Spatial and Temporal Variations of
Total Organic Carbon in the Arabian Sea

Dennis A. Hansell
Bermuda Biological Station for Research, Inc.
17 Biological Lane, Ferry Reach
St. Georges, GE-01
BERMUDA

Edward T. Peltzer¹
Marine Chemistry and Geochemistry Department
Woods Hole Oceanographic Institution
Woods Hole, MA 02543
USA

Deep-Sea Research II (1998) 45: 2171-2193.

Received: 5 September 1997.
Revised: 12 May 1998.
Accepted: 18 May 1998.
Published: November 1998.


¹: Present address: Monterey Bay Aquarium Research Institute
PO Box 628, Moss Landing, CA 95039-0628, USA.

ABSTRACT

Concentrations of total organic carbon (TOC) were determined on samples collected during six cruises in the northern Arabian Sea during the 1995 US JGOFS Arabian Sea Process Study. Total organic carbon concentrations and integrated stocks in the upper ocean varied both spatially and seasonally. Highest mixed-layer TOC concentrations (80-100 µM C) were observed near the coast when upwelling was not active, while upwelling tended to reduce local concentrations. In the open ocean, highest mixed-layer TOC concentrations (80-95 µM C) developed in the winter (NE Monsoon) and remained through mid summer (early to mid SW Monsoon). Lowest open ocean concentrations (65-75 µM C) occurred late in the summer (late SW Monsoon) and during the Fall Intermonsoon period. The changes in TOC concentrations resulted in seasonal variations in mean TOC stocks in the upper 150 m of the water column of 1.5-2.0 mole C per m², with the lowest stocks found late in the summer during the SW Monsoon-Fall Intermonsoon transition. The seasonal accumulation of TOC north of 15°N was 31-41 x 10¹² g C, mostly taking place over the period of the NE Monsoon, and equivalent to 6-8% of annual primary production estimated for that region in the mid-1970s. A net TOC production rate of 12 mmole C per m² per day over the period of the NE Monsoon represented approximately 80% of net community production. Net TOC production was nil during the SW Monsoon, so vertical export would have dominated the export terms over that period. Total organic carbon concentrations varied in vertical profiles with the vertical layering of the water masses, with Persian Gulf Water TOC concentrations showing a clear signal. Deep water (>2000m) TOC concentrations were uniform across the basin and over the period of the cruises, averaging 42.3 ± 1.4 µM C.


Acknowledgements

This research was supported by the National Science Foundation via grants OCE-9311012 to DAH and OCE-9310719 to ETP. We gratefully acknowledge the officers, crew and technicians of the R/V Thomas G. Thompson for their help and support. We thank Chief Scientists Mike Roman, John Marra, Dick Barber, Sharon Smith, Barney Balch and Wilf Gardner for cruise planning and leadership. Liz Caporelli, Nancy Hayward, Rachel Parsons and Tye Waterhouse provided outstanding support with the analyses of TOC during the cruises. Lou codispoti, John Morrison and the Hydro Team supplied high quality nutrient and hydrographic data for the program. Susan Kadar and Martin Bowen provided excellent logistical support both in the US and Oman. More than anyone lese, sharon Smith made this work possible, and we thank her for her heroic efforts.

This is contribution number 1436 from the Bermuda Biological Station for Research, contribution number 9717 from the Woods Hole Oceanographic Institution, and contribution number 418 from the US JGOFS Planning Office.


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