Search

For about three decades, the Global Navigation Satellite System (GNSS) has been used for high-precision positioning in scientific and engineering applications, such as deformation monitoring for seismicity and volcano eruption. Such high-precision positioning applications require millimeter-level positioning accuracy. There are many man-made and natural reflective surfaces near the GNSS receiving antennas. GNSS signals can be reflected and then arrive at the GNSS antenna. The multipath effect occurs when the direct signal is mixed with the reflected signal at the GNSS receiver. Choke-ring antennas are designed to mitigate the multipath effect of reflected signals from below the horizontal plane of the GNSS receiving antenna. Moreover, GNSS receiving antennas at network/permanent stations are usually installed on tall pillars or monuments to prevent multipath from “ground” reflected signals. However, part of the reflected signals can still arrive at the GNSS antenna center and cause multipath errors in GNSS measurements. How much can the multipath effect be on the real-time GNSS-measured displacements in studies on seismicity and volcano eruption? This work investigates the below-the-horizon multipath effect of choke-ring antennas on GNSS carrier-phase measurements. Here we show the differenced carrier-phase multipath errors of two commonly used GNSS antennas at the International GNSS Service (IGS) tracking stations can reach 8 mm, the maximum, with the mean and SD in a few millimeters at the 95% confidence level. The findings of this work should be applicable to other choke-ring antennas with similar architecture. [ABSTRACT FROM AUTHOR]

Ocean tide loading (OTL) displacements observed by the Global Navigation Satellite System (GNSS) are generally less accurate for solar (S2 and P1) and lunisolar (K2 and K1) tidal constituents than for lunar tidal constituents (M2, N2, O1 and Q1). We propose to construct the tidal admittance function (TAF) in the complex domain for tidal inference, aiming to refine noisier GNSS-observed solar and lunisolar constituents. The vertical OTL displacements are estimated from the single GNSS (GPS and Galileo) and multi-GNSS (GPS + Galileo + GLONASS) solutions, using kinematic precise point positioning under undifferenced ambiguity resolution to process 2.5 years of continuous GNSS observations from 49 global GNSS stations. Results show that TAF inferred P1 and K2 agree better with FES2014b model predictions than GNSS estimates for most GNSS stations. We find that the P1 and K2 inferences are only perturbed by less than 0.3 times the observed K1 and S2 errors, respectively. In contrast, the K1 and S2 inferences suffer from over three times the observed P1 and K2 errors. As a result, the tidal inference can only provide limited refinement of GNSS K1 and S2 estimates for a few stations. By comparing the two different TAF approaches for the tidal inference, we find that direct fitting of phase lags is susceptible to phase addition and subtraction of 360°, without disrupting our approach. In addition, the OTL displacements predicted at most GNSS stations are found to satisfy the smoothness of the tidal admittance, which is fundamental to the robustness of the tidal inference. Our approach is also applicable to improve the horizontal solar and lunisolar constituents estimated by GNSS, but should be used with caution in cases where smooth admittances may be distorted by the tidal resonance. [ABSTRACT FROM AUTHOR]

Global mean sea-level (GMSL) change can shed light on how the Earth system responds to warming. Glaciological evidence indicates that Earth's ice sheets retreated inland of early industrial (1850 CE) extents during the Holocene (11.7-0 ka), yet previous work suggests that Holocene GMSL never surpassed early industrial levels. We merge sea-level data with a glacial isostatic adjustment model ensemble and reconstructions of postglacial thermosteric sea-level and mountain glacier evolution to estimate Holocene GMSL and ice volume. We show it is likely (probability P = 0.75) GMSL exceeded early industrial levels after 7.5ka, reaching 0.24 m (−3.3 to 1.0 m, 90% credible interval) above present by 3.2ka; Antarctica was likely (P = 0.78) smaller than present after 7ka; GMSL rise by 2150 will very likely (P = 0.9) be the fastest in the last 5000 years; and by 2060, GMSL will as likely than not (P = 0.5) be the highest in 115,000 years. Sea level data and models of solid Earth effects and ocean thermal expansion are used to show that global mean sea level and Antarctic ice volume were likely higher and smaller, respectively, in the mid-late Holocene than at the preindustrial. [ABSTRACT FROM AUTHOR]

Coastal populations are susceptible to relative sea-level (RSL) rise and accurate local projections are necessary for coastal adaptation. Local RSL rise may deviate from global mean sea-level rise because of processes such as geoid change, glacial isostatic adjustment (GIA), and vertical land motion (VLM). Amongst all factors, the VLM is often inadequately estimated. Here, we estimated the VLM for the Oka estuary, northern Spain and compared it to the VLM component of sea-level projections in the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) and the Spanish National Climate Change Adaptation Plan (NCCAP). To estimate VLM, we updated Holocene RSL data from the Atlantic coast of Europe and compared it with two 3D GIA models. Both models fit well with RSL data except in the Oka estuary. We derived a VLM rate of − 0.88 ± 0.03 mm/yr for the Oka estuary using the residuals of GIA misfits. Comparable VLM rates of − 0.85 ± 0.14 mm/yr and − 0.80 ± 0.32 mm/yr are estimated based on a nearby Global Navigation Satellite Systems station and differenced altimetry-tide gauge technique, respectively. Incorporating the updated late Holocene estimate of VLM in IPCC AR6 RSL projections under a moderate emissions scenario increased the rate of RSL rise by 15% by 2030, 11% by 2050, and 9% by 2150 compared to the original IPCC AR6 projections, and also increased the magnitude of RSL rise by over 40% by 2035 and 2090 compared with projections from the Spanish NCCAP. Our study demonstrates the importance of accurate VLM estimates for local sea-level projections. [ABSTRACT FROM AUTHOR]

Ammonia volatilized from penguin excreta is a significant nitrogen source in Antarctic ecosystems, influencing climate through new particle formation (NPF). Freeze-thaw events can trigger ammonia emissions, but their impact on penguin-derived ammonia is understudied and overlooked in models. Here we investigate the contribution of penguins to ammonia and their climatic impacts using cruise observations and GEOS-Chem-APM simulations. High ammonia concentrations, with a maximum exceeding 7000 ng/m3, were observed over the Southern Ocean and Prydz Bay, driven by air masses from penguin colonies. Simulations showed that incorporating freeze-thaw impact improves model performance, with penguin-derived ammonia emissions enhanced by up to 20-fold and reaching a total of 49 Gg across Antarctica in November. Elevated ammonia increased simulated secondary particle number concentrations by 30−300% through NPF, enhancing simulated cloud droplet number concentrations by 10−20% and altering cloud properties. This study underscores the importance of incorporating penguin emissions into models, particularly during freeze-thaw events. [ABSTRACT FROM AUTHOR]

Branchinecta gaini Daday, 1910 is the southernmost extant Anostracan species occurring in various localities across Maritime Antarctica. Since this region was almost completely glaciated during the Last Glacial Maximum, the identification of potential glacial refugia and the colonization sequence of freshwater habitats within Maritime Antarctica remains primary biogeographic objective for understanding the evolution of the Antarctic environment. To evaluate the history of B. gaini in Maritime Antarctica, we performed phylogeographic analyses of B. gaini and its closest Patagonian congener Branchinecta granulosa Daday, 1902. We sampled 47 populations from all three Antarctic bioregions where B. gaini occurs – South Orkney Islands, North-west and North-east Antarctic Peninsula. B. granulosa was represented by 8 populations from Patagonia. Molecular analyses of two mitochondrial (16S, COI) and one nuclear (ITS2) marker showed low overall mitochondrial variability and the ambiguous nature of ITS2 variability. The species assessment revealed insufficient genetic differentiation between B. gaini and B. granulosa to consider them two separate species. Therefore, the widely accepted idea that there is a species of Branchinecta endemic to Antarctica and sub-Antarctic islands should be omitted, and B. gaini should be synonymized with B. granulosa. Molecular clock analysis of COI for two substitution rates dated the separation of B. gaini from B. granulosa to the Pleistocene (170 – 502 ka BP and 17 – 50 ka BP, respectively). Therefore, Antarctic populations of B. gaini separated from Patagonian B. granulosa before or during the Last Glacial Maximum, indicating an older association with the southern continent than previously anticipated. The geographic distribution of haplotypes further suggests that B. gaini most likely survived at least the last glacial period in an as-yet unknown refugium in Antarctica. [ABSTRACT FROM AUTHOR]

