ALBERT

Description: The Seychelles-Chagos Thermocline Ridge (SCTR) is a biologically important region of open ocean upwelling within the south west Indian Ocean (5-10°S and 45-90°E). The SCTR refers to an elongated feature which joins two local minima in thermocline depth; the Seychelles Dome (SD) and Chagos Domes (CD). We present the seasonality and physical drivers of the surface chl-a bloom for both the western (SD) and eastern (CD) extremes of the SCTR, using in situ observations and remotely sensed data. We find the buoyancy fluxes from the Indonesian Though Flow (ITF) strongly impacts surface chl-a concentrations over the CD. Here a significant correlation (r=0.33) was found between the altimeter-derived strength of the IFT and the surface chl-a concentrations. This correlation increases (r=0.58) when only the 90th percentile ITF events are considered, indicating the influence of the ITF may be overcoming other physical drivers for these years. We hypothesise the buoyancy flux of a strong ITF input suppresses the thermocline and ‘caps’ the CD with warm, less saline waters. This hypothesis is supported following a strong, significant relationship (r=0.66) between remotely sensed surface salinity and surface chl-a over the CD. This relationship is not found over the SD, where the ITF has a weaker direct impact over the bloom. The results suggest that the ITF may be an important factor for surface chl-a within the SCTR over longer-term time scales. Idealised model experiments will be used to investigate the relationship between the IFT and the spatio-temporal variability chl-a within the SCTR.