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Retreat of the Smith Sound 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. , a major connection between the Ocean and , 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 . 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 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 (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 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 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. have similar bedrock units; Archaen and 1999) and marine core Hly03-05GC from 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 (! 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 = ; PG = ; 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. 2018), and southward into northern Baffin Bay through Smith Sound (England 1999; England et al. One-gram samples were sieved to remove >2 mm clasts 2006; Margold et al. 2015). Based on the occurrence of and treated with hydrogen peroxide to oxidize organic Greenland erratics, the GIS was preeminent, flowing matter and treatedwith sodium metaphosphate to disag- onto Ellesmere Island from Kane Basin northward, but gregate them before particle size analysis (0.01–2000 the confluence between the two ice sheets was off- microns) on the Malvern Mastersizer 3000 laser diff- shore from southern Kane Basin and southward into raction particle size analyzer. IRD was quantified by Smith Sound (England 1999; England et al. 2006). The counting >2 mm clasts from the x-radiographs in con- area experienced 110–140 m of isostatic adjustment tiguous 2-cm windows (Grobe 1987). (Bennike 2002; England et al. 2006; Simon et al. 2015). The southward-flowing ice was termed the Smith Sound Quantitative x-ray diffraction mineralogy (qXRD) Ice Stream by Blake (1977). Blake et al. (1996) suggested extension of the Smith Sound Ice Stream well south of qXRDof<2 mmmilledsampleswasaccomplishedusinga 2001LSSL-014 based on sea-floor features interpreted to D5000 Siemens unit with a 40-sample carousel. Sample have been moulded by grounded ice (Fig. 1B). If the preparations of material <2 mm were undertaken by streamlined features represent an extended Smith Sound milling with a McCrone mill for 5 min with 4 ml ethyl IceStream duringthelastglacialperiod,thenthecoresite alcohol. The samples were dried at 85 °Covernight.The 014 would have been beneath grounded ice when they sediment was tapped into the side-mounted holders were formed. Northward and southward ice recession against a frosted glass plate. The samples were scanned and separation of the two ice masses in Kennedy Channel between 5 and 65 two-theta at 0.02° two theta for 2 s. The wasthefinalstepinopeningNaresStrait(England1999). intensity data were then loaded into a PC-based 50 MB Ice recession is recorded well into the Holocene on Excel macro-program called Rockjock v6 (Eberl 2003) to Washington Land, north Greenland (Bennike 2002). find the best-fit solution for estimating the weight % of Furze et al. (2017) and Pienkowski et al. (2012, 2013) non- clay and clay minerals (Eberl 2003; Andrews & Eberl have described deglacial sequences of Lancaster Sound 2011). Known weight % of mixtures of laboratory and at 13.2 and 11.5 cal. ka BP, respec- purchasedmineralsareroutinelyprocessedforestimatesof tively. Knudsen et al. (2008) dated ice retreat from the accuracy and precision of the approach. The USGS Hvalsund, Inglefield Bredning and Olrik , NW laboratory that developed Rockjock placed 3rd in an inter- Greenland to c. 12.5 cal. ka BP in core HU91-039-12PC national competition to assess different approaches to (Fig. 1B). quantitative mineral determinations (McCarty 2002).

Material and methods Chronology: radiocarbon dating and calibration Piston core 2001LSSL-014PC and its companion trigger Seven radiocarbon dates were obtained from benthic core -014TC (latitude 77°440N, longitude 75°40W; water foraminifera in 014PC (Table 1). All but one samplewere depth 657.5 m) were raised from northern Baffin Bay in analysed at the Keck Carbon Cycle AMS Facility at UC the northwestern part of the North Water Polynya Irvine; the deepest age was acquired at the Australian (Fig. 1B) from the Canadian research ship, Louis St. National University (ANU) Radiocarbon Laboratory. Laurent. The piston core is 429 cm long and the trigger For the two samples for which it was possible we dated a core is 144 cm. The cores were opened, described, x- single species (Nonionella labradorica) at its abundance rayed, photographed and sampled at the Atlantic Geo- peak, but in most cases to obtain enough material for science Center, Dartmouth, Nova Scotia, , dating we relied on mixed benthic foraminiferal species, in 2002 by Andre Rochon and Peta Mudie and re- mainlyoflargeandwell-preserved Nonionellinalabrador- photographed and x-rayed in 2014. Grain-size analysis, ica, Cassidulina neoteretis, Elphidium excavatum forma quantitative x-ray diffraction (qXRD) mineralogy, and clavata and Islandiella norcrossi. Radiocarbon dateswere foraminiferal and stable isotope analyseswereconducted calibrated using the Marine13 curve (Reimer et al. 2013; on2-cm-widesubsamplestakenat10-cmintervalsin2002 Table 1). Given the possibility that the marine reservoir andstoredincoldstorageuntiltheywereanalysedforthis offset from a well-mixed ocean has varied through the project beginning December 2015. A total of 54 sediment time represented by the core and the lackof consensus on 4 Anne E. Jennings et al. BOREAS

the correct local offset to use, we present several calibration options in Table 1: DR = 0; DR = 220Æ20; 1010 7550 8850 9460 10 710 11 000 – – – – – – and DR = 335Æ85 14C years to provide an envelope of potential calibrated ages that can be compared to ages

1-sigma range from other dated cores in the region. The assumption of a well-mixed ocean with no additional local marine reser- 335 D =

= voir correction ( R 0; Funder 1990: p. 57) provides

8720 8580 the oldest potential calibrated age of a sample. DR = Cal. age, DR 220Æ20 years is the correction proposed by Coulthard

* et al. (2010) for NE Baffin Island and has been used in Lancaster Sound (Bennett et al. 2015). Uncertainty 980 830 660 7520 7400 7240 8990 9510 9330 9240 10 790 10 600 10 490 11 110 10 870 10 730 – – – – – – about the magnitude of the local DR from this data set 910 7550 8740 9430 partially derives from the mismatch between the water 1 sigma range depth at the core site (657.5 m) and the depth of

20 collection of the regional molluscs in the calibration Æ database (<100 m), affording the possibility that the 220 organisms dated in the database and in the core would = have lived in different water-masses (ASW vs. WGC Cal. age, DR Atlantic Water). Additionally, the lack of ASW prior to opening of Nares Strait indicates that the museum

mixed benthic foram species. specimens used to build the Coulthard et al. (2010) 1080 950 7650 7490 90709580 8890 9460 10 930 10 730 10 660 11 170 11 030 10 960 = – – – – – – database are not representative of local reservoir ages for times prior to opening of the Arctic-Atlantic through-

1 sigma range flow. Acknowledging these problems, we developed an intermediate DR age model using DR = 220Æ20 years 150 (Table S1) and use Table 1 to illustrate the potential age = envelope for the record. The largest DR of 335Æ Cal age, DR

2-sigma range; MBF 85 years is suggested for the Canadian Arctic Archipe- lago(Coulthardet al.2010)andreflectsalikelyminimum *= potential calibrated age for the sample. Other reservoir 1260 1030 950 7740 7550 7450 92309760 8980 9520 8890 9450 11 120 10 840 10 720 11 310 11 100 11 030 – – – – – – corrections have been applied in the region (e.g. St-Onge & St-Onge 2014; Furze et al. 2017), but these fall