Accelerating sea level rise (SLR) and changing storm patterns will increasingly expose barrier islands to coastal hazards, including flooding, erosion, and rising groundwater tables. We assess the exposure of Cape Lookout National Seashore, a barrier island system in North Carolina (USA), to projected SLR and storm hazards over the twenty-first century. We estimate that with 0.5 m of SLR, 47% of current subaerial barrier island area would be flooded daily, and the 1-year return period storm would flood 74%. For 20-year return period storms, over 85% is projected to be flooded for any SLR. The modelled groundwater table is already shallow (< 2 m deep), and while projected to shoal to the land surface with SLR, marine flooding is projected to overtake areas with emergent groundwater. Projected shoreline retreat reaches an average of 178 m with 1 m of SLR and no interventions, which is over 60% of the current island width at narrower locations. Compounding these hazards is subsidence, with one-third of the study area currently lowering at > 2 mm/yr. Our results demonstrate the difficulty of managing natural barrier systems such as those managed by federal park systems tasked with maintaining natural ecosystems and protecting cultural resources. [ABSTRACT FROM AUTHOR]

At least two global "Snowball Earth" glaciations occurred during the Neoproterozoic Era (1000-538.8 million years ago). Post-glacial surface environments during this time are recorded in cap carbonates: layers of limestone or dolostone that directly overlie glacial deposits. Postulated environmental conditions that created the cap carbonates lack consensus largely because single hypotheses fail to explain the cap carbonates' global mass, depositional timescales, and geochemistry of parent waters. Here, we present a global geologic carbon cycle model before, during, and after the second glaciation (i.e. the Marinoan) that explains cap carbonate characteristics. We find a three-stage process for cap carbonate formation: (1) low-temperature seafloor weathering during glaciation generates deep-sea alkalinity; (2) vigorous post-glacial continental weathering supplies alkalinity to a carbonate-saturated freshwater layer, rapidly precipitating cap carbonates; (3) mixing of post-glacial meltwater with deep-sea alkalinity prolongs cap carbonate deposition. We suggest how future geochemical data and modeling refinements could further assess our hypothesis. A new formation mechanism is proposed to explain the presence and characteristics of "cap carbonates": enigmatic rocks leftover from Snowball Earth events, during which Earth was globally ice-covered for millions of years in the distant past. [ABSTRACT FROM AUTHOR]

Ganymede has an ancient impact structure called a furrow system. The furrow system is the largest impact structure in the outer solar system, and the impact should have significantly affected Ganymede's early history; however, its effects are poorly understood. No attention has been given to the center of the furrow system coinciding with Ganymede's tidal axis, indicating that mass redistribution induced by the furrow-forming impact caused a reorientation (true polar wander) of Ganymede. We propose that the impact ejecta created a mass anomaly that reoriented the impact site toward the tidal axis. We found that an impactor with a radius of 150 km and an incidence angle between 60° and 90° most accurately reproduces the current location of the furrow system. We predict that future explorations would reveal remnant topographic profiles or gravity anomalies associated with the furrow-forming impact and reorientation. Additionally, various possible explanations for the reorientation of Ganymede, such as an impactor-origin mascon beneath the basin or a thickness variation in the lithosphere, should be studied. [ABSTRACT FROM AUTHOR]

Green sea dykes, also known as ecosystem-based sea dykes, represent a novel type of coastal defense consisting of both traditional structural engineering and coastal ecosystems, designed to cope with the future trends of sea level rise and intensified storms. Here we focus on the mid-latitude mud coasts (eastern China in particular), which face the most prominent risks of storm surge, storm-induced giant waves, and shoreline erosion, and summarizes the scientific basis of green sea dykes and the current status of engineering practices. We show that the basic mechanisms of nearshore wave energy dissipation include bottom friction, sediment transport, and form drag. These explain the wave damping capacity of oyster reefs and salt marshes on mud coasts. In tidal flat environments, oyster growth increases frictional resistance and even causes wave breaking; the resuspension and transport of fine-grained sediments on salt marsh beds and the movement or resistance to hydrodynamic forcing of salt marsh vegetation stems effectively dissipate wave kinetic energy, and their efficiency increases with the elevation of the bed surface. Based on the wave damping capacity of oyster reefs and salt marshes on mud coasts, ecosystem-based sea dykes are being built in combination with traditional structured sea dykes. By utilizing natural tidal flats outside the dykes or implementing artificial modification projects, a certain scale of salt marshes and/or oyster reefs can be maintained, which serve to protect the sea dykes and enhance their wave resistance functions. From the perspective of system optimization, it is necessary to further improve the efficiency and sustainability of green sea dykes under constraints such as regional environment characteristics, ecosystem health, investment capacity, and ecological resilience. Related scientific issues include the theorization of the wave damping process of salt marshes, the niche and scale control of oyster reef and salt marsh ecosystems, the establishment of engineering standards and the design of the optimal form of sea dykes. [ABSTRACT FROM AUTHOR]

Tectonic plate motions drive the earthquake cycle, as they result in the slow accrual and sudden release of energy along plate boundaries. Steadiness of plate motions over the earthquake cycle is a central tenet of the plate tectonics theory and has long been a main pillar in models of earthquake genesis, or of plate-margins seismic potential inferred from slip-deficit estimates. The advent of geodesy in the geosciences and the availability of multi-year-long series of position measurements permit tracking the motions of tectonic plates from before to after the time of significant seismic events that occur along their margins. Here, we present evidence that large earthquakes are capable of modifying the motions of entire microplates. We use high precision Global Navigation Satellite System (GNSS) position time-series covering the periods 2001–2004 and 2014–2017 to demonstrate that, contrary to the tenet above, the South China microplate motion changed after the 2008 M W 7.9 Great Wenchuan earthquake. The GNSS data and associated uncertainties indicate a plate motion slowdown of up to 20% that is beyond the possible impact of data noise and is thus tectonically meaningful. We use quantitative models of torque balance to show that generating this kinematic change requires a force upon the South China microplate compatible with that imparted by the Great Wenchuan earthquake of 2008. The existence of a kinematic signal linked to the earthquake cycle that impacts an entire microplate might offer an additional, novel perspective to assessing the hazards of earthquake-prone tectonic regions. [ABSTRACT FROM AUTHOR]

Freshwater discharge from ice sheets induces surface atmospheric cooling and subsurface ocean warming, which are associated with negative and positive feedbacks respectively. However, uncertainties persist regarding these feedbacks' relative strength and combined effect. Here we assess associated feedbacks in a coupled ice sheet-climate model, and show that for the Antarctic Ice Sheet the positive feedback dominates in moderate future warming scenarios and in the early stage of ice sheet retreat, but is overwhelmed by the negative feedback in intensive warming scenarios when the West Antarctic Ice Sheet undergoes catastrophic collapse. The Atlantic Meridional Overturning Circulation is affected by freshwater discharge from both the Greenland and the Antarctic ice sheets and, as an interhemispheric teleconnection bridge, exacerbates the opposing ice sheet's retreat via the Bipolar Seesaw. These results highlight the crucial role of ice sheet-climate interactions via freshwater flux in future ice sheet retreat and associated sea-level rise. Ice sheet freshwater discharge interacts with the climate and affects the ice sheet's sensitivity to climate change. This study shows that the overall feedback shifts from positive to negative as the pace of future warming intensifies [ABSTRACT FROM AUTHOR]

