Glacial History Research Articles

The glaciovolcanic evolution of the Copahue volcano, Andean Southern Volcanic Zone, Argentina-Chile

Glaciovolcanism produces distinctive features that are useful paleoclimate proxies for the distribution of past ice sheets and glacier extent. The Copahue volcano located in the Andean Southern Volcanic Zone, Argentina-Chile, is an active composite volcano known to have glaciovolcanic features such as lava bodies with glassy margins and anomalous cooling fractures. However, the emplacement conditions of these products and the influence of Pleistocene glaciations on the evolution of the Copahue volcano remains poorly understood. In this contribution, we propose a model for glaciovolcanic evolution of the Copahue volcano based on the analysis, interpretation, and mapping of its products. Ten lithofacies are described on the eastern flank of Copahue volcano exhibiting several examples of glaciovolcanism. The evolution of the Copahue volcano can be divided into two main sequences: the Ancient Sequence (S1) and the Young Sequence (S2), separated by a major erosive phase. The S1 (early-middle Pleistocene-late Pleistocene) consists of an initial subaerial effusive stage followed by a major glaciovolcanic stage, during which a thick ice cap existed and the edifice grew beneath an englacial lake with the eventual formation of a lava-fed delta. The S2 (late Pleistocene-Present) is defined by mainly effusive activity during periods of glacial advance and retreat recorded by an alternation of unconfined subaerial lavas and ice-confined lavas. The evolution of the Copahue volcano therefore indicates two glaciations in the Copahue-Caviahue area during the late Pleistocene, in contrast to a single glaciation. Based on the glacial history in the area we associate the first glaciation with the end of Marine Isotope Stage 3 (57–29 ka) and/or the Last Glacial Maximum period (26.5–19.0 ka), and the second less-extensive glacial period with the Antarctic Cold Reversal (14.5–12.9 ka).

Constraints from cosmogenic nuclides on the glaciation and erosion history of Dove Bugt, northeast Greenland

AbstractThe intricate interplay between subglacial topography and ice-sheet dynamics is key to the evolution of large ice sheets, but in Greenland as elsewhere the effects of long-term glacial history on landscape evolution remain poorly constrained. Here we measure abundances of cosmogenic 10Be and 26Al in bedrock and transported boulders to unveil the glaciation and erosion history of Dove Bugt, northeast Greenland. In agreement with studies of west Greenland, we find that apparent exposure ages increase with elevation from 9 ka to 13 ka in low-lying valleys to 21 ka to 204 ka on high-elevation, blockfield-covered plateaus. We employ a Markov chain Monte Carlo inversion framework to constrain the probability of various erosion histories, and we quantify the residence time of samples within the upper 2 m of the bedrock subsurface—a measure defined as the cosmogenic nuclide memory. This cosmogenic nuclide memory exceeds 600 ka on the highest plateaus but is limited to less than 500 ka in most other high-elevation samples and to less than 100 ka at low-elevations. Our results define maximum limits for the fraction of ice cover during the past 1 Ma to ∼70% on the Store Koldewey peaks and ∼90% farther inland at Pusterdal, respectively. Minimum limits to ice cover, however, cannot be reliably constrained by the data. Finally, we propose that limited erosion on the highest plateaus of Store Koldewey since 0.6–1.0 Ma indicates a minimum age for fjord-plateau formation within this area of northeast Greenland.

Surficial geology of Pictured Rocks National Lakeshore, Michigan, USA

ABSTRACT Pictured Rocks National Lakeshore is located in the Upper Peninsula of Michigan along the southern shore of Lake Superior. The park spans approximately 300 km2 and is almost fully incorporated within the ten 7.5-minute quadrangles presented in this new, detailed surficial geology map. The western quadrangles are mainly characterized by thin accumulations of undifferentiated Quaternary sediment above shallow bedrock while the eastern quadrangles mostly show thick accumulations of various glacial outwash units. This map was produced by integrating field data with a high-resolution LiDAR digital elevation model and associated hillshade, aerial imagery, and passive seismic data. The high-resolution elevation information was essential to differentiate between outwash units, post-glacial sand accumulations, and interpreting subtle glacial features that would have otherwise remained unrecognized. This new map provides fundamental information to help decipher the glacial history of this region to enhance our understanding of how this popular landscape developed.

