ORIGINAL

Late Quaternary history of contourite drifts and variationsin Labrador Current flow, Flemish Pass, offshore eastern Canada

Nicole R. Marshall & David J. W. Piper &

Francky Saint-Ange & D. Calvin Campbell

Received: 17 February 2014 /Accepted: 20 June 2014 /Published online: 12 July 2014# Crown Copyright 2014

Abstract Contourite drifts of alternating sand and mud,shaped by the Labrador Current, formed during the late Qua-ternary in Flemish Pass seaward of the Grand Banks of New-foundland, Canada. The drifts preserve a record of LabradorCurrent flow variations through the last glacial maximum. Ahigh-resolution seismic profile and a transect of four cores werecollected across Beothuk drift on the southeast side of FlemishPass. Downcore and lateral trends in grain size and sedimenta-tion rate provide evidence that, between 16 and 13 ka, sedimentwas partitioned across Beothuk drift and the adjacent FlemishPass floor by a strong current flow but, from 29 to 16 ka,sedimentation was more of a blanketing style, represented bydraped reflections interpreted as being due to a weaker current.The data poorly resolve the low sedimentation rates since 13 ka,but the modern Labrador Current in Flemish Pass is the stron-gest it has been in at least the past 29 ka. Pre-29 ka current flowis interpreted based on reflection architecture in seismicprofiles. A prominent drift on the southwestern side ofFlemish Pass formed above a mid-Miocene erosion surface,but was buried by amass-transport deposit after the penultimateglacial maximum and after drift deposition switched to eastern

Flemish Pass. These findings illustrate the temporal complexityof drift sedimentation and provide the first detailed proxy forLabrador Current flow since the last glacial maximum.

Introduction

The Labrador Current is a surface current that flows south-ward close to the shelf break along the Labrador and New-foundland continental margin (Lazier and Wright 1993). TheLabrador Current is noteworthy for sculpting major upper-slope contourite drifts on the eastern Canadian margin(Fig. 1), whereas most drifts described in other settings resultfrom sub-surface thermohaline circulation. Variations in cur-rent flow can be recorded in (1) drift architecture (e.g., Howeet al. 1994; Koenitz et al. 2007) and (2) sortable silt signatures(e.g., McCave et al. 1995; McCave and Hall 2006). There aretwo major controls for contourite sedimentation: variations inbottom current intensity and sediment supply (seeBrackenridgeet al. 2011). Late Quaternary flow variations ofthe Labrador Current are significant because they can contrib-ute to our knowledge of the subpolar gyre circulation from thelast glacial maximum (LGM) to the present day.

Flemish Pass (referred to herein as the Pass) is a narrow,perched sedimentary basin in 1,000 to 1,300 m water deptheast of the Grand Banks of Newfoundland and west of Flem-ish Cap (Fig. 1). Sediment was deposited on the nearly flat(<0.3°) Flemish Pass seafloor from turbidites during occasion-al shelf-crossing glaciations on the Grand Banks, but mostlyfrom icebergs and proglacial sediment plumes transportedwith the Labrador Current (Piper and Pereira 1992;Huppertz and Piper 2009). A prominent contourite drift,Sackville Spur (Kennard et al. 1990), was constructed in theCenozoic at the northern end of Flemish Pass (Figs. 1 and 2).Recently collected multibeam bathymetry shows the presenceof a drift deposit south of the central constriction of Flemish

Electronic supplementary material The online version of this article(doi:10.1007/s00367-014-0377-z) contains supplementary material,which is available to authorized users.

N. R. Marshall (*) : F. Saint-AngeDepartment of Earth Sciences, Dalhousie University, Halifax,NS B3H 4R2, Canadae-mail: nrmarshall@vims.edu

D. J. W. Piper : F. Saint-Ange :D. C. CampbellGeological Survey of Canada, Bedford Institute of Oceanography,Dartmouth, NS, Canada

Present Address:N. R. MarshallVirginia Institute of Marine Science, College of William and Mary,Gloucester Point, VA 23062, USA

Geo-Mar Lett (2014) 34:457–470DOI 10.1007/s00367-014-0377-z

Pass. This drift, the Beothuk drift, has been investigated bynearly 9-m-long cores and seismic reflection profiles (Fig. 2).

