scholarly journals Cosmogenic nuclide exposure age scatter records glacial history and processes in McMurdo Sound, Antarctica

Geochronology ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 505-523
Author(s):  
Andrew J. Christ ◽  
Paul R. Bierman ◽  
Jennifer L. Lamp ◽  
Joerg M. Schaefer ◽  
Gisela Winckler
Keyword(s):  
Radioactive Decay ◽  
Bimodal Distribution ◽  
Surface Processes ◽  
Mcmurdo Sound ◽  
Glacial Sediments ◽  
Cosmogenic Nuclide ◽  
Geological Processes ◽  
Transantarctic Mountains ◽  
Radiocarbon Chronology ◽  
Exposure Ages

Abstract. The preservation of cosmogenic nuclides that accumulated during periods of prior exposure but were not subsequently removed by erosion or radioactive decay complicates interpretation of exposure, erosion, and burial ages used for a variety of geomorphological applications. In glacial settings, cold-based, non-erosive glacier ice may fail to remove inventories of inherited nuclides in glacially transported material. As a result, individual exposure ages can vary widely across a single landform (e.g., moraine) and exceed the expected or true depositional age. The surface processes that contribute to inheritance remain poorly understood, thus limiting interpretations of cosmogenic nuclide datasets in glacial environments. Here, we present a compilation of new and previously published exposure ages of multiple lithologies in local Last Glacial Maximum (LGM) and older Pleistocene glacial sediments in the McMurdo Sound region of Antarctica. Unlike most Antarctic exposure chronologies, we are able to compare exposure ages of local LGM sediments directly against an independent radiocarbon chronology of fossil algae from the same sedimentary unit that brackets the age of the local LGM between 12.3 and 19.6 ka. Cosmogenic exposure ages vary by lithology, suggesting that bedrock source and surface processes prior to, during, and after glacial entrainment explain scatter. 10Be exposure ages of quartz in granite, sourced from the base of the stratigraphic section in the Transantarctic Mountains, are scattered but young, suggesting that clasts entrained by sub-glacial plucking can generate reasonable apparent exposure ages. 3He exposure ages of pyroxene in Ferrar Dolerite, which crops out above outlet glaciers in the Transantarctic Mountains, are older, which suggests that clasts initially exposed on cliff faces and glacially entrained by rock fall carry inherited nuclides. 3He exposure ages of olivine in basalt from local volcanic bedrock in the McMurdo Sound region contain many excessively old ages but also have a bimodal distribution with peak probabilities that slightly pre-date and post-date the local LGM; this suggests that glacial clasts from local bedrock record local landscape exposure. With the magnitude and geological processes contributing to age scatter in mind, we examine exposure ages of older glacial sediments deposited by the most extensive ice sheet to inundate McMurdo Sound during the Pleistocene. These results underscore how surface processes operating in the Transantarctic Mountains are expressed in the cosmogenic nuclide inventories held in Antarctic glacial sediments.

scholarly journals Cosmogenic nuclide exposure age scatter in McMurdo Sound, Antarctica records Pleistocene glacial history and processes

2021 ◽  
Author(s):  
Andrew J. Christ ◽  
Paul R. Bierman ◽  
Jennifer L. Lamp ◽  
Joerg M. Schaefer ◽  
Gisela Winckler
Keyword(s):  
Radioactive Decay ◽  
Bimodal Distribution ◽  
Surface Processes ◽  
Mcmurdo Sound ◽  
Glacial Sediments ◽  
Cosmogenic Nuclide ◽  
Geological Processes ◽  
Transantarctic Mountains ◽  
Radiocarbon Chronology ◽  
Exposure Ages

