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At least 1,117 records · Page 62Linked to original sources
USGS2019

Improving estimates of coral reef construction and erosion with in-situ measurements

The decline in living coral since the 1970s has conspicuously slowed reef construction on a global scale, but the related process of reef erosion is less visible and not often quantified. Here we present new data on the constructional and deconstructional side of the carbonate-budget equation in the Florida Keys, U.S.A. We documented Orbicella spp. calcification rates at four offshore reefs and quantified decadal-scale rates of Orbicella-reef erosion at a mid-shore patch reef. Using Orbicella coral heads fitted with permanent markers in 1998, we measured reef-elevation loss at 28 stations over 17.3 years to estimate a mean erosion rate of -5.5 (± 3.2, SD) mm yr-1. This loss equates to an erosion rate of -8.2 (± 4.8, SD) kg m-2 yr-1 on dead Orbicella colonies, or -6.6 kg m-2 yr-1 when adjusted reef-wide. Calculating net carbonate production using a census-based approach on the same patch reef in 2017, we estimated a reef-wide bioerosion rate of -1.9 (± 2.0, SD) kg m-2 yr-1, and a net carbonate production rate of 0.5 (± 0.3, SD) kg m-2 yr-1. Substituting the erosion rate we estimated with the markers would suggest that net carbonate production at this patch reef was lower and negative, -4.2 kg m-2 yr-1. This divergence could be a function of high erosion rates measured on the tops of Orbicella colonies, which may be preferentially targeted by parrotfish. Nonetheless, our study suggests the need for new field data to improve estimates of reef-structure persistence as coral reefs continue to degrade.

Florida↗
USGS2022

Predicting larval alewife transport in Lake Michigan using hydrodynamic and Lagrangian particle dispersion models

Several species of fish in large lakes and marine environments have a pelagic larval stage, and are subject to variable transport that can ultimately regulate survival and recruitment success. Alewife, Alosa pseudoharengus , are subject to transport by complex coastal currents during their pelagic larval stage (~ 30 d). We assessed backward-trajectory simulations, consisting of a Lagrangian particle dispersion model linked to the Finite Volume Community Ocean Model, to estimate likely hatch locations of aged larval alewife collected from locations on both the eastern and western sides of Lake Michigan during July 2015. We used four deployments of three satellite-tracked drifter buoys in coastal waters to assess model skill in estimating the origin of a drifter from its final location. We found that the trajectories of drifters varied greatly, depending on wind events and associated coastal transport processes, including upwelling/downwelling and coastal jet currents. In 2 of 12 cases, the backward trajectory simulations failed to predict the drifter origin, associated with transport of 170 km in a narrow coastal jet current. In the remaining 10 cases, the known drifter origin was within 3.5 km of the spatial patch of predicted possible origins for a scenario of horizontal diffusivity (188 m 2 s −1 ) consistent with the offshore model grid resolution. Modeled backward trajectories estimated that alewife originated from the same side of the lake where they were collected, within ~ 100 km of the collection site. Our paper demonstrates the utility of hydrodynamic models to estimate a region of origin for aged larval fish.

Lake Michigan↗
USGS2024

Gulf Stream intrusion and deep current upwelling drive dynamic patterns of temperature and food supply within cold-water coral reefs

One of the most significant features of the Northwest Atlantic, the Gulf Stream influences high magnitude environmental fluctuations in deep habitats across the South Atlantic Bight. Amid this variability, the Blake Plateau harbors extensive reefs formed by cold-water corals that were previously assumed to rely on narrow ranges of temperature, currents, and particulate supply. A benthic lander collected near-bed conditions at the Richardson Reef Complex, a cold-water reef dominated by the scleractinian Desmophyllum pertusum at 830 m within the path of the Gulf Stream. Specific behavior of the Gulf Stream resulted in recurring environmental patterns at depth. During offshore meanders, deep stream components intruded onto the reef and caused rapid (3.74°C per hour) temperature increases up to 10.8°C (> 5°C above the site mean) and increased chlorophyll. Within 2 d of peak temperatures, intrusions were replaced by strong, turbid upwelling currents that rapidly cooled the site to temperature minima (4.13°C). While considerable environmental variability from the Gulf Stream may otherwise implicate a thermally stressful setting for corals, high-temperature events were likely mitigated by their short duration (< 37.4 h) and physical coupling with enhanced organic material. This hypothesis was supported by high-density clustering of D. pertusum occurrences within 50 km around the Gulf Stream's position along the South Atlantic Bight. This suggests that cold-water corals experiencing environmental variability can be sustained by relationships between food supply, temperature, and currents that vary in strength along stochastic time scales, shedding further light on the niche of cold-water corals.