The purpose of this study is to (1) document the style of driftconstruction on the upper slope in the confined Flemish Passbasin, (2) define a high-resolution history of the Labrador Cur-rent through the last 29 ka, (3) extend understanding of thisrecord back in time using seismic profiles, and (4) exploreimplications of this record for the North Atlantic Subpolar Gyre.

Geologic and oceanographic setting

Flemish Pass is partially infilled by prograding sequences ofLate Cretaceous and Cenozoic sediments that crossed theGrand Banks of Newfoundland (Piper and Normark 1989).The Quaternary sediments consist predominantly of mud withthin interbedded turbidites from the Grand Banks slope (Piper

and Pereira 1992). Piper and Campbell (2005) interpretedsome thick-bedded sand and mud along the base of the Flem-ish Cap slope as contourite deposits.

Glacial ice completely crossed most of the eastern Canadi-an continental shelf during major glacial stages (Shaw 2006),although maximum ice extent during the LGM only reachedthe middle shelf on the Grand Banks (Sonnichsen and King2005). Glacial ice extended to Flemish Pass during marineisotope stage (MIS) 6 (~130 ka) and deposited till tongues onthe upper slope (Huppertz and Piper 2009). Core MD95 2026on Sackville Spur provides age control for stratified sedimentin Flemish Pass back to MIS 6 (Piper and Campbell 2005).Previously dated, distinctive, tan-colored, ice-rafted debris(IRD)- and carbonate-rich Heinrich (H) layers provide amillennial-scale correlation within Flemish Pass (Huppertzand Piper 2009). These H layers were deposited throughoutthe North Atlantic, and resulted from periodic, intensifiediceberg discharges through Hudson Strait (Broecker et al.1992).

The Labrador Current originates in the northern LabradorSea adjacent to Greenland (Cuny et al. 2002). This flow ofcold water reaches Orphan Basin, where it splits into twobranches as it approaches Flemish Pass (Fig. 1). The innerbranch of the Labrador Current flows through Flemish Passand the outer branch flows northward around Flemish Cap. Astudy by Han et al. (2008) showed that the modeled transportthrough Flemish Pass is consistent with the observationalestimate of 5.8 Sv, whereas the outer branch north of FlemishCap has a transport of 6.6 Sv, and only 0.3 Sv flows along thecontinental shelf in water depths <300 m. Reference to vari-ations in flow of the Labrador Current throughout this paperrefers to the inner branch flowing through Flemish Pass.

The Labrador Current has varied in speed and temperaturethrough time, on a variety of timescales. Recent time-seriesmeasurements show that there are small, annual velocityvariations in the Labrador Current (Lazier and Wright 1993).Within the past 1,600 years, the distal Labrador Current inEmerald Basin offshore Nova Scotia was relatively cold andstrong until 150 years ago, based on numerous proxies incores, but after ~AD 1850 less Labrador Current flowedwestward along the Scotian margin (Keigwin et al. 2003).

Scott et al. (1984) obtained a proxy record of the LabradorCurrent strength off Newfoundland based onmicropaleontologyback to the LGM, and inferred significant variations in the flowacross the continental shelf through the Holocene, including awarming at ~6 ka. However, well-dated, continuous proxyrecords through the LGMwere lacking. This study fills that gap.

Materials and methods

Multibeam bathymetry (using a Kongsberg Simrad EM 302multibeam echosounder operating at a frequency of 30 kHz)

Fig. 1 Map of the northern Atlantic Ocean showing the location ofFlemish Pass (FP) and the principal components of the North AtlanticSubpolar Gyre (NASG; modified from Lewis et al. 2012). Hamilton Spur(1), Orphan Spur (2) and Sackville Spur (3) are previously identifiedsediment drifts on the upper slope. FC Flemish Cap, LF Laurentian Fan,OB Orphan Basin

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and acoustic backscatter data, together with TOPAS sub-bottom profiles, were collected through southern Flemish Passby the Nereida program in 2009 and 2010 (http://www.nafo.int/science/frames/nereida.html). High-resolution seismic re-flection profiles were acquired from a Huntec Deep TowSystem sparker and a 210 cubic inch G.I. gun on CCGSHudson cruise 2011031. Nearby reflectors identified fromprevious studies are correlated with the 2011031 profiles toprovide seismic stratigraphic control in the study area.