A comparison of neutral genetic differentiation and genetic diversity among migratory and resident populations of Golden-crowned-Kinglets (Regulus satrapa)

Many animals migrate seasonally between breeding and non-breeding territories and these annual movements can have a profound effect on population genetic structure. We genotyped 281 individuals from 11 populations at seven variable microsatellite loci and compared patterns of neutral genetic differentiation and neutral genetic diversity among migratory and resident breeding populations of the Golden-crowned Kinglet (Regulus satrapa), a widespread North American songbird. We predicted that resident populations would exhibit greater genetic differentiation and lower genetic diversity than migratory populations because migratory behaviour is thought to enhance gene flow. The magnitude of genetic differentiation and genetic diversity among migratory and resident populations was comparable, and the greatest levels of differentiation were observed for pairwise comparisons between Ontario and all western populations. Distance-based redundancy models and redundancy models revealed that patterns of neutral genetic differentiation and neutral genetic diversity follow an isolation-by-distance model and are not correlated with migratory behaviour. Overall it appears that genetic patterns are more closely associated with Pleistocene glacial history as proposed in a previous study.

Early glacial maximum and deglaciation at sub-Antarctic Marion Island from cosmogenic 36Cl exposure dating

Southern Hemisphere glacial chronologies can provide valuable insights into interactions between glaciation and past climate changes, but are not well constrained on most sub-Antarctic islands. We present the first cosmogenic 36Cl exposure ages of deglaciated bedrock surfaces and moraine deposits from sub-Antarctic Marion Island in the southern Indian Ocean. Results show that the ice reached a local Last Glacial Maximum before 34 ka and retreated, with no re-advances, but possibly minor stand stills, until ∼17 ka. This early deglaciation left island surfaces below 850 m a.s.l. ice-free after ∼19 ka, and any subsequent advances during the Antarctic Cold Reversal or Holocene cooling periods would have been restricted to the interior. This glacial chronology is similar to that of some other sub-Antarctic Islands (e.g. the Kerguelen archipelago, Auckland and Campbell islands, and possibly South Georgia) and a number of other Southern Hemisphere glaciers (e.g. in Patagonia and New Zealand) and adds to evidence that suggest the Southern Hemisphere was in a glacial maxima earlier than the global LGM. We suggest a combination of declining temperatures, a northward migration of oceanic fronts and the Southern Hemisphere westerly winds (causing precipitation changes), as well as the physiography of Marion Island, created optimal conditions for glacier growth during Marine Isotope Stage (MIS) 3 instead of MIS 2. Our findings redefine the glacial history of Marion Island, and have implications for future investigations on post-glacial landscape development and ecological succession.

Polyphase Mid‐Latitude Glaciation on Mars: Chronology of the Formation of Superposed Glacier‐Like Forms from Crater‐Count Dating

AbstractReconstructing Mars's glacial history informs understanding of its physical environment and past climate. The known distribution of viscous flow features (VFFs) containing water ice suggests that its mid‐latitudes were glaciated during the Late Amazonian period (the last several hundred million years). The identification of a subgroup of VFFs—called superposed glacier like forms (SGLFs)—flowing onto other VFFs, indicates multiple glacial phases may have occurred during this time. To explore the history and spatial extent of these glaciations, we record the distribution of SGLFs globally and use impact‐crater counting to date the SGLFs and the VFFs onto which they flow. Our inventory expands the handful of SGLFs reported in earlier literature to include 320 located throughout the mid‐latitudes. Our dating reveals these SGLFs to be much younger than their underlying VFFs, which implies a spatially‐asynchronous glaciation. SGLFs have been forming since ∼65 Ma, and their ages are clustered in two distinct groups around 2–20 and 45–65 Ma, whereas the ages of their underlying VFFs span the last ∼300 Ma diffusely. We discuss these results in the light of well‐known uncertainties with the crater‐dating method and infer that while ice sheets decayed over the Late Amazonian period, alpine glaciers waxed and waned in at least two major cycles before their final demise approximately two million years ago.

