Planetary fertility during the past 400 ka based on the triple isotope composition of O₂ in trapped gases from the Vostok ice core

TY - JOUR

T1 - Planetary fertility during the past 400 ka based on the triple isotope composition of O2 in trapped gases from the Vostok ice core

AU - Blunier, Thomas

AU - Bender, M.L.

AU - Barnett, B.

AU - von Fischer, J.C.

PY - 2012/10/10

Y1 - 2012/10/10

N2 - 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 affect δ17O approximately 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 δ 17O and δ18O of O2 in the atmosphere. Variations of this relationship thus allow us to estimate changes in the rate of O2 production by photosynthesis versus the rate of O 2-CO2 isotope exchange in the stratosphere. However, the analysis of the 17O anomaly is complicated because each hydrological and biological process fractionates δ17O and δ18O in slightly different proportions. In this study we present O2 isotope data covering the last 400 ka (thousand years) 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 by the land and ocean biosphere, fractionation during the hydrologic cycle, and 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 within 20% of the modern value throughout the last 400 ka. Given the presumed reduction in terrestrial oxygen productivity, the total oxygen production during glacials was likely reduced.

AB - 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 affect δ17O approximately 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 δ 17O and δ18O of O2 in the atmosphere. Variations of this relationship thus allow us to estimate changes in the rate of O2 production by photosynthesis versus the rate of O 2-CO2 isotope exchange in the stratosphere. However, the analysis of the 17O anomaly is complicated because each hydrological and biological process fractionates δ17O and δ18O in slightly different proportions. In this study we present O2 isotope data covering the last 400 ka (thousand years) 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 by the land and ocean biosphere, fractionation during the hydrologic cycle, and 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 within 20% of the modern value throughout the last 400 ka. Given the presumed reduction in terrestrial oxygen productivity, the total oxygen production during glacials was likely reduced.

U2 - 10.5194/cp-8-1509-2012

DO - 10.5194/cp-8-1509-2012

M3 - Journal article

SN - 1814-9324

VL - 8

SP - 1509

EP - 1526

JO - Climate of the Past

JF - Climate of the Past

IS - 5

ER -