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Local Glaciation in West Greenland Linked to North Atlantic Ocean Circulation During the Holocene

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Local Glaciation in West Greenland Linked to North Atlantic Ocean Circulation During the Holocene Local glaciation in West Greenland linked to North Atlantic Ocean circulation during the Holocene Avriel D. Schweinsberg1, Jason P. Briner1, Gifford H. Miller2, Ole Bennike3, and Elizabeth K. Thomas1,4 1Department of Geology, University at Buffalo, Buffalo, New York 14260, USA 2INSTAAR, and Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA 3Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark 4Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, USA ABSTRACT 2016). Ocean circulation changes in this region Recent observations indicate that ice-ocean interaction drives much of the recent increase are largely modulated by the strength of the in mass loss from the Greenland Ice Sheet; however, the role of ocean forcing in driving past western branch of Atlantic Meridional Over- glacier change is poorly understood. To extend the observational record and our understanding turning Circulation (AMOC), which links the of the ocean-cryosphere link, we used a multi-proxy approach that combines new data from West Greenland Current (WGC) to the North proglacial lake sediments, 14C-dated in situ moss that recently emerged from beneath cold-based Atlantic climate system (Lloyd et al., 2007). Here, ice caps, and 10Be ages to reconstruct centennial-scale records of mountain glacier activity for we reconstruct local glacier variability in West the past ~10 k.y. in West Greenland. Proglacial lake sediment records and 14C dating of moss Greenland through the Holocene and investi- indicate the onset of Neoglaciation in West Greenland at ca. 5 ka with substantial snowline gate whether past oceanic variability and glacier lowering and glacier expansion at ca. 3.7 ka followed by additional ice expansion phases at change are synchronous at the centennial scale. ca. 2.9, ca. 1.7, and ca. 1.4 ka and during the Little Ice Age. We find that widespread glacier growth at ca. 3.7 ka in West Greenland coincides with marked cooling and reduced strength APPROACH AND METHODS of the West Greenland Current in Disko Bugt. The transition to cooler ocean conditions at We used a multi-proxy approach to generate ca. 3.7 ka identified in Disko Bugt is registered by marine proxy data farther afield in East a detailed record of glacier change throughout Greenland and on the northwestern Icelandic shelf, implying large-scale paleoceanographic the Holocene in West Greenland by combining changes across the North Atlantic during this interval. The similarity between glacier change (1) proglacial lake sediment analysis, (2) 14C dat- on West Greenland and multiple marine and terrestrial records across the North Atlantic sug- ing of formerly ice-entombed in situ moss, and gests that glaciers are strongly influenced by changes in ocean circulation and consequently (3) 10Be dating of erratics and late Holocene implies that the ocean-cryosphere teleconnection is a persistent feature of the Arctic system. moraines. We targeted small glaciers and ice caps independent of the Greenland Ice Sheet INTRODUCTION from lake sediments and used to assess the because they respond rapidly to changes in The behavior of the Greenland Ice Sheet is response of the cryosphere to climate change mass balance (Oerlemans, 2005) and can there- of critical interest due to its predicted impact on (e.g., Larsen et al., 2013; Balascio et al., 2015). fore be used for high-resolution paleoclimate future global sea-level changes and ocean circu- On Greenland, however, the majority of gla- reconstructions. lation (e.g., Joughin et al., 2012). Whereas the cier records are discontinuous and temporally We cored Sikuiui Lake on the Nuussuaq pen- observational record has focused almost exclu- restricted, owing in part to the obliterative insula to capture a clear sedimentary record of sively on ice-sheet outlet glaciers, land-termi- nature of glacier expansion during the past glacier activity, because the close proximity of nating glaciers and ice caps in Greenland are few millennia, and in particular, extensive ice the Qangattaq ice cap to the lake results in mini- highly sensitive to changes in temperature and advances during the Little Ice Age (LIA; ca. A.D. mal sediment transport distance, and the small are rapidly losing mass today (Bolch et al., 2013). 