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Magnesium content within the skeletal architecture of the coral Montastraea faveolata: locations of brucite precipitation and implications to fine-scale data fluctuations

January 1, 2006

Small portions of coral cores were analyzed using a high-resolution laser ablation inductively coupled plasma mass spectrometer (LA ICP-MS) to determine the geochemical signatures within and among specific skeletal structures in the large framework coral, Montastraea faveolata. Vertical transects were sampled along three parallel skeletal structures: endothecal (septal flank), corallite wall, and exothecal (costal flank) areas. The results demonstrate that trace element levels varied among the three structures. Magnesium (Mg) varied among adjacent structures and was most abundant within the exothecal portion of the skeleton. Scanning electron microscopy (SEM) revealed the presence of hexagonal crystals forming thick discs, pairs or doublets of individual crystals, and rosettes in several samples. High Mg within these crystals was confirmed with energy dispersive spectroscopy (EDS), infrared spectrometry, and LA ICP-MS. The chemical composition is consistent with the mineral brucite [Mg(OH2)]. These crystals are located exclusively in the exothecal area of the skeleton, are often associated with green endolithic algae, and are commonly associated with increased Mg levels found in the adjacent corallite walls. Although scattered throughout the exothecal, the brucite crystals are concentrated within green bands where levels of Mg increase substantially relative to other portions of the skeleton. The presence and locations of high-Mg crystals may explain the fine-scale fluctuations in Mg data researchers have been questioning for years.

Citation Information

Publication Year 2006
Title Magnesium content within the skeletal architecture of the coral <i>Montastraea faveolata</i>: locations of brucite precipitation and implications to fine-scale data fluctuations
DOI 10.1007/s00338-006-0092-y
Authors N.A. Buster, C. W. Holmes
Publication Type Article
Publication Subtype Journal Article
Series Title Coral Reefs
Series Number
Index ID 70030487
Record Source USGS Publications Warehouse
USGS Organization Coastal and Marine Geology Program