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Observations of the physical structure and seasonal jet-like circulation of the Celtic Sea and St. George's Channel of the Irish Sea

Observations of the physical structure and seasonal jet-like circulation of the Celtic Sea and St. George's Channel of the Irish Sea
Observations of the physical structure and seasonal jet-like circulation of the Celtic Sea and St. George's Channel of the Irish Sea
During July–September 1998 a comprehensive survey was undertaken of the Celtic Sea and St. George's Channel of the Irish Sea in order to resolve the three-dimensional density field and circulation. Towed undulating CTD data revealed that isolated below the seasonal thermocline was a dense (cold and saline) pool flanked by strong near-bed density gradients. The trajectories of 23 satellite-tracked Argos drifters demonstrated the existence of a cyclonic (anti-clockwise) circulation pattern. This was in accord with persistent and narrow (ca. 20 km) cores of cyclonic flow (dense water to the left) as revealed by geostrophic current estimates and moored acoustic Doppler current profiler data, with velocities >0.1 m s?1 and exceeding 0.3 m s?1 in St. George's Channel.

The results are consistent with a seasonal baroclinic circulation that advects saline Atlantic water through the south and west of the region to St. George's Channel. Westward flow across St. George's Channel is directed south into the Celtic Sea and west along the Irish coast. The southward flow, an artefact of the baroclinic circulation, often appears in infrared satellite imagery as a meander in the Celtic Sea front. At the southward extension a secondary clockwise circulation is formed (diameter40 km) before water joins westward flow. Fresher water of coastal origin, present in the northern Celtic Sea in late spring, is advected westward by the summer circulation. The advent of summer thermal stratification and associated flow fields reduces exchange between the Celtic and Irish Seas.

The understanding provided by such datasets such as those described here provides the necessary basis for environmental management and knowledge of the pathways for contaminants, the dynamics of nutrients and an understanding of the movement of larvae and juvenile fish. It also provides a template against which to test the prognostic capabilities of present and emerging baroclinic numerical models.
jet, density driven, baroclinic circulation, drifters, satellite observations, contaminant advection
0278-4343
533-561
Brown, J.
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Carrillo, L.
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Fernand, L.
676e9cd7-a75c-40fc-a588-85f50c541c22
Horsburgh, K.J.
cefa02ee-5150-4d3d-a3a0-cffcc0ed28b1
Hill, A.E.
c636abfd-40b2-4545-9f81-7c56d2444525
Young, E.F.
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Medler, K.J.
91cbc0c0-5752-4aeb-875c-730d238de79f
Brown, J.
64c8be68-e3cb-49ff-b5b0-525db5f4bcd0
Carrillo, L.
75544c6f-f9ec-4325-b976-612a2b120713
Fernand, L.
676e9cd7-a75c-40fc-a588-85f50c541c22
Horsburgh, K.J.
cefa02ee-5150-4d3d-a3a0-cffcc0ed28b1
Hill, A.E.
c636abfd-40b2-4545-9f81-7c56d2444525
Young, E.F.
f60e0123-ca43-41c3-a4c5-4783ae1479a5
Medler, K.J.
91cbc0c0-5752-4aeb-875c-730d238de79f

Brown, J., Carrillo, L., Fernand, L., Horsburgh, K.J., Hill, A.E., Young, E.F. and Medler, K.J. (2003) Observations of the physical structure and seasonal jet-like circulation of the Celtic Sea and St. George's Channel of the Irish Sea. Continental Shelf Research, 23 (6), 533-561. (doi:10.1016/S0278-4343(03)00008-6).

Record type: Article

Abstract

During July–September 1998 a comprehensive survey was undertaken of the Celtic Sea and St. George's Channel of the Irish Sea in order to resolve the three-dimensional density field and circulation. Towed undulating CTD data revealed that isolated below the seasonal thermocline was a dense (cold and saline) pool flanked by strong near-bed density gradients. The trajectories of 23 satellite-tracked Argos drifters demonstrated the existence of a cyclonic (anti-clockwise) circulation pattern. This was in accord with persistent and narrow (ca. 20 km) cores of cyclonic flow (dense water to the left) as revealed by geostrophic current estimates and moored acoustic Doppler current profiler data, with velocities >0.1 m s?1 and exceeding 0.3 m s?1 in St. George's Channel.

The results are consistent with a seasonal baroclinic circulation that advects saline Atlantic water through the south and west of the region to St. George's Channel. Westward flow across St. George's Channel is directed south into the Celtic Sea and west along the Irish coast. The southward flow, an artefact of the baroclinic circulation, often appears in infrared satellite imagery as a meander in the Celtic Sea front. At the southward extension a secondary clockwise circulation is formed (diameter40 km) before water joins westward flow. Fresher water of coastal origin, present in the northern Celtic Sea in late spring, is advected westward by the summer circulation. The advent of summer thermal stratification and associated flow fields reduces exchange between the Celtic and Irish Seas.

The understanding provided by such datasets such as those described here provides the necessary basis for environmental management and knowledge of the pathways for contaminants, the dynamics of nutrients and an understanding of the movement of larvae and juvenile fish. It also provides a template against which to test the prognostic capabilities of present and emerging baroclinic numerical models.

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More information

Published date: April 2003
Keywords: jet, density driven, baroclinic circulation, drifters, satellite observations, contaminant advection

Identifiers

Local EPrints ID: 46528
URI: http://eprints.soton.ac.uk/id/eprint/46528
ISSN: 0278-4343
PURE UUID: 93204600-3f55-4f41-92b4-5cb9fb13086e

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Date deposited: 04 Jul 2007
Last modified: 15 Mar 2024 09:24

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Contributors

Author: J. Brown
Author: L. Carrillo
Author: L. Fernand
Author: K.J. Horsburgh
Author: A.E. Hill
Author: E.F. Young
Author: K.J. Medler

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