Abstract During the final retreat of the Laurentide Ice Sheet, large volumes of meltwater from the Hudson Bay region entered the North Atlantic leading to one of the strongest freshwater perturbations of the Holocene. The resulting 8.2 ka cold event is a key benchmark for understanding ice-sheet–ocean interactions, yet the timing, structure, and mechanisms of this freshwater release from Hudson Bay remain debated. New sediment records from Hudson Strait document a sequence of ice–ocean reorganisations and associated freshwater regimes between ~ 9.0 and 8.0 ka. They include (1) background deglacial meltwater and limited iceberg export prior to ~ 8.8 ka; (2) a short-lived episode of marine intrusion, ice-shelf formation, and subsequent ice-shelf breakup accompanied by transient iceberg discharge; and (3) a prolonged, multi-phase freshwater release between ~ 8.2 and 8.0 ka linked to the final collapse of the Hudson Bay ice saddle and drainage of glacial Lake Agassiz–Ojibway. Notably, the duration of this final freshwater phase is coeval, within uncertainty, with the 8.2 ka climate anomaly recorded in Greenland ice cores, consistent with a causal connection. This refined stratigraphic framework demonstrates that freshwater forcing from Hudson Bay was temporally structured and temporally sustained, highlighting the importance of ice-margin geometry and meltwater routing in modulating early Holocene climate perturbations.

The retreat of the Laurentide Ice Sheet across eastern Ontario and southwestern Quebec led to the formation of glacial Lake Barlow in the upper Ottawa River watershed. Lake Barlow expanded northward and eventually merged with glacial Lake Ojibway, forming a lake system that later coalesced with glacial Lake Agassiz near the end of deglaciation. Although Lake Barlow is central to reconstructing late deglacial events, its history and connection to Lake Ojibway remain poorly constrained. To improve understanding, extensive mapping of raised shorelines and other lake-level indicators was carried out in the Barlow basin using LiDAR-derived digital terrain models. Lake levels were reconstructed from 22,330 strandline-elevation points and paleosurfaces accounting for postglacial rebound at key deglaciation intervals (10.5 and 8.0 ka). High- and intermediate-elevation strandlines reveal a gradual lowering of the lake surface, culminating in a well-defined lake level at mid-elevation that marks a significant period of stability. The new strandline sequence shows strong continuity with that reported for the Lake Ojibway basin to the north, indicating that the lakes formed a single water body for much of the glaciolacustrine episode. These findings contrast with earlier models that proposed multiple lake phases controlled by a series of uplift-driven bedrock sills along the upper Ottawa River. Instead, the reconstructions suggest that early glaciolacustrine stages were likely dammed by the Lake McConnell Moraine and nearby glaciofluvial deposits that spread across the southern part of the basin. The emergence of a bedrock sill in the mid-basin near Angliers marked the end of the Barlow-Ojibway episode and initiated the stable phase of glacial Lake Ojibway, which was then regulated by the Angliers outlet. This stable lake configuration ended abruptly around 8.22 ka due to a major lake drawdown, as it was connected to Lake Agassiz to the west. After the drawdown, Lakes Barlow and Ojibway evolved independently until they disappeared, leaving small postglacial lakes in isolated basins. These results improve paleogeographic reconstructions and provide key data for modeling meltwater volumes needed to assess the impact of freshwater discharges on ocean circulation and climate during deglaciation.

Accurate mapping of inland waters is essential for managing freshwater resources. This mapping is usually undertaken using single beam echosounder, which provides interpolated low-resolution bathymetric maps. Over the past decade, high-resolution swath bathymetry was acquired for nine fjord-type lakes in Québec and Labrador (eastern Canada) using a multibeam echosounder or an interferometric sonar. Together, these lakes represent more than 46,000 million m3 of freshwater. The dataset includes seven lakes from the Canadian Shield (Mékinac, Jacques-Cartier, Pasteur, Pentecôte, Walker, Manicouagan in Québec, and Grand Lake in coastal Labrador) and two from the Appalachian Mountains in southeastern Québec (Pohénégamook and Témiscouata). Swath bathymetric data of these large waterbodies provides a baseline for scientific research and ongoing conservation efforts.

