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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 995

Last Page: 995

Title: Paleophosphate Determinations: Potentially Useful Paleo-Oceanographic Tool: ABSTRACT

Author(s): Anthony D. Socci, Michael A. Sommer II

Article Type: Meeting abstract


Using recent hydrographic data from the Indian Ocean, we have derived an empirical relation that predicts PO43- concentrations (µg - atoms/l) from the concentration of dissolved O2 and temperature (°C), where PO43- = 4.82 - 2.26 log T -0.30 dissolved O2. The ^dgr13C and ^dgr18O of certain species of planktonic foraminifera have been demonstrated to be functions of apparent oxygen utilization (AOU = 205.0 - 100^dgr13C) and temperature (calculated from the ^dgr18O paleotemperature equation). Utilizing the down-core ^dgr18O and ^dgr13C of planktonic foraminifera, substituted into the equation above, permits determinations of paleophosp ate concentrations for fossil oceans. In rewritten form: PO43- = (43.5(16.0) - 7.43 log T) - (43.5 O2 saturated seawater (ml/l) - 205.0 - 100 ^dgr13C)/145.0. A comparison of the PO43- values calculated from recent forams collected from 14 sites in the Indian Ocean with recent hydrographic values showed no significant differences (M = 0.91, B = 0.28, R = 0.89).

Having measured the isotopic concentrations of ^dgr13C and ^dgr18O obtained from 5 species of planktonic foraminifera from two cores in the Arabian Sea, we attempted down-core paleophosphate determinations. Foraminifera were collected from three time horizons in each core, the 0, 9, and 18 thousand years before present (KYBP) isochrons as determined from ^dgr18O ice-volume curves, using a linear age model. Our results indicate that the average surface and deep water (approximate O2 minimum depth) paleophosphate concentrations for the three isochrons are, respectively: 0.575 and 2.07 at 18 KYBP, 0.205 and 2.30 at 9 KYBP, and 0.33 and 1.92 for the Holocene. These determinations may indicate greater productivity or upwelling at 9 KYBP relative o the Holocene at 18 KYBP.

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