MIS 3 sediment stratigraphy in southern Sweden sheds new light on the complex glacial history and dynamics across southern Scandinavia

Recent studies have revealed that areas with sediments pre‐dating the Last Glacial Maximum (LGM) are more common in southern Scandinavia than previously thought. To describe and date these sediments, four deep core drillings were made in the province of Småland and one in the province of Skåne, southern Sweden, and an existing sediment core drilled in the 1960s from western Skåne was re‐examined and re‐dated, all resulting in a total of 22 AMS 14C ages and 19 OSL ages. With some variation, the Småland cores revealed a stratigraphy consisting of two tills separated by proglacial glacifluvial and glaciolacustrine sediments, dated to between 46 and 25 ka BP (Marine Isotope Stage (MIS) 3 to 2). We suggest that these sediments were deposited during the ice retreat of the MIS 3 Ristinge glaciation over southern Scandinavia and the subsequent re‐advance over the area in late MIS 3 and the transition to MIS 2, when the Fennoscandian Ice Sheet advanced towards its LGM marginal positions. This contrasts with the glacial history of southernmost Skåne, where an additional MIS 3 glacial advance through the Baltic Basin is suggested by the occurrence of a till named Allarp Till. New ages from sediments under‐ and overlying this till suggest that it was deposited by the same Baltic ice advance that deposited the Klintholm till in Denmark (Klintholm Advance, c. 34–30 ka).

Living on the edge: comparative phylogeography and phylogenetics of Oreohelix land snails at their range edge in Western Canada

BackgroundThe biodiversity and distributions of terrestrial snails at local and regional scales are influenced by their low vagility and microhabitat specificity. The accessibility of large-bodied species and their characteristically high levels of genetic polymorphism make them excellent ecological and evolutionary models for studies on the phylogeography, phylogenetics, and conservation of organisms in fragmented populations. This study aims to elucidate the biodiversity, systematics, and distributions of genetic lineages within the genus Oreohelix at the northern and western periphery of their range.ResultsWe found four mitochondrial clades, three of which are putative subspecies of Oreohelix subrudis. One clade was geographically widespread, occurring within numerous sites in Cypress Hills and in the Rocky Mountains, a second was geographically restricted to the Rocky Mountains in Alberta, and a third was restricted to the Cypress Hills region. A fourth clade was the small-bodied species, O. cooperi. ITS2 sequence and screening data revealed three genetic clusters, of which one was O. cooperi. Cluster 1 contained most individuals in COI clade X and some from clade B and cluster 2 was predominantly made up of individuals from COI clades B and B′ and a few from clade X. ITS2 alleles were shared in a narrow contact zone between two COI clades, suggestive of hybridization between the two.ConclusionsA sky island known as Cypress Hills, in southeastern Alberta, Canada, is a biodiversity hotspot for terrestrial land snails in the genus Oreohelix. The observed phylogeographic patterns likely reflect reproductive isolation during the Last Glacial Maximum, followed by secondary contact due to passive, long-range dispersal resulting from low vagility, local adaptation, and complex glacial history.

Analyzing Anomalous Topographic MapDrainage System and Landform Evidence as a Glacial History Paradigm Problem: A Literature Review

While not usually stated, detailed topographic maps show well-mapped anomalous drainage system and other erosional landform evidence the accepted North American Cenozoic geologic and glacial history paradigm (accepted paradigm) does not permit geomorphologists to satisfactorily explain. A new and fundamentally different paradigm able to explain the drainage system and other erosional landform evidence has recently emerged, but requires what the accepted paradigm considers to be the preglacial (and probably mid-Cenozoic) Bell River drainage system to have formed on a melting continental ice sheet’s floor. The new paradigm’s melting ice sheet had previously eroded bedrock underneath it and caused crustal warping that raised continental regions and mountain ranges so as to create and occupy a deep “hole” while massive and prolonged meltwater floods flowed across rising continental regions and mountain ranges to the south. The new paradigm leads to a completely different middle Cenozoic geologic and glacial history than the accepted paradigm describes and the two paradigms are analyzed according to good science expectations such as using evidence anyone can see, applying common sense logic during each research step, producing consistent results, and simplicity of paradigm generated explanations. The new paradigm uses topographic map evidence anyone can see, appears to use common sense logic during each research step, and produces remarkably consistent results leading to a simpler Cenozoic northern Missouri River drainage basin region geologic and glacial history than what the accepted paradigm describes. Further work is needed to test the new paradigm’s ability to explain drainage system and erosional landform evidence in other geographic regions such as in the Ohio River drainage basin.

