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.

残留喀斯特地貌（relict karstic features）常被称为蓝洞（blue holes），是大陆架区域的常见地貌，其下伏富含碳酸盐的沉积物或岩石。此类地貌在墨西哥湾内的西佛罗里达陆架多有分布，本数据集提及的两处分别为琥珀鱼洞（Amberjack Hole）与青香蕉坑（Green Banana Sink，下文简称青香蕉）。
美国地质调查局圣彼得堡海岸与海洋科学中心（USGS-SPCMSC，全称U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center）的科研人员参与了由美国国家海洋和大气管理局（NOAA，全称National Oceanic and Atmospheric Administration）资助的合作团队主导的采样工作，该合作团队来自莫特海洋实验室、佐治亚大学与佛罗里达大西洋大学。
琥珀鱼洞位于佛罗里达州萨拉索塔以西约50千米处，所处水深对应约30米等深线；其呈穹窿状，自海底向下延伸40米，总水深约70米。青香蕉坑位于萨拉索塔以西约80千米处，所处水深对应约45米等深线；其呈U形，自海底向下延伸80米以上，总水深约125米。
研究人员对2019年5月、2019年9月在琥珀鱼洞采集的样本，以及2020年9月在青香蕉坑采集的样本，开展了天然氡（Radon）与镭（Radium）同位素的分析。其中，对大体积水样（bulk water samples）中的总氡-222进行了检测；经海水浸泡后吸附在二氧化锰浸渍纤维（manganese dioxide impregnated fibers，下文简称锰纤维（Mn-fibers））上的残留物质，则用于检测镭-223、镭-224与稳态氡-222（supported Radon-222，即镭-226）。
利用镭延迟符合计数器（Radium Delayed Coincidence Counters，缩写RaDeCC）对锰纤维上的镭-223与镭-224活度进行了测定；采用空气中氡检测装置（RAD7，Durridge公司）对水体中的总氡-222，以及锰纤维上的稳态氡-222（镭-226）完成了检测。
本报告中的数据分别对应2019年5月、2019年9月与2020年9月的美国地质调查局野外活动编号（FAN）：2019-328-FA（19WFS01）、2019-357-FA（19WFS03）与2020-317-FA（20WFS01）。