[en] The Southern Ocean is the largest of several high-nutrient, low-chlorophyll (HNLC) regions in the world's oceans. This region plays a major role in regulating the global net transfer of carbon dioxide between the ocean and the atmosphere, in part because the annual photosynthetic uptake of CO₂ by phytoplankton and resulting export of particulate organic carbon (POC) to the deep ocean. The element thorium has multiple radioisotopes that have emerged collectively as a powerful set of tracers for particle associated processes in the oceans. Of all the Th isotopes, ²³⁴Th (half-life 24.1 d) has been the focus of increasing attention and application in the past years. The production of ²³⁴Th from ²³⁸U, coupled with the conservative behavior of ²³⁸U in seawater, makes the source of ²³⁴Th easy to characterize. Moreover, the half-life of ²³⁴Th is sufficiently short to make it sensitive to the short-term (e.g. seasonal) changes that occur in the upper water column of the open ocean or in sediments or water column in coastal areas. 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. Natural Ra isotopes have been also widely used in marine studies to trace water masses and to quantify mixing processes. This work presents results of a collaborative research on organic carbon fluxes distribution in the Bransfield Strait in order to evaluate its influence in the CO₂ drawdown. Macro-nutrients, micro-nutrients and chlorophyll-a distributions were used to examine the pathway sources. Natural radium isotopes were applied as tracers to study the movement of shelf water, while ²³⁴Th was used as a tracer of particle flux in the upper ocean, since POC export via sinking particles is the primary mechanism of carbon sequestration in the Southern Ocean. Sea water samples for total ²³⁴Th and natural Ra isotopes were collected from 9 to 14 December 2007 on the RV Ary Rongel (Brazilian Navy). Analyses of total ²³⁴Th activities were performed by gross beta counting using a gas-flow low background proportional counter. The long lived Ra isotopes were determined by low-background high efficiency gamma spectrometry. (author)