Description: The Laurentide Ice Sheet (LIS) was a large, dynamic ice sheet in the early Holocene. The glacial events through Hudson Strait leading to its eventual demise are recorded in the well-dated Labrador shelf core, MD99-2236 from the Cartwright Saddle. We develop a detailed history of the timing of ice-sheet discharge events from the Hudson Strait outlet of the LIS during the Holocene using high-resolution detrital carbonate, ice rafted detritus (IRD), d18O, and sediment color data. Eight detrital carbonate peaks (DCPs) associated with IRD peaks and light oxygen isotope events punctuate the MD99-2236 record between 11.5 and 8.0 ka. We use the stratigraphy of the DCPs developed from MD99-2236 to select the appropriate DeltaR to calibrate the ages of recorded glacial events in Hudson Bay and Hudson Strait such that they match the DCPs in MD99-2236. We associate the eight DCPs with H0, Gold Cove advance, Noble Inlet advance, initial retreat of the Hudson Strait ice stream (HSIS) from Hudson Strait, opening of the Tyrrell Sea, and drainage of glacial lakes Agassiz and Ojibway. The opening of Foxe Channel and retreat of glacial ice from Foxe Basin are represented by a shoulder in the carbonate data. DeltaR of 350 years applied to the radiocarbon ages constraining glacial events H0 through the opening of the Tyrell Sea provided the best match with the MD99-2236 DCPs; DeltaR values and ages from the literature are used for the younger events. A very close age match was achieved between the 8.2 ka cold event in the Greenland ice cores, DCP7 (8.15 ka BP), and the drainage of glacial lakes Agassiz and Ojibway. Our stratigraphic comparison between the DCPs in MD99-2236 and the calibrated ages of Hudson Strait/Bay deglacial events shows that the retreat of the HSIS, the opening of the Tyrell Sea, and the catastrophic drainage of glacial lakes Agassiz and Ojibway at 8.2 ka are separate events that have been combined in previous estimates of the timing of the 8.2 ka event from marine records. SW Iceland shelf core MD99-2256 documents freshwater entrainment into the subpolar gyre from the Hudson Strait outlet via the Labrador, North Atlantic, and Irminger currents. The timing of freshwater release from the LIS Hudson Strait outlet in MD99-2236 matches evidence for freshwater forcing and LIS icebergs carrying foreign minerals to the SW Iceland shelf between 11.5 and 8.2 ka. The congruency of these records supports the conclusion of the entrainment of freshwater from the retreat of the LIS through Hudson Strait into the subpolar gyre and provides specific time periods when pulses of LIS freshwater were present to influence climate.

Description: Geophysical data from the Kangerlussuaq Trough, E Greenland (Dowdeswell et al., 2010; Stein, 1996), and from the West Iceland shelf (Syvitski et al., 1999) indicate that there are sites where pre Last Glacial Maximum (LGM) sediments exist, but no such sites have been successfully cored. However, a significant number of cores have been recovered that penetrate a basal diamicton, sometimes containing shells and foraminifera, and which are overlain by glacial marine sediments rich in ice rafted debris (IRD) (Jennings et al., 2000; Olafsdottir, 2004). At the LGM, reconstructions and marine field data (Andrews, 2008; Andrews et al., 1998, 2000; Dunhill, 2005; Funder et al., 2004; Hubbard et al., 2006; Vasskog et al., 2015) indicate that the Iceland and Greenland ice sheets were terminating at their shelf breaks with deposition on the slopes above the Denmark Strait. Active sediment deposition ceased on the Kangerlussuaq Trough Mouth Fan (KTMF) ca. 15.3 ka 14C BP (Andrews et al., 1998; Dunhill, 2005) and retreat to the present coastline occurred prior to deposition of the Vedde tephra (Jennings et al., 2006). There is strong evidence that a major change in deep-water circulation at ~15 cal ka BP resulted in abrupt warming at the onset of the Bølling/Allerød (B/A) interstadial (Thiagarajan et al., 2014; Thornalley et al., 2011). Syvitski et al (1999) and Norddahl and Ingolfsson (2015) argued that the Iceland Ice Sheet retreated rapidly during this time, driven by a rapid rise in relative sea level. Jennings et al. (2006) also presented radiocarbon evidence from marine cores for a rapid retreat of the Greenland Ice Sheet along Kangerlussuaq Trough (KT, Fig. 1).

Description: We use quantitative X-ray diffraction to determine the mineralogy of late Quaternary marine sediments from the West and East Greenland shelves offshore from early Tertiary basalt outcrops. Despite the similar basalt outcrop area (60 000-70 000 km**2), there are significant differences between East and West Greenland sediments in the fraction of minerals (e.g. pyroxene) sourced from the basalt outcrops. We demonstrate the differences in the mineralogy between East and West Greenland marine sediments on three scales: (1) modern day, (2) late Quaternary inputs and (3) detailed down-core variations in 10 cores from the two margins. On the East Greenland Shelf (EGS), late Quaternary samples have an average quartz weight per cent of 6.2 ± 2.3 versus 12.8 ± 3.9 from the West Greenland Shelf (WGS), and 12.02 ± 4.8 versus 1.9 ± 2.3 wt% for pyroxene. K-means clustering indicated only 9% of the samples did not fit a simple EGS vs. WGS dichotomy. Sediments from the EGS and WGS are also isotopically distinct, with the EGS having higher eNd (-18 to 4) than those from the WGS (eNd = -25 to -35). We attribute the striking dichotomy in sediment composition to fundamentally different long-term Quaternary styles of glaciation on the two basalt outcrops.