1 sigma range within the envelope of reservoir ages we present in

0 Table 1. = 1200 1170 7670 7610 91709690 9110 9590 Cal. age, DR 11 220 11 140 Foraminiferal analyses Foraminiferal assemblages were counted wet from the >63 lm fraction submerged in a ‘storage’ solution of 70% distilled water and 30% ethanol with baking soda to . neoteretis N. labradorica N. labradorica dated C help preserve fragile calcareous and agglutinated tests. A wetsplitterwasusedwhen necessary toachievea countof at least 200–300 benthic foraminifers. Planktic forami- 20 15 3045 MBF MBF 25 MBF 11 050 11 000 30 Æ Æ Æ Æ Æ Æ nifers were counted in the benthic split. Equivalent dry weights of the foraminiferal samples were calculated C age (a BP) Material 14 > 50 300 MBF using the wet weights of the foram samples and the wet and dry weights of samples prepared for grain size and mineralogy from the same depths. 10 1625 41 7215 91.5118 8535 9015 151 10 035 189 10 240 345 – – – – – – –

interval (cm) Stable isotope analyses Stable oxygen and carbon isotopeswere measured for the planktic foraminifer species Neogloboquadrina pachy- derma (NPS) in 14 samples. They were analysed at the 2001LSSL-0014 PC radiocarbon dates and calibrations. Cal. ages to nearest 10 years. Oregon State University College of Earth, Oceanic and Atmospheric Sciences Stable Isotope Mass Spectrome- UCIAMS-171868 9 UCIAMS-163876 40 UCIAMS-171869UCIAMS-171870 87 116 UCIAMS-163867 147 UCIAMS-163868 187 Laboratory number Depth Table 1. SANU-42532 337 ter Facility using a Thermo-Finnigan MAT-252 mass BOREAS Retreat of the Smith Sound Ice Stream in the Early Holocene 5 spectrometer with a Kiel III carbonate device, using Lithofacies 2 (L2). Laminated red and grey mud and sand NBS-19 and Wiley (internal calcite laboratory standard) with dispersed clasts 273–204 cm. – L2 (Fig. 2C) begins to correct the data relative to VPDB, with an analytical with an abrupt transition to soft, darkreddish brown and precision of 0.05& for d18O and 0.03& for d13C. reddish brown (5YR 3/2; 4/3) and dark grey (5YR 4/1) mud close to the colour of the irregular layers and blobs Results in the underlying compact pebbly mud. This unit is crudely stratified mud and sandy mud with muddy sand layers 5 to 10 cm thick at the base trending to finely Lithofacies descriptions laminated (mm scale laminations) mud and sandy mud Lithofacies were determined on the basis of visual core with a mean grain size of very coarse silt and an descriptions,x-radiographs,corephotographyandgrain- increasing component of dark grey (5Y 4/1) laminations size analysis. The 429-cm piston core comprises four toward the top. >2 mm clasts are dispersed throughout lithofacies (Fig. 2). The trigger core has a single litho- (Fig. 3). facies that matches the top lithofacies unit in the piston core. Lithofacies3(L3).Bioturbatedpebblymud204–95cm. – This unit is massive grey sandy mud with frequent Lithofacies 1 (L1). Compact pebbly mud 429–273 cm. – dispersed clasts >2 mm (Fig. 2B). The mean grain size This unit is massive, black and very dark grey (2.5Y N 2/, ranges from fine silt through medium silt to coarse silt N3/and5Y3/1)mudandsandymudwithdispersedclasts (Fig. 3). Clasts immediately above L2 to 175 cm are >2 mm and a mean grain size of medium silt (Fig. 3). It is numerous and large, up to 5 cm in diameter. The >2mm compact and cracked in contrast to the softer overlying clast content decreases toward the top of the unit prior to units (Fig. 2D). Small patches of darker sediments were a distinct clast peak between 110 and 95 cm with a hint of suspected to be bioturbation in the visual description, stratification from 100 cm to 95 cm (Fig. 2A). Colour but burrows were not observed in x-radiographs. From changes from 7.5YR3/2 (dark reddish grey) alternating 330 cm to the top of the unit, dark reddish brown (5YR with 5YR4/2 (dark brown) at the base to very dark 3/4) sandy and silty mud occurs as irregular layers or greyish brown (2.5Y4/2) to olive grey 5Y4/2 and 3/1 from blobs that may be rip-up clasts. 110 to 95 cm coinciding with the IRD layer.

AB C D L4a L3 L2 L1

340-350 cm 208-220 cm IRD

140-155 cm

L3 83-120 cm

Fig. 2. Photographs and x-radiographs showing examples of Lithofacies L1, L2, L3 and L4a in piston core 2001LSSL-014PC. A. Transition from L3 to L4a (marked by arrow) with 15-cm-thick IRD rich layer forming the top of L3. B. L3, massive, calcareous, grey pebbly mud. C. x-radiograph (left) and photograph (right) of interval near the top of L2, stratified and laminated red and grey sand and mudwith >2 mm clasts. D. L1, compact pebbly mud. 6 Anne E. Jennings et al. BOREAS

e A TC e e te ovite olinit ectite ioti #>2 mm Mean GZ, micronsCumulative Quartz Alkali FeldsparsPlagioclaseCalcite Dolomite Fe-Dolomit PyroxeneHematiteMaghemiteAmorphousChert Ka Sm B Fe-Chlorit Musc Illite grain size silica 0 sand L4a Trans

silt 1 Depth (m) L4b clay

0124 8 12 16 20 050100 10 20 015300100100100100301020100100201005080601020 Percentages

ca B PC ili s te s ) i e e it it lom ne ite te (1M v tz clase e t i hlorite o io ite m x hemite rt lin ite c ar ali Feldspars g lo g orphou e ectite -C Cumulative u lk alc o e-Do ema h us lite #>2 mm Mean GZ, microns grain sizeQ A Pla C D F Pyro H Ma Am C Kao Sm Biot Fe M Il 0 L4b 1

Trans 7.5 L4a

8.9 1 IRD 9.5

L3 10.8 silt clay 11 2 gravel L2

Depth (m) +sand

3

>50 300 L1

4

010200 40 80 120 50 100 20 40 015300100100100100201030601020040102004080601020 Percentages

Fig. 3. >2 mm (IRD) counts, mean grain size (GZ), cumulative percent of gravel, sand, silt and clay, and mineral weight percentages against lithofacies units in 2001LSSL-014 TC (A) and PC (B). Horizontal black lines running through plots denote lithofacies boundaries. Broad grey lines demarcate transitional and IRD units discussed in the text. Arrows and bold numbers beside the lithofacies column at the far right denote the calibrated radiocarbon ages.

