Biological Oxygen Productivity Over the Last Glacial Termination From Triple Oxygen Isotope Measurements
Abstract
The atmospheric oxygen isotope signature of O2 is linked to the oxygen signature of seawater through photosynthesis and respiration. Fractionation during these processes is mass dependent affecting δ 17O about half as much as δ 18O. A mass independent fractionation process takes place during isotope exchange between O2 and CO2 in the stratosphere (Thiemens, 1999; Luz et al., 1999). The magnitude of the mass-independent anomaly in the triple isotope composition of O2 depends on relative rates of biological O2 cycling and photochemical reactions in the stratosphere. Variations of this anomaly thus allows us to estimate changes of mass dependent O2 production by photosynthesis versus mass independent O2-CO2 exchange in the stratosphere. We reconstruct total oxygen productivity for the past from δ ^ {17}O and δ ^ {18}O measurements of O2 trapped in ice cores. With a box model we estimate that the total biogenic productivity was only ~70-80 % of today for the glacial and was probably still lower than today during the glacial-interglacial transition and the early Holocene. In principle we can calculate the oxygen flux from the ocean biosphere if we know the oxygen flux from the land biosphere. Calculated ocean production is very sensitive to the estimate of land biosphere production. The latter term remains uncertain, however, and we can presently only constrain glacial ocean production to 70 to 140 % of the present value.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2001
- Bibcode:
- 2001AGUSM..OS51B09B
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- 3344 Paleoclimatology