Improved reconstruction of the southeastern Laurentide Ice Sheet deglaciation: constraining ice thinning using in-situ cosmogenic 10Be and 14C and critically evaluating different retreat rate chronometers

2020 ◽  
Author(s):  
Christopher Halsted ◽  
Jeremy Shakun ◽  
Lee Corbett ◽  
Paul Bierman ◽  
P. Thompson Davis ◽  
...  
Keyword(s):  
United States ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Ice Thickness ◽  
Northeastern United States ◽  
Terminal Moraine ◽  
Ice Volume ◽  
Ice Retreat ◽  
Exposure Ages

<p>In the northeastern United States, there are extensive geochronologic and geomorphic constraints on the deglaciation of the southeastern Laurentide Ice Sheet; thus, it is an ideal area for large-scale ice volume reconstructions and comparison between different ice retreat chronometers. Varve chronologies, lake and bog-bottom radiocarbon ages, and cosmogenic nuclide exposure ages constrain the timing of ice retreat, but the inferred ages exhibit considerable noise and sometimes disagree. Additionally, there are few empirical constraints on ice thinning, forcing ice volume reconstructions to rely on geophysically-based ice thickness models. Here, we aim to improve the understanding of the southeastern Laurentide Ice Sheet recession by (1) adding extensive ice thickness constraints and (2) compiling all available deglacial chronology data in the region to investigate discrepancies between different chronometers.</p><p>To provide insight about ice sheet thinning history, we collected 120 samples for in-situ <sup>10</sup>Be and 10 samples for in-situ <sup>14</sup>C cosmogenic exposure dating from various elevations at 13 mountains in the northeastern United States. By calculating ages of exposure at different elevations across this region, we reconstruct paleo-ice surface lowering of the southeastern Laurentide Ice Sheet during deglaciation. Where we suspect that <sup>10</sup>Be remains from pre-Last Glacial Maximum periods of exposure, in-situ <sup>14</sup>C is used to infer the erosional history and minimum exposure age of samples.</p><p>Presently, we have measured <sup>10</sup>Be in 73 samples. Mountain-top exposure ages located within 150 km of the southeastern Laurentide Ice Sheet terminal moraine indicate that near-margin thinning began early in the deglacial period (~19.5 to 17.5 ka), coincident with the slow initial margin retreat indicated by varve records. Exposure ages from several mountains further inland (>400 km north of terminal moraine) collected over ~1000 m of elevation range record rapid ice thinning between 14.5 and 13 ka. Ages within each of these vertical transects are similar within 1σ internal uncertainty, indicating that ice thinned quickly, less than a few hundred years at most. This rapid thinning occurred at about the same time that varve records indicate accelerated ice margin retreat (14.6–12.9 ka), providing evidence of substantial ice volume loss during the Bølling-Allerød warm period.</p><p>Our critical evaluation of deglacial chronometers, including valley-bottom <sup>10</sup>Be ages from this project, is intended to constrain ice margin retreat rates and timing in the region. Ultimately, we will integrate our ice thickness over time constraints with the existing network of deglacial ages to create a probabilistic reconstructions of the southeastern Laurentide Ice Sheet volume during its recession through the northeastern United States.</p>

Cosmogenic nuclide age estimate for Laurentide Ice Sheet recession from the terminal moraine, New Jersey, USA, and constraints on latest Pleistocene ice sheet history

2017 ◽  
Vol 87 (3) ◽  
pp. 482-498 ◽  
Author(s):  
Lee B. Corbett ◽  
Paul R. Bierman ◽  
Byron D. Stone ◽  
Marc W. Caffee ◽  
Patrick L. Larsen
Keyword(s):  
New Jersey ◽  
Global Climate ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Data Set ◽  
Terminal Moraine ◽  
Cosmogenic Nuclide ◽  
Fluvial Incision ◽  
Exposure Ages

