scholarly journals The Role of Climate and Bed Topography on the  Evolution of the Tasman Glacier Since the Last  Glacial Maximum

2021 ◽  
Author(s):  
◽  
Karen Aline McKinnon
Keyword(s):  
Last Glacial Maximum ◽  
Coupled Model ◽  
Coupled System ◽  
Late Glacial ◽  
Glacial Maximum ◽  
Past Climate ◽  
Last Glacial ◽  
Mountain Glaciers ◽  
Bed Topography ◽  
Glacier Flow

<p>Mountain glaciers respond to climatic changes by advancing or retreating, leaving behind a potentially powerful record of climate through moraine deposition. Estimates of past climate have been made based on the moraine record alone, using geometrical arguments; however, these methods necessarily ignore the effects of glacier dynamics and bed modification. Here, a one-dimensional coupled mass balance-flowline model is used to place constraints on the climate of the Late-glacial (13.5–11.6 kyr ago) and Last Glacial Maximum (LGM, 28 – 17.5 kyr ago) based on the well-mapped and -dated moraines at Tasman Glacier/Lake Pukaki, South Island, New Zealand. Due to the highly-dynamic nature of the system, distinct longitudinal bed profiles are considered for each of the glaciations modelled; the reconstructions show that terminal overdeepenings are likely present in all bed profiles, and hundreds of metres of sediment has been deposited in the glacier valley since the LGM. Using the coupled model and calculated bed topography, a 2.2°C temperature depression from the present is necessary to reproduce the Lateglacial ice extent, and 7.0°C is required for the early LGM, assuming presentday precipitation. The modelled Late-glacial ice extent is more sensitive to precipitation variability than that during the LGM, but the Tasman Glacier during both periods is primarily driven by temperature changes. While the Tasman Glacier shrank between the early and late LGM, modelling demonstrates that changes in bed topography due to erosion, transport and deposition of sediment are a major driver in reduction of glacier extent; a temperature increase of only 0.1°C is required to cause the transition between the two periods, which may be attributable to interannual, zero-trend climate variability. Thus, the consideration of the coupled glacier-sediment system is critical in accurately reconstructing past climate. Future work focusing on modelling this coupled system, such that the bed profile can evolve interactively with glacier flow, will be critical in better resolving transient events such as the early to late LGM transition.</p>

scholarly journals The Role of Climate and Bed Topography on the  Evolution of the Tasman Glacier Since the Last  Glacial Maximum

2021 ◽  
Author(s):  
◽  
Karen Aline McKinnon
Keyword(s):  
Last Glacial Maximum ◽  
Coupled Model ◽  
Coupled System ◽  
Late Glacial ◽  
Glacial Maximum ◽  
Past Climate ◽  
Last Glacial ◽  
Mountain Glaciers ◽  
Bed Topography ◽  
Glacier Flow

<p>Mountain glaciers respond to climatic changes by advancing or retreating, leaving behind a potentially powerful record of climate through moraine deposition. Estimates of past climate have been made based on the moraine record alone, using geometrical arguments; however, these methods necessarily ignore the effects of glacier dynamics and bed modification. Here, a one-dimensional coupled mass balance-flowline model is used to place constraints on the climate of the Late-glacial (13.5–11.6 kyr ago) and Last Glacial Maximum (LGM, 28 – 17.5 kyr ago) based on the well-mapped and -dated moraines at Tasman Glacier/Lake Pukaki, South Island, New Zealand. Due to the highly-dynamic nature of the system, distinct longitudinal bed profiles are considered for each of the glaciations modelled; the reconstructions show that terminal overdeepenings are likely present in all bed profiles, and hundreds of metres of sediment has been deposited in the glacier valley since the LGM. Using the coupled model and calculated bed topography, a 2.2°C temperature depression from the present is necessary to reproduce the Lateglacial ice extent, and 7.0°C is required for the early LGM, assuming presentday precipitation. The modelled Late-glacial ice extent is more sensitive to precipitation variability than that during the LGM, but the Tasman Glacier during both periods is primarily driven by temperature changes. While the Tasman Glacier shrank between the early and late LGM, modelling demonstrates that changes in bed topography due to erosion, transport and deposition of sediment are a major driver in reduction of glacier extent; a temperature increase of only 0.1°C is required to cause the transition between the two periods, which may be attributable to interannual, zero-trend climate variability. Thus, the consideration of the coupled glacier-sediment system is critical in accurately reconstructing past climate. Future work focusing on modelling this coupled system, such that the bed profile can evolve interactively with glacier flow, will be critical in better resolving transient events such as the early to late LGM transition.</p>