Koh-i-Noor and other world-famous diamonds such as Hope, Orloff, Great Mogul, Nizam, and Pitt, well-known in the industry as 'Golkonda Diamonds' are very well recognised for their rare colours, large carat sizes, and because of the paucity of nitrogen atoms majority of them have been classified as Type IIa diamonds. These renowned Golkonda diamonds were recovered from placers mined on the banks of the Krishna River in southern India; however, their primary source rocks (either kimberlites or lamproites) remain questioned and untraced. Precise identification of the primary sources of such large-sized, dominantly Type IIa diamonds (i.e., CLIPPIRS) is crucial for understanding their deep mantle origin, nature and timing of magmatism carrying them and essential from economic and geological perspectives. We employed a multidisciplinary approach incorporating xenocrystic mineral composition and bulk-rock geochemistry, field geological and remote sensing (GIS) studies to locate the probable primary sources of these renowned diamonds, know the origin of Type IIa Golkonda diamonds in southern India, and to understand the mechanism and timing of diamond transport and dispersal as placers in the Krishna River basin. Our study rules out the possibility of various lamproite occurrences of the Eastern Dharwar Craton and Banganapalle conglomerates as being sources of Koh-i-Noor and other Golkonda diamonds. The absence of Type IIa diamonds in the highly diamondiferous Late Cretaceous kimberlites of Wajrakarur likewise excludes them as source of Golkonda diamonds. Among southern India's two significant kimberlite fields, i.e., Wajrakarur and Narayanpet, compositions of indicator minerals from the Wajrakarur Kimberlite Field (WKF) reveal their ultimate diamond preservation potential, presence of strong diamondiferous mantle roots and deeper source regions, hence recognising them to be the potential sources of Golkonda diamonds. GIS and remote sensing tools were used to calculate moisture content, vegetation indices, and to locate paleo-channel of the Penner River, which was primarily responsible for the transportation of diamonds from their Mesoproterozoic (ca. 1.1 Ga) source rocks at Wajrakarur to their final sites of recovery, i.e., Kolluru and other mines situated on the banks of the Krishna River. The occurrence of alluvial placer deposits in Krishna River drainage system is analogous to the Orange River drainage system in South Africa. Both areas have diamonds sourced from primary kimberlite pipes, transported by rivers, and deposited in specific areas. Similarities in the origin, mechanism of diamond transport, dispersal and deposition have played a crucial role in significant diamond production from alluvial deposits in Krishna and Orange Rivers. [ABSTRACT FROM AUTHOR]

10.1007/s10712-021-09684-y 2 Koelemeijer P, Deuss A, Ritsema J. Density structure of Earth's lowermost mantle from Stoneley mode splitting observations. 10.1002/9781119528609 5 Lau HCP, Mitrovica JX, Davis JL, Tromp J, Yang HY, Al-Attar D. Tidal tomography constrains Earth's deep-mantle buoyancy. [Extracted from the article]

The baobab trees (genus Adansonia) have attracted tremendous attention because of their striking shape and distinctive relationships with fauna1. These spectacular trees have also influenced human culture, inspiring innumerable arts, folklore and traditions. Here we sequenced genomes of all eight extant baobab species and argue that Madagascar should be considered the centre of origin for the extant lineages, a key issue in their evolutionary history2,3. Integrated genomic and ecological analyses revealed the reticulate evolution of baobabs, which eventually led to the species diversity seen today. Past population dynamics of Malagasy baobabs may have been influenced by both interspecific competition and the geological history of the island, especially changes in local sea levels. We propose that further attention should be paid to the conservation status of Malagasy baobabs, especially of Adansoniasuarezensis and Adansoniagrandidieri, and that intensive monitoring of populations of Adansoniaza is required, given its propensity for negatively impacting the critically endangered Adansoniaperrieri.We carried out genomic and ecological analyses of all eight extant baobab species, providing insights into their evolutionary history and recommendations for conservation efforts. [ABSTRACT FROM AUTHOR]

When the Marinoan snowball Earth deglaciated in response to high atmospheric carbon dioxide (CO2) concentrations, the planet warmed rapidly. It is commonly hypothesized that the ensuing supergreenhouse climate then declined slowly over hundreds of thousands of years through continental weathering. However, how the ocean affected atmospheric CO2 in the snowball Earth aftermath has never been quantified. Here we show that the ocean's carbon cycle drives the supergreenhouse climate evolution via a set of different mechanisms, triggering scenarios ranging from a rapid decline to an intensification of the supergreenhouse climate. We further identify the rapid formation of carbonate sediments from pre-existing ocean alkalinity as a possible explanation for the enigmatic origin of Marinoan cap dolostones. This work demonstrates that a moderate and relatively short-lived supergreenhouse climate following the Marinoan snowball Earth is a plausible scenario that is in accordance with geological data, challenging the previous hypothesis. When the Marinoan snowball Earth deglaciated, the ocean's chemistry determined the strength and duration of the ensuing supergreenhouse climate, while the sudden warming and biological activity could have led to a rapid formation of cap dolostones. [ABSTRACT FROM AUTHOR]

Recent geologic and modeled evidence suggests that the grounding line of the Siple Coast of the West Antarctic Ice Sheet (WAIS) retreated hundreds of kilometers beyond its present position in the middle to late Holocene and readvanced within the past 1.7 ka. This grounding line reversal has been attributed to both changing rates of isostatic rebound and regional climate change. Here, we test these two hypotheses using a proxy-informed ensemble of ice sheet model simulations with varying ocean thermal forcing, global glacioisostatic adjustment (GIA) model simulations, and coupled ice sheet-GIA simulations that consider the interactions between these processes. Our results indicate that a warm to cold ocean cavity regime shift is the most likely cause of this grounding line reversal, but that GIA influences the rate of ice sheet response to oceanic changes. This implies that the grounding line here is sensitive to future changes in sub-ice shelf ocean circulation. Using ice sheet model and glacio-isostatic adjustment model simulations and paleoclimate proxies, this work demonstrates that the most likely cause of past West Antarctic grounding-line reversal was a regime shift from a warm to cold ocean cavity. [ABSTRACT FROM AUTHOR]

Sea-level rise submerges terrestrial permafrost in the Arctic, turning it into subsea permafrost. Subsea permafrost underlies ~ 1.8 million km2 of Arctic continental shelf, with thicknesses in places exceeding 700 m. Sea-level variations over glacial-interglacial cycles control subsea permafrost distribution and thickness, yet no permafrost model has accounted for glacial isostatic adjustment (GIA), which deviates local sea level from the global mean due to changes in ice and ocean loading. Here we incorporate GIA into a pan-Arctic model of subsea permafrost over the last 400,000 years. Including GIA significantly reduces present-day subsea permafrost thickness, chiefly because of hydro-isostatic effects as well as deformation related to Northern Hemisphere ice sheets. Additionally, we extend the simulation 1000 years into the future for emissions scenarios outlined in the Intergovernmental Panel on Climate Change's sixth assessment report. We find that subsea permafrost is preserved under a low emissions scenario but mostly disappears under a high emissions scenario. A pan-Arctic estimate of past and future subsea permafrost including solid Earth effects causes local sea level to differ from the global mean. Future subsea permafrost disappears faster under high than low emissions scenarios. [ABSTRACT FROM AUTHOR]

