Recent changes in north-west Greenland climate documented by NEEM shallow ice core data and simulations, and implications for past-temperature reconstructions

Valérie Masson‐Delmotte ,N Paradis,A Landais,S Falourd,Emmanuel Garnier ,Trevor Popp ,Hera Guðlaugsdóttir ,Martin Werner ,Hubert Gallée ,Didier Swingedouw ,Hans Oerter ,Anaïs Orsi ,Jason E Box ,Vasileios Gkinis ,Árný E Sveinbjörnsdóttir ,Camille Risi ,Pablo Ortega ,Jean Jouzel ,Hans Christian Steen‐Larsen ,Xavier Fettweis ,Bénédicte Minster ,Bo M Vinther ,James W C White

doi:10.5194/tc-9-1481-2015

Abstract

Abstract. Combined records of snow accumulation rate, δ18O and deuterium excess were produced from several shallow ice cores and snow pits at NEEM (North Greenland Eemian Ice Drilling), covering the period from 1724 to 2007. They are used to investigate recent climate variability and characterise the isotope–temperature relationship. We find that NEEM records are only weakly affected by inter-annual changes in the North Atlantic Oscillation. Decadal δ18O and accumulation variability is related to North Atlantic sea surface temperature and is enhanced at the beginning of the 19th century. No long-term trend is observed in the accumulation record. By contrast, NEEM δ18O shows multidecadal increasing trends in the late 19th century and since the 1980s. The strongest annual positive δ18O values are recorded at NEEM in 1928 and 2010, while maximum accumulation occurs in 1933. The last decade is the most enriched in δ18O (warmest), while the 11-year periods with the strongest depletion (coldest) are depicted at NEEM in 1815–1825 and 1836–1846, which are also the driest 11-year periods. The NEEM accumulation and δ18O records are strongly correlated with outputs from atmospheric models, nudged to atmospheric reanalyses. Best performance is observed for ERA reanalyses. Gridded temperature reconstructions, instrumental data and model outputs at NEEM are used to estimate the multidecadal accumulation–temperature and δ18O–temperature relationships for the strong warming period in 1979–2007. The accumulation sensitivity to temperature is estimated at 11 ± 2 % °C−1 and the δ18O–temperature slope at 1.1 ± 0.2 ‰ °C−1, about twice as large as previously used to estimate last interglacial temperature change from the bottom part of the NEEM deep ice core.

Highlights

Under the auspices of the International Polar Year and the International Partnership for Ice Core Science, a camp was operated in 2007–2012 at NEEM (North Greenland Eemian Ice Drilling, 77.45◦ N, 51.06◦ W, 2450 m a.s.l.; Fig. 1), in order to retrieve an ice core record spanning the last interglacial period
NEEM shallow ice core records are affected by changes in atmospheric circulation, but with weaker relationships with winter North Atlantic Oscillation (NAO) than in central or southern Greenland; we confirm the impact of the Atlantic Ridge and Greenland blocking weather regimes in north-west Greenland
NEEM climate variability is marked by a large multidecadal variability, which is closely related to the Atlantic Multidecadal Oscillation indices and enhanced at the beginning of the 19th century

Summary

Introduction

Under the auspices of the International Polar Year and the International Partnership for Ice Core Science, a camp was operated in 2007–2012 at NEEM (North Greenland Eemian Ice Drilling, 77.45◦ N, 51.06◦ W, 2450 m a.s.l.; Fig. 1), in order to retrieve an ice core record spanning the last interglacial period. Large uncertainties remain attached to the interglacial temperature reconstruction, which relies on the interpretation of water-stable isotopes (δ18O) and on the mechanisms of climate variability in north-west Greenland. In this introduction, we briefly review the state of the art with respect to the isotope–temperature relationship in Greenland and at NEEM, and the large-scale drivers of Greenland recent climate variability, before introducing our methodology and the outline of this manuscript. For warmer than present-day climates, atmospheric models produced a range of coefficients varying from 0.3 to 0.8 ‰ ◦C−1 for central Greenland, mostly depending on the patterns of North Atlantic and Arctic SST (sea surface temperature) as well as sea ice changes (Masson-Delmotte et al, 2011; Sime et al, 2013). During the last deglaciation and during several Dansgaard–Oeschger warming events, these data have revealed a higher δ18O–temperature coefficient (∼ 0.6 ‰ ◦C−1) than identified in other Greenland ice cores under glacial conditions (Guillevic et al, 2013; Buizert et al, 2014)

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