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Special Session 4: Biogeochemical cycling of trace elements in the ocean: GEOTRACES and beyond |
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First cold seep observation in the Brazilian margin with the human-occupied vehicle Shinkai 6500: Multiple geochemical investigation of the porewater and marine sediment
Monday 9th @ 1135-1155
Room 4
Jiang Kai* , Graduate School of Science and Engineering for Education, University of Toyama
Zhang Jing, Graduate School of Science and Engineering for Research, University of Toyama
Presenter Email: d1478301@ems.u-toyama.ac.jp
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| Brazilian margin has large proven oil and gas reserves, and giant oil seepage has been also found in this area. However, the research on the existence of cold seeps is still uncompleted because of few investigations conducted before. On the May of 2013, the first investigation named Iatá-piúna¡¡cruise was conducted on the Brazilian margin. It aimed to detect the cold seeps and understand the seep ecosystems. Because cold seeps contains a lot of chemical materials,and these materials bring the unique information of cold seeps. With the interaction between cold seeps and marine sediment, the information of cold seeps will be also recorded in the sediment. This research is trying to use multiple geochemical tracers in the porewater and marine sediments to detect the cold seeps in the Brazilian margin. Sediment samples were collected by human-occupied vehicle Shinkai 6500. And porewater was squeezed from sediments. The major chemical components in porewater were measured. And traditional Tessier method was used to extract rare earth elements and trace metals from sediments. Samples were analyzed by ICP-MS (HP 4500, RSD<3%). The results showed that among the three sampling sites(1343, 1345H1, 1346H2), the concentration of silicate in the pore water increases with the depth distinctly at site 1345H1, where oil seepage was found. There is high possibility that it is influenced by cold seeps since the solubility of silicate can be controlled by temperature. Manganese in sediment also shows the same distribution profile with silicate at site 1345H1. It indicates there is another material sources from the under of seafloor. The relative standard deviation (RSD) of rare earth elements concentration ration in each sites is 1343 4.9%~8.7%, 1345H1 6.9%~10.4%, 1346H2 1.6%~4.3%, respectively. Site 1345H1 has the highest RSD. And it also has distinctly different rare earth elements pattern with other two sites. Those suggest that cold seeps may exist at the site of 1345H1.Further research should be conducted on the geochemistry of rare earth elements and trace metals in the cold seeps. |
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