Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation

Abstract

An understanding of the mechanisms that control CO2 change during glacial-interglacial cycles remains elusive. Here we help to constrain changing sources with a high-precision, high-resolution deglacial record of the stable isotopic composition of carbon in CO2(δ(13)C-CO2) in air extracted from ice samples from Taylor Glacier, Antarctica. During the initial rise in atmospheric CO2 from 17.6 to 15.5 ka, these data demarcate a decrease in δ(13)C-CO2, likely due to a weakened oceanic biological pump. From 15.5 to 11.5 ka, the continued atmospheric CO2 rise of 40 ppm is associated with small changes in δ(13)C-CO2, consistent with a nearly equal contribution from a further weakening of the biological pump and rising ocean temperature. These two trends, related to marine sources, are punctuated at 16.3 and 12.9 ka with abrupt, century-scale perturbations in δ(13)C-CO2 that suggest rapid oxidation of organic land carbon or enhanced air-sea gas exchange in the Southern Ocean. Additional century-scale increases in atmospheric CO2 coincident with increases in atmospheric CH4 and Northern Hemisphere temperature at the onset of the Bølling (14.6-14.3 ka) and Holocene (11.6-11.4 ka) intervals are associated with small changes in δ(13)C-CO2, suggesting a combination of sources that included rising surface ocean temperature.

Keywords: atmospheric CO2; carbon cycle; ice cores; last deglaciation; paleoclimate.

Fig. 1.

Carbon isotope records during the last deglaciation. Taylor Glacier δ¹³C-CO₂ data from this study (red). Previous work from Taylor Dome (gray open circles) (9), Grenoble EDC data (open green squares) (10), Bern EDC data (orange circles) (11, 45), sublimation measurements from EDC (blue triangles), and Talos Dome (purple squares) with an estimate of the 1-sigma uncertainty from a compilation of previous ice core δ¹³C-CO₂ data (11).

Fig. 2.

Carbon cycle changes of the last deglaciation. WAIS Divide continuous CH₄ (green) (14) and discrete CO₂ (blue) (13) concentration data plotted with Taylor Glacier CO₂ and δ¹³C-CO₂ data (this study) (red markers, black line is a smoothing spline), the five-point running Keeling intercept with shading indicating the R² for each time interval. Blue bars indicate intervals of rapid CO₂ rise identified in the WAIS Divide ice core (13).

Fig. 3.

Cross-plot of data constraints and model experiments. (A) Shaded lines show the range of model-based constraints on various carbon cycle processes as listed in SI Appendix, Table S1 (changes in ocean biological pump/circulation, yellow; deglacial increase in SST, blue; rapid release of land carbon, green; rapid change in Southern Ocean gas exchange, purple; CaCO₃ cycle, gray). (B) All Taylor Glacier data with arrows as guides to the approximate time path. (C) The data divided into the early HS1 (yellow) and later deglaciation (blue) modes of variability. Colored markers divide the data by time period and the shaded vectors indicate the linear regressions of the data with the 1-sigma uncertainty. (D) Further division of the data into the abrupt changes at The 16.3-ka event and onset of the YD (red). See SI Appendix, Table S2 for statistics.

Fig. 4.

Climate and carbon cycle changes during the last deglaciation. (A) Proxies for Greenland temperature (46) (purple), West Antarctic temperature (37, 47) (blue), East Asian precipitation (48) (green), dust delivery to Antarctica (30) (yellow), Southern Ocean upwelling (31) (blue markers), global temperature relative to the early Holocene (blue banding) (21), and the Taylor Glacier CO₂ and δ¹³C-CO₂ data (red). The red bars indicate periods of rapid δ¹³C-CO₂ decreases; blue bars indicate rapid CO₂ increases with slight increases or little change in δ¹³C-CO₂. B and C highlight the changes in temperature and atmospheric CO₂ at the centennial scale.