Seasonal changes in the denitrification regime of the Arabian Sea

Naqvi, S.W.A.; Noronha, R.J.; Somasundar, K.; Gupta, R. Sen

doi:10.1016/0198-0149(90)90092-a

Cited by 75 publications

(24 citation statements)

References 24 publications

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“…The open-ocean suboxic zone is also influenced by monsoonal changes, albeit to a smaller extent, that should be related to both the O 2 supply and consumption within the ODZ. For example, surveys carried out during consecutive SW and NE monsoon seasons (1987 to 1988) led Naqvi et al (1990) to suggest a more vigorous denitrification (inferred from higher NO − 2 concentrations) during the latter season, a finding subsequently supported by the observations of de Sousa et al (1996) made in 1996. Morrison et al (1998Morrison et al ( , 1999) also found substantial variability in the depth profiles of NO − 2 but without a clear seasonal trend within 100 to 600 m at stations occupied repeatedly during the U.S. JGOFS expedition in 1994-1995.…”

Section: Seasonality Of O 2 Deficiencymentioning

confidence: 77%

Coastal versus open-ocean denitrification in the Arabian Sea

Naqvi

Naik²,

Pratihary³

et al. 2006

Biogeosciences

159

132

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Abstract. The Arabian Sea contains one of the three major open-ocean denitrification zones in the world. In addition, pelagic denitrification also occurs over the inner and midshelf off the west coast of India. The major differences between the two environments are highlighted using the available data. The perennial open-ocean system occupies two orders of magnitude larger volume than the seasonal coastal system, however, the latter offers more extreme conditions (greater nitrate consumption leading to complete anoxia). Unlike the open-ocean system, the coastal system seems to have undergone a change (i.e., it has intensified) over the past few decades presumably due to enhanced nutrient loading from land. The two systems also differ from each other with regard to the modes of nitrous oxide (N 2 O) production: In the open-ocean suboxic zone, an accumulation of secondary nitrite (NO

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Section: Seasonality Of O 2 Deficiencymentioning

confidence: 77%

Coastal versus open-ocean denitrification in the Arabian Sea

Naqvi

Naik²,

Pratihary³

et al. 2006

Biogeosciences

159

132

View full text Add to dashboard Cite

show abstract

“…Considered with the results of some other recent studies (Buesseler et al 1998, McCarthy et al 1999), our study also shows that the NEM is a season of relatively low export flux of POC; however, we hold a different view as to the fate of large newly produced C. We speculate that while a part of this is retained into the ensuing SI season as DOC, a significant fraction is transported downward as DOC exuded by vertically migrating salps or sinking remains of these organisms. (4) Large inputs of fresh and labile DOC to the suboxic zone may sustain high denitrification rates observed particularly during the NEM season (Naqvi et al 1990). …”

Section: Discussionmentioning

confidence: 99%

Carbon cycling in the northern Arabian Sea during the northeast monsoon: significance of salps

Naqvi¹,

Sarma²,

Jayakumar³

2002

Mar. Ecol. Prog. Ser.

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Winter cooling and mixing brings nutrients (nitrate and phosphate) to the surface waters over large parts of the northern Arabian Sea, but the rates of primary production as well as carbon export from the euphotic zone are not especially high during the northeast monsoon. A multi-disciplinary time-series study conducted over a period of 13 d around 21°N, 64°E during the northeast monsoon of 1997 revealed substantial decreases in chlorophyll stocks in the mixed layer following the occurrence of a massive swarm of salps. A large increase in DOC was also observed during the same period. We propose that a deficiency of silicate relative to nitrate during this season may often limit the growth of diatoms, creating an ecological niche for filter feeders that can efficiently utilize abundant smaller plankton. This may lead to periodic removal of chlorophyll, thereby moderating primary production as well as episodic build-up of DOC in the upper layers. This DOC pool may be used as a nutrient source for the microbial loop in the surface layer during the following spring intermonsoon season and by the denitrifying bacteria in the oxygen-minimum zone.

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“…The mixed-layer depth near southwest India changes from 80 m in January to 30 m in September (Rao et al, 1989). Associated with the monsoons is also a complete reversal of the subsurface coastal circulation (Naqvi et al, 1990). During the southwest monsoon a northward undercurrent appears to carry low nitrite and relatively well-oxygenated waters off the Indian continental margin.…”

Section: Introductionmentioning

confidence: 99%

The flow field off southwest India at 8N during the southwest monsoon of August 1993

Stramma¹,

Fischer²,

Schott³

1996

issn: 0022-2402

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The flow field off the southwest coast of India at 8N was investigated during RV Sonne cruise 89 in August 1993 by direct velocity observations from shipboard-and lowered-ADCP and geostrophic computations from CTD stations. The upper ocean between 75E and 76"52'E near the South Indian shelf was governed by a northward flow with a subsurface velocity maximum of 25 cm s-l at about 100 m depth. This flow, organized as a poleward undercurrent hugging the continental slope, is typical for the southwest monsoon season. The northward transport in August 1993 was 4.7 Sv (1 Sverdrup = lo6 m3 s-l) for the upper 300 m from the shipboard ADCP. Earlier geostrophic observations showed southward surface flow above the poleward undercurrent, but in August 1993 the northward flow reached to the surface and in the geostrophy calculations, i.e. without the southward Ekman flow near the surface, there was even no clear subsurface core. The T-S characteristics show that Bay of Bengal Water (BBW) was carried with this how, and low wind conditions seemed to be connected to the flow of BBW from the southern tip of Sri Lanka toward the southwest coast of India.Further offshore, two meridional current bands were identified in the upper 300 m of the ocean. West of the coastal undercurrent a band of southward flow existed with velocities up to 35 cm s-i above and to the east of the Chagos-Laccadive Ridge, from 72"lO'E to 75E. The associated geostrophic transport in the upper 500 m was 5.2 Sv. As the T-S relation was different from that of the northward flow, this current band was not a local recirculation of the poleward undercurrent. Further west, the how was weak, but intensified toward the central Arabian Sea, between 66E and 69"20'E, where another southward current band was found with velocities of up to 20 cm s-l and a total geostrophic transport for the upper 300 m of -7.2 Sv.

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Seasonal changes in the denitrification regime of the Arabian Sea

Cited by 75 publications

References 24 publications

Coastal versus open-ocean denitrification in the Arabian Sea

Coastal versus open-ocean denitrification in the Arabian Sea

Carbon cycling in the northern Arabian Sea during the northeast monsoon: significance of salps

The flow field off southwest India at 8N during the southwest monsoon of August 1993

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