1250–1900). In contrast to extensive research on size of the ice cap makes this site particularly Although contemporary observations are critical Greenland Ice Sheet margin changes during the sensitive to minor climate variations (Fig. 1A; for understanding the mechanisms driving gla- Holocene (e.g., Briner et al., 2016), the timing see the GSA Data Repository1 for detailed meth- cier change, geological reconstructions of former and magnitude of mountain glaciation is rela- ods, and Fig. DR1). The age-depth model for glacier change provide additional data on gla- tively unknown (Kelly and Lowell, 2009). Only Sikuiui Lake was developed using 12 14C-dated cier behavior over longer time scales and during three studies of ice caps in East Greenland pro- macrofossils. We used principal component periods that were warmer than present. Glacier vide continuous records of local glacier change analysis (PCA) to identify the leading modes of reconstructions coupled with paleoceanographic during the Holocene (Lowell et al., 2013; Levy variability among the physical parameters (mag- records can provide insight on the influence of et al., 2014; Balascio et al., 2015). netic susceptibility [MS], density, organic matter the ocean on nearby terrestrial climate, especially West Greenland is ideally suited to examine content) and elemental data from Sikuiui Lake through the influence of sea-surface conditions the influence of ocean forcing on past glacier sediments. PCA results indicate that there is one on air temperature (Thomas et al., 2016). Iden- change due to its large number of local glaciers strong primary trend in the lake sediment data tifying linkages between past glacier change and and numerous regional paleoceanographic (PC1) accounting for 56% of the total variance. forcing mechanisms, such as changes in ocean reconstructions in the adjacent Disko Bugt and circulation, can help to predict changes in glacier Baffin Bay (e.g., Moros et al., 2016). A number 1 GSA Data Repository item 2017051, materials and and ice-sheet behavior. of these paleoceanographic studies resolve ocean methods, Figures DR1–DR7, and Tables DR1–DR5, is In the North Atlantic region, continuous circulation through the Holocene on decadal to available online at www.geosociety.org /datarepository records of glacier change have been inferred multi-centennial time scales (e.g., Moros et al., /2017 or on request from [email protected]. GEOLOGY, March 2017; v. 45; no. 3; p. 195–198 | Data Repository item 2017051 | doi:10.1130/G38114.1 | Published online 9 January 2017 GEOLOGY© 2017 Geological | Volume Society 45 | ofNumber America. 3 For| www.gsapubs.org permission to copy, contact [email protected]. 195 AB55º W 51º W Greenland Figure 1. A: Central West 71º N 71º N Uummannaq Greenland; West Green- Fjord land Current (WGC) is Sermikassak depicted after Perner et al. EGC WG (2013). Inset map shows Nuussuaq C IC Greenland and relative Uigorliu locations of WGC, East Fig. 1B Disko p Greenland Current (EGC), Greenla Vaig Ice Shee 70º N 70º N Sarq Uigorliup and Irminger Current (IC). at moraines B: Eastern Nuussuaq a p t n showing tundra moss a Sikuiui Lake d serssua t sample sites (yellow dots; WG Disko see Data Repository [see C Qangattaq Fjord ice cap footnote 1] for map of all Ilulissat Jakobshavn sites), Sikuiui Lake, and Isbræ WGC Uigorliup moraines. 69º N 69º N Disko N N 55º W Bugt 51º W 25 km 2 km Trends in PC1 are similar to those in MS and ca. 10.5 ± 0.3 ka (Table DR3). The transition intervals of snowline lowering and ice expan- density, parameters typically used to reconstruct from basal mineral-rich sediments to gyttja at sion across the study region occurred at ca. 2.9 glacier extent (e.g., Bakke et al., 2005; Røthe et ca. 9.4 ka in Sikuiui Lake places a minimum ka, ca. 1.7 ka, and during the LIA, evidenced by al., 2015), and support the use of PC1 to repre- constraint on the timing of local ice-cap disap- modes of 14C ages in the moss chronology and sent changes in the lake record. pearance or significant reduction in size (see increased mineral-rich sediment flux to Sikuiui We obtained 54 14C ages of in situ moss the Data Repository). An interval of increased Lake (Figs. 2A and 2B). from 22 different ice caps across an elevation mineral-rich input punctuates the organic-rich The mean 10Be ages of nested moraines in range of 760–1500 m above sea level (asl) to sediments in the Sikuiui Lake record between the Uigorliup Lake valley date to 1.1 ± 0.2 ka examine the timing of Holocene ice expansion ca. 8.8 and 8.0 ka (Fig. 2A) and may reflect (n = 3), 1.2 ± 0.3 ka (n = 3), and 0.9 ± 0.03 ka in West Greenland (Fig. DR7 and Table DR5 a brief interval of early Holocene cooling and (n = 3) for the distal, intermediate, and proxi- in the Data Repository). We sampled recently glacier readvance correlative with the deposition mal positions, respectively (Young et al., 2015). exposed moss along cold-based sectors of poly- of nearby ice-sheet moraines (Cronauer et al., The moraines record extensive ice, but minor thermal ice caps following Miller et al. (2013). 2016). This glacier readvance may also relate to net retreat, during the Medieval Warm Period We interpret changes in glacier snowline eleva- the 8.2 ka event (e.g., Alley et al., 1997), as has (MWP) and date between 14C age clusters of in tion as a proxy for summer temperature change.
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