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Long, J.H.; Hanebuth, T.J.J.; Alexander, C.R., and Wehmiller, J.F., 2021. Depositional environments and stratigraphy of Quaternary paleochannel systems offshore of the Georgia Bight, southeastern U.S.A. Journal of Coastal Research, 37(5), 883–905. Coconut Creek (Florida), ISSN 0749-0208. Paleochannels are common subsurface geological features beneath inner continental shelves and coastal plains and are important archives of ancient depositional environments. This study, focusing on a 450-km portion of the inner continental shelf of the SE United States, adds to understanding of the timing of paleochannel development, the paleoenvironments in which they formed, and the mechanisms that drove their formation. Integrated analysis of 1089 km of high-resolution seismic reflection data and 12 sediment cores reveals that (1) most paleochannels documented here formed in backbarrier environments (estuarine or lagoonal) and were subsequently filled during transgression or following avulsion, preserving mud-rich, tidally influenced deposits; (2) the preservation of nonmarine deposits is rare; (3) paleochannels are either solitary or amalgamated, forming paleochannel complexes within which they are arranged in multistory (vertically stacked) or multilateral (horizontally offset) configurations, a product of local hydrodynamic conditions, antecedent geology, glacioeustatic cycles, and regional isostatic adjustments; and (4) a general southerly increase in the overall degree of channelization is observed across the Georgia Bight, a function of long-term accommodation, interaction with underlying stratigraphy, and dominant coastal processes. The composition and spatiotemporal distribution of paleochannel systems has implications for understanding the long-term evolution and preservation of complex coastal systems and informing regional Quaternary sea-level reconstructions. [ABSTRACT FROM AUTHOR]

Accurate glacial isostatic adjustment (GIA) models are required for correcting measurements of mass change in Antarctica and for improving knowledge of the sub‐surface, especially in areas of large current ice loss such as the Amundsen Sea Embayment (ASE). Regionally, seismic and gravity data suggests lateral differences in viscosity (3D). Furthermore, mantle flow laws allow for a stress‐dependent effective viscosity which changes over time (3D‐s). In this study we investigate whether models with 3D/3D‐s have significant effects on the uplift in the region. We use a finite element model with composite rheology consisting of diffusion and dislocation creep, forced by an ice deglaciation model starting in 1900. We use its uplift predictions as synthetic observations to test the performance of 1D model inversion in the presence of viscosity variations. Stress‐dependent rheology results in lower viscosity beneath the load and a more localized uplift pattern. We demonstrate that the background stress from earlier ice load changes can both increase or decrease the influence of stress‐induced effective viscosity changes. For the ASE, fitting 1D models to 3D model uplift results in a best fitting model with viscosity that represents the average of a large area, while for 3D‐s rheology, local viscosity is more influential. 1D models are statistically indistinguishable from 3D/3D‐s viscosity with current GPS stations. However, 3D and 3D‐s models should be taken into account when accurate uplift and gravity rate patterns are needed, as uplift can differ up to 45% compared to 1D models in between existing GPS stations. Plain Language Summary: The Amundsen Sea Embayment (ASE) is a region in West‐Antarctica, which is losing mass upstream of the grounding line faster than almost any other region. Measurements of current ice mass change are obscured by uplift due to the melting of ice sheets in that past, termed glacial isostatic gdjustment (GIA). An accurate GIA model is required. The state‐of‐the‐art GIA model for the region assumes that the viscosity depth profile is the same everywhere. However, effective viscosity can change with location and under influence of stress which changes over time. In this study we use a finite element model to simulate GIA in the ASE and compare the simulated uplift from these models to an inverted 1D model. We show that when estimating average mantle viscosities, a simpler model would suffice. When higher stresses due to rapid deglaciation are taken into account in the description of the mantle flow, the uplift at the point of rapid deglaciation has a stronger rebound effect than previously considered. This would mean that the local ice mass loss obtained after correcting with current GIA models might also be bigger than what is obtained after correcting with simpler GIA models. Key Points: Uplift rates in the Amundsen Sea Embayment since 1900 are modeled with lateral and stress‐dependent viscosity changes (composite rheology)Including stresses from earlier ice loads can both increase and decrease stress‐induced viscosity changes1D and 3D model uplift cannot be distinguished between using GPS sites but modeled uplift show significant differences in high uplift areas [ABSTRACT FROM AUTHOR]

During the last interglacial (LIG) period, global mean sea level (GMSL) was higher than at present, likely driven by greater high-latitude insolation. Past sea-level estimates require elevation measurements and age determination of marine sediments that formed at or near sea level, and those elevations must be corrected for glacial isostatic adjustment (GIA). However, this GIA correction is subject to uncertainties in the GIA model inputs, namely, Earth's rheology and past ice history, which reduces precision and accuracy in estimates of past GMSL. To better constrain the GIA process, we compare our data and existing LIG sea-level data across the Bahamian archipelago with a suite of 576 GIA model predictions. We calculated weights for each GIA model based on how well the model fits spatial trends in the regional sea-level data and then used the weighted GIA corrections to revise estimates of GMSL during the LIG. During the LIG, we find a 95% probability that global sea level peaked at least 1.2 m higher than today, and it is very unlikely (5% probability) to have exceeded 5.3 m. Estimates increase by up to 30% (decrease by up to 20%) for portions of melt that originate from the Greenland ice sheet (West Antarctic ice sheet). Altogether, this work suggests that LIG GMSL may be lower than previously assumed. [ABSTRACT FROM AUTHOR]

Information on sea level and its temporal and spatial variability is of great importance for various scientific, societal, and economic issues. This article reports about a new sea level dataset for the North Sea (named North SEAL) of monthly sea level anomalies (SLAs), absolute sea level trends, and amplitudes of the mean annual sea level cycle over the period 1995–2019. Uncertainties and quality flags are provided together with the data. The dataset has been created from multi-mission cross-calibrated altimetry data preprocessed with coastal dedicated approaches and gridded with an innovative least-squares procedure including an advanced outlier detection to a 6–8 km wide triangular mesh. The comparison of SLAs and tide gauge time series shows good consistency, with average correlations of 0.85 and maximum correlations of 0.93. The improvement with respect to existing global gridded altimetry solutions amounts to 8 %–10 %, and it is most pronounced in complicated coastal environments such as river mouths or regions sheltered by islands. The differences in trends at tide gauge locations depend on the vertical land motion model used to correct relative sea level trends. The best consistency with a median difference of 0.04±1.15 mmyr-1 is reached by applying a recent glacial isostatic adjustment (GIA) model. With the presented sea level dataset, for the first time, a regionally optimized product for the entire North Sea is made available. It will enable further investigations of ocean processes, sea level projections, and studies on coastal adaptation measures. The North SEAL data are available at 10.17882/79673. [ABSTRACT FROM AUTHOR]

Surface meltwater accumulating on Antarctic ice shelves can drive fractures through to the ocean and potentially cause their collapse, leading to increased ice discharge from the continent. Implications of increasing surface melt for future ice shelf stability are inadequately understood. The southern Amery Ice Shelf has an extensive surface hydrological system, and we present data from satellite imagery and ICESat‐2 showing a rapid surface disruption there in winter 2019, covering ∼60 km2. We interpret this as an ice‐covered lake draining through the ice shelf, forming an ice doline with a central depression reaching 80 m depth amidst over 36 m uplift. Flexural rebound modeling suggests 0.75 km3 of water was lost. We observed transient refilling of the doline the following summer with rapid incision of a narrow meltwater channel (20 m wide and 6 m deep). This study demonstrates how high‐resolution geodetic measurements can explore critical fine‐scale ice shelf processes. Plain Language Summary: Surface melting over Antarctica's floating ice shelves is predicted to increase significantly during coming decades, but the implications for their stability are unknown. The Antarctic Peninsula has already seen meltwater driven ice shelf collapses. We are still learning how meltwater forms, flows and alters the surface, and that rapid water‐driven changes are not limited to summer. We present high‐resolution satellite data (imagery and altimetry) showing an abrupt change on East Antarctica's Amery Ice Shelf in June 2019 (midwinter). Meltwater stored in a deep, ice‐covered lake drained through to the ocean below, leaving a deep, uneven 11 km2 depression of fractured ice (a "doline") in the ice shelf surface. The reduced load on the floating ice shelf resulted in flexure, with over 36 m of uplift centered on the former lake. Simple flexure modeling showed that this corresponds to about 0.75 km3 of water being lost to the ocean. ICESat‐2 observations in summer 2020 profiled a new narrow channel inside the doline as meltwater started refilling it from a new lake created by the flexure. ICESat‐2's capacity to observe surface processes at small spatial scales greatly improves our ability to model them, ultimately improving the accuracy of our projections. Key Points: Satellite images showed an 11 km2 depression on Amery Ice Shelf as an ice‐covered lake drained abruptly in winter 2019 forming an ice dolineICESat‐2 and WorldView data show elevation fell as much as 80 m in the depression, amidst 60 km2 of hydrostatic rebound and uplift over 36 mICESat‐2 photon data profiled a new meltwater channel, incised when a lake formed by the flexural uplift overflowed into the doline in 2020 [ABSTRACT FROM AUTHOR]

