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

Shin, Jinhwa; Nehrbass-Ahles, Christoph; Grilli, Roberto; Chowdhry Beeman, Jai; Parrenin, Frédéric; Teste, Grégory; Landais, Amaelle; Schmidely, Loïc; Silva, Lucas; Schmitt, Jochen; Bereiter, Bernhard; Stocker, Thomas F.; Fischer, Hubertus; Chappellaz, Jérôme (2020). Millennial-scale atmospheric CO2 variations during the Marine Isotope Stage 6 period (190–135 ka). Climate of the past, 16(6), pp. 2203-2219. Copernicus Publications 10.5194/cp-16-2203-2020

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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 highresolution
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 (ca. 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.

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