Investigations of both short-term natural climate variability, and long-term, large-scale changes in climate state are advanced by scientific ocean drilling at globally-distributed locations. Despite its global importance as both a contributor to climate change and a region that is most affected by global warming, the Arctic Ocean is the last major region on Earth where the long-term climate history remains poorly known. While many major advances in understanding were achieved in 2004 with the successful completion of IODP Expedition 302: Arctic Coring Expedition (ACEX), the record was hampered by generally poor recovery and by a 26-myr hiatus (or condensed interval depending on the age model) spanning the global transition from the Greenhouse to Icehouse climate states. In August-September 2022, IODP Expedition 377: Arctic Ocean Paleoceanography (ArcOP) will enable another step in reconstructing the detailed history of climate change in the Arctic over the last 50+ million years. The overall goal of the ArcOP drilling campaign is the recovery of a complete stratigraphic sedimentary record on the southern Lomonosov Ridge to meet the highest priority paleoceanographic objective: the continuous long-term Cenozoic climate history of the central Arctic Ocean. Key scientific themes to be addressed by ArcOP are represented in Figure 1. The expedition goals can be achieved through 1) careful site selection, 2) the use of appropriate drilling technology and ice management supported by two ice breakers, and 3) applying multi-proxy approaches to paleoceanographic, paleoclimatic, and age-model reconstructions. The expedition will complete one primary deep drill hole (LR-11B) to 900 meters below seafloor (mbsf; twice as deep as the ACEX core depth). This will be supplemented by a short drill site (LR-10B) to 50 mbsf, to recover an undisturbed Quaternary sedimentary section to ensure complete recovery for construction of a composite section spanning the full age range through the Cenozoic. Expected sedimentation rates two to four times higher than those of ACEX will permit higher-resolution studies of Arctic climate change. More information on ArcOP can be found at the expedition website: https://www.ecord.org/expedition377/.

The abundance and size distribution of marine organic particles are two major factors controlling biological carbon sequestration in the ocean. These quantities are the result of complex physical-biological interactions that are difficult to observe, and their spatial and temporal patterns remain uncertain. Here, we present a novel analysis of particle size distributions (PSD) from a global compilation of in situ Underwater Vision Profiler 5 (UVP5) optical measurements. Using a machine learning algorithm, we extrapolate sparse UVP5 observations to the global ocean from well-sampled oceanographic variables. We reconstruct global maps of PSD parameters (biovolume and slope) for particles at the base of the euphotic zone. These reconstructions reveal consistent global patterns, with high chlorophyll regions generally characterized by high particle biovolume and flatter PSD slope, i.e., a high relative abundance of large vs. small particles. The resulting negative correlations between particle biovolume and slope further suggests amplified effects on sinking particle fluxes. Our approach and estimates provide a baseline for an improved understanding of particle cycles in the ocean, and pave the way to global, three-dimensional reconstructions of sinking particle fluxes from UVP5 observations.

We consider a Bayesian multi-model fault slip estimation (BMMFSE), in which many candidates of the underground-structure model characterized by a prior probability density function (PDF) are retained for a fully Bayesian estimation of fault slip distribution to manage model uncertainty properly. We performed geodetic data inversions to estimate slip distribution in long-term slow slip events (L-SSEs) that occurred beneath the Bungo Channel, southwest Japan, in around 2010 and 2018, focusing on the two advantages of BMMFSE: First, it allows for estimating slip distribution without introducing strong prior information such as smoothing constraints, handling an ill-posed inverse problem by combining a full Bayesian inference and accurate consideration of model uncertainty to avoid overfitting; second, the posterior PDF for the underground structure is also obtained through a fault slip estimation, which enables the estimation of sequential events by reducing the model uncertainty. The estimated slip distribution obtained using BMMFSE agreed better with the distribution of deep tectonic tremors at the down-dip side of the main rupture area than those obtained based on strong prior constraints in terms of the spatial distribution of the Coulomb failure stress change. This finding suggests a mechanical relationship between the L-SSE and the synchronized tremors. The use of the posterior PDF for the underground structure updated by the estimation for the 2010 L-SSE as an input of the analysis for the one in 2018 resulted in a more preferable Bayesian inference, indicated by a smaller value of an information criterion.

