| Summary: | New ice cores retrieved from the Taylor Glacier (Antarctica) blue ice area contain ice and air spanning the Marine Isotope Stage (MIS) 5/4 transition, a period of global cooling and ice sheet expansion. Chronologies were determined for the ice and air bubbles in the new ice cores by visually matching variations in gas and ice phase tracers to preexisting ice core records. The chronologies reveal an ice age gas age difference (Δage) approaching 10 ka during MIS 4, implying very low snow accumulation in the Taylor Glacier accumulation zone. A revised chronology for the analogous section of the Taylor Dome ice core (84 to 55 ka), located to the south of the Taylor Glacier accumulation zone, shows that Δage did not exceed 3 ka. The difference in Δ age between the two records during MIS 4 is similar magnitude but opposite direction of what is observed at the last glacial maximum. This relationship implies that a spatial gradient in snow accumulation existed across the Taylor Dome region during MIS 4 that was oriented in the opposite direction of the accumulation gradient during the last glacial maximum. An enduring problem in paleoclimatology is to mechanistically explain the full 80 ppm change in atmospheric CO₂ concentration that accompanied glacial-interglacial climate cycles in the past. A record of the stable isotopic composition of atmospheric CO₂ (δ¹³ C-CO₂) was developed that spans the interval 74- 59.5 ka, including the period of global cooling and ice sheet growth known as the marine isotope stage (MIS) 5/4 transition. The interval contains small (~ 10 ppm) variability in CO₂ concentration associated with Dangaard-Oeschger (DO) event 19, the 40 ppm drop in CO₂ across the MIS 5/4 transition, and the 35 ppm rise in CO₂ associated with the MIS 4/3 transition. The δ¹³ C-CO₂ record reveals large and fast changes at specific time intervals, implying that different carbon cycle mechanisms controlled the atmospheric CO₂ concentration at distinct times. The isotope data are generally consistent with proxy data in ...
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