Reconstructions of the maximum extent and dynamics of the Laurentide Ice Sheet (LIS) during the Last Glacial Maximum (LGM) are needed for understanding how marine-based ice sheets will respond to modern climate change. The partitioning of ice masses and the location of dominant ice flows within the LIS are broadly known at regional scales, but their influence on the marine-based maximum extent of the ice sheet remains poorly constrained. Here, we provide evidence for the maximal extent of the LIS margin during the LGM in the Broughton and Merchants cross-shelf troughs off southeastern Baffin Island based on newly acquired sea floor geomorphology data. Grounding-zone wedges (GZWs), moraines and ice-stream bedforms within the Merchants cross-shelf trough delimit the maximum extent of the LIS in this sector to near the mouth of the modern fjords. Two lateral moraines, mega-scale glacial lineations (MSGLs), and iceberg scours also indicate the presence of an ice shelf extending beyond the former grounding line. In Broughton Trough, the maximum extent of the LIS is interpreted from the distribution of MSGLs and iceberg scours. The presence of sticky spots near the shelf edge may have played a role in subglacial flow and thus glacier behaviour. The difference in ice extent between the two nearby troughs is attributed to partitioning of the LIS between ice flowing from the Penny Ice Cap into Broughton Trough and ice from local alpine glaciers flowing into Merchants Trough. In addition, the presence of a dominant ice flow south of the Cumberland Peninsula may have drained ice masses of Cumberland Peninsula towards the south and caused minimal expansion in Merchants Trough to the north. These results provide a clearer understanding of the relationship between ice-sheet extent along continental margins and inland ice dynamics.

Crater lakes in core regions of former ice sheets have the potential to preserve long‐term sedimentary archives that are otherwise rare in glaciated landscapes due to pervasive glacial erosion. Lake Wiyâshâkimî, an impact crater lake located in the inner core of the Québec‐Labrador Dome of the Laurentide Ice Sheet, provides a rare example of such a setting. The lake was therefore investigated along the region surrounding it through remotely sensed mapping and acoustic sub‐bottom profiling to reconstruct its glacial to postglacial environmental evolution from its morphosedimentary record. Mapping of ice‐flow landforms suggests three distinct glacial flowsets in the region, indicating a transition from external ice‐stream influences to local topographical controls during deglaciation. Contrary to previous hypotheses, mapping evidence suggests that the Tyrrell Sea deglacial marine transgression did not reach Lake Wiyâshâkimî, with surrounding strandlines likely of glaciolacustrine origin. Five acoustic facies were identified from the analysis and interpretation of the acoustic sub‐bottom profiles: AF1, bedrock, till and/or glacifluvial sands forming the acoustic basement; AF2, an acoustically transparent deposit filling the deeper basins of the lake, a fine‐grained diamicton either associated with mass‐movements or full glacial conditions (till); AF3A and AF3B, glaciolacustrine sediments deposited proximally and distally from the ice margin, respectively; and AF4, paraglacial and postglacial deposits that have been partly, at least in the upper tens of metres of the water column, remobilized by bottom currents induced by strong winds prevailing in the large lake. While our analysis shows it is unlikely that sediments pre‐dating the last glaciation were preserved in the lake basin, the findings provide new insights into the lateglacial and deglacial history of the central Québec‐Labrador region and highlight the role of postglacial processes in shaping the lake‐bottom morphosedimentary archives.