Limnology and Oceanography↗
USGS2024

Arctic fishes reveal patterns in radiocarbon age across habitats and with recent climate change

Climate change alters the sources and age of carbon in Arctic food webs by fostering the release of older carbon from degrading permafrost. Radiocarbon ( 14 C) traces carbon sources and age, but data before rapid warming are rare and limit assessments over time. We capitalized on 14 C data collected ~ 40 years ago that used fish as natural samplers by resampling the same species today. Among resampled fish, those using freshwater food webs had the oldest 14 C ages (> 1000 yr BP), while those using marine food webs had the youngest 14 C ages (near modern). One migratory species encompassed the entire range of 14 C ages because juveniles fed in freshwater streams and adults fed in offshore marine habitats. Over ~ 40 yr, average 14 C ages of freshwater and marine feeding fish shifted closer to atmospheric values, suggesting a potential influence from “greening of the Arctic.”

Alaska↗
USGS2018

Juvenile Chinook salmon and forage fish use of eelgrass habitats in a diked and channelized Puget Sound River Delta

Eelgrass Zostera marina can form extensive meadows on Puget Sound river deltas. The extent to which these meadows provide critical rearing habitat for local estuarine fishes, especially out‐migrating juvenile salmon, is not well understood. Further, delta eelgrass has been impacted by diking and river channelization with unknown consequences for fish. We sampled fish in the Skagit River delta, Washington, during April–September with a lampara net, which is well suited to capturing fish in eelgrass. We compared abundance and body size of Chinook Salmon Oncorhynchus tshawytscha and three forage fish species between eelgrass and nearby unvegetated habitat. We also assessed combined effects of eelgrass characteristics (meadow size and morphology) and oceanographic conditions (temperature and salinity), which covaried according to proximity and orientation to channelized distributary outlets, diked shorelines, and a jetty. Chinook Salmon were more abundant in eelgrass than in unvegetated habitat in June–July and were relatively more abundant in eelgrass compared with unvegetated habitat in regions with intact eelgrass than offshore from a channelized distributary outlet. Abundances of Pacific Herring Clupea pallasii and Shiner Perch Cymatogaster aggregata were consistently severalfold higher in eelgrass than in unvegetated habitat. Surf Smelt Hypomesus pretiosus were more abundant in eelgrass than in unvegetated habitat at some locations, but never less abundant in eelgrass. Our results suggest that conservation and restoration of delta eelgrass would benefit these species and help to identify the settings in which these actions would be most beneficial.

Washington↗
USGS2022

Phenological variation in spring migration timing of adult alewife (Alosa pseudoharengus) in coastal Massachusetts

The timing of biological events in plants and animals, such as migration and reproduction, is shifting due to climate change. Anadromous fishes are particularly susceptible to these shifts as they are subject to strong seasonal cycles when transitioning between marine and freshwater habitats to spawn. We used linear models to determine the extent of phenological shifts in adult Alewife Alosa pseudoharengus as they migrated from ocean to freshwater environments during spring to spawn at 12 sites along the northeastern USA. We also evaluated broadscale oceanic and atmospheric drivers that trigger their movements from offshore to inland habitats, including sea surface temperature, North Atlantic Oscillation index, and Gulf Stream index. Run timing metrics of initiation, median (an indicator of peak run timing), end, and duration were found to vary among sites. Although most sites showed negligible shifts towards earlier timing, statistically significant changes were detected in three systems. Overall, winter sea surface temperature, spring and fall transition dates, and annual run size were the strongest predictors of run initiation and median dates, while a combination of within-season and seasonal-lag effects influenced run end and duration timing. Disparate results observed across the 12 spawning runs suggest that regional environmental processes were not consistent drivers of phenology and local environmental and ecological conditions may be more important. Additional years of data to extend time series and monitoring of Alewife timing and movements in nearshore habitats may provide important information about staging behaviors just before adults transition between ocean and freshwater habitats.

