Major Retreat Research Articles

Lessons learned from shallow subglacial bedrock drilling campaigns in Antarctica

Abstract We review successes and challenges from five recent subglacial bedrock drilling campaigns intended to find evidence for Antarctic Ice Sheet retreat during warm periods in the geologic past. Insights into times when the polar ice sheets were smaller than present serve as guiding information for modeling efforts that aim to predict the rate and magnitude of future sea level rise that would accompany major retreat of the Antarctic Ice Sheet. One method to provide direct evidence for the timing of deglaciations and minimum extent of prior ice sheets is to extract subglacial bedrock cores for cosmogenic nuclide analysis from beneath the modern ice sheet surface. Here we summarize the lessons learned from five field seasons tasked with obtaining bedrock cores from shallow depths (<120 m beneath ice surface) across West Antarctica since 2016. We focus our findings on drilling efforts and technology and geophysical surveys with ground-penetrating radar. Shallow subglacial drilling provides a high risk, high reward means to test for past instabilities of the Antarctic Ice Sheet, and we highlight key challenges and solutions to increase the likelihood of success for future subglacial drilling efforts in polar regions.

Variations in biophysical characteristics of mangroves along retreating and advancing shorelines

Mangrove shoreline retreat or advance is a natural process in a mangrove delta. However, due to various natural and anthropogenic stressors, mangrove shoreline retreat is the second largest cause of mangrove loss globally. It is important to understand the scale at which mangrove shoreline changes are causing biophysical changes along the mangrove shorelines and, in turn, understand if certain biophysical characteristics can explain the changes along the shoreline. This will help identify the response of mangroves to shoreline changes. Videography and spatial mapping were used to study temporarily and permanently changing mangrove shorelines in the Sundarbans, the largest mangrove forest in the world (~10,000 km2), located in India and Bangladesh. Data was collected along a ~ 239 km shoreline at 54 sites. 36.4 % of all the studied shorelines were experiencing major retreat, 63.8 % and 27.2 % of all (major and minor) retreating areas had 1–25 % and > 25 % dead trees. The biophysical characteristics statistically (P < 0.0001) associated with retreating mangrove shorelines were – cliff-type shoreline profiles, number of dead trees, and absence of stream and grass, with shoreline profiles as the strongest predictor of shoreline retreat. Moreover, 68.7 % and 73 % of historically retreating shorelines had a cliff-type shoreline profile and Excoecaria agallocha as the dominating species, respectively. Moreover, due to the strong correlation between historical changes and current shoreline types, it was concluded that characteristics along the shoreline are partly a product of historical shoreline transitions. Thus, the present status of the shoreline can not only predict the history of the shoreline but can also give insights into the future biophysical changes in the mangrove forests.

Long‐term drivers of shoreline change over two centuries on a headland‐embayment beach

AbstractShoreline evolution over the last two centuries was analysed for Dundrum Bay, Co. Down, Northern Ireland, using historical and recent shoreline datasets from 1833 to 2020. The area of interest comprises two sandy beaches and vegetated coastal dune fields, Newcastle–Murlough and Ballykinler, separated by an inlet channel which connects the inner with the outer bay. Twenty‐four temporal shorelines were extracted, and a quantitative assessment of their positional uncertainty was performed. This was combined with analysis of foredune volume variations by applying the Structure‐from‐Motion‐Multi‐View‐Stereo technique to 1963 aerial photography and comparing it with a 2014 Light Detection And Ranging (LiDAR) dataset to better inform on links between the sediment dynamics and the observed shoreline changes. Storm events were identified using recorded extreme water levels (EWLs) (1901–2020) and hindcasted wave data (1948–2020). In the first 87 years, the shoreline was largely stable, and change was focused at the inlet area. In the 20th century, localised retreat characterised the western (Newcastle–Murlough) sector, whereas the eastern sector (Ballykinler) experienced general shoreline advance. The rate and extent of shoreline retreat in the western sector increased post‐1997 in concert with accelerated accretion at Ballykinler. The strongest erosional episodes were recorded in 1920–1951, 1997–2005, and 2012–2014. Although no direct link was established between single storms and shoreline retreat rates, the three major retreat periods coincided with several consecutive EWLs or EWLs with a return period greater than 100 years. These were generated by storm directions ranging from south to southwest. The long‐term pattern of shoreline change points to a complex coastal system that is still evolving.

