A First synthesis of the GEOTRACES issues from the IPY BONUS GOODHOPE cruise in the Southern Ocean

Trace metals play a key role in marine ecosystems. Several oceanic processes can be inferred by trace elements and isotopes such as production and export to deep waters, water-masses ventilation and pathways, sedimentary and atmospheric sources. The multi-tracers approach is a key issue of the international GEOTRACES program which had its flying start in IPY 2007-2008. The Bonus-Goodhope expedition took place in the Atlantic sector of the Southern Ocean during late summer 2008 onboard Marion Dufresne. The section departed from Capetown and reached 57°S in the northern part of the Weddel Gyre along the zero meridian. Fe concentrations in the subtropical region reflect atmospheric inputs from South Africa advected by Indian Ocean waters or from Patagonia,and/or South-African margin inputs through eddy transportation. Deep-sea plumes of high Fe over the ocean ridge crests and in AABW are likely due to sedimentary resuspension. Fe isotopes will bring further constrains on the Fe cycle. Suspended particle compositions confirm the transport of margin material towards the ACC core. Dissolved Al, Mn, Cd, Co, Zn in combination with their speciation, the ocean and atmospheric biogeochemistry and dynamics in the section will further highlight the internal cycle of these elements. Inferences from the O 2 /Ar and oxygen isotope measurements, and 15 N uptake rates indicate high regenerated production in the oligotrophic subtropical domain, and beyond as well as at the SACCF. New production accounts for up to 40-60% of the production in the subantarctic region toward the southern side of the Polar Front, the later consisting of a late summer diatom post-bloom. Export fluxes and remineralization processes assessed by 234 Th/ 238 U and 210 Po/ 210 Pb disequilibria and particulate biogenic Bainventories, suggest relatively higher export carbon fluxes from the mixed layer in the PFZ, the PF, the SACCF and in the Antarctic Zone, and remineralization rates that are more significant in the mesopelagic zone in the PFZ. The lowest export flux of the section is observed in the Weddel Gyre, and the lowest remineralization rates in the SAZ and STZ. The CFC’s, Si* signatures and macro-nutrients were powerful tracers for tracking water-masses and the mesoscale structures that crossed the section. Finally Bonus-Goodhope and Zero&Drake aboard Polarstern achieved intercalibration stations for TEI’s providing crucial statements to accurately interpret the whole transect of several TEI’s from Capetown to the Antarctic Peninsula along the zero meridian during IPY.