Sedimentology and history of sediment sources to the NW Labrador Sea during the past glacial cycle

Quaternary Science Reviews 221 (2019) 105880

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Sedimentology and history of sediment sources to the NW Labrador Sea during the past glacial cycle Harunur Rashid a, b, *, David JW. Piper b, Julie Drapeau c, Charlotte Marin d, Mary E. Smith e a

College of Marine Sciences, Shanghai Ocean University, Shanghai, China Natural Resources Canada, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth, NS, Canada c Earth and Planetary Sciences, McGill University, Montreal, Canada d College of Marine Sciences, University of South Florida, St. Petersburg, USA e School of Earth Sciences, The Ohio State University, Columbus, USA b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 9 February 2019 Received in revised form 12 August 2019 Accepted 12 August 2019 Available online 26 August 2019

The paleoceanography and sediment dynamics of the northernmost Labrador Sea provides critical records of glacial history, glacially-dominated sedimentation, and paleocirculation. A reference core at 938 m on the SE Baffin Slope was investigated with new oxygen isotope stratigraphy, X-ray fluorescence geochemistry, and 18 14C-AMS dates and correlated to 14 regional deep-water cores. The reference core provides a paleoceanographic and sediment source record over the last 40 ka, overlying a 3-m-thick blocky mass-transport deposit over MIS 5 autochthonous sediment. Detrital carbonate-rich sediment layers H0-H4, based on bulk geochemistry, were derived principally from Hudson Strait. Shortly after H2 and H3, the shelf-crossing Cumberland Sound ice stream supplied dark brown ice-proximal stratified sediments. Minor supply of carbonate-rich sediment from Baffin Bay allows chronologic integration of the Baffin Bay and Labrador Sea detrital carbonate records and implies an open seaway through Davis Strait. The counterparts of H3, H4, and (?)H5 events in the deep Labrador basin are 4e10 m thick units of thin-bedded carbonate-rich mud turbidites from glacigenic debris flows on the Hudson Strait slope. The behavior of the Hudson Strait ice stream changed through the last glacial cycle. In H1 and H2, the ice stream retreated back across the shelf but did not deglaciate Hudson Bay; in H3eH5 it remained at the shelf break long enough to supply thick turbidites, and subsequent retreat after H4 and H5 deglaciated Hudson Bay. The maximum extent of ice streams in Hudson Strait, Cumberland Sound, and Lancaster Sound was not synchronous. © 2019 Elsevier Ltd. All rights reserved.

1. Introduction The Late Pleistocene northeastern Canadian margin was dominated by sediment supply from shelf-crossing ice streams and the southward transport of sediment in the Baffin Island Current (BIC), Labrador Current (LC) and the deep western boundary current. The major sediment input points are in NW Greenland, Lancaster Sound, and Hudson Strait (Fig. 1). The episodic supply of detrital carbonate from the Lancaster Sound and Hudson Strait ice streams provide readily recognizable stratigraphic markers in continental margin sediment successions. The most recognizable such stratigraphic marker in the NW Labrador Sea is the detrital carbonate-

* Corresponding author. College of Marine Sciences, Shanghai Ocean University, Shanghai, China. E-mail address: [email protected] (H. Rashid). https://doi.org/10.1016/j.quascirev.2019.105880 0277-3791/© 2019 Elsevier Ltd. All rights reserved.

rich Heinrich iceberg-rafted layers (Andrews and Tedesco, 1992; Hesse and Khodabakhsh, 1998; Rashid et al., 2003). In contrast to the H-layers, thin dolomite layers are found in the Baffin Bay Basin which is commonly termed as the Baffin Bay detrital carbonate (BBDC) layers (Aksu, 1981; Aksu and Piper, 1987; Simon et al., 2016; Jennings et al., 2018). The southeast Baffin margin in the northwestern Labrador Sea, southwest of Davis Strait, is the least known sector of the eastern Canadian margin. This tectonically and bathymetrically complex area developed along the Ungava Transform that linked the opening Baffin Bay and Labrador Sea oceanic spreading centers in the Paleogene (Oakey and Chalmers, 2012). It is bounded to the south by the 200 km wide Quaternary progradational bulge created by deposition from the Hudson Strait ice stream (Rashid and Piper, 2007). The central part of the SE Baffin margin has a smaller progradational bulge seaward of the Cumberland Sound ice stream

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H. Rashid et al. / Quaternary Science Reviews 221 (2019) 105880

Fig. 1. a. Map shows major physiographic and geological features of the eastern Canadian continental margin. 1b: Location of the SE Baffin Slope in the NW Labrador Sea, with positions of sediment cores used in this study. The approximate position of the ice-margin at 13 ka after Dyke et al. (2002) is shown by the white discontinuous line. Black dashed line is the maximum limit of the Hudson Strait ice-stream (Rashid and Piper, 2007). BIC ¼ Baffin Island Current, WGC ¼ West Greenland Current, NAMOC ¼ Northwest Atlantic MidOcean Channel.

(Praeg et al., 1986; Jennings, 1993). Aksu and Mudie (1985) used a suite of sediment cores to construct lithostratigraphy and paleoenvironmental in the broader NW Labrador Sea including the SE Baffin Slope. Subsequently, Andrews and his colleagues have published a series of papers interpreting stratigraphy, paleoenvironments and sediment sources from a small number of old cores collected on the SE Baffin Slope (Andrews et al., 1995, 1998; 2012; Jennings et al., 1996). Dynamics of sediment transfer in front of the mouth of one of the largest ice-streams, i.e., the Hudson Strait of the late Pleistocene Laurentide Ice Sheet (LIS) is not well known. In addition, it is postulated that there were two smaller ice-streams, namely Frobisher Bay and Cumberland Sound during the last glacial period (Jennings, 1993; Andrews and MacLean, 2003; Stokes et al., 2016; Margold et al., 2018) to the north of Hudson Strait. Whether these smaller ice-streams destabilized synchronously with respect to the Hudson Strait ice-stream and the extent to which these smaller icestreams discharged during the last glacial period is poorly known due to the lack of chronostratigraphic control. Resolving these issues have been compounded by the lack of high-resolution longer time-scale records due to (i) high sedimentation rates on the upper slope and (ii) the dynamics of sediments resulting in sediment mass-movements such as mass-transport deposit (MTD) and glacigenic debris-flow (GDF). Here we report data from a reference sediment core (Hu9704807) retrieved at the base of SE Baffin Slope that captured the longest

record of the LIS dynamics in the region, thus allowing us to delineate discharge between the two proximal ice-streams. The highly constrained stratigraphy in conjunction with other published and unpublished data also allows us to assess the extent to which exchange of sediment between the Labrador Sea and Baffin Basin occurred during the last glacial cycle. Further, three sediment records from the levees of the Northwest Atlantic Mid-Ocean Channel (NAMOC), northern deep Labrador Basin, allow us to assess sediment transfer mechanisms and flow evolution from upper to lower slopes to deep Labrador Basin.

2. Oceanographic and geological setting The principal core (Hu97048-07) used in the study was retrieved at the base of the continental slope off Cumberland Sound in SE Baffin Island. Jennings (1993) inferred that ice-filled Cumberland Sound until ~12 ka implying insignificant sediment and freshwater discharge since that time to the shelf break. At present, Baffin Bay receives freshwater through three shallow, narrow seaways: Nares Strait, Jones Sound, and Lancaster Sound of the Canadian Arctic Archipelago (CAA). In addition to the CAA freshwater, the glacial runoff from west Greenland and the northern extension of the West Greenland Current (WGC) brings additional freshwater to Baffin Bay. The East Greenland Current (EGC) feeds freshwater to the WGC (Fig. 1) from the Arctic Ocean through the Fram Strait which joins the WGC around the southern tip of Greenland (Cuny

H. Rashid et al. / Quaternary Science Reviews 221 (2019) 105880

et al., 2005). The cyclonic circulation (Münchow et al., 2015) within the Baffin Bay facilitates these freshwaters to join the CAA freshwater on the Baffin Island margin. The freshwaters eventually exit to the Labrador Sea across the 640 m deep Davis Strait sill, following the 400 m or slightly shallower isobath (Cuny et al., 2005) as the integrated Baffin Island Current (BIC). Curry et al. (2014) estimated that the net annual volume and liquid water transports through Davis Strait are 1.6 ± 0.5 Sv (1 Sv ¼ 106 m3/s) and 93 ± 6 mSv, respectively. The SE Baffin Shelf appears to be underlain by glacial till out to the shelf break (Praeg et al., 1986, their Fig. 18) but age constraints are lacking and quality of seismic profiles is poor. Off Frobisher Bay, the uppermost till tongue in a stack of four tills at the edge of Resolution Basin is dated from a nearby core at ~30 ka. Ice from the Foxe sector of the LIS filled Cumberland Sound at the last glacial maximum (LGM) and eroded lower Paleozoic limestone and Cretaceous shale bedrock in the Sound (Jennings, 1993). On the continental slope, GDF deposits extend to 62 400 N, correlative with those of H3 off Hudson Strait (Rashid and Piper, 2007). A few available cores (Andrews et al., 2012) and seismic profiles suggest that north of here, GDF deposits are absent. 3. Materials and methods One reference stratigraphic piston core (Hu97048-07) on the SE Baffin Slope and six additional cores provide a depth transect from the upper slope to deep Labrador Basin. These six piston cores are from the middle slope (77IO-5-01 and Hu87033-09), rise (Hu97048-10) and deep basin (Hu88024-08, Hu88024-10, and MD99-2229) on the NAMOC levees (Fig. 1b). Piston core Hu9704807 (hereafter Hu97-07) was collected at 938 m water depth on the SE Baffin Slope using the AGC Long corer. Core 77IO-5-01 was collected from the slope east of SE Baffin Slope at 750 m water depth by the Imperial Oil Ltd. and was initially reported by Aksu and Mudie (1985). Core Hu87033-09 was collected from the base of the SE Baffin Slope at 1437 m water depth and has been the source for numerous publications (Andrews et al., 1994, 1998, Andrews and Barber, 2002; Jennings et al., 1996). Cores Hu88024-10 and Hu88024-08 were collected between the DA and DB channels of the NAMOC (Fig. 3.3 of Klaücke, 1995) at 3131 m and 3522 m water depths, respectively. Part of the sediment record of core Hu88024-08 was reported in Rashid and Piper (2007); however, five new 14C-AMS dates are reported here for the first time. Core MD99-2229 was collected with the Calypso corer under the IMAGES program (Hillaire-Marcel and Turon, 1999). The deepwater cores in this study have been placed within the side-scan sonar imagery and swath bathymetry (acquired by Hawaii Institute of Geophysics Acoustic Wide-Angle Imaging Instrument Mapping Researcher 1; HAWAII MR-1; Klaücke, 1995). Most cores used in this study have 3.5 kHz profiles near or through the core sites. A new Hu2018029 3.5 kHz profile was run at 10 knots through core site Hu97048-07. We projected core 77IO-501 on this profile (Fig. 2). Magnetic susceptibility of core Hu97-07 was measured on the whole core rounds at 3 cm intervals (Piper, 1997) which were integrated over about 5 cm of core length centered on the measured depth interval, before splitting the core onboard CCGS Hudson. However, the magnetic susceptibility, gamma-ray attenuation, and p-wave velocity were measured at 2 cm resolution in core MD992229 using the GeoTek MSCL system onboard Marion Dufresne (Hillaire-Marcel and Turon, 1999). Wet sediment color (L, a*, and b*) was determined at 5 cm intervals on a 1 cm diameter spot using a hand-held digital spectrophotometer (Minolta CM-2002) onboard ship. A similar spectrophotometer was also used to

