Dissolved Rare Earth Elements in the Southern Ocean: Chemical Tracers of Terrigeneous Inputs and Water Masses in the Wake of Kerguelen
Abstract
The Southern Ocean is regarded as a key region in understanding the role of biogeochemical cycling on the variation of global climate. Although this Ocean is characterized by HNLC conditions, a permanent blooming zone is observed around the Kerguelen plateau (Indian Sector of the Southern Ocean). The major goal of the KEOPS program is to study this natural iron fertilization, notably aims at studying the lithogenic inputs (riverine discharges, aeolian inputs) and the inputs from the sediments to the water mass in contact with the plateau. With this aim, Rare Earth Element (REE) patterns in seawater are used to study the interactions between the lithogenic and sedimentary material and the water masses enriched in iron (origin, transport, dissolved/particulate exchange). We will present 9 full depth profiles of dissolved REE in seawater from contrasted areas around the Kerguelen plateau. KEOPS REE concentrations in deep waters ([Nd] ~ 15 ~ 25 pmol/kg) are in good agreement with previous data from the South Atlantic sector of the Southern Ocean (German et al. 1995). Station KERFIX (50°40S 68°25E), upstream of the plateau in the Antarctic Circumpolar Current, was chosen as an open ocean signal. Most of the other surface waters have higher REE concentrations than the upstream station KERFIX (about 5~ 10 pmol/kg higher for Nd). The REE patterns of the surface water enrichment (REE (enrichment) = REE (measured) - REE (Kerfix)) display positive Eu anomaly (~ 1.2), similar to the basalt one (Eu anomaly ~ 1.6). This strongly suggests that the lithogenic material of the Kerguelen formation is the source of these enrichments. Using the REE as proxy, Fe input weathered from the islands around the plateau was estimated using a one- box model at about 41000 ton/yr. This estimation will be compared to the flux coming out from the sediment by diffusion during diagenetic processes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMOS32B..04Z
- Keywords:
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- 1050 Marine geochemistry (4835;
- 4845;
- 4850);
- 4825 Geochemistry;
- 4851 Oxidation/reduction reactions (0471);
- 4875 Trace elements (0489)