Lithofacies 4 (L4). Bioturbated mud with rare IRD 95 Age models and lithofacies boundaries to 0 cm PC and 143–0cmTC.–The transition to L4 (Fig. 2A) in the PC is gradational with persistence of The Bayesian age model for 014PC was developed for small clasts and slight stratification between 90–95 cm. DR = 220Æ20 14C years and was constrained by the This lithofaciesis divided into two subfacies L4a and L4b benthic radiocarbon dates as well as two distinct litho- with a transition marked by an interval of more facies boundaries (at 35 and 204 cm depth in the core; pronounced bioturbation, increased grain size and a Fig. 4) likely to be associated with abrupt changes in colour shift (Fig. 3). The transition between 4a and 4b sedimentation rate. We used the R software routine occursbetween39and46 cmintheTCandbetween25and BChron (Haslett & Parnell 2008), set to run through 35 cm in the PC. An interval of increased numbers of 12 000 iterations based on the available constraints, >2 mmclastsfrom25to35 cm(PC)and39to46 cm(TC) generating 10 000 individual age model scenarios from coincides with this transition (Fig. 3). Unit L4a is soft, which the mean and standard deviations were derived. massive olive grey mud and sandy mud (5Y4/1 and 4/2) From 188 to 273 cm we used a linear extrapolation of the with rare clasts >2 mm. In the PC the interval from 95 to overlyingsedimentation ratebecausetheBayesianmodel 90 cm is faintly laminated (Fig. 2A). The median grain was unconstrained below 188 cm and made unreason- size is fine silt until 60 cm (PC) and 110 cm (TC) where it ably old age estimates (Table S1). For the remainder of coarsenstomediumsilt(Fig. 3).UnitL4bshowsacolour this paper we will focus on lithofacies boundary ages and changetodarkgreyishbrownmudveryrich insand-sized interpretations derived from the reservoir age scenario centric diatoms at 35 cm (PC) and 40 cm (TC) that DR = 220Æ20 years. Weacknowledge thatthe DRat this coincideswith a lackof reaction to HCl, indicating loss of site is at present poorly constrained and could be both calcite. Bioturbation becomes more pronounced in the larger and smaller through time. upper 10 cm of the piston core and in the upper 15 cm of L1, compact pebbly mud, has a date of >50 ka. This the trigger core. is much older than the overlying units and beyond BOREAS Retreat of the Smith Sound Ice Stream in the Early Holocene 7

2001LSSL-014PC with the transition andwith decreased sedimentation rates 0 in L4b and refined age control is lacking. L4b 25 cm; 4.8 ka BP trans 35 cm; 7.2 ka BP Grain-size modes 50 The Malvern grain-size data were used to define ‘grain- 35 L4a size modes’ (GSMs; Andrews et al. 2016) by applying 95 cm; 9 ka BP cluster analysis to log centred grain-size data using the 100 IRD 53 110 cm; 9.3 ka BP program ‘FuzMe’ (Minasny & McBratney 2002; Min- asny 2010). The performance indicators of the program 25 suggestedthatthemostefficientnumberofdistinctGSMs 150 L3 was four. 130

Depth (cm) Figure 5C shows average size distributions of the four GSMs in 014PC and TC. GSM1 and GSM2 have 200 204 cm; ~11.15 ka BP a primary mode of clay to very fine silt and fine silt, respectively, and both have a second mode of medium to ΔR = 220±20 14C years L2 Median age coarse sand, which is a mark of iceberg rafting (Andrews 250 +,-1σ error 2000). The very poorly sorted and fine-grained charac- Linear extrapolation 273 cm; ~11.7 ka BP teristics of GSM1 are consistent with suspension settling from turbid glacial meltwater plumes (Gilbert 1982). The >50.3 14 C ka BP at 340 cm L1 300 429 cm = coarser modal size of GSM2 is consistent with more 024681012 base of core Age (cal. ka BP) distal glacial marine settings (Powell 1981; Jennings 1993). GSM3 is fine sand reflecting high-energy condi- Fig. 4. Radiocarbon-based Bayesian age model with 1 sigma errors tions proximal to a sediment source, such as a glacier against lithofacies units in 2001LSSL-014PC. Lithofacies are shown in grounding line (Powell 1981; Jennings 1993). GSM4 is theright-handcolumnalongwiththeirboundarydepthsand calibrated radiocarbon ages based on the Bayesian model (above 188 cm) and on very poorly sorted coarse silt (Fig. 5C). Figure 5A, B linearextrapolation (below188 cm). Average sedimentation rates in cm shows the grain-size cluster membership downcore in the kaÀ1 are shown along the age depth curve between the radiocarbon TC and the PC, respectively. Fuzzy clustering allows a dates in cal. ka BP. sample to comprise a mixture of GSMs as opposed to ‘hard’ clustering in which each sample is assigned to a the radiocarbon time scale. The apparent age difference single cluster. In this study 43 of the 54 samples were between L1 and overlying units suggests that the sedi- dominated by a single GSM with ≤20% of other modes. mentsinL1eitherarereworkedorthatthereisan GSM1 characterizes L3, pebbly mud, which has high unconformity between L1 and L2. Based on the counts of >2 mm clasts interpreted as IRD and high DR = 220Æ20 years age model scenario, we estimate the sedimentation rates consistent with meltwater plumes. age of the boundary between L1 and L2 at c. 11.7 cal. ka GSM2 is associated with L1, the basal compact pebbly BP by extending the sedimentation rate of 130 cm kaÀ1 mud and it re-emerges in the upper lithofacies, L4, defined by the two deepest calibrated ages in the core to which has rare >2 mm clasts, but the coarse mode in the boundary (Fig. 4). The boundary between L2 and L3 GSM2 indicates that ice-rafting is active in L4. A similar is estimated at c. 11.15 cal. ka BP, by extending the 130 cm transition between GSM1 and GSM2 in the upper parts kaÀ1 rate downward 16 cm to the boundary between L2 of the TC and PC suggest a correlation point for the and L3 (Fig. 4). The sedimentation rate fell substantially overlap of these two cores (star in Fig. 5A, B). GSM3 is to 25.2 cm kaÀ1 in the middle part of L3. The full timing limited to L2, the laminated red and grey sand and mud, of L3 deposition extends between11.15 and 9.0 cal. ka BP. consistent with a high-energy environment proximal to a The age of the IRD layer that forms the top of L3 is grounding line. GSM4 dominates only at the transition estimated by extrapolation ofover- and underlying ages to between L2 and L3 and the transition between L4a and begin at 9.3 (9.37–9.21 1r) cal. ka BP and end at 9.0 (8.91– L4b. 9.11, 1r)cal.kaBP.TheintervalthatembracestheIRD layer has a higher sedimentation rate of 53 cm kaÀ1,twice Mineral assemblages the rate that was defined below in the upper part of L3. The boundary between L4a and L4b is 7.2 (7.04–7.33, 1r) The most abundant minerals or mineral groups are cal. ka BP. This boundary age is derived from 5 cm of showninFig. 3againstdepthandlithofacies,L1through upward extrapolation from the 7.5 cal. ka BP date at 40– L4. The overall mineralogy is dominated by quartz, 41cm.Theuppermostunit,L4b,hasalateHoloceneage alkali feldspars and carbonates (calcite, dolomite and and is estimated to begin at 4.8 (3.7–5.6, 1r)cal.kaBP,but Fe-dolomite). Clay minerals include kaolinite, smectite, the characteristics of the transitional layer suggest there is biotite, Fe-chlorite, muscovite and illite. Quartz, hema- significant bioturbation and missing sediment associated tite and chert have pronounced increases in L2, consis- 8 Anne E. Jennings et al. BOREAS

A TC B PC 0 4b L4b 1 Transition Transition 7.5 L4a 4a 8.9 Depth (m) 1 1 IRD Layer 9.5

L3 10.8 0 0.2 0.4 0.6 0.8 1 Cluster Membership, proportion 11 2

Depth (m) L2 C 5

4 GSM4 GSM2 GMS1 3 3 GSM3 GSM1 2 GSM2 L1 >50 300

Percent GSM3 GSM4 1 4 0 1000 100 10 1 Microns 0 0.2 0.4 0.6 0.8 1 Cluster Membership, proportion

