Abrupt rise in atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; at the onset of the Bølling/Allerød: in-situ ice core data versus true atmospheric signals

P Köhler,J Chappellaz,G Knorr,A Lourantou,D Buiron

doi:10.5194/cp-7-473-2011

Abstract

Abstract. During the last glacial/interglacial transition the Earth's climate underwent abrupt changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A was accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is a matter of current debate. In-situ measured CO2 in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10 ± 1 ppmv in 230 yr at the same time. Allowing for the modelled age distribution of CO2 in firn, we show that atmospheric CO2 could have jumped by 20–35 ppmv in less than 200 yr, which is a factor of 2–3.5 greater than the CO2 signal recorded in-situ in EDC. This rate of change in atmospheric CO2 corresponds to 29–50% of the anthropogenic signal during the last 50 yr and is connected with a radiative forcing of 0.59–0.75 W m−2. Using a model-based airborne fraction of 0.17 of atmospheric CO2, we infer that 125 Pg of carbon need to be released into the atmosphere to produce such a peak. If the abrupt rise in CO2 at the onset of the B/A is unique with respect to other Dansgaard/Oeschger (D/O) events of the last 60 kyr (which seems plausible if not unequivocal based on current observations), then the mechanism responsible for it may also have been unique. Available δ13CO2 data are neutral, whether the source of the carbon is of marine or terrestrial origin. We therefore hypothesise that most of the carbon might have been activated as a consequence of continental shelf flooding during MWP-1A. This potential impact of rapid sea level rise on atmospheric CO2 might define the point of no return during the last deglaciation.

Highlights

Measurements of CO2 over Termination I (20–10 kyr BP) from the EPICA Dome C (EDC) ice core (Monnin et al, 2001; Lourantou et al, 2010) (Fig. 1b) are temporally higher resolved and more precise than CO2 records from other ice cores (Smith et al, 1999; Ahn et al, 2004)
The B/A was accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is a matter of current debate
Our analysis provides evidence that changes in the true atmospheric CO2 at the onset of the B/A include the possibility of an abrupt rise by 20–35 ppmv within less than two centuries

Summary

Introduction

Measurements of CO2 over Termination I (20–10 kyr BP) from the EPICA Dome C (EDC) ice core (Monnin et al, 2001; Lourantou et al, 2010) (Fig. 1b) are temporally higher resolved and more precise than CO2 records from other ice cores (Smith et al, 1999; Ahn et al, 2004). They have an uncertainty (1σ ) of 1 ppmv or less (Monnin et al, 2001; Lourantou et al, 2010). The B/A is accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A (Peltier and Fairbanks, 2007), whose exact timing is matter of current debate (e.g. Hanebuth et al, 2000; Kienast et al, 2003; Stanford et al, 2006; Deschamps et al, 2009).

Methods

Results

Conclusion