Temporal and spatial variability of CO₂ efflux in the eastern equatorial Pacific during the last 200,000 years as monitored by sedimentary nitrogen isotope ratios

A key challenge in climate history research is to determine the cause(s) of major fluctuations in the concentration of atmospheric carbon dioxide (CO₂) in the past. Records obtained from the drilling of ice cores in Antarctica show that the carbon dioxide concentration has fallen by one-third in ice ages, only to rebound during the warmer interglacial periods. Despite an intense research effort we do not yet know why this happened. This question is not merely of purely scientific interest, for resolving it will contribute significantly to our understanding of carbon cycling between the ocean and the atmosphere, and this is a fundamental issue in determining future impacts of anthropogenic CO₂ emissions.

In the modern ocean, the equatorial eastern Pacific (EEP) is the most important oceanic source of CO 2 to the atmosphere. On average, some 75% of the total exchange of CO 2 from the ocean to the atmosphere occurs in this region between 15°N to 15°S and 160°E to 80°W. This is due to the upwelling of CO 2 enriched water from below, its subsequent heating at the surface, and the release of the gas from the warmed water. Reduction in the intensity of the upwelling and/or a decrease in its spatial extent i n the past could have contributed to lower glacial atmospheric CO 2 concentrations.

We are examining glacial-interglacial changes in the intensity and spatial distribution of upwelling in the EEP by determining a wide range of sedimentary proxies of production, nutrient utilization, sea surface temperature, upwelling strength and bottom water oxygenation in cores from the eastern equatorial and south Pacific that extend back to 250,000 years BP. We are using 230 Th assays to correct for sediment redistribution and focusing in order to estimate true vertical fluxes of the various proxies. This will allow us to estimate changes in the rate of loss of CO 2 from the ocean surface to the atmosphere in this critical area during the last glacial-interglacial cycle (0 to 200,000 years ago).

last updated October 28, 2004