The Japanese Antarctic Research Expeditions have conducted long‐term Global Navigation Satellite System (GNSS) observations at a series of bedrock outcrops along the coast of Lützow‐Holm Bay, East Antarctica, to elucidate the solid Earth response to ice mass changes. These GNSS observations capture both the viscoelastic response of the solid Earth to Antarctic Ice Sheet changes since the Last Glacial Maximum, termed glacial isostatic adjustment (GIA), and elastic deformation associated with recent surface mass changes due to snowfall variations. Here, we extract the GIA signals from the Lützow‐Holm Bay GNSS data by applying an elastic deformation correction based on the mass fluctuations observed in the Gravity Recovery and Climate Experiment and the satellite altimetry. Our results indicate that the region is currently experiencing approximately 1 mm/yr of subsidence, which is large enough to influence GIA model estimations. The resultant GIA‐induced deformation response in Lützow‐Holm Bay is 1–6 mm/yr of uplift. Plain Language Summary: The Japanese Antarctic Research Expeditions have conducted long‐term Global Navigation Satellite System (GNSS) observations at a series of bedrock outcrops along the coast of Lützow‐Holm Bay, East Antarctica. We analyzed the GNSS data and derived the vertical deformation rate to determine the glacial isostatic adjustment (GIA) signal, which is the viscoelastic response of the Earth to Antarctic Ice Sheet melting since the Last Glacial Maximum. We revealed that this region has been experiencing 1–6 mm/yr of uplift after correcting for the elastic crustal deformation response due to snowfall variations. There is a systematic deviation between our GNSS‐derived uplift rates and two GIA model predictions, the ANU and ICE‐5G models, whereas the ICE‐6G and IJ05 models predicted similar values. Key Points: GIA‐induced crustal deformation in Lützow‐Holm Bay, East Antarctica, is determined using long‐term Global Navigation Satellite System observationsThe estimated elastic deformation response in this region is ∼0.5–1 mm/yr of subsidence due to a recent increase in snowfallThe glacial isostatic adjustment‐induced deformation response in the Lützow‐Holm Bay region is 1–6 mm/yr of uplift after applying an elastic deformation correction [ABSTRACT FROM AUTHOR]

In this review we compile and document the elevation, indicative meaning, and chronology of marine isotope substage 5a and 5c sea level indicators for 39 sites within three geographic regions: the North American Pacific coast, the North American Atlantic coast and the Caribbean, and the remaining globe. These relative sea level indicators, comprised of geomorphic indicators such as marine and coral reef terraces, eolianites, and sedimentary marine- and terrestrial-limiting facies, facilitate future investigation into marine isotope substage 5a and 5c interstadial paleo-sea level reconstruction, glacial isostatic adjustment, and Quaternary tectonic deformation. The open-access database, presented in the format of the World Atlas of Last Interglacial Shorelines (WALIS) database, can be found at 10.5281/zenodo.5021306 (Thompson and Creveling, 2021). [ABSTRACT FROM AUTHOR]

The Pacific Coast of Central North America is a geodynamically complex region which has been subject to various geophysical processes operating on different timescales. Glacial isostatic adjustment (GIA), the ongoing deformational response of the solid Earth to past deglaciation, is an important geodynamic process in this region. In this study, we apply earth models with 3-D structure to determine if the inclusion of lateral structure can explain the poor performance of 1-D models in this region. Three different approaches are used to construct 3-D models of the Earth structure. For the first approach, we adopt an optimal 1-D viscosity structure from previous work and add lateral variations based on four global seismic shear wave velocity anomalies and two global lithosphere thickness models. The results based on these models indicate that the addition of lateral structure significantly impacts modelled RSL changes, but the data-model fits are not improved. The global seismic models are limited in spatial resolution and so two other approaches were considered to produce higher resolution models of 3-D structure: inserting a regional seismic model into two of the global seismic models and, explicitly incorporating regional structure of the Cascadia subduction zone and vicinity, that is the subducting slab, the overlying mantle wedge and the plate boundary interface. The results associated with these higher resolution models do not reveal any clear improvement in satisfying the RSL observations, suggesting that our estimates of lateral structure are inaccurate and/or the data-model misfits are primarily due to limitations in the adopted ice-loading history. The different realizations of 3-D Earth structure gives useful insight to uncertainty associated with this aspect of the GIA model. Our results indicate that improving constraints on the deglacial history of the southwest sector of the Cordilleran ice sheet is an important step towards developing more accurate of GIA models for this region. [ABSTRACT FROM AUTHOR]

Global patterns of sea-level change – often termed "sea-level fingerprints" – associated with future changes in ice/water mass re-distribution are a key component in generating regional sea-level projections. Calculation of these fingerprints is commonly based on the assumption that the isostatic response of the Earth is dominantly elastic on century timescales. While this assumption is accurate for regions underlain by mantle material with viscosity close to that of global average estimates, recent work focusing on the West Antarctic region has shown that this assumption can lead to significant error where the viscosity is significantly lower than typical global average values. Here, we test this assumption for fingerprints associated with glaciers and ice caps. We compare output from a (1D) elastic Earth model to that of a 3D viscoelastic model that includes low-viscosity mantle in three glaciated regions: Alaska, southwestern Canada, and the southern Andes (Randolph Glacier Inventory (RGI) regions 1, 2, and 17, respectively). This comparison indicates that the error incurred by ignoring the non-elastic response is of the order of 1 mm in most areas (or about 1 % of the barystatic signal) over the 21st century with values reaching the centimetre level in glaciated regions. However, in glaciated regions underlain by low-viscosity mantle, the non-elastic deformation can result in relative sea-level changes with magnitudes of up to several tens of centimetres (or several times the barystatic value). The magnitude and spatial pattern of this non-elastic signal is sensitive to variations in both the projected ice history and regional viscosity structure, indicating the need for loading models with high spatial resolution and improved constraints on regional Earth viscosity structure to accurately simulate sea-level fingerprints in these regions. The anomalously low mantle viscosity in these regions also amplifies the glacial isostatic adjustment signal associated with glacier changes during the 20th century, causing it to be an important (and even dominant) contributor to the modelled relative sea-level changes over the 21st century. [ABSTRACT FROM AUTHOR]

Mass loss from Antarctica's three largest ice shelves is dominated by calving, primarily of large tabular icebergs every few decades. Smaller, more frequent calving events also occur, but it is more difficult to detect them and quantify their contribution to total ice‐shelf mass loss. We used surface elevation data from NASA's ICESat‐2 laser altimeter to examine the structure of the Ross Ice Shelf front between October 2018 and July 2020. Profiles frequently show a depression a few meters deep about 200–800 m upstream of the front, with higher values on the eastern portion of the ice shelf. This structure results from bending due to buoyancy of a submerged ice bench generated by ice‐front melting near the waterline when warm water is present in summer. These bending stresses may cause small‐scale calving events whose frequency would change as summer sea ice and atmosphere–ocean heat exchanges vary over time. Plain Language Summary: Mass loss from Antarctica's floating ice shelves, which form as the ice sheet extends into the Southern Ocean, influences how quickly grounded ice flows into the ocean. Estimating future sea‐level change from grounded‐ice loss therefore requires understanding, and developing models for, the processes that affect ice shelves. We used measurements of surface height from NASA's recently launched ICESat‐2 mission to explore one such process, the calving of small icebergs due to upper‐ocean melting of the ice front. We focus on the large Ross Ice Shelf. This local melting leads to bending of the ice shelf that can be seen in ICESat‐2 profiles that cross the ice front. The bending may also fracture the ice shelf to create small icebergs. We found that these surface structures are generally larger on the eastern portion of Ross Ice Shelf than on the western portion. We suggest that this pattern is due to differences in ice, ocean, and sea ice conditions that promote or impede the melting responsible for the ice‐shelf bending. ICESat‐2 will allow us to monitor changes in these small‐scale structures and any associated calving events, which will provide clues about how ice shelves will change in the future. Key Points: We used ICESat‐2 laser altimetry to map prevalent rampart‐moat (R‐M) structures along the Ross Ice Shelf frontR‐M structures indicate a submerged buoyant bench seaward of the aerial ice front and ice stresses that may cause small‐scale calvingAlong‐front variation of R‐M height differences provides insight into sensitivity to oceanic and glaciological conditions [ABSTRACT FROM AUTHOR]

