Reconciling the Apparent Absence of a Last Glacial Maximum Alpine Glacial Advance, Yukon Territory, Canada, through Cosmogenic Beryllium-10 and Carbon-14 Measurements

Abstract. We present a new in situ produced cosmogenic beryllium-10 and carbon-14 nuclide chronology from two sets (outer and inner) of alpine glacier moraines from the Grey Hunter massif of southern Yukon Territory, Canada. The chronology potential of moraines deposited by alpine glaciers outside the limits of the Last Glacial Maximum (LGM) ice sheets potentially provide a less-ambiguous archive of mass balance, and hence climate than can be inferred from the extents of ice sheets themselves. Results for both nuclides are inconclusive for the outer moraines, with evidence for pre-LGM deposition (beryllium-10) and Holocene deposition (carbon-14). Beryllium-10 results from the inner moraine are suggestive of canonical LGM deposition, but with relatively high scatter. Conversely, in situ carbon-14 results from the inner moraines are tightly clustered and suggestive of terminal Younger Dryas deposition. We explore plausible scenarios leading to the observed differences between nuclides and find that the most parsimonious explanation for the outer moraines is that of pre-LGM deposition, but many of the sampled boulder surfaces were not exhumed from within the moraine until the Holocene. Our results thus imply that the inner and outer moraines sampled pre- and post-date the canonical LGM and that moraines dating to the LGM are lacking likely due to overriding by the subsequent Late Glacial/earliest Holocene advance.

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Supplementary material to "Reconciling the Apparent Absence of a Last Glacial Maximum Alpine Glacial Advance, Yukon Territory, Canada, through Cosmogenic Beryllium-10 and Carbon-14 Measurements"

10.5194/gchron-2021-43-supplement ◽

2021 ◽

Author(s):

Brent Goehring ◽

Brian Menounos ◽

Gerald Osbron ◽

Adam Hawkins ◽

Brent Ward

Keyword(s):

Last Glacial Maximum ◽

Yukon Territory ◽

Glacial Maximum ◽

Apparent Absence ◽

Last Glacial ◽

Carbon 14 ◽

Supplementary Material ◽

Glacial Advance

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PALEO-GLACIER EQUILIBRIUM LINE ALTITUDES FROM CENTRAL ALASKA: INSIGHTS INTO LAST GLACIAL MAXIMUM AND LATE GLACIAL CLIMATE

10.1130/abs/2020am-356805 ◽

2020 ◽

Author(s):

Caleb Walcott ◽

◽

Joseph P. Tulenko ◽

Jason P. Briner ◽

Nicolás E. Young

Keyword(s):

Last Glacial Maximum ◽

Late Glacial ◽

Glacial Maximum ◽

Equilibrium Line ◽

Last Glacial ◽

Glacial Climate

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Last Glacial Maximum and Holocene Climate in CCSM3

Journal of Climate ◽

10.1175/jcli3748.1 ◽

2006 ◽

Vol 19 (11) ◽

pp. 2526-2544 ◽

Cited By ~ 413

Author(s):

Bette L. Otto-Bliesner ◽

Esther C. Brady ◽

Gabriel Clauzet ◽

Robert Tomas ◽

Samuel Levis ◽

...

Keyword(s):

