Abstract
Abstract. Reconstructions of past temperature and precipitation are fundamental to modeling the Greenland Ice Sheet and assessing its sensitivity to climate. Paleoclimate information is sourced from proxy records and climate-model simulations; however, the former are spatially incomplete while the latter are sensitive to model dynamics and boundary conditions. Efforts to combine these sources of information to reconstruct spatial patterns of Greenland climate over glacial–interglacial cycles have been limited by assumptions of fixed spatial patterns and a restricted use of proxy data. We avoid these limitations by using paleoclimate data assimilation to create independent reconstructions of mean-annual temperature and precipitation for the last 20 000 years. Our method uses oxygen isotope ratios of ice and accumulation rates from long ice-core records and extends this information to all locations across Greenland using spatial relationships derived from a transient climate-model simulation. Standard evaluation metrics for this method show that our results capture climate at locations without ice-core records. Our results differ from previous work in the reconstructed spatial pattern of temperature change during abrupt climate transitions; this indicates a need for additional proxy data and additional transient climate-model simulations. We investigate the relationship between precipitation and temperature, finding that it is frequency dependent and spatially variable, suggesting that thermodynamic scaling methods commonly used in ice-sheet modeling are overly simplistic. Our results demonstrate that paleoclimate data assimilation is a useful tool for reconstructing the spatial and temporal patterns of past climate on timescales relevant to ice sheets.
Highlights
Predicting the future behavior of the Greenland Ice Sheet requires understanding its sensitivity to changes in temperature and precipitation (Bindschadler et al, 2013)
We focus on the last 20 000 years, which include the end of the last glacial period, the glacial to interglacial transition, and the Holocene Thermal Maximum (HTM), when temperatures at the Greenland Ice Sheet summit reached 1–2 ◦C warmer than the present (Cuffey and Clow, 1997; Dahl-Jensen et al, 1998)
At the GRIP and GISP2 ice-core sites, the reanalysis has a −14 ◦C anomaly with a standard deviation of 2 ◦C. This is in excellent agreement with the mean-temperature anomaly of −14 ◦C for the same period at the GISP2 site, which was derived from δ18O calibrated with borehole thermometry (Cuffey et al, 1995; Cuffey and Clow, 1997)
Summary
Predicting the future behavior of the Greenland Ice Sheet requires understanding its sensitivity to changes in temperature and precipitation (Bindschadler et al, 2013). On glacial–interglacial timescales, temperature, not precipitation, appears to be the dominant control on the size of the Greenland Ice Sheet (Alley et al, 2010), as evidenced by the fact that the ice sheet is largest during cold and arid glacial periods and smallest during warm and wet interglacials. The GISP2 ice core from central Greenland shows that cooling coincided with increased snowfall between the early Holocene and present (Cuffey and Clow, 1997) Despite such evidence, paleo ice-sheet models typically assume precipitation fields that are parameterized in time using a thermodynamic relationship that is constant for all locations and timescales (e.g., Huybrechts, 2002; Greve et al, 2011)
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