Holocene thinning of the Greenland ice sheet

Abstract

On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an important concern, especially in the light of new evidence of rapidly changing flow and melt conditions at the GIS margins. Studying the response of the GIS to past climatic change may help to advance our understanding of GIS dynamics. The previous interpretation of evidence from stable isotopes (delta(18)O) in water from GIS ice cores was that Holocene climate variability on the GIS differed spatially and that a consistent Holocene climate optimum-the unusually warm period from about 9,000 to 6,000 years ago found in many northern-latitude palaeoclimate records-did not exist. Here we extract both the Greenland Holocene temperature history and the evolution of GIS surface elevation at four GIS locations. We achieve this by comparing delta(18)O from GIS ice cores with delta(18)O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of delta(18)O evidence from ice cores, our new temperature history reveals a pronounced Holocene climatic optimum in Greenland coinciding with maximum thinning near the GIS margins. Our delta(18)O-based results are corroborated by the air content of ice cores, a proxy for surface elevation. State-of-the-art ice sheet models are generally found to be underestimating the extent and changes in GIS elevation and area; our findings may help to improve the ability of models to reproduce the GIS response to Holocene climate.

Solar forcing as an important trigger for West Greenland sea-ice variability over the last millennium

“…Furthermore, both proxy records indicate a decline in SIC that started around AD 1900. Our SIC reconstruction is also in broad agreement with the temperature record from the Agassiz and Renland ice cores (Vinther et al, 2009) (Fig. 3b), which exhibits warm conditions before about AD 1400, and a marked temperature shift from the MCA to the so-called LIA.…”

Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

“…Most of these records are Holocene in age and postdate the primary melting phase of the LIS during Termination I. As a result, these are likely to yield estimates of LIS d 18 O that are more positive than LGM values, following the climate signal that is seen in Greenland when comparing Holocene ice (À26 to À36‰; Vinther et al, 2009) to LGM ice (À40 to À45‰; Buizert et al, 2014;Johnsen et al, 1972;Seierstad et al, 2014). The most direct measurements of LIS remnants, from ice on the Barnes Ice Cap, yield d 18 O values of À21 to À40‰ (Hooke and Clausen, 1982) at a high-latitude site (70 N) on Baffin Island proximal to a marine isotopic source (Andrews et al, 2002).…”

“…However, mixing models of meltwater contributions to the ocean typically assume a constant d 18 O w value for the LIS (À25 or À35‰; Aharon, 2006;Carlson, 2009;Carlson et al, 2007;Hill et al, 2006;Obbink et al, 2010), and do not attempt to incorporate the complex spatial heterogeneity in d 18 O w observed in modern continental ice sheets (Masson-Delmotte et al, 2008;Vinther et al, 2009). Attempts to estimate the oxygen isotope composition of parts of the LIS have used measurements of remnant ice such as the Barnes Ice Cap (Hooke, 1976;Hooke and Clausen, 1982), Pleistocene-age groundwater (Hooke and Clausen, 1982;Remenda et al, 1994) and preserved ice wedges (Kotler and Burn, 2000); as well as indirect proxies from subglacial carbonates (Refsnider et al, 2012(Refsnider et al, , 2014 and proglacial lakes (Birks et al, 2007;Buhay and Betcher, 1998;Last et al, 1994;Moore et al, 2000).…”

The importance of insolation changes for paleo ice sheet modeling

“…The Eemian interglacial, for example, has been shown to have exhibited a considerably warmer Arctic than today (e.g., Bakker et al, 2013;, so while it is not a perfect analogue for the future due to its different orbital configuration, it can still be used to learn about ice sheet sensitivity during warmer periods . Aside from records obtained from several ice cores (e.g., Vinther et al, 2009;NEEM Community Members, 2013) and marine sediment cores (e.g., Colville et al, 2011), dynamic ice sheet modeling is the major source of information used to constrain past ice sheet conditions and evolution.…”