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gfdl's home page > gfdl on-line bibliography > 1985: The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present, 163-184
Glacial to interglacial changes in atmospheric carbon dioxide: The critical role of ocean surface water in high latitudes
| Toggweiler, J. R., and J. L. Sarmiento, 1985: Glacial to interglacial changes in atmospheric carbon dioxide: The critical role of ocean surface water in high latitudes. In The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present, Geophysical Monograph 32, Washington, DC: American Geophysical Union, 163-184. |
| Abstract: Recent measurements of the CO2 content of air bubbles trapped in glacial ice have shown that the partial pressure of atmospheric CO2 during the last ice age was baout 70 ppm lower than during the interglacial. Isotopic measurements on surface- and bottom-dwelling forams living during the ice age have shown that the 13C/12C gradient between the ocean's surface and bottom layers was 25% larger during the last ice age than at present. Broecker (1982) proposed that an increase in the phospate content of the deep sea could explain these observations. We follow up here on a proposal by Sarmiento and Toggweiler (1984) that glacial to interglacial changes in PCO2 are related to changes in the nutrient content of high-latitude surface water. We develop a four-box model of the ocean and atmosphere which includes low- and high-latitude surface boxes, an atmosphere, and a deep ocean. In simplest form the model equations show that the CO2 content of high-latitude surface water is directly connected to the huge reservoir of CO2 in deep water through the nutrient content of high-latitude surface water. The relationship between the CO2 content of low latitude surface water and the deep sea is more indirect and depends to a large extent on transport of CO2 through the atmosphere from high latitudes. We illustrate how the 14C content of the atmosphere and that of high-latitude surface water constrain model solutions for the present ocean and how ice age 13C observations constrain ice age parameters. We propose that the low ice age PCO2 can be produced by a reduction in local exchange between high-latitude surface water and deep water. The model requires that the current exchange rate of about 50 Sv be reduced to about 10 Sv. We review evidence in the geologic record for widespread changes in deep convection around Antarctica about 14,000 years ago which are synchronous with the change in atmospheric PCO2. |