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Iceberg scours along the southern U.S. Atlantic margin

¹ Coastal Carolina University, Burroughs and Chapin Center for Marine and Wetland Studies, Conway, South Carolina 29526, USA
² Scripps Institution of Oceanography, University of California–San Diego, La Jolla, California 92093, USA
³ Gray's Reef National Marine Sanctuary, National Oceanic and Atmospheric Administration, Savannah, Georgia 31411, USA

Correspondence: *E-mail: jchill{at}coastal.edu.

Rapid climate fluctuations associated with ice-sheet oscillations have resulted in pulses of iceberg discharge that are recorded by iceberg scour marks along continental shelves and ice-rafted debris deposits across the North Atlantic. Iceberg transport is largely controlled by ocean surface currents; therefore, iceberg trajectories can serve as a proxy for paleo-circulation studies. Records of iceberg transport from ice-rafted debris (i.e., Heinrich layers) in the North Atlantic suggest that most icebergs released during Quaternary glaciations were entrained in a cyclonic subpolar gyre restricted to polar and mid-latitudes; however, new data suggest that there may have been an additional southerly component of transport along the western Atlantic margin. Here, we present evidence of extensive iceberg scouring across the upper slope offshore of South Carolina, ~1000 km south of the proximal ice margin during Quaternary glacial maximums. The location and orientation of the keel marks suggest that icebergs were entrained in a southwestward-flowing coastal current. At present, warm waters of the rapid, northeastward-flowing Gulf Stream bathe the upper slope off the southeastern United States. An offshore shift in the Gulf Stream axis during sea-level lowstand may have allowed glacially fed coastal currents to penetrate farther south. This may be the first evidence of iceberg rafting to subtropical latitudes in the North Atlantic.

Key Words: iceberg scour • paleocirculation • multibeam bathymetry • Florida-Hatteras slope