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Browsing by Author "Hughes, PD"

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10Be and 26Al exposure history of the highest mountains in Wales: evidence from Snowdon and the Glyders
(International Union for Quaternary Research (INQUA), 2019-07-28) Hughes, PD; Glasser, NF; Fink, D
Cosmogenic 10Be and 26Al exposure ages from samples collected from the mountains of Glyders (1001 m) and from Snowdon (1085 m) in Wales provide new insights into the glacial history of the highest mountains in the British Isles outside of Scotland. Sample elevations range from 598 to 1013 m and taken from centimetre-thick quartz veins on bedrock and also one boulder. The summits of the Glyders are characterised by intensely modified frost-shattered surfaces and have long been recognised as exemplars of mountain summit periglacial activity in the British Isles. However, numerous glacially-transported boulders on the highest ground indicate that ice overran the summits. Bedrock samples at c. 960 m yielded 10Be exposure ages of 72 ka and 153 ka. In addition, a glacially-transported boulder at 985 m gave a 10Be age of 57 ka. This boulder sample is important because it negates issues of inheritance that are possible with bedrock samples and it provides the closest estimate of the timing of ice thinning and the true exposure age of the Glyders summits. All 26Al ages were consistent indicating non-complex histories. These results clearly confirm the Glyder summits were overtopped by the Welsh Ice Cap during marine isotope stage (MIS) 4, when ice in this area was thicker than at the global last glacial maximum (LGM) in MIS 2. The summits were revealed as ice thinned during the transition from MIS 4 to 3. Both the geomorphological evidence and our new cosmogenic ages support recent ice cap modelling predictions that the summits then stood as nunataks above the LGM ice sheet surface in MIS 2. The oldest 10Be (and 26Al) age of ~150 ka from the frost-shattered summit tor displays significant nuclide inheritance and previous work has demonstrated evidence of gibbsite in the summit soils. The wide range in 10Be apparent exposure ages and the evidence of glacially-transported boulders on intensely frost-shattered bedrock suggests erosion of the Glyder summit surfaces largely proceeded by plucking/quarrying rather than abrasion. This would have occurred under cold-based conditions with ice flow dominated by internal deformation rather than sliding. In contrast, at altitudes below 900 m ice-scoured rock surfaces on both the Glyders and neighbouring Snowdon yield exposure ages consistent with deglaciation after the global LGM in MIS 2. Based on these ages and similar results from other summits in North Wales the Welsh Ice Cap rapidly thinned after c. 20 ka leading to a phase of alpine-style glaciation. However, on Snowdon, arête crests yielded very young apparent ages of ~ 5 ka. These young ages reflect continual stripping of the arête rock surfaces through the current interglacial.
36Cl exposure-age chronology of Late Pleistocene glaciations on Mount Tymphi, Pindus Mountains, northwest Greece
(International Union for Quaternary Research (INQUA), 2019-07-27) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM
The mountains of Greece and the wider Balkans were glaciated during the Pleistocene. The most extensive glaciations occurred during the Middle Pleistocene when large ice caps and glaciers formed in several ranges including the Dinaric Alps and the Pindus Mountains. The Late Pleistocene in the Balkans, however, was characterised by smaller ice masses with glaciers restricted to the highest mountains. Nevertheless, these glaciers were important in shaping much of the high mountain landscapes that we see today and they supplied many rivers with outwash sediments. Here we present preliminary results from 36Cl terrestrial cosmogenic nuclide analyses. From samples collected in summer 2017, we have calculated exposure ages from moraine boulders and glaciated bedrock in the uppermost valleys and cirques of Mount Tymphi massif (2497 m) in northwest Greece. We address both a significant geographical gap in Mediterranean glacial chronologies and the temporal gap in the glacial history of this region by targeting the previously undated Late Pleistocene glacial record. Coupled with published U-series ages from lower elevation moraines, this is the first glacial chronology in the east-central Mediterranean based on multiple dating methods. On the southwest side of the massif, 18 exposure ages obtained from 3 moraines in the cirque and mouth of the Laccos Megalon Litharion valley and the mouth of the western cirque of Tsioumako (2155 m), indicate moraine formation between 1700 m and 2050 m a.s.l. during the Late Pleistocene. This complements previous U-series ages obtained from secondary calcites in glacial sediments below 1700 m (and elsewhere in the Balkans), which demonstrate more extensive glaciations dating to the Middle Pleistocene. At ~1430 m a.s.l. in the Laccos cirque on the northeast side of the massif, 6 exposure ages (5 boulders, 1 bedrock) from a pair of end moraines represent the first dates from this side of Mount Tymphi. They suggest small cirque glaciers persisted until at least the end of the Late Pleistocene, facilitated by avalanching snow and shading from the cliffs of Goura (2467 m). Understanding where, when and why glaciers reached their maxima during the last glacial cycle is not only important for understanding the dynamics of the glacial climate in this region, but also for the timing of sediment and meltwater delivery to river systems; the dynamics of Mediterranean refugia; and has implications for understanding the environmental context of nearby Middle and Upper Palaeolithic archaeological records.
