bs_bs_banner Retreat of the Smith Sound Ice Stream in the Early Holocene ANNE E. JENNINGS , JOHN T. ANDREWS , BRETT OLIVER, MAUREEN WALCZAK AND ALAN MIX Jennings, A. E., Andrews, J. T., Oliver, B., Walczak, M. & Mix, A.: Retreat of the Smith Sound Ice Stream in the Early Holocene. Boreas. https://doi.org/10.1111/bor.12391. ISSN 0300-9483. Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenlandice sheets duringthe last glaciation.This paper focuses on the eventsandprocesses leading to the openingofthe strait and the environmental response to establishment of the Arctic-Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon-dated cores 2001LSSL-0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with DR = 220Æ20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice-proximal (red/grey laminated, ice-proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice-rafted debris) to ice-distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. Wehypothesize that a distinctIRD layerdeposited between 9.3 and 9 (9.4–8.9 1r) cal. ka BP marks the break-up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic-Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient-rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand-sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1r)cal.kaBP.The timing ofthetransitionis poorly resolved as it coincideswiththe slow sedimentationrates that ensued after the ice margins retreated onto land. Anne E. Jennings ([email protected]), John T.Andrews and Brett Oliver,INSTAAR, Universityof Colorado, Boulder, CO 80309-0450, USA; Maureen Walczak and Alan Mix, CEOAS, Oregon State University, 104 CEOAS Admin Building, Corvallis, OR 97331, USA; received 23rd October 2018, accepted 6th February 2019. The western route of Arctic freshwater export through Labrador Sea (Jennings et al. 2011; Pienkowski et al. the channels in the Canadian Arctic Archipelago (CAA), 2012, 2014). termed the western route, is an important component In this paper we investigate the events and processes of the North Atlantic circulation (Fig. 1A). Variations leading up to the opening of Nares Strait from its southern in the flux of fresh water (comprised of solid sea ice end, and the response of the glacier and marine systems to and diluted liquid seawater) via the western route can establishment of the Arctic-Atlantic throughflow using influence the strength of the Atlantic meridional multiproxyanalysesofsedimentcores:2001LSSL-0014PC overturning circulation (AMOC; Curry & Mauritzen and TC from a site in Smith Sound, under the path of ASW 2005; Serreze et al. 2006) and deep-water formation in (Fig. 1A) and within the North Water Polynya (NOW; the Labrador Sea (Belkin et al. 1998; Belkin 2004). The Fig. 1B). western freshwater route has not operated continuously in the past. During the Last Glacial Maximum (LGM), Regional setting and previous work confluent Laurentide, Innuitian and Greenland ice sheets completely blocked the CAA channels (Dyke Nares Strait is a NE–SW orientated strait that connects et al. 2002; England et al. 2006) eliminating the south- the Arctic Ocean and Baffin Bay (Fig. 1). It is bounded wardflowofArctic SurfaceWater (ASW) into Baffin Bay by Greenland on the SE and Ellesmere Island on the NW. (Fig. 1A). Exposure age dating of glacial erratics and Glacier ice covers much of the land area along the strait. polished bedrock on islands within Nares Strait shows The ice-free areas on either side of Smith Sound and deglaciation between 9 and 10 cal. ka BP (Zreda et al. Kane Basin have similar bedrock units; Archaen and 1999) and marine core Hly03-05GC from Hall Basin Palaeoproterozoic crystalline shield rocks (gneissic with showed that Nares Strait abruptly opened c. ≤9000 cal. gabbro intrusions) underlie Mesoproterozoic to Neo- ka BP (Jennings et al. 2011), or as late as 8.3 cal. ka BP proterozoic units of the Thule Supergroup. The Thule (Georgiadis et al. 2018) when the connection between Supergroup includes basic volcanic rocks and common the Greenland and Innuitian ice sheets in Kennedy siliciclastic redbeds of the Smith Sound,NaresStrait and Channel was finally severed (England 1999). The open- Baffin Bay groups that are exposed on central Ellesmere ing of Nares Strait and other channels in the CAA Island near the core site (Fig. 1B; Dawes 1997, 2006). ushered in the modern ocean circulation in Baffin Bay Widespread Lower Palaeozoic to Devonian carbonate and must have impacted the composition and flow rocks (limestone and dolomite) of the Franklinian Basin strengthoftheBaffinCurrentthattransportsASWtothe crop out along the shores of Kane Basin (Kravitz 1976, DOI 10.1111/bor.12391 © 2019 Collegium Boreas. Published by John Wiley & Sons Ltd 2 Anne E. Jennings et al. BOREAS 100°W 90°W 80°W 70°W 60°W B Arctic Ocean 84°N 77°N Ellesmere Island 05 Agassiz (! Ice Cap HB 82°N 76°N KC POW ! Icefield BP ( Jones Sd 2B KB PG SS HG 75°N (! 