The role of sea ice formation in cycling of aluminium in northern Marguerite Bay, Antarctica
The use of dissolved Al as a tracer for oceanic water masses and atmospheric dust deposition of biologically
important elements, such as iron, requires the quantitative assessment of its sources and sinks
in seawater. Here, we address the relative importance of oceanic versus atmospheric inputs of Al, and the
relationship with nutrient cycling, in a region of high biological productivity in coastal Antarctica. We
investigate the concentrations of dissolved Al in seawater, sea ice, meteoric water and sediments
collected from northern Marguerite Bay, off the West Antarctic Peninsula, from 2005 to 2006. Dissolved
Al concentrations at 15 m water depth varied between 2 and 27 nM, showing a peak between two
phytoplankton blooms. We find that, in this coastal setting, upwelling and incorporation of waters from
below the surface mixed layer are responsible for this peak in dissolved Al as well as renewal of nutrients.
This means that changes in the intensity and frequency of upwelling events may result in changes in
biological production and carbon uptake. The waters below the mixed layer are most likely enriched in Al
as a result of sea ice formation, either causing the injection of Al-rich brines or the resuspension of
sediments and entrainment of pore fluids by brine cascades. Glacial, snow and sea ice melt contribute
secondarily to the supply of Al to surface waters. Total particulate Al ranges from 93 to 2057 mg/g, and
increases with meteoric water input towards the end of the summer, indicating glacial runoff is an
important source of particulate Al. The (Al/Si)opal of sediment core top material is considerably higher
than water column opal collected by sediment traps, indicative of a diagenetic overprint and incorporation
of Al at the sediment–water interface. Opal that remains buried in the sediment could represent
a significant sink of Al from seawater.
Authors: Hendry, Katharine R., Meredith, Michael P., Measures, Christopher I., Carson, Damien S., Rickaby, Rosalind E.M.