Piston core sediment sampling was conducted using theAGC Long Coring Facility, which recovers piston core sam-ples up to 16m in length, with a coincident trigger weight coreproviding a less disturbed section immediately below theseabed (Table 1). All cores were split, described, andphotographed (high-resolution optical and X-ray); color wasmeasured by spectrophotometer, and physical properties bymeans of a Geotek Multisensor Core Logger. Details ofstandard laboratory procedures are found in Weitzman et al.

Fig. 2 Bathymetric map of Flemish Pass showing the locations of cores (yellow dots) and selected seismic profiles (thick red lines) used for correlations.Dashed red line Industry seismic line 83-2852 from the Canada-Newfoundland and Labrador Offshore Petroleum Board

Table 1 Core locations, corelengths and water depths Core Latitude (°N) Longitude (°W) Trigger weight

core length (m)Piston corelength (m)

Water depth (m)

2011031-21 46°45.0599 46°41.0408 1.84 8.56 991

2011031-22 46°42.0054 46°48.9054 1.92 8.75 1,230

2011031-23 46°41.7189 46°53.3934 0.37 2.71 1,251

2011031-24 46°42.2507 47°02.1370 0.82 5.71 1,184

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(2014). In specific cores, samples were taken for carbonate,grain-size, 14C dating and geochemical analyses, and selectedelements were measured by downcore pXRF using an Innox-XSystems model DP-6000 in soil mode (Beam 2 and Beam 3).

H layers, originally recognized by Heinrich (1988), wereidentified and correlated using CIElab L* and a* peaks andtotal carbonate variation (Huppertz and Piper 2010), by com-parison with well-dated records from the Labrador Sea(Andrews and Barber 2002; Tripsanas and Piper 2008). Cor-relations were constrained by radiocarbon dates from previ-ously dated cores and dates from piston cores 21 and 22(Table 2). These new dates were obtained from the planktonicforaminifer Neogloboquadrina pachyderma sinistral. Calib v.6.0 was used to calibrate all 14C ages, with a local delta R(reservoir correction) of 144±38 years (McNeely et al. 2006).

Grain-size data were acquired with a Beckman Coulter LS230 laser diffraction particle size analyzer (0.04–2,000 μm)from core 21, which had the thickest sediment accumulationand thus the highest-resolution record. Working halves ofpiston core 21 were subsampled every 40 cm, and every 20cm within H layers. The accompanying trigger weight corewas subsampled every 5 cm to obtain a higher resolution ofgrain-size variations in most recent times. Carbonate contentis low (see Results, Cores), so carbonate removal prior tograin-size analysis was not a concern. Silica removal wasnot needed because smear slides showed low opaline silicacontent. The use of the laser analyzer for grain-size analysis isjustified even though McCave et al. (2006) concluded thatsortable silt measurements are biased due to the shape effect.Konert and Vandenberghe (1997) resolved the shape effect forcrushed quartz fine sediment versus normal clay-bearing ma-rine sediment. The sediments in the present study are glacialproducts and therefore the use of the laser is justified becausethe fine sediments are assumed to resemble crushed quartz.

A 4 g subsample from piston core 22 between 4.11 and3.99 m below the core top, from a moderately sorted unit ofvolcanic lapilli tuff, was wet sieved, picked, and powderedprior to geochemical analysis for major and trace elements,using inductively coupled plasma mass spectrometry (ICP-MS) following methods 4B, 4B1, and 4B2 of ActivationLaboratories (2011). A split of this sample was made into apolished thin section.

Summary raw laboratory data are provided in Table 1 of theonline electronic supplementary material for this article.