Ancient steroids: human faecal signals and environmental data from a Holocene sediment record of the Yagour Plateau, High Atlas, Morocco
(European General Assembly, 2022-05-27) Cornelissen, HL; Lupein, R; Fletcher, WJ; Hughes, PD; Bell, BA; Rhoujjati, A; Ewague, A; Fink, D
The analysis of steroids (stanols and stanols compounds) preserved within Holocene sediment records represents a novel approach to establish past periods of human and herbivore occupation in the Atlas mountains of Morocco. These organic compounds are faecally produced by omnivorous and ruminant mammals; the concentrations and ratios of the compounds are used in this study as proxies for past dynamics of human presence. In this study, stanol analysis is employed in tandem with multiproxy sedimentological, palaeoecological and geochronological data of a lake-margin sediment core to evaluate Holocene human presence around the high-elevation wetland system of the Yagour Plateau, in the High Atlas mountains (31.31°N, 7.60°W, 2460 m.a.s.l.). The site is a vital resource for modern pastoral communities, providing fodder for livestock during seasonal dry periods. Cultural institutions known as Agdals regulate access to this wetland and have been established since early-historic times at least. The Yagour Plateau is well-known for its remarkable abundance of undated petroglyphs, which may relate to the territorial delineation of these Agdals. However, direct dating of archaeological remains is rare and the timing of human presence on the High Atlas rangelands is not well known. Information gained on the dynamics of human presence of remote, high-elevation sites in the High Atlas may be helpful in improving the understanding of the relationships between Holocene climatic, anthropogenic and ecological signals. Here, we present new data from 25 stanol samples spanning the last 13 kyr, complemented by two multiproxy records that include pollen, charcoal and non-pollen palynomorphs. The temporal context of these proxy records is underpinned by high-resolution age-depth radiocarbon chronology. We observe elevated stanol ratios from 6.2 cal ka BP to modern times, likely indicating intermittent human presence on the plateau since the Mid-Holocene. High coprostanol concentrations between 4.9 to 4.0 cal ka BP are similar to modern levels and indicate peak human presence. Faecal biomarkers match well with pollen-based anthropogenic indicators, particularly Plantago pollen abundance. This study supports a significant human presence on the Yagour Plateau from the Mid-Holocene onwards, contributing to the study of long-term human presence and climate dynamics in a sensitive mountain region at the boundary of the Atlantic and Saharan climate systems. © Author(s) 2023. This work is distributed under the Creative Commons Attribution 4.0 License.
The archaeology of overburden: method within the madness at ˇSv´edův Stůl, Czech Republic
(Elsevier, 2021-08-01) Wright, D; Hughes, PD; Skopal, N; Kmošek, M; Way, A; Sullivan, M; Lisá, L; Ricardi, P; Škrdla, P; Nejman, L; Gadd, PS; Nývltová Fišáková, M; Mlejnek, O; Králík, M
In the 19th and early to mid-20th centuries, a rush to better understand the European Palaeolithic led to the substantive removal of deposits from limestone caves. In the 21st century the situation has changed. Many caves are now excavated, leaving behind a human-made environment of diminished cave sediments and large spoil heaps, with the latter now targeted by those searching for artefacts missed during the original excavations. In an age in which archaeologists are increasingly attempting to balance their roles as cultural heritage educators and destroyers, the question remains - how much do we know about the taphonomy of these features? In this paper we report results from the excavation of a large spoil heap outside Švédův Stůl Cave, in the Moravian Karst region of Czech Republic. Results show heterogeneous sediment formation (revealed primarily through their field characteristics and ED-XRF and Itrax geochemical analyses) and patterns in artefact distributions (evident through assessment of Iron Age, Neolithic and modern artefacts) and faunal remains. This allows partial context to be provided for some artefacts and a methodology to be developed for excavation of overburden. © 2021 Elsevier Ltd.
Catastrophic rock avalanches in a glaciated valley of the High Atlas, Morocco: 10Be exposure ages reveal a 4.5 ka seismic event
(The Geological Society of America, 2014-02-03) Hughes, PD; Fink, D; Fletcher, WJ; Hannah, G
Surface modification processes leading to large debris accumulations in high-relief mountain areas are important for understanding landscape evolution, especially in some of Earth’s most active orogens. The Arroumd rock avalanche at the foot of the NW face of Mount Aksoual (3912 m above sea level [masl]) in the Jebel Toubkal area of the High Atlas, Morocco, represents one of the largest mass movement landforms in North Africa. The age and origin of this extensive feature have been contested for over a century. Late Pleistocene moraines are also present in the same valley, adjacent to the avalanche debris. The mean of six 10Be cosmogenic exposure ages shows that a series of catastrophic rock slope failures occurred at 4.5 ± 0.5 ka, while a set of eight exposure ages from two of the three mapped moraines has a far larger spread from 1.5 to 7.5 ka. This suggests that the avalanche events were effective agents in modifying the true surface exposure age of the Pleistocene moraines in the Arroumd valley. This has resulted in similar mean 10Be apparent exposure ages for the preexisting Late Pleistocene moraine surfaces and Holocene catastrophic rock slope failures. Similar rock avalanche deposits are present in other glaciated valleys in the High Atlas. We conclude that the trigger for collapse was seismic activity related to proximity of the major Tizi n’Test fault. These findings have important implications for interpreting and dating glacial landforms in tectonically active settings. © 2020 Geological Society of America
The extent, timing and palaeoclimatic significance of Late-glacial and Holocene snowpatches and glaciers in the Marrakech High Atlas, Morocco
(Copernicus GmbH, 2021-03-19) Bell, BA; Hughes, PD; Fletcher, WJ; Braithwaite, RJ; Cornelissen, HL; Fink, D; Rhoujjati, A
