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      3D seismic evidence of buried iceberg ploughmarks from the mid-Norwegian continental margin reveals largely persistent North Atlantic Current through the Quaternary

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          Abstract

          Over 7500 buried linear and curvilinear depressions interpreted as iceberg ploughmarks were identified within the Quaternary Naust Formation from an extensive three-dimensional seismic dataset that covers ~ 40,000 km 2 of the mid-Norwegian continental margin. The morphology and net orientation of ploughmarks were mapped and analysed. These features are up to 28 km long, 700 m wide and are incised up to 31 m deep. On average, ploughmarks are incised 5 m deep, with median width of 185 m and median lengths ranging from 1.2 to 2.7 km for individual palaeo-surfaces. Width to depth ratio ranges from 8:1 to 400:1 and is on average 36:1. The presence of ploughmarks buried deeply within some palaeo-slope surfaces implies the occasional presence of very large icebergs since the middle Quaternary, suggesting that thick ice-sheet margins with fast-flowing ice streams were present in order to calve icebergs of such dimensions into the Norwegian Sea. The wide geographical distribution of ploughmarks suggests unrestricted iceberg drift and an open Norwegian Sea during the periods of iceberg calving since the early Quaternary. Ploughmark trajectory analysis demonstrates that the ocean current circulation, now dominated by the northeasterly flowing Norwegian Atlantic Current (NwAC), has largely persisted throughout the Quaternary. Despite the overall strikingly consistent pattern of iceberg drift, ploughmark mapping also shows evidence for short-lived NwAC reductions possibly related to major phases of iceberg discharge and/or meltwater pulses from the Fennoscandian Ice Sheet during the middle and late Quaternary.

          Highlights

          • Over 7500 buried iceberg ploughmarks were identified within the Quaternary Naust Formation

          • Statistical analysis provides detailed morphometric information on buried ploughmarks on the mid-Norwegian margin

          • The wide geographical distribution of ploughmarks suggests unrestricted iceberg drift and an open Norwegian Sea since the early Quaternary

          • Ploughmark trajectory analysis demonstrates that the Norwegian Atlantic Current (NwAC) has largely persisted throughout the Quaternary

          • There is evidence for short-lived NwAC reductions possibly related to major phases of iceberg discharge and/or meltwater pulses

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          A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

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            Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes.

            The Atlantic meridional overturning circulation is widely believed to affect climate. Changes in ocean circulation have been inferred from records of the deep water chemical composition derived from sedimentary nutrient proxies, but their impact on climate is difficult to assess because such reconstructions provide insufficient constraints on the rate of overturning. Here we report measurements of 231Pa/230Th, a kinematic proxy for the meridional overturning circulation, in a sediment core from the subtropical North Atlantic Ocean. We find that the meridional overturning was nearly, or completely, eliminated during the coldest deglacial interval in the North Atlantic region, beginning with the catastrophic iceberg discharge Heinrich event H1, 17,500 yr ago, and declined sharply but briefly into the Younger Dryas cold event, about 12,700 yr ago. Following these cold events, the 231Pa/230Th record indicates that rapid accelerations of the meridional overturning circulation were concurrent with the two strongest regional warming events during deglaciation. These results confirm the significance of variations in the rate of the Atlantic meridional overturning circulation for abrupt climate changes.
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              Origin and consequences of cyclic ice rafting in the Northeast Atlantic Ocean during the past 130,000 years

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                Author and article information

                Contributors
                Journal
                Mar Geol
                Mar. Geol
                Marine Geology
                Elsevier Scientific Pub. Co
                0025-3227
                01 May 2018
                01 May 2018
                : 399
                : 66-83
                Affiliations
                [a ]Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER, UK
                [b ]Geological Survey of Norway, Trondheim N-7491, Norway
                [c ]Department of Petroleum Engineering and Applied Geophysics, Norwegian University of Science and Technology, Trondheim N-7031, Norway
                Author notes
                [* ]Corresponding author. aim39@ 123456cam.ac.uk
                Article
                S0025-3227(17)30405-X
                10.1016/j.margeo.2017.11.016
                5890382
                6db7d1ed-91f0-425a-b5b5-25c7b86d7fcb
                © 2017 The Authors

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                History
                : 21 August 2017
                : 13 November 2017
                : 25 November 2017
                Categories
                Article

                icebergs,ploughmarks,ice stream,norwegian sea,north atlantic current,fennoscandian ice sheet,seismic stratigraphy,marine geology,palaeo-glaciology,glacial geomorphology

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