AbstractThe time at which the Laurentide Ice Sheet reached its maximum extent and subsequently retreated from its terminal moraine in New Jersey has been constrained by bracketing radiocarbon ages on preglacial and postglacial sediments. Here, we present measurements of in situ produced 10Be and 26Al in 16 quartz-bearing samples collected from bedrock outcrops and glacial erratics just north of the terminal moraine in north-central New Jersey; as such, our ages represent a minimum limit on the timing of ice recession from the moraine. The data set includes field and laboratory replicates, as well as replication of the entire data set five years after initial measurement. We find that recession of the Laurentide Ice Sheet from the terminal moraine in New Jersey began before 25.2±2.1 ka (10Be, n=16, average, 1 standard deviation). This cosmogenic nuclide exposure age is consistent with existing limiting radiocarbon ages in the study area and cosmogenic nuclide exposure ages from the terminal moraine on Martha’s Vineyard ~300 km to the northeast. The age we propose for Laurentide Ice Sheet retreat from the New Jersey terminal position is broadly consistent with regional and global climate records of the last glacial maximum termination and records of fluvial incision.

The recession of the Laurentide Ice Sheet in southeast Northwest Territories during the Pleistocene-Holocene transition

2020 ◽  
Author(s):  
Samuel E. Kelley ◽  
Brent Ward ◽  
Jason Briner ◽  
Martin Ross ◽  
Philippe Normandeau ◽  
...  
Keyword(s):  
Northwest Territories ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Lake ◽  
Lake Basin ◽  
Great Slave Lake ◽  
Northwestern Margin ◽  
Ice Retreat ◽  
Oriented Parallel ◽  
Exposure Ages

<p>The Laurentide Ice Sheet (LIS) during the Pleistocene-Holocene transition provides a useful natural laboratory for examining the behavior of a mid- to high-latitude ice sheet during a period of climatically driven ice sheet thinning and retreat. While the timing and pattern of Pleistocene recession of the LIS are well-constrained along the southern and eastern margins, there is limited chronology constraining the ice margin retreat along the northwestern margin. Here we present new cosmogenic <sup>10</sup>Be exposure ages retreat of the western margin of the LIS during the Pleistocene-Holocene transition. Sampling was performed along three transects located between the northern shore of Great Slave Lake and Lac de Gras. Each of the transects is oriented parallel to the inferred ice retreat direction in an attempt to capture a regional rate of retreat. Our new <sup>10</sup>Be cosmogenic exposure ages from the southeastern Northwest Territories demonstrate that regional deglaciation occurred around 11,000 years ago. The population of ages broadly overlaps, indicating that either the retreat occurred within the resolution of our chronology or that the ice sheet experienced widespread stagnation and rapid down-wasting. These ages, not corrected for changes in atmospheric depth due to isostatic rebound, are older than minimum limiting radiocarbon constraints by ~1000 years, indicating that existing LIS reconstructions may underestimate the timing and pace of ice margin recession for this sector. Constraining the timing of the recession of the northwest sector of the LIS has the potential to inform our understanding about the damming of large proglacial lakes, such as Glacial Lake McConnell. The ages from our southern transect, collected from elevated bedrock hills, indicate LIS retreat from through the McConnell basin occurred after 12,000 years ago, and thus constitute maximum limiting constraints on the expansion of Glacial Lake McConnell southeastward into the present-day Great Slave Lake basin. Our chronology, combined with other emerging cosmogenic exposure ages constraining LIS deglaciation indicates retreat of the ice margin over 100s of kilometres during the Pleistocene-Holocene transition, exhibiting no evidence of a significant readvance during the Younger Dryas stadial.</p>

DETERMINING THE TIMING AND RATE OF SOUTHEASTERN LAURENTIDE ICE SHEET THINNING USING IN-SITU 10BE DIPSTICKS

2018 ◽  
Author(s):  
Christopher T. Halsted ◽  
◽  
Jeremy D. Shakun ◽  
Lee B. Corbett ◽  
Paul R. Bierman ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Laurentide Ice Sheet

scholarly journals Measuring and inferring the ice thickness distribution of four glaciers in the Tien Shan, Kyrgyzstan

