The distribution of Fe in the antarctic circumpolar current

Abstract

The large-scale distributions of dissolved and total Fe in surface and deep waters of the Antarctic Circumpolar Current exhibit strong relationships with hydrography and biological processes. The mean dissolved Fe concentrations are low in surface waters of the Antarctic Circumpolar Current (0.31–0.49 nM, with a minimum of 0.17 nM) and higher (averaging 1.11.9 nM) in the Polar Frontal region. Enhanced dissolved surface water concentrations in the Polar Frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms. The effects of sea-ice melting and iceberg melting on the Fe concentrations were relatively small. Dissolved deep-water concentrations ( > 400 m) in the Antarctic Circumpolar Current ranged from 0.4 to 2.8 nM. Circumpolar Deep Water has relatively high dissolved Fe concentrations in the Polar Frontal region (0.4–2.8 nM) compared with deep waters further to the south (0.6–1.1 nM). Similarly, total dissolvable (unfiltered) Fe concentrations in the Upper Circumpolar Deep Water tend to decrease southward from the Polar Frontal region. In the Lower Circumpolar Deep Water total dissolvable Fe concentrations are higher than in the Upper Circumpolar Deep Water due to the existing nepheloid layer and sources on the Mid-Atlantic Ridge. Dissolved and total dissolvable Fe concentrations in the Antarctic Bottom Water are higher than those of other water masses in the Antarctic Circumpolar Current, consistent with the nepheloid layer as well as diagenetic input from shelf sediments. The High-Nutrient/Low-Chlorophyll areas of the Antarctic Ocean and northeast Pacific Ocean have different major Fe input sources of similar magnitude. In the Antarctic Circumpolar Current upward transport of Fe is the main input source, whereas in the North Pacific Ocean, aerosols are the dominant source.