Radiometric Ages and Descriptive Data for Late Holocene Acropora spp. Corals From Dry Tortugas National Park

Most of the samples detailed in this data release were collected by hand via self-contained underwater breathing apparatus (SCUBA)- and free-diving. For those samples, divers used a small sledgehammer and chisel to sub-sample suspected Acropora palmata or Acropora cervicornis reef frameworks and associated coral rubble within Dry Tortugas National Park. Three samples were obtained via rotary coring as described in Toth and others (2018).

The water depths where the samples were collected were recorded in the field using underwater depth gauges. The field-based measurements were corrected to mean sea level (MSL) using data from the nearest National Oceanic and Atmospheric Administration (NOAA) tidal datum. Elevation errors were incorporated and are associated with 1) estimating water depths with underwater depth gauges (0.5 meters [m]), 2) a sampling depth uncertainty based on the size of the samples collected for radiocarbon dating (0.01 m), and 3) for cores, the rotary coring method (0.15 m) as described by Hijma and others (2015) and Hibbert and others (2018). A total elevation uncertainty was estimated based on the root-sum-square of the elevation errors. The elevation uncertainty was combined with the empirical depth distribution of Acropora palmata in Florida determined by Hibbert and others (2018) to estimate paleo-water depth in which the samples were growing.

At the U.S. Geological Survey St. Petersburg Coastal and Marine Science Center (USGS SPCMSC), a tile saw equipped with a diamond blade was used on the collected coral samples to obtain small pieces of internal coral aragonite free of visually observable diagenesis for dating. These subsamples were then sonicated in warm deionized water to remove any detrital material and were further processed for either Radiocarbon or Uranium-Thorium (U-Th) dating later in a dedicated laboratory, respectively.

Radiocarbon ages of the samples were determined by accelerator mass spectrometry (AMS) performed at the Woods Hole Oceanographic Institution (WHOI) National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility (266 Woods Hole Rd., Woods Hole, MA 02543) or the Lawrence Livermore National Laboratory (7000 East Ave., Livermore, CA 94550-9234) using standard methodologies (https://www2.whoi.edu/site/nosams/radiocarbon-data-and-calculations/). Measured radiocarbon ages were corrected for the fractionation of δ13C based on δ13C measured by AMS. All radiocarbon ages were calibrated to years before present (where “present” is 1950) using the temporally-explicit local radiocarbon reservoir age offsets for the nearshore regions of south Florida derived by Toth and others (2017).

Subsamples of each coral sample were powdered and analyzed for evidence of secondary alteration to calcite by X-ray diffraction (XRD) following methods described by Abdul and others (2016) using a Philips XPert Powder Diffractometer at the Department of Chemistry at Rutgers University (123 Bevier Rd, Piscataway, NJ 08854) or at the U.S. Geological Survey in Denver, Colorado (Federal Ave, Denver, CO 80225). Only subsamples with less than 0.2% calcite were used for Uranium-Thorium (U-Th) dating. U-Th isotopes were measured using the Thermo Scientific™ NEPTUNEPLUS™ Multi-collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) at the Department of Earth and Planetary Sciences at Rutgers University following the methods described in Mortlock and others (2005), which were revised in Abdul and others (2016). All dates and activity ratios were calculated using half-lives published in Cheng and others (2013). These data were used to estimate ages before present (relative to 1950) with 2-sigma uncertainties.

Photography: Photographs were taken by USGS personnel (L. Toth, A. Stathakopoulos, A. Modys, and J. Morrison) using a GoPro™ camera in an underwater housing. The digital photographs were taken in the field of Acropora palmata reef framework and associated rubble and the samples taken from each. Images were color corrected as needed using Adobe Photoshop CC version 23.3.2 to adjust for light regime and enhance contrast and brightness.

Populating the image headers: Credit, contact information, copyright, usage terms, image descriptions, attribution url, metadata link, and georeferencing information were added to the exchangeable image file format (EXIF) header of each image using Phil Harvey’s ExifTool (version 12.2). All information in the script were the same among all images, aside from the EXIF:ImageDescription, EXIF:Artist, EXIF:GPSLatitude and EXIF:GPSLongtitude information, as that information varied between images. First, the following command was run on the images to preserve filenames: exiftool -P "-XMP:PreservedFileName<Filename" *.JPG. Second, the following command was run on the images to populate the image headers. This example command was run on all images: exiftool -IPTC:Credit="U.S. Geological Survey" -IPTC:Contact="gs-g-spcmsc_data_inquiries@usgs.gov" -EXIF:Copyright="Public Domain" -XMP:UsageTerms="Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty." -EXIF:ImageDescription="XXXX" -XMP:AttributionURL="https://doi.org/10.5066/P13L6DTF" -XMP:ExternalMetadataLink="https://www1.usgs.gov/pir/api/identifiers/USGS:33e67440-5882-4faf-af2e-9f2b19b53780" -EXIF:Artist="XXXX " -EXIF:GPSMapDatum="EPSG:4326 (WGS 84)" -EXIF:GPSLatitude="XXXX" -EXIF:GPSLatitudeRef="N" -EXIF:GPSLongitude="XXXX" -EXIF:GPSLongitudeRef="W" -sep ";" -IPTC:Keywords="coelenterates; paleoceanography; reef ecosystems; radiometric dating; marine geology; Holocene" -overwrite_original -P XXXX.jpg Third, the following command run on all images in a folder to copy information into duplicate tags: exiftool "-XMP-photoshop:Credit<IPTC:Credit" "-XMP-iptcCore:CreatorWorkEmail<IPTC:Contact" "-XMP-dc:Rights<EXIF:Copyright" "-XMP-dc:Description<EXIF:ImageDescription" -overwrite_original -P *.jpg To read out the complete imagery header information to a comma-separated values (CSV) file, run the following command line script: 'exiftool -csv *.tif > allheaders.csv'. Specific tags may be specified with this command, if preferred.