2020 ◽  
pp. 1-18
Author(s):  
Lander Van Tricht ◽  
Philippe Huybrechts ◽  
Jonas Van Breedam ◽  
Johannes J. Fürst ◽  
Oleg Rybak ◽  
...  
Keyword(s):  
Cross Validation ◽  
Thickness Distribution ◽  
Tien Shan ◽  
Ice Thickness ◽  
Ice Volume ◽  
In Situ Data ◽  
Radio Echo Sounding ◽  
Thickness Measurements ◽  
Tien Shan Mountains

Abstract Glaciers in the Tien Shan mountains contribute considerably to the fresh water used for irrigation, households and energy supply in the dry lowland areas of Kyrgyzstan and its neighbouring countries. To date, reconstructions of the current ice volume and ice thickness distribution remain scarce, and accurate data are largely lacking at the local scale. Here, we present a detailed ice thickness distribution of Ashu-Tor, Bordu, Golubin and Kara-Batkak glaciers derived from radio-echo sounding measurements and modelling. All the ice thickness measurements are used to calibrate three individual models to estimate the ice thickness in inaccessible areas. A cross-validation between modelled and measured ice thickness for a subset of the data is performed to attribute a weight to every model and to assemble a final composite ice thickness distribution for every glacier. Results reveal the thickest ice on Ashu-Tor glacier with values up to 201 ± 12 m. The ice thickness measurements and distributions are also compared with estimates composed without the use of in situ data. These estimates approach the total ice volume well, but local ice thicknesses vary substantially.

In situ 10Be exposure ages from southeastern Norway: implications for the geometry of the Weichselian Scandinavian ice sheet

2006 ◽  
Vol 25 (9-10) ◽  
pp. 1097-1109 ◽  
Author(s):  
Henriette Linge ◽  
Edward J. Brook ◽  
Atle Nesje ◽  
Grant M. Raisbeck ◽  
Françoise Yiou ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Scandinavian Ice Sheet ◽  
Exposure Ages

scholarly journals Late Pleistocene glacial chronologies and paleoclimate in the northern Rocky Mountains

2021 ◽  
Author(s):  
Brendon Quirk ◽  
Elizabeth Huss ◽  
Benjamin Laabs ◽  
Eric Leonard ◽  
Joseph Licciardi ◽  
...  
Keyword(s):  
Rocky Mountains ◽  
Ice Sheet ◽  
Northern Rocky Mountains ◽  
Mountain Ranges ◽  
Mountain Glaciers ◽  
Continental Divide ◽  
Ice Retreat ◽  
Geologic Record ◽  
Glacier Modeling ◽  
Exposure Ages

Abstract. The geologic record of mountain glaciations is a robust indicator of terrestrial paleoclimate change. During the last glaciation, mountain ranges across the western U.S. hosted glaciers while the Cordilleran and Laurentide ice sheets flowed to the west and east of the continental divide, respectively. Records detailing the chronologies and paleoclimate significance of these ice advances have been developed for many sites across North America. However, relatively few glacial records have been developed for mountain glaciers in the northern Rocky Mountains near ice sheet margins. Here, we report cosmogenic beryllium-10 surface exposure ages and numerical glacier modeling results showing that mountain glaciers in the northern Rockies abandoned terminal moraines after the end of the Last Glacial Maximum around 17–18 ka and could have been sustained by −10 to −8.5 °C temperature depressions relative to modern assuming similar or drier than modern precipitation. Additionally, we present a deglacial chronology from the northern Rocky Mountains that indicates while there is considerable variability in initial moraine abandonment ages across the Rocky Mountains, the pace of subsequent ice retreat through the Lateglacial exhibits some regional coherence. Our results provide insight on potential regional mechanisms driving the initiation of and sustained deglaciation in the western U.S. including rising atmospheric CO2 and ice sheet collapse.

scholarly journals New Last Glacial Maximum ice thickness constraints for the Weddell Sea Embayment, Antarctica

2019 ◽  
Vol 13 (11) ◽  
pp. 2935-2951 ◽  
Author(s):  
Keir A. Nichols ◽  
Brent M. Goehring ◽  
Greg Balco ◽  
Joanne S. Johnson ◽  
Andrew S. Hein ◽  
...  
Keyword(s):  
Sea Level ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Weddell Sea ◽  
Ice Thickness ◽  
Last Glacial ◽  
Cosmogenic Nuclide ◽  
Ice Stream ◽  
Exposure Ages