Abstract. The preservation of cosmogenic nuclides that accumulated during periods of prior exposure but were not subsequently removed by erosion or radioactive decay, complicates interpretation of exposure, erosion, and burial ages used for a variety of geomorphological applications. In glacial settings, cold-based, non-erosive glacier ice may fail to remove inventories of inherited nuclides in glacially transported material. As a result, individual exposure ages can vary widely across a single landform (e.g. moraine) and exceed the expected or true depositional age. The surface processes that contribute to inheritance remain poorly understood, thus limiting interpretations of cosmogenic nuclide datasets in glacial environments. Here, we present a compilation of new and previously published exposure ages of multiple lithologies in local Last Glacial Maximum (LGM) and older Pleistocene glacial sediments in McMurdo Sound, Antarctica. Unlike most Antarctic exposure chronologies, we are able to compare exposure ages of local LGM sediments directly against an independent radiocarbon chronology of fossil algae from the same sedimentary unit that brackets the age of the local LGM between 12.3 and 19.6 ka. Cosmogenic exposure ages vary by lithology, suggesting that bedrock source and surface processes prior to, during, and after glacial entrainment explain scatter. 10Be exposure ages of quartz in granite, sourced from the base of the stratigraphic section in the Transantarctic Mountains, are scattered but young, suggesting that clasts entrained by sub-glacial plucking can generate reasonable apparent exposure ages. 3He exposure ages of pyroxene in Ferrar Dolerite, which outcrops above outlet glaciers in the Transantarctic Mountains, are older, which suggests that clasts initially exposed on cliff faces and glacially entrained by rock fall carry inherited nuclides. 3He exposure ages of olivine in basalt from local volcanic bedrock in McMurdo Sound contain many excessively old ages, but also have a bimodal distribution with peak probabilities that slightly pre-date and post-date the local LGM; this suggests that glacial clasts from local bedrock record local landscape exposure. With the magnitude and geological processes contributing to age scatter in mind, we examine exposure ages of older glacial deposits and suggest that the most extensive Pleistocene ice sheet inundated McMurdo Sound during Marine Isotope Stage 8. These results underscore how surface processes operating in the Transantarctic Mountains are expressed in the cosmogenic nuclide inventories held in Antarctic glacial sediments.

Cosmogenic nuclide exposure ages and glacial history of late Quaternary Ross Sea drift in McMurdo Sound, Antarctica

1995 ◽  
Vol 131 (1-2) ◽  
pp. 41-56 ◽  
Author(s):  
Edward J. Brook ◽  
Mark D. Kurz ◽  
Robert P. Ackert ◽  
Grant Raisbeck ◽  
Françoise Yiou
Keyword(s):  
Ross Sea ◽  
Late Quaternary ◽  
Glacial History ◽  
Mcmurdo Sound ◽  
Cosmogenic Nuclide ◽  
History Of ◽  
Exposure Ages

scholarly journals A 14.5 million-year record of East Antarctic Ice Sheet fluctuations from the central Transantarctic Mountains, constrained with cosmogenic <sup>3</sup>He, <sup>10</sup>Be, <sup>21</sup>Ne, and <sup>26</sup>Al

2020 ◽  
Author(s):  
Allie Balter ◽  
Gordon Bromley ◽  
Greg Balco ◽  
Holly Thomas ◽  
Margaret S. Jackson
Keyword(s):  
Ice Sheet ◽  
Antarctic Ice Sheet ◽  
Erosion Rates ◽  
Cosmogenic Nuclide ◽  
Isostatic Uplift ◽  
Transantarctic Mountains ◽  
Exposure Ages ◽  
Free Area ◽  
Isotope Measurements ◽  
East Antarctic Ice Sheet

Abstract. The distribution of moraines in the Transantarctic Mountains affords direct constraint of past ice-marginal positions of the East Antarctic Ice Sheet (EAIS). Here, we describe glacial-geologic observations and cosmogenic-nuclide exposure ages from Roberts Massif, an ice-free area in the central Transantarctic Mountains. We measured cosmogenic 3He, 10Be, 21Ne, and 26Al in 180 dolerite and sandstone boulders collected from 24 distinct deposits. Our data show that a cold-based EAIS was present, in a configuration similar to today, for many periods over the last ~ 14.5 Myr, including the mid-Miocene, Late Pliocene, and early-to-mid Pleistocene. Moraine ages at Roberts Massif increase with distance from, and elevation above the modern ice margin, which is consistent with a persistent EAIS extent during glacial maxima, and slow, isostatic uplift of the massif itself in response to trough incision by outlet glaciers. We also employ the exceptionally high cosmogenic-nuclide concentrations in several boulders, along with multi-isotope measurements in sandstone boulders, to infer extremely low erosion rates (

scholarly journals A 14.5-million-year record of East Antarctic Ice Sheet fluctuations from the central Transantarctic Mountains, constrained with cosmogenic <sup>3</sup>He, <sup>10</sup>Be, <sup>21</sup>Ne, and <sup>26</sup>Al

2020 ◽  
Vol 14 (8) ◽  
pp. 2647-2672
Author(s):  
Allie Balter-Kennedy ◽  
Gordon Bromley ◽  
Greg Balco ◽  
Holly Thomas ◽  
Margaret S. Jackson
Keyword(s):  
Ice Sheet ◽  
Middle Pleistocene ◽  
Antarctic Ice Sheet ◽  
Current Configuration ◽  
Erosion Rates ◽  
Cosmogenic Nuclide ◽  
Transantarctic Mountains ◽  
Atmospheric Co2 Concentrations ◽  
Exposure Ages ◽  
East Antarctic Ice Sheet