Fig. 5. Grain-sizeclustermembershipagainstlithofaciesincore2001LSSL-014.A.TC;B.PC.C.Averagegrain-sizedistributionsofthefourgrain- size clusters. Arrows and bold numbers beside the lithofacies column denote the calibrated radiocarbon ages. Bold stars mark the approximate correlation depth of the TC and PC. tent with the coarse grain size and red (5YR) hue. Calcite 270 cm MF3a and MF3c are mixed, coinciding with the and Fe-dolomite have high wt. percentages in L1, are occurrence of rip-up clasts. Within L2 from 260 to very low in L2 and rise again by 160 cm (10.8 cal. ka BP) 230 cmMFbisdominant.The coincidenceoftheredand in L3. Calcite falls to low values at the transitional layer grey laminated unit, L2, with its relatively high hematite separating L4a and L4b in both the TC and PC providing content (Fig. 3) and dominance of quartz suggests that aclearsignaloftheL4a/L4bboundary(Fig. 3),although MFb owes its provenance toglacial erosion of red beds of this boundary is not detected in the mineral facies the Thule Supergroup that outcrop on central Ellesmere discussed below. Dolomite is low or absent until the Island (Fig. 1B) (Dawes 1997, 2006). In the upper part of upper part of L3; it disappears within L4a and reappears L2 and lower L3 MFb falls to low levels while MFc rises at both core tops in L4b. to high values along with a slight rise in MFa. A mineral K-means cluster analysis determined three mineral facies boundary occurs at 160 cm in L3, pebbly mud, assemblages, or mineral facies (MFa, MFb and MFc) with an abrupt change in dominance from MFc to MFa, that are used to explore changes in sediment provenance the calcite dominated facies. This transition from MFc to with depth in the cores (Andrews & Vogt 2014; Fig. 6A, MFa suggests the provenance shifts from the Thule B). A boxplot (Fig. 6C) shows the variations in weight % Supergroup beds to the Palaeozoic carbonate bedrock. of the minerals in the three mineral facies. High calcite, MFa remains the dominant mineral facies until the indicative of glacial erosion of the Palaeozoic bedrock transition from L4a to L4b (Fig. 6B). At this level calcite from southern Kane Basin and northward, distinguishes declines and the mineralogy returns to the regional signal MFa from the other two mineral clusters; high quartz of MFc.The dominance of MFc in the tops of theTCand and chert distinguish MFb. Multiple minerals including PC supports the interpretation that it represents a wide quartz, anorthoclase, total dolomite (Fe dolomite and provenance that includes a combination of local and dolomite), chert, saponite, muscovite, Fe-chlorite and regional sediment sources. biotite separate MFb from MFc, suggesting that MFc probably represents regional provenance rather than a Foraminiferal assemblages distinct sediment source. Changes in the degree of cluster membership down- Benthic foraminifera exhibited major assemblage com- core do not coincide exactly with lithofacies boundaries position changes that coincide closely with lithofacies (Fig. 6A, B) suggesting that changes in sediment prove- (Fig. 7; Table 2). L1 has relatively low abundances of nance occurred independently of sedimentation pro- foraminifers (60–20 gÀ1). The typical glacial marine cesses. L1 is dominated by cluster MF3a with a minor species Elphidium excavatum f. clavata and Cassidulina component of MFc until 322 cm. Between 322 and reniforme dominate the assemblages, but also present BOREAS Retreat of the Smith Sound Ice Stream in the Early Holocene 9

TC B PC A 0 0 1 L4b 4b Transition Transition 7.5 MFa L4a 4a MFb 1 8.9 Depth (m) 1 IRD layer MFc 9.5

L3 10.8 0 0.2 0.4 0.6 0.8 1 11 Cluster Membership 2 Depth (m) L2 C 60 MFa 50 MFb MFc 3 40 >50 300 L1 30

20 4

Mineral range (wt %) 10

0 0 0.2 0.4 0.6 0.8 1 Cluster Membership Chert Quartz Calcite Biotite KaoliniteSaponite Microcline Labradorite Fe-Chlorite Anorthoclase Illites & Mica Total Dolomite

Fig. 6. Mineral clusters denote mineral facies (MFa, MFb, MFc) in 2001LSSL-014 TC and PC. A. Mineral cluster membership in the TC. B. Mineral cluster membership in the PC. C. Mineral composition of the three clusters. Arrows and boldnumbersbeside the lithofacies columndenote the calibrated radiocarbon ages. were the chilled Atlantic Water species Cassidulina L2 is barren offoraminifera except in the top sample of neoteretis (cf. Jennings & Helgadottir 1994) and stable the unit. This single sample has a similar species compo- salinity, cold water species I. norcrossi (cf. Lloyd 2006); sition to the overlying L3 and is considered within the Arctic and sea-ice edge associated species, Stainforthia description of L3 fauna. feylingi, Islandiella helenae (cf. Polyak et al. 2002; L3 exhibits a large faunal shift at 130 cm (9.97 cal. ka Knudsen et al. 2008; Seidenkrantz 2013); productivity BP), suggesting a major environmental change within it. species, Nonionella iridea, Globobulimina auriculata arc- From 210 to 130 cm, benthic foraminifers rise to their tica, Buccella frigida, and Brizalina pseudopunctata (cf. peak abundances. Stetsonia horvathi, a perennial sea-ice Rytter et al. 2002; Knudsen et al. 2008; Duffield et al. indicator (Wollenburg & Mackensen 1998) is the domi- 2015) (Fig. 7). In addition, Bolivina pseudoplicata was nant species, ranging between 29 and 80% of the fauna. It present in all samples of L1 but only a few specimens in isaccompaniedbythestratifiedwatercolumn and chilled only three other samples in the TC and PC were found. Atlantic Water species C. neoteretis and the stable bot- Globobulimina auriculata arctica is found in L1 and L4 tom salinity species I. norcrossi. Cyclogyra sp. occurs in a only. The low faunal abundances and mixture of few samples only in the top of L2 and the lowest two palaeoenvironmental associations of these species (gla- samples of L3. This species is found in modern samples cial marine, chilled Atlantic Water, sea-ice edge, and fromthePetermann FjordandHallBasinatthenorthern productivity species groups) suggests that this unit end of Nares Strait (Jennings et al. 2017b). Planktic represents mixed assemblages. Bulimina marginata (not foraminifers (all NPS) rise throughout L3, but they reach shown in Fig. 7) was present in L1 only. It is a very rare their peak abundances immediately below the base of the speciesintheCAA(Vilks1969)andisabsentfromspecies IRD peak that forms the top of L3. NPS d18O values are listsoflateglacialandHolocenestudiesinnorthernBaffin stable, ranging between 3.1 and 2.9 in L3; d13C values Bay, highlighting the oddity of its occurrence in L1. The showaslighttrendtowardheaviervaluesrisingfrom0.2to radiocarbon date on mixed benthic species from L1 of 0.6 (Fig. 7). At 130 cm, the dominant benthic species >50 300 14C years BP suggests that the foraminifers in L1 changes to C. reniforme, a species associated not only are much older than the overlying sediments. with glacial marine environments, but also with chilled 10 Anne E. Jennings et al. BOREAS

a

arctic s A TC is rmi ata o ul sima a a c is polar i a trea ossi lowayi na bif arctic i a cr glomerata c -1 a leeanusa v concav -1 excavatum iridea rctica orquat ia feylingi ia obatulus ma hamina b ed h bar y a s a la arcti inella elegantotr troc l inat ionella tominell ononion gal n s rc neat iroplectammi lut ainforth ibicides l Benthics g Planktics g Nonionellina labradoricaBuccellaBrizalina tenerrima pseudopunctataCassidulina reniformeElphidium Stainfort No Epi MeloniEpistominellCassidulinaIslandiella neoteretis Islandiellanor St helenaeGlobobuliminaAstr C auri Bulim Ade Porta Cu Sp Egere Textularia t Agg 0 forma clavata L4b Trans

