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Presence of oxygen and aerobic communities from sea floor to basement in deep-sea sediments
D’Hondt, Steven,Inagaki, Fumio,Zarikian, Carlos Alvarez,Abrams, Lewis J.,Dubois, Nathalie,Engelhardt, Tim,Evans, Helen,Ferdelman, Timothy,Gribsholt, Britta,Harris, Robert N.,Hoppie, Bryce ,W.,Hyun Nature Publishing Group 2015 Nature geoscience Vol.8 No.4
The depth of oxygen penetration into marine sediments differs considerably from one region to another. In areas with high rates of microbial respiration, O<SUB>2</SUB> penetrates only millimetres to centimetres into the sediments, but active anaerobic microbial communities are present in sediments hundreds of metres or more below the sea floor. In areas with low sedimentary respiration, O<SUB>2</SUB> penetrates much deeper but the depth to which microbial communities persist was previously unknown. The sediments underlying the South Pacific Gyre exhibit extremely low areal rates of respiration. Here we show that, in this region, microbial cells and aerobic respiration persist through the entire sediment sequence to depths of at least 75 metres below sea floor. Based on the Redfield stoichiometry of dissolved O<SUB>2</SUB> and nitrate, we suggest that net aerobic respiration in these sediments is coupled to oxidation of marine organic matter. We identify a relationship of O<SUB>2</SUB> penetration depth to sedimentation rate and sediment thickness. Extrapolating this relationship, we suggest that oxygen and aerobic communities may occur throughout the entire sediment sequence in 15–44% of the Pacific and 9–37% of the global sea floor. Subduction of the sediment and basalt from these regions is a source of oxidized material to the mantle.
Asahi, H.,Kender, S.,Ikehara, M.,Sakamoto, T.,Takahashi, K.,Ravelo, A.C.,Alvarez Zarikian, C.A.,Khim, B.K.,Leng, M.J. Pergamon Press 2016 Deep-sea research. Part II, Topical studies in oce Vol.125 No.-
A continuous composite oxygen isotope (δ<SUP>18</SUP>O) stratigraphy from benthic foraminifera in the Bering Sea was reconstructed in order to provide insight into understanding sea-ice evolution in response to Northern Hemisphere Glaciation. Oxygen isotope records from multiple species of benthic foraminifera at Integrated Ocean Drilling Program (IODP) Expedition 323 Site U1343 (54<SUP>o</SUP>33.4'N, 176<SUP>o</SUP>49.0'E, water depth 1950m) yield a highly refined orbital-scale age model spanning the last 1.2Ma, and a refined age model between 1.2 and 2.4Ma. An inter-species calibration was used to define species offsets and to successfully obtain a continuous composite benthic δ<SUP>18</SUP>O record, correlated with the global composite benthic δ<SUP>18</SUP>O stack curve LR04 to construct an orbital-scale age model. The consistency of the benthic δ<SUP>18</SUP>O stratigraphy with biostratigraphy and magnetostratigraphy confirms the reliability of both methods for constraining age. The time difference between cyclic changes in sedimentary physical properties and glacial-interglacial cycles since 0.8Ma is notable, and suggests that physical properties alone cannot be used to construct an orbital-scale age model. Amplitude changes in physical properties and a significant drop in the linear sedimentation rate during glacials after 0.9Ma indicate that the glacial sea-ice edge extended beyond the Bering Sea Slope (Site U1343) at this time.
Rapid transition from continental breakup to igneous oceanic crust in the South China Sea
Larsen, H. C.,Mohn, G.,Nirrengarten, M.,Sun, Z.,Stock, J.,Jian, Z.,Klaus, A.,Alvarez-Zarikian, C. A.,Boaga, J.,Bowden, S. A.,Briais, A.,Chen, Y.,Cukur, D.,Dadd, K.,Ding, W.,Dorais, M.,Ferré,, E. Nature Publishing Group 2018 Nature geoscience Vol.11 No.10