234Th as tracer of organic carbon export in Bransfield Strait, Antarctic

The element thorium has multiple isotopes that have emerged collectively as a powerful set of tracers for particle associated processes in the oceans. The production of 234Th from 238U, coupled with the conservative behavior of 238U in seawater, makes the source of 234Th easy to characterize. Because of its very particle reactive behavior, 234Th is removed from a parcel of water in only two ways, through decay and through particle flux. Therefore, a steady-state 1D activity balance can be used to calculate its flux. This work presents results of a collaborative research on organic carbon fluxes distribution in the Bransfield Strait. Macro-nutrients, micro nutrients and chlorophyll-a distributions were used to examine the pathway sources. 234Th was used as a tracer of organic carbon fluxes distribution in the Bransfield Strait in order to evaluate its influence in the CO2 drawdown, since POC export via sinking particles is the primary mechanism of carbon sequestration in the Southern Ocean. Fluxes up to 15274 dmp m-2 d-1 were estimated, the highest value observed in Station 09 at 794 m depth. POC exported fluxes derived from the disequilibrium 234Th/ 238U model varied from 0.6 to 16000 mmol C m-2 d-1. (author)