Chronology of the Bayo River valley deglaciation and implications for the Late Pleistocene Atlantic-to-Pacific drainage reversal of the General Carrera-Buenos Aires palaeolake, Patagonia-Chile

We present a study on the glacial and paraglacial geomorphology of a Patagonian Cordillera Valley that is key to understanding evolution of the great lakes of Patagonia. 10Be cosmogenic nuclide exposure ages of ice-moulded surfaces from the Bayo River Valley confirm that the valley became ice-free before 13.4-14.2 ka. This valley constituted the first outlet of the Chelenko Lake, precursor of the General Carrera-Buenos Aires Lake (GCBAL), toward the Pacific Ocean. This age constrains the timing of the lake drainage reversal from the Atlantic Ocean to the Pacific Ocean. Alluvial fans and terrace levels recognized in the eastern segment of the valley at the same altitude as terrace levels observed in the GCBAL basin confirm that the Bayo Pass controlled the elevation of the lake once the drainage reversed to Pacific Ocean. 10Be cosmogenic nuclide exposure ages also confirm that the maximum advance of the Exploradores Glacier since its major retreat &gt;13.4-14.2 ka ago occurred during the Little Ice Age, the last remnant of glacial drift in these valleys.

Modelled dynamic retreat of Kangerlussuaq Glacier, East Greenland, strongly influenced by the consecutive absence of an ice mélange in Kangerlussuaq Fjord

AbstractMass loss at the Greenland Ice Sheet is influenced by atmospheric processes controlling its surface mass balance, and by submarine melt and calving where glaciers terminate in fjords. There, an ice mélange – a composite matrix of calved ice bergs and sea ice – may provide a buttressing force on a glacier terminus and control terminus dynamics. Kangerlussuaq Glacier is a major outlet of the Greenland Ice Sheet, for which recent major retreat events in 2004/2005 and 2016–2018 coincided with the absence of an ice mélange in Kangerlussuaq Fjord. To better understand the response of Kangerlussuaq Glacier to climatic and oceanic drivers, a 2D flowline model is employed. Results indicate that an ice mélange buttressing force exerts a major control on calving frequency and rapid retreat. When an ice mélange forms in Kangerlussuaq Fjord, it provides stabilising forces and conditions favourable for winter terminus re-advance. When it fails to form during consecutive years, model results indicate that Kangerlussuaq Glacier is primed to retreat into the large overdeepenings in Kangerlussuaq Fjord, and to terminus positions more than 30 km farther inland, implying that excessive mass loss from Kangerlussuaq Glacier by the year 2065 cannot be excluded.

Projected shifts in K&amp;ouml;ppen climate zones over China and its national ecological security shelter zones