Massachusetts↗
USGS2020

Electrofishing encounter probability, survival, and dispersal of stocked age-0 Muskellunge in Wisconsin lakes

Boat electrofishing is often used to sample age-0 Muskellunge Esox masquinongy for indexing recruitment or evaluating stocking success. However, electrofishing samples typically result in low CPUE, prompting concerns regarding whether catch rates reflect actual abundance or whether boat electrofishing is generally ineffective for capturing age-0 Muskellunge (i.e., if fish are not being encountered by the gear). To address these concerns, we used radiotelemetry to evaluate the probability of encountering stocked age-0 Muskellunge (230–350 mm TL) during standardized fall electrofishing surveys in three Wisconsin lakes. Our approach also allowed us to evaluate short-term survival and dispersal from stocking locations. Despite limited dispersal (<2.5 km) from the stocking locations and relatively high short-term survival (75–94%) of radio-tagged fish, few age-0 Muskellunge were located within the path of the electrofishing boat (7–30%). Furthermore, the probability of encounter by boat electrofishing varied by as much as 6.3 times among lakes. Differences in encounter probability among lakes appeared to be related to lake basin and habitat characteristics. Overlays of electrofishing sampling effort and fish locations revealed that traditional shoreline electrofishing may not be an effective way of estimating age-0 Muskellunge CPUE. Modifications to electrofishing protocols, including increased effort in offshore areas and consideration of basin characteristics and habitat, may be needed to increase encounter probabilities and the utility of boat electrofishing for sampling age-0 Muskellunge.

Wisconsin↗
USGS2023

Conservation decision support for Silver Chub habitat in Lake Erie

Objective Conservation and restoration of aquatic species is difficult, especially for rare species, because their habitats are typically disturbed, obscuring the natural ability of the habitat to support each species. The Lake Erie population of Silver Chub Macrhybopsis storeriana struggles to sustain itself in a habitat disturbed by a wide spectrum of anthropogenic factors. Application of multiple model predictions can provide indications of conservation or restoration opportunities for this species. Methods A combination of models that predict the best potential for Lake Erie habitat to support Silver Chub and the effects of anthropogenic disturbances on that population were used to identify habitat conditions throughout the western aquatic lake unit. Result As many as 76 combinations of best habitat potential and disturbance conditions were present, but the best opportunities occurred in <12% of the study area. Some of the best protection opportunities were farthest offshore, and extensive areas of least disturbed habitat for restoration were near the southern and western shores. The location-specific model predictions provide fine-scale decision support for Silver Chub habitat protection or restoration. Conclusion The approach applied here may help identify compatibilities among species to achieve the desirable fish community for Lake Erie and reconcile conflicting management actions.

Michigan, Ohio, Ontario↗
USGS2023

Spawning locations, movements, and potential for stock mixing of walleye in Green Bay, Lake Michigan

Effective fishery management in large systems relies on understanding how individual stocks contribute to a fishery over spatial and temporal scales. The current conceptual model for management of Walleye Sander vitreus in Green Bay designates Walleye in the northern and southern parts of the bay as distinct stocks, with little mixing between the northern and southern fisheries, and assumes that Walleye in both northern and southern Green Bay primarily spawn in tributaries as opposed to shoreline or offshore reef areas. We used acoustic telemetry to test this conceptual model for Walleye management in Green Bay. Telemetry indicated that the majority of Green Bay Walleye use tributaries for spawning. However, many individuals were assigned to open-water spawning locations during consecutive years in both northern (26%) and southern (21%) Green Bay, suggesting that open-water spawners may represent a larger proportion of the Walleye stocks than previously thought. Differential movement was observed between northern and southern portions of Green Bay, with 56% of Walleye tagged in northern Green Bay crossing receiver lines to move south compared to only 19% of Walleye tagged in southern Green Bay crossing receiver lines to move north. Walleye typically transitioned across these boundaries in summer and fall, suggesting that stock contributions to the fishery in each zone may differ seasonally. Differential movements of northern Green Bay Walleye may be influenced by broad-scale differences in habitat and prey availability, which are likely related to the differential effects of dreissenid mussel invasion in Green Bay. Our results suggest that adjustment of monitoring efforts to account for open-water spawners may provide a more complete picture of stock status. Additionally, more research examining potential food web effects of northern Green Bay Walleye moving into southern Green Bay may be needed to determine how these movements might influence other important species.

