During the last deglaciation, collapse of the saddle between the North American Cordilleran and Laurentide ice sheets led to rapid ice-sheet mass loss and separation, with meltwater discharge contributing to deglacial sea-level rise. We directly date ice-sheet separation at the end of the saddle collapse using 64 Be-10 exposure ages along an similar to 1200-km transect of the ice-sheet suture zone. Collapse began in the south by 15.4 +/- 0.4 ka and ended by 13.8 +/- 0.1 ka at similar to 56 degrees N. Ice-sheet model simulations consistent with the Be-10 ages find that the saddle collapse contributed 6.2-7.2 m to global mean sea-level rise from similar to 15.5 ka to similar to 14.0 ka, or approximately one third of global mean sea-level rise over this period. We determine 3.1-3.6 m of the saddle collapse meltwater was released during Meltwater Pulse 1A similar to 14.6-14.3 ka, constituting 20-40% of this meltwater pulse's volume. Because the separation of the Cordilleran and Laurentide ice sheets occurred over 1-2 millennia, the associated release of meltwater during the saddle collapse supplied a smaller contribution to the magnitude of Meltwater Pulse 1A than has been recently proposed.

Significance The Ice-Free Corridor (IFC) has long played a key role in hypotheses about the peopling of the Americas. Earlier assessments of its age suggested that the IFC was available for a Clovis-first migration, but subsequent developments now suggest a pre-Clovis occupation of the Americas that occurred before the opening of the IFC, thus supporting a Pacific coastal migration route instead. However, large uncertainties in existing ages from the IFC cannot preclude its availability as a route for the first migrations. Resolving this debate over migration route is important for addressing the questions of when and how the first Americans arrived. We report cosmogenic nuclide exposure ages that show that the final opening of the IFC occurred well after pre-Clovis occupation.

Predictive modeling of submerged archaeological sites requires accurate sea-level predictions in order to reconstruct coastal paleogeography and associated geographic features that may have influenced the locations of occupation sites such as rivers and embayments. Earlier reconstructions of the paleogeography of parts of the western U.S. coast used an assumption of eustatic sea level, but this neglects the large spatial variations in relative sea level (RSL) associated with glacial isostatic adjustment (GIA) and tectonics. Subsequent work using a one-dimensional (1-D) solid Earth model showed that reconstructions that accounted for GIA result in significant differences from those based on eustatic sea level. However, these analyses neglected the complex three-dimensional (3-D) solid Earth structure associated with the Cascadia subduction zone that has also strongly influenced RSL along the Oregon-Washington (OR-WA) coast, requiring that the paleogeographic reconstructions must also account for this effect. Here we use RSL predictions from a 3-D solid Earth model that have been validated by RSL data to update previous paleogeographic reconstructions of the OR-WA coast for the last 12 kyr based on a 1-D solid Earth model. The large differences in the spatial variations in RSL on the OR-WA continental shelves predicted by the 3-D model relative to eustatic and 1-D models demonstrate that accurate reconstructions of coastal paleogeography for predictive modeling of submerged archaeological sites need to account for 3-D viscoelastic Earth structure in areas of complex tectonics.

Anthropogenic climate change during the 21st century presents a significant challenge to the protection of cultural resources (CRs) on federal lands that encompass ∼ 28% of the U.S. In particular, CRs on this land base may be adversely affected by a wide range of climate-change hazards, including damage by sea-level rise, enhanced deterioration by increasing temperature and precipitation, and destruction by more-frequent and severe wildfire. Most current measures to manage the impacts of hazards on CRs use vulnerability assessments, but because these require that all CRs be treated as having an equal chance of being affected by climate-change hazards (i.e., equal exposure) across large landscapes, the cost and resources required for such analyses are overwhelming to land management agencies. Projections of changes in many hazards, however, show that the probability of hazard occurrence will be unevenly distributed on the landscape. Incorporating this information into a risk assessment thus allows CR managers to prioritize their efforts on assessing impacts to CRs in those areas where the probability of the hazard is greatest, thus increasing efficiency. We provide several heuristic examples of implementing the first part of a CR risk assessment by using 21st-century projections of several hazards most likely to adversely affect CRs on nine National Forests (NFs) managed by the U.S. Forest Service in northern Idaho and Montana. Overlaying the projected distribution of hazards on these NFs with the distribution of CRs identifies CR exposure that, with information on their vulnerability, is required to determine risk. Additional policy and field studies will be needed to determine how to prioritize those CRs that are most at risk according to their significance as well as identify how impacts can be reduced and managed through adaptation planning and implementation. Adaptation will follow the iterative risk management process particularly by improving projection resolution. Finer scale, process-based modeling informed by the highest priority CRs would also provide a means to assess various adaptation options that might change the estimated risk and increase the odds of CRs being as little affected as possible.