Last Glacial Maximum ◽

Ice Sheets ◽

Ocean Model ◽

Arctic Sea Ice ◽

Glacial Maximum ◽

Climate System Model ◽

Last Glacial ◽

Global Cooling ◽

Climate Forcings ◽

Continental Ice Sheets

Abstract The climate sensitivity of the Community Climate System Model version 3 (CCSM3) is studied for two past climate forcings, the Last Glacial Maximum (LGM) and the mid-Holocene. The LGM, approximately 21 000 yr ago, is a glacial period with large changes in the greenhouse gases, sea level, and ice sheets. The mid-Holocene, approximately 6000 yr ago, occurred during the current interglacial with primary changes in the seasonal solar irradiance. The LGM CCSM3 simulation has a global cooling of 4.5°C compared to preindustrial (PI) conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at LGM. Tropical sea surface temperature (SST) cools by 1.7°C and tropical land temperature cools by 2.6°C on average. Simulations with the CCSM3 slab ocean model suggest that about half of the global cooling is explained by the reduced LGM concentration of atmospheric CO2 (∼50% of present-day concentrations). There is an increase in the Antarctic Circumpolar Current and Antarctic Bottom Water formation, and with increased ocean stratification, somewhat weaker and much shallower North Atlantic Deep Water. The mid-Holocene CCSM3 simulation has a global, annual cooling of less than 0.1°C compared to the PI simulation. Much larger and significant changes occur regionally and seasonally, including a more intense northern African summer monsoon, reduced Arctic sea ice in all months, and weaker ENSO variability.

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Last Glacial Maximum (LGM) climate forcing and ocean dynamical feedback and their implications for estimating climate sensitivity

Climate of the Past ◽

10.5194/cp-17-253-2021 ◽

2021 ◽

Vol 17 (1) ◽

pp. 253-267

Author(s):

Jiang Zhu ◽

Christopher J. Poulsen

Keyword(s):

Last Glacial Maximum ◽

Ocean Circulation ◽

Climate Sensitivity ◽

Radiative Forcing ◽

Ice Sheets ◽

Glacial Maximum ◽

Ocean Dynamics ◽

Last Glacial ◽

True Value ◽

Climate Forcings

Abstract. Equilibrium climate sensitivity (ECS) has been directly estimated using reconstructions of past climates that are different than today's. A challenge to this approach is that temperature proxies integrate over the timescales of the fast feedback processes (e.g., changes in water vapor, snow, and clouds) that are captured in ECS as well as the slower feedback processes (e.g., changes in ice sheets and ocean circulation) that are not. A way around this issue is to treat the slow feedbacks as climate forcings and independently account for their impact on global temperature. Here we conduct a suite of Last Glacial Maximum (LGM) simulations using the Community Earth System Model version 1.2 (CESM1.2) to quantify the forcing and efficacy of land ice sheets (LISs) and greenhouse gases (GHGs) in order to estimate ECS. Our forcing and efficacy quantification adopts the effective radiative forcing (ERF) and adjustment framework and provides a complete accounting for the radiative, topographic, and dynamical impacts of LIS on surface temperatures. ERF and efficacy of LGM LIS are −3.2 W m−2 and 1.1, respectively. The larger-than-unity efficacy is caused by the temperature changes over land and the Northern Hemisphere subtropical oceans which are relatively larger than those in response to a doubling of atmospheric CO2. The subtropical sea-surface temperature (SST) response is linked to LIS-induced wind changes and feedbacks in ocean–atmosphere coupling and clouds. ERF and efficacy of LGM GHG are −2.8 W m−2 and 0.9, respectively. The lower efficacy is primarily attributed to a smaller cloud feedback at colder temperatures. Our simulations further demonstrate that the direct ECS calculation using the forcing, efficacy, and temperature response in CESM1.2 overestimates the true value in the model by approximately 25 % due to the neglect of slow ocean dynamical feedback. This is supported by the greater cooling (6.8 ∘C) in a fully coupled LGM simulation than that (5.3 ∘C) in a slab ocean model simulation with ocean dynamics disabled. The majority (67 %) of the ocean dynamical feedback is attributed to dynamical changes in the Southern Ocean, where interactions between upper-ocean stratification, heat transport, and sea-ice cover are found to amplify the LGM cooling. Our study demonstrates the value of climate models in the quantification of climate forcings and the ocean dynamical feedback, which is necessary for an accurate direct ECS estimation.

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Exploring the complex uncertainties in coupled climate-ice simulations of the Last Glacial Maximum

10.5194/egusphere-egu21-6693 ◽

2021 ◽

Author(s):

Lauren Gregoire ◽

Niall Gandy ◽

Lachlan Astfalck ◽

Robin Smith ◽

Ruza Ivanovic ◽

...