80°N 014 Greenland CØ 180° 74°N 12 A Bering LS St. 10 78°N 120° Beaufort 73°N Gyre 120° Transpolar CAA Drift Baffin LSJS 72°N Nares St. 76°N Bay BB 60° BC Fram WGC St. 60° Greenland N. Atl. Current EGC 70° N 71°N 0 115 230 km 0400km 60° N 0° 74°N 70°W 60°W 50°W Fig. 1. A. Arctic (yellow arrow line) and Atlantic (red dashed line with arrows) surface ocean currents in the broad study area. BC = Baffin Current; WGC = West Greenland Current; EGC = East Greenland Current; BB = Baffin Bay; CAA = Canadian Arctic Archipelago; LS = LancasterSound;JS = JonesSound.B.MapofnorthernBaffinBayandNaresStraitshowingthelocationofcores2001LSSL-014PCandTC andgeographicallocationsmentionedinthetext.RedlandareasarelocationsofThuleSupergroupoutcrops(Dawes1997).Greenlinessouthof014 denote locations of inferred subglacially moulded bedforms (Blake et al. 1996). The dashed black andwhite line outlines the average June extent of the NOW (Dunbar 1969). SS = Smith Sound; BP = Bache Penninsula; HB = Hall Basin; KB = Kane Basin; KC = Kennedy Channel; LS = Lancaster Sound; PG = Petermann Glacier; HG = Humboldt Glacier; CØ=Carey Oer. Yellow circles denote sediment cores mentioned in the text: 2B = AMD14-Kane2B; 12 = HU91-039-12PC; 05 = HLY03-05GC;10 = 2011804-0010. 1982), on western Ellesmere Island, and northward into Baffin Bay (Melling et al. 2001) and is aided by along Nares Strait (Dawes 1997, 2006). Carbonate rocks northerly winds and currents that remove newly formed are also present throughout the Thule Supergroup but ice (Ingram et al. 2002). Atlantic Water found in Smith are subordinate, especially in the lower strata exposed on Sound is from the WGC; shallow sills along Nares Strait Ellesmere Island (Dawes 2006). Mineralogical and exclude transit of all or most Atlantic Water from the lithofacies changes in core 014 are interpreted in terms Arctic Ocean. Sensible heat from upwelling of the of glacial erosion of these bedrock units. warmer WGC locally also plays a role in the polynya Cyclonic ocean circulation in Baffin Bay involves the formation on the Greenland side of the polynya (Melling north-flowing West Greenland Current (WGC) with a et al. 2001; Ingram et al. 2002). Sea ice covers nearly all strongAtlantic Watercomponent,andthesouth-flowing of Baffin Bay in winter, beginning to form in September Baffin Current comprised of ASW that enters Baffin Bay and reaching maximum coverage in March (Tang et al. through the CAA channels under steric forcing (Tang 2004). The area of the NOW has anomalously thin, low et al. 2004; Munchow€ et al. 2006, 2015; Fig. 1A). The concentration sea ice. The ice-covered area decreases ASWhasalargecomponentofnutrient-richPacificWater between April and August, initiated in the NOW region, (Joneset al.2003;Munchow€ et al.2007)thatsupportsthe with an ice-free area generally formed by June (Fig. 1B). high productivity of the NOW (Dunbar 1969; Melling Glacial geological reconstructions based on terrestrial et al. 2001) (Fig. 1A, B). The polynya forms when an ice glacial geology (Bennike et al. 1987; Funder 1990; Blake bridge consolidates on the shallow (220 m) sill at the 1992; Blake et al. 1992, 1996; England 1999; Kelly et al. head of Smith Sound, preventing passage of Arctic sea- 1999; Bennike 2002; England et al. 2004, 2006), and ice floes, but allowing throughflowof nutrient-rich ASW marine studies (Levac et al. 2001; Mudie et al. 2004; BOREAS Retreat of the Smith Sound Ice Stream in the Early Holocene 3 Knudsen et al. 2008; Vare et al. 2009; Jennings et al. samples from 014PC and TC were analysed forgrain-size 2011; Pienkowski et al. 2012, 2014; St-Onge & St-Onge and quantitative x-ray diffraction (qXRD) mineralogy. 2014; Georgiadis et al. 2018) frame the events that are Foraminiferal analyses from the same levels were con- recordedin2001LSSL-014PCandTC.DuringtheLGM, ducted on 36 samples in the PC and on 15 samples in the theGreenlandandInnuitianicesheetscoalescedinNares TC. We use all of the proxy and lithofacies data to Strait resulting in confluent ice streams that flowed determine where the two cores overlap. from a saddle in Kane Basin both northward through Kennedy Channel toward the Arctic Ocean (Jakobsson Grain-size analysis et al.