FN Archimer Export Format PT J TI Evidence for intense REE scavenging at cold seeps from the Niger Delta margin BT AF BAYON, Germain BIROT, Dominique RUFFINE, Livio CAPRAIS, Jean-Claude PONZEVERA, Emmanuel BOLLINGER, C. DONVAL, Jean-Pierre CHARLOU, Jean-Luc VOISSET, Michel GRIMAUD, S. AS 1:1;2:1;3:1;4:2;5:1;6:3,4;7:1;8:1;9:1;10:5; FF 1:PDG-REM-GM-LGM;2:PDG-REM-GM-LGM;3:PDG-REM-GM-LGM;4:PDG-REM-EEP-LEP;5:PDG-REM-GM-LGM;6:;7:PDG-REM-GM-LGM;8:PDG-REM-GM-LGM;9:PDG-REM-GM-CTD;10:; C1 IFREMER, Dept Geosci Marines, F-29280 Plouzane, France. IFREMER, Dept Etud Ecosyst Profonds, F-29280 Plouzane, France. Univ Europeenne Bretagne, F-35000 Rennes, France. Univ Brest, IUEM, CNRS, UMS 3113, F-29280 Plouzane, France. TOTAL, CSTJF Av Larribau, F-64019 Pau, France. C2 IFREMER, FRANCE IFREMER, FRANCE UEB, FRANCE UBO, FRANCE TOTAL, FRANCE SI BREST SE PDG-REM-GM-LGM PDG-REM-EEP-LEP PDG-REM-GM-CTD IN WOS Ifremer jusqu'en 2018 copubli-france copubli-univ-france IF 4.18 TC 89 UR https://archimer.ifremer.fr/doc/00066/17754/15571.pdf LA English DT Article DE ;rare earth elements;neodymium isotopes;seawater;cold seeps;Fe-Mn oxyhydroxides;benthic fluxes AB For many trace elements, continental margins are the location of intense exchange processes between sediment and seawater, which control their distribution in the water column, but have yet to be fully understood. In this study, we have investigated the impact of fluid seepage at cold seeps on the marine cycle of neodymium. We determined dissolved and total dissolvable (TD) concentrations for REE and well-established tracers of fluid seepage (CH4, TDFe, TDMn), and Nd isotopic compositions in seawater samples collected above cold seeps and a reference site (i.e. away from any fluid venting area) from the Niger Delta margin. We also analyzed cold seep authigenic phases and various core-top sediment fractions (pore water, detrital component, easily leachable phases, uncleaned foraminifera) recovered near the hydrocast stations. Methane, TDFe and TDMn concentrations clearly indicate active fluid venting at the studied seeps, with plumes rising up to about 100 m above the seafloor. Depth profiles show pronounced REE enrichments in the non-filtered samples (TD concentrations) within plumes, whereas filtered samples (dissolved concentrations) exhibit slight REE depletion in plumes relative to the overlying water column and display typical seawater REE patterns. These results suggest that the net flux of REE emitted into seawater at cold seeps is controlled by the presence of particulate phases, most probably Fe-Mn oxyhydroxides associated to resuspended sediments. At the reference site, however, our data reveal significant enrichment for dissolved REE in bottom waters, that clearly relates to diffusive benthic fluxes from surface sediments. Neodymium isotopic ratios measured in the water column range from epsilon(Nd) similar to-15.7 to -10.4. Evidence that the epsilon(Nd) values for Antarctic Intermediate waters (AAIW) differed from those reported for the same water mass at open ocean settings shows that sediment/water interactions take place in the Gulf of Guinea. At each site, however, the bottom water epsilon(Nd) signature generally differs from that for cold seep minerals, easily leachable sediment phases, and detrital fractions from local sediments, ruling out the possibility that seepage of methane-rich fluids and sediment dissolution act as a substantial source of dissolved Nd to seawater in the Gulf of Guinea. Taken together, our data hence suggest that co-precipitation of Fe-Mn oxyhydroxide phases in sub-surface sediments leads to quantitative scavenging of dissolved REE at cold seeps, preventing their emission into bottom waters. Most probably, it is likely that diffusion from suboxic surface sediments dominates the exchange processes affecting the marine Nd cycle at the Niger Delta margin. (C) 2011 Elsevier B.V. All rights reserved. PY 2011 PD DEC SO Earth And Planetary Science Letters SN 0012-821X PU Elsevier Science Bv VL 312 IS 3-4 UT 000299399900019 BP 443 EP 452 DI 10.1016/j.epsl.2011.10.008 ID 17754 ER EF