Retreat Rates Research Articles

Relative importance of the mechanisms triggering the Eurasian ice sheet deglaciation in the GRISLI2.0 ice sheet model

Abstract. The last deglaciation (21 to 8 ka) of the Eurasian ice sheet (EIS) is thought to have been responsible for a sea level rise of about 20 m. While many studies have examined the timing and rate of the EIS retreat during this period, many questions remain about the key processes that triggered the EIS deglaciation 21 kyr ago. Due to its large marine-based parts in the Barents–Kara (BKIS) and British Isles sectors, the BKIS is often considered to be a potential analogue of the current West Antarctic ice sheet (WAIS). Identifying the mechanisms that drove the EIS evolution might provide a better understanding of the processes at play in the West Antarctic destabilization. To investigate the relative impact of key drivers on the EIS destabilization, we used the three-dimensional ice sheet model GRISLI (GRenoble Ice Shelf and Land Ice) (version 2.0) forced by climatic fields from five Paleoclimate Modelling Intercomparison Project phases 3 and 4 (PMIP3, PMIP4) Last Glacial Maximum (LGM) simulations. In this study, we performed sensitivity experiments to test the response of the simulated Eurasian ice sheets to surface climate, oceanic temperatures (and thus basal melting under floating ice tongues), and sea level perturbations. Our results highlight that the EIS retreat simulated with the GRISLI model is primarily triggered by atmospheric warming. Increased atmospheric temperatures further amplify the sensitivity of the ice sheets to sub-shelf melting. These results contradict those of previous modelling studies mentioning the central role of basal melting on the deglaciation of the marine-based Barents–Kara ice sheet. However, we argue that the differences with previous works are mainly related to differences in the methodology followed to generate the initial LGM ice sheet. Due to the strong sensitivity of EIS to the atmospheric forcing highlighted with the GRISLI model and the limited extent of the confined ice shelves during the LGM, we conclude by questioning the analogy between EIS and the current WAIS. However, because of the expected rise in atmospheric temperatures, the risk of hydrofracturing is increasing and could ultimately put the WAIS in a configuration similar to the past Eurasian ice sheet.

The role of subduction and gravitational collapse in driving extension in the Aegean Sea

The Aegean domain has experienced lithospheric deformation during continuous northward subduction at the Hellenic trench. Early Cenozoic shortening and thickening were followed by late Cenozoic extension and thinning. Thickened lithosphere, in particular its crust, has excess gravitational potential energy, which is thought to promote orogenic collapse (i.e., gravity spreading). In the Aegean domain, release of this potential energy and collapse of the lithosphere has been proposed as the first-order driver for extension of the overriding plate. Here we show, using dynamically self-consistent analogue experiments of subduction and gravity spreading, that the subducting plate significantly influences overriding plate deformation, despite the overriding plate being positively buoyant. With the introduction of a subducting plate, the trench retreat velocity and overriding plate extension rate increase, which is in contrast with a continuous decline during gravity spreading. In addition, ∼E-W trending normal faults emerge, as opposed to arc-parallel faults trending ∼ENE-WSW to ∼ESE-WNW and arc-normal extensional zones that result from gravity spreading only. Similarly, the subducting plate causes overriding plate displacement to be unidirectional (trenchward), in accordance with the present-day geodetic velocity field, whereas gravity spreading causes a radially outward-directed displacement field. As the decline in trench retreat rate, radial spreading, dominantly arc-parallel normal faults, and arc-normal extensional zones are not observed in nature, this implies that gravity spreading cannot be the sole driver of extensional deformation in the overriding plate. Indeed, the models suggest that subduction-induced mantle flow is the dominant driver of overriding plate deformation because it imposes a basal shear stress on the overriding plate, dragging and extending it trenchward in a unidirectional manner. Our experimental results corroborate earlier studies that highlight the important role of subduction-induced mantle flow in driving overriding plate deformation. Additionally, we find that this role is more pronounced in experiments with a thicker brittle layer.