<p indent="0mm">Based on a set of five regional climate model 21st century climate change simulations, this study assesses future changes in Köppen-Trewartha climate types in China and its five national ecological security shelter zones. The regional climate model, the Abdus Salam International Centre for Theoretical Physics (ICTP) regional climate model RegCM4, is driven by five different global climate models, CSIRO-Mk3-6-0, EC-EARTH, HadGEM2-ES, MPI-ESM-MR and NorESM1-M, at a grid spacing of <sc>25 km</sc> under the representative concentration pathway RCP4.5. These global climate models were selected because of their high horizontal resolution and their good performance in reproducing temperature and precipitation over China. The model configuration used was customized for better performance over China. Bias correction was applied to the simulated temperature and precipitation before calculating the climate types. By the end of the 21st century (2069–2098), the annual mean temperature over China is projected to increase by 2.4°C relatives to the present day (1981–2010) annual mean temperature, with the greatest warming (&gt; <sc>2.8°C)</sc> occurring in the Three Rivers Headwaters region. The annual mean precipitation change shows a general increase in most parts of China, except for a slight decrease (&lt; 7%) in southwestern China. The increase is more pronounced over northwestern China. The distribution of climate types was well reproduced by the simulations. A subtropical humid (Cr) climate mainly covers the regions south of the Yangtze River over eastern China. Southwestern China is dominated by a subtropical winter dry (Cw) climate. The Tibetan Plateau is mostly described as tundra (FT) and arid (type B) climate. Dry arid (BW) and semiarid (BS) climates cover most of the northern regions of 35°N except over northeastern China, where temperate continental (Dc) and subarctic continental (Ec) climates exist. Compared to the present-day climates, a change of 22% in the climate types is projected to occur over the whole Chinese territory by the end of the 21st century. The changes are most significant over the Tibetan Plateau and along the climate transition zone of the Qinling Mountains-Huaihe River over China, with a dominant retreat of FT due to the profound warming and an expansion of BS and Cw being projected for the former, and a replacement of temperature oceanic (Do) by Cw being projected for the latter. Over northeastern China, the main projected change in the climate types is the replacement of Ec by Dc. Tropical wet-dry (Aw) climates will occur over all of Hainan Island. The analysis showed that most changes in climate types are driven by temperature rather than precipitation. For the national shelter zones, climate types will change by 24% over all the areas. Profound changes of ~40% will occur in the shelter zones of the Qinghai-Tibet Plateau and the Sichuan-Yunnan-Loess Plateau, followed by those in the northeastern forest. More specifically, over the Qinghai-Tibet Plateau, the replacement of FT by subarctic oceanic (Eo), BS, Ec, and Dc climates is projected to occur. While FT (62%) and BS (26%) dominate this region currently day, BS (38%) and FT (24%) will account for a greater proportion of the region by the end of the 21st century. The change in climate types on the Sichuan-Yunnan-Loess Plateau is characterized by the expansion of Cw and BS and a loss of FT. Replacement of Ec by Dc is projected in the northeastern forest shelter zone, indicating a major retreat of subarctic coniferous forest there. Greater ecological vulnerability and risks in the future under climate change are expected in the zones. Generally, the changes are in good agreement among the individual simulations, indicating a small uncertainty in the projections.

Evidence for a Highly Dynamic West Antarctic Ice Sheet During the Pliocene

AbstractMajor ice loss in the Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) is hypothesized to have triggered ice sheet collapses during past warm periods such as those in the Pliocene. International Ocean Discovery Program (IODP) Expedition 379 recovered continuous late Miocene to Holocene sediments from a sediment drift on the continental rise, allowing assessment of sedimentation processes in response to climate cycles and trends since the late Miocene. Via seismic correlation to the shelf, we interpret massive prograding sequences that extended the outer shelf by 80 km during the Pliocene through frequent advances of grounded ice. Buried grounding zone wedges indicate prolonged periods of ice‐sheet retreat, or even collapse, during an extended mid‐Pliocene warm period from ∼4.2–3.2 Ma inferred from Expedition 379 records. These results indicate that the WAIS was highly dynamic during the Pliocene and major retreat events may have occurred along the Amundsen Sea margin.