3

determine sediment color of core MD99-2229 at 5 cm intervals from wet sediment core splits onboard Marion Dufresne. X-radiographs of 1-cm thin sediment slabs were taken to determine sediment facies in addition to the sediment physical properties used in the study. New sediment color (L, a*, and b*) and magnetic susceptibility of core Hu87033-09 were determined at 1-cm intervals on dry sediment core split compared to the published coarser resolution data (at 5 cm intervals) (Andrews and Barber, 2002; Andrews and MacLean, 2003). The bulk sediment geochemistry of core Hu97-07 was determined using an Innov-X DELTA Premium (DP-6000) portable X-ray fluorescence (pXRF) core scanner at 1 cm depth intervals. The semiquantitative concentration of 25 elements was determined; however, the Ca/Ti, Zr/Ti and Rb/Ti in conjunction with physical properties of sediments were used to identify sediment sources, Heinrich (H)-layers, and other stratigraphic markers in this study. Samples at 2e10 cm intervals for oxygen isotope (d18O) and carbonate analysis were dried, disaggregated, and wet-sieved through a 63-mm sieve. Bulk sediment carbonate concentration (expressed as % CaCO3) and total organic carbon (% TOC) were analyzed using a LECO WR-112 carbon analyzer (Barber, 2001; Rashid et al., 2012). Xray diffraction (XRD) analysis was carried out on the air-dried <2 mm fraction of five representative samples in core Hu97-07 and analyzed on a Siemens Kristaloflex diffractometer using Co Ka radiation. Air-dried samples were scanned from 2 to 52 2q, with a 0.2 step (Piper et al., 2009). A Finnigan MAT253 isotope ratio mass spectrometer with a Kiel III Device was used for d18O analysis of the polar planktonic foraminifer Neogloboquadrina pachyderma (sinistral) with test diameters between 150 mm and 250 mm (Rashid et al., 2012). The overall analytical reproducibility, as determined from replicate measurements on carbonate standards NBS-18, NBS-19, and an internal standard, is routinely better than ±0.08‰ (±1s) for d18O (Hodell and Curtis, 2008). Thirty-seven 14C-accelerator mass spectrometer (AMS) dates (Table 1) were obtained from handpicked planktonic foraminifers and bulk sediments to constrain the stratigraphy and identify various rapidly deposited sediment units. The 14C-AMS dates were calibrated to calendar years before present (1950) using the CALIB 7.1 and the MARINE13.14C dataset (Stuiver et al., 2019). The age model of the reference core Hu97048-07 is tested using one of the latest age-depth modeling programs (Lougheed and Obrochta, 2019) and outlier analysis also conducted to assess the robustness of the stratigraphy. To construct the age model, 50-years for DR was applied as the core Hu97-07 was collected from a reasonably offshore site that is uninfluenced by the coastal BIC. We are aware of 144 ± 38 years for the DR for the modern western Labrador Sea (McNeely et al., 2006). Further, an additional 200 years for sea-ice correction could be applied to take into account the effect of an apparent extended sea-ice cover (Lewis et al., 2012). As a result, a correction of 344 ± 38 years, which is based on the annual sea-ice extent inferred from the dinoflagellate assemblagebased reconstruction (de Vernal et al., 2001; Lewis et al., 2012), is reasonable. Numerous studies on sea-ice reconstruction (de Vernal and Hillaire-Marcel, 2006; Levac et al., 2011) consistently showed that the extent of annual sea-ice cover on the Labrador continental margin varies from 4 to 11 months/year for the past 14 ka. Therefore, we are unable to find any basis for adding additional (XX) correction, i.e., 344 ± 38 þ XX, for DR values. In the interest of conducting an exercise, we used three DR values, i.e., 50 ± 10, 344 ± 38, and 500 ± 38 to re-assess the age model using the latest age-depth modeling program of Lougheed and Obrochta (2019) (see Supplementary Information). Stratigraphic interpretations are presented in terms of Heinrich events. In the northern Labrador Sea, major discharges of detrital

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H. Rashid et al. / Quaternary Science Reviews 221 (2019) 105880

Fig. 2. 3.5 kHz subbottom profile through core sites 77IO-5-01 and Hu97048-07 showing evacuation surface 5e10 m subbottom passing downslope into a blocky landslide deposit.

carbonate in MIS 2e3 occur only at the times of Heinrich events 1e5 (Andrews and Tedesco, 1992; Rashid et al., 2003). These detrital carbonate discharge events may be represented by predominant ice-rating transport, nepheloid-flow deposits or silt to mud turbidites. Assignment to a particular H event is based on bounding radiocarbon dates. In the Labrador Sea, H3 differs from later H events in having a high proportion of silt to mud turbidites (Rashid and Piper, 2007).

4. Results 4.1. Bathymetric and seismic setting Core Hu97-07 was collected seaward of a bulge in the shelf break that likely resulted from glacimarine progradation from the Cumberland Sound ice stream (Fig. 1b). There is an old (Hu78023) airgun seismic dip line through the core site but the resolution is too poor to interpret Quaternary features. The region was interpreted to be influenced by GDFs (cf. Fig. 2 of Rashid and Piper, 2007); however, the core site is located immediately north of the limit of the GDF deposits. Rather, a 3.3 m thick blocky masstransport deposit (MTD) was identified at about 7.10 m subbottom depth in the core. The new 3.5 kHz profile shows 5e10 m of stratified sediment overlying a high amplitude reflection against which there is local top-lap (Fig. 2). At ~1000 m water depth, this reflection passes underneath a thick unit of incoherent reflections with a highly irregular top, interpreted as a blocky landslide deposit. The overlying stratified sediment drapes the underlying morphology. Core MD99-2229 was retrieved immediately beyond the upslope limit of the sandy submarine braid plain on the left levee of the NAMOC (Fig. 3). Although there is strong asymmetry in the bathymetric profile of the levees, the upper 50 m (at the crest) is of similar thickness on both levees, but thins rapidly over 10 km (Fig. 3). The acoustic profile at the site suggest thinning of reflection packets away from the levee crest and side-scan sonar data show a streaky pattern on the muddy levee of the NAMOC. The core passes through a series of high amplitude reflections (Fig. 3b). Piston cores Hu88024-10 (Fig. 1b) and Hu88024-08 (Fig. 3) were collected from a local depression on the higher western levee of the NAMOC (Klaücke, 1995). Side-scan sonar data at site Hu88024-08 show a streaky pattern on the muddy levee of the NAMOC and an airgun profile shows local onlap. In a 3.5 kHz profile (Fig. S1), core Hu88-08 just reaches a prominent regionally correlatable reflection

overlain by acoustically transparent strata. 4.2. Sediment facies and their interpretation The sediment facies identification schemes of Wang and Hesse (1996), Barber (2001), Rashid (2002), and Rashid et al. (2003) have been followed in this study. Facies identification is based on the internal sedimentary structures, sediment color, composition, presence or absence of ice-rafted debris (IRD), and extent of bioturbation. Nepheloid-flow layer and mass-transport (formerly identified as debris-flow) deposits, mud turbidites, hemipelagic sediments with and without IRD, and contourites are the principal lithofacies identified. Nine sediment facies are identified in the studied cores which are (Table 2): (1) Detrital carbonate-rich nepheloid-flow layers mainly correspond to the detrital carbonate-rich H-layers (Andrews and Tedesco, 1992; Hesse and Khodabakhsh, 1998; Rashid et al., 2003). (2) Thick intervals of detrital carbonate-rich alternating clayey silt and silty clay mud-turbidites, which are occasionally laminated. Generally, low magnetic susceptibility ranging from ~50 to 100  105 SI units punctuated by intervals of much greater magnetic susceptibilities with greater than 200 105 SI and as high as 600  105 SI are found. Bulk density for most intervals varies from about 1.8 to 2.05 Mg/m3 interrupted by low-density intervals of less than 1.6 Mg/m3 (3e4) Olive-green (proximal to slope) to olive-grey (deep basin) hemipelagic sediments with or without IRD; (5) Laminated silt-mud couplets with IRD; (6) Dark brown mud with IRD (previously identified as coarse-grained sediment facies by Andrews et al. (2012) and termed Facies C by Aksu and Mudie (1985); (7) Contourites comprising greenish silty mud with diffuse wavy structures (e.g. Fig. 4A and Table 1 of Wang and Hesse, 1996); (8) Diamicton lacking internal structure (Rashid and Piper, 2007); and (9) High carbonate layers with or without IRD that vary from dark brown to brown. 4.3. Core stratigraphy Stratigraphy of studied cores was constructed by identifying prominent sediment facies, 14C-AMS dates, and d18O stratigraphy. The principal means of correlation was by H-layers based on radiocarbon dating, bulk sediment geochemistry, and a*-color properties. Hu97-07: It should be mentioned a priori that part of the sediment record of this core was published in Andrews et al. (2012) and

