Temperature reconstruction from 10 to 120 kyr b2k from the NGRIP ice core

M Leuenberger,M Baumgartner,M Guillevic,P Kindler,A Landais,J Schwander

doi:10.5194/cp-10-887-2014

Abstract

Abstract. In order to reconstruct the temperature of the North Greenland Ice Core Project (NGRIP) site, new measurements of δ15N have been performed covering the time period from the beginning of the Holocene to Dansgaard–Oeschger (DO) event 8. Together with previously measured and mostly published δ15N data, we present for the first time a NGRIP temperature reconstruction for the whole last glacial period from 10 to 120 kyr b2k (thousand years before 2000 AD) including every DO event based on δ15N isotope measurements combined with a firn densification and heat diffusion model. The detected temperature rises at the onset of DO events range from 5 °C (DO 25) up to 16.5 °C (DO 11) with an uncertainty of ±3 °C. To bring measured and modelled data into agreement, we had to reduce the accumulation rate given by the NGRIP ss09sea06bm timescale in some periods by 30 to 35%, especially during the last glacial maximum. A comparison between reconstructed temperature and δ18Oice data confirms that the isotopic composition of the stadial was strongly influenced by seasonality. We evidence an anticorrelation between the variations of the δ18Oice sensitivity to temperature (referred to as α) and obliquity in agreement with a simple Rayleigh distillation model. Finally, we suggest that α might be influenced by the Northern Hemisphere ice sheet volume.

Highlights

Deep ice core drilling in Greenland revealed large millennial scale variability in the water isotopic composition δ18Oice during the last glacial, reflecting local temperature variations (Johnsen et al, 1972; Dansgaard et al, 1982), known today as Dansgaard–Oeschger (DO) events
The 25 DO events identified in the North Greenland Ice Core Project (NGRIP) ice core (NGRIP members, 2004) are characterised by a rapid temperature increase followed by a gradual cooling back to stadial conditions
A southward shift of the Intertropical Convergence Zone (ITCZ) during Greenland cold events is suggested to explain the similar DO pattern seen in Greenland ice cores and in tropical records (Chiang and Bitz, 2005)

Summary

Introduction

Deep ice core drilling in Greenland revealed large millennial scale variability in the water isotopic composition δ18Oice during the last glacial, reflecting local temperature variations (Johnsen et al, 1972; Dansgaard et al, 1982), known today as Dansgaard–Oeschger (DO) events. The 25 DO events identified in the North Greenland Ice Core Project (NGRIP) ice core (NGRIP members, 2004) are characterised by a rapid temperature increase followed by a gradual cooling back to stadial conditions These rapid temperature variations are at least of northern hemispheric extent (Voelker, 2002) and can be clearly traced in different ice core climate proxies, for example, δ18Oice (Dansgaard et al, 1993), dust content (Ruth et al, 2003) and other aerosol contents (Mayewski et al, 1997), greenhouse gas concentrations (Huber et al, 2006b; Schilt et al, 2010), as well as in other climate proxies such as sea sediments (Bond et al, 1993; Deplazes et al, 2013) and speleothems (Fleitmann et al, 2009; Kanner et al, 2012; Wang et al, 2001).

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