Every year, the area of the Arctic sea-ice decreases in the boreal spring and summer and reaches its yearly minimum in the early autumn. The continuous satellite-based time series shows that the September area has decreased from 4.5*10^6 km^2 in 1979, to 2.8*10^6 km^2 in 2020. The decline has been approximately linear in global mean surface temperature, with a rate of loss of 2.7*10^6 km^2 per degree C of global warming. In the CMIP6 ensemble, however, we find that the majority of the models that reach an Arctic sea-ice free state in the SSP585 runs shows an accelerated loss of sea-ice for the last degree of warming compared to the second last degree of warming, which implies an increased sensitivity of the sea-ice to temperature changes. Both in the observational and CMIP6 data, we find that the decline in September sea-ice area is approximately proportional to the area north of which the zonal average temperature in spring and summer is lower than a critical threshold Tc. The Arctic amplification implies that the zonally averaged temperatures increase relative to the global temperatures, and with rates increasing with latitude. Linear extrapolation of the zonally averaged temperatures predicts that, with further warming, the September sea-ice area will depend non-linearly on global temperature, the sensitivity will increase and the September sea-ice area may become less that 1*10^6 km^2 for global warming between 0.9 and 1.6 degrees C above the current temperature. As a result of accelerated sea-ice loss, the average evolution of the sea-ice area among the CMIP6 models before the loss of the summer sea-ice shows an increase in the year-to-year fluctuations in minimum ice cover in the next decade. This implies exceptional accumulation of extreme events with very low or no sea-ice at all even before the final loss of the sea-ice. Likewise, an apparent short-term recovery of the sea-ice loss might be observable due to the increasing fluctuations.

Sudden Stratospheric Warmings (SSWs) are rare in the Southern Hemisphere (SH), making it difficult to study possible precursors or subsequent impacts. Using a multi-millennial coupled climate model simulation producing 161 SSWs in the SH, we present a detailed study of their lifecycle. We show that SH SSWs are predominantly displacement events forced by wave-1 planetary waves, and that the surface signature similar to the negative phase of the Southern Annular Mode (SAM) is detectable up to two months before the onset date, but there is a tendency for a transition from wave-1 before to zonally symmetric anomalies after onset. We identify a strong weakening of the Amundsen Sea Low as one of the most prominent precursors, which weakens the climatological wave-2 and wave-3 stationary waves and strengthens wave-1 forcing. Compared to their northern counterparts, SH SSWs generally have a longer timescale, and while there is evidence of pre-onset forcing related to tropical sea surface temperatures, the Indian Ocean Dipole is more important than the El Niño Southern Oscillation.

Quantifying flow and transport from hillslopes is vital for understanding surface water quality, but remains obscure because of limited subsurface measurements. A recent combination of water mass balance over a single year with the transmissivity feedback model for a lower montane hillslope in the East River watershed (Colorado) left large uncertainties in transmissivities and predicted fluxes. Because snowmelt drives subsurface flow on this hillslope, improved constraints on the transmissivity profile were obtained by optimizing flux predictions over years having large differences in precipitation minus evapotranspiration. The optimized field-scale hydraulic properties combined with water table elevations predict groundwater discharges that are consistent with wide ranges of snowmelt. As snowmelt rapidly raises the water table, solutes released primarily through bedrock weathering are largely transported out of the hillslope via its highly transmissive soil. Such pulsed water and solute exports along the soil are minimized during snow drought years. Although solute concentrations generally are lower in soils relative to the underlying weathering zone, solute exports during high recharge occur predominantly via soil because of its enlarged transmissivities under snowmelt-saturated conditions. In contrast, this shallow pathway is negligible when recharge and water table elevations are low. The multiyear calibrated subsurface properties combined with updated pore water chemistry continue to show that the weathering zone is the primary source of base cations and reactive nitrogen released from the hillslope. Subsurface export predictions can now be obtained for wide ranges of snowmelt based on measurements of water table elevation and profiles of pore water chemistry.