Calculation Method of Material Accumulation Rate at the Front of Trunk Glaciers Based on Satellite Monitoring

Glaciers continue to erode and transport material, forming an accumulation area at the front of the glacier. The trunk glacier, which has many tributary glaciers upstream and converges on the main channel, deposits vast amounts of material in the main channel. It blocks the main channel, forming barrier lakes, and eventually turns into mountain disasters, such as debris flows or outburst floods. Therefore, the accumulation rate of the material is a major parameter in such disasters and can determine the frequency of disasters. The material usually comes from bedrock erosion by glaciers, weathering of bedrock walls, and upstream landslides, and the material loss depends on river erosion. Based on this, we set up a method to calculate the material accumulation rate in the glacier front based on satellite images. Then, the Peilong catchment was taken as an example to validate the proposed method. The results indicate that climatic fluctuations may increase landslides, resulting in more actual accumulation than the calculated value according to the average rate of bedrock retreat. The material provided by the retreat of bedrock accounts for 92% of the total volume. Our method provides a practical reference for the mid- and long-term prediction of glacial catastrophic mass movement, as global warming seriously threatens glacier instability and downstream communities.

Evolution of Hvar island pocket beaches during the last 200 years (eastern Adriatic coast, Croatia)

This study examines the evolution of 30 pocket beaches on the island of Hvar in Croatia over the last ~200 years. The oldest available data was extracted from the Franciscan cadastre and dates back to 1834. The following period was analysed using State Geodetic Administration orthophotos from 1952 and 1958, while the recent period was studied using UAV, GNSS measurements, and photogrammetric techniques, aiming to create high-resolution models. All analyses were carried out using GIS and semi-automatic statistical tools. Our results show that the beaches on Hvar eroded on average 50 % of their total area during the studied period, while the shorelines retreated by 6.5 m. Significant changes in beach areas and shoreline retreat were observed in both periods, without differences in erosion rates (~2.3 m2/yr). Here we showed that rates of shoreline retreat of gravel/pebble beaches revealed to be slower compared to sand beaches (0.04 m/yr and 0.07–0.38 m/yr respectively). Most beaches are formed in alluvial fans and represent therefore part of geomorphic systems which relate beaches to their catchments. Therefore, land cover changes in the catchments, was found to be an important factor affecting beach morphology. Obtained results reveal that 85 % of the analysed catchments exhibited decline in arable land coinciding with obtained trends of beach erosion. We find out that changes in beach size correlates to the changes in shoreline retreat (r2 = 0.7) for 70 % of beaches. However, 30 % of the beaches could be also influenced by other effects, particularly socio-economic activities in the catchment, which could importantly impact on natural variability but could also be associated with errors in Cadastral mapping. This study has shown that there is a trend of beach erosion on Hvar island which is expected to continue in the future. The acquired knowledge can thus contribute to future beach vulnerability assessment.

Formation and evolution of barrier coast under condition of sand scarcity; an example from the Polish coast of the southern Baltic sea

The formation and evolutionary history of intracontinental, tideless sea barrier coasts is still poorly known in comparison to open-ocean and tidal sea barrier systems. This paper describes the morpho-geological structure of the barriers and its substrate along a 90-km section of the middle part of the Polish southern Baltic coast. The main goal of the study is a better insight into the evolution of the barriers in case of sand scarcity and relations to sea level changes. The study area was examined by analysis of the published and historical data from 120 borehole profiles supplemented by new 18 core drillings. In addition to lithological and biostratigraphical data, a large set of radiocarbon ages was acquired and analysed. The barriers during its whole middle and late Holocene history were retrogradational despite of varied geological and morphological features of its substrate. The average rate of barrier's retreat has shown considerable variation in a close relation to the rates of sea-level rise. During the period 8500-7500 yr b2k when the sea level rose by 6–5 mm/yr, the coast retreated ca. 4.6–3.5 m/yr. Between 7500 and 6000 yr b2k, the sea-level rise slowed down to ca. 1.7 mm/yr and the rate of coastline retreat fell to ca. 1.0 m/yr. During the last 6000 years, coastal retreat slowed down to ca. 0.3 m/yr as the average sea level rise was ca. 0.5 mm/yr. The permanent retrogradational history of the barrier coast, even in the case of sand availability in the barrier's substrate, is explained by the existence of a divergence zone of longshore currents and a related source zone for the alongshore sandy streams. The divergence zone is present within the study area not only today, but it has existed most probably also at least since the beginning of the late Holocene. As a result, the erosional trend (sand scarcity) dominates here, which contributes to the presence of retrogradational barriers.

Upland forest retreat lags behind sea-level rise in the mid-Atlantic coast.

