We present new d13C measurements of atmospheric CO2 covering the last glacial/interglacial cycle, complementing previous records covering Terminations I and II. Most prominent in the new record is a significant depletion in d13C(atm) of 0.5 permil occurring during marine isotope stage (MIS) 4, followed by an enrichment of the same magnitude at the beginning of MIS 3. Such a significant excursion in the record is otherwise only observed at glacial terminations, suggesting that similar processes were at play, such as changing sea surface temperatures, changes in marine biological export in the Southern Ocean (SO) due to variations in aeolian iron fluxes, changes in the Atlantic meridional overturning circulation, upwelling of deep water in the SO, and long-term trends in terrestrial carbon storage. Based on previous modeling studies, we propose constraints on some of these processes during specific time intervals. The decrease in d13C(atm) at the end of MIS 4 starting approximately 64 kyr B.P. was accompanied by increasing [CO2]. This period is also marked by a decrease in aeolian iron flux to the SO, followed by an increase in SO upwelling during Heinrich event 6, indicating that it is likely that a large amount of d13C-depleted carbon was transferred to the deep oceans previously, i.e., at the onset of MIS 4. Apart from the upwelling event at the end of MIS 4 (and potentially smaller events during Heinrich events in MIS 3), upwelling of deep water in the SO remained reduced until the last glacial termination, whereupon a second pulse of isotopically light carbon was released into the atmosphere.

These data complement previously published d13CO2 datasets: * Schmitt, J et al. (2012): Measurements of stable carbon isotope ratios of CO2 over the last 24000 years and CO2 concentration measurements on Antarctic ice cores using three different methods. doi:10.1594/PANGAEA.772713. * Schneider, R et al. (2013): A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the glacial inception. doi:10.1594/PANGAEA.817041. The CO2 concentration and stable isotope data were measured on the following three Antarctic ice cores covering the period from 149.4 - 1.5 kyr before 1950: European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) (lat = -75.10, lon = 123.40) EPICA Dronning Maud Land (EDML) (lat = -75.00, lon = 0.07) Talos Dome (lat = -72.82, lon = 159.18)

Supplement to: Eggleston, Sarah; Schmitt, Jochen; Bereiter, Bernhard; Schneider, Robert; Fischer, Hubertus (2016): Evolution of the stable carbon isotope composition of atmospheric CO2 over the last glacial cycle. Paleoceanography, 31, n/a-n/a