Mathematics – Logic
Scientific paper
Jul 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005gecoa..69.3265s&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 69, Issue 13, p. 3265-3284.
Mathematics
Logic
14
Scientific paper
Micron-scale variations in the trace-element (TE) composition of tropical coral skeletons were measured using laser-ablation ICP-MS (LA-ICP-MS) as part of an investigation into the chemical processes underlying paleoenvrionmental proxy reconstructions. Fluctuations in B, Mg, Sr, Ba and U were measured at high spatial resolution in two Porites corals from the Great Barrier Reef (Australia), and the fine-scale fluctuations (< ˜1.0 mm) were compared with seasonal TE cycles in a third coral. Fine-scale TE variations were found to have a large amplitude over distances corresponding to less than 1 month growth. Variations were quasi-periodic and appeared to have characteristic wavelengths on weekly (6 7 d) and monthly (28 d) scales, although periodicity was not continuous and variations could not be matched either within or between individual corallites. Fine-scale variations between Mg, Sr and U were significantly correlated with each other (Sr and U are positively correlated, but negatively correlated with Mg). This 3D correlation “vector” has the same slope as the seasonal-scale Mg, Sr and U correlations, suggesting that the same chemical/biologic biomineralization process mediates trace element variations at both timescales. Importantly, the fine-scale variations are too large to be caused directly by daily to monthly fluctuations in sea-surface temperature. This means that seasonal variations in these elements cannot reflect purely inorganic temperature-dependent coprecipitation. Models of physicochemical calcification were developed to test whether changes in calcification rate could explain the trace-element correlations. The calculations show that increases in calcification rate will result in correlated decreases in all TE/Ca ratios. The models reproduce the Sr partition coefficient, trace-element correlation slopes, and amplitude of fine-scale variations for an average calcifying pH of 8.5, varying by ±0.2 pH units. The models, however, predict U partition coefficients which are too low, and cannot reproduce the negative correlation between Mg and the other trace elements, which may be caused by crystallographic factors.
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