Trace metals in contemporary and seventeenth-century Galapagos coral: Records of seasonal and annual variations

Details Trace metals in contemporary and seventeenth-century Galapagos coral: Records of seasonal and annual variations Trace metals in contemporary and seventeenth-century Galapagos coral: Records of seasonal and annual variations

Feb 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990gecoa..54..387l&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 54, Issue 2, pp.387-394

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8

Scientific paper

We report trace element/calcium ratios for modern ( Cu / Ca , Mn / Ca , Cd / Ca , and Pb / Ca ) and seventeenth-century ( Cu / Ca , Mn / Ca , and Pb / Ca ) specimens of Pavona clavus collected in the Galapagos Islands. These data include the first reliable measurements of Cu / Ca ratios in coralline aragonite. We estimate that the ratio of Cu / Ca in the lattice to that in seawater (i.e., the effective distribution coefficient) is ~0.3, lower than the value of 1 observed for several other divalent elements; we estimate the effective distribution coefficient for Mn is ~ 1. Distribution coefficients in coral aragonite for 8 divalent metals are near unity despite different ionic radii and chemical speciation in seawater. Investigation of where these substituents are incorporated in the aragonite lattice is clearly warranted. In a modern Hood Island coral, quarter-annually sampled from 1964-73, Cu / Ca ratios decrease twofold from the late 1960s to early 1970s. Mn / Ca and Cd / Ca ratios vary seasonally with upwelling and the generic El Niño. The El Nino Southern Oscillation (ENSO) events of 1965, 1969, and 1972 are marked by suppression of Cd / Ca ratios by about 2.5 nmol/mol, while the Mn / Ca ratio is highest during the strong 1972 ENSO. Pb / Ca ratios were relatively constant throughout this period. From the Cu / Ca record of a seventeenth-century Urvina Bay coral annually sampled from 1600-1725 and the estimated Cu distribution coefficient, surface seawater Cu concentrations at Galapagos during the seventeenth century were similar to present day at 0.7-1.4 nmol/kg. Estimated Pb concentrations were lower at 5-20 pmol/kg, and Mn concentrations were slightly higher at 1.6-2.8 nmol/kg.

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