The historical association of time with the rotation of Earth has meant that Coordinated Universal Time (UTC) closely follows this rotation1. Because the rotation rate is not constant, UTC contains discontinuities (leap seconds), which complicates its use in computer networks2. Since 1972, all UTC discontinuities have required that a leap second be added3. Here we show that increased melting of ice in Greenland and Antarctica, measured by satellite gravity4,5, has decreased the angular velocity of Earth more rapidly than before. Removing this effect from the observed angular velocity shows that since 1972, the angular velocity of the liquid core of Earth has been decreasing at a constant rate that has steadily increased the angular velocity of the rest of the Earth. Extrapolating the trends for the core and other relevant phenomena to predict future Earth orientation shows that UTC as now defined will require a negative discontinuity by 2029. This will pose an unprecedented problem for computer network timing and may require changes in UTC to be made earlier than is planned. If polar ice melting had not recently accelerated, this problem would occur 3 years earlier: global warming is already affecting global timekeeping.Increased melting of ice in Greenland and Antarctica, measured by satellite gravity, has decreased the angular velocity of Earth more rapidly than before and has already affected global timekeeping. [ABSTRACT FROM AUTHOR]

Coastal wetland ecosystems support unique biodiversity and are imminently threatened by climate change-driven sea level rise. However, the impact of climate change on their demographic and evolutionary histories is poorly understood. To improve our understanding, we examined how past climatic events have shaped the evolutionary history of the salt marsh harvest mouse (Reithrodontomys raviventris), an endangered species and a salt marsh habitat specialist, completely restricted to coastal wetlands in the San Francisco Estuary (SFE). We used whole mitochondrial genome sequences of 102 salt marsh harvest mice to characterize phylogeography and demographic history. Then, we predicted the ancient distribution of salt marsh habitat and examined correspondence between divergence, demographic history, and changes in ancient marsh habitat caused by sea level rise. A Bayesian Skyline Plot revealed demographic expansions during periods of sea level rise, particularly during the formation of the modern SFE (~ 10 kya), and rapid decline consistent with recent anthropogenic landscape change. Bayesian estimates of divergence time were consistent with subspecies divergence ~ 10 kya, and subpopulation divergence ~ 5 kya, consistent with multiple episodes of vicariance caused by Holocene sea level rise. Spatial Analysis of Molecular Variance and ΦST revealed a mismatch between the morphological and molecular subspecies assignment of two populations. Our study implicates sea level rise as a force of demographic change and evolutionary divergence in coastal marsh ecosystems. Our study also aids conservation of an endangered species by clarifying genetic subspecies boundaries and highlighting the unique nature of isolated populations that are increasingly threatened by modern sea level rise. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Understanding the variations of the Walker Circulations during the Last Interglacial (LIG, ~ 130–115 ka BP) may advance our knowledge of climate change in an orbitally induced warmer world. Here we investigate the variations and the underpinning mechanisms of the Pacific Walker Circulation (PWC) and the Indian Ocean Walker Circulation (IWC) during the LIG, using the lig127k experiments from the Paleoclimate Modeling Intercomparison Project Phase 4. Compared to the preindustrial, annual PWC is broadened by 3° and strengthened by 3.5% during the LIG, whereas annual IWC is narrowed by 3° and weakened by 17.2%. The antiphase change between annual PWC and IWC during the LIG is dominated by the change in boreal warm seasons (June–October), which is in turn closely tied to the changes in sea surface temperatures between the Indian Ocean and the western Pacific Ocean. Specifically, the models predict a general warming over the tropical Indian Ocean but cooling over the tropical western Pacific in boreal warm seasons during the LIG. This interbasin contrast results in enhanced sea-level pressure over the tropical western Pacific and decreased sea-level pressure over the tropical Indian Ocean, together with opposite changes in precipitation. The west-to-east sea-level pressure gradient contributes to anomalous low-level easterlies in the deep tropics. These changes result in an enhancement and broadening of the PWC, whereas a reverse change for the IWC. The proposed dominating role of interbasin contrast in temperature anomaly is further confirmed by a linear baroclinic model and an atmospheric general circulation model. [ABSTRACT FROM AUTHOR]

During the Last Interglacial (LIG; 129-116 thousand years before present), the Antarctic ice sheet (AIS) was 1 to 7 m sea level equivalent smaller than at pre-industrial. Here, we assess the climatic impact of partial AIS melting at the LIG by forcing a coupled climate model with a smaller AIS and the equivalent meltwater input around the Antarctic coast. We find that changes in surface elevation induce surface warming over East Antarctica of 2 to 4 °C, and sea surface temperature (SST) increases in the Weddell and Ross Seas by up to 2 °C. Meltwater forcing causes a high latitude SST decrease and a subsurface (100–500 m) ocean temperature increase by up to 2 °C in the Ross Sea. Our results suggest that the combination of a smaller AIS and enhanced meltwater input leads to a larger sub-surface warming than meltwater alone and induces further Antarctic warming than each perturbation separately. Climate simulations of the Last Interglacial show that Antarctic ice loss induces warming of East Antarctica. Meltwater equivalent to the ice loss induces warming of the subsurface. Both effects can further enhance Antarctic ice sheet deterioration [ABSTRACT FROM AUTHOR]

In the face of current uncertainties about the processes of climate change and its consequences, the search for possible response strategies is urgently needed. One of the most serious repercussions of climate change, which threatens many coastal areas globally, is the sea-level rise. To deepen understanding of this phenomenon and its related impacts, several models have recently been developed to satisfy the unique needs of coastal zone management. These models are very useful because of their visualization and prediction capabilities as they aid in decision-making regarding the adaptation of current protected area investments. This review, therefore, provides evidence of the potential and effectiveness of recent mapping models for managing the effects of sea-level rise. This study examined current models for mapping flood risk areas as a result of sea-level rise. It also provides guidelines to help coastal zone managers and policymakers decide the applicability of various models at local, regional, and global scales. There is no universally accepted model, and each of the models reviewed in this paper has its strengths and weaknesses. However, the models provided by the National Oceanic and Atmospheric Administration are commonly used by organizations and others. These models are more accessible and comprehensible for scientists and individuals with limited scientific background knowledge on sea-level rise. [ABSTRACT FROM AUTHOR]

The Volta Basin in West Africa plays a crucial role in supporting the livelihoods of millions of people, and effective management of its water resources is essential for climate change adaptation. This study utilized remote sensing technology, specifically the Gravity Recovery and Climate Experiment (GRACE), to assess terrestrial water storage (TWS) and its response to climate variability within the Volta Basin. The methodology involved integrating GRACE data with ground-based measurements, climate models, and other satellite observations to enhance the accuracy of TWS assessment. Despite numerous studies conducted within the basin, this research employed additional statistical techniques such as Independent Component Analysis (ICA) and El Niño Southern Oscillation (ENSO). It also utilized Climate Hazard Group Infrared Precipitation with Station (CHIRPS) to determine variations in TWS and climate variability observed within the Volta Basin. The results provide valuable insights into TWS dynamics, highlighting the complex interplay between precipitation patterns, groundwater storage, and surface water availability. Also, it was revealed that rainfall signals were strongest in the northernmost part of the basin, reaching a maximum value of 10 mm, while the lowest value of 5.5 mm was recorded in the southern part of the basin. Similarly, TWS signals were highest in the northern and lowest in the southern part of the basin, exhibiting values related to that of rainfall. Additionally, the highest TWS value of 250 mm was identified between 2010 and 2012. The increase in TWS during this period correlates with the occurrence of La Niña that happened between 2010 and 2012. This study offers essential information for water resource management, drought monitoring, flood forecasting, and climate change adaptation strategies not only within the Volta Basin but also in other basins across the globe. [ABSTRACT FROM AUTHOR]

Multi-GNSS solutions are typically considered to improve GPS-only ocean tide loading (OTL) displacements, as they effectively mitigate the constraints imposed by the single-system GPS orbital configuration on resolving various tidal constituents. Most of such solutions, however, are ambiguity-float solutions, particularly affecting the solar tidal constituents (K2, S2, K1, P1) for which the ambiguity resolution (AR) is critical. We comprehensively evaluate the performance of OTL displacements derived from the single-system and multi-GNSS solutions by processing 2.5 years of GPS, GLONASS and Galileo observations from 49 global GNSS stations using kinematic precise point positioning (PPP) with undifferenced AR. Our results show that Galileo improves over GPS by 0.2–0.5 mm for solar tidal constituents (excluding the S2 up component) compared to FES2014b model predictions. GPS + Galileo outperforms GPS, Galileo, GPS + GLONASS and GLONASS + Galileo for most tidal constituents, except for K2 where Galileo and GLONASS + Galileo hold a slight advantage. Ambiguity-float GLONASS limits improvements in results after combining with GPS or Galileo. Despite this, GPS + GLONASS + Galileo with the largest number of visible satellites estimates the best vertical OTL displacements. Since short-term (a few hours) static PPP can provide position time series with sufficient accuracy and temporal resolution while rarely used for OTL estimation, we also compare the results from kinematic and static PPP. Indeed we find that the static PPP with a suitable processing session of 1–2 h can estimate OTL displacements (excluding K2) better than the kinematic PPP. Although the static PPP of 3–4 h is too long to capture M2, N2 and S2 tidal variation without aliasing, the proposed amplitude correction can well correct these tidal constituents. Finally, we report that the residual OTL displacements are generally larger at low latitudes (30°S–30°N) than at mid/high latitudes (30°–90°N/S), possibly associated with S2 atmospheric tide loading effects and higher positioning noise at low latitudes. [ABSTRACT FROM AUTHOR]

The saltwater intrusion occurs in many coastal areas worldwide and has become a serious menace to freshwater quality. In the Pearl River estuary, saltwater intrusion has threatened the water supply for residential, agricultural, and industrial uses in the past decades, resulting in ecological and economic losses. In this study, the observed saltwater intrusion records of 10 years (2012 ~ 2021) at 9 stations in the Modaomen waterway, the largest inlet of the Pearl River estuary, were compiled. The time duration of saltwater intrusion was analyzed rather than the traditional distance length, along with the reported annual sea level records and river discharge volumes. The annual duration of saltwater intrusion exhibits spatial variations and is inversely related to the distance from the the Pearl River estuary mouth. In the study area which is near the main estuary mouth of the Pearl River, results from a multiple linear regression show that the observed annual saltwater intrusion days near the main Pearl River estuary mouth could be quantitatively explained by the combination of river discharge (dominant) and relative sea level. This work presents an example to investigate the combined river discharge and sea level impact on saltwater intrusion with annually compiled observed data and from a time-change perspective. [ABSTRACT FROM AUTHOR]

The terminal Pleistocene witnessed significant paleoclimatic changes that influenced the adaptive behavior of human populations. Situated in the tropical-subtropical zone of Southwest China, a newly excavated cave site, Fodongdi, revealed evidence for substantive changes in technology between 18.37 to 13.85 cal ka BP. Here, we present the results of a technological analysis on lithic assemblage formation across three main sequential phases at Fodongdi Cave. Diachronic changes in lithic technology document the co-existence of diverse reduction techniques and toolkits, corresponding with climatic fluctuations over a five-thousand-year period. [ABSTRACT FROM AUTHOR]

The seasonality of Earth's climate is driven by two factors: the tilt of the Earth's rotation axis relative to the plane of its orbit (hereafter the tilt effect), and the variation in the Earth–Sun distance due to the Earth's elliptical orbit around the Sun (hereafter the distance effect). The seasonal insolation change between aphelion and perihelion is only ~ 7% of the annual mean and it is thus assumed that the distance effect is not relevant for the seasons. A recent modeling study by the authors and collaborators demonstrated however that the distance effect is not small for the Pacific cold tongue: it drives an annual cycle there that is dynamically distinct and ~ 1/3 of the amplitude from the known annual cycle arising from the tilt effect. The simulations also suggest that the influence of distance effect is significant and pervasive across several other regional climates, in both the tropics and extratropics. Preliminary work suggests that the distance effect works its influence through the thermal contrast between the mostly ocean hemisphere centered on the Pacific Ocean (the 'Marine hemisphere') and the hemisphere opposite to it centered over Africa (the 'Continental hemisphere'), analogous to how the tilt effect drives a contrast between the northern and southern hemispheres. We argue that the distance effect should be fully considered as an annual cycle forcing in its own right in studies of Earth's modern seasonal cycle. Separately considering the tilt and distance effects on the Earth's seasonal cycle provides new insights into the workings of our climate system, and of direct relevance to paleoclimate where there are outstanding questions for long-term climate changes that are related to eccentricity variations. [ABSTRACT FROM AUTHOR]

Dykes and sills occupy Mode I (extension), Mode II (shear), or hybrid mode fractures and most of the time transport and store magma from deep reservoirs to the surface. Subject to their successful propagation, they feed volcanic eruptions. Yet, dykes and sills can also stall and become arrested as a result of the crust's heterogeneous and anisotropic characteristics. Dykes can become deflected at mechanical discontinuities to form sills, and vice versa. Although several studies have examined dyke propagation in heterogeneous and anisotropic crustal segments before, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear. Here, we coupled field observations with 2D FEM numerical modelling to explore the mechanical conditions that encourage (or not) dyke-sill transitions in volcanotectonic or glacial settings. We used as a field example the Stardalur cone sheet-laccolith system, which lies on the Esja peninsula, close to the western rift zone, NW of the southern part of the Icelandic rift. The laccolith is composed of several vertical dykes that transition into sills and form a unique stacked sill 'flower' structure. Here, we investigate whether the Stardalur laccolith was formed under the influence of stresses caused by glacial retreat due to thickness variations (0–1 km) in addition to regional and local tectonic stresses (1–3 MPa extension or compression) and varied magma overpressure (1–30 MPa), as well as the influence of the mechanical properties of the lava/hyaloclastite contact. Our results show that the observed field structure in non-glacial regimes was formed as a result of either the mechanical (Young's modulus) contrast of the lava/hyaloclastite contact or a compressional regime due to pre-existing dykes or faulting. In the glacial domain, the extensional stress field below the ice cap encouraged the formation of the laccolith as the glacier became thinner (subject to a lower vertical load). In all cases, the local stress field influenced dyke to sill deflection in both volcanotectonic regimes. [ABSTRACT FROM AUTHOR]

The existence of a thin, weak asthenospheric layer beneath Earth's lithospheric plates is consistent with existing geological and geophysical constraints, including Pleistocene glacio-isostatic adjustment, modeling of gravity anomalies, studies of seismic anisotropy, and post-seismic rebound. Mantle convection models suggest that a pronounced weak zone beneath the upper thermal boundary layer (lithosphere) may be essential to the plate tectonic style of convection found on Earth. The asthenosphere is likely related to partial melting and the presence of water in the sub-lithospheric mantle, further implying that the long-term evolution of the Earth may be controlled by thermal regulation and volatile recycling that maintain a geotherm that approaches the wet mantle solidus at asthenospheric depths. [ABSTRACT FROM AUTHOR]

