Abstract (300-400 words)
1. Introduction (1-2 pages; 1 figure)
In 2010 and 2012, Petermann Gletscher’s floating ice tongue calved icebergs sizing 130 and 250 km2 (Münchow et al., 2014; Nick et al., 2012; Cai et al., 2017; Peano et al., 2017), respectively. These icebergs are examples of mass ice loss events that directly contribute to sea level rise (Khan et al., 2014; Nick et al., 2013; Shepherd et al., 2012). Petermann Gletscher is one of over 200 marine-terminating outlet glaciers of the Greenland Ice Sheet (GrIS), which have shown an increased rate of mass loss over the past two decades (e.g. Moon et al., 2012; Carr et al., 2017; Rignot et al., 2011; Jensen et al., 2016). Amplified arctic temperatures from contemporary oceanic and atmospheric warming (e.g. Huang et al., 2017; Stocker et al., 2013) have been linked to this recent accelerated ice mass loss from dynamic processes such as calving (Aschwanden et al., 2016; Csatho et al., 2014; Howat et al., 2007). However, uncertainties exist about the long-term contribution of dynamic processes of the GrIS to sea level rise under a rapidly changing climate (Clark et al., 2016; Pfeffer et al., 2008). Land-terminating margins of the GrIS, which are influenced to a lesser degree by dynamic processes than marine-terminating outlet glaciers (e.g. Sole et al., 2008), provide additional information about the sensitivity of the GrIS to climate variability (e.g. Lesnek and Briner, 2018; Felikson et al., 2017). The Petermann Gletscher and the nearby Humboldt Gletscher and Washington Land region of NW Greenland (Figure 1) offer the opportunity to test the sensitivity of past ice sheet fluctuations in both the marine and land-terminating environment of the GrIS. A new record of past ice retreat in this high Arctic region will add valuable paleoclimate constraints to potential future ice response to increasing temperatures.
Erratic boulders and moraines indicate the former presence of an ice sheet or glacier, and direct age control on these landscape features can constrain the magnitude and timing of past ice margin changes. On the islands within Nares Strait and Washington Land, NW Greenland, features such as glacial striations, erratic boulders, and moraines are ubiquitous across the landscape, at positions proximal and distal to the modern Petermann Gletscher and GrIS, all evidence of past glacial movement. Washington Land (Figure 1) is a ~1300 km2 [currently] ice-free area consisting of flat-lying carbonate bedrock of Cambrian-Silurian in age (GEUS, 2013), dissected into isolated plateaus, with elevations ranging from sea level to 1500 m. GrIS velocity divides projected on to a bedrock geologic map constructed from extrapolating coastal exposures, indicates that ~1600 km2 of ice would transport crystalline boulders to Washington Land during a glacial advance (Rignot and Kanagaratnam, 2006; Dawes, 2009), where limited knowledge of the bedrock is known (e.g. Schaefer et al., 2016).
Geochronological constraints of past glaciations in Washington Land region are limited radiocarbon ages of shells deposited on the moraines (Bennike, 2002; England, 1985, 1999), 36Cl surface exposure ages from erratic boulders Hans Island within Nares Strait (Figure 1; Zreda et al., 1999), and paleooceanographic reconstructions from sediment cores
collected within Nares [EC1] Strait (Jackson et al., 2017; Jennings et al., 2011).
10Be exposure chronologies exist for other regions of Greenland (compiled in Sinclair et al., 2016), with the closest site located ~500 km southwest of the Petermann Gletscher (Corbett et al., 2015), therefore, the 10Be record of GrIS fluctuations in the Washington Land regions remains sparse.
Here, we reconstruct the latest Pleistocene and early Holocene history of both marine-terminating and land-terminating ice in the Petermann Gletscher region of the GrIS. By obtaining new 10Be exposure age constraints on erratic boulders across Washington Land, we test the hypothesis that the exposed boulders record a widespread response of the northwestern sector of the land-terminating GrIS to latest Pleistocene and early Holocene abrupt warming events. Additionally, we test the hypothesis that erratic boulders located proximal to Petermann Gletscher and on a lateral moraine of Humboldt Gletscher represent the response this marine-terminating outlet glacier to abrupt climate events, thus constraining its sensitivity to documented Holocene climate change.