Abstract. We describe new Last Glacial Maximum (LGM) ice thickness constraints for three locations spanning the Weddell Sea Embayment (WSE) of Antarctica. Samples collected from the Shackleton Range, Pensacola Mountains, and the Lassiter Coast constrain the LGM thickness of the Slessor Glacier, Foundation Ice Stream, and grounded ice proximal to the modern Ronne Ice Shelf edge on the Antarctic Peninsula, respectively. Previous attempts to reconstruct LGM-to-present ice thickness changes around the WSE used measurements of long-lived cosmogenic nuclides, primarily 10Be. An absence of post-LGM apparent exposure ages at many sites led to LGM thickness reconstructions that were spatially highly variable and inconsistent with flow line modelling. Estimates for the contribution of the ice sheet occupying the WSE at the LGM to global sea level since deglaciation vary by an order of magnitude, from 1.4 to 14.1 m of sea level equivalent. Here we use a short-lived cosmogenic nuclide, in situ-produced 14C, which is less susceptible to inheritance problems than 10Be and other long-lived nuclides. We use in situ 14C to evaluate the possibility that sites with no post-LGM exposure ages are biased by cosmogenic nuclide inheritance due to surface preservation by cold-based ice and non-deposition of LGM-aged drift. Our measurements show that the Slessor Glacier was between 310 and up to 655 m thicker than present at the LGM. The Foundation Ice Stream was at least 800 m thicker, and ice on the Lassiter Coast was at least 385 m thicker than present at the LGM. With evidence for LGM thickening at all of our study sites, our in situ 14C measurements indicate that the long-lived nuclide measurements of previous studies were influenced by cosmogenic nuclide inheritance. Our inferred LGM configuration, which is primarily based on minimum ice thickness constraints and thus does not constrain an upper limit, indicates a relatively modest contribution to sea level rise since the LGM of < 4.6 m, and possibly as little as < 1.5 m.

scholarly journals Evaluation of Daily Precipitation from the ERA5 Global Reanalysis against GHCN Observations in the Northeastern United States

Climate ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 148
Author(s):  
Caitlin C. Crossett ◽  
Alan K. Betts ◽  
Lesley-Ann L. Dupigny-Giroux ◽  
Arne Bomblies
Keyword(s):  
United States ◽  
Daily Precipitation ◽  
Atlantic Coast ◽  
Heavy Precipitation ◽  
Northeastern United States ◽  
Primary Input ◽  
Spatial Continuity ◽  
June July ◽  
Global Reanalysis

Precipitation is a primary input for hydrologic, agricultural, and engineering models, so making accurate estimates of it across the landscape is critically important. While the distribution of in-situ measurements of precipitation can lead to challenges in spatial interpolation, gridded precipitation information is designed to produce a full coverage product. In this study, we compare daily precipitation accumulations from the ERA5 Global Reanalysis (hereafter ERA5) and the US Global Historical Climate Network (hereafter GHCN) across the northeastern United States. We find that both the distance from the Atlantic Coast and elevation difference between ERA5 estimates and GHCN observations affect precipitation relationships between the two datasets. ERA5 has less precipitation along the coast than GHCN observations but more precipitation inland. Elevation differences between ERA5 and GHCN observations are positively correlated with precipitation differences. Isolated GHCN stations on mountain peaks, with elevations well above the ERA5 model grid elevation, have much higher precipitation. Summer months (June, July, and August) have slightly less precipitation in ERA5 than GHCN observations, perhaps due to the ERA5 convective parameterization scheme. The heavy precipitation accumulation above the 90th, 95th, and 99th percentile thresholds are very similar for ERA5 and the GHCN. We find that daily precipitation in the ERA5 dataset is comparable to GHCN observations in the northeastern United States and its gridded spatial continuity has advantages over in-situ point precipitation measurements for regional modeling applications.