Relative Sea Levels (RSLs) derived primarily from marine bivalves near Petermann Glacier, NW Greenland, constrain past regional ice-mass changes through glacial isostatic adjustment (GIA) modeling. Oxygen isotopes measured on bivalves corrected for shell-depth habitat and document changing melt-water input. Rapid RSL fall of up to 62 m/kyr indicates ice loss at or prior to-9 ka. Transition to an RSL stillstand starting at-6 ka reflects renewed ice-mass loading followed by further mass loss over the past few millennia. GIA simulations of rapid early RSL fall suggest a low regional upper-mantle viscosity. Early loss of grounded ice tracks atmospheric warming and pre-dates the eventual collapse of Petermann Glacier's floating ice tongue near-7 ka, suggesting grounding zone stabilization during early phases of deglaciation. We hypothesize mid-Holocene regrowth of regional ice caps in response to cooling and increased precipitation, following loss of the floating shelf ice. Remnants of these ice caps remain present but are now melting.(c) 2022 Published by Elsevier Ltd.

On 1 April 1999, Akimiski Island of the western James Bay region of northern Ontario, Canada, was included in the newly formed territory of Nunavut, Canada—an Inuit-dominated territory—even though the Inuit had never asserted Aboriginal title to the island. By contrast, the Omushkegowuk Cree of the western James Bay region have asserted Aboriginal title to Akimiski Island. The Government of Canada by their action (or inaction) has reversed the onus of responsibility for proof of Aboriginal title from the Inuit to the Cree. In other words, the Government of Canada did not follow their own guidelines and the common-law test for proof of Aboriginal title. In this paper, we documented and employed Cree oral history as well as a sea-level retrodiction (based on state-of-the-art numerical modeling of past sea-level changes in James Bay), which incorporated a modified ICE-6G ice history and a 3-D model of Earth structure, to establish that criterion 2 of the test for Aboriginal title has now been fully met. In other words, Cree traditional use and occupancy of Akimiski Island was considered sufficiently factual at the time of assertion of sovereignty by European nations. As all the criteria of the common-law test for proof of Aboriginal title in Canada, with respect to Akimiski Island, have now been addressed, the Cree have sufficient basis to initiate the process of a formal land claim.

During the last glacial maximum, the Cordilleran and Laurentide ice sheets met just to the east of the Canadian Rocky Mountains, forming an ice-sheet saddle. When this saddle disappeared has implications on deglacial global sea-level rise and abrupt climate change as well as human migration patterns to the Americas. We will present new 10-Be boulder ages from six sites on a ~1100 km transect along the ice-sheet suture zone, to date Cordilleran-Laurentide ice-sheet separation. Results will directly test whether or not Cordilleran-Laurentide separation contributed to abrupt sea-level rise during meltwater pulse 1a (14.6-14.3 ka) in response to abrupt Bølling warming (14.6-14.0 ka).

Records of post-glacial sea-level change in the Cascadia subduction zone (North American Pacific coast) analyzed using one-dimensional Earth models suggest upper mantle viscosities <similar to 10(20)Pa.s, significantly weaker than those based on observations from cratonic regions in North America. We explore this variability by comparing predictions based on a three-dimensional (3-D) model of the glacial isostatic adjustment process with relative sea-level histories from sites along the Oregon and Washington (USA) and Hudson Bay (northeastern Canada) coasts. We demonstrate that a 3-D mantle viscosity field, with a geometry constrained by seismic tomography and that reflects the tectonic setting of the Cascadia subduction zone, can simultaneously reconcile the rapid rate of late Holocene adjustment observed in central Cascadia and the longer decay times of post-glacial uplift curves in Hudson Bay. Specifically, below the Cascadia subduction zone, this field is characterized by a shallow subduction wedge of low viscosity (<similar to 10(20)Pa.s) and higher viscosity material associated with subduction of the Juan de Fuca plate.

During the late Pleistocene, multiple floods from drainage of glacial Lake Missoula further eroded a vast anastomosing network of bedrock channels, coulees, and cataracts, forming the Channeled Scabland of eastern Washington State (United States). However, the timing and exact pathways of these Missoula floods remain poorly constrained, thereby limiting our understanding of the evolution of this spectacular landscape. Here we report cosmogenic Be-10 ages that directly date flood and glacial features important to understanding the flood history, the evolution of the Channeled Scabland, and relationships to the Cordilleran Ice Sheet (CIS). One of the largest floods occurred at 18.2 +/- 1.5 ka, flowing down the northwestern Columbia River valley prior to blockage of this route by advance of the Okanogan lobe of the CIS, which dammed glacial Lake Columbia and diverted later Missoula floods to more eastern routes through the Channeled Scabland. The Okanogan and Purcell Trench lobes of the CIS began to retreat from their maximum extent at ca. 15.5 ka, likely in response to onset of surface warming of the northeastern Pacific Ocean. Upper Grand Coulee fully opened as a flood route after 15.6 +/- 1.3 ka, becoming the primary path for later Missoula floods until the last ones from glacial Lake Missoula at 14.7 +/- 1.2 ka. The youngest dated flood(s) (14.0 +/- 1.4 ka to 14.4 +/- 1.3 ka) came down the northwestern Columbia River valley and were likely from glacial Lake Columbia, indicating that the lake persisted for a few centuries after the last Missoula flood.