ABSTRACT The final deglaciation stages of the Laurentide Ice Sheet in northern Quebec–Labrador were marked by the incursion of the d'Iberville Sea into the coastal areas of Ungava Bay. Remote and field mapping of raised marine strandlines along the Ungava Peninsula east coast show that the maximum marine limit decreases from south (165 m) to north (100 m), reflecting differential uplift linked to an ice mass remnant located to the southwest of the bay. Reconstruction of the uppermost marine limit in two east–west transects extending into the Peninsula interior reveals distinct sea‐level stands with limited extents towards the west, indicating that the early stages of the marine incursion occurred in contact with the ice margin. The reconstruction also identifies the maximum eastward extent of ice‐dammed lakes that occupied the Arnaud River and Aux‐Feuilles River valleys. 10 Be surface exposure dating of marine strandlines yielded consistent 10 Be ages that indicate a rapid deglaciation of Ungava Bay between 8900 ± 200 a (north) and 7900 ± 200 a (south). These results provide constraints on the position of the Labrador Sector eastern and western ice margins during the late deglaciation, in addition to the timing of ice and meltwater discharges from the Ungava Bay region.

Multibeam bathymetric and seismostratigraphic data collected in the Clyde fjord-cross-shelf trough system (eastern Baffin Island, Canadian Arctic Archipelago) display glacial landforms and depositional assemblages that enable the identification of the maximal extent of the Laurentide Ice Sheet (LIS) margin and delineating the patterns and controls on its subsequent retreat. Additionally, 10 new sediment cores – from which seven radiocarbon ages were acquired – allow the recognition of depositional processes. Results show that, during the Last Glacial Maximum, the LIS margin extended almost to the edge of the continental shelf. Early deglaciation of the trough was marked by an initial ice-shelf collapse and rapid retreat of the ice stream, as evidenced by the absence of ice marginal landforms and the presence of extensive iceberg ploughmarks across a large portion of the outer trough. It was followed by a slow retreat and successive stabilizations of the ice margin that led to the deposition of recessional moraines and grounding-zone wedges (GZWs). Deglaciation of the fjord in the early Holocene occurred in an episodic style, whereby rapid retreat was punctuated by relatively long standstills that enabled major moraine formation. Long-term stabilizations of the ice margin in the Clyde fjord-cross-shelf trough system are interpreted to coincide with major climatic cooling events, such as the Younger Dryas and early Holocene cold reversals. Ages derived from sediment cores and previous work suggest that higher retreat rates correspond with periods of significant global sea level rise, suggesting that oceanic forcing exerted a minor control on the deglaciation. GZWs and large moraine ridges are observed at pinning points in the trough and fjord, indicating that the location of ice margin stabilizations was influenced by topography. The reconstruction of the deglaciation of the Clyde fjord-cross-shelf trough system allows us to refine deglacial models for similar systems of northeastern Baffin Island, in particular beyond the coast and along the steeper section of the fjord where chronological gaps remained.

We present a series of 1-km spatial resolution rebound (isobase) surfaces based on publicly distributed predictions obtained from the glacio-isostatic adjustment models known as ICE-5G (VM2 L90), ICE-6G_C (VM5a) and ICE-7G_NA (VM7). Our objective is to provide readily accessible tools for a broad range of geological and paleoenvironmental studies, and to facilitate direct comparison between models’ predictions and field-based observations. Rebound surfaces were interpolated at the scale of North American ice sheets (35.5°-89.5°N; 45°-165°W) and for each time increment of the models (1,000-500 yrs, between 26,000-21,000 yrs BP and present-day). The assessment of the interpolations indicates that the rebound surfaces have an overall vertical accuracy of ∼0.4 m compared to original ICE-xG outputs. These rebound surfaces were combined with the GEBCO 2021 present-day elevation grid to reconstruct the paleotopography for each time increment of the models and are all presented as raster files that can be easily integrated into geographical information systems. The resulting datasets therefore provide a unique support for geological, paleoenvironmental and archeological studies.