Glacial isostatic adjustment is largely governed by rheological properties of the Earth's mantle. Large mass redistributions in the ocean-cryosphere system and the subsequent response of the visco-elastic Earth have led to dramatic sea level changes in the past. This process is ongoing and in order to understand and predict current and future sea level changes the knowledge of mantle properties such as viscosity is essential. In this study we present a method to obtain estimates of mantle viscosities by assimilation of relative sea level data into a visco-elastic model of the lithosphere and mantle. We set up a particle filter with probabilistic resampling. In an identical twin experiment we show that mantle viscosities can be recovered in a glacial isostatic adjustment model of a simple three layer earth structure consisting of an elastic lithosphere and two mantle layers of different viscosity. In two scenarios we investigate the dependence of the ensemblebehavior on the ensemble initialization and observation uncertainties and show that the recovery is successful if the target parameter values are properly sampled by the initial ensemble probability distribution. This even includes cases in which the target viscosity values are located far in the tail of the initial ensemble probability distribution. We then successfully apply the method to two special cases that are relevant for the assimilation of real observations: 1) using observations taken from a single region only, here Laurentide and Fennoscandia, respectively, and 2) using only observations from the last 10 kyrs. [ABSTRACT FROM AUTHOR]

As recovering the crust–mantle/Moho density contrast (MDC) significantly depends on the properties of the Earth's crust and upper mantle, varying from place to place, it is an oversimplification to define a constant standard value for it. It is especially challenging in Antarctica, where almost all the bedrock is covered with a thick layer of ice, and seismic data cannot provide a sufficient spatial resolution for geological and geophysical applications. As an alternative, we determine the MDC in Antarctica and its surrounding seas with a resolution of 1° × 1° by the Vening Meinesz-Moritz gravimetric-isostatic technique using the XGM2019e Earth Gravitational Model and Earth2014 topographic/bathymetric information along with CRUST1.0 and CRUST19 seismic crustal models. The numerical results show that our model, named HVMDC20, varies from 81 kg m−3 in the Pacific Antarctic mid-oceanic ridge to 579 kg m−3 in the Gamburtsev Mountain Range in the central continent with a general average of 403 kg m−3. To assess our computations, we compare our estimates with those of some other gravimetric as well as seismic models (KTH11, GEMMA12C, KTH15C and CRUST1.0), illustrating that our estimates agree fairly well with KTH15C and CRUST1.0 but rather poor with the other models. In addition, we compare the geological signatures with HVMDC20, showing how the main geological structures contribute to the MDC. Finally, we study the remaining glacial isostatic adjustment effect on gravity to figure out how much it affects the MDC recovery, yielding a correlation of the optimum spectral window (7≤ n ≤12) between XGM2019e and W12a GIA models of the order of ∼0.6 contributing within a negligible |$ \pm 14$| kg m−3 to the MDC. [ABSTRACT FROM AUTHOR]

Earth system and climate modelling involves the simulation of processes on a wide range of scales and within and across various compartments of the Earth system. In practice, component models are often developed independently by different research groups, adapted by others to their special interests and then combined using a dedicated coupling software. This procedure not only leads to a strongly growing number of available versions of model components and coupled setups but also to model- and high-performance computing (HPC)-system-dependent ways of obtaining, configuring, building and operating them. Therefore, implementing these Earth system models (ESMs) can be challenging and extremely time consuming, especially for less experienced modellers or scientists aiming to use different ESMs as in the case of intercomparison projects. To assist researchers and modellers by reducing avoidable complexity, we developed the ESM-Tools software, which provides a standard way for downloading, configuring, compiling, running and monitoring different models on a variety of HPC systems. It should be noted that ESM-Tools is not a coupling software itself but a workflow and infrastructure management tool to provide access to increase usability of already existing components and coupled setups. As coupled ESMs are technically the more challenging tasks, we will focus on coupled setups, always implying that stand-alone models can benefit in the same way. With ESM-Tools, the user is only required to provide a short script consisting of only the experiment-specific definitions, while the software executes all the phases of a simulation in the correct order. The software, which is well documented and easy to install and use, currently supports four ocean models, three atmosphere models, two biogeochemistry models, an ice sheet model, an isostatic adjustment model, a hydrology model and a land-surface model. Compared to previous versions, ESM-Tools has lately been entirely recoded in a high-level programming language (Python) and provides researchers with an even more user-friendly interface for Earth system modelling. ESM-Tools was developed within the framework of the Advanced Earth System Model Capacity project, supported by the Helmholtz Association. [ABSTRACT FROM AUTHOR]

Robert Westaway was a structural and hard-rock geologist who turned his attention to the study of Late Cenozoic fluvial archives, believing that the preservation of staircases of river terraces, particularly representing the Middle and Late Pleistocene, could only be explained in terms of crustal activity in response to surface processes, the latter affected by climatic change. His entry into this research area coincided with the realisation that such terrace sequences required surface or crustal uplift to have taken place over the time interval represented. Workers were unable to explain the observed amounts of uplift in terms of erosional isostasy, a process that could potentially have explained such one-way crustal movement. Westaway envisaged a mechanism by which mobile lower crust migrated to beneath uplifting areas, maintaining and reinforcing their uplift. The mechanism requires complex mathematics to explain it, as well as lending itself to mathematical modelling of the process, based on varying crustal properties and changes in the rates of surface processes in response to climatic fluctuation. Essentially the lower-crustal effect can be envisaged as a positive-feedback enhancement of erosional isostasy. It became apparent that Westaway's theories could explain geomorphological and sedimentary fluvial archives that were otherwise difficult to elucidate. Mantle-based erosional isostasy could not explain terrace staircases, for example. Many of these occur in regions that are tectonically inactive, and so cannot be attributed to neotectonic activity. A game-changer in terms of persuading the wider community came from the recognition of crustally ultrastable regions in which progressive long-timescale uplift has not occurred: Archaean cratons. Westaway's envisaged lower-crustal flow would not be expected in such regions, which have cold, brittle and immobile crust to its full depth. Ancient fluvial deposits are found close to modern valley-floor levels in such areas. Regions of younger Precambrian crust (Proterozoic) showing intermediate situations were subsequently identified. Other dilemmas could be resolved, such as the 'back-tilting' of the early-Middle Pleistocene Bytham River in the English Midlands, caused by its drainage crossing crustal blocks with different properties that have accordingly experienced differential uplift. Although glacio-isostasy, mostly seen in the effects of rebound since the Last Glacial Maximum (LGM), is largely accommodated in the mantle, and thus is reversed as a response to glacial loading and unloading, in areas of suitable crustal type there is evidently a small lower-crustal component that is less readily reversible. Westaway's important contribution has yet to be fully integrated into received wisdom in geomorphological and Quaternary circles, although much of it is now widely accepted and more will be explored and published in due course. [ABSTRACT FROM AUTHOR]

Glacial isostatic adjustment (GIA) is the solid Earth's viscoelastic response to ice sheet deglaciations. Studies of GIA provide insights into crustal and mantle rheology, mass redistribution, relative paleo sea-level variations, and polar wander. In North America, GIA causes large-scale and low-gradient vertical displacement, but limited ground-based measurements in some places hinder accurate detection of such signals. This study proposes a workflow to extract GIA-induced land deformation using interferometric synthetic aperture radar (InSAR) time-series over the southern Hudson Bay land region. The workflow incorporates several model-based corrections to account for multiple elastic lithospheric responses and atmospheric phase disturbances, significantly reducing variances in the estimated time-series. It further separates the GIA signals from residual short-period noise through a spatiotemporal filter, as demonstrated in variogram analyses. With the workflow we produced the first high-resolution InSAR-based GIA vertical velocity map in the southern Hudson Bay land area at an estimated uncertainty of 2 mm/yr. Our result exhibits first-order agreement with contemporary GIA model predictions, and suggests that higher-level complexities such as 3D rheology structures or spatially uneven loading dynamics may exist in this region. • First InSAR-derived high-res GIA-induced land deformation in Hudson Bay. • A comprehensive workflow with model-based corrections and spatiotemporal filtering. • Noise contribution from different confounding factors is analyzed. • Variograms show significant reduction of noise at different processing stages. • InSAR-derived velocity shows a different gradient pattern from ICE-6G_D predictions. [ABSTRACT FROM AUTHOR]

