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

Abstract:

Stack records of accumulation, d¹⁸O and deuterium excess were produced from up to 4 shallow ice cores at NEEM (North-West Greenland), spanning 1724-2007 and updated to 2011 using pit water stable isotope data. Signal-to-noise ratio is high for d¹⁸O (1.3) and accumulation (1.2) but is low for deuterium excess (0.4). No long-term trend is observed in the accumulation record. By contrast, NEEM d¹⁸O shows multi-decadal increasing trends in the late 19^th century and since the 1980s. Decadal d¹⁸O and accumulation variability is in phase with Atlantic Multi-decadal Oscillation indices, and enhanced at the beginning of the 19^th century. Large-scale spatial coherency is detected between NEEM and other Greenland ice core and temperature records, strongest for North-West Greenland d¹⁸O and summer South-West coastal temperature instrumental records. The strength of correlations with the North Atlantic Oscillation is smaller than in central or south Greenland. The strongest positive d¹⁸O values are recorded at NEEM in 2010, followed by 1928, while maximum accumulation occurs in 1933. The coldest/driest decades are depicted at NEEM in 1815-1825 and 1836-1836. The spatial structure of these warm/ wet years and cold/dry decades is investigated using all available Greenland ice cores. During the period 1958-2011, the NEEM accumulation and d¹⁸O records are highly correlated with simulated precipitation, temperature and d¹⁸O from simulations performed with MAR, LMDZiso and ECHAM5iso atmospheric models, nudged to atmospheric reanalyses. Model-data agreement is better using ERA reanalyses than NCEP/NCAR and 20CR ones. Model performance is poor for deuterium excess. Gridded temperature reconstructions, instrumental data and model outputs at NEEM are used to estimate the d¹⁸O-temperature relationship for the strong warming period in 1979-2007. The estimated slope of this relationship is 1.1±0.2‰ per °C, about twice larger than previously used to estimate last interglacial temperature change from the deep NEEM ice core.