Showing papers by "Todd Sowers published in 1994"

Climate correlations between Greenland and Antarctica during the past 100,000 years

Abstract: THE ice cores recovered from central Greenland by the GRIP1,2 and GISP23 projects record 22 interstadial (warm) events during the part of the last glaciation spanning 20–105 kyr before present. The ice core from Vostok, east Antarctica, records nine interstadials during this period4,5. Here we explore links between Greenland and Antarctic climate during the last glaciation using a high-resolution chronology derived by correlating oxygen isotope data for trapped O2 in the GISP2 and Vostok cores. We find that interstadials occurred in east Antarctica whenever those in Greenland lasted longer than 2,000 years. Our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between Greenland and Antarctica. Ice older than 115 kyr in the GISP2 core shows rapid variations in the δ18O of O2 that have no counterpart in the Vostok record. The age–depth relationship, and thus the climate record, in this part of the GISP2, core appears to be significantly disturbed.

The Dole Effect and its variations during the last 130,000 years as measured in the Vostok Ice Core

Abstract: We review the current understanding of the Dole effect (the observed difference between the {delta}{sup 18}O of atmospheric O{sub 2} and that of seawater) and its causes, extended the record of variations in the Dole effect back to 130 kyr before present using data on the {delta}{sup 18}O of O{sub 2} obtained from studying the Vostok ice core, and discuss the significance of temporal variations. The Dole effect reflects oxygen isotope fractionation during photosynthesis, respiration, and hydrologic processes (evaporation, precipitation, and evapotranspiration). Our best prediction of the present-day Dole effect, +20.8 {per_thousand}, is considerably lower than the observed value, +23.5 {per_thousand}, and we discuss possible causes of this discrepancy. During the past 130 kyr, the Dole effect has been 0.05 {per_thousand} lower than the present value, on average. The standard deviation of the Dole effect from the mean has been only {+-} {per_thousand}, and the Dole effect is nearly unchanged between glacial maxima and interglacial periods. The small variability in the Dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant. Most periodic variability in the Dole effect is in the precession band, suggesting that changes in this global biogeochemical termmore » reflects variations in low-latitude land hydrology and productivity or possibly variability in low-latitude oceanic productivity. 65 refs., 4 figs., 3 tabs.« less

Changes in the O2/N2 ratio of the atmosphere during recent decades reflected in the composition of air in the firn at Vostok Station, Antarctica

Abstract: Samples of air at various depths in firn were collected at Vostok Station, Antarctica, and analyzed for δ15N of N2, O2/N2 ratio, and CO2. The ultimate objective of this work is to constrain the recent rate of the atmospheric [O2] decrease, thereby providing a direct experimental constraint on net CO2 fluxes into the ocean and the land biosphere. δ15N increases with depth, because of gravitational enrichment, at approximately the rate predicted by the barometric equation. Gravitationally corrected CO2 decreases with depth to 308 ppmV at 101.9 m depth, because deeper air is older and less contaminated with anthropogenic CO2. The gravitationally corrected O2/N2 ratio increases with depth mainly because burning fossil fuel consumes O2. Samples in the top 20 m of the firn have anomalously high CO2 concentrations and anomalously low O2/N2 ratios. Samples below 96.2 m depth have anomalously high O2/N2 ratios. Between 30 and 96.2 m depth, the gravitationally corrected increase in the O2/N2 ratio is nearly equal to that computed from the rate of O2 consumption by combustion of fossil fuels. Our results indicate that the rate of anthropogenic O2 consumption can be accurately constrained by future firn air studies.