Duration of Greenland Stadial 22 and ice-gas Δage from counting of annual layers in Greenland NGRIP ice core

Abstract

Abstract. High-resolution measurements of chemical impurities and methane concentrations in Greenland ice core samples from the early glacial period allow the extension of annual-layer counted chronologies and the improvement of gas age-ice age difference ( age) essential to the synchronization of ice core records. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses in order to constrain the duration of the Greenland Stadial 22 (GS-22) between Greenland Interstadials (GIs) 21 and 22, for which inconsistent durations and ages have been reported from Greenland and Antarctic ice core records as well as European speleothems. Depending on the chronology used, GS-22 occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21). From annual layer counting, we find that GS-22 lasted between 2696 and 3092 years and was followed by a GI-21 pre-cursor event lasting between 331 and 369 yr. Our layer-based counting agrees with the duration of stadial 22 as determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr) or an alternative chronology based on gas-marker synchronization to EPICA Dronning Maud Land ice core. These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the possible ranges of NorthGRIP depth (5.49 to 5.85 m) and age (498 to 601 yr) at the warming onset of GI-21 as well as the age range at the onset of the GI-21 precursor warming (523 to 654 yr), observing that temperature (represented by the δ 15 N proxy) increases before CH 4 concentration by no more than a few decades.

A first chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core

“…The δ 15 N provides a strong constraint on both the timing and magnitude of abrupt temperature changes over Greenland through the imprint of thermal isotopic fractionation (Leuenberger et al, 1999;Severinghaus et al, 1998) and on past firn column thickness through the imprint of gravita- (Chappellaz et al, 2013). tional isotopic fractionation (Sowers et al, 1992). CH 4 variations are in phase with Greenland temperature, with CH 4 lagging temperature by 0-70 yr Landais et al, 2004;Severinghaus and Brook, 1999;Vallelonga et al, 2012). Thus, we obtain additional timing constraints by assuming the midpoint of the CH 4 transition to slightly lag the midpoint in the δ 18 O transition at the abrupt onset of Greenland interstadials (GI); for simplicity we use a constant lag of 30 yr for most transitions, with the exception of interstadials 9-11 where available δ 15 N data indicate no lag.…”

Annual proxy data from Lago Grande di Monticchio (southern Italy) between 76 and 112 ka: new chronological constraints and insights on abrupt climatic oscillations

“…MON 4 (Melisey 2) correlates with GS 22. The duration of GS 22 is still under discussion and varies in different ice core chronologies between 2480 years (GICC05 modelext ), 2620 years (revised GICC05 modelext timescale; Vallelonga et al, 2012) and 2760 years (AICC2012; Veres et al, 2013). All ages suggest a shorter duration than determined in the NALPS record (3250 ± 526 varve yr), which in turn is in good agreement with the Monticchio estimate of MON 4 (3162 ± 51 varve yr; Table 2; Fig.…”

“…7). The δ 18 O ice NorthGRIP record is displayed both on the updated GICC05 modelext (Wolff et al, 2010) and the AICC2012 timescales (Bazin et al, 2013;Veres et al, 2013) uncertainties. Since we do not presume synchronicity between climate change in the different regions and different proxy responses, we explicitly omit from shifting either of the chronologies in order to match them together.…”

“…On the other hand, the NALPS chronology provides good dates but the record shows discontinuities during the stadial periods, when the stalagmites stopped growing due to cooler conditions. Thus, there are still dating differences of several millennia between the ice-core chronologies and between those and the NALPS timescale (Veres et al, 2013).…”

“…However, a detailed discussion about regional synchronicity is still hampered by the large dating uncertainty due to limitations in the chronologies. The NorthGRIP ice core record is not annually layered beyond 60 ka, hence the age depth models show bigger absolute uncertainties: for instance, the GICC05 modelext timescale, which is based on data from the Greenland ice core records (Wolff et al, 2010), and the AICC2012 chronology, which was developed for four Antarctic ice cores and the NorthGRIP record (Bazin et al, 2013;Veres et al, 2013). On the other hand, the NALPS chronology provides good dates but the record shows discontinuities during the stadial periods, when the stalagmites stopped growing due to cooler conditions.…”