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Table 1 14 C-AMS dates used in the study. Depth (cm) Hu75009-061 1 490e492 77IO-5-01 2a 122e124 2b 122e124 3 350e352 4 608e610 5 643e645 6 803e806 7 848e850 8 900e902 Hu87033-09 9 652e654 Hu88024-08 10 20e22 11 52e53 12 80e82 13 925e926 14 962e964 Hu97048-07 15 20e25 16 65e70 17 155e160 18 175e180 19 185e190 20 207e211

14

Calibrated agea (1s range)

DR

Species

Lab ID

Reference

21,350 ± 140

25036e25442

50

N. pachyderma (s)

AA-41991

This study

13,095 ± 30 15,935 ± 35 23,890 ± 260 14,750 ± 30 14,940 ± 40 17,450 ± 35 18,175 ± 35 19,650 ± 45

14967e15145 18695e18797 27430e27794 17345e17512 17554e17738 20431e20583 21356e21555 22981e23239

50 50 50 50 50 50 50 50

N. pachyderma (s) Total organic carbon N. pachyderma (s) N. pachyderma (s) N. pachyderma (s) N. pachyderma (s) N. pachyderma (s) N. pachyderma (s)

UCI-212970 UCI-213012 AA-9356 UCI-212973 UCI-212974 UCI-212975 UCI-212976 UCI-212977

This study This study Andrews et al. (1994) This study This study This study This study This study

20,910 ± 80

23637e23896

50

N. pachyderma (s)

UCI-215356

This study

13,992 ± 80 19,660 ± 70 20,710 ± 180 34,160 ± 420 34,300 ± 270

16167e16434 22987e23276 24079e24552 37477e38650 37990e38673

50 50 50 50 50

N. N. N. N. N.

AA-43070 UCI-207803 AA-43069 UCI-207804 OS-28670

This This This This This

11,045 ± 25 11,125 ± 25 12,030 ± 35 13,825 ± 50 14,165 ± 40 14,660 ± 120

12523e12600 12573e12645 13366e13471 15998e16188 16414e16650 17119e17468

50 50 50 50 50 50

Mixed planktonics N. labradoricum N. labradoricum Mixed planktics-benthics Mixed planktics N. pachyderma (s)

UCI-45237 UCI-45238 UCI-45239 UCI-207807 UCI-89067 AA-31260

C-AMS dates

pachyderma pachyderma pachyderma pachyderma pachyderma

(s) (s) (s) (s) (s)

study study study Study study

21 22

250e255 279e283

16,910 ± 60 17,624 ± 160

19742e19973 20507e20919

50 50

N. pachyderma (s) N. pachyderma (s)

UCI-207808 AA-27758

23

351e356

21,370 ± 270

24878e25589

50

N. pachyderma (s)

AA-31269

24 25 26 27 28

355e357 455e460 480e485 500e505 572e576

20,810 ± 60 22,390 ± 60 23,160 ± 60 24,480 ± 130 25,360 ± 240

24324e24536 26023e26204 26976e27233 27876e28208 28688e29217

50 50 50 50 50

N. N. N. N. N.

labradoricum pachyderma (s) pachyderma (s) pachyderma (s) pachyderma (s)

UCI-45240 UCI-214049 UCI-214050 UCI-207809 AA-35170

26,740 ± 170 27,300 ± 190 32,000 ± 600 35,290 ± 880

30422e30806 30851e31100 34861e36036 38434e40393

50 50 50 50

N. N. N. N.

pachyderma pachyderma pachyderma pachyderma

(s) (s) (s) (s)

UCI-207810 UCI-207811 AA-35171 AA-27759

Rashid et al. (2012) Rashid et al. (2012) Rashid et al. (2012) This study This study Rashid et al. (2012); Andrews et al. (2012) This study Rashid et al. (2012); Andrews et al. (2012) Rashid et al. (2012); Andrews et al. (2012) Rashid et al. (2012) This study This study This study Rashid et al. (2012); Andrews et al. (2012) This study This study Andrews et al. (2012) Andrews et al. (2012)

20,500 ± 90 24,200 ± 110 30,400 ± 340 33,360 ± 480 >45,200

23981e24239 27708e27906 33750e34318 36342e37704 Beyond the calib. limit

50 50 50 50 50

N. N. N. N. N.

pachyderma pachyderma pachyderma pachyderma pachyderma

(s) (s) (s) (s) (s)

OS-36264 OS-36265 OS-36266 TO-8649 OS?

This This This This This

29 596e600 30 615e620 31 680e684 32 715e718 MD99-2229 33 124e126 34 194e196 35 1481e83 36 1501e03 37 2585e2595

study study study study Study

N. pachyderma (s) ¼ Neogloboquadrina pachyderma (sinistral). AA ¼ Arizona Accelerator Mass Spectrometry Laboratory. UCI ¼ The University of California at Irvine Keck Carbon Cycle AMS Program. a All 14C-AMS dates were converted to calendar age (BP) using CALIB 704 calibration program (Stuiver et al., 2019).

Rashid et al. (2012). However, the d18O and bulk sediment geochemistry in addition to sediment facies are reported here for the first time. Most of the upper 7 m of the core comprise olivegreen mud with variable amounts of IRD. This background sedimentation is interrupted by the carbonate layers. In addition, packets of laminated silt-mud couplets (facies 5) occur immediately above H2 and 15 cm above H3. Dark brown mud with IRD (facies 6) immediately overlies H1 and H4. A blocky MTD with a variety of lithologies extends for more than 3 m below H4. Blocks are up to 1 m thick. Autochthonous olive-green mud is found in the bottom meter of the core. Sediment color a*-trace (green to red) and whole-core magnetic susceptibility are higher and lower, respectively, in H-layers (Fig. 4) (Andrews et al., 2012). The co-variation in IRD with the a*-color is prominent; however, the a*-color sometimes chronologically leads the IRD peaks. Eight new 14C-AMS dates in addition to published

ten 14C-AMS dates (Barber, 2001; Andrews et al., 2012; Rashid et al., 2012) are used to constrain the stratigraphy between 12.56 ka and 38.42 ka. H-layers 0, 1 and 2 are identified at 15e65 cm, 195e201 cm and 325e355 cm subsurface depth (Fig. 4) which are accompanied by lighter d18O values, constrained by nine 14C-AMS dates (Table 1). A high carbonate peak centered at 595 cm with two dates of 30.61 ka and 30.98 ka at 598 cm and 617.5 cm, respectively, suggests that the carbonate layer is most likely the H-layer 3. The high carbonate-layer at 642e680 cm and two 14C-AMS dates at 680e684 cm and 715e718 cm (Table 1) suggest that the layer most likely correlated to H-layer 4. Andrews et al. (2012) determined calcite/dolomite ratios between 0 and 765 cm sub-bottom depth and we added five XRD samples targeted at specific facies (Fig. 4) to provide a second proxy for the identification of H-layers. XRD data show high ratios in H1-H4 layers (Fig. 4f) compared to H0-layer. The dolomite (%) also allowed us to identify additional minor

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Fig. 3. (a) Side-scan sonar mosaic from the northern Labrador Sea (Klaücke, 1995, p. 57) showing the Northwest Atlantic Mid-Ocean Channel (NAMOC) and location of sediment cores used in the study. Normal polarity such that low and high backscatter are dark and bright, respectively, interpreted as fine-grained (i.e., mud-rich) and coarse-grained (i.e., sandy) sediment. (b) 3.5 kHz seismic profile across the NAMOC that illustrates differences in the thickness of sediment packages between the left and right levees and their relief. (c) Position of H-layers 3, 4, and 5 in core MD99-2229 in the seismic stratigraphy: (A) shows measured depth, (B) is proposed correction for core stretching.

carbonate events centered at 145 cm, 290 cm, and 450 cm and a concurrent increase in the a* is centered at 450 cm subsurface depth (Fig. S2). This a* peak is constrained by two 14C-AMS dates at 450e460 cm and 480e485 cm (Table 1). A few high and low carbonate layers between 720 and 1050 cm subsurface depth appear to be within the blocky MTD. A clear lack of any trend in the d18O within the interval supports this identification. The lighter d18O between 1050 cm and 1185 cm could correlate to the marine isotope stage (MIS) 5, consistent with the MIS stratigraphy identified in the southern Labrador Sea (e.g., IODP Site U1302/03 and MD95-2024; Fig. S3) using the same planktonic foraminifera, N. pachyderma (s) (Channell et al., 2012). The very light peak in Hu97-07 represents either MIS 5a or MIS 5e. 77IO-5-01: Aksu (1981) and Aksu and Mudie (1985) initially reported three facies A and seven facies C from this core and

subsequently Andrews et al. (1994) updated the stratigraphy by obtaining one 14C-AMS date of 23,890 ± 260 at 350e352 cm (Table 1). Seven new 14C-AMS dates (Table 1) were acquired for this core to further constrain the stratigraphy. Given that the five 14CAMS dates are in stratigraphic order between 608 cm and 902 cm subsurface depth (Fig. S4), it is considered that the 14C-AMS date of 23,890 ± 260 (Table 1) at 350e352 cm in facies A (H1) is too old, probably because the sample contained minor lithic carbonate, and hence, the date was discarded in constructing the age model. Too low biogenic carbonate content between 122 cm and 608 cm prevented us from constraining the chronology of that interval. However, the similarity in d18O stratigraphy between cores 77IO-501 and Hu97-07 (Fig. S4) provide credence to the age model. In any event, if the new age model of core 77IO-5-01 is taken at its face value, it suggests that the core contains H1 (630e642 cm) and H2

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Table 2 Sediment facies identified and used in the study. Facies name

Characteristic features

Cores

1

Nepheloid-flow layer (brown to beige color)

