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Plankton metabolic balance in the Indian Ocean during spring intermonsoon
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  • VSS Sarma Vedula,
  • Prasad M.H.K,
  • Sherin C.K.,
  • Mangalaa K.R.
VSS Sarma Vedula
CSIR-National Institute of Oceanography, Visakhapatnam

Corresponding Author:[email protected]

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Prasad M.H.K
CSIR-National Institute of Oceanography
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Sherin C.K.
CSIR-National Institute of Oceanography
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Mangalaa K.R.
CSIR-National Institute of Oceanography
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Abstract

In order to examine the spatial variability in plankton metabolic rates and their balance, deck incubation experiments were conducted in the Indian Ocean during spring intermonsoon. Nutrients in the mixed layer is low in the South Indian Ocean (SIO) compared to Arabian Sea (AS) and Bay of Bengal (BoB) associating with stratification in the former region suggesting that existence of oligotrophic conditions. Picophytoplankton biomass contributed to 70-90% of total biomass in the upper 50m of water column followed by nanoplankton. Dominant net autotrophy (positive NCP) was noticed in the AS whereas net heterotrophy (negative NCP) in the BoB and SIO. Higher community respiration (CR) was observed in the SIO followed by BoB and AS. NCP displayed inverse (linear) relationship with temperature (salinity) in the BoB, Andaman Sea and SIO suggesting that stratification driven by river discharge reduced nutrients inputs through vertical mixing resulting in formation of net heterotrophy. The photic zone integrated nutrients displayed linear relationship with NCP and GPP indicating that availability of nutrients controlled the plankton metabolic rates in the Indian Ocean. The threshold of GPP for plankton metabolic balance (6.1 mmol O2 m-3 d-1) was higher than global mean and such higher threshold GPP may be caused by warmer waters resulting in high CR. This study suggests that plankton metabolic balance is noticed in the AS and BoB and dominant heterotrophy in the SIO may be supported by excess carbon produced in the northern Indian Ocean.