Late Quaternary high-resolution seismic stratigraphy and core-based paleoenvironmental reconstructions in Ona Basin, southwestern Scotia Sea (Antarctica)

The variability of sedimentation patterns and processes driven by late Quaternary glacial-interglacial paleoclimatic and paleoceanographic changes are investigated in Ona Basin, southwestern Scotia Sea. The interest of this area lies in the fact that the nearby Antarctic Peninsula has recorded extreme climatic variability, and the Drake Passage-Scotia Sea oceanic domain is influenced by two major Southern Ocean water masses, the eastward-flowing Antarctic Circumpolar Current (ACC) and the westward-flowing Weddell Sea Deep Water (WSDW). These goals are achieved through the examination of a grid of very high-resolution sub-bottom profiles and two gravity cores collected in Ona Basin. Multi-proxy data derived from the gravity cores include 14C-derived ages, descriptions of sedimentary units and diatom assemblages, and continuous logging of physical properties and micro-XRF core scanning.The sub-surface seismic stratigraphy is composed of four seismic units (U4 to U1) with a dominant sub-parallel configuration, with local occurrence of wavy facies and intercalations of transparent seismic facies. Additionally, four sedimentary units were recognized through sediment core analysis from bottom to top: Unit IV is composed of slightly bioturbated diatom-rich mud and silty mud with sparse ice-rafted debris (IRDs); Unit III is composed of gravelly silty to sandy mud with large amounts of IRDs; Unit II mostly contains bioturbated diatomaceous mud; and Unit I is composed of diatom-rich silty to sandy mud. The highest diatom abundances are found in Unit II, whereas highly variable abundances are found in Unit IV. The most common diatoms are Fragilariopsis kerguelensis and Chaetoceros subg. Hyalochaete. Overall, these characteristics document a change in the depositional style from terrigenous during the Last Glacial Maximum (LGM) to hemipelagic sedimentation during the deglaciation.The high-resolution seismic stratigraphy analysis reveals significant fluctuations in the regional bottom-current patterns during the late Quaternary (i.e., after 0.4 Ma) glacial-interglacial cycles. An overall strengthening of the westward-flowing WSDW is postulated in relation to latitudinal displacements of the interphase between the deeper ACC and the WSDW, together with enhanced interactions between along- and downslope processes. In addition, sedimentological, geochemical, and micropaleontological analyses revealed two distinctive phases during the late Pleistocene, in terms of paleoenvironments and paleoceanographic conditions. During the LGM, extensive sea-ice coverage limited biogenic productivity in the ocean. Increased terrigenous input was largely supplied by the westward-flowing WSDW, under a reduced ACC influence due to the northward location of fronts. During deglaciation, the sediment record indicates reduced sea-ice cover and increased open-ocean conditions and surface water productivity, as well as a long-term intensification of the WSDW flow. We postulate bottom-current strengthening was driven by an increased Weddell Sea water export and the southward migration of fronts as a consequence of major retreat of sea ice, enhancing the ACC influence in the southern Ona Basin, and thus, affecting the sloping interphase between the deeper ACC and the WSDW.

The AD 365 Ammianus tsunami in Alexandria, Egypt, and the Crete ca. 365 fault and tsunami

The traditional interpretation of a legendary, though controversial, fourth century text of Ammianus Marcellinus is that an earthquake-generated tsunami hit Alexandria on 21 July 365. The causative earthquake is usually associated with the Aegean Arc, and it has been modeled through elastic dislocation of the up to 9 m uplift of Crete which occurred in ca. 365. A rather steep, intra-plate fault was inferred, and this predicts a regional tsunami, with about 0.6-m-high waves just offshore Alexandria. However, modeling does not reproduce the tsunami polarity clearly described by Ammianus, first major retreat of the sea and then flooding; this polarity can better be explained by a slump-generated tsunami in the eastern part of the Nile Delta. On the other hand, analysis of historical and archaeological evidence excludes the possibility of a major destruction of Alexandria in 365. The possible explanation for this puzzle is that Ammianus mixes at least two events: a slump-generated, locally impressive tsunami to east and a regional tsunami from Crete. None of these events produced significant destruction in Alexandria, which was protected by fortification walls and by an islet to the north, and in addition, it was exposed mostly to longshore waves of the 365 tsunami. These results do not mean that Alexandria has not been affected by other historical tsunamis and that the modern town is not exposed to earthquake and tsunami hazards.

