On the Upwelling off the Southern Tip and along the West Coast of India

Smitha, B. R.; Sanjeevan, V. N.; VimalKumar, K.G.; Revichandran, C.

doi:10.2112/06-0779.1

Cited by 115 publications

(39 citation statements)

References 15 publications

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“…With the advent of the summer monsoon (June-August), the westerly monsoon winds drive a very strong offshore Ekman transport in the western Bay of Bengal and near the STI , resulting in an upwelling signal, which shoals the OCD and TCD up to 60 m at the STI ( Fig. 6b and f; Smitha et al, 2008;Gupta et al, 2016). Further north, the winds are almost perpendicular to the coast of western India ) and hence do not induce upwelling there.…”

Section: Physical Control Of the Seasonal Oxygen Variability Off The Wcimentioning

confidence: 99%

Positive Indian Ocean Dipole events prevent anoxia off the west coast of India

et al. 2017

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Abstract. The seasonal upwelling along the west coast of India (WCI) brings nutrient-rich, oxygen-poor subsurface waters to the continental shelf, favoring very low oxygen concentrations in the surface waters during late boreal summer and fall. This yearly-recurring coastal hypoxia is more severe during some years, leading to coastal anoxia that has strong impacts on the living resources. In the present study, we analyze a 1/4 • resolution coupled physical-biogeochemical regional oceanic simulation over the 1960-2012 period to investigate the physical processes influencing the oxycline interannual variability off the WCI, that being a proxy for the variability on the shelf in our model. Our analysis indicates a tight relationship between the oxycline and thermocline variations in this region on both seasonal and interannual timescales, thereby revealing a strong physical control of the oxycline variability. As in observations, our model exhibits a shallow oxycline and thermocline during fall that combines with interannual variations to create a window of opportunity for coastal anoxic events. We further demonstrate that the boreal fall oxycline fluctuations off the WCI are strongly related to the Indian Ocean Dipole (IOD), with an asymmetric influence of its positive and negative phases. Positive IODs are associated with easterly wind anomalies near the southern tip of India. These winds force downwelling coastal Kelvin waves that propagate along the WCI and deepen the thermocline and oxycline there, thus preventing the occurrence of coastal anoxia. On the other hand, negative IODs are associated with WCI thermocline and oxycline anomalies of opposite sign but of smaller amplitude, so that the negative or neutral IOD phases are necessary but not the sufficient condition for coastal anoxia. As the IODs generally start developing in summer, these findings suggest some predictability to the occurrence of coastal anoxia off the WCI a couple of months ahead.

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Section: Physical Control Of the Seasonal Oxygen Variability Off The Wcimentioning

confidence: 99%

Positive Indian Ocean Dipole events prevent anoxia off the west coast of India

et al. 2017

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“…Propagation of coastal Kelvin wave from the Bay of Bengal and thus the radiation of Rossby waves and their dynamics in this region and their role in formation of Lakshadweep 'High' and 'Low', both in respect to sea level and SST and their role during the upwelling period is reflected in the works of Shankar and Shetye (1997), Shenoi et al (1999) and Rao et al (2010). The upwelling as a result of equator-ward alongshore winds lowers the sea surface temperature commences at the southern tip of India and propagates northward along the coast with the advancement of monsoon (Madhupratap et al 2001;Luis and Kawamura 2004;Smitha et al 2008). Apart from all these studies, there is still more to understand on changes in the wind pattern and the rise in global SST from this region with respect to upwelling phenomenon.…”

Section: Articlementioning

confidence: 99%

“…The coastal upwelling index is defined as the temperature difference between the coastal waters and of those waters which are five meridians offshore, along the same latitude. In some of the previous studies of similar kind, by Smitha et al (2008) and Naidu et al (1999), along with Munikrishna (2009), the offshore limit for computing temperature gradients were taken as three degrees and mid ocean, respectively. In yet another study on the inter-annual variability of upwelling along the North African coast by Nykaer and Camp (1994), the five meridians distance was selected as the outer limit of offshore box and results were found to be fruitful.…”