Time-variable gravity field models obtained from satellite gravimetric techniques allow for the assessment of ice sheet mass changes in remote polar regions, such as Greenland and Antarctica. So far, GRACE has been the primary mission for obtaining the global time-variable gravity field models. However, GRACE was launched in 2002, thus very little is known about the global mass changes before this data, as well as between GRACE and its successor – GRACE Follow-On. We derive a method of gravity field recovery based on Satellite Laser Ranging (SLR) data to geodetic satellites that allows for obtaining direct ice mass change estimates for a period longer by 10 years than that provided by the GRACE missions. The developed method is based on splitting normal equation systems and re-stacking the solutions which allow for stable inversion, reduces the correlations between obtained parameters, stabilizes the ice mass estimates in polar regions, and reduces the noise over oceans by a factor of four. The secular trends obtained from SLR are equal to −113.5 and −82.8 Gt/year, whereas these are −119.1 and −83.3 Gt/year from GRACE and GRACE-FO to degree and order 10 for Greenland and West Antarctica, respectively, for the common period of 2002–2021 and after removing the post-glacial rebound effect. Despite the conformity of the trend and patterns, an underestimation is observed in the solutions expanded to degree and order 10. Therefore, scaling factors between GRACE/GRACE-FO expanded up to a degree and order 10 × 10 and 60 × 60 were derived and applied to SLR solutions to account for the differences in mass estimates due to the truncation of the models. SLR data revealed that in Greenland the smallest ice mass trends are for 1995–2000, 2000–2005, and 2015–2020 which are equal to +54.3, −15.5, and −75.9 Gt/year. The largest ice mass depletion periods took place in 2005–2010, 2010–2015, and recently in 2019–2021 with trends of −213.9, −287.2, and −276.1 Gt/year, respectively. For Greenland and West Antarctica, the period 2010–2015 is characterized by the most enormous ice depletion events, whereas the later 5-year period of 2015–2020 provided a near mass-equilibrium for Antarctica reducing the negative trend and returning to the situation from the '90s when no significant ice mass changes were observed. [Display omitted] • Satellite laser ranging (SLR) allows for ice mass change studies in polar regions. • No significant ice mass changes in Greenland and Antarctica are observed in the 90s. • Scaling factors can handle omission errors in solution expanded up to degree 10. • In Greenland, the years 2010–2015 are characterized by the largest ice mass loss. • The process of ice loss decelerated in 2015–2019 to speed up again afterwards. [ABSTRACT FROM AUTHOR]

The University of Glasgow awarded Paul an Honorary Research Fellowship on retirement in 2016. Paul Bishop moved from Sydney to Monash in 1989 before settling in Glasgow in 1998 where he became Professor of Physical Geography. Paul Bishop commenced his life in universities at Macquarie University in the School of Earth Sciences. [Extracted from the article]

We distinguish between two models of solid Earth's viscoelastic response to unloading of the Laurentide ice sheet over the past 26,000 years. The upper mantle viscosity in both models is 0.5 × 1021 Pa s. The viscosity of the top 500 km of the lower mantle (670–1,170 km) in model L17 is 13 × 1021 Pa s, eight times larger than the value of 1.6 × 1021 Pa s in ICE‐6G_D (VM5a). In ICE‐6G_D (VM5a), viscous relaxation of solid Earth was rapid 8,000 years ago and is slow today, with present‐day uplift at the Laurentide ice center being 12 mm/yr. In L17, solid Earth relaxed more slowly 8,000 years ago but is faster today, with present uplift of the ice center occurring at 20 mm/yr. The significant difference is not due to different ice histories given that total ice loss in L17 is just 12% less than in ICE‐6G_D. We determine a comprehensive set of GPS uplift rates for North America that is more accurate than in prior studies due to (1) more sites and a longer data time history, (2) removal of elastic loading produced by increase in Great Lakes water, and (3) technical advances in GPS positioning that have significantly reduced the dispersion in position estimates. We find uplift at the ice center to be about 12 mm/yr, supporting the low value of the viscosity of the top 500 km of the lower mantle in ICE‐6G_D (VM5a), but ruling out the high value in L17. Key Points: Laurentia is today rising at just ≈12 mm/yr, showing that solid Earth has to a large extent viscously relaxed in response to ice unloadingThe viscosity of the top third of the lower mantle is roughly 1.6 × 1021 Pa s, not 10 × 1021 Pa s or higherCorrecting Gravity Recovery and Climate Experiment data for glacial isostatic adjustment using the high viscosity value results in implausibly fast estimates of water loss [ABSTRACT FROM AUTHOR]

Building our capacity to predict the effect of sea-level rise on mangrove ecosystems can support management of the coastal zone in a way that is beneficial for mangroves and the communities that depend upon them. A commentary on Kerrylee Rogers' 'Accommodation space as a framework for assessing the response of mangroves to relative sea-level rise' If there is sufficient sediment, either delivered from the sea or through organic matter produced by the trees through root growth, mangroves could remain intact, essentially riding on top of the rising sediment pile as sea-level rise and accommodation space is filled (Saintilan I et al i ., 2020). [Extracted from the article]

Classical analyses of basal crevasse opening do not account for the free surface of a floating ice layer. We describe a high‐resolution numerical treatment of the opening of a single crevasse in a finite thickness elastic layer floating on an inviscid substrate. For low extensional stress (less than about half of the expected maximum for a freely floating shelf) the resulting crevasse height and width match previous studies. For larger magnitude applied extensional stresses, the new results predict basal crevasse widths an order of magnitude greater than the classical solution. An analysis using the thin‐layer approximation shows that the greatly increased predicted width of basal crevasse opening results from layer bending. Given that the height and width of basal crevasses are non‐linear functions of the stress experienced by an ice shelf, the new model results may enable better estimation of buttressing stresses for different parts of ice shelves. Plain Language Summary: Basal crevasses are water filled cracks the cut through much of the ice shelves and so contribute to their breakup. A new analysis shows that basal crevasses can break through significantly more of a floating ice layer than previous models that could not consider the bending of the ice layer. This more consistent approach suggests that basal crevasses can be an order of magnitude wider than estimated by the earlier studies. A simple analytic description of flexure of ice layers correctly predicts the maximum width of basal crevasses. Key Points: The first numerical analysis of basal crevasse opening including ice shelf bending is presentedBasal crevasses can be an order of magnitude wider than predicted by classical studiesAn analytic thin elastic plate description matches the numerical results in terms of crevasse width for a freely floating ice layer [ABSTRACT FROM AUTHOR]

The 4th order differential equation describing elastic flexure of the lithosphere is one of the cornerstones of geodynamics, key to understanding topography, gravity, glacial isostatic rebound, foreland basin evolution and a host of other phenomena. Despite being fully formulated in the 1940's, a number of significant issues concerning the basic equation have remained overlooked to this day. We first explain the different fundamental forms the equation can take and their difference in meaning and solution procedures. We then show how numerical solutions to flexure problems in general as they are currently formulated, are potentially unreliable in an unpredictable manner for cases where the coefficient of rigidity varies in space due to variations of the elastic thickness parameter. This is due to fundamental issues related to the numerical discretisation scheme employed. We demonstrate an alternative discretisation that is stable and accurate across the broadest conceivable range of conditions and variations of elastic thickness, and show how such a scheme can simulate conditions up to and including a completely broken lithosphere more usually modelled as an end loaded, single, continuous plate. Importantly, our scheme will allow breaks in plate interiors, allowing for instance, the creation of separate blocks of lithosphere which can also share the support of loads. The scheme we use has been known for many years, but remains rarely applied or discussed. We show that it is generally the most suitable finite difference discretisation of fourth order, elliptic equations of the kind describing many phenomena in elasticity, including the problem of bending of elastic beams. We compare the earlier discretisation scheme to the new one in 1 dimensional form, and also give the 2 dimensional discretisation based on the new scheme.We also describe a general issue concerning the numerical stability of any second order finite difference discretisation of a fourth order differential equation like that describing flexure where contrasting magnitudes of coefficients of different summed terms lead to round off problems which in turn destroy matrix positivity. We explain the use of 128 bit, floating point storage for variables to mitigate this issue. [ABSTRACT FROM AUTHOR]