Ghost forests consisting of dead trees adjacent to marshes are striking indicators of climate change, and marsh migration into retreating coastal forests is a primary mechanism for marsh survival in the face of global sea-level rise. Models of coastal transgression typically assume inundation of a static topography and instantaneous conversion of forest to marsh with rising seas. In contrast, here we use four decades of satellite observations to show that many low-elevation forests along the US mid-Atlantic coast have survived despite undergoing relative sea-level rise rates (RSLRR) that are among the fastest on Earth. Lateral forest retreat rates were strongly mediated by topography and seawater salinity, but not directly explained by spatial variability in RSLRR, climate, or disturbance. The elevation of coastal tree lines shifted upslope at rates correlated with, but far less than, contemporary RSLRR. Together, these findings suggest a multi-decadal lag between RSLRR and land conversion that implies coastal ecosystem resistance. Predictions based on instantaneous conversion of uplands to wetlands may therefore overestimate future land conversion in ways that challenge the timing of greenhouse gas fluxes and marsh creation, but also imply that the full effects of historical sea-level rise have yet to be realized.

Patterns and processes of channel and floodout adjustment in a discontinuous dryland river, semi-arid eastern Australia

Alluvial rivers in semi-arid and arid landscapes are prone to episodic geomorphic adjustments related to long-term sediment accumulation and occasional reworking by flash floods. However, few studies document the rates, patterns and processes leading to channel breakdown, particularly avulsion and floodout. These intrinsically driven adjustments may pose a risk to water resource availability through redistribution of water and sediment on the floodplain. To address this knowledge gap, channel change associated with avulsion and flooding in the last ∼30 years were quantified for Little Faulkenhagen Creek, a dryland river of the Murray-Darling Basin, Australia. The semi-arid, low gradient catchment promotes transmission losses, which with loss of valley confinement leads to channel adjustment and contraction to occur where water, sediment and energy are spread across the floodplain. Pronounced downstream changes occur in channel capacity (i.e., reductions in bankfull width, depth and area) and hydrology (i.e., reductions in bankfull discharge and stream power) as the river enters the floodout zone. Vegetation roughness increases in and around the floodout, where shrubs and river redgum trees line and encroach upon the channel. Mapping and analysis of hydro-geomorphological parameters using cross sections from 1991 to 2021 reveal recent changes in channel capacity, discharge and stream power. The upper reach has experienced substantial channel widening from erosion, while the lower reach leading into the floodout has contracted because of sediment deposition within the channel. Unchannelised floodwaters are deflected around a raised alluvial ridge and over the floodout eventually dropping into several migrating upstream knickpoints (head-cutting gullies) with retreat rates up to 32 m a−1. Therefore, both the existing channel slope (i.e., decline) and potential avulsion courses (i.e., increase) are affected by reduced energy and enhanced sedimentation. The net result of upstream in-channel sedimentation and aggradation on the floodout and downstream incision and gullying is that the floodout has migrated ∼1 km upstream and the river is at risk of a secondary avulsion as gullies retreat towards the main channel, potentially circumventing the floodout within ∼11 years. An erosion cell conceptual model is suitable for this system, where sediment from the local upstream production (erosion) zone is transferred downstream to a sink (deposition) zone. Erosion and deposition will fluctuate over the long-term, leading to periods with dominantly incisional or aggradational processes. Cycles of erosion and deposition will vary over time and external forces may influence a wholesale shift to a new fluvial state. Understanding the context and patterns of recent dryland river adjustments, as well as the dominant processes and their variability, can assist water and land management.

The effects of Sesarma reticulatum (L.) herbivory and sea level rise on creek expansion in Cape Cod salt marshes

High densities of herbivorous purple marsh crabs (Sesarma reticulatum) have caused major vegetation loss in salt marshes across Cape Cod (Massachusetts, USA). As creekbanks are a preferred habitat for this species, much of the damage is concentrated along these edges, resulting in an elevated potential for creek widening through erosion and bank slumping. The presence and/or spatial distribution of S. reticulatum is variable across this region with impacts ranging from minor to severe, and this provides an opportunity to distinguish between background vs. S. reticulatum-enhanced widening. To accomplish this, GIS tools were used to delineate portions of tidal creek systems in 18 marshes, half of which have experienced substantial creekbank vegetation losses from crab-driven herbivory. Delineations were based on georeferenced aerial photography between 2005 and 2021. In addition, creek widths at discrete locations in the delineated systems were measured in each photo year using GIS tools to estimate rates of bank retreat. A smaller number of narrow <2.0 m mosquito ditches were analyzed in the same way to further stratify the data by initial width. Between 2010 and 2021, all tidal conduits ranging from the larger, natural creeks to mosquito ditches widened at a rate that was significantly higher in marshes with no Sesarma damage. While all marshes are under threat from SLR, creek-widening in those experiencing intense crab herbivory may have a greatly shortened lifespan.

