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Denitrification in the Arabian Sea: a 3D ecosystem modelling study

Denitrification in the Arabian Sea: a 3D ecosystem modelling study
Denitrification in the Arabian Sea: a 3D ecosystem modelling study
A three-dimensional hydrodynamic-ecosystem model was used to examine the factors determining the spatio-temporal distribution of denitrification in the Arabian Sea. The ecosystem model includes carbon and nitrogen as currencies, cycling of organic matter via detritus and dissolved organic matter, and both remineralization and denitrification as sinks for material exported below the euphotic zone. Model results captured the marked seasonality in plankton dynamics of the region, with characteristic blooms of chlorophyll in the coastal upwelling regions and central Arabian Sea during the southwest monsoon, and also in the northern Arabian Sea during the northeast monsoon as the mixed layer shoals. Predicted denitrification was 26.2 Tg N yr?1,the greatest seasonal contribution being during the northeast monsoon when primary production is co-located with the zone of anoxia. Detritus was the primary organic substrate consumed in denitrification (97%), with a small (3%) contribution by dissolved organic matter. Denitrification in the oxygen minimum zone was predicted to be fuelled almost entirely by organic matter supplied by particles sinking vertically from the euphotic zone above (0.73 mmol N m?2 d?1) rather than from lateral transport of organic matter from elsewhere in the Arabian Sea (less than 0.01 mmol N m?2 d?1). Analysis of the carbon budget in the zone of denitrification (north of 10°N and east of 55°E) indicates that the modelled vertical export flux of detritus, which is similar in magnitude to estimates from field data based on the 234Th method, is sufficient to account for measured bacterial production below the euphotic zone in the Arabian Sea.
Denitrification, Biogeochemical cycles, Ecosystem modelling, Detritus, Export flux, Arabian Sea
0967-0637
2082-2119
Anderson, T.A.
dfed062f-e747-48d3-b59e-2f5e57a8571d
Ryabchenko, V.A.
772f8b0c-5d7f-4314-bed1-6099c3f7736e
Fasham, M.J.R.
7fb86485-8cfc-4199-bde4-2276abefdf2e
Gorchakov, V.A.
4e0e93a9-4bc1-42ed-8dbc-c823923011a2
Anderson, T.A.
dfed062f-e747-48d3-b59e-2f5e57a8571d
Ryabchenko, V.A.
772f8b0c-5d7f-4314-bed1-6099c3f7736e
Fasham, M.J.R.
7fb86485-8cfc-4199-bde4-2276abefdf2e
Gorchakov, V.A.
4e0e93a9-4bc1-42ed-8dbc-c823923011a2

Anderson, T.A., Ryabchenko, V.A., Fasham, M.J.R. and Gorchakov, V.A. (2007) Denitrification in the Arabian Sea: a 3D ecosystem modelling study. Deep Sea Research Part I: Oceanographic Research Papers, 54 (12), 2082-2119. (doi:10.1016/j.dsr.2007.09.005).

Record type: Article

Abstract

A three-dimensional hydrodynamic-ecosystem model was used to examine the factors determining the spatio-temporal distribution of denitrification in the Arabian Sea. The ecosystem model includes carbon and nitrogen as currencies, cycling of organic matter via detritus and dissolved organic matter, and both remineralization and denitrification as sinks for material exported below the euphotic zone. Model results captured the marked seasonality in plankton dynamics of the region, with characteristic blooms of chlorophyll in the coastal upwelling regions and central Arabian Sea during the southwest monsoon, and also in the northern Arabian Sea during the northeast monsoon as the mixed layer shoals. Predicted denitrification was 26.2 Tg N yr?1,the greatest seasonal contribution being during the northeast monsoon when primary production is co-located with the zone of anoxia. Detritus was the primary organic substrate consumed in denitrification (97%), with a small (3%) contribution by dissolved organic matter. Denitrification in the oxygen minimum zone was predicted to be fuelled almost entirely by organic matter supplied by particles sinking vertically from the euphotic zone above (0.73 mmol N m?2 d?1) rather than from lateral transport of organic matter from elsewhere in the Arabian Sea (less than 0.01 mmol N m?2 d?1). Analysis of the carbon budget in the zone of denitrification (north of 10°N and east of 55°E) indicates that the modelled vertical export flux of detritus, which is similar in magnitude to estimates from field data based on the 234Th method, is sufficient to account for measured bacterial production below the euphotic zone in the Arabian Sea.

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More information

Published date: December 2007
Keywords: Denitrification, Biogeochemical cycles, Ecosystem modelling, Detritus, Export flux, Arabian Sea

Identifiers

Local EPrints ID: 49781
URI: http://eprints.soton.ac.uk/id/eprint/49781
ISSN: 0967-0637
PURE UUID: 6eca7c65-2236-4869-9a54-1a8717d006a7

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Date deposited: 30 Nov 2007
Last modified: 15 Mar 2024 09:59

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Contributors

Author: T.A. Anderson
Author: V.A. Ryabchenko
Author: M.J.R. Fasham
Author: V.A. Gorchakov

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