Phytoplankton size structure in the southern Bay of Bengal modified by the Summer Monsoon Current and associated eddies: Implications on the vertical biogenic flux

Jyothibabu, R.; Vinayachandran, P. N.; Madhu, N.V.; Robin, R.S.; Karnan, C.; Jagadeesan, L.; Anjusha, A.

doi:10.1016/j.jmarsys.2014.10.018

Cited by 71 publications

(37 citation statements)

References 64 publications

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“…In this region N 2 fixation rates vary, however, with maximum rates of 840 µmol N m −2 d −1 detected in nitrogenous sulfidic waters off the coast of Peru (Löscher et al, 2014) and 117 µmol N m −2 d −1 in the oxygen-depleted zone . Low N 2 fixation rates close to the detection limit were reported from the same area (Chang et al, 2019); another set of N 2 fixation rates estimated from sediment trap analyses were in the range of 0-23 µmol N m −2 d −1 (Knapp et al, 2016). Taken together, these rates suggest either a strong temporal variation or spatial patchiness.…”

Section: Introductionmentioning

confidence: 62%

No nitrogen fixation in the Bay of Bengal?

et al. 2020

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The Bay of Bengal (BoB) has long stood as a biogeochemical enigma, with subsurface waters containing extremely low, but persistent, concentrations of oxygen in the nanomolar range which -for some, yet unconstrained, reason -are prevented from becoming anoxic. One reason for this may be the low productivity of the BoB waters due to nutrient limitation and the resulting lack of respiration of organic material at intermediate waters. Thus, the parameters determining primary production are key in understanding what prevents the BoB from developing anoxia. Primary productivity in the sunlit surface layers of tropical oceans is mostly limited by the supply of reactive nitrogen through upwelling, riverine flux, atmospheric deposition, and biological dinitrogen (N 2 ) fixation. In the BoB, a stable stratification limits nutrient supply via upwelling in the open waters, and riverine or atmospheric fluxes have been shown to support only less than one-quarter of the nitrogen for primary production. This leaves a large uncertainty for most of the BoB's nitrogen input, suggesting a potential role of N 2 fixation in those waters.Here, we present a survey of N 2 fixation and carbon fixation in the BoB during the winter monsoon season. We detected a community of N 2 fixers comparable to other oxygen minimum zone (OMZ) regions, with only a few cyanobacterial clades and a broad diversity of non-phototrophic N 2 fixers present throughout the water column (samples collected between 10 and 560 m water depth). While similar communities of N 2 fixers were shown to actively fix N 2 in other OMZs, N 2 fixation rates were below the detection limit in our samples covering the water column between the deep chlorophyll maximum and the OMZ. Consistent with this, no N 2 fixation signal was visible in δ 15 N signatures. We sug-gest that the absence of N 2 fixation may be a consequence of a micronutrient limitation or of an O 2 sensitivity of the OMZ diazotrophs in the BoB. Exploring how the onset of N 2 fixation by cyanobacteria compared to non-phototrophic N 2 fixers would impact on OMZ O 2 concentrations, a simple model exercise was carried out. We observed that both photic-zone-based and OMZ-based N 2 fixation are very sensitive to even minimal changes in water column stratification, with stronger mixing increasing organic matter production and export, which can exhaust remaining O 2 traces in the BoB.

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Section: Introductionmentioning

confidence: 62%

No nitrogen fixation in the Bay of Bengal?

et al. 2020

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“…This region is mainly affected by the Indian monsoon. In JuneSeptember, the Summer Monsoon Current flows into the southern Bay of Bengal from the highsalinity waters of the Arabian Sea, which leads to heavy rainfall and river influx associated with the Indian summer monsoon, and the surface salinity drops clearly to a seasonal minimum (~35 psu in the south and ~28 psu in the north) (Prasannakumar et al, 2002;Vinayachandran et al, 2013;Jyothibabu et al, 2015). During the northeastern monsoon (November-February) circulation is weaker and characterized by a north equatorial current (northeastern monsoon drift), and flowing equatorial current to the south and a moderately developed cyclonic gyre in the Bay of Bengal (Gupta et al, 2002).…”

Section: Oceanographic Settingmentioning

confidence: 99%

Taxonomy and species diversity of Holocene pylonioid radiolarians from surface sediments of the northeastern Indian Ocean

Zhang

Suzuki

2017

Palaeontologia Electronica

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“…Physical forcings disrupting salinity stratification in the bay provide favorable biological conditions for bloom generation [Gomes et al, 2000]. In the southern bay, mixing and upwelling forced by monsoon winds transport nutrients from subsurface layers to the euphotic zone, enhancing productivity [Vinayachandran and Mathew, 2003;Vinayachandran et al, 2004Vinayachandran et al, , 2005Jyothibabu et al, 2015]. Tropical cyclones are also observed to simulate shortlived, isolated patches of intense chlorophyll blooms in the southern bay [Madhu et al, 2002;Vinayachandran and Mathew, 2003;Rao et al, 2006;Vinayachandran, 2009].…”

Section: Introductionmentioning

confidence: 99%

Formation of summer phytoplankton bloom in the northwestern Bay of Bengal in a coupled physical-ecosystem model

Thushara

Vinayachandran

2016

J. Geophys. Res. Oceans

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The Bay of Bengal (BoB) is considered to be a region of low biological productivity, owing to nutrient limitation, caused by strong salinity stratification induced by the freshwater influx from rivers and precipitation. Satellite and in situ observations, however, reveal the presence of prominent regional blooms in the bay in response to monsoonal forcings. Bloom dynamics of the BoB are presumably determined by freshwater as well as the local and remote effect of winds and remain to be explored in detail. Using a coupled physical‐ecosystem model, we have examined the oceanic processes controlling productivity in the northwestern BoB during the summer monsoon. The region exhibits a prominent bloom lasting for a period of about 2 months, supporting major fishing zones along the northeast coast of India. The ecosystem model simulates the spatial and temporal evolution of the surface bloom in good agreement with Sea‐Viewing Wide Field‐of‐View Sensor (SeaWiFS) observations. Vertical distribution of upper ocean physical and biological tracers and a nitrate budget analysis reveal the dominant role of coastal upwelling induced by alongshore winds in triggering the bloom. Horizontal advection plays a secondary role by supplying nutrients from coastal to offshore regions. The bloom decays with the weakening of winds and upwelling by the end of summer monsoon. The simulated bloom in the northwestern bay remains largely unaffected by the freshwater effects, since the peak bloom occurs before the arrival of river plumes.

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Phytoplankton size structure in the southern Bay of Bengal modified by the Summer Monsoon Current and associated eddies: Implications on the vertical biogenic flux

Cited by 71 publications

References 64 publications

No nitrogen fixation in the Bay of Bengal?

No nitrogen fixation in the Bay of Bengal?

Taxonomy and species diversity of Holocene pylonioid radiolarians from surface sediments of the northeastern Indian Ocean

Formation of summer phytoplankton bloom in the northwestern Bay of Bengal in a coupled physical-ecosystem model

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