2

Turbidites

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Olive-green sediments Olive-grey sediments Olive-green sediments with IRD Olive-grey sediments with IRD

5

Laminated silty mud couplets with IRD in the couplets Dark-brown mud with IRD Contouritea Diamicton High carbonate layer with IRD Brown high-carbonate layer with IRD High-carbonate layer

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(945e1000 cm), in contrast to the earlier chronology of Aksu and Mudie (1985) and Andrews et al. (1994; their Fig. 3). Hu87033-09: H0, H1, H2, and H4 layers (Fig. S5) are identified at 10e55 cm, 480e508 cm, 648e702 cm, and 956e1017 cm, respectively (Andrews and Tedesco, 1992; Andrews et al., 1994; Jennings et al., 1996). In addition to the published thirteen 14C-AMS dates, we obtained one 14C-AMS date at 652e654 cm (Table 1) subsurface depth to further constrain the H2 layer. Moreover, twenty new d18O values in N. pachyderma (s) between 628 and 669 cm were acquired to refine the d18O records during H2. It appears that both H1 and H2 layers can confidently be identified with lighter d18ONps values, similar to the lighter d18ONps values in core Hu97-07. Hu88024-08: Detrital carbonate-rich H-layers 2 and 4 at 22e43 cm and 925e957 cm subsurface depth, respectively, in core Hu88024-08 (Fig. 5) were constrained by five 14C-AMS dates (Table 1). The 8.40 m thick silt-mud carbonate-rich mud turbidites between 82 cm and 922 cm is correlated to H-layer 3 (Rashid and Piper, 2007). Hu88024-010: This core contains ~70 cm thick post-H1 sediment (Fig. 6). H-layers 1, 2 and 4 are identified at 70e102 cm, 88e240 cm and 750e834 cm subsurface depth, respectively. Hlayer 3 exhibits silt-mud carbonate-rich turbidites at 310e665 cm, similar to the findings in core Hu88024-08 (Fig. 5) except for the H3 which is 4.85 m thinner in core Hu88024-010. MD99-2229: This 36 m long core consists principally of parallel laminated carbonate-rich mud turbidites, with characteristic graded laminated silt packages (Piper and Stow, 1991), with local bioturbation in the mud tops (b in Fig. 7). The uppermost 2 m of the core consists of olive grey mud, and thin (<50 cm) beds of olivegrey mud with IRD are found at depths of ~14.8 m, ~25.6 m, ~34.6 m and at the extreme base of the core. The intervals of high supply of detrital carbonate are correlated with H-event supply of detrital carbonate upslope off Hudson Strait. Mud turbidite units equivalent to H-layers 3 and 4 at 2.20e14.65 m and 15.25e25.80 m subsurface depth are constrained by three 14C-AMS dates at 1.94e1.96 m, 14.81e14.83 m, and 15.01e15.03 m (Table 1). Acquiring a date around 36 m subsurface depth was not possible due to the paucity of foraminifers which would have allowed us to constrain the high-carbonate layer between 26.15 m and 36.05 m; however, the high carbonate mud turbidites between 26.15 m and 36.05 m subsurface depth are most likely H5. 4.4. Indicators of provenance X-ray diffraction (XRD) data of H2 layer in core Hu97-07 (Fig. 4)

shows the characteristic composition of Labrador Sea H-layers (Skene and Piper, 1991) with abundant calcite, lesser dolomite, and chlorite > kaolinite (Fig. 8). The two ice-proximal facies at ~310 cm and ~551 cm show identical diffractograms, with high kaolinite, an 11 Å clay mineral, low chlorite, and no detectable carbonate. The hemipelagic facies with IRD at ~1110 cm is remarkably similar to those of the ice-proximal facies, suggesting that the predominant sediment supply was from the same source. The high-carbonate bed with IRD at ~955 cm has prominent peaks in chlorite and dolomite, a little kaolinite and no calcite is detected. To assess sediment provenance in H-layers and other sediment facies, the pXRF-derived concentration of Ti, Zr, and K in the bulk sediments of cores Hu97-07, 09, and 16 are plotted in Fig. 9. Hlayers data show distinctly different element abundances compared to the ice-proximal lithofacies 5 (Fig. 9aeb). Ti and K are abundant in all H-layers, but K concentration is the highest in H2. In contrast to H-layers, high K, Ti, and Zr concentrations were found in the ice-proximal facies. There is no discernible difference in the Zr concentration among H0, H1, and H2 (Fig. 9b). As the Hudson Bay Lowlands, Hudson Bay, and Hudson Strait are all floored by the Lower Paleozoic limestones, dolostones, and shales, it is hypothesized that the high K was derived from shales (illite) and high Sr from carbonate rocks. Ti concentration is higher in the Precambrian bedrock sources. The concentrations of Zr are also characteristic of crystalline bedrock sources (Fig. 9ced) and suggest limited supply from polycyclic sandstone sources. 5. Discussion 5.1. Provenance of sediment facies on the SE Baffin Slope The SE Baffin Slope has long been recognized as an area with sediment supply from multiple sources (Jennings et al., 1996) and some of the details of changing supply from Baffin Bay, Cumberland Sound, Frobisher Bay, and Hudson Strait have been resolved by Andrews et al. (2012). In this contribution, new pXRF and a* data allow us to place the SE Baffin Slope stratigraphy more confidently in a regional context. Bulk sediment elemental concentrations of Ti, K, Zr, Sr and Ca, CaCO3 (%) and XRD data suggest at least three distinct sediment provenances represented in (a) H-layers; (b) laminated silt-mud couplets with IRD and dark brown muds and (c) dolomite-rich IRD intervals. Other core intervals may show a mixture of these

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Fig. 4. Downcore plots of core Hu97048-07: (a) sediment facies; (b1eb2) Ca/Ti and CaCO3 (%); (c1ec2) a*-trace and >150 mm (%); (d) Ti (ppm) concentration by pXRF; (e) calcite (%), (f) calcite/dolomite and (g) kaolinite (%) by XRD (Andrews et al., 2012); and (h) oxygen isotopes (d18O) in the polar planktonic foraminifera Neogloboquadrina pachyderma (s). 14CAMS dates are shown by left-directed arrows in column (b). H0e4 ¼ detrital carbonate-rich Heinrich layers; BBDC ¼ Baffin Bay Detrital Carbonate, and MIS ¼ Marine Isotope Stage. The position of new XRD data (Fig. 8) is shown by red dots on the right side of sediment facies (a). X-radiographs of the 1-cm thin sediment slabs of the Heinrich- and ice-proximal layers are shown at the extreme right to illustrate the sedimentary structures with variable bulk carbonate composition. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

three provenances, or show additional unresolved sources (Rashid and Grosjean, 2006). H-layers (facies 1) show identical geochemical signatures regardless of whether identified seaward off Hudson Strait or on the SE Baffin Slope (Fig. 9). H-layer sediments on the SE Baffin Slope (<5% IRD) contrast with more IRD-rich (>25%) east and southeast of Hudson Strait (Rashid et al., 2003). Surface currents are counterclockwise, so that iceberg and surface plume trajectories out of Hudson Strait would be to the south following the Coriolis force. The lack of simultaneous or delayed increase of the IRD after the carbonates (%) suggests that the fine-grained carbonate sediments at core site Hu97-07 may have been transported by mid-depth plumes. Andrews et al. (2012) suggested that the sediments in the H-layers were transported as very fine-grained sediments due

to the simultaneous increase of clay (wt %) and carbonates (%), similar to the proposition by Hesse and Khodabakhsh (1998). These findings demonstrate the distinct differences in the deposition of H-layers between the ice-marginal and open North Atlantic setting (Dowdeswell et al., 1995; Rashid et al., 2003; Rashid and Boyle, 2007). Laminated silt-mud couplets with IRD (facies 5): Lack of any detrital carbonate signature in facies 5 (300e325 cm and 520e570 cm; Figs. 4 and 8) but the distinct high Ti, Zr, and K and low Ca and Sr concentrations suggest different sources compared to H-layers. Andrews et al. (2012) reported clay minerals (kaolinite, smectites, and illite with minor amounts of chlorite and vermiculite) from dark mid-Cretaceous shales in Cumberland Sound (MacLean and Williams, 1983) and from H-layers, facies 5 and facies

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Fig. 5. Downcore plot of sediment core Hu88024-08 showing sediment facies (a), CaCO3 (%) (b), and >150 mm (%) which is interpreted as a proxy for the ice-rafted detritus (IRD). Core was collected on the right levee between channel D and the NAMOC at 3522 m water depth (Fig. 3). Five 14C-AMS dates (Table 1) are used to identify the detrital carbonate-rich Heinrich layers 2 and 4.