The May 2nd and 3rd, 2023 landslide in Rwanda's Western Province caused a devastating natural disaster, resulting in the tragic loss of 95 lives. Ngororero, Rubavu, Nyabihu, and Karongi were the worst-hit areas, as reported by Rwanda Broadcasting Agency (RBA). Such recurring disasters have posed significant challenges to the affected communities, requiring strong measures like susceptibility mapping to address their impact in the future. The literature review indicates that statistic and machine-learning susceptibility mapping efforts have been applied in the study region. However, these studies have not focused explicitly on localized scale studies of the western province; instead, they have mainly concentrated on examining the entire country. Using artificial neural networks (ANN), Shannon entropy (SE), and frequency ratio (FR), this paper aims to fill some gaps in the Rwandan landslide literature by integrating localized studies of the landslide susceptibility mapping (LSM) of the western province of Rwanda using the available higher data resolution. The LSM studies took 1157 landslide inventory locations and considered a broader range of landslide-conditioning factors compared to the previous studies on the region (distance from the road, aspect, elevation, slope degree, stream power index, normalized differential vegetation index, plan curvature, distance from the river, topographic wetness index, geology, and rainfall). In model training, 70% (810 points) of the landslide points underwent utilization, while the remaining 30% (347 points) served the purpose of model testing. The obtained area under the curve (AUC) values from model validation and testing provided reliable accuracy measures for the three LSM methods: ANN (AUC = 0.929 and 0.924), FR (AUC = 0.895 and 0.889), and SE (AUC = 0.768 and 0.750). Despite varying data handling, the models show that Rutsiro, Ngororero, and Karongi in Rwanda's Western Province have the highest landslide concentration. The relative importance of conditioning factors indicates that geology, rainfall, distance to the road, slope, and NDVI factors played a crucial role in landslides in the studied area. The slope can be stabilized by enhancing drainage, modifying slope angles, and implementing structural fortifications. It is hoped that the findings of this study will aid Rwandan policymakers and global researchers mitigate landslides and their dynamics. [ABSTRACT FROM AUTHOR]

Sea level variations at the coast can have drastic environmental and socio-economic impacts in particular in the context of an ever-increasing coastal population and anthropogenic climate change. Regional to global climate variability influences all these factors and exerts a strong control on the coastal sea level over a wide range of time scales. Here, we focus on understanding interannual changes which is paramount to improve interannual forecasting systems as well as to constrain and reduce uncertainties on the secular trend in global mean sea level. We consider the coastal total water level (TWL) as the compound effect of three main components: the wave setup, mean regional sea level anomaly (i.e., steric and ocean circulation influences) and atmospheric surge (i.e., influence of local wind and surface atmospheric pressure). To understand their variability at a global scale, we focus on the effect of four climate modes that affect the major oceanic basins: the El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), the North Atlantic Oscillation (NAO) and the Southern Annual Mode (SAM). The contrasted regional influence of these different climate modes on the interannual variations of TWL components are quantified. Results suggest that even if the regional mean sea level is overall the main contributor to the interannual variations of TWL variations at the coast and mostly related to ENSO, the contributions from wave setup and atmospheric surge are not negligible in particular at high latitudes and mostly related to the NAO in the Northern Atlantic and to the SAM in the Southern Hemisphere. Such influences from the NAO and SAM can be seen far away from their extratropical regions of action due to their atmospheric forcing of ocean waves that can significantly propagate their imprint towards tropical areas. Implications for interannual to decadal forecasts of the coastal TWL and related hazards are discussed in the light of regression statistical models and the climate modes own predictability. [ABSTRACT FROM AUTHOR]

Socioeconomic development, subsidence, and climate change have led to high flood risks in coastal cities, making the vulnerable, especially elderly people, more prone to floods. However, we mostly do not know how the accessibility of life-saving public resources for the elderly population will change under future scenarios. Using Shanghai as a case, this study introduced a new analytical framework to fill this gap. We integrated for the first time models of coastal flooding, local population growth, and medical resource supply-demand estimation. The results show that under an extreme scenario of coastal flooding in the year 2050, in the absence of adaptation, half of the elderly population may be exposed to floods, the supply of medical resources will be seriously insufficient compared to the demand, and the accessibility of emergency medical services will be impaired by flooding. Our methodology can be applied to gain insights for other vulnerable coastal cities, to assist robust decision making about emergency responses to flood risks for elderly populations in an uncertain future. [ABSTRACT FROM AUTHOR]

A general assumption in geodesy is that solid Earth deformation in the presence of recent hydrological and ice loading is well approximated by a purely elastic response. In cases where there is clear evidence that thermal and petrological conditions exist that favor vigorous high-temperature creep behavior, such as in the mantle beneath Iceland, Patagonia, Alaska, Japan, and Svalbard, many response models have been approximated by using a Maxwell viscoelasticity. However, non-Maxwellian transient viscoelastic rheology is required for many post-seismic relaxation studies. Here, we reconsider the solid Earth response in light of highly temperature-dependent transient viscoelastic responses currently favored in the mineral physics and seismological communities. We develop a mantle response Green’s function that accounts for the vertical isostatic motion of the mantle caused by the acceleration of ice mass loss for Greenland and Patagonia measured by spaceborne and airborne remote sensing since 1992 and 1945, respectively. The Green’s function may be used to examine how anelasticity influences the uplift associated with accelerated surface mass loss. We perform a parameter exploration of the constants that define the Extended Burgers Material model, a rheology having firm experimental and theoretical underpinnings, in order to isolate those material model parameters that have the greatest impact on anelastic-isostatic uplift over interannual and interdecadal timescales. Anelasticity corrections may be required for solid Earth vertical uplift in space gravimetric solutions for long-term hydrology and cryospheric change. [ABSTRACT FROM AUTHOR]

Satellite data have revealed that the Greenland and Antarctic Ice Sheets are changing rapidly due to warming air and ocean temperatures. Crucially, Earth Observations can now be used to measure ice sheet mass balance at the continental scale, which can help reduce uncertainties in the ice sheets' past, present, and future contributions to global mean sea level. The launch of satellite missions dedicated to the polar regions led to great progress towards a better assessment of the state of the ice sheets, which, in combination with ice sheet models, have furthered our understanding of the physical processes leading to changes in the ice sheets' properties. There is now a three-decade-long satellite record of Antarctica and Greenland mass changes, and new satellite missions are planned to both continue this record and further develop our observational capabilities, which is critical as the ice sheets remain the most uncertain component of future sea-level rise. In this paper, we review the mechanisms leading to ice sheets' mass changes and describe the state of the art of the satellite techniques used to monitor Greenland's and Antarctica's mass balance, providing an overview of the contributions of Earth Observations to our knowledge of these vast and remote regions. [ABSTRACT FROM AUTHOR]

Coastal regions (including estuaries and deltas) are very complex environments with diverse hydrodynamic and bio-geomorphological contexts and with important socio-economic and ecological problems. These systems are among the most affected by human impact through urbanization and port activities, industrial and tourism activities. They are directly affected by the impact of climate change on sea level, storm surges frequency and strength, as well as recurrence of coastal river floods. A sustainable future for coastal zones depends on our capacity to implement systematic monitoring with focus on: (1) forcings affecting coastal zones at different spatio-temporal scales (sea level rise, winds and waves, offshore and coastal currents, tides, storm surges, river runoff in estuaries and deltas, sediment supply and transport, vertical land motions and land use); (2) morphological response (e.g., shoreline migration, topographical changes). Over the last decades, remote sensing observations have contributed to major advances in our understanding of coastal dynamics. This paper provides an overview of these major advances to measure the main physical parameters for monitoring the coastal, estuarine and delta environments and their evolution, such as the water level and hydrodynamics near the shoreline, water/sediment contact (i.e., shoreline), shoreline position, topography, bathymetry, vertical land motion, bio-physical characteristics of sediments, water content, suspended sediment, vegetation, and land use and land cover. [ABSTRACT FROM AUTHOR]

Reliable sea-level observations in coastal regions are needed to assess the impact of sea level on coastal communities and ecosystems. This paper evaluates the ability of in-situ and remote sensing instruments to monitor and help explain the mass component of sea level along the coast of Norway. The general agreement between three different GRACE/GRACE-FO mascon solutions and a combination of satellite altimetry and hydrography gives us confidence to explore the mass component of sea level in coastal areas on intra-annual timescales. At first, the estimates reveal a large spatial-scale coherence of the sea-level mass component on the shelf, which agrees with Ekman theory. Then, they suggest a link between the mass component of sea level and the along-slope wind stress integrated along the eastern boundary of the North Atlantic, which agrees with the theory of poleward propagating coastal trapped waves. These results highlight the potential of the sea-level mass component from GRACE and GRACE-FO, satellite altimetry and the hydrographic stations over the Norwegian shelf. Moreover, they indicate that GRACE and GRACE-FO can be used to monitor and understand the intra-annual variability of the mass component of sea level in the coastal ocean, especially where in-situ measurements are sparse or absent. [ABSTRACT FROM AUTHOR]

The regional sea level variability and its projection amidst the global sea level rise is one of the major concerns for coastal communities. The dynamic sea level plays a major role in the observed spatial deviations in regional sea level rise from the global mean. The present study evaluates 27 climate model simulations from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) for their representation of the historical mean states, variability and future projections for the Indian Ocean. Most models reproduce the observed mean state of the dynamic sea level realistically; however, consistent positive bias is evident across the latitudinal range of the Indian Ocean. The strongest sea level bias is seen along the Antarctic Circumpolar Current (ACC) regime owing to the stronger than observed south Indian Ocean westerlies and its equatorward bias. This equatorward shift of the wind field also results in a stronger positive windstress curl across the southeasterly trade wind regime in the southern tropical basin and an easterly wind bias along the equatorial waveguide. Owing to the anomalous easterly equatorial winds, the thermocline in the eastern tropical basin is shallower in the models than observed, resulting in enhanced variability there. Such spurious variability in the eastern part of the basin causes models to become biased towards the dipole zonal mode or Indian Ocean dipole patterns in the tropics. In the north Indian Ocean, the summer monsoon winds are weak in the model leading to weaker coastal upwelling and positive sea level bias along the western Arabian Sea. Further, it is noted that the high-resolution models compare better in simulating the sea level variability, particularly in the eddy-dominated regions like the ACC regime in interannual timescale. However, these improved variabilities do not necessarily produce a better mean state likely due to the spurious enhanced mixing driven by parametrizations set in these high-resolution models. Finally, the overall pattern of the projected dynamic sea level rise is similar for the mid (SSP2-4.5) and high-end (SSP5-8.5) scenarios, except that the magnitude is higher under the high emission situation. Notably, the projected dynamic sea level change is milder when only the best-performing models are used compared to the complete ensemble. [ABSTRACT FROM AUTHOR]

The evolution of Sahel summer rainfall in the context of global warming is a severe socio-economic concern because of its widespread influences on local agriculture, water resource management, food security, infrastructure planning, and ecosystems. Based on the mid-Pliocene simulations from the Pliocene Model Intercomparison Project Phase 2 and the historical simulations and shared socio-economic pathway 5–8.5 experiments from the Coupled Model Intercomparison Project phase 6, the present study contrasts the Sahel summer rainfall changes between the past mid-Pliocene and near future global warming climates. The results show that the Western African summer monsoon (WASM) circulation, closely linked with the Sahel summer rainfall change, tends to strengthen in both the past and future global warming climates, but the monsoonal circulation strengthening is much more intense in the past warm period than in the projected warm future. This causes that the multi-model ensemble (MME) mean increase ratio of Sahel summer rainfall in the past warming climate is about twice to three times larger than that in the future warming climate for the same increase of global mean surface temperature (the regional rainfall increase ratio in the MME mean: about 19.6% per one degree Celsius of global warming in the mid-Pliocene simulations versus about 7.7% per one degree Celsius of global warming in the SSP5-8.5 future projections). Such a striking discrepancy in the regional circulation and hydrological cycle changes is mainly attributed to a dramatically stronger warming over the Canadian Archipelago and Greenland during the mid-Pliocene warm period relative to the projected near future. The more significant northern high-latitude warming during the mid-Pliocene enhances the meridional temperature gradient between the extratropical and tropical regions, which could induce an excessive northward shift of the Intertropical Convergence Zone and a stronger WASM, and thus result in a more intense hydrological cycle around the Sahel region. Our results highlight that besides the global mean temperature increase, meridional warming patterns are also essential for the changes of WASM and regional hydrological cycle in a warmer world. Implications for projecting the regional monsoon and hydrological cycle changes at longer time scales than in the near future are discussed. [ABSTRACT FROM AUTHOR]

We seek to quantify and understand the residual signal in GPS and GLONASS estimates of ocean tide loading displacements (OTLDs) after removing state-of-the-art model estimates. To consider contributions over a broad spatial scale, we estimate OTLD over the Australian continent using ∼ 5.5 years of continuous GPS and GLONASS data from 360 sites. We compare these with modelled estimates, with a focus on the lunar semidiurnal M 2 and diurnal O 1 constituents. We observe spatially coherent patterns of residual OTLD in each of the east, north, and up coordinate components after the removal of tidal loading using elastic models. We subsequently assess the impact of including anelastic dispersion in the model and show a 0.2 mm reduction in range of the up component residuals at coastal sites. A similar reduction at all sites is observed in the east and north components. Of the seven ocean tide models used, we find that three recent models, FES2014b, GOT4.10c and TPXO9.v1, perform similarly, noting these comparisons are made in the CE frame. However, we show that the latter contains centre of mass (CoM) biases in amplitude up to 0.2 mm and 0.5 mm for M 2 and O 1 , respectively, due to the assimilated altimetry data having not been corrected for geocentre motion. We find OTLD estimates are sensitive to the chosen orbit and clock products used in our analysis, with differences of up to 0.5 mm in the east component between solutions using the JPL and either of ESA or CODE products (GPS-only). Our analysis shows that current GNSS estimates of OTLD over Australia are typically accurate to ∼ 0.2 mm at which point we are unable to explain spatially coherent residuals when compared to modelled quantities. These may depend on the appropriate treatment of the CoM variation, anelasticity and/or three-dimensional Earth structure. As such, we recommend great care is taken when interpreting OTLD at the level of 0.1 or 0.2 mm, even if it is regionally coherent. [ABSTRACT FROM AUTHOR]

Ice, snow, and liquid water on the surface of the Earth exert downward force onto the solid earth and deform the lithosphere typically in seasonal timescale. Space techniques, such as Global Navigation Satellite System (GNSS), made it possible to directly measure subtle displacements caused by loading. We can also observe such loads with time-variable gravity using gravity recovery and climate experiment satellites. These techniques made surface loads an attracting scientific target of modern geodesy. In this paper we briefly review the history of geophysical studies of surface loads through geodetic observations of crustal deformation and time-variable gravity. We also review advanced topics such as short-term crustal deformation due to severe meteorological episodes and monitoring of terrestrial water storages. We also present a few related topics such as the change of the obliquity of the Earth due to loads and artificial crustal subsidence signals caused by snow accretion onto GNSS antenna radomes. [ABSTRACT FROM AUTHOR]