The lasting legacy of glacial landscape dynamics: Capturing the transport of boulder armor and hillslope retreat with geochronology in the Flint Hills of Kansas

We present new geochronological data derived from hillslope boulder armor in the Flint Hills in northeastern KS, United States, that provides insights into the rates and timing of lateral retreat in this landscape. Our results show that the surfaces of these limestone boulders date back to the Pleistocene era, well within the last glacial period. We also found that there is a significant increase in the ages of hillslope armor with increasing distance downslope from the modern limestone bench, the source of the boulders. Based on the age-distance relationship of the boulders, we estimate the rate of lateral retreat in this landscape to be 0.02 mm/yr, which falls between the geometrically estimated retreat rates based on calculated denudation rates of the Flint Hills region. We propose that the cooler temperatures and higher effective moisture due to less efficient evapotranspiration during the late Pleistocene period resulted in more effective freeze-thaw and transport processes, such as creep due to soil expansion and contraction. The production and transport of new boulder armor would then have effectively ceased once the climate transitioned to warmer conditions during the Holocene. Our findings suggest that the boulder armor we observe on the soil mantled hillslopes today are relict features from before the LGM-Holocene transition. These results provide important insights into the long-term evolution of these ubiquitous layered sedimentary landscapes.

Deglaciation of the north American ice sheet complex in calendar years based on a comprehensive database of chronological data: NADI-1

The most recent deglaciation of the North American Ice Sheet Complex (NAISC: comprising the Innuitian, Cordilleran, and Laurentide ice sheets) offers a broad perspective from which to analyze the timing and rate of ice retreat, deglacial sea-level rise, and abrupt climate change events. Previous efforts to portray the retreat of the NAISC have been focused largely on minimum-limiting radiocarbon ages and ice margin location(s) tied to deglacial landforms that were not, for the most part, chronologically constrained. Here, we present the first version of North American Deglaciation Isochrones (NADI-1) spanning 25 to 1 ka in calendar years before present. Key new features of this work are (i) the incorporation of cosmogenic nuclide data, which offer a direct constraint on the timing of ice recession; (ii) presentation of all data and time-steps in calendar years; (iii) optimal, minimum, and maximum ice extents for each time-step that are designed to capture uncertainties in the ice margin position, and; (iv) extensive documentation and justification for the placement of each ice margin. Our data compilation includes 2229 measurements of 10Be, 459 measurements of 26Al and 35 measurements of 36Cl from a variety of settings, including boulders, bedrock surfaces, cobbles, pebbles, and sediments. We also updated a previous radiocarbon dataset (n = 4947), assembled luminescence ages (n = 397) and gathered uranium-series data (n = 2). After scrutiny of the geochronological dataset, we consider >90% of data to be reliable or likely reliable. Key findings include (i) a highly asynchronous maximum glacial extent in North America, occurring as early as 27 ka to as late as 17 ka, within and between ice sheets. In most marine realms, extension of the ice margin to the continental shelf break at 25 ka is somewhat speculative because it is based on undated and spatially scattered ice stream and geomorphic evidence; (ii) detachment of the Laurentide and Cordilleran ice sheets took place gradually via southerly and northerly ‘unzipping’ of the ice masses, starting at 17.5 ka and ending around 14 ka; (iii) the final deglaciation of Hudson Bay began at 8.5 ka, with the collapse completed by 8 ka. The maximum extent of ice during the last glaciation occurred at 22 ka and covered 15,470,000 km2. All North American ice sheets merged at 22 ka for the first time in the Quaternary. The highly asynchronous Last Glacial Maximum in North America means that our isochrones (starting at 25 ka) capture ice advance across some areas, which is based on limited evidence and is therefore somewhat speculative. In the Supplementary Data, the complete NADI-1 chronology is available in PDF, GIF and shapefile format, together with additional visualizations and spreadsheets of geochronological data. The NADI-1 shapefiles are also available at https://doi.org/10.5281/zenodo.8161764.

