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Seasonal variations of the Bransfield Current: dynamic horizontal/vertical structure and transport
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  • Marta Veny,
  • Borja Aguiar-González,
  • Ángeles Marrero-Díaz,
  • Ángel Rodríguez-Santana
Marta Veny
Grupo de Investigación en Oceanografía Física y Geofísica Aplicada (OFYGA), Departamento de Física, Universidad de Las Palmas de Gran Canaria

Corresponding Author:[email protected]

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Borja Aguiar-González
Grupo de Investigación en Oceanografía Física y Geofísica Aplicada (OFYGA), Departamento de Física, Universidad de Las Palmas de Gran Canaria
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Ángeles Marrero-Díaz
Grupo de Investigación en Oceanografía Física y Geofísica Aplicada (OFYGA), Departamento de Física, Universidad de Las Palmas de Gran Canaria
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Ángel Rodríguez-Santana
Grupo de Investigación en Oceanografía Física y Geofísica Aplicada (OFYGA), Departamento de Física, Universidad de Las Palmas de Gran Canaria
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Abstract

The Bransfield Strait is a semi enclosed region located between the Antarctic Peninsula and the South Shetland Islands (SSI), where the Bransfield Current (BC) is a relatively warm baroclinic jet (0-250 m) flowing northeastward along the southern slope of the SSI. Recent studies have shown that the BC propagates as a buoyant gravity current, recirculating around the north-eastern tip of the islands while shedding an anticyclonic eddy. However, most previous works are based on summertime measurements and a more comprehensive spatio-temporal view of the regional circulation is still lacking. In this study we provide the first seasonal description of the BC based on an extensive dataset of direct velocity measurements. These measurements were routinely collected along ship tracks from 275 cruises between 1999 and 2014. Seasonally, the horizontal structure of the BC flowing as a coastal jet appears more prominent during spring and summer, when its pathway extends along the island slopes over 180 km at velocities up to 45 cm/s, from Deception Island towards King George Island. During these seasons, the BC is consistently narrower at the beginning of its path (15-20 km wide), and wider before starting its recirculation around the SSI (30 km wide). Through autumn, this pattern is also apparent but less intense, especially south off Livingston-Robert Islands, where subsurface velocities (150 m) are lower at about 10-15 cm/s. The scarcity of winter data confirms the existence of a relatively strong coastal jet with mean velocities about 34 cm/s at least south off Nelson Island. Vertically, the BC also displays a distinctive pattern. At the wake of the islands, the core of the current flows hugging the island slopes with velocities about 35 cm/s at 150 m. Differently, when located at channels between islands, the core of the current migrates offshore flowing at 30-45 cm/s. In terms of zonal volume transport (0-250 m), our estimates indicate that the BC transports about 0.85, 0.93, 0.90 and 1.01 Sv from spring to winter, respectively, at the location where all seasons are covered by data (south off Nelson Island). These results support the BC is a recurrent feature of the circulation in Bransfield Strait, flowing northeastward all along the southern slope of the SSI not only during summer but also during spring and autumn.