PICE Talk by Michael Dyonisius

Recent development in 14CO2 proxy from ice cores and case for using it to disentangle the sources of abrupt CO2 rise during Heinrich stadial 1.

Michael Dyonisius1, Kathleen Wendt2, Christo Buizert2, Vasilii Petrenko3

1Physics of Ice Climate and Earth, Niels Bohr Institute, University of Copenhagen

2College of Earth, Ocean, and Atmospheric Sciences, Oregon State University

3Department of Earth and Environmental Sciences, University of Rochester

Radiocarbon (14C) dating of glacial ice and accurate reconstruction of paleoatmospheric 14CO2 from ice cores have been a longstanding goal in ice core science (Oeschger et al., 1966). Achieving these goals had hitherto been challenging because 14C in ice is also produced in situ (directly in the ice lattice) from reactions with secondary cosmic rays (Lal et al., 1990). This talk will be divided into two parts. First, I will provide an overview on our recent paper (Dyonisius et al. 2022) where we constrained the in situ 14C production rate using 14C measurements in old (>50 kyr) ablating ice from Taylor Glacier, Antarctica. We then calculated how well can we reconstruct the paleoatmospheric Δ14CO2 signal from the Hercules Dome ice core (which is likely the next available deep Antarctic ice core in the US Drilling Program). The abrupt (~15 ppm) [CO2] rise over Heinrich stadial (HS) 1 (16,140 to 16,070 yr BP; Marcott et al., 2014) provides an ideal case study. The largest depletion in atmospheric δ13C-CO2 during the deglaciation (Bauska et al., 2016) also occurred concurrently with this abrupt [CO2] rise. Several hypotheses such as reduced iron fertilization, CO2 release from terrestrial sources, and increased circumpolar deepwater upwelling (due to enhanced southern hemisphere westerlies) have been put forward to explain the [CO2] rise and δ13C-CO2 depletion. However, constraints from [CO2] and δ13C-CO2 alone were not enough to disentangle these processes (Bauska et al., 2016). ). As both reduced iron fertilization and CO2 release from terrestrial source do not affect atmospheric Δ14CO2, a high resolution reconstruction of paleoatmospheric Δ14CO2 can provide a definitive constraint on the contribution of old carbon from Southern Ocean upwelling (Menviel et al., 2018). Unfortunately, Δ14CO2 ­reconstruction from IntCal20 (Reimer et al., 2020) is not available at high enough resolution and precision for this time period. We show that using our state-of-the-art extraction and measurement system, we can reconstruct paleoatmospheric (age-corrected) Δ14CO2 to ±47‰ (absolute) and ±35‰ (relative) precision (1σ) for HS1 (16kyr BP). These measurements would allow us to specifically test the hypothesis put forward by Menviel et al. (2018) and quantify the contribution of old carbon from Southern Ocean upwelling during HS1 at centennial scale – if we drill a replicate core in Hercules Dome because we need 1kg of ice per measurement.  


Bauska, T. K., et al.: Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation, PNAS, 113, 3465–3470, https://doi.org/10.1073/pnas.1513868113, 2016.

Dyonisius, M.N., et al.: Using ice core measurements from Taylor Glacier, Antarctica to calibrate in situ cosmogenic 14 C production rates by muons." The Cryosphere. in press (2022): 1-35.

Lal, D., et al.: Polar ice ablation rates measured using in situ cosmogenic 14C, Nature, 346, 350–352, https://doi.org/10.1038/346350a0, 1990.

Marcott, S. A., et al.: Centennial-scale changes in the global carbon cycle during the last deglaciation, Nature, 514, 616–619, https://doi.org/10.1038/nature13799, 2014.

Menviel, L., et al.: Southern Hemisphere westerlies as a driver of the early deglacial atmospheric CO2 rise, Nat Commun, 9, 2503, https://doi.org/10.1038/s41467-018-04876-4, 2018.

Oeschger, H., et al.: Radiocarbon dating of ice, Earth and Planetary Science Letters, 1, 49–54, 1966.

Reimer, P. J., et al.: The IntCal20 northern hemisphere radiocarbon age calibration curve (0–55 cal kBP), Radiocarbon, 62, 725–757, 2020.