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The Northeast Monsoon's Impact on Mixing, Phytoplankton Biomass and Nutrient Cycling in the Arabian SeaIn the northern Arabian Sea, atmospheric conditions during the Northeast (winter) Monsoon lead to deep convective mixing. Due to the proximity of the permanent pyncnocline to the sea surface, this mixing does not penetrate below 125 m. However, a strong nitracline is also present and the deep convection results in significant nitrate flux into the surface waters. This leads to nitrate concentrations over the upper 100 m that exceed 4 micrometers toward the end of the Monsoon. During the 1994/1995 US JGOFS/Arabian Sea expedition, the mean areal gross primary production over two successive Northeast Monsoons was determined to be 1.35gC/sq m/d. Thus, despite the deep penetrative convection, high rates of primary productivity were maintained. An interdisciplinary model was developed to elucidate the biogeochemical processes involved in supporting the elevated productivity. This model consists of a 1-D mixed-layer model coupled to a set of equations that tracked phytoplankton growth and the concentration of the two major nutrients (nitrate and ammonium). Zooplankton grazing was parameterized by rate constant determined by shipboard experiments. Model boundary conditions consist of meteorological time-series measured from the surface buoy that was part of the ONR Arabian Sea Experiment's central mooring. Our numerical experiments show that elevated surface evaporation, and the associated salinization of the mixed layer, strongly contributes to the frequency and penetration depth of the observed convective mixing. Cooler surface temperatures, increased nitrate entrainment, reduced water column stratification, and lower near-surface chlorophyll a concentrations all result from this enhanced mixing. The model also captured a dependence on regenerated nitrogen observed in nutrient uptake experiments performed during the Northeast Monsoon. Our numerical experiments also indicate that variability in mean pycnocline depth causes up to a 25% reduction in areal chlorophyll a concentration. We hypothesize that such shifts in pycnocline depth may contribute to the interannual variations in primary production and surface chlorophyll a concentration that have been previously observed in this region.
Document ID
20010021837
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Wiggert, J. D.
(Maryland Univ. College Park, MD United States)
Jones, B. H.
(University of Southern California Los Angeles, CA United States)
Dickey, T. D.
(California Univ. Santa Barbara, CA United States)
Brink, K. H.
(Woods Hole Oceanographic Inst. MA United States)
Weller, R. A.
(Woods Hole Oceanographic Inst. MA United States)
Marra, J.
(Lamont-Doherty Geological Observatory Palisades, NY United States)
Codispoti, L. A.
(Old Dominion Univ. Norfolk, VA United States)
Date Acquired
August 20, 2013
Publication Date
October 22, 2000
Publication Information
Publication: Deep Sea Research
Publisher: Elsevier Science Ltd.
Volume: 47
Issue: Part 2
ISSN: 0967-0645
Subject Category
Meteorology And Climatology
Report/Patent Number
AD-A384575
US-JEGOFS-CONTRIB-486
Funding Number(s)
CONTRACT_GRANT: N00014-96-1-0505
CONTRACT_GRANT: NAS5-32484
CONTRACT_GRANT: NSF OCE-97-12577
CONTRACT_GRANT: N00014-94-1-0161
CONTRACT_GRANT: N00014-94-1-0450
CONTRACT_GRANT: NSF OCE-93-10577
CONTRACT_GRANT: NAS5-98181
CONTRACT_GRANT: N00014-94-1-0362
CONTRACT_GRANT: N00014-94-1-0226
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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