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.  

References

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.