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Abstract
Abstract. 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 (∼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 carbon-rich, southern-sourced waters into the Northern Hemisphere in MIS 6, providing a larger carbon reservoir that requires more time to be depleted.
Highlights
Ice core studies allow us to considerably extend our knowledge about natural climate–carbon cycle feedbacks by directly reconstructing atmospheric CO2 from gas preserved in Antarctic ice sheets (Lüthi et al, 2008; Petit et al, 1999)
To improve the resolution of our new dataset even further, we made a composite dataset by aligning previous sets of CO2 measurements made over the Marine Isotope Stage (MIS) 6 period on the EPICA Dome C ice core (EDC) ice core to our new data
Similar to the Antarctic Isotope Maxima (AIM) amplitude (Capron et al, 2010; EPICA Community Members, 2006), we found that the amplitude of atmospheric CO2 variations is well correlated to the North Atlantic (NA) stadial duration during MIS 6 and MIS 3, which implies that the amplitude of CO2 variations might be affected by the duration of Atlantic Meridional Overturning Circulation (AMOC) disruption during the early MIS 6 period (Margari et al, 2010)
Summary
Ice core studies allow us to considerably extend our knowledge about natural climate–carbon cycle feedbacks by directly reconstructing atmospheric CO2 from gas preserved in Antarctic ice sheets (Lüthi et al, 2008; Petit et al, 1999). A phase difference can be observed between millennial-scale variations of temperature in the NH and SH (Northern Hemisphere and Southern Hemisphere, respectively), which is referred to as the bipolar seesaw phenomenon (Blunier and Brook, 2001; Pedro et al, 2018; Stocker and Johnsen, 2003) Potential triggers for this climatic variability on the millennial scale are fresh water perturbation in the North Atlantic (NA) or alterations of sea ice extent, surface temperature and salinity in the NA (Bond et al, 1992; Broecker et al, 1992; Heinrich, 1988; McManus et al, 1998), which may reduce the strength of the Atlantic Meridional Overturning Circulation (AMOC). This would cause a reduction in heat transport from the SH to the NH, which leads to an abrupt cooling in the NA region and a gradual warming in the SH (Stocker and Johnsen, 2003) and the opposite behavior when AMOC is strengthened
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