Results

Multibeam bathymetry

The multibeam bathymetry (Fig. 3a) shows a prominent ter-race above the main floor of the Pass, extending southwardfrom the narrowest constriction in central Flemish Pass andalong the southeastern side of the Pass. To the south, theterrace abuts a bedrock high known as Beothuk Knoll. Theterrace sits nearly 200 m above the floor of the Pass and is >15km wide.

Acoustic backscatter (Fig. 3b) shows areas of highly andweakly reflective seafloor, which generally represents changesfrom coarser- (high reflectivity) to finer-grained (low reflec-tivity) seafloor sediments. The coarser-grained sediments arefound through the center and western side of Flemish Pass; thefiner-grained sediments are concentrated predominately onthe eastern side of the Pass, including the terrace.

Seismic stratigraphy

Regional seismic stratigraphic markers from previous studieswere correlated into the study area to provide seismic strati-graphic control for this study. Prominent unconformities arerecognized in industry seismic profiles in central Flemish Passand are dated in the Gabriel C-60 well as mid-to-late Mioceneand Late Cretaceous (Piper and Pereira 1992; Edwards andMcAlpine 1999). The mid-Miocene unconformity, which cor-responds to the F’ reflector of Piper and Normark (1989) andPiper and Pereira (1992), was correlated southward to thestudy area using industry seismic line 83-2852 (not illustrated,available from the Canada-Newfoundland and Labrador Off-shore Petroleum Board). In addition, correlation was madewith the Plio-Pleistocene record on the Grand Banks slope(Piper and Normark 1989; Huppertz and Piper 2009). Theyellow reflector (MIS 6; termed FP75 by Huppertz and Piper2009) identified by Piper and Campbell (2005) is correlated tothe main profile used in this study (Fig. 4). The basal shelf-crossing glaciation is marked by a regional unconformity onthe outermost shelf (B reflector in Figs. 5 and 6, and correlatedto Fig. 4) and is overlain by a unit interpreted as glacial till

Table 2 Selected reservoir corrected ages from cores 87008-013 (Piperand Pereira 1992; Huppertz 2007), 96018-06 (Huppertz and Piper 2010)and 2011031 (this study) in Flemish Pass (Calib v. 6.0; local delta R(reservoir correction) of 144 ± 38 years, McNeely et al. 2006)

Core 14C age (BP) Calibrated age (2σ) Depth (cm)

87008-013 11,900 ± 110 13,228 249 75

13,120 ± 100 14,746 492 597

23,130 ± 190 27,294 642 920

96018-06 17,860 ± 60 20,566 412 207

24,940 ± 140 29,226 457 386

26,250 ± 170 30,538 360 440

2011031-21 12,155 ± 35 13,450 141 82–87

12,555 ± 35 13,891 152 177–182

2011031-22 21,950 ± 90 25,732 204 393–397

35,270 ± 420 39,248 888 818–824

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(Huppertz and Piper 2009). An overlying reflector, A, isrecognized throughout the study area.

Figure 4 illustrates the seismic stratigraphy for the studyarea. The eastern side of the profile shows that the seismic

Fig. 3 a Multibeam bathymetryimagery and b backscatterimagery of the study area(courtesy of the Nereida Program)

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stratigraphy underlying the terrace imaged in the multibeamdata comprises mounded and divergent reflections. Based onthis reflection geometry, the terrace is interpreted to representa contourite drift and is informally termed the Beothuk drift. Adeeper contourite drift is interpreted on the western side of theline, forming a distinctive and large drift deposit overlying aregional unconformity. Subsequently, a large mass-transportdeposit (MTD) that originated from failure of the westernslope of Flemish Pass buried the deeper drift. This buriedMTD is frontally emergent (Frey-Martinez et al. 2006), withthe top of the MTD extending downslope over previouslydeposited sediment.

Cores

Four piston cores up to 9 m long were collected in an E–Wtransect across Flemish Pass. Core 21 penetrates the top ofBeothuk drift. There are significant variations in L*and a* (allcores), and Ca and carbonate downcore (only measured incore 21; Fig. 7). Core 22 is at the foot of the drift. Core 23penetrates into an area of highly reflective horizons in thecenter of Flemish Pass, where erosion is prominent. Core 24 is

near the foot of the Grand Banks slope and penetrates a smallMTD. The cores consist predominately of sand and sandy silton the floor of Flemish Pass and sandy silt and silty clay on thedrift. All cores include carbonate-rich layers of tan silty claywith IRD.

