Chronologic and geomorphic evidence of past glaciations is largely recorded in areas at relatively low elevation and/or landscapes defined by high glacial erosion. As a result, data from areas that did not experience significant glacial erosion and the highest elevation locations are lacking from reconstructions of past ice masses. Here, we use paired Be-10 and C-14 exposure dating on quartz derived from glacial erratics and bedrock to resolve past ice mass fluctuations across an elevation and geomorphic gradient in the Cairngorm Mountains of Scotland. We find that the highest elevation samples in our dataset, at 1140 m above sea level, yield Be-10 ages indicating 23 000 years of exposure and are at secular equilibrium for C-14, indicative of a single period of exposure starting as a nunatak during the Last Glacial Maximum. Other samples from above 1000 m elevation produce C-14 exposure ages indicating deglaciation during the Bolling-Allerod Interstadial, while Be-10 concentrations display varying levels of inheritance due to local variations in glacial and non-glacial erosion. Samples from lower elevations indicate a Lateglacial moraine building event 15 000 years ago, coincident with the Wester Ross readvance, followed by a period of glacier retreat interrupted by moraine deposition at similar to 14 000 and similar to 11 000 years ago. This dataset reconstructs both thinning and marginal recession of paleo-ice masses within the Cairngorm Mountains across a >600 m vertical gradient during the most recent glacial-interglacial transition, demonstrating the utility of paired Be-10/C-14 exposure dating in ice mass reconstructions in areas of low glacial erosion, increasing the geomorphic diversity of chronologic data available for glacial reconstructions. (c) 2025 The Authors Journal of Quaternary Science Published by John Wiley & Sons Ltd.

Most extant ice caps mantling low-relief Arctic Canada landscapes remained cold based throughout the late Holocene, preserving in situ bryophytes killed as ice expanded across vegetated landscapes. After reaching peak late Holocene dimensions ∼1900 CE, ice caps receded as Arctic summers warmed, exposing entombed vegetation. The calibrated radiocarbon ages of entombed moss collected near ice cap margins (kill dates) define when ice advanced across the site, killing the moss, and remained over the site until the year of their collection. In an earlier study, we reported 94 last millennium radiocarbon dates on in situ dead moss collected at ice cap margins across Baffin Island, Arctic Canada. Tight clustering of those ages indicated an abrupt onset of the Little Ice Age at ∼1240 CE and further expansion at ∼1480 CE coincident with episodes of major explosive volcanism. Here we test the confidence in kill dates as reliable predictors of expanding ice caps by resampling two previously densely sampled ice complexes ∼15 years later after ∼250 m of ice recession. The probability density functions (PDFs) of the more recent series of ages match PDFs of the earlier series but with a larger fraction of early Common Era ages. Post 2005 CE ice recession has exposed relict ice caps that grew during earlier Common Era advances and were preserved beneath later ice cap growth. We compare the 106 kill dates from the two ice complexes with 80 kill dates from 62 other ice caps within 250 km of the two densely sampled ice complexes. The PDFs of kill dates from the 62 other ice caps cluster in the same time windows as those from the two ice complexes alone, with the PDF of all 186 kill dates documenting episodes of widespread ice expansion restricted almost exclusively to 250–450 CE, 850–1000 CE, and a dense early Little Ice Age cluster with peaks at ∼1240 and ∼1480 CE. Ice continued to expand after 1480 CE, reaching maximum dimensions at ∼1880 CE that are still visible as zones of sparse vegetation cover in remotely sensed imagery. Intervals of widespread ice cap expansion coincide with persistent decreases in mean summer surface air temperature for the region in a Community Earth System Model (CESM) fully coupled Common Era simulation, suggesting the primary forcings of the observed snowline lowering were both modest declines in summer insolation and cooling resulting from explosive volcanism, most likely intensified by positive feedbacks from increased snow cover and sea ice and reduced northward heat transport by the oceans. The clusters of ice cap expansion defined by moss kill dates are mirrored in an annually resolved Common Era record of ice cap dimensions in Iceland, suggesting this is a circum-North-Atlantic–Arctic climate signal for the Common Era. During the coldest century of the Common Era, 1780–1880 CE, ice caps mantled >11 000 km2 of north-central Baffin Island, whereas <100 km2 is glaciated at present. The peak Little Ice Age state approached conditions expected during the inception phase of an ice age and was only reversed after 1880 CE by anthropogenic alterations of the planetary energy balance.