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

2021 ◽  
Author(s):  
Brent Goehring ◽  
Brian Menounos ◽  
Gerald Osbron ◽  
Adam Hawkins ◽  
Brent Ward
Keyword(s):  
Last Glacial Maximum ◽  
Ice Sheets ◽  
Late Glacial ◽  
Yukon Territory ◽  
Glacial Maximum ◽  
Alpine Glacier ◽  
Last Glacial ◽  
Carbon 14 ◽  
Glacial Advance

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.

scholarly journals A Last Glacial Maximum forcing dataset for ocean modelling

2020 ◽  
Vol 12 (4) ◽  
pp. 2971-2985
Author(s):  
Anne L. Morée ◽  
Jörg Schwinger
Keyword(s):  
Last Glacial Maximum ◽  
Coupled Model ◽  
Research Data ◽  
Glacial Maximum ◽  
Specific Humidity ◽  
Wave Radiation ◽  
Last Glacial ◽  
Model Set ◽  
Ocean Models ◽  
Fully Coupled

Abstract. Model simulations of the Last Glacial Maximum (LGM; ∼ 21 000 years before present) can aid the interpretation of proxy records, can help to gain an improved mechanistic understanding of the LGM climate system, and are valuable for the evaluation of model performance in a different climate state. Ocean-ice only model configurations forced by prescribed atmospheric data (referred to as “forced ocean models”) drastically reduce the computational cost of palaeoclimate modelling compared to fully coupled model frameworks. While feedbacks between the atmosphere and ocean and sea-ice compartments of the Earth system are not present in such model configurations, many scientific questions can be addressed with models of this type. Our dataset supports simulations of the LGM in a forced ocean model set-up while still taking advantage of the complexity of fully coupled model set-ups. The data presented here are derived from fully coupled palaeoclimate simulations of the Palaeoclimate Modelling Intercomparison Project phase 3 (PMIP3). The data are publicly accessible at the National Infrastructure for Research Data (NIRD) Research Data Archive at https://doi.org/10.11582/2020.00052 (Morée and Schwinger, 2020). They consist of 2-D anomaly forcing fields suitable for use in ocean models that employ a bulk forcing approach and are optimized for use with CORE forcing fields. The data include specific humidity, downwelling long-wave and short-wave radiation, precipitation, wind (v and u components), temperature, and sea surface salinity (SSS). All fields are provided as climatological mean anomalies between LGM and pre-industrial (PI) simulations. These anomaly data can therefore be added to any pre-industrial ocean forcing dataset in order to obtain forcing fields representative of LGM conditions as simulated by PMIP3 models. Furthermore, the dataset can be easily updated to reflect results from upcoming and future palaeo-model intercomparison activities.

Constraining past bedrock surface temperatures at the Gorner glacier, Switzerland, using feldspar thermoluminescence for surface paleothermometry. 

2021 ◽  
Author(s):  
Joanne Elkadi ◽  
Rabiul Biswas ◽  
Georgina King ◽  
Frédéric Herman
Keyword(s):  
Last Glacial Maximum ◽  
Room Temperature ◽  
Continuous Distribution ◽  
Planetary Science ◽  
Glacial Maximum ◽  
Past Climate ◽  
Last Glacial ◽  
Exposure Ages ◽  
The Last Glacial Maximum ◽  
The Last Glacial