The Green Edge project was designed to investigate the onset, life, and fate of a phytoplankton spring bloom (PSB) in the Arctic Ocean. The lengthening of the ice-free period and the warming of seawater, amongst other factors, have induced major changes in Arctic Ocean biology over the last decades. Because the PSB is at the base of the Arctic Ocean food chain, it is crucial to understand how changes in the Arctic environment will affect it. Green Edge was a large multidisciplinary, collaborative project bringing researchers and technicians from 28 different institutions in seven countries together, aiming at understanding these changes and their impacts on the future. The fieldwork for the Green Edge project took place over two years (2015 and 2016) and was carried out from both an ice camp and a research vessel in Baffin Bay, in the Canadian Arctic. This paper describes the sampling strategy and the dataset obtained from the research cruise, which took place aboard the Canadian Coast Guard ship (CCGS) Amundsen in late spring and early summer 2016. The sampling strategy was designed around the repetitive, perpendicular crossing of the marginal ice zone (MIZ), using not only ship-based station discrete sampling but also high-resolution measurements from autonomous platforms (Gliders, BGC-Argo floats …) and under-way monitoring systems. The dataset is available at https://doi.org/10.17882/86417 (Bruyant et al., 2022).

Abstract. The Green Edge project was designed to investigate the onset, life and fate of a phytoplankton spring bloom (PSB) in the Arctic Ocean. The lengthening of the ice-free period and the warming of seawater, amongst other factors, have induced major changes in arctic ocean biology over the last decades. Because the PSB is at the base of the Arctic Ocean food chain, it is crucial to understand how changes in the arctic environment will affect it. Green Edge was a large multidisciplinary collaborative project bringing researchers and technicians from 28 different institutions in seven countries, together aiming at understanding these changes and their impacts into the future. The fieldwork for the Green Edge project took place over two years (2015 and 2016) and was carried out from both an ice-camp and a research vessel in the Baffin Bay, canadian arctic. This paper describes the sampling strategy and the data set obtained from the research cruise, which took place aboard the Canadian Coast Guard Ship (CCGS) Amundsen in spring 2016. The dataset is available at https://doi.org/10.17882/59892 (Massicotte et al., 2019a).

The glaciological significance of ice shelves is relatively well established for the stability of modern ice sheets of Antarctica. Past ice shelves of the Arctic, however, are poorly documented while their role for the stability of former ice sheets remains mostly unknown. Here we present swath bathymetry data and seismostratigraphic profiles that reveal a large moraine system extending along the continental slope off Baffin Island, demonstrating that a 500-m thick ice shelf covered northern Baffin Bay during the last glacial episode. We suggest that this ice shelf had a profound impact on the stability of a series of major ice streams that drained the interior of the Laurentide, Innuitian and Greenland ice sheets. Climate warming and global sea-level rise in the early stage of deglaciation possibly contributed to a large-scale break-up of the ice shelf, which led to the destabilisation and reorganisation of tributary ice streams from these three ice sheets.

Hydroacoustic surveys were conducted in eight fjord-lakes of Québec-Labrador in order to analyse their Late-Quaternary geomorphological and stratigraphic record of glaciation, paleoseismicity and postglacial environmental changes. This large morphostratigraphic dataset provided a unique opportunity to establish a conceptual model of the evolution for fjord-lakes in relation to deglaciation, glacio-isostatic rebound, sediment fluxes and paleoseismicity. The analysis of the morphology and distribution of many morainic deposits into the fjord-lakes (hummocky moraines, morainic sills and morainic complexes) allows relating their formation to the glacial erosion potential, as well as to climatic and topographic controls. During past glaciations, a topographic sill was left uneroded at the opening of valleys due to the decrease in the glacial erosion potential associated with the lateral extension of the glacier down-ice; this bedrock sill created in turn an anchoring point to the ice during deglaciation. Hummocky moraines were documented at the outlet of five fjord-lakes that are located within the deepest and narrowest valleys of the studied systems. Based on our analysis of these sublacustrine landform-sediment assemblages, fjord-lakes constitute distinct sedimentary systems that should be differentiated from typical fjord system (i.e., in marine waters). The large-scale landforms contained in the fjord-lakes of Québec-Labrador (i.e., esker, moraines, gullies, lateral banks, turbidity channels and circular cavities) are inherited from their past subglacial, glaciomarine and paraglacial conditions, while only small deltaic bedforms (i.e., sediment waves and crescent-shaped bedforms) were formed in postglacial times. The present-day hydrological regime of fjord-lakes of Québec-Labrador is considered river-driven, except for the lakes located near active seismic zones where widespread postglacial mass-movements are documented.