Pleistocene glaciers were extensive in the Marrakech High Atlas, Morocco. Today, semi-permanent snowpatches survive in topoclimatic settings and there is evidence of niche glaciers as recently as the Little Ice Age and early 20th Century. However, little is known about the state of permanent snow and niche glaciers through the Holocene. One hypothesis is that Little Ice Age glaciers were the largest snow and ice masses since the end of the Late-glacial (Younger Dryas 12.9-11.7 ka). Another possibility is that snow and ice expanded to similar or greater extents at other points in the Holocene. To test these hypotheses, moraine boulders have been sampled on moraine successions in the highest parts of the High Atlas, including moraine successions in front of the névé permanent below the north-facing cliffs of Tazaghart (3890 m a.s.l.), a semi-permanent snowpatch that survives many summers today. This site is bounded by prominent moraine ridges with no soil development and no lichens on surface boulders. Several other high-level sites have been targeted and over 40 samples are currently being processed for 10Be and 36Cl exposure dating. Establishing the relative difference in extent and altitude of Late-glacial and the most recent glaciers in the High Atlas is important for understanding landscape and climate evolution in high mountain areas in the subtropics (31ºN). The dated geomorphological records for late-lying snow and glaciers will be compared to high-resolution 14C dated continuous parasequences from sediment cores from marshes at the Yagour Plateau and Oukaïmeden, both high-level sites in the High Atlas (~2700 m a.s.l.). The proximity of these sites (5-30 km, respectively) from the snowpatch/glacier sites will provide an important independent record of environmental change, spanning the Late-glacial and Holocene. This geomorphological record of former glaciers and snowpatches (moraines and pronival ramparts) is inherently fragmentary in time and the continuous core records from these alpine marshes will provide crucial insights into changing moisture conditions over time, which at these altitudes are closely related to the extent and volume of snowpack. The climates associated with perennial snow cover and niche glaciers, and the associated annual snowpack melt, will be quantified using degree-day modelling. This allows melt rates to be predicted and this can be compared against observed modern climate in the High Atlas region. This involves interrogation of existing meteorological datasets from across the High Atlas and the development of algorithms for interpolation and extrapolation to ungauged higher altitudes. Changes in the nature of the cryosphere through time in the High Atlas Mountains is crucial for understanding human activity and socioeconomic development in the wider region. Today, snowmelt from the High Atlas represents the most important ground water recharge used for a wide variety of purposes. Understanding changes in snow conditions, and as a consequence the behaviour of niche glaciers, in the High Atlas through the Holocene has important implications not only for water supply for humans but also for biological refugia and the evolution of cold-adapted flora and fauna.
Extent, timing and paleoclimatic significance of glaciation in the High Atlas, Morocco
(18th INQUA Congress, 2011-07-21) Hughes, PD; Fenton, C; Fink, D; Schnabel, C; Rother, H
Glacial geomorphological mapping, 10Be terrestrial cosmogenic isotope analyses and palaeoglacier-climate modelling in the highest peaks of the Atlas Mountains, Morocco (31.1°N, 7.9°W), provides new and novel data toward understanding the history and evolution of the largest desert region on Earth. The Atlas Mountains display evidence of extensive and multiple Pleistocene glaciations. The largest ice field and valley glaciers formed in the Toubkal massif. Here, the oldest moraines have yielded 10Be ages scattered in the range 74-31 ka. A later phase of glaciation is dated to c. 24 ka. Moraines belonging to a third phase of glaciation has yielded a series of very close exposure ages (within error) at around 12 ka, and falling within the Younger Dryas (12.9-11.7 ka). The glacial record of the High Atlas effectively reflects moisture supply to the north-western Sahara Desert and can provide an indication of shifts between arid and pluvial conditions. The low altitude of the glaciations in all three glacial episodes indicate that climate was not only significantly cooler than today, but also very much wetter. The new evidence on the extent, timing and palaeoclimatic significance of glaciations in this region has major implications for understanding moisture transfer between the North Atlantic Ocean and the Sahara Desert during Pleistocene cold stages. The findings are highly significant for understanding atmospheric circulation during pluvial phases recorded in the Sahara, such as during the African Humid Period at the Pleistocene/Holocene transition (15 to 6 ka). Glacier advance in the High Atlas during this interval provides insight into the seasonal distribution of precipitation and provides valuable insight into the respective roles of moisture supply from the North Atlantic depressions and the West African Monsoon. This in turn then has important bearing on the strengths of meridional vs. zonal circulation at mid-latitudes during pluvial phases. Copyright (c) 2011 INQUA 18
A first 10Be cosmogenic glacial chronology from the High Atlas, Morocco, during the last glacial cycle
(Geophysical Research Abstracts, 2014-04-27) Fink, D; Hughes, PD; Fenton, C
Glacial geomorphological mapping, 10Be cosmogenic exposure ages of 21 erratics from cirque-valley systems and paleo-glacier climate modelling in the High Atlas Mountains, Morocco (31.1°N, 7.9°W), provides new and novel insights as to the history and evolution of the largest desert region on Earth. The Atlas Mountains display evidence of extensive and multiple Late Pleistocene glaciations whose extent is significantly larger than that recognised by previous workers. The largest glaciers formed in the Toubkal massif where we find 3 distinct phases of glacial advances within the last glacial cycle. The oldest moraines occurring at the lowest elevations have yielded eight 10Be ages ranging from 30 to 88 ka. Six of eight samples from moraines at intermediate elevations gave ages of 19 to 25 ka (2 outliers) which correlates well with the global Last Glacial Maximum (ca. 26-21 ka) and the last termination during marine isotope stage 2. Five erratics from the youngest and most elevated moraines yielded a suite of normally distributed exposure ages from 11 to 13 ka which supports a correlation with the northern hemisphere Younger Dryas (12.9-11.7 ka). The glacial record of the High Atlas effectively reflects moisture supply to the north-western Sahara Desert and can provide an indication of shifts between arid and pluvial conditions. The plaeo equilibrium line altitudes (ELA) of these three glacier phases was more than 1000 m lower than the predicted ELA based on today’s temperatures. Glacier-climate modelling indicates that for each of these glacier phases climate was not only significantly cooler than today, but also much wetter. The new evidence on the extent, timing and palaeoclimatic significance of glaciations in this region has major implications for understanding moisture transfer between the North Atlantic Ocean and the Sahara Desert during Pleistocene cold stages. © Author(s) 2014, CC Attribution 3.0 License.
