Bio‐physical coupling and ocean dynamics in the central equatorial Indian Ocean during 2006 Indian Ocean Dipole

The high‐frequency time series data collected during 28th October to 21st November 2006 onboard R/V Mirai provided the first evidence of short‐term bio‐physical coupling in the central equatorial Indian Ocean (EIO). The predominant feature of the thermal structure was the down‐sloping of 28°C‐isotherm and up‐sloping of 14°C‐isotherm indicating deepening of surface‐layer and shoaling of lower‐thermocline respectively. Concomitant with the deepening of surface‐layer, nitracline and subsurface chlorophyll maximum (SCM) also deepened. From the prominent bi‐weekly periodicity in the 14°C‐isotherm and the upward phase propagation in the meridional current velocity, we infer that shoaling was the response of mixed Rossby‐Gravity (MRG) waves. Based on temperature and currents we propose that deepening of surface‐layer was caused by the eastward advection of warmer waters associated with the weakening of Indian Ocean Dipole (IOD). This made the upper ocean more nutrient‐depleted and biologically less‐productive, an indication that the central EIO is returning to its pre‐IOD condition.