Abstract. The distribution of moraines in the Transantarctic Mountains affords direct constraint of past ice-marginal positions of the East Antarctic Ice Sheet (EAIS). Here, we describe glacial geologic observations and cosmogenic-nuclide exposure ages from Roberts Massif, an ice-free area in the central Transantarctic Mountains. We measured cosmogenic 3He, 10Be, 21Ne, and 26Al in 168 dolerite and sandstone boulders collected from 24 distinct deposits. Our data show that a cold-based EAIS was present, in a configuration similar to today, for many periods over the last ∼14.5 Myr, including the mid-Miocene, late Pliocene, and early to Middle Pleistocene. Moraine ages at Roberts Massif increase with distance from, and elevation above, the modern ice margin, which is consistent with a persistent EAIS extent during glacial maxima and slow, isostatic uplift of the massif itself in response to trough incision by outlet glaciers. We also employ the exceptionally high cosmogenic-nuclide concentrations in several boulders, along with multi-isotope measurements in sandstone boulders, to infer extremely low erosion rates (≪5 cm Myr−1) over the period covered by our record. Although our data are not a direct measure of ice volume, the Roberts Massif glacial record indicates that the EAIS was present and similar to its current configuration during at least some periods when the global temperature was believed to be warmer and/or atmospheric CO2 concentrations were likely higher than today.

scholarly journals <sup>10</sup>Be depth profiles in glacial sediments on the Swiss Plateau: deposition age, denudation and (pseudo-) inheritance

2017 ◽  
Vol 66 (2) ◽  
pp. 57-68 ◽  
Author(s):  
Lorenz Wüthrich ◽  
Claudio Brändli ◽  
Régis Braucher ◽  
Heinz Veit ◽  
Negar Haghipour ◽  
...  
Keyword(s):  
Radioactive Decay ◽  
Glacial Sediments ◽  
Depth Profiles ◽  
Denudation Rates ◽  
Last Glaciation ◽  
The Alps ◽  
Swiss Plateau ◽  
High Concentrations ◽  
Cosmogenic 10Be

Abstract. During the Pleistocene, glaciers advanced repeatedly from the Alps onto the Swiss Plateau. Numeric age control for the last glaciation is good and thus the area is well suited to test a method which has so far not been applied to till in Switzerland. In this study, we apply in situ produced cosmogenic 10Be depth profile dating to several till deposits. Three sites lie inside the assumed Last Glacial Maximum (LGM) extent of the Rhône and Aare glaciers (Bern, Deisswil, Steinhof) and two lie outside (Niederbuchsiten, St. Urban). All sites are strongly affected by denudation, and all sites have reached steady state, i.e., the 10Be production is in equilibrium with radioactive decay and denudational losses. Deposition ages can therefore not be well constrained. Assuming constant denudation rates of 5 cm kyr−1, total denudation on the order of 100 cm for sites within the extent of the LGM and up to tens of meters for older moraines are calculated. Denudation events, for example related to periglacial conditions during the LGM, mitigate the need to invoke such massive denudation and could help to explain high 10Be concentrations at great depths, which we here dub pseudo-inheritance. This term should be used to distinguish conceptionally from true inheritance, i.e., high concentrations derived from the catchment.

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.

The local Last Glacial Maximum in McMurdo Sound, Antarctica: Implications for ice-sheet behavior in the Ross Sea Embayment

2019 ◽  
Vol 132 (1-2) ◽  
pp. 31-47 ◽  
Author(s):  
Andrew J. Christ ◽  
Paul R. Bierman
Keyword(s):  
Last Glacial Maximum ◽  
Ross Sea ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Significant Advance ◽  
Ice Flow ◽  
Mcmurdo Sound ◽  
Last Glacial ◽  
Transantarctic Mountains ◽  
Western Ross Sea

AbstractDuring the Last Glacial Maximum (LGM), a grounded ice sheet filled the Ross Sea Embayment in Antarctica and deposited glacial sediments on volcanic islands and peninsulas in McMurdo Sound and coastal regions of the Transantarctic Mountains. The flow geometry and retreat history of this ice are debated, with contrasting views yielding divergent implications for the interaction between and stability of the East and West Antarctic ice sheets during late Quaternary time. Here, we present terrestrial geomorphologic evidence and reconstruct former ice-marginal environments, ice sheet elevations, and ice-flow directions in McMurdo Sound. Fossil algae in ice-marginal sediments provide a coherent radiocarbon chronology of maximum ice extent and deglaciation. We integrate these data with marine records to reconstruct grounded ice dynamics in McMurdo Sound and the western Ross Sea. The combined data set suggests ice flow toward the Transantarctic Mountains in McMurdo Sound during peak glaciation, with thick, grounded ice at or near its maximum position between 19.6 and 12.3 ka. Persistent grounded ice in McMurdo Sound and across the western Ross Sea after Meltwater Pulse 1a (14.0–14.5 ka) suggests that this sector of Antarctica did not significantly contribute to this rapid sea-level rise event. Our data show no significant advance of locally derived ice from the Transantarctic Mountains into McMurdo Sound during the local LGM.