It is increasingly recognised that most sheet-like igneous intrusions such as sills and dykes have segmented, rather than planar margins. The geometry of these segments and their connectors can provide insights into magma propagation pathways and host-rock deformation mechanisms during their emplacement. Here we report the results of scaled laboratory experiments on the emplacement of shallow-crustal, saucer-shaped sills with a focus on their propagation and segmentation. Visco-elasto-plastic Laponite RD® (LRD) and Newtonian paraffin oil were used as analogues for layered upper crust rocks and magma, respectively. Our results indicate that: 1) experimental saucer-shaped intrusions are highly segmented with marginal lobes and fingers; 2) the evolution and geometry of marginal segments and their connectors are different within the horizontal inner sill and the inclined outer sill; and 3) the bimodal nature of segment aspect ratios is linked to propagation of the inner sill along a horizontal host-rock interface versus interaction of the inclined outer sill with a homogenous upper layer. Measurements of inlet magma pressure and structural analysis suggest that marginal finger and lobe segments propagate in a repetitive sequence that starts with segmentation, followed by merging of segments and new growth of fingers/lobes. Based on the 3D geometry of segments, we suggest that sill segmentation is linked to smaller scale visco-plastic instabilities that occur within the inner sill and large scale mixed mode (I+III) fracturing during the inclined sheet propagations.

The high albedos and zenith angles in the Arctic cause mixed-phase clouds to warm the Arctic surface during most of the year by absorbing long wavelength (LW) terrestrial radiation and re-emitting LW radiation back to the surface. Most of the LW radiation is absorbed by super-cooled liquid droplets near the top of the cloud. These clouds may be glaciated by seeding with ice crystals, allowing most of the LW radiation to escape into space and thereby cooling the Arctic surface. This study proposes cooling the Arctic by seeding Arctic mixed-phase clouds during the fall, winter, and spring with 200 nm diameter ice crystals sprayed into the clouds by effervescent nozzles deployed on aircraft.

We investigate the conditions under which saucer-shaped sills form through the upper crust and their geometries. We performed a series of scaled laboratory experiments that employ visco-elastic-plastic Laponite RD® (LRD) gels to model upper crustal rocks, and Newtonian paraffin oil as the magma analogue. Both homogenous and layered analogue upper crust is considered. In homogenous 3 wt. % LRD, the injected oil formed a saucer-shaped intrusion with the shortest inner sill observed among all of the experiments. Saucer-shaped sills always formed in experiments with a two-layer upper crust. These experiments show sharp transitions from an inner flat sill to outer inclined sheets, which are characterised by non-planar margins. The experimental results show that: (1) the transition from an inner flat sill to outer inclined sheet occurs when the sill radius to overburden depth ratio (r/H) is between 0.5 and 2.5; (2) the inclined sheets propagate upwards with angles, θ = 15° to 25°; (3) the ratio of the Young’s modulus (E*) between the layers controls when the inner flat sill to outer inclined sheet occurs; and (4) irregular finger-like and/or lobe segment geometries form at the propagating tip of the intrusion. The results also suggest that there is no strict requirement for high horizontal stresses to form natural saucer-shaped sill geometries. We conclude that the layered visco-elastic-plastic crustal analogues better represent natural, complex saucer-shaped sill geometries. Furthermore, the observed sharp transitions between inner and outer sills are compatible with brittle-elastic fracture mechanisms operating at the intrusion scale.

Understanding triggers and evolution of post-depositional sediment intrusion is of major importance to decrease the risk associated with hazards to infrastructure and environment from events such as submarine landslides and fluid escape. Whereas deep-sourced intrusions (>1 km) are widely documented, early burial examples are poorly recognized and have been described only in large deltas. Their formation had not yet been documented in deformed foredeep. Here, we show an exceptionally well-exposed, early burial mud diapir in the Northern Apennines fold and thrust belt. Disequilibrium compaction and tectonic basin tilt led to lateral pressure migration within shallow (<200 m) sediments. As a result, near-lithostatic overpressure developed at the basin margin causing sediment intrusion and destabilization of the slope. This work shows that early burial mud diapirs can develop in deformed foredeep with similar characteristics to their deep-rooted counterparts, with important implications for hazard assessment in areas non-traditionally prone to shallow overpressure buildup.

