Skeletal Sr content and density in Porites spp. in relation to environmental factors |
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| Authors: | R C Schneider S V Smith |
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| Institution: | (1) Department of Oceanography, University of Hawaii, 2525 Correa Road, 96822 Honolulu, Hawaii, USA;(2) Hawaii Institute of Marine Biology, University of Hawaii, 96744 Kaneohe, Hawaii, USA;(3) Present address: Department of Zoology, University of Western Australia, 6009 Nedlands, Western Australia, Australia |
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| Abstract: | The coral genus Porites was investigated to evaluate the use of skeletal strontium content as a recorder of seasonal and annual temperature oscillations. In the Hawaiian archipelago, the mean annual water temperature fluctuates by ±0.5C°, with seasonal temperature ranges of 4 to 8C°; the resolution of the Sr thermometer appears to be ±1.5C°. Of this error term, ±0.7C° is analytical, the remainder is  biological . Corals from some locations yield temperatures which are consistently offset from the Sr vs temperature calibration line, suggesting genetic population differences. Analysis of cores collected in 1980 from Hawaiian Porites spp. showed no discernible long-term trends over a 100 yr period. Although absolute temperatures are poorly resolved, subannual oscillations in skeletal Sr values accurately reflect recorded seasonal temperature variations. The most useful application of the Sr thermometer is in deciphering the skeletal density band pattern. Subannual oscillations in Sr-temperature values when correlated with density values showed a consistent pattern. When the sections chosen for x-radiography closely followed the growth axis, an abrupt shift from minimum to maximum skeletal density was evident in September/October each year, followed by a gradual decrease in density. The density pattern, shown by microdensitometry, is independent of latitude or temperature range over the Hawaiian archipelago. The annual density shift coincides with high but declining water temperature and solar insolation. If low-density growth represents optimum calcification conditions, the density shift in Hawaiian Porites spp. reflects a change in conditions from optimal to suboptimal. Analyses of samples from other Indo-Pacific locations confirm the generality of this density pattern and suggest a complex relationship between density and environmental light and temperature.Hawaii Institute of Geophysics Contribution No. 1209; Hawaii Institute of Marine Biology Contribution No. 618 |
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