6 (facies C of Aksu and Mudie, 1985) in core Hu97-07. The high kaolinite (Fig. 4) in facies 5 suggests a source in Cumberland Sound (Jennings, 1993), as neither Precambrian bedrock nor outer shelf Cenozoic strata are an important source of kaolinite (Piper and Slatt, 1977). The high K indicates a shale source and high Zr suggests a source with sandstone and siltstone. The high Ti is a characteristic of Lower Cretaceous sediments elsewhere on the eastern Canadian margin (Pe-Piper et al., 2011). These observations suggest that facies 5 is related to transport by a shelf-crossing ice stream in Cumberland Sound. There is no evidence at these intervals for carbonate supply from Foxe Basin (Andrews et al., 1994). Dark brown mud beds (facies 6): Using a suite of sediment cores on the SE Baffin Slope including cores 77IO-5-01 and 77IO-102 (Fig. 1), Aksu and Mudie (1985) reported three sediment facies: A, B, and C, in which facies C was described as “black gravelly sandy muds”. Andrews et al. (2012) reported seven similar black beds in core Hu97-07 which were based on the preliminary onboard identification of sediment facies using the magnetic susceptibility and L*-color (Piper, 1997; Barber, 2001). However, the combination of 1-cm resolution Ca/Ti, a*-color, IRD (% >150 mm), X-radiographs, and core photographs suggest that the “black beds” can more accurately be described as “dark brown” in core Hu97-07 and correspond to both facies 6 and facies 9 (Fig. 4). All these sediment units have high a*-color, but variable CaCO3 and IRD contents. Only those beds with low CaCO3 (%) are included in facies 6, such as the

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Fig. 6. Downcore plot of sediment core Hu88024-10 showing sediment facies and CaCO3 (%) (in Heinrich layer 2 only). The core was collected on the right levee of the NAMOC between channels DA and DB (Klaücke, 1995) at 2725 m water depth.

dark brown bed between 1080 cm and 1120 cm with low carbonate content and the bed at 350e370 cm with low IRD and carbonate content. Andrews et al. (2012) suggested that the sediments in facies 6 were also derived from the Cretaceous mudstones based on the simultaneous increase of kaolinite (%) and TOC (%). Further, the L* and a* colors of the Cretaceous mudstones are 32e40 and 2.5e3.2, respectively and thus “dark” and “red-toned” as described by Andrews et al. (2012). The source of the red color (hematite) is uncertain, as red beds are not known in the exposed Cretaceous sections around Baffin Island (L. Dafoe, pers. comm. 2018). However, proximal terrestrial facies in the Lower Cretaceous elsewhere on the eastern Canadian margin have abundant hematite in paleosols (Piper et al., 2009). Brown mud with high dolomite (facies 9): A second type of dark brown mud bed has both high IRD and elevated CaCO3 (%), such as the dark brown bed immediately overlying H-layer 1 and the bed at 955e985 cm. The latter bed has high dolomite and no detectable calcite (Fig. 8). Jennings et al. (1996) reported two IRD rich “dark grey” beds above H1 and H4 from core Hu87033-09 (Fig. 1), which also correspond to facies 9 and have high dolomite. This facies from both core Hu97-07 and Hu87-09 contain some kaolinite and smectite perhaps derived locally from

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Hu97-07. Two hundred kilometers farther south, two dark brown beds underneath the H1 and H2 layers are present in core Hu97048-16 on the Saglek Bank Slope, one dark brown bed underlies H1 in core Hu97048-09, and another bed underlies H2 in cores Hu2006040-45 and H2006040-47 (Saint-Ange et al., 2013), farther offshore from core Hu97-16 (Fig. 1a, b, and Fig. S6). In contrast to these slope cores, no dark brown beds were identified in the rise core Hu97-10 at 2725 m water depth (Fig. 1: Rashid et al., 2003). Therefore, the seaward limit of the sediment plume bearing the dark brown sediments lies between cores Hu2006040-47 and Hu97-10. The dark brown sediment plume was thus less extensive than the carbonate-rich plume that deposited during H-events. In summary, sediments in H-layers (facies 1) were derived from the Hudson Strait whereas the dark brown beds (facies 6) most likely originated from the Cumberland Sound. The source of carbonates in dark-brown beds with dolomite and IRD peaks (facies 9) was through long-distance transport from Baffin Bay carbonate sources, but whether the red-brown mud also came from Baffin Bay or was from Cumberland Sound is not known. Both red-brown facies (6, 9) represent downslope sediment supply that may have been dispersed southward by contour currents along the midslope. 5.3. Correlation between the NW Labrador Sea DC events and Hevents of the North Atlantic

Fig. 7. Downcore plot of calypso core MD99-2229 showing sediment facies, L*- and -a* color parameters, and magnetic susceptibility. Core was collected from the right levee of the NAMOC (Fig. 3) at 3400 m water depth. Four 14C-AMS dates are used to identify Heinrich-layer equivalent detrital carbonate-rich parallel-laminated mud-turbidites. Two representative X-radiographs are shown to detail the sediment structure. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Cumberland Sound (Jennings, 1993). The high carbonate dark brown facies 9 with IRD differs from Cumberland Sound sourced sediment in having abundant chlorite and dolomite (Andrews et al., 1998, 2012). The dolomite component of these beds is presumably ice-rafted from Baffin Bay since dolomite is absent in the iceproximal facies but is dominant over calcite in Baffin Bay sources (Jackson et al., 2017). Detrital carbonate-rich beds in Baffin Bay have elevated a* and a chlorite/kaolinite ratio of 2:1 (Aksu and Piper, 1987; Hiscott et al., 1989; Simon et al., 2012) similar to our one XRD analysis in this facies (Fig. 8). 5.2. Distribution of dark brown mud beds Facies 6 and 9 can only be discriminated in cores in which IRD and dolomite content has been determined. Thus, these facies are indistinguishable in the older work of Aksu and Mudie (1985). Their core 77IO-5-01 is upslope from Hu97-07 (Fig. 2) and 77IO-1-02 lies 100 km to the north (Fig. 1). In core 77IO-5-1 (Fig. S4), dark brown beds are more frequent than in Hu97-07, with 6 beds above H1 and one between H1 and H2, compared to only one bed just above H1 in

H-layers in the NW Labrador Sea are lithologically different from H-layers in the open North Atlantic Ocean (Hesse and Khodabakhsh, 1998; Rashid et al., 2003; Andrews and Voelker, 2018). Andrews and Voelker (2018) pointed out challenges and pitfalls to correlate. DC-layers from Hudson Strait with open North Atlantic icerafted layers which not necessarily correlate to H-layers as originally described by Heinrich (1988). In this contribution, we first identified the nepheloid-flow layer facies and the mud turbidite facies that are characteristic of H-layers in the NW Labrador Sea (Rashid and Piper, 2007) based on the X-radiographs of 1-cm thick sediment slabs (Hesse and Khodabakhsh, 1998; Rashid et al., 2003). These identifications were confirmed by high detrital carbonate content and Ca/Ti ratio (Fig. 4). We assigned H-layers to these high detrital carbonate layers using 14C-AMS dates to the revised stratigraphy of the North Atlantic (Lisiecki and Stern, 2016) and have no radiocarbon dates that contradict the hypothesis that detrital carbonate layers identified as H1 to H4 in the NW Labrador Sea correspond to H-layers in the North Atlantic (Hemming, 2004). 5.4. Asynchroneity between DC events in Baffin Bay and Labrador Sea H-events The identification of H-layers 0, 1, 2, 3 and 4 in core Hu97-07 is constrained by 18 14C-AMS dates (Table 1). Further, the identification of the marine isotope stage (MIS) 5 between 1050 and 1182 cm (Fig. 4) allowed us to construct a stratigraphy which suggests that core Hu97-07 provides a robust climate record between 12.5 ka and 44 ka (Fig. 10), with a discontinuous record possibly back to at least 88 ka (Fig. S3). The younger part of the d18O stratigraphy of core Hu97-07 is consistent with the revised d18O stratigraphy of SE Baffin Slope cores 77IO-1-02 and 77IO-5-01 (Aksu and Mudie, 1985; Andrews et al., 1994, 1998) although our interpretation of d18O sharply differ from that of Aksu and Mudie (1985) (see below). In addition to the H-layers in core Hu97-07, three Baffin Bay detrital carbonate (BBDC) events are also identified. Construction of the robust stratigraphy allowed us to place the timing of H-events and BBDC events in the context of the exchange between the Labrador

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Fig. 8. X-ray diffractograms of the <2 mm fraction (i.e. enhancing clay-sized minerals) of selected sediment facies (Table 2) of core Hu97048-07 showing d-spacing (Å) and interpreted minerals present.

Sea and Baffin Bay and to assess the timing of the instability among the ice-streams of the NW Labrador Sea and Baffin Bay. The H0 detrital carbonate event in core Hu97-07 is compared with two cores south and east of Hudson Strait. H0 thickness in core Hu97-07 is similar to core Hu97-16, a little thinner than core Hu9709 (Fig. 1; S6). Two 14C-AMS dates of 12.56 ka and 12.61 ka at 20e25 cm and 65e70 cm, respectively, in core Hu97-07 are in stratigraphic order and therefore, we suggest that the high carbonate peak between 10 and 60 cm is H-layer 0 (Andrews et al., 1995; Rashid et al., 2011, 2012) rather than the BBDC0 (11e12.7 ka; Jackson et al., 2017). This age corresponds to a narrow Ca/Sr peak in core GeoTü SL 174 (Fig. 10), at the base of an extended BBDC0 (Jackson et al., 2017). Seaward of Hudson Strait, in the upper slope cores Hu97-16 and Hu97-09, the extended BBDC0 may be synchronous with one or more of the minor carbonate peaks derived through Hudson Strait in the early Holocene (Fig. S6). However, in all the lower slope Hudson Strait outlet cores, the section above H0 is condensed and age is inadequately constrained; therefore, those cores do not allow correlation with the upper part of BBDC0. The absence of post-H0 sediments at site Hu97-07 and lower slope cores but the presence of post-H0 in cores Hu97-16, Hu97-09, Hu2006040-45 and 47 suggests a narrow transport and deposition path in the NW Labrador Sea. BBDC events 1, 2, and 3 are identified by a minor increase in the CaCO3 (%), a sharp increase in the a*-color, and distinct peak in

dolomite (%). BBDC6 in the MTD has a high chlorite/kaolinite ratio (Fig. 8). The high a*, dolomite (%) and chlorite/kaolinite ratio are characteristic of carbonate-rich facies from Lancaster Sound (Aksu and Piper, 1987), but Greenland ice sources also contribute to the BBDC events (Simon et al., 2014, 2016; Jackson et al., 2017). The supply of sediment from Baffin Bay during the maximum ice advances of the BBDC events demonstrates that the hypothesis of grounded ice in Davis Strait (Hughes et al., 1977; Hulbe et al., 2004; Jennings et al., 2018) is untenable. Seven 14C-AMS dates either on the depth-horizons or bounding depths provide ages for the BBDC events 1e3 at 13.42 ka, 21.3 ka and 26.7 ka (Fig. 10). Using three cores from the SW Baffin Slope and the Baffin Bay basin, Jackson et al. (2017) and Simon et al. (2014, 2016) defined the BBDC events using XRF derived Ca/Sr ratio and XRD carbonates (%), respectively. However, the duration of these events is longer compared to the BBDC events on the SE Baffin Slope at site Hu97-07. It is plausible that the inadequate age constraints might attribute to the discrepancy of the age models between cores Hu2008029-016 (Simon et al., 2014) and Hu97-07 (this study). However, that is unlikely given the dense age constraints in both cores GeoTü SL 174 (Jackson et al., 2017) and Hu97-07, and it is, therefore, likely that only during a short part of the BBDC event are carbonate sediments swept as far south as the SE Baffin Slope. Small areas of dolostone floor part of Cumberland Sound (Jennings, 1993; Jennings et al., 1996). Therefore, the extent to which these two

