No abstract

No abstract

No abstract

Iron is a limiting micronutrient for primary production in the Ross Sea, Antarctica. Recent observations reveal low dissolved Fe (dFe) concentrations in the Ross Sea polynya following high initial rates of primary production in summer, after the dFe winter reserve has been consumed. Significant new sources of dFe are therefore required to further sustain phytoplankton blooms. Iron from aeolian sand and dust (ASD) released from melting sea ice is one potential source. To constrain aeolian Fe inputs, we determined ASD mass accumulation rates and the total and soluble Fe content of ASD on sea ice in McMurdo Sound, southwestern (SW) Ross Sea. The mean mass accumulation rate was~1.5 g m À2 yr À1, total Fe content of this ASD was 4 ± 1 wt %, and the percentage of soluble Fe was 11 ± 1%. Our mean estimate of the bulk aeolian dFe flux of 122.1 μmol m À2 yr À1 for the McMurdo Sound region suggests that aeolian Fe can support between 9.0 × 10 9 and 4.1 × 10 11 mol C yr À1 (0.1-4.9 Tg C yr À1) of new primary production. This equates to only~15% of new primary production in the SW Ross Sea, suggesting that aeolian dFe is a minor component of seasonal Fe supply. The very high ASD accumulation on sea ice in McMurdo Sound compared to other regions of Antarctica suggests that our results represent the upper limit of dFe supply to the ocean from this source in the Ross Sea.

Associate Editor -Nick LancasterABSTRACT Aeolian sand and dust in polar regions are transported offshore over sea ice and released to the ocean during summer melt. This process has long been considered an important contributor to polar sea floor sedimentation and as a source of bioavailable iron that triggers vast phytoplankton blooms. Reported here are aeolian sediment dispersal patterns and accumulation rates varying between 0Á2 g m À2 yr À1 and 55 g m À2 yr À1 over 3000 km 2 of sea ice in McMurdo Sound, south-west Ross Sea, adjacent to the largest ice free area in Antarctica. Sediment distribution and the abundance of southern McMurdo Volcanic Group-derived glass, show that most sediment originates from the McMurdo Ice Shelf and nearby coastal outcrops. Almost no sediment is derived from the extensive ice free areas of the McMurdo Dry Valleys due to winnowed surficial layers shielding sand-sized and silt-sized material from wind erosion and because of the imposing topographic barrier of the north-south aligned piedmont glaciers. Southerly winds of intermediate strength (ca 20 m sec À1 ) are primarily responsible for transporting sediment northwards and offshore. The results presented here indicate that sand-sized sediment does not travel more than ca 5 km offshore, but veryfine sand and silt grains can travel >100 km from source. For sites >10 km from the coast, the mass accumulation rate is relatively uniform (1Á14 AE 0Á57 g m À2 yr À1 ), three orders of magnitude above estimated global atmospheric dust values for the region. This uniformity represents a sea floor sedimentation rate of only 0Á2 cm kyr À1 , well below the rates of >9 cm kyr À1 reported for biogenic-dominated sedimentation measured over much of the Ross Sea. These results show that, even for this region of high-windblown sediment flux, aeolian processes are only a minor contributor to sea floor sedimentation, excepting areas proximal to coastal sources.