Downcore variations in grain size (Fig. 8) in both piston andtrigger weight core 21 are illustrated as clay and fine silt (<10μm), sortable silt (10–63 μm) and fine sand (63–250 μm). Theclay and sortable silt curves closely follow each other, with theexception of within 1 m of the seafloor, where the % of claydeclines and the sortable silt % (SS%) increases (following theincrease in % of fine sand). Correlation of the trigger weightcore with the piston core suggests that the piston core did notsample the upper 0.40 m of the sediment column.

A bed of volcanic lapilli tuff at a depth of 4.11 to 3.99 m inpiston core 22 is moderately sorted and shows normal sizegrading. The base of this tuff appears erosional. The lapilli aredark brown, glassy and highly vesicular. Major element chem-istry confirms the glass is basaltic (Fig. 9a) and trace elementsshow it to be highly alkaline (Fig. 9b, c).

Four new radiocarbon dates were obtained (Table 2). Twodates of 13.5 and 13.9 cal ka in the upper part of core 21

Fig. 4 Seismic reflection G.I. gun profile across Beothuk drift showing the shallow architecture of the drift and core locations (red arrows)

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suggest that the upper meter of the core has a condensedHolocene section.

Discussion

Core chronology and correlation

Core correlations in the transect across Beothuk drift, with eachother and with previously correlated and dated cores in FlemishPass, are important to confirm and refine an age model. Previ-ous studies of the eastern Canadian margin have shown that Hlayers and red mud beds are of regional extent and can be usedfor correlation (Tripsanas and Piper 2008; deGelleke et al.

2013). These red mud beds are interpreted as a red meltwaterplume facies, also found throughout Orphan Basin (Rashid etal. 2011) with a possible origin from Upper Paleozoic sand-stones and siltstones beneath the NE Newfoundland shelf(Piper and DeWolfe 2003; Tripsanas and Piper 2008; Rogeret al. 2013). The increases in L*, a*, Ca, and carbonate in pistoncore 21 correspond to H layers. Independent peaks in a* colorcorrespond to red muds (silty clays). The H layers with high L*and a*, and red muds with high a* can be correlated betweenpiston cores 21–24 (Fig. 7). Within the shallow seismic intervalthat the cores penetrate, Huntec profiles show no evidence oferosion throughout Flemish Pass on a scale commensurate withthe typical H layer thicknesses, although there is local erosionaround core 23. Correlation with core 22 is confirmed by thedistinctive alternation of H layers and red beds (Fig. 7).

Fig. 5 Strike seismic profilealong the lower slope of theGrand Banks of Newfoundland.Reflector FP75 identified fromFig. 6 of Huppertz and Piper(2009)

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Correlation with previously dated cores further confirms theage model. Core 96018-06 on the northeast flank of FlemishPass (Fig. 2) has previous radiocarbon dates (Huppertz andPiper 2010) that were recalibrated (Table 2), and serves as adated reference core 125 km upflow from core 21. Correlationto core 21 is based on downcore peaks in measured Ca and/orcarbonate and peaks in L* and a* spectrophotometry (Fig. 10).Further confirmation is provided by core 87008-13, also on theeastern flank of Flemish Pass and only 30 km upflow from core21 (Fig. 2). The first prominent peak of Ca, L*, and a* in core21 has the age of H1 (~16 ka). In core 22, one date of 25.7 calka just below an H layer at ~3.5 m suggests the H layer is H2.Another date of 39.2 cal ka below an H layer at ~8 m in core 22

suggests this H layer is H4. Correlation with cores 96018-06and 87008-13 (Table 2), together with the two new dates,allows an age model to be developed for core 21 (Fig. 11).