Late Pleistocene deglaciation history of the SW British Isles: new evidence from Lundy and the outer Bristol Channel
(International Union for Quaternary Research (INQUA), 2019-07-27) Rolfe, C; Hughes, PD; Brown, T; Bateman, M; Gibbard, P; Fink, D
The SW British Isles was glaciated by the British-Irish Ice Sheet during the Late Pleistocene. Glacial deposits are widely preserved in the Bristol Channel and are revealed in boreholes and geophysical data. Lundy, an island in the Outer Bristol Channel, displays unique terrestrial evidence of glaciation in the Outer Bristol Channel. The evidence is dominated by erosional evidence of ice-scouring, although there are wide spreads of erratic cobbles and pebbles several of which contain evidence of striae and faceting. In addition, subsurface thick silt-clay deposits are common on the island with clay mineralogy indicating limited weathering, in contrast to occasional pockets of strongly weathered granite (growan). These deposits are interpreted as subglacial in origin. Offshore of Lundy, especially to the E and NE, geophysical data reveals the presence of thick glacial deposits and dense fields of boulders. This suggests that an ice limit occurred between Lundy and the mainland. This allowed the drainage of the proto-Severn to drain between this ice limit and the mainland in Devon, and the course of this palaeochannel can be traced in bathmetry and geophysical survey data. Periglacial activity after deglaciation is recorded by the presence of coversands, loess, ventifacts, scree slopes and associated colluvial deposits. Luminescence ages from colluvial sands on Lundy date to 24-26 ka indicating that this island was deglaciated by marine isotope stage (MIS) 2. This is consistent with deglaciation and exposure of the island in MIS 3 following glaciation in MIS 4 or possibly earlier. Previously obtained exposure ages from ice-scoured bedrock surfaces have been recalculated using the most recent production rate models and support this interpretation. In addition, a new programme of cosmogenic exposure dating of glacially-transported boulders and displaced tors will further test the previously obtained exposure age data from glaciated bedrock surfaces. In contrast to other weathered granite surfaces in the British Isles, Lundy has not experienced a prolonged weathering history through multiple glacial cycles. Whilst the precise timing of deglaciation is undergoing further testing, the current evidence overwhelmingly indicates that Lundy was eroded by an ice sheet during the Late Pleistocene. Morphometric analysis of weathering pits in the ice-moulded granite bedrock on Lundy supports this exposure history as do the OSL ages from sands overlying the bedrock surfaces. Evidence from elsewhere around the Celtic Sea indicates that the glaciation of Lundy most likely occurred in MIS 4 with ice retreating in MIS 3. However, during MIS 2 ice reached to the continental shelf in the Celtic Sea. This apparent paradox may be explained by a highly mobile Irish Sea Ice Stream which changed its configuration in response to fluctuating marine incursions in MIS 3 before exploiting the exposed continental shelf to the southwest during MIS 2. ©The Authors.
Late Pleistocene glacial chronologies in the Balkans: new 36Cl exposure-age dating from Montenegro and Greece
(Copernicus GmbH, 2020-05-04) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM; Tomkins, M
The timing and extent of mountain glaciation during the Late Pleistocene shows considerable variability around the world. Identifying the nature and timing of glaciation is important for understanding landscape evolution and changing climatic conditions (precipitation and temperature). In the Balkans, glaciers were actually larger during the Middle Pleistocene when large ice caps formed in several mountain ranges including the Dinaric Alps, Montenegro, and the Pindus Mountains, Greece. Glaciations younger than Marine Isotope Stage 6 were characterised by smaller ice masses with glaciers mainly restricted to the highest mountains. The behaviour of Late Pleistocene glaciers in this region influenced the timing of sediment and meltwater delivery to river systems; the migration of modern humans across Europe; and the dynamics of biological refugia. However, dating control is limited for Late Pleistocene glaciers in the Balkans. Here we report new in-situ 36Cl terrestrial cosmogenic nuclide exposure ages from moraine boulders sampled in the Velika Kalica valley, in the Durmitor massif, Montenegro. This valley was targeted because it contains the Debeli Namet glacier - the last remaining glacier in Montenegro. We have sampled 25 limestone boulders from 5 moraines situated down-valley of the current glacier at altitudes between 1650–2000 m. AgCl targets for 36Cl assay were prepared at The University of Manchester and 36Cl concentrations were measured on the SIRIUS 6MV accelerator at the Centre for Accelerator Science at the Australian Nuclear Science and Technology Organisation. At the last local glacial maximum, the Debeli Namet glacier extended almost 3 km beyond its current position. These 36Cl analyses are part of a wider regional Mediterranean study, totalling >50 new exposure ages, which also includes Mount Tymphi in the Pindus Mountains, NW Greece. The project will address both a significant spatial and temporal gap in Mediterranean glacial chronologies by targeting the hitherto undated Late Pleistocene glacial record. The work in Montenegro will also shed light on the nature of Holocene glaciation in the Balkans. © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 Licence.
Late Pleistocene glaciers and climate in the High Atlas, North Africa
(GeoScienceWorld, 2020-04-07) Hughes, PD; Fink, D; Fletcher, WJ
Extensive glaciers covered the High Atlas mountains in Morocco during the late Pleistocene. On the northern escarpments of the Marrakech High Atlas, a series of cirques perched at ~3000–3500 m above sea level (asl) fed their valley glaciers that, in some cases, extended to as low as 2000 m asl. Cosmogenic exposure dating with 10Be and 36Cl has shown that at least three phases of glaciation are preserved in glacial deposits over the last glacial cycle at 50, 22, and 12 ka, which appear to correlate with marine isotope stage (MIS) 3, the global Last Glacial Maximum (LGM), and the Younger Dryas chronozone. This geochronological framework is sufficiently robust to allow for time-constrained glacier-climate reconstructions. The glaciers associated with these three phases of advance had equilibrium line altitudes (ELAs) of 2761 m asl (ca. 50 ka), 2919 m asl (ca. 22 ka), and 3213 m asl (ca. 12 ka). Glacier-climate modeling suggests that all of these phases were driven by both colder temperatures and wetter conditions than today. The dominant moisture supply to these glaciers in all phases would have been sourced from Atlantic depressions. The influence of an extended and enhanced West African monsoon on glacier development during African Humid Periods is unlikely to have been a significant influence on glacier dynamics. The climate conditions associated with the three glacier phases indicate sustained moisture supply to the highest mountain areas when records from other areas, such as the Middle Atlas lakes and marine sediment cores offshore, indicate marked aridity. © 2020 The Geological Society of America
Late Pleistocene glaciers in Greece: a new 36Cl chronology
(Elsevier, 2020-10-01) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM
Glaciers formed in the highest mountains of Greece during the Late Pleistocene, but the timing of glacier maxima is poorly understood. This paper presents 27 36Cl terrestrial cosmogenic nuclide exposure ages from glacial boulders on Mount Tymphi (2497 m a.s.l., 40oN) in Epirus, northwest Greece. These ages address both a significant geographical gap in Mediterranean glacial chronologies and a temporal gap in the glacial history of this region by targeting the previously undated Late Pleistocene record. Late Pleistocene glaciers were restricted to the cirques and upper valleys of Mount Tymphi. Terminal and lateral moraines between 1700 m and 2050 m a.s.l. mark the extent of Late Pleistocene glaciers on the southern side of Mount Tymphi. Moraines marking the maximum extent of Late Pleistocene glaciation date to 29.0 ± 3.0 ka and 25.7 ± 2.6 ka, taking the oldest ages as most representative of moraine emplacement. Glaciers had retreated to the high cirques by 24.5 ± 2.4 ka during Heinrich Stadial 2. Rock glaciers formed under cold and drier conditions during this period of glacier retreat. This 36Cl dataset complements published U-series ages from secondary calcites in glacial sediments below 1700 m elevation, which demonstrate more extensive Middle Pleistocene glaciations in MIS 6 and MIS 12. A Late Pleistocene glacier maxima on Mount Tymphi at 25.7–29 ka is in good agreement with well-preserved outwash sediments dating to 24–28 ka in the Voidomatis River record downstream and is consistent with the Ioaninna basin pollen record indicating cool and wet conditions, most favourable for glacier growth, at 25–30 ka. Crown Copyright © 2020 Published by Elsevier Ltd.
Late Pleistocene glaciers to present-day snowpatches: a review and research recommendations for the Marrakech High Atlas
(Springer Nature, 2020-05-08) Hughes, PD; Fletcher, WJ; Bell, BA; Braithwaite, RJ; Cornelissen, HL; Fink, D; Rhoujjati, A
There are no glaciers today in the High Atlas, Morocco. However, there is evidence that niche glaciers and late-lying snowpatches in the High Atlas were present as recently as the last century and there are at least four sites where snowpatches appear to survive some summer seasons today. Many other sites also support non-perennial late-lying snow below steep shaded north and northeast-facing cliffs at altitudes > 3100 m. Coarse sediment ridges interpreted as moraines or pronival ramparts enclose most of these snowpatches. These landforms most likely record the positions of former niche glaciers and late-lying snowpatches in the Little Ice Age. The niche glaciers and late-lying snowpatches survived below the regional equilibrium line altitude because of strong local topoclimatic controls. In addition to strong shading, many of the current late-lying snowpatches are fed by long deep gullies which funnel avalanching snow from the cirque backwalls. The disappearance of many perennial snowpatches in the last few decades coincides with a strong trend towards warmer summer air temperatures since the 1970s (> 2 °C). However, inter-annual changes in snowpack mass balance are affected by very large variations (> 400% variability) in winter precipitation. A new research programme is underway investigating the history of late-lying snow and cirque glaciers in the High Atlas. A particular focus of this research is to utilise geomorphological and geochronological evidence to understand fluctuations in snow and ice through the Holocene and link this to continuous records of environmental change in the High Atlas region. © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License.
