HR: 17:15h
AN: OS22D-06    [PDF]
TI: Physico Chemical Control of the Oceanic Iron Cycle in the Crozet Basin (Indian Sector of the Southern Ocean)
AU: * Bucciarelli, E
EM: Eva.Bucciarelli@univ-brest.fr
AF: LEMAR, UMR CNRS 6539, IUEM, Place Nicolas Copernic, Plouzane, 29280 France
AU: Sedwick, P
EM: psedwick@bbsr.edu
AF: Bermuda Biological Station for Research, 17 Biological Lane, Ferry Reach, St George's, GE01 Bermuda
AU: Blain, S
EM: Stephane.Blain@univ-brest.fr
AF: LEMAR, UMR CNRS 6539, IUEM, Place Nicolas Copernic, Plouzane, 29280 France
AU: Treguer, P
EM: Paul.Treguer@univ-brest.fr
AF: LEMAR, UMR CNRS 6539, IUEM, Place Nicolas Copernic, Plouzane, 29280 France
AB: The Subantarctic Southern Ocean between the Polar and Subtropical water masses is among the largest oceanic sinks for atmospheric CO$_{2}$, partly because of biological uptake by phytoplankton. As iron was demonstrated by numerous studies to exert a prevailing role on the oceanic primary production, the study of its biogeochemical cycle is of the greatest importance. As part of the Antares 4 JGOFS cruise, ultra clean samplings were performed in the water column of the Southern Ocean (open ocean: Crozet Basin) in order to better understand the oceanic biogeochemistry of iron. Three watermasses were sampled (subantarctic, subtropical, and at the confluence between subantarctic and subtropical watermasses), at depth varying from 0 m to 300 m. We measured two fractions of Fe: dissolved iron (acidified 0.4 $\mu$m filtered samples) and total dissolvable iron (acidified unfiltered samples). The vertical distributions of dissolved iron in the water column were characteristics of open ocean profiles, with an enrichment in the sub-surface, a depletion in the photic zone, and an increase with depth. These profiles are generally assimilated to nutrient-type profiles, although the dissolved iron concentrations in the photic zone vary with depth. We also applied a crustal ratio of 0.33 to concentrations of particulate aluminium (Cattaldo and Cardinal, pers. com.) to estimate the concentrations of refractory particulate iron. We established a linear relationship between the three fractions of iron, whatever the watermass and depth sampled. This indicated a distribution controlled by physical and chemical processes (e.g. scavenging) and excluded a control by biological uptake. This hypothesis could explain why vertical distributions of dissolved iron are not homogeneous in the photic zone, but decrease when particles, both lithogenic and biogenic, scavenge this micro nutrient.
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL
DE: 4805 Biogeochemical cycles (1615)
DE: 4875 Trace elements
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting