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      Methane release from the southern Brazilian margin during the last glacial

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          Abstract

          Seafloor methane release can significantly affect the global carbon cycle and climate. Appreciable quantities of methane are stored in continental margin sediments as shallow gas and hydrate deposits, and changes in pressure, temperature and/or bottom-currents can liberate significant amounts of this greenhouse gas. Understanding the spatial and temporal dynamics of marine methane deposits and their relationships to environmental change are critical for assessing past and future carbon cycle and climate change. Here we present foraminiferal stable carbon isotope and sediment mineralogy records suggesting for the first time that seafloor methane release occurred along the southern Brazilian margin during the last glacial period (40–20 cal ka BP). Our results show that shallow gas deposits on the southern Brazilian margin responded to glacial−interglacial paleoceanographic changes releasing methane due to the synergy of sea level lowstand, warmer bottom waters and vigorous bottom currents during the last glacial period. High sea level during the Holocene resulted in an upslope shift of the Brazil Current, cooling the bottom waters and reducing bottom current strength, reducing methane emissions from the southern Brazilian margin.

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          Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years.

          Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability. Its concentrations over the past 650,000 years have varied between approximately 350 and approximately 800 parts per 10(9) by volume (p.p.b.v.) during glacial and interglacial periods, respectively. In comparison, present-day methane levels of approximately 1,770 p.p.b.v. have been reported. Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world. Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is approximately 380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by approximately 100,000 yr glacial-interglacial cycles up to approximately 400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles. We suggest that changes in the strength of tropical methane sources and sinks (wetlands, atmospheric oxidation), possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone, controlled the atmospheric methane budget, with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending periglacial wetlands. Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles.
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            Glacial water mass geometry and the distribution of δ13C of ΣCO2in the western Atlantic Ocean

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              On the water masses and mean circulation of the South Atlantic Ocean

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                Author and article information

                Contributors
                rcpramos@marum.de
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                13 April 2018
                13 April 2018
                2018
                : 8
                : 5948
                Affiliations
                [1 ]ISNI 0000 0001 2297 4381, GRID grid.7704.4, MARUM - Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, ; 28359 Bremen, Germany
                [2 ]ISNI 0000 0001 2184 6919, GRID grid.411173.1, Programa de Pós Graduação em Geoquímica, Universidade Federal Fluminense, Outeiro São João Batista S/N, ; 24020-141 Niterói RJ, Brazil
                [3 ]ISNI 0000 0004 1937 0722, GRID grid.11899.38, Institute of Geosciences, University of São Paulo, Rua do Lago 562, ; 05508-080 São Paulo SP, Brazil
                [4 ]ISNI 0000 0000 9639 8885, GRID grid.253553.7, Department of Geological Sciences, , California State University Bakersfield, 9001 Stockdale Highway, ; Bakersfield, CA USA
                [5 ]ISNI 0000 0001 2116 4512, GRID grid.419222.e, Center for Weather Forecasting and Climate Studies (CPTEC), National Institute for Space Research (INPE), ; Cachoeira Paulista, Brazil
                [6 ]ISNI 0000 0001 2155 4756, GRID grid.15606.34, BGR – Federal Institute for Geosciences and Natural Resources, Stilleweg 2, ; 30655 Hannover, Germany
                [7 ]Aix-Marseille University, CNRS, IRD, CEREGE UM34, 13545 Aix-en-Provence, France
                [8 ]ISNI 0000 0004 1937 0722, GRID grid.11899.38, School of Arts, Sciences and Humanities, University of São Paulo, Av. Arlindo Béttio 1000, ; 03828-000 São Paulo SP, Brazil
                Author information
                http://orcid.org/0000-0002-1182-1547
                http://orcid.org/0000-0002-7973-460X
                http://orcid.org/0000-0002-3842-1447
                http://orcid.org/0000-0002-9916-0340
                http://orcid.org/0000-0003-3318-8022
                Article
                24420
                10.1038/s41598-018-24420-0
                5899165
                29654329
                dbeed27d-93c0-4c1b-a941-e318b3848c55
                © The Author(s) 2018

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 18 August 2017
                : 26 March 2018
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