Palynological evidence from a sub-alpine marsh of enhanced Little Ice Age snowpack in the Marrakech High Atlas, North Africa
(Springer Nature, 2021-05-18) Bell, BA; Fletcher, WJ; Hughes, PD; Cornelissen, HL; Fink, D; Rhoujjati, A
The grazing lands of the High Atlas are vulnerable to climate change and the decline of traditional management practices. However, prior to the mid-20th century, there is little information to examine historical environmental change and resilience to past climate variability. Here, we present a new pollen, non-pollen palynomorph (NPP) and microcharcoal record from a sub-alpine marsh (pozzine) at Oukaïmeden, located in the Marrakech High Atlas, Morocco. The record reveals a history of grazing impacts with diverse non-arboreal pollen assemblages dominant throughout the record as well as recurrent shifts between wetter and drier conditions. A large suite of radiocarbon dates (n = 22) constrains the deposit to the last ~ 1,000 years although multiple reversed ages preclude development of a robust age-depth model for all intervals. Between relatively dry conditions during the Medieval period and in the 20th century, intervening wet conditions are observed, which we interpret as a locally enhanced snowpack during the Little Ice Age. Hydrological fluctuations evidenced by wetland pollen and NPPs are possibly associated with centennial-scale precipitation variability evidenced in regional speleothem records. The pollen record reveals an herbaceous grassland flora resilient against climatic fluctuations through the last millennium, possibly supported by sustainable collective management practices (agdal), with grazing indicators suggesting a flourishing pastoral economy. However, during the 20th century, floristic changes and increases in charcoal accumulation point to a decline in management practices, diversification of land-use (including afforestation) and intensification of human activity. © The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License.
Rapid environmental changes of the Late-glacial and Holocene in a sediment record from the Yagour Plateau, High Atlas, Morocco
(Copernicus GmbH, 2021-04-19) Cornelissen, HL; Fletcher, WJ; Hughes, PD; Bell, BA; Rhoujjati, A; Ewague, A; Fink, D
The High Atlas mountains of Morocco represent a climatological frontier between the Atlantic and Saharan realms as well as a site of major Pleistocene glacier expansion. However, Late-glacial and Holocene environmental change is weakly constrained, leaving open questions about the influence of high- and low-latitude climate forcing and the expression of North Atlantic rapid climate changes. High elevation lakes on the sandstone plateaux of the High Atlas have been recognised as archives of Late Quaternary environmental change but remain little explored. Here, we present findings from new sedimentological, palaeoecological and geochronological investigation of a lake marginal sediment core recovered in June 2019 from the Ifard Lake located on the Yagour Plateau. The plateau is a distinctive sandstone upland located to the southeast of Marrakech in the High Atlas (31.31°N, 7.60°W, 2460 m.a.s.l.). The lake is located within a small, perched catchment area, offering an opportunity to isolate catchment effects and investigate atmospheric deposition of organic and inorganic tracers of past environmental change. The core stratigraphy reveals shifts between inorganic sands and lake muds with fluctuations in grain sizes and sediment reddening. The differences in these stratigraphic layers are most likely linked to hydrological changes associated with changing snowpack conditions and local catchment erosion dynamics. The core chronology is well-constrained by AMS radiocarbon dating of pollen concentrates, with the core sequence spanning the last ca. 14,000 years. The driving agents of environmental change on the plateau are inferred using a multiproxy approach, combining sedimentological analyses (particle-size by laser granulometry, elemental analysis by core-scanning XRF, C/H/N/S analysis), palynology (pollen, spores, non-pollen palynomorphs) and contiguous macrocharcoal analysis. High-resolution, well-constrained proxies therefore permit novel regional insights into past environmental and climatic changes at centennial timescales. A prime working hypothesis is that the imprint of wider palaeoclimatic changes of both the North Atlantic region and Saharan realm (African Humid Period, AHP) is detected at this site. Key climatic periods such as the Younger Dryas and multi-centennial cooling episodes around 8000 and 4200 years ago are distinctly characterised in the record by finer grain sizes and the accumulation of pollen-rich material and charcoal. These responses are thought to be governed by regional climate forcing and local snowmelt moisture supply to the Yagour Plateau. An increase in fine sediment supply, magnetic susceptibility and Fe content in the upper part of the core may be related to enhanced atmospheric dust deposition following the end of the AHP. Whilst taking anthropological influences on the local environment into account, this study will contribute to the detection of long-term and rapid climate changes in a sensitive mountain region at the rim of the Atlantic and Saharan climate systems.