Groundwater (GW)-surface water (SW) interactions in karst areas may have a strong impact on the quantity and quality of the groundwater system. Although knowledge of karst hydrology has improved in recent decades, the interaction patterns of GW-SW, and understanding of the hyporheic zone (HZ) on improving or deteriorating groundwater remains very limited. Here, we document HZ in a karst basin through study of hydrological, hydrochemical, and biological processes. The depths of some sinkholes or karst windows in the karst plain are more than 100 m, which are dozens of meters lower than the river elevations. The HZ is not limited to the riverbed, but extends into aquifer along the karst conduits. And their interaction patterns are not limited to the mixing GW and SW, but also include mixing of groundwater with other water bodies. Due to the existence of karst conduits, the types of HZ and the dynamic process of hyporheic flow are unique within karst aquifers. We defined these generally in karst groundwater systems dominated by conduits as karst cave hyporheic zones (KCHZ), with the meaning of the place or area where conduit flow interacts with other types of water bodies. The KCHZ was further classified into four types. Research on the five springs in the study area showed the formation of KCHZ is related to the karst development and the hydrogeochemical gradient of water environment. Once the quality of one type of water deteriorates, or the amount of water decreases, the function of hyporheic zone will degenerate.

Atmosphere-only experiments are widely used to investigate climate feedbacks simulated in more computationally expensive fully-coupled global climate model simulations. We confirm that this remains a valid approach by comparing the radiative feedbacks and forcing between coupled and atmosphere-only simulations for the latest models taking part in the 6th phase of the Coupled Model Intercomparison Project (CMIP6). For cloud feedbacks, we find a better than previously known correspondence between these experiments, which applies even to the response of individual cloud properties (amount, altitude and optical depth), is present at nearly every geographic location, and holds even when considering atmosphere-only simulations of only 1 year duration. In the tropics, the correspondence between the two experiments is better revealed when considering feedbacks stratified by vertical motion rather than by geography, owing to the non-uniform warming pattern in the coupled experiment. For the lapse rate and surface albedo feedbacks, the correspondence between the two experiments is weaker due to the lack of sea-ice changes in the atmosphere-only experiment. For the across-model relationship between 4xCO2 radiative forcing and feedback, we find a different behavior across experiments in CMIP6 than in CMIP5, casting doubt on the physical significance of previous results that highlighted an anti-correlation between the two quantities. Overall, these results confirm the utility of atmosphere-only experiments particularly to study cloud feedbacks, which are the dominant source of inter-model spread in climate sensitivity.

The western United States experienced a record-breaking wildfire season in 2020. This study quantifies the contribution of wildfire emissions to the exceedances of health-based National Ambient Air Quality Standard (NAAQS) for fine particles (PM2.5) by comparing two CMAQ simulations, with and without wildfire emissions. During August to October 2020, western wildfires contributed 23% of surface PM2.5 in the contiguous US (CONUS), with a larger contribution in Pacific Coast (43%) and Mountain Region (42%). Consequently, wildfires were the primary contributor to the 3,720 observed exceedances. The wildfire influence peaked on September 14th, 2020, when 273 exceedances were recorded and wildfire emissions contributed 41%, 81%, and 72% to surface PM2.5 concentrations in the CONUS, Pacific Coast, and Mountain regions, respectively. Our finding highlights the predominating influence of wildfires on air quality, and potentially human health, that is expected to grow with increasing fire activities, while anthropogenic emissions decrease.

A new analytical model is presented in order to better understand the depth-dependent wave-induced steady current caused by submerged aquatic canopy-oscillatory flow interaction. The analytical model takes into account the wave and canopy properties. The model is developed by determining the dominant terms in the momentum equation by means of dimensional analysis and satisfying the mass conservation. The dimensional analysis reveals that the pressure gradient (due to wave decay) is of the same order of magnitude as the drag force, wave stress and Reynolds stress terms. In addition, the balance between the pressure gradient and mass conservation induces a seaward current above the canopy, and the presence of the pressure gradient in the momentum equation contributes to intensify the skimming flow at the top of the canopy. Finally, given that the model follows a polynomial function it can be easily implemented in large scale models such as phase average models.