In three of the cores, H1 is within 1 m of the seabed, and incore 21 a date of 13.5 ka was obtained 1.2 m below the seabed.This implies that there is not a high-resolution record ofHolocene sedimentation preserved in the cores. Studies ofbox cores from Flemish Pass, including radiocarbon dates(Weitzman et al. 2014), show a surface sediment layer 0.15–0.3 m thick across the floor of the Pass, thinning out andbecoming sandier along the margins. The base of this surficialunit is dated at 5–7 ka. Most <60 cm long box cores do notpenetrate sediment older than 12 ka.

Fig. 6 Dip seismic profile acrossthe upper Grand Banks slopeshowing seismic tie to the base ofshelf-crossing glaciation on theGrand Banks. Reflector A can becorrelated to Fig. 5

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Fig. 7 Cores 21–24 showing correlations based on spectrophotometerL* and a* values. Sedimentation rates are based on intervals between theseafloor, H1, H2, H3 and H4 (where present), and in core 21, the 13 ka

horizon. Piston core 21 additionally shows XRF Ca measurements, andspot LECO analyses of organic carbon (OC) and inorganic carbonateassuming calcite (IC)

Fig. 8 Variations in clay and finesilt, sortable silt and fine sand incore 21

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The four cores in this study are of varying lengths (Table 1),depending on the type of sediment at the core locations. Moresands tend tomake it more difficult for the piston corer to obtaina long core. Core 21 on the drift penetrates 0.80 m below H2,but does not appear to reach H3, although there is an increase incarbonate at the very base of core 21, which is probably the top

of H3, suggesting that the base of core 21 dates from 29 ka(Ahn and Brook 2014). Core 22 penetrates through four Hlayers, H1–H4, above the 39.2 cal ka dated horizon, with apossible fifth H layer (?H5) at the base of the core. Core 23penetrates two H layers with the core extending 20 cm belowH2. Core 24 penetrates through two distinct H layers (H1 andH2), overlying a MTD deposit at ~1.50–3.30 m downcore.

The lapilli tuff in core 22 was investigated as a possiblechronological marker. The glassy character of this basalt im-plies contemporary volcanism, likely from Iceland, JanMayen, or the Faroe Islands, and transported by ice rafting(Lackschewitz and Wallrabe-Adams 1997; Haflidason et al.2000). Using the Ferguson and Church (2004) settling veloc-ity equation, it would have taken hours for the tuff to depositfrom the sea surface, perhaps during capsizing of ice that wascarrying the tuff. Its closest geochemical match is with theVZ1(X) tephra (Lackschewitz and Wallrabe-Adams 1997),but the chemical similarity is not sufficiently good to confi-dently make the correlation.

Current strength from cores

The dynamics of sediment erosion, deposition, and aggregatebreakup suggest that fine sediment is cohesive below diame-ters of 10 μm, and noncohesive above (McCave et al. 1995).Silt sizes greater than 10μmdisplay size sorting in response toflow processes, and these silts and their properties can be usedto infer relative current strength (McCave et al. 1995). The10–63 μm fraction is designated as sortable silt because it issorted by its primary particle size, but finer silt is not since itoccurs in aggregates (McCave 2008). Since short-term flowevents cannot usually be resolved in deep water, the informa-tion gained from the sortable silt fraction provides insights onaverage current speed (Hass 2002).

The grain-size distribution in core 21 (Fig. 8) on Beothukdrift suggests there were two styles of Labrador Current flowover the past 29 ka (Fig. 11). The interval aboveH1 has a higherpercentage of both sortable silt and fine-grained sand than theinterval from H1 to the base of the core (?H3), suggestinggreater Labrador Current flow since H1. The upper 0.40 m ofthe trigger weight core is remarkable for both high percentagesof both sortable silt and fine-grained sand. The average SS%between the dated (~13 ka) horizon at PC 0.87 m to PC top is52 SS%. The average SS% from above H1 to the dated ~13 kahorizon at 0.87 m is 42 SS%. The average SS% below H1 andthe PC base (excluding H2) is 36 SS%, suggesting that Labra-dor Current strength has generally increased since 29 ka.