1 L4a Depth (m)

0 2000 4000 100 200 0204004060102030 0204002001001020 010100201003020102030100102003010010200801020020406080 Percentages

PC a ta B ric is o m t yi uncta s a ad ssi ava r p iforme atu o c low us o v a athi r a ul d e v c n ic % id eeanu lenae o ct -1 -1 eu ir l e c na r gal bat d, s excata sp. h a n o p la i imi io e frigida va l bar ia hor a lla th l la a s ata a tics g el n gyr or l hics g c nforthia feylingi ione ni lo nf lutinat O NPS c n o i tronon 13 C NPS 18 u rizali ai o a s ibicides l Bent Plank δ δ Nonionellina labB B Cassidulina ren Elphidium St N Epistominella arcticaMel Stetson Cassidulina neotereIslandiella nor Cyc Islandie St Globobuuricu A C Agg & B. tenerrima forma cla a 0 1 L4b Trans 7.5

L4a 8.9 1 IRD 9.5

10.8 L3 11 2 Depth (m) L2

3 L1 >50 300

4

030000400 1 3.2 2.8 020 01001202040020400204001001020 04030609001020020010 0508030120102002550 Percentages

Fig. 7. Foraminiferal assemblages against lithofacies units in 2001LSSL-014. A. TC. B. PC. PC includes stable isotope data on Neogloboquadrina pachyderma. Buccella frigida in the PC is the unfilled bar and B. tenerrima is the filled bar. Arrows and bold numbers beside the lithofacies column on the far right denote the calibrated radiocarbon ages in cal. ka BP.Bold stars mark the approximate correlation depth of the TC and PC. Horizontal black lines running through plots denote lithofacies boundaries. Broad grey lines demarcate transitional and IRD units discussed in the text.

AtlanticWaterandseasonallyice-coveredwaters(Polyak indicative of unstable environmental conditions includ- et al. 2002). S. horvathi declines and C. neoteretis disap- ing lowered salinity (Hald et al. 1994) and that is pears. This faunal shift suggests a change from a severely intolerant of perennial sea ice (Vilks 1980), enters the stratifiedwatercolumnwithnearlyperennialseaicecover, assemblages and becomes dominant at the top of L4a. implying a freshwater lid, overlying chilled Atlantic Spiroplectammina biformis, an agglutinated species asso- Water probably from the West Greenland Current to a ciated with ASW and glacial meltwater in Arctic period of seasonal sea ice cover. Near the top of L3 (Schafer & Cole 1986; Jennings & Helgadottir 1994), also Stainforthia feylingi, an opportunistic species associated occurs in this interval. At the top of L4a, Nonionellina with sea-ice edge productivity (Seidenkrantz 2013) and labradorica, an indicator of pulsed phytodetrital food strong freshwater stratification (Jennings et al. 2017a) supply (Cedhagen 1991; Rytteret al. 2002; Jennings et al. increases to equal C. reniforme. The fauna indicates a 2004)enterstheassemblage(Itprovidesthe 14Cdateatthe transitionwithin L3fromperennialornear-perennialsea top of L4a). Despite the marked changes in benthic icetoseasonalseaicecoveroverastronglystratifiedwater foraminiferal assemblages and planktic foram abun- column, in the presence of submerged Atlantic Water. dances, NPS d18O and d13C values are stable and similar Interestingly,thesamplewithintheIRDlayeratthetopof tothevalueswithinL3(Fig. 7).Bothplankticandbenthic L3 shows a transient return to increased S. horvathi and abundances decline in this interval. L4a assemblages are C. neoteretis,similartoconditionsofheavierseaiceinthe consistentwithdistalglacialmarineconditions,withIRD lower part of L3. andseasonalsea-iceandsea-iceedge marine productivity. A major faunal boundary coincides with L4a. Marine The transitional layer between L4a and L4b coin- productivity indicators, Nonionella iridea, Buccella ten- cides with the beginning of the agglutinated zone errima,Brizalinapseudopunctata,appearinthelowerpart in both TC and PC (Fig. 7). L4b assemblages including of L4a, along with Epistominella arctica, which reflects agglutinated species are best represented in the TC pulsed food supply in an overall oligotrophic environ- (Fig. 7A). Agglutinated foraminifers make up 25 to ment (Wollenburg & Kuhnt 2000) and sea-ice edge 80% of the fauna while the faunal abundances decline indicatorS. feylingiincreases, while C. reniforme steadily by an order of magnitude. Centric diatoms form a large declines. E. excavatum clavate, an opportunistic species part of the sand size fraction in L4b. Given the low BOREAS Retreat of the Smith Sound Ice Stream in the Early Holocene 11

Table 2. List of foraminifera mentioned in text with their original references. Correlation of PC and TC