The aim of this study was to create a 3D crustal deformation model for Estonia, based on dense Global Navigation Satellite System (GNSS) data (geodetic points with velocities) and validate the existing models of horizontal and vertical crustal deformations with velocities from Estonian GNSS measurements. The observations performed for at least eight years at Estonian GNSS permanent stations and during the GNSS campaign measurements of 1997, 2008 and 2017 on the Estonian 1st-order geodetic reference network were used as input data. Coordinates of the geodetic points were calculated in the ITRF2008 reference frame using the Precise Point Positioning method. Horizontal and vertical velocities (in the North, East and Up directions) were calculated for a total of 22 GNSS points. Models for horizontal and vertical velocities were calculated using the remove-compute-restore method. The model of glacial isostatic adjustment (GIA) of the Nordic Geodetic Commission NKG2016GIA was used as a reference model. Residual velocities of GNSS points showed a good fit with respect to the reference model. The residual velocities were analysed by geostatistical methods and the prediction surfaces of the residual velocities were modelled. After adding the surface of the residual velocities back to the reference model NKG2016GIA, the modelled surface EST2020VEL was obtained. The obtained model was compared with the up-to-date intraplate deformation model NKG_RF17VEL. It was found that recent Fennoscandian intraplate deformation models NKG2016LU and NKG_RF17VEL fitted well with the Estonian GNSS data. However, both models are systematically shifted with respect to the Estonian GNSS data. For applications in Estonia, it is better to use the fitted model EST2020VEL. The uncertainty of the model is estimated to be lower than ±0.5 mm/a. [ABSTRACT FROM AUTHOR]

Most of the carbon accumulated into peatlands is derived from Sphagnum mosses. During peatland development, the relative share of vascular plants and Sphagnum mosses in the plant community changes, which impacts ecosystem functions. Little is known on the successional development of functional plant traits or functional diversity in peatlands, although this could be a key for understanding the mechanisms behind peatland resistance to climate change. Here we aim to assess how functionality of successive plant communities change along the autogenic peatland development and the associated environmental gradients, namely peat thickness and pH, and to determine whether trait trade‐offs during peatland succession are analogous between vascular plant and moss communities.We collected plant community and trait data on successional peatland gradients from post‐glacial rebound areas in coastal Finland, Sweden and Russia, altogether from 47 peatlands. This allowed us to analyse the changes in community‐weighted mean trait values and functional diversity (diversity of traits) during peatland development.Our results show comparative trait trade‐offs from acquisitive species to conservative species in both vascular plant and Sphagnum moss communities during peatland development. However, mosses had higher resistance to environmental change than vascular plant communities. This was seen in the larger proportion of intraspecific trait variation than species turnover in moss traits, while the proportions were opposite for vascular plants. Similarly, the functional diversity of Sphagnum communities increased during the peatland development, while the opposite occurred for vascular plants. Most of the measured traits showed a phylogenetic signal. More so, the species common to old successional stages, namely Ericacae and Sphagna from subgroup Acutifolia were detected as most similar to their phylogenetic neighbours.Synthesis. During peatland development, vegetation succession leads to the dominance of conservative plant species accustomed to high stress. At the same time, the autogenic succession and ecological engineering of Sphagna leads to higher functional diversity and intraspecific variability, which together indicate higher resistance towards environmental perturbations. [ABSTRACT FROM AUTHOR]

Information on sea level and its temporal and spatial variability is of great importance for various scientific, societal and economic issues. This article reports about a new sea level dataset for the North Sea (named NorthSEAL) of monthly sea level anomalies (SLA), absolute sea level trends and sea level mean annual amplitudes over the period 1995-2019. Uncertainties and quality flags are provided together with the data. The dataset has been created from multi-mission cross-calibrated altimetry data, preprocessed with coastal dedicated approaches and gridded with innovative methods to a 6-8 km wide triangular mesh. The comparison of SLA and tide gauge time series shows a good consistency with average correlations of 0.85 and maximum correlations of 0.93. The improvement with respect to existing global gridded altimetry solutions amounts to 8-10%, and it is most pronounced in complicated coastal environments such as river mouths or regions sheltered by islands. The differences in trends at tide gauge locations depend on the vertical land motion model used to correct relative sea level trends. The best consistency with a median difference of 0.04 ± 1.15 mm/year is reached by applying a recent glacial isostatic adjustment (GIA) model. With the presented sea level dataset, for the first time, a regionally optimized product for the entire North Sea is made available. It will enable further investigations of ocean processes, sea level projections and studies on coastal adaptation measures. The NorthSEAL data is available at https://doi.org/10.17882/79673 (Müller et al., 2021). [ABSTRACT FROM AUTHOR]

Sea-level budgets account for the contributions of processes driving sea-level change, but are predominantly focused on global-mean sea level and limited to the 20th and 21st centuries. Here we estimate site-specific sea-level budgets along the U.S. Atlantic coast during the Common Era (0–2000 CE) by separating relative sea-level (RSL) records into process-related signals on different spatial scales. Regional-scale, temporally linear processes driven by glacial isostatic adjustment dominate RSL change and exhibit a spatial gradient, with fastest rates of rise in southern New Jersey (1.6 ± 0.02 mm yr−1). Regional and local, temporally non-linear processes, such as ocean/atmosphere dynamics and groundwater withdrawal, contributed between −0.3 and 0.4 mm yr−1 over centennial timescales. The most significant change in the budgets is the increasing influence of the common global signal due to ice melt and thermal expansion since 1800 CE, which became a dominant contributor to RSL with a 20th century rate of 1.3 ± 0.1 mm yr−1. Sea-level rise is an important part of climate change, but most sea-level budgets are global and cannot capture important regional changes. Here the authors estimate sea-level budgets along the U.S. Atlantic coast, finding a faster rate of rise during the 20th century than any time in the past 2000 years. [ABSTRACT FROM AUTHOR]

In this study, we present a new Moho depth model in Fennoscandia and its surroundings. The model is tailored from data sets of XGM2019e gravitationl field, Earth2014 topography and seismic crustal model CRUST1.0 using the Vening Meinesz-Moritz model based on isostatic theory to a resolution of 1° × 1°. To that end, the refined Bouguer gravity disturbance is determined by reducing the observed field for gravity effect of topography, density heterogeneities related to bathymetry, ice, sediments, and other crustal components. Moreover, stripping of non-isostatic effects of gravity signals from mass anomalies below the crust due to crustal thickening/thinning, thermal expansion of the mantle, Delayed Glacial Isostatic Adjustment (DGIA), i.e., the effect of future GIA, and plate flexure has also been performed. As Fennoscandia is a key area for GIA research, we particularly investigate the DGIA effect on the gravity disturbance and gravimetric Moho depth determination in this area. One may ask whether the DGIA effect is sufficiently well removed in the application of the general non-isostatic effects in such an area, and to answer this question, the Moho depth is determined both with and without specific removal of the DGIA effect prior to non-isostatic effect and Moho depth determinations. The numerical results yield that the RMS difference of the Moho depth from our model HVMD19 vs. the seismic CRUST19 and GRAD09 models are 3.8/4.2 km and 3.7/4.0 km when the above strategy for removing the DGIA effect is/is not applied, respectively, and the mean value differences are 1.2/1.4 km and 0.98/1.4 km, respectively. Hence, our study shows that the specific correction for the DGIA effect on gravity disturbance is slightly significant, resulting in individual changes in the gravimetric Moho depth up to − 1.3 km towards the seismic results. On the other hand, our study shows large discrepancies between gravimetric and seismic Moho models along the Norwegian coastline, which might be due to uncompensated non-isostatic effects caused by tectonic motions. [ABSTRACT FROM AUTHOR]

The transition to a post‐orogenic state in mountain ranges has been identified by a change from active subsidence to isostatic rebound of the foreland basin. However, the nature of the interplay between isostatic rebound and sediment supply, and their impact on the topographic evolution of a range and foreland basin during this transition, has not been fully investigated. Here, we use a box model to explore the syn‐ to post‐orogenic evolution of foreland basin/thrust wedge systems. Using a set of parameter values that approximate the northern Pyrenees and the neighbouring Aquitaine foreland basin, we evaluate the controls on sediment drape over the frontal parts of the retro‐wedge following cessation of crustal thickening. Conglomerates preserved at approximately 600‐m elevation, which is ~ 300 m above the present mountain front in the northern Pyrenees are ca. 12 Ma, approximately 10 Myrs younger than the last evidence of crustal thickening in the wedge. Using the model, this post‐orogenic sediment drape is explained by the combination of a sustained, high sediment influx from the range into the basin relative to the efflux out of the basin, combined with cessation of the generation of accommodation space through basin subsidence. Post‐orogenic sediment drape is considered a generic process that is likely to be responsible for elevated low‐gradient surfaces and preserved remnants of continental sedimentation draping the outer margins of the northern Pyrenean thrust wedge. [ABSTRACT FROM AUTHOR]

