Jenna C. Hill

Iceberg scours along the southern U.S. Atlantic margin

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.

Coastal Geophysical Data Collected in 2016 nearshore Cape Canaveral, Florida

Geophysical data including multibeam bathymetry and backscatter, side scan sonar, and chirp subbottom were collected by Coastal Carolina University Center for Marine and Wetland Studies, Conway, South Carolina, in June 2016 in collaboration with the USGS St. Petersburg Coastal and Marine Science Center in the nearshore environment of Cape Canaveral, Florida. The goal of the effort was to broadly characterize the geology of the shelf to identify spatial linkages with previously measured coastal change and bathymetric variability (https://pubs.er.usgs.gov/publication/ofr20151180). This USGS Data Release includes the: 1) processed elevation point data (xyz) and digital elevation model (DEM), 2) processed images of backscatter and side scan sonar, and 3) chirp subbottom profile data (segy). For further information regarding data collection and/or processing please see the metadata associated with this data release.A geophysical survey was conducted offshore Cape Canaveral, Florida by Coastal Carolina University offshore of Cape Canaveral, Florida using high-resolution chirp sub-bottom, multibeam bathymetry and side scan sonar (SSS) systems on June 13, 14, 16, and 17 of 2016. This USGS data release includes the resulting processed elevation point data (xyz), an interpolated digital elevation model (DEM), with processed backscatter, side scan sonar, and seismic chirp data.A geophysical survey was conducted offshore Cape Canaveral, Florida by Coastal Carolina University offshore of Cape Canaveral, Florida using high-resolution chirp sub-bottom, multibeam bathymetry and side scan sonar (SSS) systems on June 13, 14, 16, and 17 of 2016. This USGS data release includes the resulting processed elevation point data (xyz), an interpolated digital elevation model (DEM), with processed backscatter, side scan sonar, and seismic chirp data.