean ventilation and a subsequent polynya event such as observed in the 1970s.

AB - Regional hydrographic and current observations from the 2005 MaudNESS winter field campaign in the Maud Rise seamount region of the eastern Weddell Sea show that an annular Halo consisting largely of Warm Deep Water (WDW) encircled the Rise at depths just below the mixed layer. The Halo was associated with elevated isopycnals and, on the northern flank of the Rise, strong subsurface velocities up to 20 cm s-1. Intercomparison of these observations with winter 1986 and 1994 conditions confirms the presence of the Halo and suggests that it, and associated warm pools west of the Rise, are at least semipermanent features of the region. These observational results compare well with the output from an isopycnic ocean model for a variety of parameters including shape of the seamount, inflow conditions and vertical stratification. The model captures processes associated with a steady westward flow impinging on the isolated seamount and shows (1) that the dynamics of the warm-water Halo with a shallow mixed layer are related to the formation of a jet surrounding the Rise and the overlying Taylor column and (2) that eddies of alternating sign (cyclones and anticyclones) are formed from instability of the jet-like flow structure, and are subsequently shed from the western flanks of the Rise. The eddies closest to the rise are dominated by cyclones which tend to adhere to the flanks more strongly than anticyclones. The formation and passage of approximately 3-5 eddies per year is seen in the sea-surface-height anomalies over a 12-year period. Despite apparent spatial and temporal variability in the dynamics of the Halo and shedding of eddies, the time-mean picture is such that significantly elevated isopycnals with WDW below the mixed layer are always present on the flanks of Maud Rise. This mechanism likely contributes annually to earlier seasonal ice loss in the eastern Weddell Sea than farther west. For unusually strong inflow conditions, possibly due to large-scale interannual variability, the Halo becomes more intense and overlies a much larger part of Maud Rise, potentially preconditioning the area for deep ocean ventilation and a subsequent polynya event such as observed in the 1970s.

KW - Eddies

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KW - Upper-ocean processes

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