Summary of Abstract Submission

Abstract Submission No. IO50-11-0014PresentationOral

INADEQUATE BIOGEOCHEMICAL RESPONSE TO THE UPWELLING ALONG SEYCHELLES-CHAGOS THERMOCLINE RIDGE REGION IN THE TROPICAL INDIAN OCEAN

Amit Sarkar*1, Melena Soares1, Sabu P1, Ravi K Naik1, Jenson George1, N Anilkumar1

1 ESSO-National Centre for Antarctic & Ocean Research, Goa, India

ABSTRACT :

The Seychelles-Chagos Thermocline Ridge (SCTR) hosts substantial ocean-atmosphere interactions being region of potential upwelling. Shallow thermocline and strong Ekman pumping induces phytoplankton bloom in this region, which exhibits strong intraseasonal variability due to Rossby Waves and Madden-Julian Oscillation (MJO) as shown primarily based on satellite or moored buoy data combined with mathematical modeling. We performed in situ 10 days time-series investigation to capture the MJO signal and its influence on the dynamics of inorganic nutrients, oxygen, carbon dioxide and biological productivity at 8oS and 67oE location. Ekman Pumping was prominent during the study period and its intensity varied considerably. Changes in mixed layer depth (MLD) showed well compliance with physical forcing. However, dissolved inorganic nutrients didn┐t show any lateral advection to the mixed layer and remained nearly constant. Phosphate (~1 ÁM) and silicate (~4 ÁM) concentrations during the study period were relatively high and followed the expected trend; however, the system was oligotrophic in terms of inorganic nitrogen as a strong nitrate deficit environment was observed. This reduction cannot be attributed to biological uptake as very low phytoplankton biomass (chlorophyll a) was found in the euphotic depths. Primary productivity data revealed very low gross photosynthesis. Net biological carbon production was negative with very high respiration rates. This net heterotrophic system showed fluxes of CO2 (~8 mmol C m-2 d-1) from the ocean to the atmosphere during the present study.