Greenland-wide accelerated retreat of peripheral glaciers in the twenty-first century

The long-term response of Greenland’s peripheral glaciers to climate change is widely undocumented. Here we use historical aerial photographs and satellite imagery to document length fluctuations of >1,000 land-terminating peripheral glaciers in Greenland over more than a century. We find that their rate of retreat over the last two decades is double that of the twentieth century, indicating a ubiquitous transition into a new, accelerated state of downwasting.

Divergent glacier area and elevation changes across the Tibetan Plateau in the early 21st century

With accelerated warming, mountain glaciers in most parts of the world have been in a state of continuous retreat in recent decades. Assessing glacier change and analyzing its influencing factors are essential for developing climate change mitigation and adaptation measures for a given region. This study provides a spatially explicit assessment and quantification of glacier changes in the early 21st century on the Tibetan Plateau (TP) at individual glacier and basin scales. We established a one-to-one correspondence between the Second Chinese Glacier Inventory (CGI-2, collected from 2004 to 2011) and a dataset of glacier inventory in Western China during 2017–2018 (CGI-2018). The majority of TP’s glaciers decreased in size with a mean area retreat rate during the investigated period of 4.1%/decade. In addition, a mean change of the median elevation of the glaciers of 6.7 m/decade was detected. Approximately 2.5% of the total number of glaciers mapped in CGI-2 disappeared, while 681 of them divided to 1758 glaciers as they retreated. The observed variations follow local trends and have different regional characteristics. Generally, the glaciers with the lowest retreat rates are found in the Karakorum and Kunlun Mountains, while those with high retreat rates are concentrated along the Gangdis and Tangula ranges. The observed changes in glaciers are mainly attributed to a significant increase in temperature. Other factors including glacier size, debris cover, orientation and mean elevation also contribute to the heterogeneity of glacier variability. This study provides for the first time a detailed spatially explicit analysis of the glacial changes on the TP in the early 21st century, substantially improving the understanding of glacier response patterns and supporting more sustainable utilization of regional water resources in the TP in the context of climate warming in the 21st century.

Assessing the state, parameter-interlinkages and dynamic shift of glaciers in the western Himalaya

The present study remotely investigates multiple parameters of 25 well-distributed glaciers in the western Himalaya (WH) for ~1990–2015 period to understand their state. Glacier changes for 1990–2000 (pre-2000) and 2000–2015 (post-2000) were analysed separately to assess the shift in glacier dynamics. Results reveal a clear glacier terminus retreat (13.4 ± 2.1 m/y), deglaciation (0.2 ± 0.1%/y), surface velocity slowdown (21%) and increase in number of glacial lakes (28 to 38) as well their area (5%/y) during 1990–2015. Notably, average terminus retreat and deglaciation rates were reduced post-2000 (retreat: 12.5 ± 3.2 m/y; deglaciation: 0.1 ± 0.1%/y) compared to pre-2000 (retreat: 15.3 ± 6.8 m/y; deglaciation: 0.2 ± 0.2%/y). Further, the average surface velocity was found to be increasing (0.9%/y) over 1990–2000. This can be linked with suggested less negative or slightly balanced condition of the WH glaciers over 1990s by previous studies. Present study also finds low downwasting during pre-2000 (−0.24 ± 0.14 m/y). Post-2000, studied glaciers downwasted (−0.50 ± 0.06 m/y) and slowed down (2%/y) significantly showing a decadal time lag in geometrical adjustment. Supraglacial debris, largely influenced by slope characteristics, increased with a uniform rate of 0.9%/y during pre- and post-2000 periods. Systematic analysis of interlinkages among various glacier parameters reveals a large interdependency. Further, presence of debris cover and pro- and supra-glacial lakes modify the glacier response to a great extent. Overall, the present study shows that (a) studied glaciers were in overall depleting phase over 1990–2015, (b) balanced conditions during 1990s prevailed over the studied glaciers, followed by accelerated mass wastage, (c) topography and local surface conditions introduce the intraregional heterogeneity in glacier response to climate.