We have developed a method for measuring radiocarbon in carbonate minerals as CO2 gas via a NEC MCSNICS hybrid sputter gas ion source (HGIS). The method uses helium as a carrier gas to displace CO2 from sample vials to an open split, where a glass capillary samples the mixture for delivery directly to the HGIS. This method skips the gas transfer and quantification steps used in a closed inlet HGIS system, simplifying sample measurement. Samples larger than 8 mg carbonate can be measured. Results from measurements of consensus standards (TIRI I, IAEA C2, and an internal modern shell standard), and samples from a marine core (F14C = 0.4–1.15) show that the method agrees well with traditional AMS measurement of the same samples as graphite, and that the 1σ uncertainty is about 1%. We discuss advantages and disadvantages of continuous flow sample introduction, and the effect of reduced precision on calibrated age-depth models produced using gas-source data.

It has long been hypothesized that periodic meltwater input from a retreating Laurentide Ice Sheet (LIS) inhibited North Atlantic deep water (NADW) formation, weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC), and triggered several cold periods in the North Atlantic region during the last deglaciation (21-8ka yrs BP). Since the establishment of this hypothesis more than thirty years ago, geomorphic and chronologic evidence of meltwater flows from the LIS have been shown to roughly coincide with centennial-to-millennial scale cool periods (e.g., Younger Dryas, the 8.2 ka event). Here, we use realizations of the MITgcm ocean model to investigate the possibility that meltwater discharge from the Hudson River, New York City, USA ~13,300 yrs BP triggered the Inter-Allerød Cold Period (IACP). Using estimates of flood volumes, we assess the sensitivity of AMOC to both short duration (1 month), and long duration (1 year) flood events. We also evaluate the impact of successive flood events on AMOC to determine if sequential floods impact AMOC differently than a single flood event. Finally, we also assess whether the continuous background flux of meltwater from the paleo-Hudson River played role in ‘pre-conditioning’ the AMOC to weaken in response to short duration outburst floods. We find that in all of our experiments, regardless of flood magnitude, duration, reoccurrence interval (frequency) or background meltwater flux, there is no significant weakening of the AMOC. This limited impact suggests that although the Hudson Valley floods occurred near the beginning of the IACP, they are unlikely the sole driver. Additional modeling experiments are needed to determine if the combination of multiple drainage pathways from the LIS could have been a trigger and/or contributor to the IACP. Our results have significant implications for determining whether other isolated deglacial flood events triggered periods of climatic cooling: for example, the millennial-length Younger Dryas cooling is thought to have been triggered by a flood only 3-times larger than the one from the Hudson River, which again questions the role short-lived outburst floods played in triggering centennial to millennial scale climate cooling.

Beryllium-10 has become the premiere cosmogenic nuclide for quantifying Earth-surface process. Routine measurement of 10Be at the ≤ 2–3% precision level, coupled with precise 10Be production-rate calibrations, now allow for 10Be-based records of glacier and ice-sheet change to be reliably compared to independent records of climate variability. Here, we review efforts over the last 10+ years to characterize the Holocene behavior of ice sheets and glaciers fringing Baffin Bay using in situ 10Be. Hundreds of 10Be measurements present a detailed picture of ice-margin migration through the early Holocene. Widespread net deglaciation was interrupted by ice-margin readvances or stillstands, marked by modes of moraine deposition, near the end of the Younger Dryas (12.9–11.7 ka BP), 10.4–10.2 ka BP, 9.3 ka BP, and 8.2 ka BP, with perhaps additional widespread moraine deposition occurring ca. 9.7 ka BP and 7.3 ka BP. Modes of moraine deposition encompass independent and glaciologically distinct ice masses – the Greenland and Laurentide ice sheets and local alpine glaciers situated on Baffin Island and western Greenland – providing a robust, albeit discontinuous, record of widespread climatic changes in the Baffin Bay region in the early Holocene. Periods of glacier advance coincide with abrupt cooling events documented in Summit Greenland ice cores indicating that i) Baffin Bay ice masses largely followed the pattern of temperature change displayed in Greenland ice cores, ii) abrupt cooling events were of sufficient magnitude and duration to briefly synchronize the behavior of independent and glaciologically distinct ice masses across Baffin Bay despite varying degrees of dynamical influence, and iii) centennial-scale synchronization of ice masses requires that abrupt temperature changes recorded at Summit Greenland also occurred during the summertime within glacier ablation zones. Advancements in 10Be methodology combined with an environment conducive towards developing 10Be-based records of ice-margin change has resulted in ice-margin reconstructions that identify a potentially fundamental negative feedback mechanism inherent to melting ice sheets in the Baffin Bay region – elevated and episodic meltwater delivery into the Labrador Sea results in a decrease in the Atlantic meridional overturning circulation and regional cooling, which, in turn, drives a brief reversal of deglaciation. Under the right conditions 10Be can be used to develop centennial-scale, climatically relevant records of glacier and ice-sheet change.

