ALUMAN

INTERNATIONAL POLAR YEAR – The Netherlands

IPY-GEOTRACES	ALUMAN

Dissolved Aluminium and Manganese as Source Tracers for Iron in Polar Oceans
NIOZ Project Leader: - Prof. dr. ir. H.J.W. (Hein) de Baar Other contributors: - R. (Rob) Middag (PhD student) - P. (Patrick) Laan (Technician) - Dr. L.J.A. (Loes) Gerringa Abstract: The two opposing Fe source hypotheses of Fe coming either from above by aeolian dust input from adjacent continents, or from below sediments will be assessed by obtaining a reliable dataset of dissolved Fe, Mn, Al in the polar oceans. The high accuracy dataset of dissolved (<0.2 micron filtrate) Fe in seawater (subpr. 1), will be taken at a series of stations, at a resolution of 48 sampling depths per station, along two transects at zero meridian and across Drake Passage, and at stations in the Arctic Ocean. For the same sampling grid, the dissolved Al will be measured as source tracer for aeolian dust input, and dissolved Mn as the source tracer for reductive dissolution input from underlying sediments (this subproject 3). In collaboration with Dr. Baker (UEA), aerosol dust samples will be collected with an air pump filtration system while the Polarstern is underway between stations, as to obtain estimates of abundance of Fe, Mn, Al in aerosols, from which by dissolution experiments and transport modeling, models for settling and partial dissolution of aerosol dust will be pursued. Maxima of reduced Fe(II) in surface waters (subpr. 1) may serve as indicator of wet deposition/dissolution events. In collaboration with dr. Rutgers vd Loeff (AWI), additional natural radio-isotope tracers 228Ra and 227Ac will be measured to furthermore serve as source tracers for dissolved Fe from sediments at continental margin and deep abyssal seafloor, respectively. The above tracers (Fe, Al, Mn, 228Ra, 227Ac) in combination with the relative distribution in seawater of dissolved Fe between colloids and dissolved organic states (subpr. 2), will serve to validate a budget model including the two external source terms (above and below), biological uptake and decomposition, and adsorptive scavenging removal.