Wisconsin↗
USGS2025

Evaluation of juvenile salmon behavior to inform downstream fish passage development at a high head dam

F ish passage development is a priority at Tieton Dam, on the Tieton River in Washington state, because passage options were not included when the dam was constructed nearly 100 years ago. To inform downstream passage design, we conducted a study to evaluate migration and near-dam behavior of juvenile salmon. The primary goal of the study was to determine how fish approached the dam and to identify areas where they congregated. In its current configuration, water is passed through a deep intake located approximately 548 m upstream of the dam, so there was interest in determining if juvenile salmon spent more time near the intake or at the dam. We found that tagged fish primarily entered the dam forebay offshore and arrived at the dam near the spillway on the left bank of the reservoir. Tagged fish had extended residence times in the forebay and moved repeatedly between the intake and the dam. Using thermal profile data, we inferred that juvenile salmon likely occupied the upper 5 m of the water column during May and June before moving to deeper portions of the water column (10–27 m) during July–September when the reservoir became thermally stratified. We found that a small percentage of tagged fish passed the dam when the reservoir was rapidly drawn down during August–October, but additional research may be needed to fully assess entrainment risk through the intake. These findings suggest that downstream fish passage could be developed at Tieton Dam with a high probability of success, given that most fish survived reservoir passage and spent considerable time near the dam where they would be available to discover and utilize new passage routes.

Washington↗
USGS2013

A kinematic model for the formation of the Siletz-Crescent forearc terrane by capture of coherent fragments of the Farallon and Resurrection plates

The volcanic basement of the Oregon and Washington Coast ranges has been proposed to represent a pair of tracks of the Yellowstone hotspot formed at a mid-ocean ridge during the early Cenozoic. This interpretation has been questioned on many grounds, especially that the range of ages does not match the offshore spreading rates and that the presence of continental coarse clastic sediments is difficult to reconcile with fast convergence rates between the oceanic plates and North America. Updates to basement geochronology and plate motion history reveal that these objections are much less serious than when they were first raised. Forward plate kinematic modeling reveals that predicted basement ages can be consistent with the observed range of about 55–49 Ma, and that the entire basement terrane can form within about 300 km of continental sources for clastic sediments. This kinematic model indicates that there is no firm reason to reject the near-ridge hotspot hypothesis on the basis of plate motions. A novel element of the model is the Resurrection plate, previously proposed to exist between the Farallon and Kula plates. By including the defunct Resurrection plate in our reconstruction, we are able to model the Farallon hotspot track as docking against the Oregon subduction margin starting about 53 Ma, followed by docking of the Resurrection track to the north starting about 48 Ma. Accretion of the Farallon plate fragment and partial subduction of the Resurrection fragment complicates the three-dimensional structure of the modern Cascadia forearc. We interpret the so-called “E” layer beneath Vancouver Island to be part of the Resurrection fragment. Our new kinematic model of mobile terranes within the Paleogene North American plate boundary allows reinterpretation of the three-dimensional structure of the Cascadia forearc and its relationship to ongoing seismotectonic processes.

Washington;Oregon↗
USGS2000

Predicting the physical effects of relocating Boston's sewage outfall

Boston is scheduled to cease discharge of sewage effluent in Boston Harbor in Spring 2000 and begin discharge at a site 14 km offshore in Massachusetts Bay in a water depth of about 30 m. The effects of this outfall relocation on effluent dilution, salinity and circulation are predicted with a three-dimensional hydrodynamic model. The simulations predict that the new bay outfall will greatly decrease effluent concentrations in Boston Harbor (relative to the harbour outfall) and will not significantly change mean effluent concentrations over most of Massachusetts Bay. With the harbour outfall, previous observations and these simulations show that effluent concentrations exceed 0??5% throughout the harbour, with a harbour wide average of 1-2%. With the bay outfall, effluent concentrations exceed 0??5% only within a few km of the new outfall, and harbour concentrations drop to 0??1-0??2%, a 10-fold reduction. During unstratified winter conditions, the local increase in effluent concentration at the bay outfall site is predicted to exist throughout the water column. During stratified summer conditions, however, effluent released at the sea bed rises and is trapped beneath the pycnocline. The local increase in effluent concentration is limited to the lower layer, and as a result, surface layer effluent concentrations in the vicinity of the new outfall site are predicted to decrease (relative to the harbour outfall) during the summer. Slight changes are predicted for the salinity and circulation fields. Removing the fresh water associated with the effluent discharge in Boston Harbor is predicted to increase the mean salinity of the harbour by 0??5 and decrease the mean salinity by 0??10-0??15 within 2-3 km of the outfall. Relative to the existing mean flow, the buoyant discharge at the new outfall is predicted to generate density-driven mean currents of 2-4 cm s-1 that spiral out in a clockwise motion at the surface during winter and at the pycnocline (15-20 m depth) during summer. Compensating counterclockwise currents are predicted to spiral in toward the source at the bottom. Because the scale of the residual current structure induced by the new discharge is comparable to or smaller than typical subtidal water parcel excursions, Lagrangian trajectories will not follow the Eulerian residual flow. Thus, mean currents measured from moorings within 5 km of the bay outfall site will be more useful for model comparison than to indicate net transport pathways.

