Global and marine paleoproductivity over the last 4 glacial cycles, constrained by the triple isotope composition of atmospheric O2

Details Global and marine paleoproductivity over the last 4 glacial cycles, constrained by the triple isotope composition of atmospheric O2 Global and marine paleoproductivity over the last 4 glacial cycles, constrained by the triple isotope composition of atmospheric O2

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmos52a..05b&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #OS52A-05

Mathematics

Logic

4805 Biogeochemical Cycles (1615), 4267 Paleoceanography, 0400 Biogeosciences

Scientific paper

Photochemical reactions in the stratosphere impart a mass-independent fractionation to O2 in the global atmosphere that is attenuated by photosynthesis and respiration. The mass-independent fractionation is approximated by the term D17O = d17O - 0.5 d18O; d17O and d18O are the normal delta terms, with values in per mil. One can calculate rates of photosynthesis and respiration by the biosphere from measurements of the triple isotope composition of paleoatmospheric O2 (accessed from ice cores) and estimates of relative rates of stratospheric photochemical reactions through time. This approach invokes the fact that the magnitude of D17O depends on relative rates of stratospheric reactions, which produce the anomaly, and biological processes, which consume anomalous ambient O2 and replace it with photosynthetic O2, which is normally fractionated (D17O = 0). We present a record of D17O of paleoatmospheric O2 back to 400 ka based on analyses of Vostok and other deep ice cores. We estimate rates of stratospheric reactions in the past, and use these results to estimate past variations in planetary fertility. The results lead to two significant conclusions. First, gross ocean productivity, estimated after subtracting inferred terrestrial productivity from the global value, was generally higher during the ice ages than in interglacial times. Second, global productivity was not strongly forced by orbital variations, in contrast to the Dole effect (d18O of atmospheric O2 - d18O of seawater). This discordance raises the question of how the isotopic composition of O2 in the atmosphere can vary independent of variations in production.

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