Air flows may be decoupled from the underlying surface either due to strong stratification of air or due to canopy drag suppressing cross-canopy mixing. During decoupling, turbulent fluxes vary with height and hence identification of decoupled periods is crucial for the estimation of surface fluxes with the eddy-covariance (EC) technique and computation of ecosystem-scale carbon, heat, and water budgets. A new indicator for identifying the decoupled periods is derived using forces (buoyancy and canopy drag) hindering movement of a downward propagating air parcel. This approach improves over the existing methods since 1) changes in forces hindering the coupling are accounted for and 2) it is based on first principles and not on ad-hoc empirical correlations. The applicability of the method is demonstrated at two contrasting EC sites (flat open terrain, boreal forest) and should be applicable also at other EC sites above diverse ecosystems (from grasslands to dense forests).

Volcanic activity is a main natural climate forcing and an accurate representation of volcanic aerosols in global climate models is essential. This is, however, a complex task involving many uncertainties related to the magnitude and vertical distribution of volcanic emissions as well as in observations used for model evaluation. We analyse the performance of the aerosol-chemistry-climate model SOCOL-AERv2 for three medium-sized volcanic eruptions. We investigate the impact of differences in the volcanic plume height and SO2 content on the stratospheric aerosol burden. The influence of internal model variability and dynamics are addressed through an ensemble of free-running and nudged simulations at different vertical resolutions. Comparing the modeled evolution of the stratospheric aerosol loading to satellite measurements reveals a good performance of SOCOL-AERv2. However, the large spread in emission estimates leads to differences in the simulated aerosol burdens resulting from uncertainties in total emitted sulfur and the vertical distribution of injections. The tropopause height varies among the free-running simulations, affecting model results. Conclusive model validation is complicated by uncertainties in observations. In nudged mode, changes in convection and tropospheric clouds affect SO2 oxidation paths and cross-tropopause transport, leading to increased burdens. This effect can be reduced by leaving temperatures unconstrained. A higher vertical resolution of 90 levels increases the stratospheric residence time of sulfate aerosol by reducing the diffusion out of the tropical reservoir. We conclude that the model set-up (vertical resolution, free-running vs. nudged) as well as forcing parameters (volcanic emission strength, plume height) contribute equally to the model uncertainties.

Faults and fractures play a significant role in drilling operations, trapping hydrocarbon, and reservoir development in oilfields; exploring faults quickly and accurately can help to reach the target more manageable. In this approach, to improve faults and fractures detection, applicable seismic attributes have been combined using a Multilayer Perceptron (MLP) neural network and applied to a 3-D seismic cube of the Changuleh oil field. First of all, high probabilistic faulted areas, as an interesting area, have been identified using a hand-picking method on a single seismic section. It is used as a pattern and one input set for the MLP neural network. Then, some single seismic attributes (e.g., Similarity, Coherency, Curvature, Instantaneous, etc.) were applied to the data. Next, the Multilayer Perceptron (MLP) neural network has been used to assess and determine the most contributed attributes. The less contributed ones are eliminated and the best seismic attributes, as another input set, combined using the MLP. Finally, the outputs of the MLP network will be two cubes named ‘faulted cube’ and ‘non-faulted cube’. Differences between faulted zones and non-faulted zones on each cube were conspicuous, and there was no need to be interpreted manually. By comparing initial seismic sections and the MLP network’s outputs, it is easy to see where the faulted and fractured zones are.

Surface winds are an important factor in wildfire growth and the decision-making process of when utility companies shut off power to suppress fire ignitions. However, long-term trends in surface winds and their implications for fire weather have received less attention compared to trends in temperature, humidity, and precipitation. This article uses the ERA5 reanalysis to calculate surface wind trends over California during 1979--2019. We find statistically significant increases in surface easterlies during autumn on the western slopes of the Sierra Nevada Mountains and increases in Hazardous Wind Events of heightened wind-related fire risk. Using the Canadian Fire Weather Index, we also show that wildfire risk has mainly increased over the Sierra Nevada Mountains, indicating that strengthening winds has contributed to a growing risk of wind-driven wildfires in this region compared to 40 years ago.