The Labrador Sector of the Laurentide Ice Sheet is characterized by a complex network of ice divides and an extensive landform record outlining two broad and opposing ice flows that are separated by a narrow Horseshoe Intersection Zone (HIZ). This geomorphic system gave rise to contrasting reconstructions, which reflect uncertainties on the temporal evolution of ice divides, the nature and age of the main landform systems and the overall pattern of ice retreat during the last deglaciation. Here, we address these issues through systematic mapping of glacial landforms and ice-flow indicators in a large area of northeastern Quebec and Labrador. The application of cosmogenic (10Be and 26Al) dating to esker-fed glaciomarine deltas and different rock surfaces brings new constraints on the chronological framework and insights on the subglacial thermal regime. Our results outline four main landform assemblages, two of which relating to a major system of opposite ice flows that delineate the position of the eastern Ancestral Labrador ice divide. Our reconstruction shows that the HIZ occurs several tens of km to the west of this divide and that these two features are genetically distinct. The HIZ relates to the late-glacial development of ice streams showing a massive convergent ice flow into Ungava Bay. The upstream extent of this ice flow system shows a strong coupling with the outline of Ungava Bay drainage divide, suggesting that the configuration of the HIZ could be the expression of a topographic control on the late-glacial ice sheet dynamics. Landforms also indicate a significant shift in the deglaciation mode, which evolved from an overall warm-based to an areally-confined cold-based ice retreat near the center of the former ice mass – a change in dynamics that also played a role in the configuration of the HIZ. Overall, areas indicative of cold-based ice conditions are limited to highly elevated terrains, thus ruling out models arguing for an extensive cold-based ice cover over Ungava Bay throughout the last deglaciation.

The climate variability of the last deglaciation is often linked to meltwater discharges from the melting of large ice sheets. One of the best examples comes from the drainage of glacial Lake Agassiz-Ojibway (LAO) and its attendant perturbation of the Atlantic Meridional Overturning Circulation (AMOC), which has long been held responsible for a rapid cooling at similar to 8.2 ka. However, recent modeling studies have argued that a large and sustained freshwater flux linked to increased surface melt and ensuing collapse of the Laurentide Ice Sheet (LIS) dam may have formed an efficient forcing for this cooling event. Yet, empirical (geological) evidence for a long-lasting meltwater flux is still equivocal while paleoceanographic data show that the freshening of the North Atlantic around the 8.2-ka cold event is characterized by multiple freshwater pulses. Part of this uncertainty arises from the lack of constraints on the structure (number) and timing of meltwater discharges involved in the drainage of LAO, which prevents a detailed assessment of the freshwater forcing mechanisms at work and their potential impact on AMOC-an important issue given the present-day increase in the melting of the cryosphere around the North Atlantic. Here, we review 597 C-14 ages from marine and continental sediment archives and use 296 of these C-14 ages along with LAO geomorphological and varve records to present an integrated framework constraining the timing of LAO meltwater outbursts across the final deglaciation interval. Results show that LAO drained through two distinct events: first subglacially at similar to 8.22 cal ka BP and then after the breakup of the ice dam at similar to 8.16 cal ka BP. These LAO meltwater discharges are coeval with two important freshwater pulses in North Atlantic sediment cores, with the largest meltwater outburst matching the onset of the 8.2 ka event in Greenland ice cores. These results suggest that, in a fast-changing ocean-climate system influenced by melting ice sheets like that of the late deglaciation, massive and short-lived freshwater injections can potentially have an impact on AMOC. (C) 2021 Elsevier Ltd. All rights reserved.