Rila-West Rhodopes Batholith and petrographical diversity of Rila Geopark

The full retrospective of the petrographic study of the Rila granitoids, which are an essential part of the geodiversity of Rila Geopark, is crucial for the impartial assessment of its geoconservation value and for developing appropriate promotional materials in a language accessible to the general public. The Rila-West Rhodopes batholith, the largest batholith in the Balkans, contributes to the continental significance of Rila Geopark with its remarkable petrographic diversity of granitoid rocks and numerous pegmatite, aplite and quartz veins, vein-like granite and diorite bodies favorable for demonstrations of the principle of cross-cutting relationships in geology and illustrating the crystallization processes in igneous rocks as well as magmatic structures and textures. Due to their extremely wide distribution in Rila, the granitoids of the Rila-West Rhodopes batholith crop out along the routes of all previously described geotrails and are native rocks for most glacial forms that define the concept of Rila Geopark. From this point of view, a full review of the geological study of the batholith is a necessary condition for any subsequent step in the geopark development and its nomination for the UNESCO Geopark. This article offers a brief but comprehensive historical overview of the current petrographic studies, which will serve as a basis for the development of information panels located along the described geotrails. Particular emphasis should be placed on the connection between petrology and local crafts in the past, which is contained in the very slogan of Rila Geopark “Land of Iron and Water”. It includes the memory of the primitive crafts associated with the extraction and forging of iron in the Middle Ages, and water in its three states – ice (the glacial history of the mountain), steam (geysers and geothermal springs) and liquid phase – the source of the longest rivers in the Balkans.

Phylogeography and Mitochondrial Polymorphism of Asian Coho Salmon

Multiple Pleistocene glaciations significantly affected the gene pool of many species inhabiting the Northern part of the Pacific Rim, an area with a rich glacial history. This paper is devoted to the study of intraspecific polymorphism of the coho salmon and the routes of its settlement throughout the Asian part of its range. Such problems are traditionally solved by comparing parts of the mitochondrial genome. Here, two fragments of mtDNA, the control region (D-loop) and the cytochrome b gene (cytb), were investigated. It was shown that the settlement of the Asian Pacific coast by the coho salmon was preceded by a chain of successive migration events from the refugium located on the North American continent to the South of the ice sheet covering the area of modern Canada and southern Alaska. The low level of genetic polymorphism in Asian coho populations seems to be a result of a pronounced founder effect, rather than being characteristic of the species as a whole.

LakeCC: a tool for efficiently identifying lake basins with application to palaeogeographic reconstructions of North America

ABSTRACTAlong the margins of continental ice sheets, lakes formed in isostatically depressed basins during glacial retreat. Their shorelines and extent are sensitive to the ice margin and the glacial history of the region. Proglacial lakes, in turn, also impact the glacial isostatic adjustment due to loading, and ice dynamics by posing a marine‐like boundary condition at the ice margin. In this study we present a tool that efficiently identifies lake basins and the corresponding maximum water level for a given ice sheet and topography reconstruction. This algorithm, called the LakeCC model, iteratively checks the whole map for a set of increasing water levels and fills isolated basins until they overflow into the ocean. We apply it to the present‐day Great Lakes and the results show good agreement (∼1−4%) with measured lake volume and depth. We then apply it to two topography reconstructions of North America between the Last Glacial Maximum and the present. The model successfully reconstructs glacial lakes such as Lake Agassiz, Lake McConnell and the predecessors of the Great Lakes. LakeCC can be used to judge the quality of ice sheet reconstructions. © 2019 The Authors Journal of Quaternary Science Published by John Wiley & Sons Ltd.