The Southeast Asian Economies in the Age of Discontent

This paper investigates the effects on and responses of five middle‐income Southeast Asian economies to the current global environment of authoritarian populism, the retreat from economic liberalism, and the appeal of anti‐globalization movements. While the political histories and institutional capabilities of the five – Indonesia, Malaysia, Philippines, Thailand and Vietnam – vary greatly, these economies have a history of at least moderately fast economic growth for extended periods, and of increasing regional and global economic integration. We argue that most of the factors behind the discontent with globalization in the rich economies are not present to the same degree in these countries, and that there has therefore been no major retreat from the economic policy settings that have underpinned their past economic success. However, there are no grounds for complacency. Economic growth is slowing in some of the countries, economic insecurity remains widespread, and the development of durable independent institutions has lagged economic growth.

A Major Collapse of Kangerlussuaq Glacier's Ice Tongue Between 1932 and 1933 in East Greenland

AbstractIn recent years, several large outlet glaciers in Greenland lost their floating ice tongue, yet little is known regarding their stability over a longer timescale. Here we compile historical documents to demonstrate a major ice tongue collapse of Kangerlussuaq Glacier between 1932 and 1933. This event resulted in a 9‐km retreat, exceeding any of the glacier's recent major retreat events. Sediment cores from the fjord are used to reconstruct sea surface temperatures and to investigate a potential sedimentological trace of the collapse. During the 1920s, local and regional sea surface temperatures and air temperatures increased rapidly, suggesting a climatic trigger for the collapse. Fjord bathymetry played an important role too, as the (partially) pinned ice tongue retreated off a submarine moraine during the event. This historical analogue of a glacier tongue collapse emphasizes the fragility of remaining ice tongues in North Greenland within a warming climate.

A significant acceleration of ice volume discharge preceded a major retreat of a West Antarctic paleo–ice stream

AbstractFor the period between 14.7 and 11.5 cal. (calibrated) kyr B.P, the sediment flux of Bindschadler Ice Stream (BIS; West Antarctica) averaged 1.7 × 108 m3 a−1. This implies that BIS velocity averaged 500 ± 120 m a−1. At a finer resolution, the data suggest two stages of ice stream flow. During the first 2400 ± 400 years of a grounding-zone stillstand, ice stream flow averaged 200 ± 90 m a−1. Following ice-shelf breakup at 12.3 ± 0.2 cal. kyr B.P., flow accelerated to 1350 ± 580 m a−1. The estimated ice volume discharge after breakup exceeds the balance velocity by a factor of two and implies ice mass imbalance of −40 Gt a−1 just before the grounding zone retreated &amp;gt;200 km. We interpret that the paleo-BIS maintained sustainable discharge throughout the grounding-zone stillstand first due to the buttressing effect of its fringing ice shelf and then later (i.e., after ice-shelf breakup) due to the stabilizing effects of grounding-zone wedge aggradation. Major paleo–ice stream retreat, shortly after the ice-shelf breakup that triggered the inferred ice flow acceleration, substantiates the current concerns about rapid, near-future retreat of major glaciers in the Amundsen Sea sector where Pine Island and Thwaites Glaciers are already experiencing ice-shelf instability and grounding-zone retreat that have triggered upstream-propagating thinning and ice acceleration.

A multi-century estimate of suspended sediment yield from Lillooet Lake, southern Coast Mountains, Canada

We use annually laminated lake sediments to estimate suspended sediment yield for a 3850 km2 montane catchment in the British Columbia Coast Mountains. Sediment yield over the past 369 years averages 213 ± 38 Mg·km−2·a−1. Sediment yield increases to 285 ± 50 Mg·km−2·a−1 during the first half of the twentieth century and declines thereafter. The frequency of high-yield events during the 369 year period is irregular: 11 of the 34 events occur in the early part of the twentieth century, a time when glaciers in the watershed underwent major retreat. We fitted a generalized extreme value (GEV) model to estimate quantiles of the sediment yield distribution, and we used epoch analysis to examine persistence in sediment yield following 34 of the largest events. Persistence is greatest for the most extreme events; it is more variable for events that recur, on average, every 10–25 years. Our results indicate that sediment yield is linked to long-term changes in sediment supply to the lake. The results of this study extend earlier sediment yield estimates and improve understanding of linkages to watershed geomorphology, recent glacier retreat, and landslides in the Lillooet River watershed.