The colonization of land by fungi had a significant impact on the terrestrial ecosystem and biogeochemical cycles on Earth surface systems. Although fungi may have diverged ~1500–900 million years ago (Ma) or even as early as 2400 Ma, it is uncertain when fungi first colonized the land. Here we report pyritized fungus-like microfossils preserved in the basal Ediacaran Doushantuo Formation (~635 Ma) in South China. These micro-organisms colonized and were preserved in cryptic karstic cavities formed via meteoric water dissolution related to deglacial isostatic rebound after the terminal Cryogenian snowball Earth event. They are interpreted as eukaryotes and probable fungi, thus providing direct fossil evidence for the colonization of land by fungi and offering a key constraint on fungal terrestrialization. Fungi may have evolved up to 2.4 billion years ago, but it is unclear when they first colonized land. Here Gan and colleagues report filamentous Ediacaran microfossils from South China that may represent early terrestrial fungi. [ABSTRACT FROM AUTHOR]

Satellite altimetry missions provide a quasi-global synoptic view of sea level variations over more than 25 years and provide regional sea level (SL) indicators such as trends and accelerations. Estimating realistic uncertainties on these quantities is crucial to address current climate science questions. While uncertainty estimates are available for the global mean sea level (GMSL), information is not available at local scales so far. We estimate a local satellite altimetry error budget and use it to derive local error variance-covariance matrices, and estimate confidence intervals on trends and accelerations at the 90% confidence level. Over 1993–2019, we find that the average local sea level trend uncertainty is 0.83 mm.yr−1 with values ranging from 0.78 to 1.22 mm.yr−1. For accelerations, uncertainties range from 0.057 to 0.12 mm.yr−1, with a mean value of 0.062. We also perform a sensitivity study to investigate a range of plausible error budgets. Local error levels, error variance-covariance matrices, SL trends and accelerations, along with corresponding uncertainties are provided. Measurement(s) sea surface height Technology Type(s) satellite radar altimetry Factor Type(s) year of data collection Sample Characteristic - Environment sea • ocean Sample Characteristic - Location global Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.13297757 [ABSTRACT FROM AUTHOR]

Retrospective sea-level mapping advances a promising geographic solution to the longstanding mystery about when, where, and how the first Americans crossed over from Asia. A paleotopographic reconstruction accounting for Glacial Isostatic Adjustment digitally explores an archipelago about 1400 km long that likely existed from >30,000 BP to 8000 BP. Here the authors examine this Bering Transitory Archipelago in regard to established hypotheses—Clovis-first, Ice-free (deglaciation) Corridor, Kelp Highway, and Beringian Standstill hypotheses—and a new Stepping-Stones hypothesis. Scores of islands at that time would meet all requirements previously proposed for a viable hypothesis: a source population in Asia, a pathway with abundant sustenance, settlements in North America soon after but not before, and an isolated sanctuary where Beringians could have become genetically distinct. [ABSTRACT FROM AUTHOR]

We assess how recent glacial isostatic adjustment (GIA) and inter‐earthquake stress transfer modulated the state of stress on major faults in Southeast Alaska, and how these effects may have influenced recent large and moderate earthquakes. The Glacier Bay Icefield has lost >3,000 km3 of ice since ca. 1770, with ice thinning up to 1.5 km, and the rest of southeast Alaska has been deglaciating since ca. 1900. The resulting GIA response in the solid earth produces present‐day surface uplift rates of up to ∼4 cm/yr, among the fastest on Earth. This rapid deformation occurs directly alongside and atop the Fairweather Fault, which accommodates 4–5 cm/yr of right‐lateral motion through slip in frequent large earthquakes, recently including a Mw∼7.8 earthquake in 1958. We find that the 1958 earthquake nucleated very close to the location of maximum GIA‐induced Coulomb stress increase on the Fairweather Fault between 1770 and 1958 (estimated at ∼0.2–0.6 MPa), on the only section of fault where GIA‐induced stress changes had involved both right‐lateral shearing and unclamping. The September 10, 1899 Mw∼8.1 Yakutat Bay earthquake also promoted failure on at least the northwest part of the eventual 1958 rupture. In turn, the 1899 and 1958 earthquakes and GIA promoted failure along the St. Elias compressional margin, the site of a Mw∼7.4 event in 1979. While rapid tectonic loading is very likely the main driver of earthquakes in southeast Alaska, we estimate that 23 of 30 instrumentally constrained Mw ≥ 5.0 earthquakes in this region were also promoted by post‐1770 GIA. Key Points: The 1958 Fairweather Fault earthquake nucleated very close to the maximum post‐1770‐GIA‐induced Coulomb stress increase on the faultThe September 10, 1899 Mw∼8.1 earthquake promoted failure at the northwest end of the 1958 rupture, and on thrust faults of the St. Elias marginPost‐1770 GIA likely promoted failure in 23 of the 30 Mw ≥ 5.0 recorded earthquakes in southeast Alaska since 1920 [ABSTRACT FROM AUTHOR]

Macaronesia is a complex oceanic region spanning three tectonic plates in the northeast Atlantic ocean. It is composed of four archipelagos, widely distributed and limited to the east by the Iberian Peninsula and north-western coast of Africa. This study aims to clarify recent Macaronesian kinematics from 19 GNSS stations located on the four archipelagos and the Iberian and African coastlines. The analysis is based on nearly 15 years of common data acquisition and aimed to detect new effects of intraplate tectonics or similar local/regional events consistent with calculated ground displacements. Evaluating the GNSS stations residual velocities relative to those expected from the NNR-MORVEL56 model, higher residuals were found at continental coastal stations (Africa) than at oceanic ones (Canaries and Madeira). From the computed strain rate map, the possible existence of a shear zone connecting the Gloria and Transmoroccan fault systems, already mentioned by other authors, was depicted. Cluster statistical analysis of the horizontal residual velocities helped to identify tectonic boundaries in Macaronesia and four groups of analogous intraplate residual velocities within this region. Three of four groups were identified in the Azores, highlighting the African-Nubian-Eurasian diffuse plate boundary in this region. Furthermore, in the Canary Islands, two distinct kinematic behaviours were detected, possibly due to the activity along a previously detected tectonic fault between Tenerife and Gran Canaria, where some stations have similar intraplate residuals to those at Madeira and Cape Verde stations, while others have similar intraplate residuals to those of continental stations. Finally, all stations on oceanic crust, except Cape Verde, present recent ground subsidence which may be attributed to isostatic adjustment. [ABSTRACT FROM AUTHOR]

During the last deglaciation of Fennoscandia, large earthquakes may have induced secondary effects on the high-latitude coastal regions and continental margins primarily from surface rock avalanches, large and small submarine slides, local and regional flooding, and tsunamis. In this overview, we show that the climate-earthquake-slide-tsunami causal sequence is particularly important, as is structural inheritance and rejuvenation. However, there are potential earthquake-generating early Holocene faults also beyond the previously defined Lapland Fault Province. Thus, we introduce the term the Greater Lapland Fault Province. Earthquakes in the expanded fault province are candidates for triggering the 8.1 ka Storegga Megaslide and/or its predecessors and coeval tsunamis. The events might have released other submarine slides, gas hydrate expulsion leaving large pockmark fields and rock avalanches and submarine mass wasting in fjord and lake settings. Moreover, seismic events may also have triggered local and regional flooding by breakup of ice and sediment barriers. [ABSTRACT FROM AUTHOR]

Earthquake-induced deformations located near Murmansk City were investigated for information on the age, tectonic position and spatial occurrence of paleo-earthquakes. The main earthquake-generating zone is identified to be the system of strike slip faults and reverse-oblique faults trending NNW along the Kola River valley. We used radiocarbon analysis and paleogeographic reconstructions and revealed three episodes of increased seismic activity: from 9500 to 10 500 cal BP, from 892 to 1182 cal BP, and from 200 to 300 cal BP. Based on the peak ground velocity estimation method we suggest that an earthquakes with a maximum moment magnitude up to Mw ≈ 6.0-6.5 may have taken place in the studied area. The recorded location of seismogenic deformation near faults indicates area of strong Late Glacial and Holocene earthquakes occurring in the northern Kola Peninsula; this is also consistent with observations concerning the historical events of 1772 and 1873, which took place near the area. Combined with previous data on palaeoseismicity in Kola region, our studies indicate a longer lasting and more complex spatial and temporal history of postglacial seismicity in the Northeastern Fennoscandian Shield area. In contrast to the generally accepted opinion, strong seismic events occurred not only during the deglaciation period or immediately after it, but continued until the late Holocene and the last centuries. Glacial isostasy as a factor giving rise to stresses has become minimal by the present time, while the tectonic factor continues to be felt. [ABSTRACT FROM AUTHOR]

