Summary of Abstract Submission

Abstract Submission No. IO50-09-0071PresentationPoster

VARIATION OF PHYTOPLANKTON BIOMASS AND PRODUCTION IN THE SOUTHWESTERN TROPICAL INDIAN OCEAN DURING MONSOON 2014

Sarat Chandra Tripathy*1, S. Patra2, P. Sabu1, R. K. Naik1, A. Sarkar1, V. Venkataramana1, N. Anilkumar1

1 ESSO-National Centre for Antarctic and Ocean Research, Goa, India
2 ESSO-ICMAM Project Directorate, Ministry of Earth Sciences, NIOT Campus, Velachery, Chennai-600100 , India

ABSTRACT :

To understand the controlling environmental forcings for the variability in phytoplankton biomass (Chl a) and primary productivity (PP), time series (@6 h intervals over 10 days) and point measurements were carried out in the southwestern tropical Indian Ocean (SWTIO) during southwest monsoon (June), 2014. Results indicate that low-saline and warm-water mass formed a stratified surface layer resulting in shallow (35-40 m) mixed layer depth (MLD). Subsurface Chl a maximum was distinct and existed just beneath the MLD. Light availability at the time of sampling was highly favourable for algal growth within the MLD; however, nutrient ratios indicated N- and Si-limitation suggesting unfavourable condition for diatoms and/or silicoflagellates growth in the mixed layer. Column integrated PP (IPP) varied from 176 - 268 (241+43 mgC m-2 d-1) and was relatively stable, except with low value on 11-June, which was ascribed to the drastic dropdown in incident light due to overcast conditions. Higher PP rates in the subsurface layers were directly related to higher Chl a concentrations. The assimilation number (PB) varied from 1.6 - 16.7 (9.7+4.1 mgC (mgChl a)-1 d-1)), was higher within the MLD and showed no surface photoinhibition, which was due to the dominance of nano- and pico-sized phytoplankton in the surface layer. Highest integrated Chl a (39 mg m-2) and IPP (328 mgC m-2 d-1) observed at RT-2, was because of the cyclonic disturbance and associated positive Ekman pumping, as evidenced from low sea surface height anomaly (SSHA). However, at other stations high SSHA prevailed, indicating strong stratified conditions.