The Last Glacial and Holocene history of mountain woodlands in the southern part of the Western Carpathians, with emphasis on the spread of Fagus sylvatica

The Western Carpathians have recently been examined in several palaeoecological studies. However, some of their parts remain underexplored in terms of the Holocene history of mountain woodlands. We analysed an 8000-year-old peat sequence from the southern part of the Western Carpathians (the Bykovo site) for pollen, needles and stomata, and reviewed the data on the occurrence and spread of beech since the Last Glacial times in order to put results from Bykovo into the context of the whole Western Carpathians. For pre-industrial times, we reconstructed mixed beech–fir or beech–fir–spruce woodlands in zonal habitats, noble hardwood woodlands on screes, and spruce woodlands in peaty and wet habitats. A meta-analysis of available pollen data for beech revealed that a few sites in Pannonia and on the southern Carpathian fringes reached beech pollen abundances exceeding 0.5% at the very beginning of the Holocene (12–10 cal BP). Moreover, the pattern of reaching greater pollen abundance limits showed a clear south-to-north gradient starting in the Pannonian lowland. Therefore, the direction of the spread of beech based on pollen abundances and the absence of beech macrofossil evidence during the Last Glacial Maximum do not support local glacial refugia of beech directly in the Western Carpathians. The timing of local beech occurrence (empirical pollen limit of 1.4–2%) and its expansion (rational pollen limit of up to 5%) at the Bykovo site fits well this gradual spread of beech from the south. The first period of beech spread in the Bykovo area around 6250 cal BP coincides well with the period of increased precipitation between 6100 and 6800 cal BP, as reconstructed by different proxies (e.g. stable isotopes) for the Western Carpathians.

Late Quaternary depositional and glacial history of the Arliss Plateau off the East Siberian margin in the western Arctic Ocean

Sedimentary stratigraphy and facies analysis along with seismostratigraphic and multibeam bathymetry data are used to reconstruct the last glacial impact on the Arliss Plateau (AP) and attendant sedimentation in the adjacent Chukchi Basin (CB) in the western Arctic Ocean off the East Siberian margin. Sediment core ARA02B/16B-GC from the AP lower slope captures glacier-related depositional history during the last estimated ca. 100 ka (Marine Isotope Stage, MIS 1 to 5c) based on regional lithostratigraphic correlation. The sedimentary record shows distinguishable interglacial (interstadial) and glacial (stadial) patterns. The identified sedimentary facies reflect several modes of glaciogenic deposition by drifting icebergs, suspension settling from turbid meltwater plumes and/or detached underflows, and turbidity currents. Based on strong seismic reflectors related to lithological boundaries, a downslope subbottom profile from AP to CB is divided into seismostratigraphic units (SSU) 1 and 2 corresponding in the core record to MIS 1–3 and MIS 3-5c, respectively. An acoustically transparent lens within SSU 2 correlates on the upper slope to debris lobes downslope from the AP top covered by megascale glacial lineations. This geomorphic/sedimentary pattern indicates a glacial erosional impact on the AP and proglacial deposition of eroded sediments on the slope and in the basin. Based on the developed sediment stratigraphy and facies analysis, the last debris lobe horizon was deposited in glacial/deglacial environments during late MIS 4 to early MIS 3. The absence of similar glaciogenic debris lobes within SSU 1 indicates no direct glacial impact on the AP during the Last Glacial Maximum (LGM). These results suggest that the last glacial erosion of the AP occurred during or immediately after MIS 4, possibly related to major glaciation in northern Siberia at ∼50–70 ka.

Major Ice Sheet Change in the Weddell Sea Sector of West Antarctica Over the Last 5,000 Years

AbstractUntil recently, little was known about the Weddell Sea sector of the West Antarctic Ice Sheet. In the last 10 years, a variety of expeditions and numerical modelling experiments have improved knowledge of its glaciology, glacial geology and tectonic setting. Two of the sector's largest ice streams rest on a steep reverse‐sloping bed yet, despite being vulnerable to change, satellite observations show contemporary stability. There is clear evidence for major ice sheet reconfiguration in the last few thousand years, however. Knowing precisely how and when the ice sheet has changed in the past would allow us to better understand whether it is now at risk. Two competing hypotheses have been established for this glacial history. In one, the ice sheet retreated and thinned progressively from its Last Glacial Maximum position. Retreat stopped at, or very near, the present position in the Late Holocene. Alternatively, in the Late Holocene, the ice sheet retreated significantly upstream of its present grounding line and then advanced to today's location due to glacial isostatic adjustment and ice shelf and ice rise buttressing. Both hypotheses point to data and theory in their support yet neither has been unequivocally tested or falsified. Here we review geophysical evidence to determine how each hypothesis has been formed, where there are inconsistencies in the respective glacial histories, how they may be tested or reconciled, and what new evidence is required to reach a common model for the Late Holocene ice sheet history of the Weddell Sea sector of West Antarctica.