Benthic foraminifera The correlation depth between the PC and the TC is Agglutinated taxa: consistent amongst most of the proxies. We estimate that Adercotryma glomerata (Brady 1878) 80 cm (Æ10 cm) in the PC is equivalent to the base of the Cribrostomoides crassimargo (Norman 1892) TC (144 cm). The TC ends above the IRD layer that Cribrostomoides jeffreysi (Williamson 1858) forms the top of L3, while the faunal data suggest that the Cuneata arctica (Brady 1881) ~ Eggerella arctica Hoglund€ 1947 base of the TC cannot be more than 10 cm from this Portatrochammina bipolaris Bronnimann€ &Whittaker 1980 boundary. We also base the tie point on the transition Recurvoides turbinatus (Brady 1881) between GSM1 and GSM2 (Fig. 5); the occurrence of Saccammina difflugiformis (Brady 1879) Nonionella iridea in thebase of L4b also provides a strong Spiroplectammina biformis (Parker & Jones 1865) Textularia earlandi Parker 1952 correlation (Fig. 7). The mineralogy does not provide Textularia torquata Parker 1952 specific evidence for correlation of the two cores. Calcareous taxa: Astrononion gallowayi Loeblich & Tappan 1953 Discussion Bolivina pseudoplicata Heron-Allen & Earland 1930 Brizalina pseudopunctata (Hoglund€ 1947) Buccella frigida (Cushman 1922) Interpretation of the depositional setting and provenance Buccella tenerrima (Bandy 1950) through time Bulimina marginata D’Orbigny 1826 Buliminella elegantissima (d’Orbigny 1839) The sediment sequence in 014PC and TC is interpreted to Cassidulina neoteretis Seidenkrantz 1995 recordretreatoftheSmithSoundIceStreamfromnorthern Cassidulina reniforme Nørvang 1945 BaffinBayintoNaresStraitduringtheEarlyHolocenewith Cibicides lobatulus (Walker & Jacob 1798) agesbasedontheagemodelshowninFig.4.L1is Elphidium excavatum forma clavata Cushman 1930 interpreted as a subglacial unit. Although it is fossiliferous, Eoeponidella pulchella (Parker 1952) Epistominella arctica Green 1959 the species have mixed environmental preferences and Epistominella takayanagii Iwasa 1955 include one species that has not been reported from Epistominella vitrea Parker 1953 Holocene sediments of the region. The >50 300 14C year Globobulimina auriculata arctica Hoglund€ 1947 BP date on foraminifera and the presence of >2mmclasts Islandiella helenae Feyling-Hanssen & Buzas 1976 Islandiella norcrossi (Cushman 1933) suggest that the unit represents subglacial reworking of Melonis barleeanus (Williamson 1858) previous marine and glaciomarine sediments that were Nonionella iridea Heron-Allen & Earland 1932 overrun by the Smith Sound Ice Stream and deposited as Nonionellina labradorica (Dawson 1860) till. Shells >40 000 years old occur abundantly in the area € Stainforthia concava (Hoglund 1947) and have been reported from tills and marine sediments on Stainforthia feylingi Knudsen & Seidenkrantz 1994 Ø Stetsonia horvathi Green 1960 Carey er adjacent to subglacially moulded sea-floor Triloculina tricarinata D’Orbigny in Deshayes 1832 features (Fig. 1B; Funder 1990; Blake et al. 1996; Kelly et al. 1999). Based on their unusual foraminiferal assem- Planktonic foraminifera blages, the sediments of L1 may be derived from glacial Neogloboquadrina pachyderma (Ehrenberg 1861) reworking of last interglacial (Qarmat marine event) and warm interstadial marine sediments that record late Quaternary intrusion of Atlantic Water and Subarctic numbers per gram, it seems likely that the rise in foraminiferaandmolluscsintonorthernBaffinBay agglutinated percentages is partly a result of dissolution (Funder 1990; Kelly et al. 1999). Radiocarbon dates on of CaCO3 tests. The chronology indicates that the shellsandforaminiferathatareeitherinfiniteormucholder agglutinated zone begins at about 6 cal. ka BP, within thanoverlyingsedimentshavebeenreportedfairlycom- the transitional layer and intensifies within L4b. It is monly on Arctic and Subarctic continental shelves (e.g. associated as well with a dramatic decline in sedimen- Jennings et al. 2006; Andrews et al. 2018), but tills also are tation rates and detrital calcite deposition. Several commonly barren of dateable fossil material (Jennings species indicative of marine productivity continue or 1993). The bulk density and shear strength of L1 were not increase in L4b: N. labradorica, Globobulimina auricu- measured, but the unit is noticeably compact, cracked and lata arctica, Brizalina pseudopunctata, Epistominella dense. The blobs of reddish sandy mud suggest that there vitrea, Buliminella elegantissima. The presence of I. he- was shearing by overriding ice but the preservation of the lenae may indicate sea-ice edge influence on food marinesedimentsbeneathglaciericeindicateseitherlimited production. Arctic agglutinated species Cuneata arctica duration of ice flow or incomplete erosion of the previous joins S. biformis, underscoring cold Arctic conditions sediments. (Schafer & Cole 1988) involving seasonal sea ice as The overlying L2 is interpreted to be proximal glacial indicated by the marine productivity species in the marine sediments exposed to the high-energy conditions fauna of L4b. at the grounding line (Fig. 5). Ice retreat began as earlyas 12 Anne E. Jennings et al. BOREAS

c. 11.7 cal.kaBPoraslateasc. 11.15 cal.kaBP(Fig. 4). 9 The presence of IRD (GSM1 and 2 and >2 mm clasts) A throughout the unit suggests that the ice stream did not

0 -1 Agassiz Temp (°C) 3000 terminate in an ice shelf at the time of retreat overthe core B g site. That does not eliminate the possibility that an ice 2000 shelf extended from the grounding line prior to retreat as 1000 -1

g 400 has been interpreted for the Lancaster Sound ice stream C 0 Benthics (Furze et al. 2017). The absence of foraminifera in L2 is 200 Marine Barren consistent with the interpretation of an ice-proximal Optimum

Planktics 0 40 environment (Fig. 7). The mineralogy of L2 (MFb) D indicates that its provenanceis linked toglacialerosion of 20 Thule Supergroup red beds that outcrop along Smith Lower Salinity Sound (Fig. 1B). Because the core site is more proximal 20 0

E E. excavatum clavata (%) to EllesmereIsland it seems most likely that L2 sediments High 10 Produc- were contributed by Innuitian ice entering Smith Sound tivity 0 from central Ellesmere Island to Bache Peninsula, the E. arctica (%) F 20 northward limit of the Thule Supergroup outcrop on Ellesmere Island (Dawes 2006). 10

L3 is a glaciomarine unit reflecting sedimentation from 50 G 0 turbid meltwater plumes and iceberg rafting (Fig. 5). The WGC 25 Seasonal C. neoteretis (%) dominance of MFa (Fig. 6) suggests that it reflects sea ice glaciomarine sedimentation when the grounding line 0 90 of the ice stream retreated north of Bache Peninsula (i.e. C. reniforme (%) H off of the Thule Supergroup red beds) into Kane Basin Heavy 45 Ice Proximal Heavy sea ice and onto the Palaeozoic carbonate bedrock (Fig. 1B). The Sea Ice 0 40 I S. horvathi (%) abrupt rise in MFa is at 160 cm (10.8 cal. ka BP). L3 represents progressively more distal glaciomarine 20