The imprint of marine atmospheric boundary layer (MABL) dynamical structures on sea surface roughness, as seen from Sentinel-1 Synthetic Aperture Radar (SAR) acquisitions, is investigated. We focus on February 13th, 2020, a case study of the EUREC4A (Elucidating the role of clouds-circulation coupling in climate) field campaign. For clear sky conditions, convective rolls and cells imprints on sea surface roughness is confirmed through the intercomparison with MABL turbulent organization deduced from airborne measurements. A discretization of the SAR wide swath into 25 x 25 km$^2$ tiles allows us to capture the spatial variability of the turbulence organization varying from rolls to cells. We then objectively detect cold pools within the SAR image and combine them with geostationary brightness temperature. The geometrical or physically-based metrics of cold pools are correlated to cloud properties. This provides a promising methodology to analyze the dynamics of convective systems as seen from below and above.

The Goddard Earth Observing System (GEOS) global atmospheric model tracks and transports several individual aerosol species. A key contribution by these aerosols is to interact with solar radiation. When calculating the aerosol-radiation interactions, pre-computed look-up tables of aerosol optical properties are used.We have recently finished an effort to update the aerosol optical properties used in the GEOS model. This has been accomplished with a full rewrite of the optical property simulation code into a Python-based version. In addition to structural changes to the code (outlined below), there are some concrete changes to the aerosol particle definitions. First, truncated lognormal size distributions have been replaced with non-truncated ones, and sub-bin size resolutions of all simulations have been enhanced. Additionally, non-spherical dust accuracy has been improved due to switching to a different spheroidal kernel database. Finally, dust size distribution has been changed from a continuous power law distribution to a bin-specific lognormal distributions.There are also significant changes in the convenience and flexibility of adding or modifying aerosol types for future work and other investigations. Particle properties are now defined exclusively in resource files rather than in the code. This allows for easy addition or modification of aerosol particles, with no need to touch the code. Relatedly, the code can be run either with a provided command-line interface, or via a custom script or notebook. That is, no Python knowledge is needed to generate aerosol particle optics, making the tool easy to use. Additionally, particle types are fully decoupled from specific size distributions, hydration schemes, and other type-specific properties. This also means changing, e.g., a particle size distribution type for a given particle is simple. Performance is significantly improved due to novel Mie simulation optimizations. This enables the aforementioned high size resolutions to be used without concerns for processing time.

Analysis of 35 years (1987-2022) of time-lapse data derived from Landsat imagery and SRTM DEM has revealed significant changes in planform morphology at the confluence of the River Niger and River Benue in West Africa. The Niger is flanked by high elevation plateaus of ca. 400 m altitude and low-lying floodplains on its western bank. The Benue is characterized by more abundant intra-channel and bank-attached bars relative to the Niger. Over the 35-year period, a net downstream migration of 880 m was observed at the junction, its angle decreased from ca. 175° in 1987 to 50° in 2006 and to ca. 16° in 2022 and showed varied segmentation patterns. We establish a linkage between this decrease in confluence angle and increase in annual runoff in the study area. Expansion along the banks of the Niger, Benue, and post-confluence channels was found to be low and non-uniform, suggesting varied resistance of the banks to erosion, which is linked to the abundance of vegetation. These decadal changes in confluence planform are important for understanding river confluence dynamics in major river systems around the world.

Information concerning the types, patterns, and intensity of hydroclimatic variability is needed in various sectors, including water resources planning and climate change adaptation, among numerous others. In transboundary river basins, the nature of hydroclimatic variability frequently is a critical input in the treaties governing water resources allocation to competing parties and sectors. Yet, the pattern of hydroclimatic variability across Africa’s Transboundary Rivers Basins (ATRB) remains poorly investigated owing primarily to lack of access to required data. To the extent that such studies exist, they often have been conducted at different times using different data sets and reference periods, making comparisons across the continent difficult. In this paper, we make use of NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite data to extend the Terrestrial Water Storage (TWS) +50 years prior GRACE era using the unique Generalized Additive Model for Location Scale and Shape (GAMLSS) approach on the Global Land Data Assimilation System Version 2 data (GLDAS V2). The results revealed a downward trend of the TWS over Africa with a decrease rate of 0.14 cm/yr. The spatial patterns of TWS in ATRB showed a significant decreasing trend for Nile, Niger, Chad, Volta, and Congo River Basins, compared to the insignificant trends for Zambezi, Okavango, Limpopo and Orange River Basins. The spatial trends in annual TWS is primarily related to the regional variation in the precipitation trends. The largest negative trend in precipitation were observed over West Africa and Sahel region. The dry trend over south Africa were intervened by wet records. The nature of these hydroclimatic patterns are explained by the significant reduction in the total precipitation and the increasing demands on water resources.

