FN Archimer Export Format PT J TI Rare earth elements and neodymium isotopes in sedimentary organic matter BT AF FRESLON, Nicolas BAYON, Germain TOUCANNE, Samuel BERMELL, Sylvain BOLLINGER, Claire CHERON, Sandrine ETOUBLEAU, Joel GERMAIN, Yoan KHRIPOUNOFF, Alexis PONZEVERA, Emmanuel ROUGET, Marie Laure AS 1:1,2;2:1;3:1;4:1;5:2,3;6:1;7:1;8:1;9:4;10:1;11:2,3; FF 1:PDG-REM-GM-LGM;2:PDG-REM-GM-LGM;3:PDG-REM-GM-LES;4:PDG-REM-GM-CTDI;5:;6:PDG-REM-GM-LGM;7:PDG-REM-GM-LGM;8:PDG-REM-GM-LGM;9:PDG-REM-EEP-LEP;10:PDG-REM-GM-LGM;11:; C1 IFREMER, Unite Rech Geosci, F-29280 Plouzane, France. UEB, F-35000 Rennes, France. Univ Bretagne Occidentale, IUEM, CNRS, UMS 3113, F-29280 Plouzane, France. IFREMER, Unite Rech Environm Profonds, F-29280 Plouzane, France. C2 IFREMER, FRANCE UNIV RENNES, FRANCE UBO, FRANCE IFREMER, FRANCE SI BREST SE PDG-REM-GM-LGM PDG-REM-GM-LES PDG-REM-GM-CTDI PDG-REM-EEP-LEP AUTRE IN WOS Ifremer jusqu'en 2018 copubli-france copubli-univ-france IF 4.331 TC 109 UR https://archimer.ifremer.fr/doc/00191/30250/28682.pdf LA English DT Article CR WACS BO Pourquoi pas ? AB We report rare earth element (REE) and neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n=25), estuaries (n=18), open-ocean settings (n=15), and cold seeps (n=12). Sedimentary Organic Matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2 – 0.02M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H202 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases. The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with ΣREE = 109 ± 86 ppm (mean ± s; n=58). The organic fractions leached from cold seep sediments display even higher concentration levels (285 ± 150 ppm; mean ± s; n=12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea- water). The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display εNd values that typically range between the εNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit εNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition. Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation. PY 2014 PD SEP SO Geochimica Et Cosmochimica Acta SN 0016-7037 PU Pergamon-elsevier Science Ltd VL 140 UT 000341925300012 BP 177 EP 198 DI 10.1016/j.gca.2014.05.016 ID 30250 ER EF