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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 5. (May)

First Page: 633

Last Page: 633

Title: Productivity Gradients for Paleo-Oceans: A New Application of Isotopes of C-13 and O-18: ABSTRACT

Author(s): Anthony Socci

Article Type: Meeting abstract

Abstract:

Based on the coincident relationship between the ^dgr13C and ^dgr18O of modern ocean water, above the O2 minimum, I have constructed a series of ocean-specific models designed to calculate open-ocean values of PO4 for paleo-oceans. Inherent in these models are the assumptions that the ^dgr18O and ^dgr13C of ocean water vary as functions of temperature and dissolved O2 (or AOU), respectively. In the Atlantic, for example, the derived model is:

PO4 = 4.95 - 2.54 [log 16.9 - 4.206(^dgr18Oc - ^dgr18Ow) + (^dgr18Oc - ^dgr18Ow)2] - 0.32 [O2 saturation - (e7.15 - 3.45 ^dgr13Cw/43.5)].

Above the O2 minimum, foraminiferally derived values of ^dgr13C and ^dgr18O can be used to calculate PO4 concentrations at the levels at which the tests were secreted, resulting in a restratification of the PO4 concentration with depth for paleo-oceans. A more powerful application of these models is the construction of productivity (PO4) gradients using average concentrations of PO4 obtained from the sedimented tests of surface (0 to 50 m) and deep-dwelling (below 150 m) planktonic Foraminifera. The higher the value of PO4, the greater the productivity. Preliminary results for the Sargasso Sea suggest that plots of PO4 values are very effective in delineating water masses, and possibl strong surface currents. Calculated PO4 gradients are in agreement with observed PO4 gradients. Calculated concentrations of PO4 with depth in the Atlantic compare well with observed trends. Concentrations of PO4, derived from Holocene planktonic Foraminifera from the Indian Ocean, are noticeably similar to observed PO4 concentrations in the overlying water in which the tests were secreted. These results, although preliminary, suggest that PO4 gradients can be calculated and used to delineate water masses for paleo-oceans throughout the Cenozoic.

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