Atmospheric carbon dioxide occluded in the Siple Dome ice core, Antarctica, and its application to climate change

Understanding how the atmospheric concentration of CO2 changed in the past in response to other changes in the climate system provides us with a better understanding of how current and future changes in the carbon cycle will influence our future climate.; This study found that the general trend of the CO2 concentration from the Siple Dome ice follows the temperature and is mostly in agreement with other Antarctic ice core CO2 records. During the last glacial termination, a lag of CO2 versus Siple Dome isotopic temperature is suggested. These results strongly support previous suggestions of a close link between Antarctic temperature and CO2 change during the last deglaciation.; Studying melt layers contained in the core provided unique information on CO2 diffusion in ice. On the basis of a combined study of noble gases (Xe/Ar and Kr/Ar), electrical conductivity, and Ca2+ ion content, for the first time it was confirmed that substantial CO 2 diffusion through the ice occurs on timescales of thousands of years. The product of the diffusion constant and the solubility was obtained as 4.3 (+/-2.1) x 10-21 m2s -1 molCO2 m-3ice (PaCO 2)-1 at -23°C. This work shows that the smoothing of the CO2 record in the core by diffusion is one to two orders of magnitude smaller than the smoothing induced by the gas age distribution at the depth of 287 m (gas age = 2.74 kyrBP, thousand years before 1950) in the Siple Dome ice.; Further results of this research found that Siple Dome CO2 concentrations during the last deglaciation and in the Holocene are at certain times greater than those in other Antarctic ice cores by up to 20 ppm (mumol CO2/mol air). Snow melting/refreezing is suggested as the main cause of the excess CO2. These results show that Antarctic ice samples from relatively warm sites are not an accurate proxy for paleoatmospheric CO2.; Finally, carbon isotope studies on CO2 for the Siple Dome (last 40 kyr) and Vostok (160--110 kyr) ice cores from Antarctica, extend and confirm the previous results from the Taylor Dome ice core covering the last 28 kyr. However, the data are scattered and depleted on average compared to those from the Taylor Dome ice core, and are not considered a reliable atmospheric record. Future studies should include a sublimation method for bubble-free ice in order to avoid isotopic fractionation during gas extraction from the ice.