Seasonal and spatial variability of remotely sensed chlorophyll and physical fields in the SAZ-Sense region

The Sub Antarctic Zone Sensitivity to environmental change (SAZ-Sense) project focused on the northern boundary of the Southern Ocean south of Tasmania where there is a persistent and large summer zonal gradient in remote sensed ocean color surface chlorophyll (Chl). This paper presents the seasonality and spatial variability of surface Chl, nutrients, temperature, light availability in the region. First, we verify that remotely sensed ocean color zonal gradient reflects a real gradient in Chl. From seasonal and spatial patterns in the region, we conclude that neither temperature, macro-nutrients nor light availability can account for the observed large zonal gradient in the surface Chl. Other factors such as iron or ecosystem structure must explain the gradient. We also explore variability in the remote sensed observations during the cruise. At the SAZ east station, there is high mesoscale variability with corresponding high variability in Chl concentrations, with the spatial variability around the station exceeding the expected difference between the SAZ east and SAZ west processes stations. The interpretation of the collected cruise station data, particularly at the SAZ east site needs to consider mesoscale variability. Comparison of Seawifs images with cruise data shows good agreement, particularly for low Chl values (less than 1.5 mg m−3).