Chronology of deglaciations over the last 800,000 years based on glacial and marine archives

The Quaternary period is marked by cycles of deglaciation. These large-scale changes mark the transition from glacial to interglacial conditions and are typically associated with a rise in the sea level, recorded in marine cores, as well as an increase in atmospheric CO2 concentration, recorded in ice cores. The exact sequence of events during deglaciations remains a subject of debate. It is therefore essential to understand the cause-effect relationships between orbital forcing and climatic response (atmospheric greenhouse gas concentration, sea level, and temperature).

Temporal offset in the onset and end of significant increases in atmospheric CO2 and sea level during deglaciations are observed and generate considerable interest. However, each paleoclimate site and archive employs its own dating methods, which are not always consistent with each other. Therefore, disagreements between chronologies are observed if no harmonization is performed. This makes it difficult to estimate the lag between the two climatic parameters variations during deglaciations.

To address this problem, we propose a methodology for constructing a coherent, relative, and absolute chronology between marine and ice archives over the last seven deglaciations using the statistical tool Paleochrono-1.1; and provide robust uncertainty esti mates. By fitting ramp functions to the deglacial rises observed in sea level proxy and atmospheric CO2content, we found a lead from 1 to 5.5 kyr of atmospheric CO2 with respect to the sea level proxy across six of the seven latest deglaciations. The lead-lag relationships identified in our study sometimes disagree (by more than 1σ) with the timings estimated using independent and thus incomparable chronologies. article…

Fig: Temporal phasing at the onset and end for the past seven Terminations between the benthic δ18O records of a north Atlantic core and the atmospheric CO2 concentration records of EDC. The timings of end/onset are identified by the Rampfit model as well as visually for the end of TV and TIV for which a pronounced overshoot is observed in the CO2. A negative/positive phasing posits that the onset or end of the deglacial increase in atmospheric CO2 concentration leads/lags the change in the benthic δ18O record. The gray rectangles represent the results for the onset of each Termination. The temporal phasing estimates provided by coherent chronologies shown by garnet, orange and purple dots respectively. The vertical bars indicate the envelope of the posterior uncertainty yielded by the Paleochrono-1.1 model. The temporal phasing that can be estimated using independent chronologies are also depicted by blue squares (EDC age on AICC2023 vs. U1308 age by Hodell et al. (2008)) and red squares (EDC age on AICC2023 vs. LR04 stack age by Lisiecki and Raymo (2005)).

authors: Ellyn Auriol, Amaëlle Landais, Marie Bouchet