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      Oman coral δ 18O seawater record suggests that Western Indian Ocean upwelling uncouples from the Indian Ocean Dipole during the global-warming hiatus

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          Abstract

          The Indian Ocean Dipole (IOD) is an interannual mode of climate variability in the Indian Ocean that has intensified with 20 th century global-warming. However, instrumental data shows a global-warming hiatus between the late-1990s and 2015. It is presently not clear how the global-warming hiatus affects modes of climate variability such as the IOD, and their basin-wide ocean-atmosphere teleconnections. Here, we present a 26-year long, biweekly record of Sr/Ca and δ 18O from a Porites coral drilled in the Gulf of Oman. Sea surface temperature (SST anom) is calculated from Sr/Ca ratios, and seawater δ 18O (δ 18O sw-anom) is estimated by subtracting the temperature component from coral δ 18O. Our δ 18O sw-anom record reveals a significant regime shift in 1999, towards lower mean δ 18O sw values, reflecting intensified upwelling in the western Indian Ocean. Prior to the 1999 regime shift, our SST anom and δ 18O sw-anom show a clear IOD signature, with higher values in the summer of positive-IOD years due to weakened upwelling. The IOD signature in SST anom and δ 18O sw-anom disappears with the overall intensification of upwelling after the 1999 regime shift. The inferred increase in upwelling is likely driven by an intensified Walker circulation during the global-warming hiatus. Upwelling in the Western Indian Ocean uncouples from the IOD.

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          Inter-decadal modulation of the impact of ENSO on Australia

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            Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing.

            Since the mid-nineteenth century the Earth's surface has warmed, and models indicate that human activities have caused part of the warming by altering the radiative balance of the atmosphere. Simple theories suggest that global warming will reduce the strength of the mean tropical atmospheric circulation. An important aspect of this tropical circulation is a large-scale zonal (east-west) overturning of air across the equatorial Pacific Ocean--driven by convection to the west and subsidence to the east--known as the Walker circulation. Here we explore changes in tropical Pacific circulation since the mid-nineteenth century using observations and a suite of global climate model experiments. Observed Indo-Pacific sea level pressure reveals a weakening of the Walker circulation. The size of this trend is consistent with theoretical predictions, is accurately reproduced by climate model simulations and, within the climate models, is largely due to anthropogenic forcing. The climate model indicates that the weakened surface winds have altered the thermal structure and circulation of the tropical Pacific Ocean. These results support model projections of further weakening of tropical atmospheric circulation during the twenty-first century.
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              The monsoon circulation of the Indian Ocean

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                Author and article information

                Contributors
                nabe@sci.hokudai.ac.jp
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                13 February 2019
                13 February 2019
                2019
                : 9
                Affiliations
                [1 ]ISNI 0000 0001 2173 7691, GRID grid.39158.36, Department of Natural History Sciences, , Faculty of Science, Hokkaido University, ; Sapporo, 060-0810 Japan
                [2 ]KIKAI Institute for Coral Reef Sciences, Kikai town, 891-6151 Japan
                [3 ]ISNI 0000 0001 2242 4849, GRID grid.177174.3, Department of Earth and Planetary Sciences, Faculty of Science, , Kyusyu University, ; Fukuoka, 819-0395 Japan
                [4 ]ISNI 0000 0001 2153 9986, GRID grid.9764.c, Institut für Geowissenschaften, , Christian-Albrechts Universität zu Kiel, ; 24118 Kiel, Germany
                [5 ]ISNI 0000 0001 0726 9430, GRID grid.412846.d, Department of Marine Science and Fisheries, College of Agricultural and Marine Sciences, , Sultan Qaboos University, ; Box 34 Al-Khod 123, Sultanate of Oman
                Article
                38429
                10.1038/s41598-018-38429-y
                6374511
                30760830
                91b8e513-23d7-4ea4-b6de-9f5a947298df
                © The Author(s) 2019

                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/.

                Funding
                Funded by: FundRef https://doi.org/10.13039/501100001691, MEXT | Japan Society for the Promotion of Science (JSPS);
                Award ID: JP25257207
                Award ID: 17H04708
                Award Recipient :
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