Local Ice Mass Balance Rates via Bayesian Analysis of Mars Polar Trough Migration

AbstractWith the aim of better understanding the past depositional environment of the north polar region of Mars, we infer local ice accumulation and retreat rates in the area between 86° and 87°N and 16°–20°E. We follow a novel approach utilizing a Bayesian framework with observations of bounding surfaces associated with the migration of two polar spiral troughs. Over time, spiral troughs have migrated toward the north pole due to ice accumulation, sublimation, and wind transport. We relate the record of trough migration with local ice accumulation and retreat rates using a phenomenological migration model and explore the climate parameters that affect these rates using a Markov chain Monte Carlo algorithm. Using this data‐driven approach, we find best fit mean accumulation rates of 0.11–0.18 mm/yr in the upper 500 m of the stratigraphy of our study region. These mean accumulation rates correspond to trough ages of over 4 Myr, which implies that the north polar cap is older than most current assumptions. We also find that the relationship between accumulation rates and the obliquity of Mars is complex, with periods of positive correlation occurring in the last several Myr. Future work extending this analysis to all troughs in the cap will further constrain these relationships and ages.

Decoupling of Arctic variability from the North Pacific in a warmer climate

The sea level pressure variability in the North Pacific modulates the climate of the Arctic and surrounding continents, substantially impacting ecosystems and indigenous communities. Our analysis based on data from the CESM2 Large Ensemble and different Model Intercomparison Project datasets reveals that the interannual variability of Arctic surface air temperature (SAT) gradually decouples from the contemporaneous atmospheric conditions over the North Pacific as external forcing increases in intensity in the future. Future projections show that the North Pacific-Arctic relationship during the fall season consistently weakens in magnitude until the end of this century, and in the 22nd and 23rd centuries, the relationship is negligible throughout the year. We show that under increased greenhouse gas emissions, the regional heat fluxes extensively control the Arctic temperature variability, and the strength of the projected North Pacific-Arctic relationship is strongly dependent on the Arctic sea ice extent. Our results suggest that under future warming, a strong coupling of Arctic SAT with the underlying ocean and a weakening of the meridional pressure gradient driven by an enhanced rate of sea ice retreat will weaken the interannual footprint of North Pacific variability on Arctic SAT. Therefore, we propose that the alarming rate of sea-ice decline over recent decades and projected in the near future could accelerate the rate of decoupling. Further, we suggest that mitigation strategies for the Arctic should focus on regional mechanisms operating on interannual and seasonal timescales.

Paleoglaciological reconstruction and geomorphological mapping of Dobrowolski Glacier, King George Island, Antarctica

The paper aims to reconstruct the fluctuations of Dobrowolski Glacier, a tidewater glacier located in the inner position of the Admiralty Bay (King George Island, Antarctica), from the Little Ice Age (1400-1700) until the present. Measurements of the glacier’s area and length were based on multitemporal satellite imagery and submarine glacial landforms. The glacier surface area variations between the Little Ice Age and 2014 A.D were estimated. Morainic banks and paleoglacial reconstructions provided evidence of fluctuations in the surface area of the glacier between PIG and 2014 AD. Therefore, four stages of analysis were established: Stage I (Part I) (1400 to 1700), Stage I (Part II) (1700 until the mid-20th century), Stage II (mid-20th century until the 1980s), Stage III (1980 to 2000), and Stage IV (2000 to 2020). The climate during the Little Ice Age triggered the last major glacial advance, and their grounding line position was recorded by an external and prominent morainic bank. After the major glacial advance position of the grounding line, the ice-margin has undergone higher retreat rates (stage I) as response to the warming trend and the loss of anchoring point. The stage II (Unit B) is recorded by distal and discontinuous morainal ridges and glacial lineations formed in the context of an active ice flow at a deeper point in the fjord. During stage III (Unit C) glacial lineations and steep slopes occur, while landforms are less preserved, revealing a fast shrinkage phase. Stage IV is characterized by discontinuous morainic ridges (Unit D), when the glacier presents the highest annual glacial area loss. Currently, the accelerated shrinkage may be linked to the loss of anchorage on seamounts (serving as pinning points) and increased warming. The U-shaped valley geometry has also influenced the glacier shrinkage processes and the redirection of glacial paleoflow during the last 300 years. The retreat rate to mid-20th century-2020 period is higher than Little Ice Age- mid-20th century period.