Section: Computation Of Upwelling Indices Latitudinal Temperature Gramentioning

confidence: 99%

Interannual variability of upwelling indices in the Southeastern Arabian Sea: A satellite based study

et al. 2010

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Increase in sea surface temperature with global warming has an impact on coastal upwelling. Past two decades (1988 to 2007) of satellite observed sea surface temperatures and space borne scatterometer measured winds have provided an insight into the dynamics of coastal upwelling in the southeastern Arabian Sea, in the global warming scenario. These high resolution data products have shown inconsistent variability with a rapid rise in sea surface temperature between 1992 and 1998 and again from 2004 to 2007. The upwelling indices derived from both sea surface temperature and wind have shown that there is an increase in the intensity of upwelling during the period 1998 to 2004 than the previous decade. These indices have been modulated by the extreme climatic events like El-Nino and Indian Ocean Dipole that happened during 1991-92 and 1997-98. A considerable drop in the intensity of upwelling was observed concurrent with these events. Apart from the impact of global warming on the upwelling, the present study also provides an insight into spatial variability of upwelling along the coast. Noticeable fact is that the intensity of offshore Ekman transport off 8 o N during the winter monsoon is as high as that during the usual upwelling season in summer monsoon. A drop in the meridional wind speed during the years 2005, 2006 and 2007 has resulted in extreme decrease in upwelling though the zonal wind and the total wind magnitude are a notch higher than the previous years. This decrease in upwelling strength has resulted in reduced productivity too.

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“…and spring intermonsoon periods (4 ± 2 m S -1 ). Although there are differences of opinion on the mechanism responsible for the initiation of upwelling along the southwest coast of India, the pivotal role of strong south westerly winds has been well established (Shetye et al, 1985;Muraleedharan and Prasannakumar, 1996;Smitha et al, 2007). Now, it is fairly understood that the strong ) but cooler than the former region.…”

Section: Pattern Of Chlorophyll a With Respect To Sst And Wind Speedmentioning

confidence: 99%

Re-evaluation of ‘paradox of mesozooplankton’ in the eastern Arabian Sea based on ship and satellite observations

Jyothibabu

Madhu

Habeebrehman

et al. 2010

Journal of Marine Systems

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In the central and eastern Arabian Sea (EAS), biomass and production of phytoplankton are known to vary spatially and seasonally whereas, biomass of mesozooplankton (MSP) is reported to be constant. This apparent contradiction has been called 'Arabian Sea Paradox'. However, it is important to note that the paradox of MSP is based on a very limited seasonal data (from 5-7 locations). Therefore, we reconsidered the paradox of MSP based on intensive in-situ observations at 39 -40 locations in the EAS. In agreement with the known seasonal difference in phytoplankton standing stock in the EAS, we analysed the MSP data in two ways using two-way nested ANOVA. In 'basin scale' analysis, MSP data were analysed from the EAS were pooled and seasonal and inshore -offshore variations were analysed for the entire region. In 'regional scale' analysis, MSP data were analysed separately for (a) northern region (north of 15°N) and (b) southern regions (15°N and south of it). Satellite data of chlorophyll a, SST and wind speed were also analysed to show the major differences in oceanographic features in the northern and southern EAS. The analyses showed prominently high chlorophyll a (av. 1mg m ) in the southern region during most of the year mainly due to thermohaline stratification. The MSP biomass was distributed almost in a similar way as that of phytoplankton stock with statistically significant spatial and seasonal variations in the northern and southern regions. In this paper, we review the 'paradox of MSP' and present clear and new evidences to show that this concept is not logically applicable for EAS.

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On the Upwelling off the Southern Tip and along the West Coast of India

Cited by 115 publications

References 15 publications

Positive Indian Ocean Dipole events prevent anoxia off the west coast of India

Positive Indian Ocean Dipole events prevent anoxia off the west coast of India

Interannual variability of upwelling indices in the Southeastern Arabian Sea: A satellite based study

Re-evaluation of ‘paradox of mesozooplankton’ in the eastern Arabian Sea based on ship and satellite observations

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