 |
| Titel |
Planetary fertility during the past 400 ka based on the triple isotope composition of atmospheric oxygen in trapped gases from the Vostok ice core |
| VerfasserIn |
T. Blunier, M. L. Bender, B. Barnett, J. C. von Fisher |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063694
|
|
|
|
|
|
| Zusammenfassung |
| The productivity of the biosphere leaves its imprint on the isotopic composition of
atmospheric oxygen. Ultimately atmospheric oxygen, through photosynthesis, originates
from seawater. Fractionations during the passage from seawater to atmospheric O2 and during
respiration are mass dependent, affecting δ17O about half as much as δ18O. An
"anomalous" (also termed mass independent) fractionation process changes δ17O
about 1.7 times as much as δ18O during isotope exchange between O2 and CO2 in
the stratosphere. The relative rates of biological O2 production and stratospheric
processing determine the relationship between δ17O and δ18O of O2 in the atmosphere.
Variations of this relationship thus allow us to estimate changes in the rate of mass
dependent O2 production by photosynthesis versus the rate of mass independent
O2-CO2 exchange in the stratosphere. However, the analysis of the 17O anomaly is
complicated because each hydrological and biological process influencing δ17O and δ18O
fractionates 17O and 18O in slightly different proportions. In this study we present
oxygen data covering the last 400 kyr from the Vostok ice core. We reconstruct
oxygen productivities from the triple isotope composition of atmospheric oxygen
with a box model. Our steady state model for the oxygen cycle takes into account
fractionation during photosynthesis and respiration of the land and ocean biosphere as
well as fractionation when oxygen passes through the stratosphere. We consider
changes of fractionation factors linked to climate variations taking into account
the span of estimates of the main factors affecting our calculations. We find that
ocean oxygen productivity was likely elevated relative to modern during glacials.
However, this increase probably did not fully compensate for a reduction in land ocean
productivity resulting in a slight reduction in total oxygen production during glacials. |
|
|
|
|
|
|