Influence of phytoplankton pigment composition and primary production on pCO2 levels in the Indian Ocean.

The tropical Indian Ocean is a net sink for the carbon dioxide (CO2) in the atmosphere and phytoplankton production plays a crucial role in CO2 fixation and determines the direction of CO2 flux at the sea-to-air interface. In order to assess the influence of phytoplankton composition and primary production on pCO2 levels in the Indian Ocean, sampling was conducted at 25 stations during the spring intermonsoon period under the auspices of the Indian GEOTRACES program. The pCO2 was significantly correlated with salinity due to the discharge of low pCO2 water by major rivers to the Bay of Bengal (BoB). The stronger negative correlation observed between pCO2 and major phytoplankton marker pigments, net primary production and oxygen saturation levels suggesting significant influence of biological processes on pCO2 levels in the Indian Ocean. This study indicates that pCO2 levels are strongly modulated by biological processes than hitherto hypothesized as solubility pump in the Indian Ocean. Research highlights: Surface pCO2 levels are undersaturated in the Indian Ocean compared to atmosphere, except Arabian Sea. Oligotrophic conditions prevailed in the entire tropical Indian Ocean. Picophytoplankton (cyanobacteria) is the dominant phytoplankton in the Indian Ocean. 4.Significant relation between phytoplankton groups and pCO2 indicates strong biological control on surface pCO2. [ABSTRACT FROM AUTHOR]