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Fig. 9. Cross plots of elemental abundances by pXRF in core Hu97048-07 as indicators of sediment provenance. (aeb) The concentration of Ti (ppm), K (ppm), and Zr (ppm) in Heinrich-layers (facies 1) and ice-proximal facies (5). (ced) The concentration of Ti (ppm), K (ppm), and Zr (ppm) in Heinrich layers H0, H1, and H2, with cores Hu97048-10 and 16 for comparison.

sources of dolomite deposited concurrently at site Hu97-07 on the SE Baffin Slope cannot be resolved at present. 5.5. Styles of ice-margin sedimentation The new information on lithofacies and chronological correlation of cores from the NW Labrador Sea allows new interpretations of the style and variation of ice-proximal sedimentation on the SE Baffin Slope possibly back to 88 ka. Carbonate-rich nepheloid-flow layer deposits (facies 1) of Hevents are recognized in the studied cores regardless of location on the slope, rise, or basin (Fig. 11), suggesting the broader influence of the discharge from Hudson Strait even though some sites including Hu97-07 are located on the slope north of the Hudson Strait ice stream. The arcuate bulge of the shelf edge seaward of Hudson Strait (Fig. 1b) marks the limit of progradation of the Hudson Strait ice stream and extends to within 40 km of core Hu97-07 (Fig. 3). The core was closer to the ice margin discharge points than core Hu97-16 (Rashid et al., 2003). However, the H-layers in cores 77IO5-01 and 77IO-1-02 are thinner (<10e~20 cm), suggesting that the mid-depth carbonate-rich sediment plumes originating from Hudson Strait had limited influence on the upslope core sites. Ice-proximal sediments exhibiting alternating laminated siltmud couplets with IRD (facies 5) are similar to the deposits reported by Roger et al. (2013) from the slope off the NE Newfoundland Shelf. Such deposits form only when the ice margin is close to the shelf-break allowing dense sediment flows to develop from meltwater (Stokes et al., 2015). The abundance of IRD reflects the proximal location of the ice margin. In contrast, the dark brown mud facies 6, with similar provenance, has less IRD, reflecting retreat of ice back across the shelf and greater diversion of icebergs to the south by the Baffin Island Current. The distal decrease in thickness of dark brown beds, from 10 to 25 cm thick on the upper slope (cores Hu97-07, 16, 09, Hu2006040-45) to ~4 cm on the lower slope (Hu2006040-47) (Fig. S6) defines the southward pathway of the “dark-brown plume”. The lack of any dark-brown

bed in cores immediately south of Hudson Strait on the Labrador shelf or slope suggests dilution or complete depletion of the limited supply of dark-brown sediment in the sediment plume as it flowed southward along the Labrador margin. GDF deposits are absent possibly back to 88 ka on the SE Baffin Slope, either as the distinctive facies in cores (Tripsanas and Piper, 2008; Li et al., 2011) or in seismic profiles. The MTD intersected in core Hu97-07 comprises coherent blocks of normal slope sediment facies (facies 4a, 9b, and 9c; Fig. 4) and it's downslope equivalent has an irregular blocky surface (Fig. 2). In contrast, GDF deposits have a smooth surface (King et al., 1998; Tripsanas and Piper, 2008). The MTD thus resembles blocky landslides on the SE Grand Banks Slope described by Rashid et al. (2019). Whether the failure was in any way related to MIS 4 ice advance is unknown. The lack of GDF deposits on the SE Baffin Slope is surprising because the gradient of the upper slope is even less than that of the slope off Hudson Strait. On steeper slopes, GDFs break up and mix with ambient water to form turbidity currents (Hampton, 1970; Piper and Normark, 2009). On the slope off Hudson Strait, GDF deposits are very rare or absent at the time of H1 and H2. This was interpreted by Rashid and Piper (2007) to be a consequence of the only short-lived extension of ice to the shelf edge, followed by rapid retreat across the deep-water Hatton Basin, where H1 and H2 ice was not grounded. Younger H-events (H1 and H2) are predominantly represented by nepheloid-flow layer and IRD deposits on both the slope and deep Labrador Basin (Fig. 11) (Hesse and Khodabakhsh, 1998; Rashid et al., 2003). In contrast to post H3-layers, the Hudson Strait ice stream eroded Hatton Basin during H3 (Rashid and Piper, 2007) and was stable at the shelf edge for long enough for thick GDF deposits to accumulate. These deposits are intersected in core Hu97-10 (Fig. 1) and imaged in seismic (Fig. 4 of Rashid and Piper, 2007). Farther seaward in the deep Labrador Basin, the H3 interval is represented by a unit of carbonate-rich silt-mud turbidites many meters thick in cores Hu88-08, 10 and MD99-29 (Figs. 1 and 11). Similar thick siltmud turbidite units are present in the H4 interval of cores Hu88-08

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Fig. 9. (continued).

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Fig. 10. (a1ea2) CaCO3 (%) concentration and pXRF-derived Ca/Ti in the bulk sediments, (b) > 150 mm (wt %), and (c) a* of core Hu97408-07 (this study) are plotted as a function of age (see Fig. S1 for details about the age model). (d) Ca/Sr of central Baffin Bay core GeoTü SL 174 (Jackson et al., 2017). (e) XRD-derived calcite/dolomite of core Hu97048-07 (Andrews et al., 2012); (f) dolomite (%) of central Baffin Bay core Hu2008029-16 (Simon et al., 2014); (g) a* of core Hu2008029-16 (Campbell and de Vernal, 2009); and (h) oxygen isotopes (d18O) in N. pachyderma (s) of core Hu97048-07 (this study). Discontinuous horizontal lines in (a1), (b), and (g) reflect 20% CaCO3 (%), 10% > 150 mm (wt %), and a* value of 0, respectively. Vertical grey bars and discontinuous lines represent the detrital carbonate-rich Heinrich layers (Hx) and the Baffin Bay detrital carbonate events (BBDCx), respectively. All the proxy-climate records are plotted according to the original age model as published.

and MD99-2229 (Fig. 6; 11) and the deepest part of core MD992229 has similar silt-mud turbidites below a thick hemipelagic interval at the base of H4, perhaps corresponding to H5. Similar siltmud turbidites are present in core MD99-2233 (Rashid and Piper, 2007). We interpret the silt-mud turbidites as deposited from muddy turbidity currents developed from some of the GDF by in mixing of ambient water (Hampton, 1970). The duration of such deposition is not well constrained but is likely at least several hundreds of years based on similar deposits on the Laurentian Fan (Leng et al., 2018). These deposits are not the result of the direct flow of sediment-laden meltwater from the ice margin because the facies is quite different from the “nepheloid-flow layer” facies (Hesse and Khodabakhsh, 1998) in H1 and H2 of the same cores. No similar silt-mud turbidites are found in Baffin Bay seaward of the Lancaster Sound GDF (Li et al., 2011), suggesting that greater amounts of meltwater may have been involved in the Hudson Strait system. The numerous tributaries of the NAMOC (Klaücke, 1995) on the slope may have functioned as conduits for focussing and thus

maintaining turbidity current flow to the deep Labrador basin. The silt-mud turbidite units in H3, H4, and (?) H5 are much thicker in core MD99-2229 compared to those in cores Hu88-08 and Hu88-10. This core is located on the left levee (Fig. 3a) where 3.5 kHz profiles show thinner sediment packages compared to the right levee (Fig. 3b), as expected from the Coriolis effect. The greater thickness at core MD99-2229 is due most likely to stretching while coring (cf. Skene and Piper, 2003). Core log A in Fig. 3c shows the measured thickness of H-layers, but the acoustic impedance contrasts at the base of the H-layers due to density contrasts between carbonate and terrigenous sediment (Fig. 7) do not match 3.5 kHz reflections (Fig. 3c). The proposed un-stretching of the core by ~20% (B in Fig. 3c) achieved a good match. The H3 silt-mud turbidite unit in core Hu88-08, only 10 km from the NAMOC (Fig. 3a) is 8.1 m thick compared to 3.6 m in core Hu88-10, which is located 60 km from the NAMOC, showing the normal thinning of deposits distally on a channel-levee system. The presence of thick silt-mud turbidite units provide clues to

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Fig. 11. (a) Bathymetric profile between the SE Baffin Slope and deep Labrador Basin showing the approximate location of sediment cores used to construct the lithostratigraphic summary in (b). (b) Downcore facies distribution of sediment cores that provide a depth transect (935 me3400 m water depths) on the SE Baffin Slope to deep northern Labrador Basin. The base of the detrital carbonate-rich Heinrich layer 2 is used to illustrate the correlative sediment events. Note change in vertical scale for core MD99-2229.

the past position of the Hudson Strait ice-stream on the shelf and shelf-edge. If the position of the Hudson Strait ice-stream during the H3 is used as a reference point, the relationship between the GDF and silt-mud turbidites suggests that the position of the Hudson Strait ice stream was similar (i.e., stable at the shelf-edge) during the H4 and H5 events. Therefore, it is hypothesized that the periodic expansion and contraction of the Hudson Strait icestream eroded tills and probably bedrock on the outer shelf and was stable at the shelf-edge during H3, H4, and H5. This finding has important glaciological implications. During the periods between H3 and H4 (ca. 35 ka) and H4 and H5 (ca. 46 ka), the Hudson Bay Lowlands were ice-free (Dalton et al., 2016, 2019). Only immediately after H3, H2 and H1 did the Hudson Strait ice stream not retreat all the way back into Hudson Bay, suggesting the presence of a thicker Keewatin ice dome at that time. In contrast to H1 and H2, the Hudson Strait ice stream extended right across the continental shelf for a prolonged period during H3, H4 and an event tentatively identified as H5. This might have been the result of greater ice

supply from the mountainous areas bounding Hudson Strait. 6. Conclusions We report a comprehensive paleoceanographic and sediment source record from the SE Baffin ice-sheet margin, with a depth transect that covers the last 40 ka from the shelf to basin floor. Minor supply of proglacial sediment from Baffin Bay allows chronologic integration of the detrital carbonate events in Baffin Bay and the Labrador Sea. The Cumberland Sound ice stream crossed the shelf twice, after H2 and H3, supplying dark-brown, iceproximal stratified sediments but no glacigenic debris-flow deposits. The maximum extent of ice streams in Hudson Strait, Cumberland Sound, and Lancaster Sound was not synchronous. A 3-m-thick blocky mass-transport deposit between 40 and 70 ka, likely of MIS 4 slope sediment, is the only evidence of slope instability. The deep-water counterpart of H3, H4, and H5 detrital carbonate events derived from Hudson Strait are 4e10 m thick

