From the POC/234Th ratios on the large filtered particles, it appears that the POC export fluxes were very low and in agreement with the POC fluxes measured in the sediment traps. Small and large particles analysis indicated that the POC/234Th ratios decrease when the particle size increase. From these 234Th fluxes, the POC export fluxes can be derived if the POC/234Th ratio in the vertical flux is known. From the 234Th/238U disequilibrium, we applied a steady state 234Th model to estimate the 234Th export fluxes. The water column deficiencies of 234Th were used to estimate the Particulate Organic Carbon (POC) fluxes. Samples were collected in January-February 1999 in a frontal zone from 42 to 47^oS and from 60 to 66^oS during the ANTARES 4 cruise. In the Indian sector of the Southern Ocean, three thorium isotopes (234Th, 232Th and 230Th) were studied in order to constrain the marine particle dynamics. Moreover, major differences occurred in the taxa at the+Fe and HNLC sites revealing the crucial role that surface oceanic conditions play in changing and structuring deep-sea benthic communities. The species composition was also very different, with the+Fe site showing similarities to eutrophic sites in other ocean basins. The +Fe site also had greater densities and biomasses of large deep-sea animals with lower levels of evenness in community structuring. We found that the+Fe area had greater supplies of organic matter inputs to the seafloor, including polyunsaturated fatty acid and carotenoid nutrients. Our results suggest that long-term geo-engineering of surface oceanic waters via artificial OIF would lead to significant changes in deep-sea ecosystems. We compared two closely-located deep-sea sites (,400 km apart and both at,4200 m water depth) to the East (naturally iron fertilized +Fe) and South (HNLC) of the Crozet Islands in the southern Indian Ocean. Natural OIF, through the addition of iron leached from volcanic islands, has been shown to enhance primary productivity and carbon export and so can be used to study the effects of OIF on life in the ocean. Large-scale artificial ocean iron fertilization (OIF) has been proposed as a means of mitigating anthropogenic atmospheric CO2, but its impacts on ocean ecosystems below the photic zone are unknown. The addition of iron to high-nutrient low-chlorophyll (HNLC) oceanic waters stimulates phytoplankton, leading to greater primary production.
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