We report 80 Be-10 ages on 14 moraines from Irish cirques that show a previously unrecognized signal of at least eight millennialscale fluctuations between 24.5 +/- 0.7 ka and 11.0 +/- 0.3 ka. Several moraine ages may be correlative with abrupt warming at the onset of the Bolling-Allerod interval (14.7 ka) and the end of the Younger Dryas interval (11.7 ka), suggesting a forced response. Our ages also identify glacier fluctuations that occurred when regional temperatures were relatively stable. This finding is consistent with modeling results showing several hundred-meter-scale glacier fluctuations in response to interannual variability. At the same time, our composite record of cirque-glacier average equilibrium line altitudes (ELAs) shows a response to warming due to increasing greenhouse gases and summer insolation modulated by abrupt climate changes. Our new 10Be chronology thus records both forced and unforced millennialscale glacier fluctuations superimposed on a lower-frequency ELA signal of forced response to climate change.

Sea-level and ice-sheet databases have driven numerous advances in understanding the Earth system. We describe the challenges and offer best strategies that can be adopted to build self-consistent and standardised databases of geological and geochemical information used to archive palaeo-sea-levels and palaeo-ice-sheets. There are three phases in the development of a database: (i) measurement, (ii) interpretation, and (iii) database creation. Measurement should include the objective description of the position and age of a sample, description of associated geological features, and quantification of uncertainties Interpretation of the sample may have a subjective component, but it should always include uncertainties and alternative or contrasting interpretations, with any exclusion of existing interpretations requiring a full justification. During the creation of a database, an approach based on accessibility, transparency, trust, availability, continuity, completeness, and communication of content (ATTAC(3)) must be adopted. It is essential to consider the community that creates and benefits from a database. We conclude that funding agencies should not only consider the creation of original data in specific research question-oriented projects, but also include the possibility of using part of the funding for IT -related and database creation tasks, which are essential to guarantee accessibility and maintenance of the collected data.

Reconstructions of the extent and height of the Irish Ice Sheet (IIS) during the Last Glacial Maximum (LGM, similar to 19-26 ka) are widely debated, in large part due to limited age constraints on former ice margins and due to uncertainties in the origin of the trimlines. A key area is southwestern Ireland, where various LGM reconstructions range from complete coverage by a contiguous IIS that extends to the continental shelf edge to a separate, more restricted southern-sourced Kerry-Cork Ice Cap (KCIC). We present new Be-10 surface exposure ages from two moraines in a cirque basin in the Macgillycuddy's Reeks that provide a unique and unequivocal constraint on ice thickness for this region. Nine Be-10 ages from an outer moraine yield a mean age of 24.5 +/- 1.41 ka while six ages from an inner moraine yield a mean age of 20.4 +/- 1.2 ka. These ages show that the northern flanks of the Macgillycuddy's Reeks were not covered by the IIS or a KCIC since at least 24.5 +/- 1.4 ka. If there was more extensive ice coverage over the Macgillycuddy's Reeks during the LGM, it occurred prior to our oldest ages. (C) 2016 Elsevier Ltd. All rights reserved.

Sea-level rise during the last deglaciation and through the Holocene was influenced by deformational, gravitational, and rotational effects (henceforth glacial isostatic adjustment, GIA) that led to regional departures from eustasy. Deglacial sea-level rise was particularly variable spatially in areas adjacent to the Cordilleran and Laurentide Ice Sheets. Such regional variability in sea level due to GIA is important to identify when investigating potential coastal migration pathways used by early Americans. An improved understanding of regional sea-level rise may also be used for predictive modeling of potential archaeological sites that are now submerged. Here we compute relative sea-level change across the California–Oregon–Washington and Bering Sea continental shelves since the Last Glacial Maximum using an ice-age sea-level theory that accurately incorporates time-varying shoreline geometry. The corresponding non-uniform sea-level rise across these continental shelves reveals significant departures from eustasy, which has important implications for improved understanding of potential coastal migration routes and predictive modeling of the location of now-submerged archaeological sites.