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units of thin-bedded carbonate-rich silt-mud turbidites, which evolved from glacigenic debris flows on the Hudson Strait slope. At these times, grounded ice in Hatton Basin remained at the shelf break for long enough to form these thick deposits. In contrast, during H2eH0 only thin nepheloid layer plume deposits accumulated. Data availability Data used in this article can be found at http://ed.gdr.nrcan.gc. ca/index_e.php. Acknowledgments HR wishes to acknowledge support from the Research and Development Corporation (RDC) of the province of Newfoundland and Labrador, Atlantic Canada Opportunities Agency (ACOA), and Natural Science Foundation of China (Grant #: 41776064). Part of the study was carried out when the senior author was supported through the McGill University Reinhardt fellowship. M. Zeng, X.-X. Ye, D. Wang, and Q.-Q. Lu are thanked for their help in processing sediment samples and picking foraminifers. Seismic profiles and the piston core were collected from the CCGS Hudson with funding from the Geological Survey of Canada. A. Normandeau is thanked for the 2018028 3.5 kHz seismic profile. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.quascirev.2019.105880. References Aksu, A.E., 1981. Late Quaternary Stratigraphy, Paleoenvironments and Sedimentation History of Baffin Bay and Davis Strait. Ph.D. thesis, Dalhousie University, Halifax, NS. Aksu, A.E., Mudie, P.J., 1985. Late Quaternary stratigraphy and paleoecology of northwest Labrador Sea. Mar. Micropaleontol. 9, 537e557. Aksu, A.E., Piper, D.J.W., 1987. Late Quaternary sedimentation in Baffin Bay. Can. J. Earth Sci. 24, 1833e1846. https://doi.org/10.1139/e87-174. Andrews, J.T., Tedesco, K., 1992. Detrital carbonate-rich sediments, northwestern Labrador Sea: implications for ice-sheet dynamics and iceberg rafting (Heinrich) events in the North Atlantic. Geology 20, 1087e1090. Andrews, J.T., Barber, D.C., 2002. Dansgaard-oeschger events: is there a signal off the Hudson Strait ice stream? Quat. Sci. Rev. 21, 443e454. Andrews, J.T., MacLean, B., 2003. Hudson Strait ice streams: a review of stratigraphy, chronology and links with North Atlantic Heinrich events. Boreas 32, 4e17. Andrews, J.T., Erlenkeuser, H., Tedesco, K., Aksu, A.E., Jull, A.J.T., 1994. Late quaternary (Stage-2 and stage-3) meltwater and Heinrich events, northwest Labrador Sea. Quat. Res. 41, 26e34. Andrews, J.T., Tedesco, K., Briggs, W.M., Evans, L.W., 1995. A Heinrich- like event, H0 (DC-0): sources for detrital carbonate in the North Atlantic during the Younger Dryas chronozone. Paleoceanography 10, 943e952. Andrews, J.T., Kirby, M., Jennings, A.E., Barber, D.C., 1998. Late Quaternary stratigraphy, chronology, and depositional processes on the slope of SE Baffin Island, detrital carbonate and Heinrich events: implications for onshore glacial history.
ogr. Phys. Quat. 52, 1e15. Ge Andrews, J.T., Barber, D.C., Jennings, A.E., Eberl, D.D., Maclean, B., Kirby, M.E., Stoner, J.S., 2012. Varying sediment sources (Hudson Strait, Cumberland Sound, Baffin Bay) to the NW Labrador Sea slope between and during Heinrich events 0 to 4. J. Quat. Sci. https://doi.org/10.1002/jqs.2535. Andrews, J.T., Voelker, A.H.L., 2018. “Heinrich events” (& sediments): a history of terminology and recommendations for future usage. Quat. Sci. Rev. 187, 31e40. Barber, D.C., 2001. Laurentide Ice Sheet Dynamics from 35 to 7 Ka: Sr-Nd- Pb Isotopic Provenance of NW North Atlantic Margin Sediments. unpub. Ph.D. thesis. University of Colorado, Boulder, CO, p. 142. Campbell, D.C., de Vernal, A., 2009. Marine Geology and Paleoceanography of Baffin Bay and Adjacent Areas. Geological Survey of Canada. Open File # 5989. Channell, J.E.T., Hodell, D.A., Romero, O., Hillaire-Marcel, C., de Vernal, A., Stoner, J.S., €hl, U., 2012. A 750-kyr detrital-layer stratigraphy for the north Mazaud, A., Ro Atlantic (IODP sites U1302eU1303, Orphan Knoll, Labrador Sea). Earth Planet. Sci. Lett. 317e318, 218e230. Cuny, J., Rhines, P.B., Ron, K., 2005. Davis Strait volume, freshwater and heat fluxes. Deep Sea Res. 53, 519e542. Curry, B., Lee, C.M., Petrie, B., Moritz, R.E., Kwok, R., 2014. Multiyear volume, liquid

freshwater, and sea ice transports through Davis Strait, 2004e10. J. Phys. Oceangr. 44 https://doi.org/10.1175/JPO-D-13-0177.1. Dalton, A.S., Finkelstein, S.A., Barnett, P.J., Forman, S.L., 2016. Constraining the late Pleistocene history of the Laurentide ice sheet by dating the Missinaibi formation, Hudson Bay Lowlands, Canada. Quat. Sci. Rev. 146, 288e299. Dalton, A.S., Finkelstein, S.A., Forman, S.L., Barnett, P.J., Pico, T., Mitrovica, J.X., 2019. Was the Laurentide ice sheet significantly reduced during marine isotope stage 3? Geology 47, 111e114. de Vernal, A., Hillaire-Marcel, C., 2006. Provincialism in trends and high frequency changes in the northwest North Atlantic during the Holocene. Glob. Planet. Chang. 54, 263e290. de Vernal, A., et al., 2001. Dinoflagellate cyst assemblages as tracers of sea-surface conditions in the northern North Atlantic, Arctic and sub-Arctic seas: the new ‘n¼677’ data base and its application for quantitative paleoceanographic reconstruction. J. Quat. Sci. 16, 681e698. Dowdeswell, J., Maslin, M., Andrews, J.T., McCave, I., 1995. Iceberg production, debris rafting, and the extent and thickness of Heinrich layers (H-1, H-2) in North Atlantic sediments. Geology 23, 301e304. Dyke, A.S., Andrews, J.T., Clark, P.U., England, J.H., Miller, G.H., Shaw, J., Veillette, J.J., 2002. The Laurentide and Innuitian ice sheets during the last glacial maximum. Quat. Sci. Rev. 21, 9e31. Hampton, M.A., 1970. Subaqueous Debris Flow and Generation of Turbidity Currents [unpubl. Ph.D. Thesis]. Stanford University, Stanford, CA, p. 180. Heinrich, H., 1988. Origin and consequences of cyclic ice rafting in the northeast Atlantic Ocean during the past 130,000 years. Quat. Res. 29, 143e152. Hemming, S.R., 2004. Heinrich events: massive late Pleistocene detritus layers of the North Atlantic and their global climate imprint. Rev. Geophys. 42 https:// doi.org/10.1029/2003RG000128. Hesse, R., Khodabakhsh, S., 1998. Depositional facies of late Pleistocene Heinrich events in the Labrador Sea. Geology 26, 103e106. Hillaire-Marcel, C., Turon, J.-L., 1999. Preliminary cruise report IMAGES-V onboard the marion Dufresne, Junee24 july, 1999. Geol. Surv. Can. Open file # 3782. Hiscott, R., Aksu, A.E., Nielsen, O., 1989. Provenance and dispersal patterns, Pliocene-Pleistocene section at site 645, Baffin Bay. Proc. Ocean Drill. Progr. 105, 31e52. Hodell, D.A., Curtis, J.H., 2008. Oxygen and carbon isotopes of detrital carbonate in North Atlantic Heinrich events. Mar. Geol. 256, 30e35. Hughes, T., Denton, G.H., Grosswald, M.G., 1977. Was there a late-Würm Arctic ice sheet? Nature 266, 596e602. Hulbe, C.L., MacAyeal, D., Denton, G.H., Kleman, J., Lowell, T.V., 2004. Catastrophic ice shelf breakup as the source of Heinrich event icebergs. Paleoceanography 19, PA1004. https://doi.org/10.1029/2003PA000890. Jackson, R., Carlson, A.E., Hillaire-Marcel, C., Wacker, L., Vogt, C., Kucera, M., 2017. Asynchronous instability of the North American-Arctic and Greenland ice sheets during the last deglaciation. Quat. Sci. Rev. 164, 140e153. https://doi.org/ 10.1016/j.quascirev.2017.03.020.
Cofaigh, C., St-Onge, G., Belt, S.T., Cabedo-Sanz, P., Jennings, A.E., Andrews, J.T., O Pearce, C., Hillaire-Marcel, C., Campbell, D.C., 2018. Baffin Bay paleoenvironments in the LGM and HS1: resolving the ice-shelf question. Mar. Geol. 402, 5e16. Jennings, A.E., Tedesco, K., Andrews, J.T., Kirby, M.E., 1996. Shelf erosion and glacial ice proximity in the Labrador Sea during and after Heinrich events (H3 or 4 to H0) as shown by foraminifers. Geol. Soc. Spec. Publ. 111, 29e49. Jennings, A.E., 1993. The quaternary history of Cumberland Sound, southeastern
ogr. Phys. Quat. 47, 21e42. Baffin Island: the marine evidence. Ge King, E.L., Haflidason, H., Sejrup, H.P., Løvlie, R., 1998. Glacigenic debris flows on the north sea trough mouth fan during ice stream maxima. Mar. Geol. 152, 217e246. Klaücke, I., 1995. The submarine drainage system of the Labrador Sea: result of glacial input from the Laurentide Ice sheet. In: Unpublished Ph.D. Thesis: Montreal, Quebec, Canada. McGill University, p. 248. Leng, W., von Dobeneck, T., Bergmann, F., Just, J., Mulitza, S., Chiessi, C.M., StOnge, G., Piper, D.J.W., 2018. Sedimentary and rock magnetic signatures and event scenarios of deglacial outburst floods from the Laurentian Channel Ice Stream. Quat. Sci. Rev. 186, 27e46. Levac, E., Lewis, C.F.M., Miller, A.A.L., 2011. The impact of Lake Agassiz flood recorded in northeast Newfoundland and northern Scotian shelves: new subcentennial palynological data. In: Rashid, H., Polyak, L., Mosley-Thompson, E. (Eds.), Abrupt Climate Change. Geophysical Monograph 193. American Geophysical Union, Washington, DC, pp. 139e160. Lewis, C.F.M., Miller, A.A., Levac, L.E., Piper, D.J.W., Sonnichsen, G.V., 2012. Lake Agassiz outburst age and routing by Labrador Current and the 8.2 cal ka cold event. Quat. Int. 260, 83e97. https://doi.org/10.1016/j.quaint.2011.08.023. Li, G., Piper, D.J.W., Campbell, D.C., 2011. The quaternary lancaster Sound Troughmouth fan, NW Baffin Bay. J. Quat. Sci. 26, 511e522. https://doi.org/10.1002/ jqs.1479. Lisiecki, L.E., Stern, J.V., 2016. Regional and global benthic d18O stacks for the last glacial cycle. Paleoceanography 31, 1368e1394. Lougheed, B.C., Obrochta, S.P., 2019. A rapid, deterministic age-depth modeling routine for geological sequences with inherent depth uncertainty. Paleoceanogr. Paleoclimatol. 34, 122e133. MacLean, B., Williams, G.L., 1983. Geological investigations of Baffin Island Shelf in 1982. In: Current Research, Part B, Geological Survey of Canada Paper 83-1B, pp. 309e315. McNeely, R., Dyke, A.S., Southon, J.R., 2006. Canadian Marine Reservoir Ages,