Earth’s thermal cycles and geological events

2020 ◽  
Author(s):  
Bin Gong ◽  
Chun‘an Tang ◽  
Tiantian Chen ◽  
Zhanjie Qin ◽  
Hua Zhang
Keyword(s):  
Plate Tectonics ◽  
Biological Evolution ◽  
Radioactive Decay ◽  
Thermal Cycles ◽  
Red Beds ◽  
Cold Event ◽  
Geological Processes ◽  
The Earth ◽  
New Perspective ◽  
The Relationship

&lt;p&gt;Alternative cooling and warming have occurred many times in the history of Earth since its formation. In the meantime, active and quiescent periods of geological activity have also alternatively occurred in this same planet. When Earth became hotter, it shows widespread geological activities, such as LIPs, whereas during the colder stage, it became relatively quiet without too much magma activities. Although various models have been used to explain the trigger for each of these activities, there is no consensus about the fundamental relationships between the thermal cycles and episodically geological processes. The major energy sources for Earth after ~3.8 Ga include primordial heat left from the accretion, differentiation, and the radioactive decay of heat-producing elements. Surface tectonics and magmatism control the transport of heat from the interior to the surface and most surface tectonic features of Earth are the expression of their interior dynamics. Supercontinental breakup and aggregation have occurred for many times in the Earth history, accompanied by episodic cooling and warming on the Earth surface. This breakup and aggregation regime is known as plate tectonics and is characterized by high average surface heat flow fluctuations. Based on the thermodynamic principle, a thermodynamic equilibrium equation describing the earth&amp;#8217;s thermal cycles is established. We realized that this thermal cycle may drive Earth itself to evolve, and is the fundamental reason for the periodicity or rhythmicity of geological events such as tectonic movements, orogenies, glacial periods and biological extinctions. Following this principle, we then introduced a project of Wall Chat to compile global data or evidences using a variety of literatures in Geology of early investigations of geological events to explore the relationship between geological events and Earth&amp;#8217;s thermal cycles. The data includes the supercontinent cycle, tectonic movement, plate tectonics, extremely hot event, extremely cold event, evaporite, marine red bed, biological evolution and extinction, sea level fluctuation, etc. The Wall Chat reveals that most of the geological events have their relation to the Earth&amp;#8217;s thermal cycles. We found that there may exist a good correlation between the occurrence of evaporites and marine red beds and the higher temperature periods, which then provides a new perspective to understand the triggering of these events. The Wall Chat also raises an interest and important question on why are the two Great Oxidation Events (GOE) both related to the two snowball events? We have several clear objectives for the future. First, we are currently cooperating with some of the related institutes of geology to obtain additional evidence data to fill in many of the gaps in the chat; targeted areas include Paleontology, Glaciology, evaporite and red beds. Second, to understand fully the relationship between thermal cycles and, at least, most of the great geological events. Such studies, when sufficiently constrained by event data, should lead to a greatly improved understanding of the earth evolution.&lt;/p&gt;

scholarly journals Cosmogenic nuclide ages for Last Glacial Maximum moraine at Schnells Ridge, Southwest Tasmania

2004 ◽  
Vol 61 (3) ◽  
pp. 335-338 ◽  
Author(s):  
Kevin Kiernan ◽  
L. Keith Fifield ◽  
John Chappell
Keyword(s):  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Cosmogenic Nuclide ◽  
Southeast Australia ◽  
Exposure Ages

Moraines on Schnells Ridge, southwest Tasmania, have been dated using in situ 10Be. An age of 19,400 ± 600 yr is indicated for the well-preserved innermost moraine from consistent measurements on four large quartzite boulders. This corresponds closely with exposure ages reported by T.T. Barrows et al. (2002, Quaternary Science Reviews 21, 159–173) for Last Glacial Maximum glacial features farther north in Tasmania and southeast Australia. In contrast, ages between 39,000 and 141,000 yr were obtained from a series of boulders on a more extensive outer moraine, indicating that this has had a more complex history.

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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