The National Science Foundation provided support to the American Geophysical Union (AGU) to engage its relevant community and help clarify the need for a Near-Surface Geophysics (NSG) Center and identify how it could advance key science questions, provide benefits for society, and develop the geophysical workforce of the future. This report synthesizes the broad input from the community. The listed authors represent the Steering Committee, led by Sarah Kruse and Xavier Comas, and AGU staff leads. They were responsible for most of the editing and connective writing. The major conclusions are: ● The capability and importance of NSG is expanding rapidly, and NSG is providing key science and knowledge to many specific scientific challenges in diverse disciplines–from ecology and anthropology to hydrology, oceanography, cryosphere science, soil and critical zone science, and more. ● This has been thanks to diverse new instruments and approaches, expanded monitoring, improved resolution, interoperable data sets, and new computing power and approaches, among other developments. ● As a result, advancing NSG is critical to addressing many societal challenges at local to global scales. Human society depends on and interacts with the NSG environment in deep and diverse ways at all scales. ● Despite these developments, integration of NSG approaches and awareness of these across related disciplines are not nearly robust enough for these needs. ● Major challenges include providing equipment and training around its use, developing and deploying new equipment and sensors, developing interoperable data, and developing computation techniques. ● In particular, educating both current researchers and developing an NSG-enabled workforce is a major challenge. ● Integrating education with societal and scientific challenges provides a great opportunity and means to expand inclusivity and diversity in the Earth sciences and to address climate justice and equity challenges. ● Thus there was a strong consensus for support of an NSG Center designed to address these challenges and needs and to foster convergent science, provide broad and hands-on educational training, and engage communities and the public meaningfully. ● We were not charged with envisioning the specific model for a Center—and indeed emphasized that the term “Center” was generic and did not necessarily imply that these efforts were envisioned to be in one location–but note that NSF is supporting important complementary facilities include the new EarthScope Consortium combining IRIS and UNAVCO, NCALM, and CTEMPS. ● In sum, we strongly encourage the NSF to take the next step in considering the best implementation model for a NSG Center that addresses these needs, enables these opportunities, and leverages and complements existing efforts.

Ocean transform faults often generate characteristic earthquakes that repeatedly rupture the same fault patches. The westernmost Gofar transform fault quasi-periodically hosts ~M6 earthquakes every ~5 years, and microseismicity suggests that the fault is segmented into five distinct zones, including a rupture barrier zone that may have modulated the rupture of adjacent M6 earthquakes. However, the relationship between the systematic slip behavior of the Gofar fault and the fault material properties is still poorly known. Specifically, the role of pore fluids in regulating the slip of the Gofar fault is unclear. Here, we develop a new method using differential arrival times between nearby earthquakes to estimate the in-situ Vp/Vs ratio of the fault-zone materials. We apply this technique to the dataset collected by an ocean-bottom-seismometer network deployed around the Gofar fault in 2008, which recorded abundant microearthquakes, and find a moderate Vp/Vs ratio of 1.75–1.80 in the rupture barrier zone and a low Vp/Vs ratio of 1.61–1.69 in the down-dip edge of the 2008 M6 rupture zone. This lateral variation in Vp/Vs ratio may be caused by both pore fluids and chemical alteration. We also find a 5–10% increase in Vp/Vs ratio in the barrier zone during the nine months before the mainshock. This increase may have been caused by fluid migrations or slip transients in the barrier zone.