Large-scale evolution of the central-east Greenland margin: New insights to the North Atlantic glaciation history

Abstract The continental shelf of central-east Greenland is shaped by several glacially carved transverse troughs that form the oceanward extension of the major fjord systems. The evolution of these troughs through time, and their relation with the large-scale glaciation of the Northern Hemisphere, is poorly understood. In this study seismostratigraphic analyses have been carried out to determine the morphological and structural development of this important sector of the East Greenland glaciated margin. The age of major stratigraphic discontinuities has been constrained by a direct tie to ODP site 987 drilled in the Greenland Sea basin plain off Scoresby Sund fan system. The areal distribution and internal facies of the identified seismic units reveal the large-scale depositional pattern formed by ice-streams draining a major part of the central-east Greenland ice sheet. Initial sedimentation along the margin was, however, mainly controlled by tectonic processes related to the margin construction, continental uplift, and fluvial processes. From late Miocene to present, progradational and erosional patterns point to repeated glacial advances across the shelf. The evolution of depo-centres suggests that ice sheet advances over the continental shelf have occurred since late Miocene, about 2 Myr earlier than previously assumed. This cross-shelf glaciation is more pronounced during late Miocene and early Pliocene along Blosseville Kyst and around the Pliocene/Pleistocene boundary off Scoresby Sund; indicating a northward migration of the glacial advance. The two main periods of glaciation were separated by a major retreat of the ice sheet to an inland position during middle Pliocene. Mounded-wavy deposits interpreted as current-related deposits suggest the presence of changing along-slope current dynamics in concert with the development of the modern North Atlantic oceanographic pattern.

Post‐LGM Grounding‐Line Positions of the Bindschadler Paleo Ice Stream in the Ross Sea Embayment, Antarctica

AbstractThe West Antarctic Ice Sheet (WAIS) retreated more than 1,000 km since last grounding at the Ross Sea outer continental shelf. Here we show an interpretation of former grounding line positions from a new large‐area multibeam survey and a regional grid of chirp cross‐sectional data from the Whales Deep Basin in eastern Ross Sea. The basin is a paleo‐glacial trough that was occupied by the Bindschadler Ice Stream when grounded ice advanced to the shelf edge during the Last Glacial Maximum. These new geophysical data provide unambiguous evidence that the WAIS occupied at least seven grounding line positions within 60 km of the shelf edge. Four of seven grounding zone wedges (GZWs) are partly exposed over large areas of the trough. The overlapping stratal arrangement created a large‐volume compound GZW. Some of the groundings involved local readvance of the grounding line. Subsequent to these seven outer continental shelf groundings, the ice sheet retreated more than 200 km towards Roosevelt Island on the middle continental shelf. The major retreat across the middle continental shelf is recorded by small‐scale moraine ridges that mantle the top of GZW7, and these are suggestive of relatively continuous grounding line recession. The results indicate that retreat was considerably more complex than was possible to reconstruct with reconnaissance‐level data. The added details are important to climate models, which must first be able to reproduce the recent retreat pattern in all of its complexities to improve confidence in model predictions of the system's future response.