Cave deposits are powerful archives for reconstructing past sea levels as they are generally protected from weathering and erosion by their location and can be dated with U-series methods. Two main categories of cave deposits are recognized as sea level indicators: phreatic overgrowth on speleothems (POS) and submerged vadose speleothems (SVS). POS have the great advantage that they precipitate on preexisting vadose supports at a brackish water level equivalent to sea level when air-filled chambers of coastal caves are flooded by rising sea. SVS are also useful, but sea level is inferred indirectly as periods of growth provide constraints on maximum sea level positions, whereas growth hiatuses, sometimes difficult to observe, may indicate times when cave passages are submerged by sea high stands, hence they record minimum sea level elevations. Here we describe a compilation that summarizes the current knowledge of MIS 5 (sensu lato) sea level captured by cave deposits. We used the framework of the World Atlas of Last Interglacial Shorelines (WALIS), a comprehensive sea level database, to provide a standardized format in order to facilitate scientific research on MIS 5 sea level. The discussion is MIS 5e-centered, but records that capture MIS 5c and 5a are also included. We present the data from 59 cave deposits (26 sea-level index points and 33 limiting points) in coastal caves located in eight different locations, and we include the spatial coverage, the samples used and their accuracy as indicators of sea level, the isotopic characteristics used to generate the U-Th chronologies, and their scientific relevance to understand past sea-level changes. The paper also emphasizes how some of these indicators are useful not only for the information they offer about the eustatic sea level, but more importantly: i) those from tectonically stable areas provide information on Earth deformation and regional ice sheet histories, thus refining the glacial isostatic adjustments models and ii) those from active regions can constrain regional tectonic uplift rates. The standardized sea-level database presented here is the first of its kind derived from cave deposits and contains all the information needed to assess former paleo relative sea level and the chronological constraints associated with them. The database is available open-access at http://doi.org/10.5281/zenodo.4313861 (Dumitru et al., 2020). [ABSTRACT FROM AUTHOR]

Greenland Ice Sheet surface elevation is changing as mass loss accelerates. In understanding elevation change, the magnitudes of physical processes involved are important for interpretation of altimetry and assessing changes in these processes. The four key processes are surface mass balance (SMB), firn densification, ice dynamics, and isostatic adjustment. We quantified these processes at Summit, Greenland, where monthly Global Navigation Satellite System (GNSS) snowmobile traverses measured elevation change from 2008 to 2018. We find an elevation increase of 0.019 m a−1. The sum of the effects of the four processes reproduces the measured elevation time series, in linear trend and in intra‐annual variability. The short‐term variability in elevation is primarily explained by the variability in SMB. Since SMB has not changed significantly over the last century, and the other processes change over longer time scales, the elevation change likely has been ongoing for at least the last 100 years. Key Points: Measurements of ice sheet elevation, flow divergence, firn densification, and accumulation are self‐consistent at Summit, GreenlandThe ice sheet surface at Summit, Greenland, is rising at 1.9 cm/year over the last decade, a trend likely unchanged in the last centuryShort‐term ice sheet elevation changes are dominated by surface mass balance changes [ABSTRACT FROM AUTHOR]

The Arctic Tern (Sterna paradisaea; takatakiaq in Inuttitut) breeds in the circumpolar Arctic and undertakes the longest known annual migration. In recent decades, Arctic Tern populations have been declining in some parts of their range, and this has been a cause of concern for both wildlife managers and Indigenous harvesters. However, limited scientific information is available on Arctic Tern abundance and distribution, especially within its breeding range in remote areas of the circumpolar Arctic. Knowledge held by Inuit harvesters engaged in Arctic Tern egg picking can shed light on the ecology, regional abundance and distribution of this marine bird. We conducted individual interviews and a workshop involving 12 Inuit harvesters and elders from Kuujjuaraapik, Nunavik (northern Québec), Canada, to gather their knowledge of Arctic Tern cultural importance, ecology, and stewardship. Interview contributors reported a regional decline in Arctic Tern numbers which appeared in the early 2000s on nesting islands near Kuujjuaraapik. Six possible factors were identified: (1) local harvest through egg picking; (2) nest disturbance and predation; (3) abandonment of tern nesting areas (i.e., islands that have become connected to the mainland due to isostatic rebound); (4) climate change; (5) natural abundance cycles within the Arctic Tern population; and (6) decline of the capelin (Mallotus villosus) in the region. Recommendations from Inuit contributors related to Arctic Tern stewardship and protection included: (1) conduct more research; (2) let nature take its course; (3) conduct an awareness campaign; (4) implement an egg picking ban; (5) coordinate local egg harvest; (6) start 'tern farming'; (7) protect Arctic Terns across their migration route; and (8) harvest foxes predating on terns. Our study highlighted complementarities between Inuit knowledge and ecological science, and showed that Inuit harvesters can make substantial contributions to ongoing and future Arctic tern research and management initiatives. [ABSTRACT FROM AUTHOR]

The article informs about how rising sea levels have been associated with human migration and behavioral shifts throughout prehistory, often with an emphasis on landscape submergence and consequent societal collapse. It also mentions how climate warming and persistent sea-level rise will cause increased extreme sea levels as a result of changes in water levels, tidal dynamics, wave climates, and storm surges.

Vertical land motion (VLM) from past and ongoing glacial changes can amplify or mitigate ongoing relative sea level change. We present a high‐resolution VLM model for the wider Arctic, that includes both present‐day ice loading (PDIL) and glacial isostatic adjustment (GIA). The study shows that the nonlinear elastic uplift from PDIL is significant (0.5–1 mm yr−1) in most of the wider Arctic and exceeds GIA at 15 of 54 Arctic GNSS sites, including sites in nonglaciated areas of the North Sea region and the east coast of North America. Thereby the sea level change from PDIL (1.85 mm yr−1) is significantly mitigated from VLM caused by PDIL. The combined VLM model was consistent with measured VLM at 85% of the GNSS sites (R=0.77) and outperformed a GIA‐only model (R=0.64). Deviations from GNSS‐measured VLM can be attributed to local circumstances causing VLM. Plain Language Summary: From 2003 to 2015, the Northern Hemisphere lost more than 6,000 gigatons of land ice, which added nearly 18 mm to the global mean sea level rise. Loss of land‐based ice results in the vertical deformation of the Earth's surface. Ongoing rebounding or subsidence caused by the end of the last ice age is often assumed to govern vertical deformation. However, present‐day ice loss from Greenland and Arctic glaciers also cause an immediate vertical deformation. By using an vertical deformation model, that includes both components, we can explain GPS‐measured deformation occurring in the Arctic. Our results show that the present‐day Arctic ice loss contribution to vertical deformation is ∼0.5 to 1 mm yr−1 in the wider northern region. This exceeds deformation caused by the disappearance of the last ice ages at many coastal regions, including the North Sea region and the North American Atlantic coast. The Arctic present‐day ice loss included in the VLM model equals a global sea level rise of 1.5 mm yr−1, which means that 30–80% of the sea level rise caused by Arctic ice loss is mitigated by surface uplift caused by the same ice loss. Key Points: Elastic VLM from present‐day ice loss in the Arctic causes significant uplift of coastlines in North America and Northern EuropeA combined VLM model that includes GIA and elastic VLM yields good agreement with GNSS stations in the wider ArcticResiduals between GNSS and modeled VLM provide an approximation of extraordinary VLM caused by local circumstances [ABSTRACT FROM AUTHOR]

The extended Burgers material (EBM) model provides a linear viscoelastic theory for interpreting a variety of rock deformation phenomena in geophysics, playing an increasingly important role in parameterizing laboratory data, providing seismic wave velocity and attenuation interpretations, and in analyses of solid planetary tidal dispersion and quality factor Q. At the heart of the EBM approach is the assumption of a distribution of relaxation spectra tied to rock grain boundary and interior granular mobility. Furthermore, the model incorporates an asymptotic long-term limiting behavior that is Maxwellian. Here we use the extensively developed linear theory of viscoelasticity to isolate those parameters of EBM that apply to both post-seismic relaxation processes involving flow of olivine rich upper mantle material and to studies of tides, where periods of forcing range from 12 h to 18.6 years. The isolated EBM parameters should also apply to theoretical and geodetic studies of glacial isostatic adjustment, especially when the initiation of continuous cryospheric surface unloading dates to the 20th or 21st century. Using analytical Laplace transformed solutions of Boussinesq's half-space load problem, we show that the effects of EBM transient rheology may have substantial influence on geodetic interpretations of unloading induced crustal motions even on time scales that are sub-decadal. [ABSTRACT FROM AUTHOR]

