The deglaciation and neoglaciation of Upernavik Isstrøm, Greenland Jason P. Briner a, ⁎, Lena Håkansson b,c,1 , Ole Bennike b a Department of Geology, University at Buffalo, Buffalo, NY 14260, USA b Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen-K, Denmark c Department of Geology and Mineral Resources Engineering, Norwegian University of Science and Technology, Sem Særlands veg 1, N-7491 Trondheim, Norway abstract article info Article history: Received 11 July 2013 Available online 21 October 2013 Keywords: Greenland Ice Sheet Upernavik Isstrøm Holocene Be dating Lake sediments Little Ice Age We constrain the history of the Greenland Ice Sheet margin during the Holocene at Upernavik Isstrøm, a major ice stream in northwestern Greenland. Radiocarbon-dated sediment sequences from proglacial-threshold lakes adjacent to the present ice margin constrain deglaciation of the sites to older than 9.6 ± 0.1 ka. This age of deglaciation is confirmed with 10 Be ages of 9.9 ± 0.1 ka from an island adjacent to the historical ice position. The lake sediment sequences also constrain the ice margin to have been less extensive than it is today for the remainder of the Holocene until ~1100 to ~700 yr ago, when it advanced into two lake catchments. The ice margin retreated back out of these lake catchments in the last decade. The early Holocene deglaciation in Melville Bugt, one of few locations around Greenland where a vast stretch of the current ice margin is marine-based, preceded deglaciation in most other parts of Greenland. Earlier deglaciation in this ice-sheet sector may have been caused by additional ablation mechanisms that apply to marine-based ice margins. Furthermore, despite ice-sheet models depicting this sector of Greenland as relatively stable throughout the Holocene, our data indi- cate a N 20 km advance-retreat cycle within the last millennium. © 2013 University of Washington. Published by Elsevier Inc. All rights reserved. Introduction Understanding the sensitivity of the Greenland Ice Sheet to ongoing and future climate change will narrow uncertainties about future sea- level rise (Alley et al., 2010). Yet, the observational record of ice-sheet behavior reveals a complex relationship to climate change (e.g., Kelley et al., 2012). Reconstructions of Greenland Ice Sheet changes during the Holocene provide a longer-term period over which to examine ice-sheet response to climate change. In addition, constraints on ice- margin positions spanning the Holocene provide tests for numerical ice-sheet models (e.g., Simpson et al., 2009). However, despite the emergence of new glacial chronologies from around Greenland, detailed reconstructions of ice-margin positions during the Holocene remain geographically sparse. Northwestern Greenland consists largely of marine-based ice margins with fast-flowing outlet glaciers and ice streams entering Melville Bugt over and between dozens of island archipelagos, peninsulas, nunataks and seminunataks (Fig. 1). A major outlet glacier in northwestern Greenland is Upernavik Isstrøm, which comprises four distinct branches (Nielsen et al., 2012). The distance of retreat of Upernavik Isstrøm since the first historical observation in 1849 (~20–30 km) rivals that of other fast flowing outlet glaciers along western Greenland, such as Jakobshavn Isbræ (~40 km) and Kangiata Nunata Sermia (~20 km; Weidick, 1958, 1968; Weidick et al., 2012; Csatho et al., 2008). The chronology of ice-margin retreat from the latest Pleistocene maximum position on the continental shelf (Funder et al., 2011; Ó Cofaigh et al., 2013) to the Holocene minimum behind the current ice margin was variable throughout Greenland (Bennike and Björck, 2002). For example, deglaciation occurred 9.6 to 9.1 ka at sites in north- ern Melville Bugt and N 10 ka at some localities in southern Greenland, yet it occurred much later (as late as 6.2 ka) elsewhere around Greenland (Bennike and Björck, 2002). Little is known about the glacial history of Melville Bugt because few studies have focused on ice-margin changes there during the Holocene (Bennike, 2008; Funder et al., 2011). Numerical ice-sheet models depict significant inland retreat of the western Greenland Ice Sheet during the middle Holocene (e.g., Simpson et al., 2009). In this area, there is also terrestrial evidence to support model depictions of the ice margin being inland of its present position during the early–middle Holocene (e.g., Weidick, 1968; Long et al., 2009). The margin of the ice sheet reestablished a position similar to the present location during the last few centuries—during the Little Ice Age (LIA; 1250–1900 AD; Kaplan et al., 2002; Weidick, 1968; Weidick and Bennike, 2007; Weidick et al., 2012; Briner et al., 2010). These same models depict a non-fluctuating, relatively stable ice-sheet position throughout the Holocene elsewhere around Greenland, includ- ing the Melville Bugt region. However, there are few field data available from Melville Bugt to compare with these modeling results. Here, we use 10 Be dating and radiocarbon-dated sediment cores from proglacial-threshold lakes adjacent to Upernavik Isstrøm to constrain ice- margin positions throughout the Holocene. Our goal is to add information Quaternary Research 80 (2013) 459–467 ⁎ Corresponding author. E-mail address: jbriner@buffalo.edu (J.P. Briner). 1 Current address: Department of Geology, Lund University, Sölvegatan 12, S-22362 Lund, Sweden. 0033-5894/$ – see front matter © 2013 University of Washington. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.yqres.2013.09.008 Contents lists available at ScienceDirect Quaternary Research journal homepage: www.elsevier.com/locate/yqres