The samples at the base and top of H1 contained coarse IRD,resulting in a lower percentage of sortable silt, which cannot beused to infer relative current strength (Prins et al. 2002;McCave and Hall 2006). The assumption that the source sizesignature from multiple erosional and depositional sortingevents will be erased and replaced by a current-related signature

Fig. 9 Lapilli tuff from core 22. a TAS diagram showing IUGS rocknomenclature. b REE plot and c spidergram of incompatible trace ele-ments normalized to primitive mantle (Sun and McDonough 1989)

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(McCave et al. 1995, 2006; McCave and Hall 2006) is invalidwithin H layers, so that grain-size variations within these layerscannot be used to infer changes in current velocity.

Current strength from drift architecture

The inferred variations in Labrador Current strength can befurther confirmed from variations in sedimentation rates(Fig. 7) in the core transect across Flemish Pass and fromthe seismic stratigraphic architecture of Beothuk drift. Theaverage sedimentation rates across Flemish Pass includingBeothuk drift between H2 to H1 had less lateral variationcompared to the variations in sedimentation rates across Flem-ish Pass from H1 to the present day (principally the intervalfrom H1 to 13 ka; Fig. 7). These changes in sedimentationrates across the Pass suggest sediment was deposited in moreof a draping or blanketing style across the Pass between H2 toH1, whereas after H1 (until ~13 ka) most sediment accumu-lated on the drift, with significantly lower sedimentation rateson the floor of the Pass. The seabed sediment texture

approximated by the acoustic backscatter from the multibeamdata (Fig. 3b) supports this interpretation. The multibeamsystem used during the surveys was a 30 kHz system, whichmeans that the acoustic backscatter is average backscatterintensity for the upper 5−15 cm of sediment.

Significance for the subpolar gyre and elsewhere

The relative variations of the strength of the Labrador Currentflowing through Flemish Pass may be an imperfect proxy forthe overall flux of water in the Labrador Current. The innerbranch of the Labrador Current could have flowed over theouter Grand Banks even at the LGM, but with ice retreat to theshoreline by ~16 cal ka (Shaw 2006) the inner branch couldextend over a much wider shelf. The proportion of waterflowing in the outermost Labrador Current east of FlemishCap may also have varied through time. Hydrographic condi-tions in all of these parts of the Labrador Current changedthrough time, due to changes in water supply to the LabradorCurrent from theWest Greenland Current or waters exiting the

Fig. 10 Correlation of core 21 with dated core 96018-06 from northernFlemish Pass, and core 87008-013 from central Flemish Pass, based onspectrophotometry and abundance of carbonate. All reported dates are

calibrated (Table 2), and Heinrich layers in core 96018-06 are based onPiper and Campbell (2005)

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Arctic Ocean through Nares Strait and the Canadian ArcticArchipelago, as well as direct supply from melting glaciersand rivers (Scott et al. 1984; Keigwin et al. 2003).

The timing of the main change in Labrador Current flow,around H1 (~16 ka), is earlier than other major changes insupply to the subpolar gyre. Flow of Arctic waters throughFram Strait increased at ~9.8 cal ka BP (Zamelczyk et al.2012), the Arctic Island channels became free of glacial iceat ~9.5 cal ka (England et al. 2000), and Nares Strait did notopen until about 8.5–9 cal ka (England 1999). After ~9.5 calka, the relatively warm Irminger Current became established,leading to an increase in the strength of the Labrador Current(Rahman and de Vernal 1994). These latter changes broughtabout the Holocene current regime of winnowed sandy sedi-ment with a low net sedimentation rate.

Neogene history of drift development

The drift development in southern Flemish Pass has changedthrough the Neogene from drift deposition on the western side

of Flemish Pass to the eastern side of Flemish Pass (Fig. 4).The mid-Miocene unconformity (F’) recognized in the Gabri-el well in central Flemish Pass (Piper and Normark 1989;Piper and Pereira 1992; Edwards and McAlpine 1999) ap-pears to be directly below the buried drift deposit in westernFlemish Pass. The time when erosion gave way to drift depo-sition is uncertain in southern Flemish Pass, but deposition onthe western drift continued well into the Pleistocene, as thebase of the glacial section on the outer Grand Banks can becorrelated into the central part of the buried drift deposit.

