Chronology reconstruction for the disturbed bottom section of the GISP2 and the GRIP ice cores: Implications for Termination II in Greenland

Abstract

[1] We have reconstructed chronology for the disturbed bottom parts of the GRIP and GISP2 ice cores using the combined paleoatmospheric records of CH 4 concentration and d18 O atm in the trapped gases. Our reconstructed ages for basal ice samples are based on comparison of published measurements of CH 4 and d18 O atm from the disturbed section of the GRIP and GISP2 cores with the same properties in the Vostok ice core. NGRIP d18 O ice values are also used to constrain the chronology during the end of marine isotope stage 5e. For each sample, we assign an age that represents the unique or most probable time of gas trapping, given its gas composition. Of 157 samples with CH 4 and d 18 O atm data, 10 give unique ages. Twenty-five newly measured values of the triple isotope composition of O 2 from the disturbed section of the GISP2 core add a third time-dependent gas property that agrees with our reconstruction. Our reconstruction supports earlier conclusions of Landais et al. (2003) that the disturbed section primarily includes ice from the last interglacial (MIS 5e) and the penultimate glacial period (MIS 6). The oldest ice in the basal layer of GISP2 and GRIP has an age !237 ka. The climate history we derive suggests that the last interglacial at Summit, Greenland, around 127 ka was slightly warmer than the current interglacial period. Reduction of various ion concentrations in ice and thickening of the ice sheet during Termination II was similar to that in Termination I.Citation: Suwa, M., J. C. von Fischer, M. L. Bender, A. Landais, and E. J. Brook (2006), Chronology reconstruction for the disturbed bottom section of the GISP2 and the GRIP ice cores: Implications for Termination II in Greenland,

Sea level ~400 000 years ago (MIS 11): analogue for present and future sea-level?

“…Others (Rohling et al, 2009), however, estimated that a 20 m rise in sea-level would involve the melting of both West Antarctic and Greenland ice-sheets. Note, the Greenland ice sheet did not melt entirely during MIS 7 (Suwa et al, 2006) when sea-level was below present (Bard et al, 2002;Dutton et al, 2009), and the potential to raise present sea-levels with contributions of meltwater from the Greenland or Antarctic ice sheets is dominated by uncertainties (Alley et al, 2005). An MIS 11 sea-level at or close to present does not require melting of the West Antarctic and Greenland ice sheets because only 140 m of sea-level rise is required.…”

A brief history of ice core science over the last 50 yr

“…Due to the proximity of the bedrock, such disturbances can be identified by a mismatch between the gas records derived for a given period from this Greenland ice and from the Antarctic undisturbed record (Bender et al, 1994b;Fuchs and Leuenberger, 1996;Chappellaz et al, 1997), and/or by the lack of a depth difference between a climatic event, such as a rapid change, recorded both in the ice and in the entrapped air (Landais et al, 2004c). Combined with isotopic measurements in ice, these gas data can also be used to recontruct, at least partly, the correct ice sequence Suwa et al, 2006). The same strategy has been used to extend the Greenland Eemian sequence from the NEEM folded ice core, partly covered in the North GRIP core (North GRIP community, 2004), back to 128.5 kyr BP (NEEM community).…”

Melting of Northern Greenland during the last interglaciation

“…Due to the expansion of ice at the last glacial maximum and the erosion of potential archives, few reliable proxy data exist for Eemian ice extent except for the Greenland ice cores. The bottom sections of the summit cores (GISP2, GRIP, NGRIP) and the northwestern core at Camp Century contain Eemian ice (Dansgaard et al, 1985;Chappellaz et al, 1997;NGRIP-members, 2004;Landais et al, 2004;Suwa et al, 2006), indicating that the GrIS covered these locations. Tentative results from the NEEM also suggest the existence of Eemian ice (Foresta, 2011).…”