H. Rashid et al. / Quaternary Science Reviews 221 (2019) 105880 Preliminary Data Assessment. Geological Survey of Canada. Open File # 5049. Margold, M., Stokes, C.R., Clark, C.D., 2018. Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet. Quat. Sci. Rev. 189, 1e30. Münchow, A., Falkner, K.K., Melling, H., 2015. Baffin Island and west Greenland current systems in northern Baffin Bay. Prog. Oceanogr. 132, 305e317. Oakey, G.N., Chalmers, J.A., 2012. A new model for the Paleogene motion of Greenland relative to North America: plate reconstructions of the Davis Strait and Nares Strait regions between Canada and Greenland. J. Geophy. Res.: Solid Earth 117 (B10). Pe-Piper, G., Karim, A., Piper, D.J.W., 2011. Authigenesis of titania minerals and the mobility of Ti: new evidence from pro-deltaic sandstones, Cretaceous Scotian Basin, Canada. J. Sediment. Res. 81, 762e773. Piper, D.J.W., Slatt, R.M., 1977. Late quaternary clay-mineral distribution on the eastern continental margin of Canada. Geol. Soc. Am. Bull. 88, 267e272. Piper, D.J.W., Stow, D., 1991. Fine-grained turbidites. In: Einsele, G., Ricken, W., Seilacher, A. (Eds.), Cycles and Events in Stratigraphy. Springer-Verlag Berlin and Heidelberg GmbH & Co., pp. 360e376 Piper, D.J.W., 1997. Cruise Report Hudson 97-048. Geological Survey of Canada (Atlantic), Dartmouth, NS, p. 64. Piper, D.J.W., Normark, W.R., 2009. Processes that initiate turbidity currents and their influence on turbidites: a marine geology perspective. J. Sediment. Res. 79, 347e362. Piper, D.J.W., Hundert, T., Pe-Piper, G., Okwese, A.C., 2009. The roles of pedogenesis and diagenesis in clay mineral assemblages: lower Cretaceous fluvial mudrocks, Nova Scotia, Canada. Sediment. Geol. 213, 51e63. Praeg, D.B., MacLean, B., Hardy, I.A., Mudie, P.J., 1986. Quaternary geology of the southeast Baffin Island continental shelf. Geol. Surv. Can. Pap. 38. Rashid, H., 2002. The Deep-sea Record of Rapid Late Pleistocene Paleoclimate Change and Ice-Sheet Dynamic from the Labrador Sea Sediments. McGill University, Montreal, p. 203. Unpubl. Ph.D. thesis. Rashid, H., Grosjean, E., 2006. Detecting the source of Heinrich layers: an organic geochemical study. Paleoceanography 21. https://doi.org/10.1029/ 2005PA001240. Rashid, H., Piper, D.J.W., 2007. The extent of ice on the continental shelf off Hudson Strait during Heinrich events 1-3. Can. J. Earth Sci. 44, 1537e1549. Rashid, H., Boyle, E.A., 2007. Mixed-layer deepening during Heinrich events: a multi-planktonic foraminiferal d18O approach. Science 318, 439e441. Rashid, H., Hesse, R., Piper, D.J.W., 2003. Origin of unusually thick ice-proximal Heinrich layers H1 to H3 in the northwest Labrador Sea. Earth Planet. Sci. Lett. 208, 319e336. Rashid, H., Piper, D.J.W., Flower, B.P., 2011. The role of Hudson Strait outlet in younger Dryas sedimentation in the Labrador Sea. In: Abrupt Climate Change: Mechanisms, Patterns, and Impacts, vol. 193, pp. 93e110. Geophysical Monograph. Rashid, H., Saint-Ange, F., Barber, D.C., Smith, M.E., Devalia, N., 2012. Fine-scale sediment structure and geochemical signature between eastern and western

17

North Atlantic during Heinrich events 1 and 2. Quat. Sci. Rev. 46, 136e150. ~ oz, A., Rashid, H., Piper, D.J.W., MacKillop, K., Ouellette, D., Vermooten, M., Mun
nez, P., 2019. Dynamics of sediments on a glacially influenced, sediment Jime starved, current-swept continental margin: the SE Grand Banks Slope off Newfoundland. Mar. Geol. 408, 67e86.
ndez-Molina, F.J., Van Rooij, D., Wåhlin, A., 2014. Contourites and Rebesco, M., Herna associated sediments controlled by deep-water circulation processes: State-ofthe-art and future considerations. Mar. Geol. 352, 111e154. Roger, J., Saint-Ange, F., Lajeunesse, P., Duchesne, M.J., St-Onge, G., 2013. Late Quaternary glacial history and meltwater discharges along the northeastern Newfoundland Shelf. Can. J. Earth Sci. 50, 1178e1194. Saint-Ange, F., Piper, D.J.W., Mackillop, K., Jarrett, K.A., Higgins, J., Ledger-Piercey, 2013. Logs of piston cores, deep-water Labrador Sea. Geol. Surv. Can. Open File 7109, 193. Simon, Q., Hillaire-Marcel, C., St-Onge, G., Andrews, J.T., 2014. North-eastern Laurentide, western Greenland and southern Innuitian ice stream dynamics during the last glacial cycle. J. Quat. Sci. 29, 14e26. https://doi.org/10.1002/jqs.2648. Simon, Q., St-Onge, G., Hillaire-Marcel, C., 2012. Late Quaternary chronostratigraphic framework of deep Baffin Bay glaciomarine sediments from high resolution, paleomagnetic data. Geochem. Geophys. Geosyst. 13 https://doi.org/ 10.1029/2012GC004272. s, D.L., Nuttin, L., Hillaire-Marcel, C., St-Onge, G., Simon, Q., Thouveny, N., Bourle 2016. Authigenic 10Be/9Be ratios and 10Be-fluxes (230Thxs-normalized) in central Baffin Bay sediments during the last glacial cycle: paleoenvironmental implications. Quat. Sci. Rev. 140, 142e162. https://doi.org/10.1016/j.quascirev.2016. 03.027. Skene, K.I., Piper, D.J.W., 1991. Clay sized mineralogy of core 87008-003 from the Janomaly ridge and from comparison cores along the eastern Canadian continental margin: down-core variation and source area interpretation. GSC Open File #2424. Skene, K.I., Piper, D.J.W., 2003. Late Quaternary stratigraphy of Laurentian Fan: a record of events off the eastern Canadian continental margin during the last deglacial period. Q. Int. 99, 135e152. Stokes, C.R., Margold, M., Clark, C.D., Tarasov, L., 2016. Ice stream activity scaled to ice sheet volume during Laurentide Ice Sheet deglaciation. Nature 530, 322e326. Stokes, C.R., 26 co-authors, 2015. On the reconstruction of palaeo-ice sheets: recent advances and future challenges. Quat. Sci. Rev. 125, 15e49. Stuiver, M., Reimer, P.J., Reimer, R.W., 2019. CALIB 7.1 [WWW program] at. http:// calib.org. (Accessed 15 June 2019). Tripsanas, E.K., Piper, D.J.W., 2008. Glaciogenic debris-flow deposits of Orphan Basin, offshore eastern Canada: sedimentological and rheological properties, origin, and relationship to meltwater discharge. J. Sediment. Res. 78, 724e744. Wang, D., Hesse, R., 1996. Continental slope sedimentation adjacent to an icemargin. II. Glaciomarine depositional facies on Labrador Slope and glacial cycles. Mar. Geol. 135, 65e96.