Rapid thinning of the Welsh Ice Cap at 20–19 ka Based on 10Be Ages
(Cambridge University Press, 2017-01-20) Hughes, PD; Glasser, NF; Fink, D
New 10Be ages from the summits of three mountain areas of North Wales reveal a very similar exposure timing as the Welsh Ice Cap thinned after the global Last Glacial Maximum. Eight bedrock and one boulder sample gave a combined arithmetic mean exposure age of 19.08 ± 0.80 ka (4.2%, 1σ). Similar exposure ages over a 320 m vertical range (824 to 581 m altitude) show that ice cap thinning was very rapid and spatially uniform. Using the same production rate and scaling scheme, we recalculated six published 10Be exposure ages from the nearby Arans, which also covered a similar elevation range from 608 to 901 m and obtained an arithmetic mean of 19.41 ± 1.45 ka (7.5%, 1σ). The average exposure age of all 15 accepted deglaciation ages is 19.21 ± 1.07 (5.6%, 1σ). The complete dataset from North Wales provides very strong evidence indicating that these summits became exposed as nunataks at 20–19 ka. This result provides important insight to the magnitude of ice surface lowering and behavior of the Welsh Ice Cap during the last deglaciation that can be compared to other ice masses that made up the British-Irish Ice Sheet. © University of Washington
A tale of two bogs - new 10Be production rates from UK and NZ calibrated by basal 14C ages
(Copernicus GmbH, 2021-04-19) Fink, D; Hughes, PD; Fülöp, RH; Wilcken, KM; Adams, PM; Craig, W; Shulmeister, J; Fujioka, T; Ryan, P
Cosmogenic production rates (PRs) are the essential conversion factor between AMS cosmogenic concentrations and absolute exposure ages. The accuracy of cosmogenic glacial chronologies and reliability in their comparison to other paleoclimate systems is largely contingent on the precision and accuracy of the adopted production rate. This is particularly critical in determining past glacial geochronologies at the scale of millennial temporal resolution. Most PR calibrations are carried out at deglaciation sites where radiocarbon provides the independent chronometric control usually based on 14C ages in basal sediments or varves from lake or bog cores which is assumed to represent the minimum age for glacial retreat. Under these conditions and hence provide PRs as maximum values. Given that today most AMS facilities can deliver 10-Be, 26-Al and 36-Cl data with total analytical errors less than 2% ( for 10 ka exposure), the precision of a PR remains largely dependent on the error in the independent chronology and accuracy of AMS standards. The history over the past 20 years of the ever-decreasing value of SLHL 10-Be cosmogenic spallation PRs from initial estimates of about 7 atoms/g/a to the current ‘accepted‘ (global average) values of ~4 atoms/g/a, is an interesting story in itself and demonstrates the complexity in such determinations. Over the past few years new web-based calculators are now available to calculate uniformly new production rates from either new data or combinations of any set of published data (CRONUS-Earth, CRONUS-UW, CosmoCalc, ICE-D, CREp). This delivers a means by which new production rates can be seamlessly integrated and compared using identical constants, methods and statistics that were used to generate (currently accepted) global average or regional production rates. For the British Isles, there are a number of 10-Be reference sites that give PRs (Lm scheme) between 3.89±3% atoms/g/a (Putnam, QG, v50, 2019) to 4.20±1% atoms/g/a (Small, JQS, v30, 2015) which convert to 3.95 and 4.28, respectively, using datasets in the ICE-D calculator). This difference in 10-Be spallation PRs has recently raised some debate and challenges for the timing of the local-LGM and demise of the British Ice Sheet. This work provides a new British Isles site specific 10Be PR from the Arenig Mountains in North Wales where radiocarbon dating of basal sediments from a bog core associated with a series of nearby cirque moraines provides independent age control. Similarly in the South Island of New Zealand, the current accepted 10Be PR is 3.76±2% (Putnam, QG 2009; converts to 3.94±1% using ICE-D) and is the only available PR that is used for these southern hemispheric glacial sites. This work provides a new Australasian site specific 10Be PR from Arthurs Pass retreat moraines where radiocarbon dating of basal sediments from three cores extracted from a bog impounded by the moraine provides independent age control.
The timing of deglaciation from mountain summits to cirques in Wales: 10Be and 26Al exposure dates from Cadair Idris
(Copernicus GmbH, 2021-04-19) Hughes, PD; Glasser, NF; Fink, D; Dortch, J; Fülöp, RH; Wilcken, KM; Fujioka, T
Cosmogenic 10Be and 26Al exposure ages from 20 erratic samples collected from Cadair Idris (893 m), a mountain in southern Snowdonia, Wales, provide evidence for the timing of deglaciation from summits to cirques at the end of the Late Pleistocene. The summit of the mountain is characterised by intensely modified frost-shattered surfaces that have long been identified as a representing a former nunatak. Numerous glacially-transported quartz boulders on the highest ground indicate that ice overran the summit at some point in the Pleistocene. Two quartz boulders, one with preserved striations, sampled at c. 856 m near the summit of Cadair Idris yielded consistent 10Be and 26Al paired exposure ages of 75 ka to 60 ka (using anuhigh-latitude sea level 10Be spallation production rate of 4.20 at/g/y, scaled by the Lal/Stone scheme). A glacially polished bedrock quartzite outcrop at 735 m gave an age of 17.5 ka. Immediately below this, cirque and down-valley recessional moraine ages, covering an elevation of 480 m to 350 m ranged from 10 to 15 ka respectively. These results confirm that Cadair Idris was overridden by the Welsh Ice Cap during marine isotope stage (MIS) 4, when ice was thicker than at the global last glacial maximum (LGM) in MIS 2. This is consistent with findings from northern Snowdonia. The highest Welsh summits, including Cadair Idris, emerged above a thinning Welsh Ice Cap (British Irish Ice Sheet) during the transition from MIS 4 to 3. The summit area above ~800 m then stood as nunataks above the LGM ice sheet surface in MIS 2. The Welsh Ice Cap then rapidly thinned over Cadair Idris at ~20-17 ka based on ages from high-level ice-moulded bedrockThis is supported by more new ages from high-level paired erratics and bedrock samples on several other mountains throughout Snowdonia, leading to a phase of alpine-style deglaciation. Valley glaciers initiated their retreat up-valley from ~17 to 14 ka after Heinrich Event 1. A later phase of glacier stabilisation or still stand formation produced classic cirque moraines near the rim of a present cirque lake basin (480 m elevation) yielding 10Be ages of 13-10 ka during the Younger Dryas.