Urban water utilities, facing rising demands and limited supply expansion options, increasingly partner with neighboring utilities to develop and operate shared infrastructure. Inter-utility agreements can reduce costs via economies of scale and help limit environmental impacts, as substitutes for independent investments in large capital projects. However, unexpected shifts in demand growth or water availability, deviating from projections underpinning cooperative agreements, can introduce both supply and financial risk to utility partners. Risks may also be compounded by asymmetric growth in demand across partners or inflexibility of the agreement structure itself to adapt to changing conditions of supply and demand. This work explores the viability of both fixed and adjustable capacity inter-utility cooperative agreements to mitigate regional water supply and financial risk for utilities that vary in size, growth expectations, and independent infrastructure expansion options. Agreements formalized for a shared regional water treatment plant with fixed or adjustable treatment capacities, coupled with structured financing for partner utilities, are found to significantly improve regional supply reliability and financial outcomes. Regional improvements in performance, however, mask tradeoffs among individual agreement partners. Adjustable treatment capacity allocations add flexibility to inter-utility agreements but can compound the financial risk of each utility as a function of the decision-making of the other partners. Often the sensitivity to partners' decision-making under an adjustable agreement degrades financial performance, relative to agreements with fixed capacities allocated to each partner. Our results demonstrate the significant benefits cooperative agreements offer, providing a template to aid decision-makers in development of water supply partnerships.

Magnetosheath jets are localized high-dynamic pressure pulses originating at Earth’s bow shock and propagating earthward through the magnetosheath. Jets can influence magnetospheric dynamics upon impacting the magnetopause; however a significant fraction dissipate before reaching it. In this study we present a database of 13,096 jets observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft from 2008–2018, spanning a solar cycle. Each jet is associated with upstream solar wind conditions from OMNI. We statistically examine how solar wind conditions control the likelihood of jets forming at the shock, and the conditions favorable for jets to propagate through the magnetosheath and reach the magnetopause. We see that, for each solar wind quantity, these two effects are separate, but when combined, we find that jets are nearly 12 times more likely to reach and potentially impact the magnetopause when the interplanetary magnetic field (IMF) is at a low cone angle, and approximately 5 times more likely during fast solar wind. Low IMF magnitude, high Alfvén Mach number, and low density approximately double the number of jets at the magnetopause, while plasma beta and dynamic pressure display no net effect. Due to the strong dependence on wind speed, we infer that jet impact rates may be solar cycle dependent as well as vary during solar wind transients. This is an important step towards forecasting the space weather effects of magnetosheath jets, as it allows for predictions of jet impact rates based on measurements of the upstream solar wind.

To advance the understanding of crustal deformation and earthquake hazards in Canada, we analyze seismic and geodetic datasets and robustly estimate the crust strain accumulation and release rate by earthquakes. We find that less than 20% of the accumulated strain is released by earthquakes across the study area providing evidence for large-scale aseismic deformation. We attribute this to Glacial Isostatic Adjustment (GIA) in eastern Canada, where predictions from the GIA model accounts for most of the observed discrepancy between the seismic and the geodetic moment rates. In western Canada, only a small percentage (< 20%) of the discrepancy can be attributed to GIA-related deformation. We suspect that this may reflect the inaccuracy of the GIA model to account for heterogeneity in Earth structure or indicate that the present-day effect of GIA in western Canada is limited due to the fast response of the upper mantle to the de-glaciation of the Cordillera Ice Sheet. At locations of previously identified seismic source zones, we speculate that the unreleased strain is been stored cumulatively in the crust and will be released as earthquakes in the future. The Gutenberg-Richter (GR) model predicts, however, that the recurrence interval can vary significantly in Canada, ranging from decades near plate boundary zones in the west to thousands of years in the stable continental interior. Our attempt to quantify the GIA-induced deformation provides the necessary first step for the integration of geodetic strain rates in seismic hazard analysis in Canada.