The periodic input of meltwater into the ocean from a retreating Laurentide Ice Sheet is often hypothesized to have weakened the Atlantic meridional overturning circulation (AMOC) and triggered several cold periods during the last deglaciation (21,000 to 8,000 years before present). Here, we use a numerical model to investigate whether the Intra-Allerød Cold Period was triggered by the drainage of Glacial Lake Iroquois, ~13,300 years ago. Performing a large suite of experiments with various combinations of single and successive, short (1 month) and long (1 year) duration flood events, we were unable to find any significant weakening of the AMOC. This result suggests that although the Hudson Valley floods occurred close to the beginning of the Intra-Allerød Cold Period, they were unlikely the sole cause. Our results have implications for re-evaluating the relationship of meltwater flood events (past and future) to periods of climatic cooling, particularly with regards to flood input location, volume, frequency, and duration.

This Review quantitatively and qualitatively describes 10 representative Baffin Island fjords chosen to explore the nature of a glaciation in delivering sediment to a fjord, with focus on deglacial (within 13–6.7 kyr BP) and postglacial conditions (within 8.2–0 kyr BP). Fjords are compared using observed sediment thicknesses (49–175 m, averaged) and volumes (0.7–14.6 km3), and modeled sediment yields: (1) deglacial 140–1060 t/m2/yr; (2) paraglacial 45–350 t/m2/yr; (3) neoglacial 30–150 t/m2/yr; (4) Little Ice Age 70–440 t/m2/yr; and (5) Anthropocene 60–290 t/m2/yr. Modeled sediment loads, when converted to deposit volumes, compare favorably to observations from geophysical surveys and terrestrial mapping, or separately to sediment accumulation rates (SAR) determined from marine sediment cores. Fjord-averaged SAR during deglaciation range from 4.6 to 25 mm/yr, and 0.6–3.1 mm/yr for the postglacial interval. Fjords directly impacted by the Laurentide Ice Sheet (central and northern Baffin Island) are 2–3 times larger in dimensions than southern Baffin Island fjords, with ∼4.5x deglacial and ∼5x postglacial larger deposits, including well-defined ice-proximal outwash deposits. To the south, Penny Ice Cap associated fjords with no withholding sills, lose 30–40% of their incoming fjord sediment to Broughton Trough that dissects the continental shelf. Sunneshine is the only sampled fjord that was neither directly nor indirectly impacted by the Wisconsin continental ice sheet; Sunneshine responded instead to local maritime conditions and an alpine glaciation.

The North Atlantic was a key locus for circulation-driven abrupt climate change in the past and could play a similar role in the future. Abrupt cold reversals, including the 8.2 ka event, punctuated the otherwise warm early Holocene in the North Atlantic region and serve as useful paleo examples of rapid climate change. In this work, we assess the cryospheric response to early Holocene climate history on Baffin Island, Arctic Canada, using cosmogenic radionuclide dating of moraines. We present 39 new 10Be ages from four sets of multi-crested early Holocene moraines deposited by cirque glaciers and ice cap outlet glaciers, as well as erratic boulders along adjacent fiords to constrain the timing of regional deglaciation. The age of one moraine is additionally constrained by in situ 14C measurements, which confirm 10Be inheritance in some samples. All four moraines were deposited between ∼9.2 and 8.0 ka, and their average ages coincide with abrupt coolings at 9.3 and 8.2 ka that are recorded in Greenland ice cores. Freshwater delivery to the North Atlantic that reduced the flux of warm Atlantic water into Baffin Bay may explain brief intervals of glacier advance, although moraine formation cannot be definitively tied to centennial-scale cold reversals. We thus explore other possible contributing factors, including ice dynamics related to retreat of Laurentide Ice Sheet outlet glaciers. Using a numerical glacier model, we show that the debuttressing effect of trunk valley deglaciation may have contributed to these moraine-building events. These new age constraints and process insights highlight the complex behavior of the cryosphere during regional deglaciation and suggest that multiple abrupt cold reversals—as well as deglacial ice dynamics—likely played a role in early Holocene moraine formation on Baffin Island.

