Abstract
The Anthropocene is the idea that human impacts are now great enough to set the Earth on a new and radically different geological trajectory compared to the rest of the Geological Time Scale. The Anthropocene Working Group (AWG), a working group of the Subcommission on Quaternary Stratigraphy of the International Commission on Stratigraphy, is facilitating the process that will lead to the submission of formal proposals to define the Anthropocene as a chronostratigraphic unit. The AWG is leading a worldwide campaign to sample and analyze modern strata, including annual density bands of tropical massive coral skeletons that hold promise to provide the long-sought geological 'golden spike' for the Anthropocene. This AWG project is developing the Tropical Atlantic candidate from West Flower Garden Bank (27 degrees 52.5'N, 93 degrees 49'W) in the Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico, an open ocean location with a submerged coral reef (top is approximately 18 m) and few direct human impacts and perhaps the most pristine coral reef in United States waters. We are analyzing a core from a large Siderastrea siderea coral spanning 1753-2005 CE for a large array of geochemical proxies and coral growth histories (extension and density). Sea surface temperature (SST) with be reconstructed with a variety of coral proxies (Sr/Ca, Mg/Ca, Li/Mg, Li/Ca, and U/Ca) coupled with delta (super 18) O for hydroclimate reconstructions, and delta (super 13) C for reconstruction the of Suess effect, the shift in atmospheric delta (super 13) C resulting from burning fossil fuels that started in the 1800s. Additional analyses in progress to trace global anthropogenic changes include NO (sub 3) and delta (super 15) N related to agricultural activities, heavy metals including V (fossil fuel derivative), and Pb (pollution and fossil fuel derivative), nuclear testing by-products ( (super 14) C, (super 239) Pu, (super 241) Am, and (super 137) Cs), and fly ash (black carbon). Coral delta (super 13) C shows the progression to lower values ( approximately 1 ppm) especially in 1956. Coral Sr/Ca-SST reveals an increasing trend in winter minima from approximately 1910 to 2005 and coral delta (super 18) O shows evidence of hydrological shifts during the 20th century. Lastly, we find a large significant mean shift in coral Ba/Ca (1.76+ or -0.41 mu mol/mol, 2sigma ) that corresponds to offshore oil drilling operations that use barite (BaSO (sub 4) ) using in drilling muds.