Diapirism and the Fold Zone controversy of the Ordovician glaciomarine Pakhuis Formation, South Africa

Abstract The Fold Zone controversy centers around firstly, the relationship between the direction of ice-flow and the geometry of the fold structures, and secondly the relative importance of subglacial or proglacial buckling as a folding process compared to the role of load casts or ball-and-pillow structures. The more recent recognition of diapirs associated with the Fold Zone resulted in further field investigations. Understanding the advance-retreat sequence constrains the interpretation of the glaciotectonic processes. The Sneeukop Member, the unconformity and Steenbras Member are interpreted as a continuum ice-expansion sequence without a major retreat interlude. The palaeo-ice-flow data are reinterpreted to accommodate the regional variation of ice-flow patterns. It is concluded that the Pakhuis ice sheet expansion overriding the Peninsula basin took place by means of tributary troughs converging on the main Peninsula trough thus explaining the relationship between the direction of ice-flow and fold trend variations across the basin. The folds also vary regionally in style between upright and overturned. Diapirs were recognized both as blind mushroom structures below the unconformity and piercing upwards. Chaotic breccias and lit-par-lit intermixing of tillite and deformed, attenuated banded sandstone are interpreted as blowout material presumably formed by a piercement diapir venting at the surface. Diapirism in the Pakhuis glacial context is understood as the consequence of an ice sheet expansion over a water-logged Peninsula sand aquifer. The over-pressurized sand aquifer gave rise to diapirs and associated structures. The main features of the Fold Zone are compared to modern examples as described in the literature. Push moraine and crevasse-filling examples are considered as the best-fit models to explain the genesis of the Fold Zone.

Subglacial sediment pathways and deglacial chronology of the northern Barents Sea Ice Sheet

New information is presented on the configuration of the northern Barents Sea Ice Sheet (BSIS) during the last glacial and deglaciation (21–11.5 ka). The glacial dynamics of the BSIS that we discuss are based on clay‐mineral compositions of subglacial tills and a distinct kaolinite source in the central Barents Sea where previous workers have placed a large, single ice dome for the last glacial BSIS. Our results, which appear to show that subglacial sediments were sourced locally, suggest that the BSIS consisted at least temporarily of multiple domes and may have been more dynamic than previously thought. New radiocarbon dates are presented along with new ice‐extent reconstructions for 16.5–15, 14, 13.5 and 11.5 ka. Our reconstructions add information to previous regional and continental‐scale efforts in areas east of Svalbard. Ice retreat in the northern Barents Sea progressed as follows. (i) 19–16.5 ka. Major calving led to dynamic thinning in shelf troughs and was accompanied by significant ice‐sheet thinning inland as a result of ice drawdown. (ii) 16.5–15 ka. Rapid ice‐margin retreat of between 75–100 km occurred, via lift‐off and iceberg calving, in Hinlopen and Kvitøya troughs, as well as major retreat (&gt;300 km) in Franz Victoria Trough (FVT) further east. (iii) 15–13.5 ka. Retreat progressed westwards from the FVT towards Svalbard with troughs east of Svalbard (Kvitøya, Olga, and Erik Eriksen) mostly ice‐free by 13.5 ka. (iv) 13.5–11.5 ka. Ice retreated gradually towards residual ice masses on Svalbard, Kong Karls Land and possibly Storbanken. Our data require a modification of earlier views of the BSIS because they point toward a more dynamic ice sheet and decay that, once initiated at the shelf break, was dominated by the withdrawal of ice from the FVT that progressed westwards towards the Svalbard archipelago.

Benign Neglect or Active Destruction? A Critical Analysis of Refugee and Informal Sector Policy and Practice in South Africa

To fully comprehend the disabling policy environment in which refugees in South Africa attempt to carve out a livelihood, it is important to analyse two largely independent but overlapping streams of policy-making. This paper first examines the post-apartheid refugee protection regime and traces how and why a generous right-based approach has been progressively comprised by growing restrictionism, exclusion and bureaucratic ineptitude. The 2017 Refugees Amendment Act and White Paper on International Migration represent the culmination of this process. While both are probably unimplementable and will be the subject of numerous court challenges, they can be seen as a major retreat and an increasing failure to protect. The second part of the paper traces the history of national and municipal informal sector governance since the early 1990s. Since so many refugees are forced or choose to work informally, the uncertainty and confusion this history has produced is of particular relevance. Refugee entrepreneurs have regularly been the victims of general and targeted informal sector eradication campaigns.

