DOI: 10.25921/g86a-rg88
title: NOAA/WDS Paleoclimatology - Dry Tortugas National Park Coral Sr/Ca data for 1734 to 2008

description: This study uses skeletal variations in coral Sr/Ca from three Siderastrea siderea coral colonies within the Dry Tortugas National Park in the southeastern Gulf of Mexico (24°42′N, 82°48′W) to reconstruct monthly sea surface temperature (SST) variations from 1734 to 2008 Common Era (C.E.). Calibration and verification of the replicated coral Sr/Ca-SST reconstruction with local, regional, and historical temperature records reveals that this proxy-temperature relationship is stable back to 1879 C.E. The coral SST reconstruction contains robust interannual (~2.0°C) and multidecadal variability (~1.5°C) for the past 274 years, the latter of which does not covary with the Atlantic Multidecadal Oscillation. Winter SST extremes are more variable than summer SST extremes (±2.2°C versus ±1.6°C, 2σ) suggesting that Loop Current transport in the winter dominates variability on interannual and longer time scales. Summer SST maxima are increasing (+1.0°C for 274 years, σMC = ±0.5°C, 2σ), whereas winter SST minima contain no significant trend. Colder decades (~1.5°C) during the Little Ice Age (LIA) do not coincide with decades of sunspot minima. The coral SST reconstruction contains similar variability to temperature reconstructions from the northern Gulf of Mexico (planktic foraminifer Mg/Ca) and the Caribbean Sea (coral Sr/Ca) suggesting areal reductions in the Western Hemisphere Warm Pool during the LIA. Mean summer coral SST extremes post-1985 C.E. (29.9°C) exceeds the long-term summer average (29.2°C for 1734–2008 C.E.), yet the warming trend after 1985 C.E. (0.04°C for 24 years, σMC = ±0.5, 2σ) is not significant, whereas Caribbean coral Sr/Ca studies contain a warming trend for this interval.
description: The data set contains the ratio of strontium-to-calcium (Sr/Ca) for three Atlantic coral colonies (Siderastrea siderea) from the Dry Tortugas National Park (centered on 24.7°N, 82.8°W) in the Gulf of Mexico that were cross-dated into one continuous chronology. Two cores (08PS-A2 and 08PS-F1) had dead tops thus unknown ages and these cores were uranium-thorium (U-Th) dated. Samples for geochemical analysis were extracted from each slab surface using a computer-driven tri-axial micromill system [Quinn et al., 1996] with a 1.0 mm diameter dental drill bit that moves in a continuous manner for the user defined sampling increment (Table A1 in DeLong et al., 2014) extracting approximately monthly samples with a 1 mm sampling depth. Sampling paths were selected parallel to the extending corallites along the synapticulothecal corallite wall; the optimal sampling location for this species [Maupin et al., 2008; DeLong et al., 2011]. Multiple paths were sampled to assess intracolony variability. Coral Sr/Ca determinations were made using a PerkinElmer 4300 Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) at the University of Texas (UT) at Austin and a PerkinElmer 7300 ICP-OES at the USGS Coastal and Marine Science Center in St. Petersburg, FL. A laboratory internal gravimetrical standard (IGS) was measured before and after each dissolved coral sample to correct for instrumental drift. The average drift corrected IGS precision for Sr/Ca was 0.025 mmol mol–1 (2s, n = 862; UT) and 0.024 mmol mol–1 (2s, n = 212; USGS). The average drift corrected precision for Sr/Ca of a coral standard (PL) was 0.030 mmol mol–1 (2s, n = 1194; UT) and 0.039 mmol mol–1 (2s, n = 286; USGS). The values determined for these standards at both laboratories are consistent within analytical error. The coeval paths were averaged together to produce mean Sr/Ca variations for each core. The core records were averaged into a master chronology using the cross-dated and U-Th dates for chronology control and the standard error of the mean for each month was determined for assigning weights in linear regression. The master coral Sr/Ca variations were calibrated using weighted least squares linear regression with local sea surface temperature (SST) records from NOAA National Data Buoy Center (NDBC; www.ndbc.noaa.gov) DRYF1 and PLSF1, and then verified with NDBC buoy SANF1, NOAA Surface Air temperature from Key West, FL and SST from historical records from the Dry Tortugas Lighthouse. The dataset contains two spreadsheets, one labeled "Data colonies calibration" and the other "Data master reconstruction." The "Data colonies calibration" dataset contains the coral Sr/Ca variations assigned to monthly intervals from four cores sampled in this study (08PS-A1, 08PS-A2, 08PS-F1, and 93DRYSS2). The master chronology is the average of the three colonies (08PS-A, 08PS-F1, and 93DRYSS2) and the colony 08PS-A is the average of the two cores from that colony (08PS-A1 and 08PS-A2). Each core record is comprised of the average between paths in that core. The coral Sr/Ca (mmol/mol) for each core with the number of samples for that core and standard error of the mean for each month are given in this dataset. Additionally, the SST data used for calibration and verification are given with their respective errors for weighted least squares regression. The SST data includes Monthly mean SST from NDBC (www.ndbc.noaa.gov) buoys DRYF1 and PLSF1 (collectively referred to as DRTO SST) and SANF1; Monthly mean Surface Air Temperature (ºC) from Key West (COOPID 84570) US Historical Climatology Network, and Dry Tortugas Lighthouse Monthly mean SST (ºC) from Vaughan 1918. These are the results shown in Figures 3 and 4 in DeLong et al., 2014. The "Data master reconstruction" dataset contains the master chronology coral Sr/Ca variations assigned to monthly intervals with the reconstructed SST, SST anomalies (SSTA; determined as mean monthly SST with respect to the interval from 1971-2000), mean annual SST, summer maximum SST, winter minimum SST, and error of regression for each month based on the number of colonies sampled for that month (Table 5 in DeLong et al., 2014). Additionally, the 7-month and 36-month filtered SSTA with their respectively error of regressions are given. These are the results shown in Figures 4 and 5 in DeLong et al., 2014. The "Extensions" dataset contains the annual linear extensions for each core determined from the coral Sr/Ca variations from each February-to-February. For cores with multiple paths, these are the average extensions between the paths from that core. These are the results shown in Figures 3d and Appendices in DeLong et al., 2014. This coral Sr/Ca record updates the previous NOAA contribution, https://www.ncei.noaa.gov/access/paleo-search/study/11935, for cores 08PS-F1 and 08PS-A1.