Seminar Details

Reconstructing dust input to the global ocean using thorium isotopes measurements in marine sediments (Special Seminar)




Prof. Stephanie Kienast - Dalhousie University, Canada


Dust input into the ocean-atmosphere system has significant ramifications for biogeochemical cycles and global climate, especially in marine ecosystems that are limited by iron and silicon availability such as parts of the Eastern Equatorial Pacific (EEP) and the Southern Ocean. However, direct observations of dust deposition in the ocean are very scarce. The long-lived isotope Thorium-232 is greatly enriched in upper continental crust compared to oceanic crust and mid-ocean ridge basalts. In open ocean areas, away from hemipelagic sources of continental material, 232Th is therefore assumed to be of aeolian origin. In conjunction with 230Th-flux normalization, 232Th measurements are thus a promising new proxy for dust accumulation in the present and past ocean. Here, we present a new and growing global database of 232Th fluxes ("ThoroMap") based on >300 surface sediment and downcore records. We compare these data with estimates of dust accumulation derived from coupled atmosphere, land, ocean, and sea-ice models (CAM4, CCSM3). Agreement between the Th-232 based dust fluxes and numerical models is good in lower latitudes, suggesting that thorium-232 offers a reliable paloedust proxy in this region that can be applied to both modern processes and paleo studies.

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