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CONSTRAINING A NATURAL IRON SOLUBILITY BASELINE AND SOLUBLE IRON FLUXES FROM DUST TO THE SOUTHERN OCEAN DURING GLACIAL INTERVALS

Enhanced dust supply to the Southern Ocean during colder glacial intervals, with consequent relief of iron (Fe) limitation in the Southern Ocean, has been invoked as a potential driver of glacial-interglacial carbon dioxide cycling. While ice and marine sediment records clearly show that the supply of atmospheric dust to the oceans increased dramatically during cold intervals, uncertainty remains about atmospheric Fe fluxes at these times. In fact, converting dust flux to soluble Fe flux is not straightforward, with uncertainty from Fe content, mineralogy and solubility complicating efforts. Previous efforts to determine Fe fluxes in Antarctic ice using strong acid leaches may not be representative of the dissolution of aerosol Fe at high-pH in surface seawater. Here, using new sublimation and filtration methods, we present representative estimates of water- and seawater-soluble Fe in glacial-age dust from the EPICA Dome C and Berkner Ice cores. Focusing largely on the Last Glacial Maximum (LGM; 21-26 kybp), we found that Fe solubility in aerosol dust deposited to Antarctica was spatially and temporally variable (1-42%), and often higher than is typically assumed by modellers. These data also provide a natural baseline for interpreting modern aerosol Fe solubility measurements in the context of natural vs anthropogenic iron sources, by demonstrating that truly natural aerosol Fe can be highly soluble. Calculated soluble atmospheric fluxes to Dome C at the LGM were 0.01–0.84  mg/m2 per year, >10x modern values. These data suggest that enhanced Fe deposition to the nearby Southern Ocean at this time could have been large enough to rival the supply of Fe from upwelling.

http://www.tconway.co.uk/

Authors

Conway, T. M., University of South Florida, USA, conway.tm@gmail.com

Wolff, E. W., University of Cambridge, United Kingdom

Röthlisberger, R., Federal Office for the Environment, Switzerland

Mulvaney, R., British Antarctic Survey, United Kingdom

Elderfield, H., University of Cambridge, United Kingdom

Details

Oral presentation

Session #:025
Date: 02/27/2017
Time: 12:45
Location: 323 A

Presentation is given by student: No