Arctic temperatures are increasing faster than the Northern Hemisphere average due to strong positive feedbacks unique to polar regions. However, the degree to which recent Arctic warming is unprecedented remains debated. Ages of entombed plants in growth position preserved by now receding ice caps in Arctic Canada help to address this issue by placing recent conditions in a multi-millennial context. Here we show that pre-Holocene radiocarbon dates on plants collected at the margins of 30 ice caps in Arctic Canada suggest those locations were continuously ice covered for > 40 kyr, but are now ice-free. We use in situ 14 C inventories in rocks from nine locations to explore the possibility of brief exposure during the warm early Holocene. Modeling the evolution of in situ 14 C confirms that Holocene exposure is unlikely at all but one of the sites. Viewed in the context of temperature records from Greenland ice cores, our results suggest that summer warmth of the past century exceeds now any century in ~115,000 years.

Holocene paleotemperature reconstructions across the western Arctic suggest strong spatial variations in air temperature despite zonally uniform Northern Hemisphere insolation forcing. Although most paleotemperature reconstructions across the Eastern Canadian Arctic place the Holocene thermal maximum >3 kyr after peak summer insolation, other records indicate maximum summer warmth was coincident with peak summer insolation. To address this discrepancy, we use radiocarbon inventories in plants and rocks recently exposed by receding ice caps to reconstruct early Holocene changes in glacier dimensions, a reliable proxy for summer air temperature. Fourteen radiocarbon ages from newly exposed plants in growth position collected at the margins of eight retreating ice caps on Baffin Island indicate ice caps expanded 9.3 +/- 0.3 ka, and remained over these sites until recent summer warming, indicating peak early Holocene summer warmth occurred prior to similar to 9.3 ka. We test this conclusion using in situ cosmogenic C-14 (in situ C-14) inventories in rocks at four sites with dated plants. In situ C-14 production simulations using realistic Holocene ice-cover histories constrained by plant C-14 ages show that measured in situ C-14 concentrations are consistent with centuries to millennia of pre-93 ka exposure, followed by continuous ice burial. The combination of plant and in situ C-14 data provide firm evidence that the Eastern Canadian Arctic experienced peak Holocene summer warmth prior to similar to 9.3 ka, consistent with peak summer insolation, followed by continuously colder summers until modern warming. (C) 2019 Elsevier Ltd. All rights reserved.

Understanding patterns of ice-sheet deglaciation is key for predicting the rate of future ice-sheet melt, yet the processes underlying deglaciation remain elusive. The early Holocene (11.7 ka to 8.2 ka; Greenlandian Stage) represents the most recent period when the Laurentide and Greenland ice sheets underwent large-scale recession. Moreover, this ice-sheet recession occurred under the backdrop of regional temperatures that were similar to or warmer than today, and comparable to those projected for the upcoming centuries. Reconstructing Laurentide and Greenland ice sheet behavior during the early Holocene, and elucidating the mechanisms dictating this behavior may serve as a partial analog for future Greenland ice-sheet change in a warming world. Here, we present 123 new 10Be surface exposure ages from two sites on Baffin Island and southwestern Greenland that constrain the behavior of the Laurentide and Greenland ice sheets, and an independent alpine glacier during the early Holocene. On Baffin Island, we focus on a unique area where moraines deposited by the Laurentide Ice Sheet rest directly adjacent to moraines deposited by an independent alpine glacier. Sixty-one 10Be ages reveal that advances and/or stillstands of the Laurentide Ice Sheet and an alpine glacier occurred in unison around 11.8 ka, 10.3 ka, and 9.2 ka. Sixty-two 10Be ages from southwestern Greenland indicate that the Greenland Ice Sheet margin experienced re-advances or stillstands around 11.6 ka, 10.4 ka, 9.1 ka, 8.1 ka, and 7.3 ka. Our results reveal that ice sheets respond to climate perturbations on the same centennial timescale as small alpine glaciers. We hypothesize that during the warming climate of the early Holocene, freshening of the North Atlantic Ocean induced by ice-sheet melt resulted in regional cooling and brief periods of ice-sheet stabilization superimposed on net glacier recession. These observations point to a negative feedback mechanism inherent to melting ice sheets in the Baffin Bay region that slows ice-sheet recession during intervals of otherwise rapid deglaciation.