Radioanalytical Measurements on Samples From Submarine, Karstic Carbonate Features Along the West Florida Shelf

Relict karstic features, often referred to as blue holes, are common features along continental shelves that are underlain by carbonate rich sediments and/or rocks. Several of these features occur along the west-Florida shelf within the Gulf of Mexico, including the two mentioned in this data product: Amberjack Hole and Green Banana Sink (hereafter referred to as Green Banana). Scientists from U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center (USGS-SPCMSC) participated in sampling efforts lead by the NOAA-funded collaborative team from Mote Marine Laboratory, University of Georgia, and Florida Atlantic University. Amberjack Hole is located at approximately the 30 meter (m) isobath, 50 kilometers (km) west of Sarasota, Florida; it is a dome-shaped feature that extends 40 m below the seafloor (approximately 70 m total water depth). Green Banana is located at approximately 45 m isobath, 80 km west of Sarasota; it is a U-shaped feature that extends 80 m or more below the seafloor (approximately 125 m total water depth). Naturally occurring radioisotopes of Radon and Radium were analyzed on samples collected from Amberjack Hole during cruises in May and September 2019, and Green Banana in September 2020. Total Radon-222 was measured on bulk water samples, while Radium-223, Radium-224, and supported Radon-222 (Radium-226) were measured on residue retained on manganese (di)oxide impregnated fibers (referred to as Mn-fibers from hereon) following exposure to seawater. Radium-223 and Radium-224 activity on Mn-fibers were measured on a set of Radium Delayed Coincidence Counters (RaDeCC). Total Radon-222 in water and supported Radon-222 (Radium-226 on Mn-fibers) were measured on radon-in-air detectors (RAD7, Durridge, inc). Data in this report correspond to USGS Field Activity Numbers (FAN) 2019-328-FA (19WFS01), 2019-357-FA (19WFS03), 2020-317-FA (20WFS01) in May 2019, September 2019, and September 2020 respectively.