Circumpolar patterns of Arctic freshwater fish biodiversity: A baseline for monitoring

Abstract Climate change, biological invasions, and anthropogenic disturbance pose a threat to the biodiversity and function of Arctic freshwater ecosystems. Understanding potential changes in fish species distribution and richness is necessary, given the great importance of fish to the function of freshwater ecosystems and as a resource to humans. However, information gaps limit large‐scale studies and our ability to determine patterns and trends in space and time. This study takes the first step in determining circumpolar patterns of fish species richness and composition, which provides a baseline to improve both monitoring and conservation of Arctic freshwater biodiversity. Information on species presence/absence was gathered from the Circumpolar Biodiversity Monitoring Program's Freshwater Database and used to examine patterns of freshwater fish γ‐, α‐, and β‐diversity across 234° of longitude in the Arctic. The metrics of diversity provided information on species richness and composition across hydrobasins, ecoregions, and Arctic zones. Circumpolar patterns of fish species biodiversity varied with latitude, isolation, and coarse ecoregion characteristics; patterns were consistent with historic and contemporary barriers to colonisation and environmental characteristics. Gamma‐diversity was lower in the high Arctic compared to lower latitude zones, but α‐diversity did not decrease with increasing latitude below 71°N, reflecting glacial history. Alpha‐diversity was reduced to a single species, Arctic charr Salvelinus alpinus, in ecoregions above 71°N, where γ‐diversity was the lowest. Beta‐diversity indicated little variation in the composition and richness of species across the High Arctic; at lower latitudes, ecoregions contained more species, although species composition turned over across large spatial extents. In an analysis of five ecoregions in the circumpolar Arctic, physical isolation, and ecoregion area and topography were identified as strong drivers of γ‐, α‐, and β‐diversity. Physical isolation reduced the γ‐ and α‐diversity, and changes in β‐diversity between adjacent locations were due mainly to losses in species richness, rather than due to differences in species composition. Heterogeneity of habitats, environmental gradients, and geographic distance probably contributed to patterns of fish dissimilarity within and across ecoregions. This study presents the first analysis of large‐scale patterns of freshwater fish biodiversity in the circumpolar Arctic. However, information gaps in space, time, and among taxonomic groups remain. Future inclusion of extensive archive and new data will allow future studies to test for changes and drivers of the observed patterns of biodiversity. This is important given the potential impacts of ongoing and accelerating climate change, land use, and biotic exchange on Arctic fish biodiversity.

Glacial history of the Greenland Ice Sheet and a local ice cap in Qaanaaq, northwest Greenland

ABSTRACTIn this study, we present new information on the glacial history of the Greenland Ice Sheet (GrIS) and a local ice cap in Qaanaaq, northwest Greenland. We use geomorphological mapping, 10Be exposure dating of boulders, analysis of lake cores, and 14C dating of reworked marine molluscs and subfossil plants to constrain the glacial history. Our 14C ages of reworked marine molluscs reveal that the ice extent in the area was at or behind its present‐day position from 42.2 ± 0.4 to 30.6 ± 0.3k cal a BP after which the GrIS expanded to its maximum position during the Last Glacial Maximum. We find evidence of early ice retreat in the deep fjord (Inglefield Bredning) at 11.9 ± 0.6 ka whereas the Taserssuit Valley was deglaciated ~4 ka later at 7.8 ± 0.1k cal a BP. A proglacial lake record suggests that the local ice cap survived the Holocene Thermal Maximum but moss kill‐dates reveal that it was smaller than present for a period of time before 3.3 ± 0.1k until 0.9 ± 0.1k cal a BP, following which the ice in the area expanded towards its Little Ice Age extent. Copyright © 2019 John Wiley & Sons, Ltd.

