The distribution and behavior of dissolved and particulate iron and zinc in the Ross Sea and Antarctic circumpolar current along 170°W

Dissolved and particulate iron and zinc were measured in water samples collected from the Antarctic Circumpolar Current (ACC) region and the Ross Sea during the US JGOFS Antarctic Environment Southern Ocean Process Study (AESOPS). Dissolved and particulate zinc showed strongly seasonal variation, indicating efficient recycling in the upper 150 m of the water column in both regions. Seasonal zinc utilization is 21-118 μmol m−2 in the ACC and 134-192 μmol m−2 in the Ross Sea. Only 10-25% of the particulate zinc is exported below 150 m. Generally low dissolved (<0.05 nmol kg−1) and particulate iron concentrations (<0.2 nmol kg−1) were observed in the mixed layer year-around in the ACC region whereas seasonal depletion of dissolved iron and relatively high particulate iron (>1 nmol kg−1) were found in the Ross Sea. Seasonal iron utilization is 7-45 μmol m−2 in the ACC and 450-938 μmol m−2 in the Ross Sea, which yields an estimated Fe/C ratio of 15 and 100 (μmol Fe:mol C) for the ACC and the Ross Sea, respectively. More than 50% of the total iron production is exported below 150 m in the ACC region. Iron input through vertical mixing was minimal, in contrast to the vertical input of dissolved zinc and macronutrients in the ACC region. Upwelling may supply 50% of the export production of iron near the Southern ACC Front. In the Ross Sea, more iron is available due to the variety of inputs, in contrast to the ACC region. In addition to the input of dissolved and particulate iron from melting sea-ice, there is substantial input of particulate iron from the suspended materials of sediments.