Terminating the Last Interglacial: The Role of Ice Sheet–Climate Feedbacks in a GCM Asynchronously Coupled to an Ice Sheet Model

2011 ◽  
Vol 25 (6) ◽  
pp. 1871-1882 ◽  
Author(s):  
Adam R. Herrington ◽  
Christopher J. Poulsen
Keyword(s):  
Ice Sheet ◽  
Stationary Wave ◽  
Rapid Expansion ◽  
Laurentide Ice Sheet ◽  
Interglacial Period ◽  
Climate Feedbacks ◽  
Last Interglacial ◽  
Ice Volume ◽  
Ice Cap

Abstract Climatic deterioration in northeastern Canada following the last interglacial resulted in the formation and abrupt expansion of the Laurentide Ice Sheet. However, the physical mechanisms leading to rapid ice sheet expansion are not well understood. Here, the authors report on experiments using an ice sheet model asynchronously coupled to a GCM to investigate the role of ice sheet–climate feedbacks in terminating the last interglacial period. In agreement with simpler models, the experiments indicate that a specific type of ice–albedo feedback, the small ice cap instability, is the dominant process controlling rapid expansion of the Laurentide Ice Sheet. As ice elevations increase in northeastern Canada, a stationary wave forms and strengthens over the Laurentide Ice Sheet, which acts to hinder further expansion of the ice margin and reduce the effect of the small ice cap instability. The sensitivity of these feedbacks to ice topography results in a reduction in simulated ice volume when the communication interval between the GCM and ice sheet model is lengthened since this permits larger gains in ice elevation between GCM updates and biases the simulation toward a stronger stationary wave feedback. The shortest communication interval (500 yr) leads to a Laurentide ice volume of 6 × 106 km3 in 10 kyr, which is less than ice volume estimates based on the geological record but is a substantial improvement over previous GCM studies. The authors discuss potential improvements to the asynchronous coupling scheme that would more accurately resolve ice sheet–climate feedbacks, potentially leading to greater simulated ice volume.

scholarly journals New Last Glacial Maximum Ice Thickness constraints for the Weddell Sea sector, Antarctica

2019 ◽  
Author(s):  
Keir A. Nichols ◽  
Brent M. Goehring ◽  
Greg Balco ◽  
Joanne S. Johnson ◽  
Andrew A. Hein ◽  
...  
Keyword(s):  
Sea Level ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Weddell Sea ◽  
Ice Thickness ◽  
Last Glacial ◽  
Cosmogenic Nuclide ◽  
Global Sea Level ◽  
Exposure Ages

Abstract. This paper describes new Last Glacial Maximum (LGM) ice thickness constraints for three locations spanning the Weddell Sea Embayment (WSE) of Antarctica. Samples collected from the Shackleton Range, Pensacola Mountains, and the Lassiter Coast constrain the LGM thickness of the Slessor Glacier, Foundation Ice Stream, and grounded ice proximal to the modern Ronne Ice Shelf Edge on the Antarctic Peninsula, respectively. Previous attempts to reconstruct LGM-to-present ice thickness changes around the WSE used measurements of long-lived cosmogenic nuclides, primarily 10Be. An absence of post-LGM apparent exposure ages at many sites led to LGM thickness reconstructions that were spatially highly variable, and inconsistent with flowline modeling. Estimates for the contribution of the ice sheet occupying the WSE at the LGM to global sea level since deglaciation vary by an order of magnitude, from 1.4 to 14.1 m of sea level equivalent. Here we use a cosmogenic nuclide, in situ produced 14C, to evaluate the possibility that sites with no post-LGM exposure ages are biased by cosmogenic nuclide inheritance due to surface preservation by cold-based ice and nondeposition of LGM-aged drift. Our measurements show that the Slessor Glacier was between 310 and 650 m thicker than present at the LGM. The Foundation Ice Stream was at least 800 m thicker, and ice on the Lassiter Coast was at least 385 m thicker than present at the LGM. With evidence for LGM thickening at all of our study sites, our in situ 14C measurements indicate that the long-lived nuclide measurements of previous studies were influenced by cosmogenic nuclide inheritance. Our LGM thickness constraints point toward a modest contribution from the Weddell Sea Embayment to global sea-level since deglaciation, with an estimated range of 2.2 to 5.8 m.

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