&lt;p&gt;Our ability to quantify past climate conditions is crucial for predicting future scenarios and landscape evolution. To date, reconstructions of the Earth&amp;#8217;s past climate have mostly relied on the use of climate proxies to infer previous surface conditions (e.g. Jones and Mann, 2004 for a review). However, few methods exist that are capable of directly measuring past temperature histories, particularly in terrestrial settings.&lt;/p&gt;&lt;p&gt;The aim of this study is to contribute towards a more detailed understanding of glacial and interglacial temperature fluctuations across the Central and Western Alps, from the Last Glacial Maximum to present day, by constraining past temperatures of exposed bedrock surfaces adjacent to the Gorner glacier in Zermatt, Switzerland. This is done through the recently developed application of feldspar thermoluminescence to surface paleothermometry (Biswas et al., 2018; 2020). The thermoluminescence signal of feldspar, from room temperature to 450&amp;#176;C, is sourced from a continuous distribution of electron traps within the crystal lattice (Biswas et al., 2018). The release of this trapped charge is temperature dependent and thus, at room temperature, results in traps with a range of thermal stabilities with electron residence times ranging from less than a year to several billion years (Aitken 1985). Traps sensitive to typical surface temperature variations (e.g. &amp;#8764;10&amp;#176;C) have been shown to lie between 200&amp;#176;C and 250&amp;#176;C of the TL glow curve (Biswas et al., 2020). From this temperature range, five thermometers (200&amp;#176;C to 250&amp;#176;C in 10&amp;#176;C intervals) can be used together as a multi-thermometer, and subsequently combined with a Bayesian inversion approach to constrain thermal histories over the last &amp;#8764;50 kyr (Biswas et al., 2020).&lt;/p&gt;&lt;p&gt;In this study, the preliminary temperature histories of five bedrock samples with independently constrained exposure ages, exposed progressively since the Last Glacial Maximum, will be presented.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Aitken, M.J., 1985. Thermoluminescence Dating. Academic Press, London.&lt;/p&gt;&lt;p&gt;Jones, P.D., Mann, M.E., 2004. Climate over past millennia. Reviews of Geophysics, 42, 2004.&lt;/p&gt;&lt;p&gt;Biswas, R.H., Herman, F., King, G.E., Braun, J., 2018. Thermoluminescence of feldspar as a multi-thermochronometer to constrain the temporal variation of rock exhumation in the recent past. Earth and Planetary Science Letters, 495, 56-68.&lt;/p&gt;&lt;p&gt;Biswas, R.H., Herman, F., King, G.E., Lehmann, B., Singhvi, A.K., 2020. Surface paleothermometry using low temperature thermoluminescence of feldspar. Climate of the Past, 16, 2075-2093.&lt;/p&gt;

Last Glacial Maximum to near present 10Be chronology of the Universidad glacier fluctuations in the Subtropical Chilean Andes (34° S): paleoclimate implications  

2021 ◽  
Author(s):  
Hans Fernández ◽  
Juan-Luis García ◽  
Samuel U. Nussbaumer ◽  
Alessa Geiger ◽  
Isabelle Gärtner-Roer ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Late Glacial ◽  
Glacial Maximum ◽  
Ice Age ◽  
Climate History ◽  
Last Glacial ◽  
Exposure Dating ◽  
Glacier Fluctuations ◽  
History Of ◽  
The Last Glacial

&lt;p&gt;The geochronological and geomorphological reconstruction of glacier fluctuations is required to assess the timing and structure of climate changes of the last glacial cycle in the subtropical Andes of Chile. The scarcity of data in this region limits the knowledge related to the timing of glacial landscape changes during this long-term period. To provide a new framework to better understand the climate history of the semiarid Andes of Chile, we have reconstructed the glacial history of the Universidad glacier (34&amp;#176; S).&lt;/p&gt;&lt;p&gt;Our mapping shows the existence of four moraine belts (UNI I to UNI IV, from outer to inner) that are spatially unequally distributed along the 13 km of the valley between ~2500 and ~1400 m a.s.l. We applied &lt;sup&gt;10&lt;/sup&gt;Be cosmogenic surface exposure dating to 26 granodioritic boulders on moraines and determined the age of the associated glacial advances. UNI I moraine represents the distal glacier advance between 20.8&amp;#177;0.8 and 17.8&amp;#177;0.8 kyr ago (number of &lt;sup&gt;10&lt;/sup&gt;Be samples = 11). Other two significative glacier advances terminated one and four km up-valley from the UNI I moraine, respectively, formed 16.1&amp;#177;0.9 kyr (n=1) (UNI II) and 14.6&amp;#177;1 to 10&amp;#177;0.5 kyr ago (n=3) (UNI III). A sequence of six distinct and smaller moraine ridges has been identified in the proglacial area. They are part of last significative glacier advances labeled as UNI IV. The four distal ridges have been dated to between 645-150 years ago (n=11), while the most proximal moraines coincide with mid-20&lt;sup&gt;th&lt;/sup&gt; century and 1997 aerial photographs.&lt;/p&gt;&lt;p&gt;The results indicate that the Universidad glacier advanced during the Last Glacial Maximum (LGM) (UNI I). Deglaciation was punctuated by glacier readvances during the Late Glacial when the UNI II and UNI III moraines were deposited. Finally, UNI IV moraine shows six glacier fluctuations developed between the 14th and 20&lt;sup&gt;th&lt;/sup&gt; centuries.&lt;/p&gt;&lt;p&gt;Our data suggest that the glacier advances by the Universidad glacier were triggered by intensified southern westerly winds bringing colder and wetter conditions to subtropical latitudes in the SE Pacific. Moreover, our data indicate that more or less in-phase Late-Glacial advances along the tropical and extratropical Andes occurred. We discuss different climate forcings that explain these glacier changes. Finally, we illustrate the influence of the &amp;#8220;Little Ice Age&amp;#8221; in the Semiarid Andes.&lt;/p&gt;

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