Quartz (%) J sedimentation. Between 11.15 and c. 10.4 cal. ka BP, 0 12 Subglacial foraminifers indicate strongly stratified conditions with 6 chilled Atlantic Water originating with the WGC as 20 K 0 Calcite (%) indicated by C. neoteretis (to 10.8 cal. ka BP) and a sea grounding ice covered surface, possibly promoted by freshwater flux 10 line N of Bache Penn from the retreating ice, indicated by dominance of S. hor- 0 vathi (Figs 7, 8). The faunal shift to dominance of >2mm (#/2 cm) Calving bay ice retreat Open Nares St. C. reniforme after 10.4 cal. ka BP indicates a change to L1 L2 L3 IRD L4a L4b seasonal sea ice. The benthic and planktic foraminiferal 12 11 10 9 8 7 abundances reach their highest levels between 10.4 and Age (cal. ka BP) 9.4 cal. ka BP indicating an Early Holocene marine optimum (Fig. 8). Fig. 8. Summary figure showing key proxies and lithofacies against The marine optimum was cut short by a transient age (DR = 220Æ20 years) calibrated ka BP in piston core 2001LSSL- event between c. 9.3 and 9 cal. ka BP involving a return 014. A. Lecavalier et al. (2017) temperature estimates from the Agassiz . B. Number of benthic foraminifera per gram dry sediment. C. to high IRD counts, more rapid sedimentation rates, Number of planktonic foraminifers per gram of dry sediment. D. and fauna indicative of strong water-column stratifica- Elphidium excavatum forma clavata percentages. E. Epistominella tion and heavy sea ice. This event is followed by unit arcticapercentages.F.Cassidulinaneoteretispercentages.G.Cassidulina L4a and transition to a new foraminiferal fauna reniforme percentages. H. Stetsonia horvathi percentages. I. Quartz weight percentages. J. Calcite weight percentages. K. Counts of >2mm indicative of seasonal sea-ice edge marine productivity clasts from x-radiographs. and reduced bottom-water salinity (Fig. 8). The faint sediment stratification that spans the transition from the upper 5 cm of the IRD event and the lower 5 cm of After the IRD event, L4b shows continued glacio- L4a suggests current activity at this boundary. The marine conditions until c. 7.2 cal. ka BP with deposition transient IRD unit is the most likely marker for retreat of calcite bearing MFa indicating continued erosion of of the Humboldt Glacier from Kennedy Channel and the Palaeozoic outcrop from the full extent of Nares the opening of Nares Strait (Fig. 8). We argue that the Strait, but reduced numbers of large IRD clasts suggest- opening of Nares Strait would probably involve a large ing that ice margins had retreated well into the fjords or flux of icebergs and fresh water, and a later change in onto land along the strait. The transitional unit that productivity as nutrient-rich ASW entered Baffin Bay separates L4a and L4b marks a pronounced slowing of as is shown in 014PC. sedimentation rates and loss of detrital calcite in BOREAS Retreat of the Smith Sound Ice Stream in the Early Holocene 13 response to glacier recession (Fig. 4). The strong rise in consistent with capture of the continued retreat of the agglutinated foraminifera and centric diatoms in L4b Humboldt Glacier and all others to the north of the site reflects increased calcium carbonate dissolution poten- afteropeningofthestrait.TheageoftheopeningofNares tially related to postglacial shallowing of Nares Strait in Strait defined from HLY05GC on the northern end of response to isostatic uplift and relative increase in ASW Nares Strait is as old as 9 cal. ka BP (DR = 0) and as undersaturated with respect to CaCO3 (Azetsu-Scott young as c. 8.5 cal. ka BP (DR = 335) (Jennings et al. et al. 2010) as has been suggested for Lancaster Sound/ 2011). In terms of the maps summarizing knowledge of BarrowStraitbyPienkowski et al.(2012).L4bextendsto deglaciation of the area the opening is estimated to have the surface sediments in Smith Sound and must reflect occurred by 8.45 cal. ka BP (Dyke et al. 2002). Given the establishment of modern conditions including the NOW. uncertainties of DR at both ends of Nares Strait and the However, the data herein do not indicate conclusively close spacing of events in the cores, we suggest that the when the NOW formed. timing of the opening of the strait is difficult to pin down, butcurrentevidencesuggestsitcouldbeasoldas9 cal.ka BP and as young as 8.3 cal. ka BP. Contributions and conflicts with previous reconstructions Thedeglaciationofcoresite014recordsalatephaseofthe Early Holocene paleoenvironments in northern Baffin Bay retreat of northern Baffin Bay ice streams, which began after Heinrich Event 1 as inferred from the timing of The ice-proximal sedimentation at core site 014 coincides Baffin Bay Detrital Carbonate (BBDC) events (Simon with early Holocenewarmth inthe Agassiz IceCore, high et al. 2016; Jackson et al. 2017; Jennings et al. 2017a). solar insolation at high latitudes (Fisher et al. 2012; BBDC1 (c. 14.5–13.7 cal. ka BP) marks the early part of Lecavalier et al. 2017) and Atlantic Water foraminiferal the retreat of the northern Baffin Bay ice streams and assemblages that suggest an extensive WGC in the Early precedes the evidence of ice retreat so fargathered in shelf Holocene (Knudsen et al. 2008; Pienkowski et al. 2014; cores from northern Baffin Bay; BBDC0 (12.7–10.6 cal. Jennings et al. 2017a).The Early Holocene foraminiferal ka BP) overlaps the deglaciation of the shelf. Outer assemblages in 014PC support northward extension of Lancaster Sound core 2011804-0010 (Fig. 1B) dates the WGC Atlantic Water,beginning with evidence for chilled initial retreat of the Lancaster Sound ice stream at Atlantic Water underlying cold meltwaters and sea ice >13.2 cal. ka BP (DR = 185Æ40) (Furze et al. 2017). cover, prior to the opening of Nares Strait from 11.15 to Core91039-012PCoffNWGreenlandindicatesretreatof 10.4 cal. ka BP, transitioning to a marine optimum with the Smith Sound ice stream was underway by 12.3 cal. ka peak faunal abundances between 10.4 and 9.3 cal. ka BP BP (DR = 0; Knudsen et al. 2008; Fig. 1B). Data from indicative of seasonal sea ice. The marine optimum 014PC indicate that the ice retreated from the site probably was delayed from the atmospheric optimum by >11.15 cal. ka BP (or as early as c. 11.7 cal. ka BP by the pronounced local effects of the retreating ice margin linear extension of the age model downward to the L1/L2 as has also been noted in Lancaster Sound/Barrow Strait contact; Fig. 4; DR = 220Æ20). In addition, the shift (Ledu et al. 2010). A transient return to high IRD and from MFc to MFa at 10.8 cal. ka BP (Æ) indicates that heavy sea-ice indicators from 9.3 to 9 cal. ka BP is grounded ice on theEllesmereIsland side ofthe straithad immediately followed by evidence for a major environ- moved off of the Thule red beds (i.e. north of Bache mental shift to high productivity fauna, fresher bottom Peninsula; Fig. 1B) and into Kane Basin by this time. waters and seasonal sea ice, which we interpret to be in Georgiadis et al. (2018) present a new record of the response to entryof ASW with opening of Nares Strait to deglaciation of southwestern Kane Basin with core the Arctic-Atlantic throughflow (Fig. 8). Relatively high Kane2B, northeast of 2001LSSL-014 PC and TC marine productivity associated with seasonal sea ice (Fig. 1B). The site of Kane2B deglaciated at 9 ka along with relatively high sedimentation rates and (DR = 240 years), which would correspond in timing to deposition of detrital carbonate continue until 7.2 cal. the IRD unit at the end of L3 in 014PC interpreted in this ka BP while ice margins retreated. But, the slow paper to record the opening of Nares Strait. However, a sedimentation after deglaciation corresponds with an subsequentcoarseunitinKane2Bdepositedc. 8.3 cal.ka agglutinated foraminiferal zone in Smith Sound that is BP has been interpreted by Georgiadis et al. (2018) to matched along the Baffin Island and the inner Labrador record opening of the strait. Alternatively, it may be that shelvesandhasbeenconsideredtobeanexpressionofthe this 8.3 ka unit was deposited in response to recession of increasing dominance of the corrosive ASW that devel- the Humboldt Glacier at 8.3Æ1.7 cal. ka BP (Reusche oped as isostatic adjustment shallowed channels of the et al. 2018) and thus may have occurred after opening of CAA (Williams et al. 1995). It began byc. 6 cal. ka BP in the strait. Core 014 does not have a distinct event at Smith Sound (Fig. 7); between 7.7 and 6.5 cal. ka BP in 8.3 cal. ka BP that can be attributed to the Humboldt Barrow Strait (Pienkowski et al. 2012) and Strathcona Glacierrecession,butitdoesshowevidenceforcontinued Sound (Short et al. 1994); by 6 14C ka BP on the Baffin glaciomarine sedimentation until 7.2 cal. ka BP,which is margin (Osterman & Nelson 1989) and in Cumberland 14 Anne E. Jennings et al. BOREAS

Sound (Jennings 1993). The exact timing of the onset of the qXRD data and ran the statistical analyses on the grain-size and the agglutinated zone is not well constrained in 14PC and qXRD data. B. Oliver counted foraminiferal assemblages and made the map for Fig. 1B. M. Walczakacquired the radiocarbon dates and made TC. the Bayesian age model. A. Mix did the stable isotope analyses.

