Field Testing the Fidelity of δ18O and δ13C in Reconstructing Upper Ocean Hydrography

Abstract

Stable isotope data from tests of four planktonic foraminifer species in core tops on the Rio Grande Rise (RIO) fail a field test of reproducibility until corrections are made for various environmental effects. The regionally uniform and strongly stratified surface ocean hydrography across RIO allows the identification of causes of variability in δ18O and δ13C data in addition to the effects of surface ocean temperature and nutrient content. A previously calibrated calcite dissolution proxy indicates that the dissolution of foraminifer shells in sediments has no effect on δ18O and δ13C in tests of foraminifers from core tops on RIO. Furthermore, vital effects within and among foraminifer species are not sufficient to explain the large variability of δ18O and δ13C data observed on RIO. Instead, correctly estimating species-specific habitat depth ranges and adjusting δ13C values for ocean/atmosphere carbon exchange are necessary to accurately reconstruct the hydrography of surface waters on RIO.