Ice core, records

Research should be conducted to understand how the oceans have operated under past climates. This would involve paleoclimatic studies including analysis of sediment and ice core records coupled with tracer-style ocean models or box models. 

Mayewski, P. A. et al. (1990). An ice-core record of atmospheric response to anthropogenic sulfate and nitrate. Nature 346, 554-556. 

A very important complication in interpreting ice core records, and in defining depth-age relations, is the fact that snow transforms to ice 50 to 100 m below the surfaces of most polar ice sheets. This means the gas trapped in ice is actually younger than the solid ice at the same depth, and that a variety of processes can transport and redistribute gases in this snowy upper layer (called the fim). To imderstand this, and to prepare for subsequent discussions, we must discuss how snow converts to ice near the ice sheet surface. 

Longer ice-core records show that methane concentrations have varied on a variety of time scales over the past 220 000 years (Fig. 18-15) Qouzel et al, 1993 Brook et al, 1996). Wetlands in tropical (30° S to 30° N) and boreal (50° N to 70° N) regions are the dominant natural methane source. As a result, ice-core records for preanthropogenic times have been interpreted as records of changes in methane emissions from wetlands. Studies of modem wetlands indicate that methane emissions are positively correlated with temperature, precipitation, and net ecosystem productivity (Schlesinger, 1996). 

Fig. 18-17 Ice core records of N2O. (a) Data of Machida et al. (1995) from the H15 ice core, east Antarctica, for the time period 1750-1950, and monthly atmospheric N2O measurements at the South Pole from the NOAA Climate and Diagnostics Laboratory, Boulder, CO, for the period 1989-1998. (b) Data from Leuenberger and Siegenthaler (1992) from the Byrd ice core in West Antarctica.

Dansgaard, W., Johnsen, S. J., Clausen, H. B. et al. (1993). Evidence for general instability of past climate from a 250-kyr ice-core record. Nature 364, 218-220. 

Jouzel, J., Barkov, N. 1., Barnola, J. M. et al. (1993). Extending the Vostok ice-core record of paleoclimate to the penultimate glacial period. Nature 364, 407-412. 

Legrand, M., Feniet-Saigne, C., Saltzman, E. S. et al. (1991). Ice core record of oceanic emissions of dimethyl sulphide during the last climate cycle. Nature 350,144-146. 

Lorius, C., Jouzel, J., Raynaud, D. et al. (1990). The ice-core record climate sensitivity and future greenhouse warming. Nature 347,139-145. 

Thompson, L. et al. (1995). Late glacial stage and Holocene tropical ice core records from Huascaran, Peru. Science 269, 46-50. 

Figures 19-3d-f depict both the recent data from ice cores and the contemporary records of N2O, CH4, and CO2 during the most recent 250 years. These illustrate the profound changes that have occurred since the industrial revolution. Although the exact causes of the increases of N2O and CH4 are not yet fully agreed upon, there is no debate regarding the relationship of the increase of CO2 to the burning of fossil carbon and deforestation. In the case of CH4 and CO2, there is also excellent agreement between the ice-core records and the records from direct sampling of the atmosphere, which began in 1957 for CO2 and in ca. 1973 for CH4.

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