Seasonal variation of hydrographic and nutrient fields during the US JGOFS Arabian Sea Process Study

Morrison, John M.; Codispoti, Louis A; Gaurin, Steve; Jones, Burton H.; Manghnani, V; Zheng, Zhiyin

doi:10.1016/s0967-0645(98)00063-0

Cited by 254 publications

(199 citation statements)

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“…Consistent with previous observations (Morrison et al, 1998;Woodward et al, 1999), signatures of upwelling (low SST and elevated NO − 3 ) could be seen up to ∼1000 km from the Omani coast (Fig. 2), but there was no indication of intensification of the process -surface temperatures were actually higher while nutrient levels were lower close to the coast in 2004 relative to 1995.…”

Section: Evidence Against Intensification Of Upwellingsupporting

confidence: 91%

“…The first cruise covered the Indian shelf and a part of the trans-Arabian Sea section up to longitude 72 • E from 22 to 31 August, whereas the second cruise sampled the rest of the stations from 4 to 25 September. The coastperpendicular line off Oman tracked the southern leg of the US JGOFS expedition (Morrison et al, 1998;Measures and Vink, 1999) (Fig. 1).…”

Section: Methodsmentioning

confidence: 96%

“…Extensive enrichment of the euphotic zone with macronutrients occurs seasonally, particularly during the summer or Southwest Monsoon (SWM), both along the western and eastern boundaries of the Arabian Sea (off Somalia (Smith and Codispoti, 1980;Van Veering et al, 1997;Hitchcock et al, 2000) and Arabia (Morrison et al, 1998;Woodward et al, 1999), and western India (Jayakumar et al, 2001;Naqvi et al, 2003)). However, a direct comparison of biogeochemical conditions prevailing in these two hydrographically different regions could not be made so far because of scarcity of data.…”

Section: Introductionmentioning

confidence: 99%

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The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon

et al. 2010

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Abstract.Extensive observations were made during the late Southwest Monsoon of 2004 over the Indian and Omani shelves, and along a transect that extended from the southern coast of Oman to the central west coast of India, tracking the southern leg of the US JGOFS expedition (1994)(1995) in the west. The data are used, in conjunction with satellite-derived data, to investigate long-term trends in chlorophyll and sea surface temperature, indicators of upwelling intensity, and to understand factors that control primary production (PP) in the Arabian Sea, focussing on the role of iron. Our results do not support an intensification of upwelling in the western Arabian Sea, reported to have been caused by the decline in the winter/spring Eurasian snow cover since 1997. We also noticed, for the first time, an unexpected development of high-nutrient, low-chlorophyll condition off the southern Omani coast. This feature, coupled with other characteristics of the system, such as a narrow shelf and relatively low iron concentrations in surface waters, suggest a close similarity between the Omani upwelling system and the Peruvian and California upwelling systems, where PP is limited by iron. Iron limitation of PP may complicate simple relationship between upwelling and PP assumed by previous workers, and contribute to the anomalous offshore occurrence of the most severe oxygen (O 2 ) depletion in the region. Over the much wider Indian shelf, which experiences large-scale bottom water O 2 -depletion in summer, adequate iron supply from reCorrespondence to: S. W. A. Naqvi (naqvi@nio.org) ducing bottom-waters and sediments seems to support moderately high PP; however, such production is restricted to the thin, oxygenated surface layer, probably because of the unsuitability of the O 2 -depleted environment for the growth of oxygenic photosynthesizers.

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Section: Evidence Against Intensification Of Upwellingsupporting

confidence: 91%

Section: Methodsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon

et al. 2010

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“…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. In any case, the substantial shortterm changes evident in these data sets imply that the intermediate waters in the Arabian Sea must be quickly renewed (Swallow, 1984;Naqvi, 1987;Somasundar and Naqvi, 1988;Naqvi and Shailaja, 1993).…”

Section: Seasonality Of O 2 Deficiencymentioning

confidence: 93%

Coastal versus open-ocean denitrification in the Arabian Sea

Naqvi

Naik²,

Pratihary³

et al. 2006

Biogeosciences

161

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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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“…During the summer monsoon, strong upwelling occurs in the western Arabian Sea, offshore of Somalia and Oman (Elliott and Savidge 1990;McCreary et al 1993). A notable observational program in the region was the Arabian-Sea Process Study program conducted during 1994-1995, which was designed to investigate the interaction of biological activity and ocean dynamics in the region (Lee et al 1998;Morrison et al 1998;Shi et al 1999). Among other things, it was found that mesoscale variability efficiently redistributes nutrients offshore from Oman during the upwelling season.…”

Section: Introductionmentioning

confidence: 99%

Western boundary upwelling dynamics off Oman

et al. 2017

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Despite its climatic and ecosystemic significance, the coastal upwelling that takes place off Oman is not well understood. A primitive-equation, regional model forced by climatological wind stress is used to investigate its dynamics and to compare it with the better-known Eastern Boundary Upwellings (EBUs). The solution compares favorably with existing observations, simulating well the seasonal cycles of thermal structure, surface circulation (mean and turbulent), and sea-surface temperature (SST). There is a 1.5-month lag between the maximum of the upwellingfavorable wind-stress-curl forcing and the oceanic response (minima in sea-surface height and SST), which we attribute to onshore-propagating Rossby waves. A southwestwardflowing undercurrent (opposite to the direction of the nearsurface flow) is also simulated with a core depth of 1000 m, much deeper than found in EBUs (150-200 m). An EKE budget reveals that, in contrast to EBUs, the upwelling jet is more prone to barotropic than baroclinic instability and the contribution of locally-generated instabilities to EKE is higher by an order of magnitude. Advection and redistribution of EKE by standing mesoscale features also play a significant role in EKE budget.

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Seasonal variation of hydrographic and nutrient fields during the US JGOFS Arabian Sea Process Study

Cited by 254 publications

References 0 publications

The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon

The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon

Coastal versus open-ocean denitrification in the Arabian Sea

Western boundary upwelling dynamics off Oman

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