Deglaciation of Boknafjorden, south‐western Norway

ABSTRACTWe present 30 10Be ages from glacial erratic boulders to constrain the deglaciation of the Scandinavian Ice Sheet in the Boknafjorden region, south‐western Norway. The southern part of the island Karmøy, located at the mouth of this fjord system, became free of glacier ice before 16 ka, probably because of the sudden break up of the Norwegian Channel Ice Stream at 20–18 ka. The ice sheet margin then stabilized at the fjord mouth until a second retreat phase commenced at or slightly before 16 ka. A calving bay developed in Boknafjorden after 16 ka, and in the course of the next millennium the ice front retreated to the inner fjord branches. In contrast, a major outlet glacier that filled the Hardangerfjorden farther to the north did not start to retreat from the fjord mouth until after 15 ka, probably in response to the Bølling warming. Thus, not only did Boknafjorden experience major retreat before Bølling warmth, but there was a variable response of south‐western fjord glaciers in Norway consistent with prior observations of non‐climatic forcing of marine‐terminating outlet glaciers.

A data-constrained large ensemble analysis of Antarctic evolution since the Eemian

Reconstructing the historical behaviour of the Antarctic Ice Sheet is essential for understanding and predicting climatic interactions, ice sheet sensitivities, and sea level contributions. Furthermore, to interpret such reconstructions with any degree of confidence, meaningful uncertainty estimates are required. Working toward this goal, this article presents results from a large-ensemble data-constrained study of Antarctic evolution over the Last Glacial cycle.Ice sheet chronologies have been generated using a 3-D glacial systems model that includes sheet/stream/shelf flow; a parametrized basal drag coefficient (accounting for sub-grid topographic roughness, sediment likelihood, and systematic model-to-observation thickness misfits); a sub-grid grounding-line flux parametrization; a visco-elastic bedrock response component; parametrized climate forcing; separate shelf and tidewater calving treatments; and a physically-motivated, empirically derived, sub-shelf melt component. There are 31 ensemble parameters to capture uncertainties in the glacial cycle climate, mass-balance processes, and ice dynamics. Once generated, the ensemble of model runs is constrained using a suite of observational data (including constraints on relative sea level, past ice thickness and grounding line retreat data-points, as well as present-day ice volumes and configuration) and an evaluation methodology that produces a misfit-to-observations score for each run. Assuming variants of a Gaussian error model, the scores are used to generate probability distributions for the past evolution of the ice sheet.In our ensemble-based analysis the Last Glacial Maximum (LGM) of Antarctic ice volume occurs at ∼25–24 ka. The LGM ice volume excess relative to present-day is likely between 5.6 and 14.3 m equivalent sea level (mESL), and with less confidence >10 mESL. There is little change in the grounded ice volume from 24 ka until 17–16 ka at which time widespread deglaciation commences. The Ross and Weddell Sea sectors are the largest sources of ice mass loss. The major period of grounding line retreat in the Weddell Sea sector, resulting in the present-day Ronne–Filchner shelf system, occurs after 10 ka; the grounding line in the Ross Sea sector start its major retreat phase after 12 ka. There is no significant contribution (<1.8 mESL) to meltwater pulse 1a.During the Eemian, the modelled Antarctic Ice Sheet has a minimal ice volume at 114 ka contributing ∼2 mESL relative to present-day. The mass loss is principally due to a major retreat of the grounding line in the Siple Coast sector of the Ross Sea.We present standard deviation plots of the ensemble results for present day and at the LGM. These plots highlight geographic areas that would most benefit from additional constraint and therefore offer priorities and guidance for future field campaigns.