Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores

• Published in: Climate of the Past
• Main Authors: Bazin, Lucie, Landais, Amaelle, Capron, Emilie, Masson-Delmotte, Valérie, Ritz, Catherine, Picard, Ghislain, Jouzel, Jean, Dumont, Marie, Leuenberger, Markus, Prié, Frédéric
• Format: Text
• Language: English
• Published: 2018
• Subjects: Antarctic; Dome F; Greenland; Antarc*; EPICA; Greenland ice cores; ice core
• Online Access: https://doi.org/10.5194/cp-12-729-2016; https://cp.copernicus.org/articles/12/729/2016/

Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousands of years before 1950) for Greenland ice cores. While several complementary orbital tuning tools have recently been developed using δ 18 O atm , δ O 2 ⁄N 2 and air content with different orbital targets, quantifying their uncertainties remains a challenge. Indeed, the exact processes linking variations of these parameters, measured in the air trapped in ice, to their orbital targets are not yet fully understood. Here, we provide new series of δ O 2 ∕N 2 and δ 18 O atm data encompassing Marine Isotopic Stage (MIS) 5 (between 100 and 160 ka) and the oldest part (340–800 ka) of the East Antarctic EPICA Dome C (EDC) ice core. For the first time, the measurements over MIS 5 allow an inter-comparison of δ O 2 ∕N 2 and δ 18 O atm records from three East Antarctic ice core sites (EDC, Vostok and Dome F). This comparison highlights some site-specific δ O 2 ∕N 2 variations. Such an observation, the evidence of a 100 ka periodicity in the δ O 2 ∕N 2 signal and the difficulty to identify extrema and mid-slopes in δ O 2 ∕N 2 increase the uncertainty associated with the use of δ O 2 ∕N 2 as an orbital tuning tool, now calculated to be 3–4 ka. When combining records of δ 18 O atm and δ O 2 ∕N 2 from Vostok and EDC, we find a loss of orbital signature for these two parameters during periods of minimum eccentricity (∼ 400 ka, ∼ 720–800 ka). Our data set reveals a time-varying offset between δ O 2 ∕N 2 and δ 18 O atm records over the last 800 ka that we interpret as variations in the lagged response of δ 18 O atm to precession. The largest offsets are identified during Terminations II, MIS 8 and MIS 16, corresponding to periods of destabilization of the Northern polar ice sheets. We therefore suggest that the occurrence of Heinrich–like events influences the response of δ 18 O atm to precession.