Data availability statement. – The datathat support the findings of this Conclusions study are openly available in [PANGAEA e.g “figshare”] at [https://doi. pangaea.de/10.1594/PANGAEA.897572]. • 2001LSSL-014PC captures retreat of the confluent Innuitian and Greenland ice sheets from northern- References most Baffin Bay into Smith Sound. Ice retreated from the site as early as c. 11.7 cal. ka BPor as late as 11.15 Andrews, J. T. 2000: Icebergs and iceberg rafted detritus (IRD) in the – cal. ka BP. North Atlantic: facts and assumptions. Oceanography 13, 100 108. Andrews, J.T.& Eberl, D. D. 2011: Surface (sea floor) and near-surface • Lithofacies 1 (L1), compact, grey pebbly mud, is (box cores) sediment mineralogy in Baffin Bay as a key to sediment considered to be a till comprised of consolidated, provenance and variations. Canadian Journal of Earth reworked marine sediments. The faunal content and Sciences 48, 1307–1328. Andrews, J. T. & Vogt, C. 2014: Source to Sink: Statistical identification of an infinite radiocarbon age suggest that the reworked regional variations in the mineralogy of surface sediments in the marine sediments originally were deposited during western Nordic Seas (58°N – 75°N; 10° W- 40°W). Marine Geology 357, warm interstadial and MIS 5e marine events recorded 151–162. Andrews, J.T.,Cabedo-Sanz, P.,Jennings, A. E., Olafsdottir, S., Belt, S. in onshore sediments from the Thule region.   • & Geirsdottir, A. 2018: Sea ice, ice-rafting, and ocean climate across Ice retreat from this site did not involve an ice shelf Denmark Strait during rapid deglaciation (  16–12 cal. ka BP) of although an ice shelf could havebeen presentwhen the the Iceland and East Greenland shelves. Journal of Quaternary Smith Sound Ice Stream was at its maximum extent. Science 33, 112–130. Ice-proximal sediments are laminated and >2 mm Andrews, J. T., Stein, R., Moros, M. & Perner, K. 2016: Late Quaternary changes in sediment composition on the NE Greenland margin clasts are dispersed throughout, suggesting instead (~73 degrees N) with a focus on the fjords and shelf. Boreas 45,381–397. grounding line retreat from a calving margin. The Azetsu-Scott,K.,Clarke,A.,Falkner,K.,Hamilton,J.,Jones,P.E.,Lee, mineralogy and red colour implicate glacial erosion C., Petrie, B., Prinsenberg, S., Starr, M. & Yeats, P. 2010: Journal of Geophysical Research 115, C11021, https://doi.org/10.1029/2009jc by the Innuitian Ice Sheet of Thule Supergroup red 005917. beds on Ellesmere Island adjacent to Smith Sound. Belkin, I. M. 2004: Propagation of the ‘‘Great Salinity Anomaly’’ of the • Foraminiferal assemblages indicate a strongly strati- 1990s around the northern North Atlantic. Geophysical Research fied water column with WGC Atlantic water sub- Letters 31, L08306, https://doi.org/10.1029/2003gl019334. Belkin,I.M.,Levitus,S.,Antonov,J.&Malmberg,I.S.-A.1998:‘‘Great merged beneath a meltwater lid with pervasive sea ice SalinityAnomalies’’ intheNorthAtlantic.ProgressinOceanography coverfromc. 11.15to10.4 cal.kaBP,toglacialmarine 41,1–68. conditions associated with seasonal sea ice cover and Bennett, R., Campbell, D. C., Furze, M. F.A. & Haggart, J.W.2015: The shallow stratigraphy and geohazards of the NE Baffin Shelf and marineoptimumconditionsfrom10.4to9.3 cal.kaBP. LancasterSound.BulletinofCanadianPetroleumGeology62,217–231. • OpeningofNaresStraitasanArctic-Atlanticthrough- Bennike, O. 2002: Late Quaternary historyof WashingtonLand, North flowmayberecordedbyanIRDlayerboundedbyages Greenland. Boreas 31, 260–277. ofc. 9.3to9 cal. kaBP.Theolder thanexpectedageof Bennike, O.,Dawes, P.R., Funder,S., Kelly,M.& Weidick,A. 1987:The late Quaternary history of , Northwest Greenland: this layer compared to other records suggests that the discussion. Canadian Journal of Earth Sciences 24, 370–374. reservoir correction applied may be too small. Con- Blake, W. Jr. 1977: Glacial sculpture along the east-central coast of tinued carbonate deposition through L4a indicates Ellesmere Island, Arctic Archipelago. Report of Activities, Part C, – continuediceretreatfromtheseauntilthetimingofthe Geological Survey of Canada, Paper 77-1C, 107 115. Blake, W.Jr. 1992: Holocene emergence at Cape Herschel, east-central transition to L4b (7.2 cal. ka BP). Ellesmere Island, Arctic Canada: implications for ice sheet config- • Onset of conditions similar to ‘modern’, with slower uration. Canadian Journal of Earth Sciences 29, 1958–1980. sedimentation rates and the beginning of the aggluti- Blake,W.Jr.,Boucherle,M.M.,Fredskild,B.,Jannssens,J.A.&Smol,J. P.1992: The geomorphological setting, glacial history and Holocene nated foraminifer zone, began by 4.8 cal. ka BP. development of ‘Kap Inglefield Sø’, Inglefield Land, North-West Greenland. Meddelelser om Grønland, Geoscience 27,1–42. Blake, W.Jr., Jackson, H. R. & Currie, C. G. 1996: Seafloor evidence for Acknowledgements. – Funding for this research was supplied by glaciation, northernmost Baffin Bay. Bulletin of the Geological National Science Foundation grants PLR-ANS 1417784 and OPP Society of Denmark 43, 157–168. 1804504. We thank the Atlantic Geoscience Center, Dartmouth, Cedhagen, T. 1991: Retention of chloroplasts and bathymetric distribu- Canada, for providing samples, data and access to the cores. In tion in the sublittoral foraminiferan Nonionellina labradorica. Ophelia particular, we acknowledge Kate Jarrett and Peta Mudie for their help 33,17–30. at AGC. AndreRochonand Peta Mudie did thevisual core descriptions Coulthard, R. D., Furze, M. F. A., Pienkowski, A. J., Nixon, F. C. & and initial core sampling. We thank Wendy Roth and June Padman for England, J. H. 2010: New marine DR values for Arctic Canada. theirtechnicalhelp insampleprocessingfor sedimentandstableisotope Quaternary Geochronology 5, 419–434. analyses, respectively. We thank reviewers Svend Funder and Morten Curry, R. & Mauritzen, C. 2005: Dilution of the northern North Hald for their helpful comments and critique of this manuscript. Atlantic Ocean in recent decades. Science 308, 1772–1774. Dawes, P.R. 1997: The Proterozoic Thule Supergroup, Greenland and Author contributions. – A. Jennings led the project and supervised the Canada: history, lithostratigraphy and development. Geology of faunalanalysesandpickingforradiocarbondating.J.Andrewsacquired Greenland Survey Bulletin 174, 120 pp. BOREAS Retreat of the Smith Sound Ice Stream in the Early Holocene 15

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