The study of vertical crustal motion in the contiguous United States (CONUS) has traditionally focused on the high‐amplitude deformation caused by glacial isostatic adjustment. To better understand more subtle vertical crustal motion resulting from other geophysical processes, we take advantage of the ongoing expansion of continuous Global Positioning System (GPS) networks, whose geodetic observations provide ever‐increasing accuracy and spatial resolution of surface deformation. Using position data for 2,782 GPS stations operating between 2007 and 2017, we produce a new vertical crustal velocity field for the CONUS region. We estimate our own station velocities to ensure consistent treatment of time series outliers, noise, and offsets, and we use adaptive smoothing and interpolation to account for spatially varying station density. Our velocity field reveals spatially coherent vertical features that are representative of regional tectonics, hydrologic, and anthropogenic processes. By removing the effects of modeled glacial isostatic adjustment and hydrologic loading estimated from Gravity Recovery and Climate Experiment (GRACE) data, we reduce the variance in our velocity field by 36% and show residuals potentially due to geocenter motion and underlying tectonics. Key Points: GPS vertical velocity field of CONUS reflects tectonics, surface mass loading, and isostatic reboundResidual velocities may reflect Earth's center of mass translation motionRemoving GIA model predictions and GRACE‐derived hydrologic loading reduces velocity field variance by 36% [ABSTRACT FROM AUTHOR]

Holocene relative shore level (RSL) changes and Stone Age palaeogeography of Hiiumaa Island are reconstructed using airborne LiDAR elevation data, sedimentological and archaeological proxies as well as GIS‐based landscape modelling. Altogether, 38 RSL index and limiting points are used in modelling and presented in the current paper. The highest raised shorelines of the Ancylus Lake and Litorina Sea, mapped at the elevations of 47 and 26 m a.s.l., formed around 10.3 and 7.4 cal. ka BP, respectively. The reconstructed RSL curve reveals a 20‐m drainage of Ancylus Lake followed by a land‐uplift‐driven 3‐m regression during the Initial Litorina Sea period. RSL rise during the Litorina Sea transgression remained below 4 m and its maximum was reached later than proposed previously, discarding therefore the idea of highly diachronous Litorina culmination in the eastern Baltic Sea. During the period 7.4–6.0 cal. ka BP,RSL fall was about 4.3 mm a−1, and afterwards in average at about 1 mm‐1 less suggesting deceleration in isostatic rebound. suggesting deceleration in isostatic rebound. Palaeogeographical reconstructions show that during its earliest occupation at about 7.6 cal. ka BP less than 1% of the terrain of Hiiumaa was above the sea level and that wind‐protected SE exposed shores were the most preferred campsite locations of Late Mesolithic and Neolithic settlers. These campsites are located successively at lower elevations following the shoreline retreat and show repeated use of this coastal area between 7.6 and 4.6 cal. ka BP. Due to the spread of the Corded Ware culture around 4.8–4.0 cal. ka BP the settlements of Hiiumaa Island and many other coastal areas of the eastern Baltic moved from the coast to more suitable places for agriculture and animal husbandry. [ABSTRACT FROM AUTHOR]

Global choke points are preeminent nodes in geographic networks and geopolitical touchpoints subject to control by nations. They appear today as recurring theaters of conflict worldwide and also in archaeological investigations delving thousands of years back in time. How different were today's global choke points at the Last Glacial Maximum (LGM) ~ 20,000 years ago? For the first time, we map nine of them to visualize their conditions at LGM. The global feature aquaterra—all lands inundated and exposed repeatedly during the Late Pleistocene ice ages—initially was mapped as first approximations of sea level. Here we refine its boundaries using Glacial Isostatic Adjustment (GIA) models to account for the Earth's deformation and horizontal migrations of shorelines in response to glacial melting. We found three choke points sufficiently open to navigation, but six others presented substantially greater barriers than today. Implications include strategic insights on where to search for submerged evidence of human settlement. [ABSTRACT FROM AUTHOR]

Understanding future impacts of sea-level rise at the local level is important for mitigating its effects. In particular, quantifying the range of sea-level rise outcomes in a probabilistic way enables coastal planners to better adapt strategies, depending on cost, timing and risk tolerance. For a time horizon of 100 years, frameworks have been developed that provide such projections by relying on sea-level fingerprints where contributions from different processes are sampled at each individual time step and summed up to create probability distributions of sea-level rise for each desired location. While advantageous, this method does not readily allow for including new physics developed in forward models of each component. For example, couplings and feedbacks between ice sheets, ocean circulation and solid-Earth uplift cannot easily be represented in such frameworks. Indeed, the main impediment to inclusion of more forward model physics in probabilistic sea-level frameworks is the availability of dynamically computed sea-level fingerprints that can be directly linked to local mass changes. Here, we demonstrate such an approach within the Ice-sheet and Sea-level System Model (ISSM), where we develop a probabilistic framework that can readily be coupled to forward process models such as those for ice sheets, glacial isostatic adjustment, hydrology and ocean circulation, among others. Through large-scale uncertainty quantification, we demonstrate how this approach enables inclusion of incremental improvements in all forward models and provides fidelity to time-correlated processes. The projection system may readily process input and output quantities that are geodetically consistent with space and terrestrial measurement systems. The approach can also account for numerous improvements in our understanding of sea-level processes. [ABSTRACT FROM AUTHOR]

Earthquakes have been studied by means of seismometers recording the elastic waves travelling through the interior of our planet. Global Navigation Satellite System and Synthetic Aperture Radar surveys, measuring surface displacements, have provided additional information on earthquakes, as well as on those solid Earth processes responsible for them, such as subduction, collision and extension and the inter-seismic strain accumulation. This instrumentation is deployed over land and thus misses the seas, often surrounding regions where large earthquakes occur. This limitation is nowadays overcome by space gravity missions, thanks to their uniform coverage of the Earth, both inland and offshore. In this perspective, Gravitational Seismology has been identified as a new application of the Next-Generation Gravity Mission (NGGM), with the aim of evaluating its overall performance and of assessing the detectability of earthquake gravity signatures, as well as of those from active tectonics and inter-seismic deformation. Within the framework of self-gravitating viscoelastic Earth models, we have simulated the co- and post-seismic gravity signatures of 291 scenario earthquakes, with different occurrence times and geographical locations, focal mechanisms, depths and lines of strike, and included into the background gravity feeding the NGGM closed-loop simulation which provides observables of multiple pairs of GRACE-like satellites, given the instrument noise. NGGM earthquake detectability is herein defined on the possibility of estimating the amplitude of the original gravity signature of each earthquake by inversion of synthetic NGGM gravity data, consisting of 156 28-day gravity field solutions (about 11 years). For about two thirds of earthquakes of magnitude as low as 7, comparable with the 1980 Irpinia intraplate earthquake, the amplitudes have been estimated with a relative error less than 10% (and less than 50% for almost all the earthquakes), assuming as known the time variable contributions from atmosphere, oceans, hydrology, continental ice and glacial isostatic adjustment. When these contributions are inverted simultaneously with the earthquake ones, instead, we have had to increase the earthquake magnitude to 7.8 in order to estimate more than half of their amplitudes with a relative error less than 10%. We thus have shown that the NGGM will be able to detect, in most cases, the co- and post-seismic signatures of earthquakes of at least magnitude 7.8 and that this lower magnitude threshold can decrease down to magnitude 7 by improving the modelling of the background gravity field. [ABSTRACT FROM AUTHOR]

Accurate measurement of the local component of geodetic motion at GPS stations presents a challenge due to the need to separate this signal from the tectonic plate rotation. A pressing example is the observation of glacial isostatic adjustment (GIA) which constrains the Earth's response to ice unloading, and hence, contributions of ice-covered regions such as Antarctica to global sea level rise following ice mass loss. While both vertical and horizontal motions are of interest in general, we focus on horizontal GPS velocities which typically contain a large component of plate rotation and a smaller local component primarily relating to GIA. Incomplete separation of these components introduces significant bias into estimates of GIA motion vectors. We present the results of a series of tests based on the motions of GPS stations from East Antarctica: (1) signal separation for sets of synthetic data that replicate the geometric character of non-separable, and separable, GIA-like horizontal velocities; and (2) signal separation for real GPS station data with an appraisal of uncertainties. For both synthetic and real motions, we compare results where the stations are unweighted, and where each station is areal-weighted using a metric representing the inverse of the spatial density of neighbouring stations. From the synthetic tests, we show that a GIA-like signal is recoverable from the plate rotation signal providing it has geometric variability across East Antarctica. We also show that areal-weighting has a very significant effect on the ability to recover a GIA-like signal with geometric variability, and hence on separating the plate rotation and local components. For the real data, assuming a rigid Antarctic plate, fitted plate rotation parameters compare well with other studies in the literature. We find that 25 out of 36 GPS stations examined in East Antarctica have non-zero local horizontal velocities, at the 2σ level, after signal separation. We make the code for weighted signal separation available to assist in the consistent appraisal of separated signals, and the comparison of likely uncertainty bounds, for future studies. [ABSTRACT FROM AUTHOR]