The glacial inception as recorded in the NorthGRIP Greenland ice core: timing, structure and associated abrupt temperature changes

Abstract

The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception ($123-100 kyears BP) encompassing Dansgaard-Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of 10±2.5 and 16±2.5°C, amplitudes which mimic those observed in full glacial conditions. We use records of d 18 O of O 2 to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years, and to examine the interhemispheric sequence of events over this period. After a synchronous North-South temperature decrease, the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to intermediate levels of CO 2 and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24 and 23 appear similar to typical full glacial DO events.

Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period

“…The uncertainties associated with the durations of GIS/GS 24, 23, 22 and 21 represent less than 19% of the duration of each DO event. This general agreement makes the Huber et al (2006) and Landais et al (2006) provide a quantification of abrupt temperature change through air isotopes measurements of most of the rapid events over the last glacial period and our study provides new results of temperature estimates at the onset of GIS 21 and GIS 22. d Spatial slope deduced at the onset of each rapid event as α= δ 18 O ice / T . Note that a ±2.5 • C uncertainty on temperature change is translated to an error of ∼0.2 in the calculation of α. e GS durations are given (1) on the GICC05 age scale for GS 2 to GS 12 Svensson et al, 2008), (2) on ss09sea age scale for GS 18 to GS 20 (NorthGRIP c.m., 2004) and (3)on the EDML-NorthGRIP synchronised timescale for GS 21 to GS 24 .…”

“…The "iconic" DO event structure is depicted as a GIS, beginning with an abrupt warming of 8 to 16 • C in mean annual surface temperature within a few decades (Severinghaus et al, 1998;Lang et al, 1999;Landais et al, 2004a;Landais et al, 2006; see also Wolff et al, 2009a for a review). The GIS is then usually characterized by a gradual cooling phase lasting several centuries and its end is marked by a rapid cooling towards a relatively stable cold phase (GS) that persists over several centuries to a thousand of years.…”

Spatial gradients of temperature, accumulation and δ<sup>18</sup>O-ice in Greenland over a series of Dansgaard–Oeschger events

“…Using δ 15 N data and firn modeling, past surface temperature variations can be reconstructed (Schwander et al, 1997;Goujon et al, 2003). This method has already been applied to specific DO events on the NGRIP, GRIP and GISP2 ice cores (Lang et al, 1999;Huber et al, 2006;Landais et al, 2004aLandais et al, , 2005Goujon et al, 2003;Severinghaus and Brook, 1999;Capron et al, 2010) and will be applied here for the first time to the NEEM ice core.…”

A tropical speleothem record of glacial inception, the South American Summer Monsoon from 125 to 115 ka

“…3. The δ 18 O atm values reach a first minimum following MIS 5.5 that is coincident with the first minimum in atmospheric methane, which the speleothem chronologies place at 116 ka, just at the transition from Glacial Stadial (GS) 25 to GIS 25 (Landais et al, 2006). We show the EDC ice core methane record because it is higher resolution than Vostok methane (note that both are on the same timescale).…”