Pedogenic evolution on the arid Bishop Creek moraines, eastern Sierra Nevada, California

Soil chronosequences on alpine moraine complexes have been used to help unravel the glacial histories of the eastern Sierra Nevada. The moraine sequence along Bishop Creek includes well-preserved moraines that have been previously dated using cosmogenic 36Cl surface exposure ages. The goal of this study was to interpret pedogenesis within a soil geomorphic context on these quantitatively dated moraines. Soil development, surface clast cover, and moraine morphology were studied on seven of the moraines, ranging in age from 15 to 170 ka. Older moraines had gentler slopes, broader crests, and decreased surface rock cover. Soils showed weak development across the chronosequence of moraines. Pedogenesis involved slight increases in clay, the formation of clay lamellae, development of a vesicular horizon in a surface layer of aeolian dust, and weathering of surface and subsurface granitic clasts. Soil reddening and structure development were minimal. Soil formation was likely inhibited by the arid to semi-arid climate and intermittent wind and water erosion during the time span of the chronosequence.

Reconstructions of Antarctic topography since the Eocene–Oligocene boundary

Accurate models of past Antarctic ice sheet behaviour require realistic reconstructions of the evolution of bedrock topography. However, other than a preliminary attempt to reconstruct Antarctic topography at the Eocene–Oligocene boundary, the long-term evolution of Antarctica's subglacial topography throughout its glacial history has not previously been quantified. Here, we derive new reconstructions of Antarctic topography for four key time slices in Antarctica's climate and glacial history: the Eocene–Oligocene boundary (ca. 34 Ma), the Oligocene–Miocene boundary (ca. 23 Ma), the mid-Miocene climate transition (ca. 14 Ma), and the mid-Pliocene warm period (ca. 3.5 Ma). To reconstruct past topography, we consider a series of processes including ice sheet loading, volcanism, thermal subsidence, horizontal plate motion, erosion, sedimentation and flexural isostatic adjustment, and validate our models where possible using onshore and offshore geological constraints. Our reconstructions show that the land area of Antarctica situated above sea level was ~25% larger at the Eocene–Oligocene boundary than at the present-day. Offshore sediment records and terrestrial constraints indicate that the incision of deep subglacial topographic troughs around the margin of East Antarctica occurred predominantly in the Oligocene and early Miocene, whereas in West Antarctica erosion and sedimentation rates accelerated after the mid-Miocene. Changes to the topography after the mid-Pliocene were comparatively minor. Our new palaeotopography reconstructions provide a critical boundary condition for models seeking to understand past behaviour of the Antarctic Ice Sheet, and have implications for estimating changes in global ice volume, temperature, and sea level across major Cenozoic climate transitions.

Timing of the local last glacial maximum in Terra Nova Bay, Antarctica defined by cosmogenic dating

The Jangbogo Hills are erratic-covered landforms consisting of a series of benches that are parallel to the length of Campbell Glacier, northern Victoria Land, Antarctica. We sampled 41 erratic cobbles from six benches to reveal the exposure times of glacier erratics using in situ 10Be and 26Al. The erratics from the upper three benches yield exposure ages older than Marine Isotope Stage (MIS) 4, with most exposed since MIS 5. However, the lower three benches exhibit tight clusters of exposure ages that range from MIS 3 to the Holocene. Campbell Glacier underwent rapid downwasting during MIS 5, centered at 98.3 ka from its maximum position at the penultimate glacial maximum (PGM). This downwasting continued throughout the last glacial period, with a potential minor stagnation around a bench (∼90 m asl) between 35.4 and 17.0 ka. Our cosmogenic nuclides surface exposure dating results highlight three important points concerning the glacial history of Terra Nova Bay since the penultimate glacial maximum (PGM) in northern Victoria Land, Antarctica: 1) Campbell Glacier was thicker at the PGM than at the global last glacial maximum (LGM); 2) the local LGM occurred during MIS 4; and 3) the extent of Campbell Glacier during the global LGM (90 m) was much smaller than previously assumed (300–400 m). Hence, the previous view that the local LGM (MIS 4) in Victoria Land, Antarctica was synchronous with the global LGM (MIS 2) should be treated with caution.