Irrigation is the largest human intervention in the water cycle that can modulate climate extremes, yet global irrigation water use (IWU) remains largely unknown. Microwave remote sensing offers a practical way to quantify IWU by monitoring changes in soil moisture caused by irrigation. This study evaluates the ability to quantify IWU by assimilating high-resolution (1km) SMAP-Sentinel 1 (SMAP-S1) remotely sensed soil moisture with a physically-based land surface model (LSM) using a particle batch smoother (PBS). A suite of synthetic experiments is devised to evaluate different error sources. Results from the synthetic experimentation show that unbiased simulations with known irrigation timing can produce an accurate irrigation estimate with a mean annual bias of 0.45% and the mean R2 of 96.5%, relative to observed IWU. Unknown irrigation timing can significantly deteriorate the model performance by increasing the mean annual bias to 23% and decreasing the mean R2 to 36%. In real-world experiments, the PBS data assimilation approach provides a mean bias of -18.6% when the timing of irrigation water use is known. This underestimation is possibly attributable to missing part of the irrigation signal. Yet, significantly higher irrigation was estimated over the irrigated pixels compared to the non-irrigated pixels, indicating that data assimilation can skillfully convey irrigation signals to LSMs. LSM calibration provides a 10% improvement to soil moistrue RMSE relative to the open-loop simulation. PBS data assimilation provides an additional 50% improvement to simulated soil moisture RMSE by correcting the model state and superimposing the optimal (unmodeled) irrigation on precipitation forcing.

The mining industry produces a considerable amount of stone waste and tailings, posing an ecological danger. This industrial waste is often disposed of via landfill, which leads to soil degradation and water and air pollution while obtaining valuable land. It can be recycled via a variety of methods, including the promising geopolymerization approach, which converts waste into value. This research investigates recent advancements in the production of geopolymer composites derived from industrial waste and mine tailings as a potential sustainable construction material. This research also provides indepth analyses of the features and behaviours of mine tailings mixtures utilized in geopolymer production, such as their durability, microstructure, thermal and leaching capabilities. This study also reveals an information gap that must be addressed to progress mine tailings composites for cementitious materials.

The biological pump and deep-ocean ventilation in eastern equatorial Pacific (EEP) Ocean are thought to play a crucial role in cases of global CO2 change. However, the integral role of these two processes in regulating atmospheric CO2 perturbations over major climate transitions are still unknown. Here, we present the magnetofossil record in EEP sediments from Sites 1333 and 1218 across the Eocene-Oligocene Transition (EOT) when the major ice-sheet was first established on Antarctica. We find that the EEP dust fertilization and bottom-water oxygenation were well co-archived by magnetofossil in characteristics of abundance and morphology, respectively. Our observations show a coeval decline of EEP biological productivity and deep-ocean ventilation during the Antarctic glacial expansion, and suggest that the reduced deep-ocean ventilation contributed to the global CO2 decline across the EOT, whereas the superimposed biological pump action provided a negative (stabilizing) feedback in the meantime.

The region of Japanese island arc is one of the most seismically active regions of the world due to very high plate convergence rate. On March 11, 2011., the great Mw=9.0 Tohoku earthquake occurred in the central segment of the Japanese subduction zone, the region where the previous megathrust earthquake was in 869. To identify the spatiotemporal variations of surface deformations following the 2011 earthquake we analyzed more than 7 years of continuous GNSS observations from over 1400 stations of GEONET network that covers the entire territory of Japanese islands. Coseismic displacements captured by GNSS stations allowed us to model the slip distribution in the earthquake source and to revealed significant effect of Fossa Magna Graben on the coseismic deformations pattern. The observed surface displacements before, during and after the Tohoku earthquake exhibited good agreement with the expected motions implied by the keyboard model of subduction zones [Lobkovsky and Baranov, 1984] at the appropriate stages of the seismic cycle. At the same time, analysis of the displacement rate variations estimated over 1-year intervals after the Tohoku earthquake showed an intense ongoing postseismic motion of complex mechanism. We tested a hypothesis of significant afterslip in the earthquake source using 1-month cumulative displacements for the first half of the year after the earthquake. The slip distribution in the earthquake source and afterslip process were modelled using open-source software package STATIC1D of F. Pollitz. We also used the open-source software package VISCO1D of F. Pollitz to test the influence on surface deformations of rapid viscoelastic relaxation caused by coseismic slip. Our analysis of the afteslip process showed that its maximal contribution rapidly decreases in the first six months after the earthquake from 1-3 meters to 10-20 centimeters per month and cannot predict the observed long-term displacements.

