High Arctic Holocene temperature record from the Agassiz ice cap and Greenland ice sheet evolution

Abstract

We present a revised and extended high Arctic air temperature reconstruction from a single proxy that spans the past ∼12,000 y (up to 2009 CE). Our reconstruction from the Agassiz ice cap (Ellesmere Island, Canada) indicates an earlier and warmer Holocene thermal maximum with early Holocene temperatures that are 4-5°C warmer compared with a previous reconstruction, and regularly exceed contemporary values for a period of ∼3,000 y. Our results show that air temperatures in this region are now at their warmest in the past 6,800-7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene. The warmer early Holocene inferred from the Agassiz ice core leads to an estimated ∼1 km of ice thinning in northwest Greenland during the early Holocene using the Camp Century ice core. Ice modeling results show that this large thinning is consistent with our air temperature reconstruction. The modeling results also demonstrate the broader significance of the enhanced warming, with a retreat of the northern ice margin behind its present position in the mid Holocene and a ∼25% increase in total Greenland ice sheet mass loss (∼1.4 m sea-level equivalent) during the last deglaciation, both of which have implications for interpreting geodetic measurements of land uplift and gravity changes in northern Greenland.ice core | temperature reconstruction | Holocene climate | Greenland ice sheet I nstrumented records of temperature and environmental change extend for a few centuries at most. Although these records provide evidence of climate warming, the time span covered is relatively short compared with the centuries to millennia response times of some climate system components (1). In this respect, reconstructions of temperature and environmental changes obtained from climate proxies (e.g., sediment cores, ice cores) play a complementary role to the instrumented records by providing a longer temporal context within which to interpret the magnitude and rate of recent changes (2). Furthermore, the relatively large spatial and temporal variability captured in these reconstructions represents a useful dataset to test models of the climate system (3). Of particular interest are periods during Earth's history when the climate was warmer than at present, as these provide information that is potentially more relevant to changes in the future.In this study, we focus on the reconstruction of past climate using ice cores from the Agassiz ice cap, located on Ellesmere Island in the Canadian Arctic Archipelago (Fig. 1A). This site is of particular interest as it is located in the high Arctic, and temperature reconstructions can be compared with those from more southerly locations to estimate polar amplification of climate in the past (4). Furthermore, it is located proximal to the Greenland ice sheet, and so can be used to better constrain the climate forcing used to model the past evolution of this ice sheet.In a recent study (5), δ 18 O measurements in ice from the Agassiz (81°N) and Renland (70°N) ice caps (Fi...

Greenland‐Wide Seasonal Temperatures During the Last Deglaciation

“…The GISP2 melt layers suggest a summer thermal maximum from roughly 9-6 ka BP, shorter in duration than, but overlapping in time with, the broad HTM that we find in Greenland SAT between 10 and 6 ka BP (Figure 2d). Recently, Lecavalier et al (2017) suggested that the timing of the HTM is earlier (11-10 ka BP) on Ellesmere Island, based on elevation-corrected records of summer melt and water isotopes-at that same location our merged product suggests maximum HTM warmth to occur around 9.5 ka BP (Figure 2h). Recently, Lecavalier et al (2017) suggested that the timing of the HTM is earlier (11-10 ka BP) on Ellesmere Island, based on elevation-corrected records of summer melt and water isotopes-at that same location our merged product suggests maximum HTM warmth to occur around 9.5 ka BP (Figure 2h).…”

“…(b) TraCE-21Ka simulated AMOC strength (gray) and AMOC strength required to bring TraCE-21 K simulations and ice core reconstructions into agreement (orange). (h) Ellesmere Island temperature reconstruction (red curve) by Lecavalier et al (2017) and our merged product (gray curve) at that site. Horizontal bars denote data averages during the Last Glacial Maximum (22-18 ka BP) and "stable" part of the Holocene (10-0 ka BP).…”

The sensitivity of the Greenland Ice Sheet to glacial–interglacial oceanic forcing

“…The resulting GrIS isostatic adjustment is therefore the combination of these local and non-local responses which make the GIA treatment rather complex. In principle, these nonlocal effects should be taken into account as they contribute to the sea-level variability, becoming especially relevant at the beginning of deglaciations when the ice mass loss is significantly induced by sea-level rise (Lecavalier et al, 2017). However, for the sake of simplicity, the GrIS isostatic adjustment is assumed here to be only due to local ice mass variations, as other works have done in the past (Greve and Blatter, 2009;Helsen et al, 2013;Huybrechts, 2002;Langebroek and Nisancioglu, 2016;Stone et al, 2013).…”

Recent Progress in Greenland Ice Sheet Modelling

“…The retreat history of the GrIS during the last deglaciation was reconstructed using an ice sheet model constrained with evidence of past margin positions and relative sea-level indicators [103,112]. The reconstruction provides important constraints for model spin-up to the present day, when representing the correct loading history and isostatic response.…”