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Subtropical iceberg scours and meltwater routing in the deglacial western North Atlantic

Abstract

Abrupt centennial-to-millennial shifts in Northern Hemisphere climate during the last deglaciation are thought to have been triggered by the discharge of large volumes of meltwater and icebergs to the subpolar North Atlantic1. Here we show that meltwater and icebergs were also transported directly from the Laurentide ice margin to the subtropical North Atlantic in a narrow coastal current. We present high-resolution bathymetric data from south of Cape Hatteras showing numerous scours that we interpret as relict iceberg keel marks. This indicates that icebergs up to 300 m thick drifted to southern Florida (24.5° N). In simulations with an ocean circulation model, during deglaciation, fresh water and icebergs routinely reached as far south as 32.5° N, in a period of less than four months. The southernmost scours formed only during periods of high meltwater discharge from the Northern Hemisphere ice sheets. In the simulations, such extreme periods of meltwater release led to a reversal of the typically northward surface flow in the nearshore subtropical western North Atlantic. We therefore suggest that significant volumes of iceberg-laden meltwater routinely bypassed subpolar regions and spread across the subtropical North Atlantic.

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Figure 1: Southern US Atlantic margin iceberg scour locations.
Figure 2: Iceberg scours along the Florida margin.
Figure 3: Advection pathway of meltwater released from Hudson Bay.

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Acknowledgements

Multibeam bathymetry data were obtained from the NOAA NGDC Multibeam Bathymetry data repository, as well as from D. Naar. S. Okano assisted with multibeam bathymetry data reprocessing. We thank L. Keigwin and T. Cronin for helpful comments and discussions on an earlier version of the manuscript and D. Menemenlis for assistance with the numerical model. This research was supported by the Office of Science (BER) US Department of Energy grant DE-FOA-0000452 and by National Science Foundation grant ARC-1204112. The numerical simulations used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under Contract No. DE-AC02-05CH11231.

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J.C.H. was responsible for the seafloor data interpretation; A.C. performed the modelling studies. Both authors contributed to the discussion of results and preparation of the manuscript.

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Correspondence to Jenna C. Hill.

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The authors declare no competing financial interests.

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Hill, J., Condron, A. Subtropical iceberg scours and meltwater routing in the deglacial western North Atlantic. Nature Geosci 7, 806–810 (2014). https://doi.org/10.1038/ngeo2267

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