Keyword(s):

Mass Balance ◽

Last Glacial Maximum ◽

Ice Sheets ◽

Ice Sheet ◽

Glacial Maximum ◽

Sea Surface ◽

Surface Mass ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

<p>Simulating the co-evolution of climate and ice-sheets during the Quaternary is key to understanding some of the major abrupt changes in climate, ice and sea level. Indeed, events such as the Meltwater pulse 1a rapid sea level rise and Heinrich, Dansgaard&#8211;Oeschger and the 8.2 kyr climatic events all involve the interplay between ice sheets, the atmosphere and the ocean. Unfortunately, it is challenging to simulate the coupled Climate-Ice sheet system because small biases, errors or uncertainties in parts of the models are strongly amplified by the powerful interactions between the atmosphere and ice (e.g. ice-albedo and height-mass balance feedbacks). This leads to inaccurate or even unrealistic simulations of ice sheet extent and surface climate. To overcome this issue we need some methods to effectively explore the uncertainty in the complex Climate-Ice sheet system and reduce model biases. Here we present our approach to produce ensemble of coupled Climate-Ice sheet simulations of the Last Glacial maximum that explore the uncertainties in climate and ice sheet processes.</p><p>We use the FAMOUS-ICE earth system model, which comprises a coarse-resolution and fast general circulation model coupled to the Glimmer-CISM ice sheet model. We prescribe sea surface temperature and sea ice concentrations in order to control and reduce biases in polar climate, which strongly affect the surface mass balance and simulated extent of the northern hemisphere ice sheets. We develop and apply a method to reconstruct and sample a range of realistic sea surface temperature and sea-ice concentration spatio-temporal field. These are created by merging information from PMIP3/4 climate simulations and proxy-data for sea surface temperatures at the Last Glacial Maximum with Bayes linear analysis. We then use these to generate ensembles of FAMOUS-ice simulations of the Last Glacial maximum following the PMIP4 protocol, with the Greenland and North American ice sheets interactively simulated. In addition to exploring a range of sea surface conditions, we also vary key parameters that control the surface mass balance and flow of ice sheets. We thus produce ensembles of simulations that will later be used to emulate ice sheet surface mass balance. &#160;</p>

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

The Cryosphere ◽

10.5194/tc-13-2935-2019 ◽

2019 ◽

Vol 13 (11) ◽

pp. 2935-2951 ◽

Cited By ~ 4

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.

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Ice-sheet mass balance during the last glacial maximum

Annals of Glaciology ◽

10.3189/s026030550001394x ◽

1997 ◽

Vol 25 ◽

pp. 145-152 ◽

Cited By ~ 2

Author(s):

Gilles Ramstein ◽

Adeline Fabre ◽

Sophie Pinot ◽

Catherine Ritz ◽

Sylvie Joussaume

Keyword(s):

Last Glacial Maximum ◽

General Circulation ◽

Ice Sheets ◽

Ice Sheet ◽

General Circulation Models ◽

Glacial Maximum ◽

Last Glacial ◽

Intercomparison Project ◽

The Last Glacial Maximum ◽

The Last Glacial

In the framework of the Paleoclimate Modelling Intercomparison Project (PMIP), simulations of the Last Glacial Maximum (LGM) have- been performed. More than 10 different atmospheric general circulation models (AGCMs) have been used with the same boundary conditions: sea-surface temperatures prescribed by CLIMAP (1981), ice-sheet reconstruction provided by Peltier (1994), change in insolation, and reduced CO2 content. One of the major questions is to investigate whether the simulations of the LGM are in equilibrium with the prescribed ice-sheet reconstruction. To answer this question, we have used two different approaches. First, we analyze the results of a sel of LGM simulations performed with different versions of the Laboratoire de Meteorolo-gie Dynamique (LMD) AGCM and study the hydrologic and snow- budgets over the Laurcntide and Fennoscandian ice sheets. Second, we use the AGCM outputs to force an ice-sheet model in order to investigate its ability to maintain the ice sheets as reconstructed by CLIMAP (1981) or Peltier (1994).

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