Timing of Pleistocene glaciations in the High Atlas, Morocco: New 10Be and 36Cl exposure ages
(Elsevier, 2018-01-15) Hughes, PD; Fink, D; Rodés, A; Fenton, CR; Fujioka, T
This paper presents data from 42 new samples yielding Late Pleistocene cosmogenic 10Be and 36Cl exposure ages of moraine boulders across a series of glaciated valleys in the Toubkal Massif (4167 m a.s.l.), High Atlas, Morocco. This represents the first comprehensive Pleistocene glacial chronology in North Africa and one of the largest datasets from the Mediterranean region. The timing of these glacier advances has major implications for understanding the influence of Atlantic depressions on moisture supply to North Africa and the Mediterranean basin during the Pleistocene. The oldest and lowest moraines which span elevations from ∼1900 to 2400 m a.s.l. indicate that the maximum glacier advance occurred from MIS 5 to 3 with a combined mean 10Be and 36Cl age of 50.2 ± 19.5 ka (1 SD; n = 12, 7 outliers). The next moraine units up-valley at higher elevations (∼2200–2600 m a.s.l.) yielded exposure ages close to the global Last Glacial Maximum (LGM) with a combined mean 10Be and 36Cl age of 22.0 ± 4.9 ka (1 SD; n = 9, 7 outliers). The youngest exposure ages are from moraines that were emplaced during the Younger Dryas with a combined mean 10Be and 36Cl age of 12.3 ± 0.9 ka (1 SD; n = 7, no outliers) and are found in cirques at the highest elevations ranging from ∼2900 to 3300 m a.s.l. From moraines predating the Younger Dryas, a large number of young outliers are spread evenly between 6 and 13 ka suggesting a continuing process of exhumation or repositioning of boulders during the early to mid-Holocene. This attests to active seismic processes and possibly intense erosion during this period. © 2017 Elsevier Ltd.
Yet another in-situ cosmogenic 10-Be local production rate for the British Isles : Llyn Arenig Fach, North Wales
(Copernicus GmbH, 2020-05-04) Fink, D; Hughes, PD; Fülöp, RH; Wilcken, KM; Adams, P; Ryan, P
Cosmogenic production rates (PRs) are the essential conversion factor between AMS cosmogenic concentrations and absolute exposure ages. The accuracy of cosmogenic glacial chronologies and reliability in their comparison to other plaeoclimate systems is largely contingent on the precision and accuracy of the adopted production rate. This is particularly critical in determining past glacial geochronologies at the scale of millennial temporal resolution. Most PR calibrations are carried out at deglaciation sites where radiocarbon provides the independent chronometric control usually based on calibrated 14C ages in basal sediments or varves from lake or bog cores which is assumed to represent the minimum age for glacial retreat. Under these conditions PRs should be considered as maximum-limiting values. Given that today most AMS facilities can deliver 10-Be, 26-Al and 36-Cl data with analytical errors less than 2%, the accuracy of a PR for a given scaling method (ie transfer function of the site-specific production rate to a reference sea-level high latitude (SLHL) PR) remains largely dependent on the error in the independent chronology and accuracy of AMS standards. The history over the past 20 years of the ever-changing value of SLHL 10-Be cosmogenic spallation PRs with a continual decreasing value from initial estimates of about 7 atoms/g/a to the current ‘accepted ‘ value of ~4 atoms/g/a, is an interesting story in itself and demonstrates the complexity in such determinations. Today there are both global (average) SLHL PRs and also regional-specific PR values (referenced to SLHL). For the British Isles, there are a number of 10-Be ‘British Isles’ choices that, for the Lm scaling scheme, range between 3.92±0.11 atoms/g/a (Putnam et al., QG, v50, 2019) to 4.41±0.25 atoms/g/a (Small et al., JQS, v30, 2015). This range in 10-Be spallation PRs has recently raised some debate and challenges for the assumed extent and timing of the local-LGM and demise of the British Ice Sheet. This work provides a new British Isles site specific 10-Be PR from the Arenig Mountains in North Wales. We have measured 10-Be concentrations in 13 selected moraine boulders that are tentatively mapped as outer and inner Younger Dryas deglacial deposits hugging a cirque lake, Llyn Arenig Fach, just below the head wall at Arenig Fach. Radiocarbon dating of basal sediments from a number of intermorainal core bogs has provided independent age control. We will present our results and compare them to the current collection of other British Isles 10-Be production rates. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 Licence.

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