SS4.06 Speciation, Bioavailability, and Impacts of Atmospheric Trace Metals in Aquatic Systems
Date: Wednesday, June 12, 2002
Time: 3:00:00 PM
Location: Esquimalt
SiefertRL, UMCES - Chesapeake Biological Laboratory, Solomons, USA,
Chen, Y, , UMCES - Chesapeake Biological Laboratory, Solomons, USA,
Bioavailable Iron in Aerosols Collected Over the Tropical and sub-Tropical North Atlantic Ocean
Atmospheric deposition is a major source of iron (Fe) to both high nutrient low chlorophyll (HNLC) and oligotrophic ocean regions where Fe may be a rate limiting nutrient for the growth of primary producers and nitrogen fixing organisms. The predominant source of iron to the atmosphere is from wind-derived (aeolian) suspension of dust from arid terrestrial regions. The chemical speciation of atmospheric Fe is believed to be a controlling factor for determining the fraction of Fe that is bioavailable. In this study, fine (less than 3 um diameter) and coarse (greater than 3 um diameter) aerosol samples were collected during research cruises over the tropical and sub-tropical North Atlantic Ocean during 2001. Dissolved Fe(II), total dissolved Fe and reducible Fe concentrations were three species of labile Fe measured immediately after collection on board the ship. Reducible Fe was measured by using a chemical reductant. This reducible Fe provides a measurement of the total labile Fe that is available for reactions in seawater and cloudwater. Total reducible Fe was highly variable ranging from 0.19 ng/m3 to 68.7 ng/m3. We hypothesize that marine microorganisms can also utilize these forms of labile Fe. On-board incubations were performed using aerosol samples and Trichodesmium spp. to investigate bioavailable iron and itís relationship to the labile Fe species measured. These results will be presented and discussed in terms of aerosol source regions, atmospheric processing of Fe during transport, deposition fluxes to the ocean and the release of atmospherically derived Fe to seawater.