Phytoplankton, nutrients and hydrography in the frontal zone between the Southwest Indian Subtropical gyre and the Southern Ocean
Phytoplankton, nutrients and hydrography in the frontal zone between the Southwest Indian Subtropical gyre and the Southern Ocean
A survey was made of the Southwest Indian Ocean frontal region between 30 and 50°E containing the Agulhas Return, Subtropical and Subantarctic Fronts. From CTD, SeaSoar and extracted samples the distribution of nitrate, silicate and chlorophyll a is shown to be strongly linked to the front and water mass structure, varying zonally and meridionally. Surface chlorophyll a concentrations were low to the north and south leaving a band of elevated chlorophyll between the Subtropical and Subantarctic Fronts. The low concentration of chlorophyll a to the north, in Subtropical Water, was clearly due to nitrate limitation. Between the Subtropical and Subantarctic Fronts, where the chlorophyll a concentrations were highest, the surface layer showed silicate depletion limiting diatom growth. South of the Subantarctic Front there were deep extending, low concentrations of chlorophyll a, but despite plentiful supplies of macro-nutrients and a well-stratified surface layer, high concentrations of chlorophyll a were absent. Changes from west to east were associated with the meandering of the Southern Ocean Fronts, especially the Subtropical Front, and their strength and proximity to each other. Concentrations of chlorophyll a peaked where the Agulhas Return, Subtropical and Subantarctic Fronts were in close proximity. Combined frontal structures appear to have particularly pronounced vertical stability and are associated with enhanced upwelling of nutrients and leakage of nutrients across the front. Light levels are high within the shallow stable layer. Such conditions are clearly favourable for biological growth and support the development of larger-celled phytoplankton communities.
AGULHAS RETURN CURRENT, OCEAN FRONTS, SUBTROPICAL GYRES, WOCE
2341-2368
Read, J.F.
913784a2-30c1-4aa7-aa60-63824998e845
Lucas, M.I.
1d860b0b-ec20-428d-afaa-0f5ca576e369
Holley, S.E.
2f74a439-395a-4ee7-89a2-eff4cc8d9481
Pollard, R.T.
0c78b909-8a95-4bd2-82fd-9b11022888fd
2000
Read, J.F.
913784a2-30c1-4aa7-aa60-63824998e845
Lucas, M.I.
1d860b0b-ec20-428d-afaa-0f5ca576e369
Holley, S.E.
2f74a439-395a-4ee7-89a2-eff4cc8d9481
Pollard, R.T.
0c78b909-8a95-4bd2-82fd-9b11022888fd
Read, J.F., Lucas, M.I., Holley, S.E. and Pollard, R.T.
(2000)
Phytoplankton, nutrients and hydrography in the frontal zone between the Southwest Indian Subtropical gyre and the Southern Ocean.
Deep Sea Research Part I: Oceanographic Research Papers, 47 (12), .
(doi:10.1016/S0967-0637(00)00021-2).
Abstract
A survey was made of the Southwest Indian Ocean frontal region between 30 and 50°E containing the Agulhas Return, Subtropical and Subantarctic Fronts. From CTD, SeaSoar and extracted samples the distribution of nitrate, silicate and chlorophyll a is shown to be strongly linked to the front and water mass structure, varying zonally and meridionally. Surface chlorophyll a concentrations were low to the north and south leaving a band of elevated chlorophyll between the Subtropical and Subantarctic Fronts. The low concentration of chlorophyll a to the north, in Subtropical Water, was clearly due to nitrate limitation. Between the Subtropical and Subantarctic Fronts, where the chlorophyll a concentrations were highest, the surface layer showed silicate depletion limiting diatom growth. South of the Subantarctic Front there were deep extending, low concentrations of chlorophyll a, but despite plentiful supplies of macro-nutrients and a well-stratified surface layer, high concentrations of chlorophyll a were absent. Changes from west to east were associated with the meandering of the Southern Ocean Fronts, especially the Subtropical Front, and their strength and proximity to each other. Concentrations of chlorophyll a peaked where the Agulhas Return, Subtropical and Subantarctic Fronts were in close proximity. Combined frontal structures appear to have particularly pronounced vertical stability and are associated with enhanced upwelling of nutrients and leakage of nutrients across the front. Light levels are high within the shallow stable layer. Such conditions are clearly favourable for biological growth and support the development of larger-celled phytoplankton communities.
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Published date: 2000
Keywords:
AGULHAS RETURN CURRENT, OCEAN FRONTS, SUBTROPICAL GYRES, WOCE
Identifiers
Local EPrints ID: 8929
URI: http://eprints.soton.ac.uk/id/eprint/8929
ISSN: 0967-0637
PURE UUID: a2f1d2bf-9e0b-4f91-8e6f-c85e0b1e3293
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Date deposited: 10 Sep 2004
Last modified: 15 Mar 2024 04:53
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Contributors
Author:
J.F. Read
Author:
M.I. Lucas
Author:
S.E. Holley
Author:
R.T. Pollard
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