Evaluating the impact of the Central Chile Mega Drought on debris cover, broadband albedo, and surface drainage system of a Dry Andes glacier

In recent years, Chile has experienced an extraordinary drought that has had significant impacts on both the livelihoods of people and the environment, including the Andean glaciers. This study focuses on analyzing the surface processes of Universidad Glacier, a benchmark glacier for the Dry Andes. Multiple remote sensing datasets are used alongside a novel spectral index designed for mapping of rock material located on the glacier's surface. Our findings highlight the precarious state of the glacier, which serves as a crucial water source for the region. The glacier exhibits locally varied debris accumulation and margin retreat. The most significant impacts are observed on the tongue and secondary accumulation cirques, with the latter at risk of disappearing. The debris cover on the tongue is expanding, reaching higher elevations, and is accompanied by glacier retreat, especially at higher altitudes. The equilibrium line is rapidly shifting upglacier, although the mid-season snow cover still frequently reaches the 2013 equilibrium line, even in 2020. Changes in stream density on the glacier tongue indicate an increased water supply in this area, likely due to enhanced melting of glacial ice. These observed processes align well with meteorological data obtained from reanalysis products. The behavior of dust and debris is influenced by precipitation amount, while the rate of retreat is linked to air temperature.

Monitoring of a Coastal Protection Scheme through Satellite Remote Sensing: A Case Study in Ghana

Earth observation can provide managers with valuable information on ongoing coastal processes and major trends in coastline evolution, especially in data-poor regions. This paper examines the use of optical satellite images in the mapping of the changes in shoreline position before, during, and after the implementation of a protection scheme. The aim of this paper is twofold: (i) to demonstrate the potential of satellite imagery as an effective, robust, and low-cost tool to remotely monitor the effectiveness of protective structures based on a large-scale case study in West Africa; and (ii) to compile lessons learned from this case study that can be used in the design of future interventions. The analysis shows that before the implementation of the protection scheme, the coastal sector was retreating at a rate of −1.6 m/year, which is in line with the average retreat rates reported in other studies for the region. After project implementation, this trend reversed into shoreline accretion at a rate of +1.0 m/year, locally experiencing positive and negative oscillations in the short term. Furthermore, the shoreline-extracted positions proved useful in assessing the impact of differences in the groynes’ permeability with respect to temporary leeside erosion. Finally, it is recommended to continue this monitoring to assess long-term trends.

A Review of Karakoram Glacier Anomalies in High Mountains Asia

Influenced by global warming, glaciers in High Mountains Asia (HMA) generally show a trend of retreat and thinning, but in Karakoram, Pamir, and West Kunlun there is a trend of glacier stabilization or even a weak advance. In this study, using a bibliometric analysis, we systematically sorted the area, mass balance, and elevation changes of the glaciers in Karakoram and summarized the glacier surges in HMA. The study shows that, since the 1970s, the glaciers in the Karakoram region have experienced a weak positive mass balance, with weakly reducing area and the increasing surface elevation. The north slope of Chogori Peak and the Keltsing River Basin presented a glacier retreat rate with a fast to slow trend. The anomaly is mainly due to low summer temperatures and heavy precipitation in winter and spring in the Karakoram region. There are a large number of surging glaciers in the Karakoram Mountains, the Pamir Plateau, and the West Kunlun region in the western part of HMA, especially in the Karakoram Mountains and the Pamir Plateau, which account for more than 70% of the number of surging glaciers in the entire HMA. The glaciers in the Karakoram and Kunlun Mountains are mainly affected by the synergistic influence of various factors, such as hydrothermal conditions, atmospheric circulation, and topography. However, the glaciers in the Pamir region are mainly influenced by the thermal mechanism of the glacier surge. The glaciers in and around Karakoram are critical to the hydrological response to climate change, and glacial meltwater is an important freshwater resource in arid and semi-arid regions of South and Central Asia, as well as in western China. Therefore, changes in the Karakoram anomaly will remain a hot research topic in the future.

EROSION PROCESS IN THE CARIBBEAN SANDY BEACHES

Beach erosion is a widespread phenomenon on Caribbean beaches, with rates of coastline retreat between 2.2 and 0.5 m/year and higher reports in some areas. Different investigations indicate the combination of natural and anthropogenic causes and highlight the current influence of climate change related sea level rise. It is recorded as a generalizing trend the landward displacement of the beach profile, with sand transfer above the dunes and sand bars in a process that fits better the model proposed by Dean and Maurmeyer (1983) than the recognized model by Brunn (1962).