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

  • Author(s): Linn, LJ
  • Delaney, ML
  • Druffel, ERM
  • et al.
Abstract

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. © 1990.

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