This award will provide funds to obtain new proxy records of the Atlantic Multidecadal Oscillation (AMO) over time periods between 100 to 1000 years using sclerosponge aragonite geochemistry (18O/16O and Sr/Ca), and to investigate possible artifacts in stable oxygen and carbon (13C/12C) isotope data due to alteration during the sampling of aragonitic skeletal material. Specific objectives include 1) the generation of sclerosponge geochemical data, combined with improved dating, to confirm a correlative link between salinity and AMO at multiple locations in the Bahamas and Caribbean both prior to and after the instrumental record (~1850), 2) improvement of the geochemical calibrations between temperature and Sr/Ca and d18O based on a new collection of ~ 24 sclerosponge specimens collected between 1986 and 1996 and 3) investigation of additional minor and trace elements as recorders of environmental conditions in the tropical subsurface environment. The Broader Impacts include the societal relevance of research directed at understanding a fundamental question of the climate system that could have a synergistic impact on human-contributed forcings of the climate system and support of research by undergraduate and graduate students.
This proposal represents an effort funded by the National Science Foundation to calibrate and use sclerosponges for paleoenvironmental purposes. The project started with a series of experiments to calibrate the geochemistry of sclerosponges to environmental variables (Sr/Ca and d18O). Specimens of sclerosponges were stained with Calcein dye and grown for three years in the field. Numerous publications have been produced as a result of this research. Significant accomplishments of this work are: 1) A calibration between the Sr/Ca ratio andt emperature in the skeleton of sclerosponges has been established , 2) Significant changes in the salinity of the Atlantic Ocean have been identified, 3) Sclerosponge age models have been greatly improved both statistically and conceptually , 4) An improvement of the existing d18O calibration , 5) An increased understanding of the distribution of trace elements in sclerosponges, and 6) A new calibration between d18O and temperature for sclerosponges. The latest efforts on this project utilize sclerosponges to examine past variations in the AMO. In total these proposals have supported three PhD students. In the latest work we have further investigated the potential of sclerosponges to record changes in salinity and temperature of the salinity maximum underwater at a wide range of localities in the Bahamas and Caribbean. We intended to produce records of the Atlantic Multi-Decadel Oscillation (AMO) and relate this to the Meridional Overturning Circulation. The major completed product of this research has been the PhD of Amanda Waite. In the work completed we have investigated additional sclerosponge records, replicating them at a number of localities, improved previously published calibration between Sr/Ca (and d18O) and temperature, improved the dating of these records using additional U/Th dates and the annual cycle in the Sr/Ca ratio, extended the period of record to 1400, and investigate the utilization of additional geochemical proxies (clumped isotopes). These data have further improved our ability to examine long term changes in the temperature and salinity dynamics of the sub-tropics and improve our understanding of the dynamics of the AMO and its link to AMOC. In addition the work of Waite has identified a major problem during the sampling of coral skeletons using a micromill, namely the conversion of the skeleton to calcite and the effect upon the oxygen isotopic composition. Random effects were introduced by random alteration of the skeleton during the drilling. Luckily there was minimal influence upon the d13C and the Sr/Ca ratio. The attached figure show the d13C results of three replicate transects in a sclerosponge skeleton.
