Millennial-scale atmospheric CO2 variations during the Marine Isotope Stage 6 period (190-135 ka)

Using new and previously published CO2 data from the EPICA Dome C ice core (EDC), we reconstruct a new high-resolution record of atmospheric CO2 during Marine Isotope Stage (MIS) 6 (190 to 135 ka) the penultimate glacial period. Similar to the last glacial cycle, where high-resolution data already exists, our record shows that during longer North Atlantic (NA) stadials, millennial CO2 variations during MIS 6 are clearly coincident with the bipolar seesaw signal in the Antarctic temperature record. However, during one short stadial in the NA, atmospheric CO2 variation is small (similar to 5 ppm) and the relationship between temperature variations in EDC and atmospheric CO2 is unclear. The magnitude of CO2 increase during Carbon Dioxide Maxima (CDM) is closely related to the NA stadial duration in both MIS 6 and MIS 3 (60-27 ka). This observation implies that during the last two glacials the overall bipolar seesaw coupling of climate and atmospheric CO2 operated similarly. In addition, similar to the last glacial period, CDM during the earliest MIS 6 show different lags with respect to the corresponding abrupt CH4 rises, the latter reflecting rapid warming in the Northern Hemisphere (NH). During MIS 6i at around 181.5 +/- 0.3 ka, CDM 6i lags the abrupt warming in the NH by only 240 +/- 320 years. However, during CDM 6iv (171.1 +/- 0.2 ka) and CDM 6iii (175.4 +/- 0.4 ka) the lag is much longer: 1290 +/- 540 years on average. We speculate that the size of this lag may be related to a larger expansion of carbonrich, southern-sourced waters into the Northern Hemisphere in MIS 6, providing a larger carbon reservoir that requires more time to be depleted.