THE DOLE EFFECT AND ITS VARIATIONS DURING THE LAST 130,000 YEARS AS MEASURED IN THE VOSTOK ICE CORE

We review the current understanding of the Dole effect (the observed d ifference between the delta(18)O of atmospheric O-2 and that of seawat er) and its causes, extend the record of variations in the Dole effect back to 130 kyr before present using data on the delta(18)O of O-2 Ob tained from studying the Vostok ice core (Sowers et al., 1993), and di scuss the significance of temporal variations. The Dole effect reflect s oxygen isotope fractionation during photosynthesis, respiration, and hydrologic processes (evaporation, precipitation, and evapotranspirat ion). Our best prediction of the present-day Dole effect, + 20.8 parts per thousand, is considerably lower than the observed value, + 23.5 p arts per thousand, and we discuss possible causes of this discrepancy. During the past 130 kyr, the Dole effect has been 0.05 parts per thou sand lower than the present value, on average. The standard deviation of the Dole effect from the mean has been only +/- 0.2 parts per thous and, and the Dole effect is nearly unchanged between glacial maxima an d interglacial periods. The small variability in the Dole effect sugge sts that relative rates of primary production in the land and marine r ealms have been relatively constant. Most periodic variability in the Dole effect is in the precession band, suggesting that changes in this global biogeochemical term reflects variations in low-latitude land h ydrology and productivity or possibly variability in low-latitude ocea nic productivity.