(Table 2) Upper mixed layer depth and average Fe concentration during POLARSTERN cruises in the Atlantic Sector of the Southern Ocean

Distance to coast = distance from the nearest Antarctic Peninsula, South Sandwich Islands, or western Weddell Sea shorelines. For stations in the ACC further away than 2000 km, the East Antarctic mainland (about 2000 km away) and South Africa (about 1800 km away) become closer than the West Antarctic continental shelves. However, in light of the general easterly circulation and limited cross-frontal exchange between the ACC and subtropical waters, we deem the distance to the West Antarctic continental shelves as the most relevant parameter. Diffusivity Kh was allowed to increase with scale length [Okubo, 1971] until a value of 1000 m**2/s [Marshall et al., 2006, doi:10.1175/JPO2949.1] was reached.