TY - JOUR
T1 - Significance of euxinic condition in the middle Eocene paleo-Arctic basin
T2 - A geochemical study on the IODP Arctic Coring Expedition 302 sediments
AU - Ogawa, Yusuke
AU - Takahashi, Kozo
AU - Yamanaka, Toshiro
AU - Onodera, Jonaotaro
N1 - Funding Information:
We thank the co-chief scientists Prof. Jan Backman and Prof. Kate Moran, who materialized the ACEX, and the ACEX scientists as well as the captains and crew of the IODP Expedition 302 who assisted us in various phases of this work. We are grateful to Prof. Hitoshi Chiba of Okayama University for assistance in the sulfur isotope analyses. This manuscript was greatly improved with constructive comments provided by two reviewers, for which we thank. This work has been benefited using the following funding: MEXT Grants-in-Aid-for Scientific Research B1 Project No. 13440152, B2 Project No. 15310001 and JSPS B Project No. 17310009.
PY - 2009/7/30
Y1 - 2009/7/30
N2 - Integrated Ocean Drilling Program (IODP) Expedition 302 Arctic Coring Expedition (ACEX) obtained the first relatively continuous long sediment cores from the Lomonosov Ridge in the central Arctic Ocean in 2004. Preceding microfossil studies indicated the dominance of low salinity surface waters in the early to middle Eocene Arctic basin. The main purpose of this study is to reconstruct paleoceanographic conditions including the extent of saline (seawater) mass presence. To attain this goal we performed geochemical analyses of total sulfur (%TS), total organic carbon (%TOC) and stable sulfur isotopic composition (δ34S) on the early to middle Eocene section of the ACEX cores. The %TS were high in all the examined intervals and the sedimentary sulfur occurred mainly as framboidal pyrite, indicating that sufficient sulfate, indicative of seawater, was present in the deep layer of the paleo-Arctic basin and that the pyrite was formed in the sediments under sufficient iron input. The high %TS values with low δ34S values also indicate the continuous existence and supply of seawater. The high accumulation of sulfide in Unit 1/6 was due to a significant increase of TOC supply which increased sulfate reduction rates by bacteria. The %TOC-%TS diagram shows excess sulfur content relative to the TOC, suggesting euxinic condition of the bottom water during the studied period. Such an oxygen depleted environment was brought about by salinity stratification and restricted water circulation. The patterns observed in the ACEX data can be comparable with the Mediterranean sapropels. The global δ34S of seawater sulfate abruptly increased from + 17 to + 22‰ in the early to middle Eocene. Previous studies suggested that enhanced pyrite burial caused the isotopic shift during this period. The large pyrite burial in the anoxic Arctic basin could have contributed to the remarkable isotopic event accounting for about 3‰ of the global increase during this period.
AB - Integrated Ocean Drilling Program (IODP) Expedition 302 Arctic Coring Expedition (ACEX) obtained the first relatively continuous long sediment cores from the Lomonosov Ridge in the central Arctic Ocean in 2004. Preceding microfossil studies indicated the dominance of low salinity surface waters in the early to middle Eocene Arctic basin. The main purpose of this study is to reconstruct paleoceanographic conditions including the extent of saline (seawater) mass presence. To attain this goal we performed geochemical analyses of total sulfur (%TS), total organic carbon (%TOC) and stable sulfur isotopic composition (δ34S) on the early to middle Eocene section of the ACEX cores. The %TS were high in all the examined intervals and the sedimentary sulfur occurred mainly as framboidal pyrite, indicating that sufficient sulfate, indicative of seawater, was present in the deep layer of the paleo-Arctic basin and that the pyrite was formed in the sediments under sufficient iron input. The high %TS values with low δ34S values also indicate the continuous existence and supply of seawater. The high accumulation of sulfide in Unit 1/6 was due to a significant increase of TOC supply which increased sulfate reduction rates by bacteria. The %TOC-%TS diagram shows excess sulfur content relative to the TOC, suggesting euxinic condition of the bottom water during the studied period. Such an oxygen depleted environment was brought about by salinity stratification and restricted water circulation. The patterns observed in the ACEX data can be comparable with the Mediterranean sapropels. The global δ34S of seawater sulfate abruptly increased from + 17 to + 22‰ in the early to middle Eocene. Previous studies suggested that enhanced pyrite burial caused the isotopic shift during this period. The large pyrite burial in the anoxic Arctic basin could have contributed to the remarkable isotopic event accounting for about 3‰ of the global increase during this period.
KW - Arctic basin
KW - Integrated Ocean Drilling Program Expedition 302
KW - TOC
KW - TS
KW - euxinic bottom water
KW - pyrite
KW - salinity stratification
KW - sulfur isotope
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U2 - 10.1016/j.epsl.2009.06.011
DO - 10.1016/j.epsl.2009.06.011
M3 - Article
AN - SCOPUS:67650594615
SN - 0012-821X
VL - 285
SP - 190
EP - 197
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
IS - 1-2
ER -