Fig. 11 Age model for variations in the Labrador Current using sortablesilt % from core 21 (black piston core, PC; red trigger weight core, TWC)plotted against age. The Labrador Current strength axis is a relativechange and cannot be used to infer flow velocity. This age model is basedon H layers (end of H3 is 29 ka), three radiocarbon dates and TWC coretie to Nereida core 194. All other intervals are based on extrapolation.Distal events: A Nares Strait ice free ~8.5–9 cal ka (England 1999), BArctic Island channels free of ice ~9.5 cal ka (England et al. 2000), CIrminger Current established after ~9.5 cal ka (Rahman and de Vernal1994), D Labrador Current intensified after 10 cal ka, strong by ~9.5 calka (Rahman and de Vernal 1994), E flow of Arctic waters through FramStrait increased by ~9.8 cal ka (Zamelczyk et al. 2012), F ice retreat toNewfoundland shoreline by ~16 cal ka (Shaw 2006), G small eruption inIceland ~28 cal ka depositing VZI(X) tephra (Lackschewitz andWallrabe-Adams 1997), H Fugloyarbanki Tephra widespread, depositedaround Iceland ~28.5 cal ka (Haflidason et al. 2000; Davies et al. 2008)

Fig. 12 Illustration of western buried drift and Beothuk drift growth

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Deptuck (2003) found that deposition in the Flemish Passregion was high from the latest Miocene to recent times. Thelarge 0.06-ms-thick MTD overlying the buried western driftappears to be capping the drift deposition at the western sideof the Pass. The abrupt shallowing of the seafloor after theMTD event may have diverted the main thread of the Labra-dor Current eastward, accelerating erosion on the floor ofFlemish Pass, and over time leading to the dominant growthof the Beothuk drift that had already started to form prior tothe MTD (Fig. 12). At the same time, Sackville Spur wasgrowing, altering the trajectory of the Labrador Current as itenters Flemish Pass (Kennard et al. 1990). Seismic correlation(Fig. 4) shows that the age of the MTD is younger than FP 75(<MIS 6.4, or <170 ka), based on seismic interpretation of theMTD deposition being frontally emergent (Frey-Martinez etal. 2006) over the pre-landslide downslope seabed, whichincludes FP 75.

Conclusions

There are previously unrecognized contourite drifts in southernFlemish Pass, such as the Beothuk drift that has been the focusof this study, with a complex history of drift formation south ofthe maximum constriction of the Pass. A drift formed on thewestern side of Flemish Pass following the mid-Miocene, andcontinued to grow until it was buried by a large mass-transportdeposit sometime after the penultimate glacial maximum (MIS6). Beothuk drift began to form at the onset of, or shortly after,the first shelf-crossing glaciation on the Grand Banks.

The Labrador Current in Flemish Pass has experienced threeperiods of long-term flow variations in at least the past 29 ka.The Labrador Current from 29 to 16 ka was weaker—whendrift sedimentation was less pronounced and sedimentation wasmore of a blanketing style—than from 16 to at least 13 ka whenthere was prominent sediment partitioning across Flemish Pass,with significant drift growth as a result of a swifter current. Thepast 13 ka are unresolved but seem to be a periodwith very littlesedimentation on Beothuk drift, and indeed in many parts ofFlemish Pass. The Labrador Current in Flemish Pass is strongertoday than it has been in at least the past 29 ka.

Acknowledgements Work was funded by Geological Survey of Can-ada Offshore Geoscience and Public Safety Geoscience programs, theProgram for Energy R&D project B13.002, and an NSERC DiscoveryGrant to DJWP. This paper is Geological Survey of Canada contribution20130352. We thank the CCGS Hudson crew for the successful cruise toFlemish Pass. Jenna Higgins and Kate Jarrett assisted with core process-ing and Owen Brown with grain-size analyses. Multibeam bathymetrywas collected by TRAGSA, Spain as part of the Nereida project: we thankthe senior scientists Araceli Munoz, Patricia Jimenez and Mar Sacau fortheir collaboration. We thank two anonymous reviewers as well as theeditors Burg W. Flemming and Monique T. Delafontaine for their com-ments that significantly improved this manuscript.

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