Fjords can transition from marine embayments to lacustrine waterbodies under glacio-isostatic change following their deglaciation. However, little is known on how a transition from fjord to lake is influenced by glacial dynamics and how it influences sedimentation in and around the basin. Here, we analyse swath bathymetry imagery and subbottom profiles pri in Lake Mékinac (southern Québec) as well as glacial landforms from LiDAR imagery around the lake to document the evolution of a fjord basin into a lacustrine body during the transition from the Late Pleistocene to the Holocene. These analyses helped refine local glacial history and show that the study area was probably under the up-ice reach of the St. Lawrence Ice Stream during full glacial conditions. The mapping of moraines in and around Lake Mékinac shows that deglaciation of the study area was marked by stabilization of the ice-margin during the Mars-Batiscan Event, which is traditionally correlated to the climate deterioration at the end of the Younger Dryas. The architecture of acoustic facies in the lake indicates a transition from glacial conditions (U1), to proglacial-paraglacial (U2) and to postglacial conditions (U3). The bottom of Lake Mékinac also contains multiple mass movement deposits related to progradation of the Du-Milieu River delta and probably to late-Holocene earthquakes. The acoustic architecture of sediments within the lake indicates that the sedimentation regime was most dependant on the sediment input regime and that the transition from fjord to lake did not significantly influence sedimentation during deglaciation of the watershed. Further work on dating the mass movement deposits that characterise the sediment architecture should provide a better assessment of natural hazard associated with seismological events.

Three sediment cores recovered on the lower slope of the continental shelf in western Baffin Bay (Arctic Canada) as well as swath bathymetry and subbottom profiler data collected on the shelf and slope of the region were analysed to investigate whether the Laurentide Ice Sheet (LIS) reached the shelf edge offshore Home Bay during the Last Glacial Maximum (LGM). Physical, sedimentological and palaeomagnetic analyses of the cores were also used to constrain the chronostratigraphy of upper sedimentary facies of the Home Bay trough-mouth fan (TMF). Seven lithofacies were identified in the cores and reveal that the sediments recorded a genuine geomagnetic signal and that the cores span the last 40 ka. In the Home Bay Trough, sets of elongated ridges are discernible on swath bathymetry imagery and are interpreted as mega-scale glacial lineations (MSGLs) resulting from an ice stream eroding the trough and delivering glacigenic sediments to the TMF. The geomorphology of the TMF, combined with the sedimentary records and the chronostratigraphy, indicates that a series of debris flows and turbidity currents were generated between 35 and 15 ka BP. These results indicate that the LIS margin extended near the shelf edge during the LGM and allow us to propose a new maximum extent of the LIS during the Last Glacial episode.

The maximal extent and subsequent deglaciation of the Laurentide Ice Sheet (LIS) across eastern Baffin Island during the last glacial cycle (MIS-2) has been widely debated during the last decades as different palaeo-glaciological models have been proposed. Spatial and temporal variability of ice sheets extension during Quaternary glaciations complicate the establishment of a reliable reconstruction of the ice dynamics in the area. Furthermore, the lack of geophysical data in most of the fjords, and seaward, makes it difficult to reconcile the proposed terrestrial and marine glacial margins. High-resolution swath-bathymetric data, collected between 2003 and 2017, display a diversity of glacial bedforms in the Clyde Inlet fjord-cross-shelf-trough system (Eastern Baffin Island, Arctic Canada). These bedforms reveal a potential position of the LIS margin during the Last Glacial Maximum (LGM) near the shelf break. Early deglaciation of the Clyde Trough was marked by an initial break up of the ice sheet. This rapid retreat of the ice margin was punctuated by episodic stabilizations forming GZWs. This retreat was followed by a readvance and subsequent slow retreat of the LIS, as indicated by the presence of recessional moraines. Long-term stabilizations within the trough possibly coincided with major climatic cooling episodes, such as the end of Heinrich event 1 (H1) and the Younger Dryas. However, these stabilizations appear to have been influenced by topography, as GZWs can be found at pinning points in the trough. Deglaciation of the fjord occurred during the early Holocene and was faster, probably due to increased water depths. The presence of multiple moraine systems however indicate that deglaciation of Clyde Inlet was marked by stages of ice margin stabilization.

The Lake Saint-Jean lowland is a particular area in eastern Canada as it constitutes an important Late Quaternary depocenter compared with other surrounding onshore regions. Here, the recent literature about the Late Quaternary history of the Lake Saint-Jean depocenter from the glaciated period to present-day is summarized; subsequently, we present some preserved landscape features that record such history.