The impact of global warming presents an increased risk to the world's shorelines. The Intergovernmental Panel on Climate Change (IPCC) reported that the twenty-first century experienced a severe global mean sea-level rise due to human-induced climate change. Therefore, coastal planners require reasonably accurate estimates of the rate of sea-level rise and the potential impacts, including extreme sea-level changes, floods, and shoreline erosion. Also, land loss as a result of disturbance of shoreline is of interest as it damages properties and infrastructure. Using a nonlinear autoregressive network with an exogenous input (NARX) model, this study attempted to simulate (1991 to 2012) and predict (2013–2020) sea-level change along Merang kechil to Kuala Marang in Terengganu state shoreline areas. The simulation results show a rising trend with a maximum rate of 28.73 mm/year and an average of about 8.81 mm/year. In comparison, the prediction results show a rising sea level with a maximum rate of 79.26 mm/year and an average of about 25.34 mm/year. The database generated from this study can be used to inform shoreline defense strategies adapting to sea-level rise, flood, and erosion. Scientists can forecast sea-level increases beyond 2020 using simulated sea-level data up to 2020 and apply it for future research. The data also helps decision-makers choose measures for vulnerable shoreline settlements to adapt to sea-level rise. Notably, the data will provide essential information for policy development and implementation to facilitate operational decision-making processes for coastal cities. [ABSTRACT FROM AUTHOR]

Sea level rise has accelerated during recent decades, exceeding rates recorded during the previous two millennia, and as a result many coastal habitats and species around the globe are being impacted. This situation is expected to worsen due to anthropogenically induced climate change. However, the magnitude and relevance of expected increase in sea level rise (SLR) is uncertain for marine and terrestrial species that are reliant on coastal habitat for foraging, resting or breeding. To address this, we showcase the use of a low-cost approach to assess the impacts of SLR on sea turtles under various Intergovernmental Panel on Climate Change (IPCC) SLR scenarios on different sea turtle nesting rookeries worldwide. The study considers seven sea turtle rookeries with five nesting species, categorized from vulnerable to critically endangered including leatherback turtles (Dermochelys coriacea), loggerhead turtles (Caretta caretta), hawksbill turtles (Eretmochelys imbricata), olive ridley turtles (Lepidochelys olivacea) and green turtles (Chelonia mydas). Our approach combines freely available digital elevation models for continental and remote island beaches across different ocean basins with projections of field data and SLR. Our case study focuses on five of the seven living sea turtle species. Under moderate climate change scenarios, by 2050 it is predicted that at some sea turtle nesting habitats 100% will be flooded, and under an extreme scenario many sea turtle rookeries could vanish. Overall, nesting beaches with low slope and those species nesting at open beaches such as leatherback and loggerheads sea turtles might be the most vulnerable by future SLR scenarios. [ABSTRACT FROM AUTHOR]

The Pannonian basin is an extensional back-arc basin that has undergone neotectonic inversion and is currently shortening. The understanding and quantification of present-day deformation processes during this inversion are still incomplete. To this end, we investigate the active deformation of the Circum-Pannonian region via the interpolation of GNSS-derived velocity field and the derivation of the strain rate fields. For the interpolation of the velocity field, we use ordinary kriging, a strochastic interpolation method. Our results show that estimating a strain rate field that is virtually free of short-wavelength noise requires the scaling of the velocity uncertainties, i.e. assuming a minimum standard deviation of 1 mm/yr in our case. The deformation of the Circum-Pannonian region is defined by the 2–3 mm/yr, NNE-directed motion of the Dinarides, and by the 0.5–1.5 mm/yr, WSW to SSW directed motion of the eastern areas (European foreland, East Carpathians, South Carpathians, Transylvanian basin). These opposite-sense motions define a large-scale, on average NE-SW shortening and transpression-type deformation in the Dinarides as well as in the Pannonian basin, while the East and South Carpathians undergo regional N–S extension. Neotectonic structures generally show good agreement with the strain rate field, for example in the Dinarides, Eastern Alps, or in the western Pannonian basin. However, the presence of fault-parallel shortening or biaxial shortening along sinistral neotectonic structures in the central and eastern Pannonian basin show some discrepancy between current geodetic and observed neotectonic deformation. The vertical velocity field shows dominantly 100 and 1000 km wavelength signals, the former is probably related to the response of the Pannonian lithosphere-asthenosphere system to neotectonic basin inversion, while latter can possibly be explained by far-field subsidence patterns induced by the mantle response to melting of the Fennoscandian ice sheet during the current interglacial period. [ABSTRACT FROM AUTHOR]

The Great Amazon Reef System is a living biogenic mesophotic reef ecosystem that has been recently described along the shelf break of Brazil. An oceanographic cruise was carried out in 2019 along the outer edge of the French Guiana Shelf. A side-scan sonar survey was conducted to locate reef outcrops and allowed twelve in situ 80- to 120-m depth dives and sampling of the reef rocks and peripheral sands. The majority of the hard rocks are composed of biological concretions. However, several fragments revealed the inside presence of sandstone clasts. These clasts, more or less enveloped by biogenic coatings, probably represent destroyed clasts of underlying or neighboring beachrock banks. Their dominant cement is micritic (high-magnesian calcite); the intergranular or extragranular porous field was later filled with low-magnesian sparry calcite. The sand or gravel that accumulated near the barrier mainly consists of the blunt debris of coastal fauna and flora associated with different carbonate or ferruginous neoformed ooids. At 104-m depth, ooids extracted from dive 11 samples dated from the start of MIS2 (27,370 cal yr BP) and attest to the presence of a significant coastal accumulation. At this same site, cementing did not take place until about 3500 years later (23,990 cal yr BP). The cement of a nearby beachrock indicates a much more recent age (16,170 cal yr BP). Lastly, the age of 4100 yr BP measured on the barnacles attached to the top of the reef attests to the late Holocene reef's biological activity. [ABSTRACT FROM AUTHOR]

Mean sea-level rise (MSLR) will induce shoreline recession, increasing the stress on coastal systems of high socio-economic and environmental values. Localized mega-nourishments are meant to alleviate erosion problems by diffusing alongshore over decades and thus feeding adjacent beaches. The 21-st century morphological evolution of the Delfland coast, where the Sand Engine mega-nourishment was built in 2011, was simulated with the Q2Dmorfo model to assess the Sand Engine capacity to protect the area against the effects of MSLR. The calibrated and validated model was forced with historical wave and sea-level data and MSLR projections until 2100 corresponding to different Representative Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5). Results show that the Sand Engine diffusive trend will continue in forthcoming decades, with the feeding effect to adjacent beaches being less noticeable from 2050 onward. Superimposed to this alongshore diffusion, MSLR causes the shoreline to recede because of both passive-flooding and a net offshore sediment transport produced by wave reshaping and gravity. The existing feeding asymmetry enforces more sediment transport to the NE than to the SW, causing the former to remain stable whilst the SW shoreline retreats significantly, especially from 2050 onward. Sediment from the Sand Engine does not reach the beaches located more than 6 km to the SW, with a strong shoreline and profile recession in that area, as well as dune erosion. The uncertainties in the results are dominated by those related to the free model parameters up to 2050 whilst uncertainties in MSLR projections prevail from 2050 to 2100. [ABSTRACT FROM AUTHOR]