Geophysical logs collected from a deep borehole drilled to the Canadian Shield in Northeastern Alberta shed valuable lights on the state of stress in stable cratons. Observed breakout azimuths rotate between three depth intervals, from N100°E at 1650-2000 m to N173°E at 2000-2210 m, and finally to N145°E at the bottom. No obvious fractures that might disturb stresses were found; and these rotating breakouts can be interpreted either as being due to a heterogenous stress field or formation elastic and strength anisotropy. The latter interpretation is favored because the breakout azimuths are strongly controlled by rock metamorphic textures as validated by their close correlations with both dip directions of foliation planes and polarization directions from dipole sonic logs. Monte Carlo realizations further demonstrate that anisotropic metamorphic rocks subjected to a uniform horizontal stress direction could result in the observed azimuth-rotating breakouts. The stress magnitudes inferred from this analysis, which incorporates both the rock anisotropy and weak foliation failure planes, suggest a normal faulting regime and a maximum horizontal compression direction consistent with that in the overlying Western Canadian Sedimentary Basin (NE-SW) and the motion of the North American plate. The inferred stress magnitudes are low and Mohr-Coulomb analyses demonstrate that the formation is not near the critical loading for slip on weak planes. However, more detailed investigations should be conducted since Monte Carlo calculations indicate that analyses from breakout widths, particularly when a conventional Kirsch-based formula is employed, are highly nonunique, allowing for large variations in potential stress states.

A document by Georgia Sotiropoulou. Click on the document to view its contents.

In the field geophysical instruments, various seismic sensors (an accelerometer, a velocimeter) and auxiliary equipment in the form of recorders (loggers) have been designed, which provide wireless information transfer to the data collecting and processing center. On the basis of these, instrumental earthquake observation systems have been developed to ensure the integrated security of critical facilities. These systems can be transformed to control global seismic monitoring of the territories, dams, also facilities of critical importance such as nuclear power plants, bridges, tunnels and technological pipelines for chemical and oil-processing plants. The report presents the technical characteristics of the above mentioned instruments and the possibilities of their wide application in different countries. Additionally, monitoring of seismicity of Armenian regions is implemented for the earthquake research.

Percolation theory addresses the spatial and temporal scaling properties of disordered networks, both for topological and transport-related processes. The critical zone is, effectively, a random network. The ability to predict the dimensions of the critical zone as a function of time, as well as its carbon storage properties, are both critical to the understanding of its dynamics. In addition, combining the scaling relationships with the principal that represented ecosystems will tend to optimize net primary productivity, generates a basic understanding of the water cycle. When the future of hydrology is discussed, these facts should be of central importance. Furthermore, although the definition of complex systems is not necessarily generally agreed on, it is usually understood that phase transitions, such as described by percolation theory, are emergent phenomena within the range of topics encompassed. Thus, this topic is of fundamental relevance to the present conference.

The Chilean subduction zone is one of the most seismically active regions on Earth. Focal zones of earthquakes with magnitude M>8, registered in this region for the last 200 years, cover almost the entire length of the Chilean coast. In 2010 the Darwin seismic gap existing from 1835 between the focal zones of 1960 Great Chilean earthquake and the 1985 Valparaiso earthquake was interrupted by the Maule earthquake Mw = 8.8. We analyzed the data of 8 years of continuous observations at 27 sites of the Chilean GPS network in order to distinguish coseismic and postseismic deformations in the vicinity of the 2010 earthquake. The analysis of postseismic deformations is based on the ground displacement velocities estimated over 1-year intervals. We used the keyboard model of subduction zones [Lobkovsky and Baranov, 1984] combined with the model of viscoelastic relaxation in the asthenosphere and the upper mantle to explain the variety of motions observed in the region of Central Chile. We model viscoelastic relaxation caused by coseismic slip using the open-source software package VISCO1D of F. Pollitz. The coseismic displacements captured by the sites close to the epicenter of the 2010 event amounted to 1 to 3 meters, which characterizes the magnitude of the displacements of seismogenic blocks at the time of the earthquake. All the coseismic displacements are directed toward the ocean, which agrees well with the predicted movements of the blocks in the seismic stage of the seismic cycle. Data from the first two years after the 2010 event show attenuating site offsets toward the ocean over the whole Central Chile region which indicates passage of aftershock stage of the seismic cycle. Over the next 5 years the observed displacements can be explained by the process of restoring the stationary state of stress accumulation for seismogenic blocks in the frontal part of the subduction zone in combination with the continuing motion of the rear block with viscous asthenospheric flow. The duration of the viscoelastic relaxation process for the Maule earthquake is estimated to last for more than 15 years.