HR: 16:30h
AN: B14B-03    [Abstracts]
TI: Elevated Levels of Magnesium in the Coral {\it Montastraea faveolata} as determined by SEM/EDS and LA ICP-MS
AU: * Buster, N A
EM: nbuster@usgs.gov
AF: Noreen A Buster, 600 Fourth Street South, St.Petersburg, Fl 33701 United States
AU: Holmes, C W
EM: cholmes@usgs.gov
AF: Noreen A Buster, 600 Fourth Street South, St.Petersburg, Fl 33701 United States
AB: Using a high-resolution laser ablation inductively coupled plasma mass spectrometer (LA ICP-MS) technique, a small portion of a coral core was analyzed to determine the geochemical signatures within and among specific skeletal structures in the large framework coral Montastraea faveolata. Data reveal potential problems in geochemical analysis and interpretation. Depending upon sample size and location of sampling within the skeleton, results may differ. Vertical transects (spot/raster sampling) were conducted along three parallel skeletal structures: endothecal (septal flank), corallite wall, and exothecal (costal flank) areas. The results reveal that trace element levels vary among the three structures. The amount of magnesium (Mg) varied prominently among the adjacent structures and is most abundant within the exothecal portion of the skeleton. Using a scanning electron microscope (SEM), we found hexagonal crystals forming discs, pairs, and rosettes in several coral samples of M. faveolata. High levels of Mg within these crystals have been confirmed with energy dispersive spectrometry (EDS) and LA ICP-MS. The chemical composition is consistent with the mineral brucite (MgOH$_{2}$). The crystals, located exclusively in the exothecal area of the skeleton, are associated with green endolithic algae and are commonly associated with increased Mg levels found in the adjacent corallite walls. The excess Mg precipitated within the microenvironment of the exothecal area may be a result of photosynthetic processes. The presence and locations of high-Mg crystals found within microenvironments of the coral may explain anomalous Mg data researchers have been questioning for years.
DE: 1045 Low-temperature geochemistry
DE: 1065 Trace elements (3670)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting