St. Petersburg Coastal and Marine Science Center
In order to better understand how the morphology and ecology of our coastal reefs has changed during the Holocene (past 10,000 years), we are analyzing coral skeletons to document past environmental changes and determine the relationships between the changing environment and coral growth. This information is critical to our understanding of the natural history of coral reefs and will provide clues to the future of reef accretion processes and climate change.
Scleractinian or "hard" corals deposit a skeleton of calcium carbonate (CaCO3), and serve as important geochemical archives for the reconstruction of paleo-environmental conditions on the reef. Mound corals are long-lived (100-300 years) and their skeletons have alternating light and dark layers that result from seasonal changes in growth rates. The couplets of light and dark layers represent annual bands, similar to tree rings, that can be used to determine the age of the coral skeleton. Variations in the chemical composition of the skeleton can be calibrated to environmental parameters such as seawater temperature, salinity, and pH as the coral grows.
In order to generate a time series of environmental variability, we drill a path of continuous samples along the growth axis of a coral using a computer driven triaxial micro-milling machine. This results in sub-annual sampling with 10-20 samples/year, depending on the coral linear extension rate. Using this approach we can reconstruct centuries-long records of seasonally resolved δ18O and Sr/Ca from long-lived Atlantic coral species such as Siderastraea siderea and Montastraea faveolata.
The Strontium to Calcium ratio (Sr/Ca) of the coral aragonite is related to the water temperature at which a coral calcifies. This is because Sr2+ and Ca2+ are both divalent cations with similar properties (they occupy the same column in the periodic table), so Sr2+ can substitute for Ca2+ in the CaCO3 of coral aragonite. As temperature increases, there is less Sr2+ substitution, and the Sr/Ca ratio decreases. The Sr/Ca to temperature relationship can differ between different species and different colonies of the same species of coral. We have empirically determined the Sr/Ca-temperature calibration equations for both M. faveolata and S. siderea in Dry Tortugas National Park, and applied those calibrations to time series covering the past 100-300 years.
The oxygen isotopic composition (δ18O) of coral aragonite is related to the temperature and the salinity of seawater. We are pairing Sr/Ca and δ18O measurements in corals to make inferences about past changes in temperature and salinity.
We are also exploring additional geochemical proxies in corals (e.g., B/Ca, Ba/Ca, δ11B, Li/Ca), which may tell us more about water nutrients, pH, salinity and temperature.
Busch, T.E., Flannery, J.A., Richey, J.N., and Stathakopoulos, Anastasios, 2015, The relationship between the ratio of strontium to calcium and sea-surface temperature in a modern Porites astreoides coral—Implications for using P. astreoides as a paleoclimate archive: U.S. Geological Survey Open-File Report 2015–1182, 10 p., http://dx.doi.org/10.3133/ofr20151182.
DeLong K.L., Flannery J.A., Poore R.Z., Quinn T.M., Maupin C.R., Lin, K., Shen, C., 2014, A reconstruction of sea surface temperature variability in the southeastern Gulf of Mexico from 1734 to 2008 C.E. using cross-dated Sr/Ca records from the coral Siderastrea siderea. Paleoceanography, 29, PA002524.
Flannery, J.A., and Poore, R.Z., 2013, Sr/Ca Proxy Sea-Surface Temperature Reconstructions from Modern and Holocene Montastraea faveolata Specimens from the Dry Tortugas National Park, Florida, U.S.A.: Journal of Coastal Research: Special Issue 63: 20-31. Doi:10.2112/SI63-003.1.
Muslic, Adis, Flannery, J.A., Reich, C.D., Umberger, D.K., Smoak, J.M., and Poore, R.Z., 2013, Linear extension rates of massive corals from the Dry Tortugas National Park (DRTO), Florida: U.S. Geological Survey Open-File Report 2013–1121, 22 p.
Hickey, T.D., Reich, C.D., DeLong, K.L., Poore, R.Z., and Brock, J.C., 2012, Holocene core logs and site methods for modern reef and head-coral cores: Dry Tortugas National Park, Florida. U.S. Geological Survey Open-File Report 2012-1095, 34 p.
Reich, C., Streubert, M., Dwyer, B., Godbout, M., Muslic, A., and Umberger, D., 2012, St. Petersburg Coastal and Marine Science Center's core archive portal: U.S. Geological Survey Data Series 626.
Flannery, J.A., and Poore, R.Z., 2010, Corals as Climate Recorders: U.S. Geological Survey Fact Sheet 2010-3085, 2 p.
Reich, C.D., Hickey, T.D., DeLong, K.L., Poore, R.Z., and Brock, J.C., 2009, Holocene core logs and site statistics for modern patch-reef cores—Biscayne National Park, Florida: U.S. Geological Survey Open-File Report 2009–1246, 26 p.
Brock, J.C., Palaseanu-Lovejoy, M., Wright, C.W., and Nayegandhi, A., 2008, Patch-reef morphology as a proxy for Holocene sea-level variability: Coral Reefs, doi: 10.1007/s00338-008-0370-y.
DeLong, K.L., Quinn, T.M., Taylor, F.W., Lin, K., and Shen, C.C., 2008, Inter-Decadal to Multi-Decadal Sea Surface Temperature Variability in the Southwest Tropical Pacific Since AD 1648: Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract PP21D-03.
Hine, A.C., et al, 2008, Coral Reefs, Present and Past, on the West Florida Shelf and Platform Margin, in: Reigl, B. and Dodge, R., ed., Coral Reefs of the USA, Netherlands, Springer, p. 127-173.
Lidz, B.H., Brock, J.C., and Nagle, D.B., 2008, Utility of shallow-water ATRIS images in defining biogeologic processes and self-similarity in skeletal Scleractinia, Florida reefs: Journal of Coastal Research, v. 25, no. 5, p. 1320-1338.
Maupin, C.R., Quinn, T.M., and Halley, R.B., 2008, Extracting a climate signal from the skeletal geochemistry of the Caribbean coral Siderastrea siderea: Geochemistry, Geophysics, and Geosystems, v. 9., doi:10.1029/2008GC002106, 13p.
Maupin, C.R., Quinn, T.M., Poore, R.Z., Lin, K., and Shen, C.C., 2008, Inter-Colony Fidelity of Sr/Ca Variability in the Massive Caribbean Coral Siderastrea siderea: a Sub-Fossil Example: Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract PP31A-1469.