Simulation of chlorophyll and iron supplies in the Sub Antarctic Zone South of Australia

The Sub Antarctic Zone (SAZ) is part of the high nutrient low chlorophyll region of the Southern Ocean where low iron availability limits phytoplankton productivity. In the Tasman Sea, the SAZ displays a unique and large zonal gradient in the surface chlorophyll concentrations. In situ measurements show higher dissolved iron in the east than in the west which could explain the zonal chlorophyll gradient. To assess and quantify the major sources of iron in this region, we use an eddy-resolving model to simulate the dissolved Fe distribution arising from both the shelf and the dust supply of iron. The simulation showed that dissolved Fe from the shelf is only transported eastward to about 155°E and the shelf source of dissolved iron is unable to supply iron to the entire Tasman Sea SAZ region even when we assume that there no iron losses. The simulation with the atmospheric source of iron showed that through a combination of atmospheric transport and ocean transport, enough dissolved Fe can be supplied to the entire Tasman Sea SAZ region to relieve iron limitation. From the model simulations, we conclude that atmospheric iron supply is essential to generating the observed gradient of the chlorophyll in the SAZ region of the Tasman Sea.