Massachusetts↗
USGS1997

Distribution of seabirds in the northern Gulf of Mexico in relation to mesoscale features: Initial observations

The presence of seabirds was related to offshore surface eddies and the freshwater plume of the Mississippi River in the northern Gulf of Mexico during autumn, winter, spring, and summer 1992-1993. Skuas (Stercorarius spp.) were the most common bird seen in autumn, whereas skuas and gulls (Larus spp.) were the most common in winter. Few birds were seen in the spring, and terns (Sterna spp.) were the most common birds seen in late summer. During summer, terns were associated with the freshwater plume of the Mississippi River. In the winter, herring (Larus argentatus) and laughing gulls (L. artricilla) were associated with areas with steep thermoclines, while pomarine skuas (Stercorarius pomarinus) were found in areas of low productivity. Herring and laughing gulls in the winter, all birds in the spring, and terns in the summer were more common outside eddies. Only pomarine skuas in the winter were seen more commonly inside warm-core eddies.

Conference Paper↗
USGS2020

On the use of statistical analysis to understand submarine landslide processes and assess their hazard

Because of their inaccessibility, submarine landslides are typically studied individually and at great effort and expense to provide knowledge of the specific site conditions where these landslides occur. Statistical analysis of submarine landslide scars can offer generalized perspectives on the processes that initiate submarine landslides and can help toward hazard assessment in areas that have not been studied in detail. The following review discusses more than a decade of development of statistical approaches to studying submarine landslides. Landslides were previously viewed together with other natural hazards, such as earthquakes and fires, as a phenomenon whose size distribution obeys an inverse power law. Inverse power law distributions are the result of self-organized avalanche processes, in which the final hazard size cannot be predicted at the onset of the disturbance. We find that volume and area distributions of submarine landslides along the U.S. Atlantic continental slope and along nine other margins worldwide do not follow an inverse power law. Rigorous statistical tests of several different probability distribution models indicate that the lognormal model is most appropriate for these siliciclastic environments. Lognormal distributions can be simulated by assuming that the area of slope failure depends on earthquake magnitude, in other words, failure occurs simultaneously over the area affected by horizontal ground shaking and does not cascade from nucleating sources. Therefore, the maximum landslide size can be predicted from the earthquake magnitude and the distance from the rupturing fault. Moreover, earthquakes <~M4.5 cannot generate significant submarine landslides. We further demonstrate that empirical, offshore landslide hazard curves can be developed from these lognormal landslide size distributions, if the duration of mapped landslide activity is known. In addition to hazard estimation, scaling relationships can yield insights on the physical processes associated with landslide failure. For example, the log-log relationship between volume and area of landslide scars in siliciclastic margins is observed to be almost linear implying that most landslides are translational. Carbonate margins, in contrast, show a power-law distribution of scar volumes and their volume to area relationship is ~1.3. These results suggest that landslides in carbonate margins are governed by the random distributions of existing fissures, and they act like rock falls on land. Although earthquakes are the principal trigger of submarine landslides, the effects of earthquake frequency on slope stability can be counterintuitive. The average size of landslide scars decreases non-linearly with increasing frequency of earthquakes and increases with increasing sedimentation rate. The effect is interpreted as evidence for densification and shear strength increase of margin sediment, induced by repeated seismic shaking.

Book chapter↗
USGS2021

Sea otter predator avoidance behavior

Predators directly affect their prey as a source of mortality, and prey respond by employing antipredator strategies. Sea otters are a keystone predator within the nearshore community, but higher trophic level avian, terrestrial, and pelagic predators (e.g., bald eagles, brown bears, wolves, white sharks, and killer whales) prey on them. Three antipredator strategies used by sea otters are vigilance (group or sentinel detection of danger), avoidance (seeking a location that is inaccessible to predators), and crypsis (the ability to avoid observation or detection). Vigilant behavior allowed sea otters to escape total extinction during the Maritime Fur Trade of the eighteenth and nineteenth centuries. Female otters with pups practice vigilance when they reduce their foraging time and move along meandering paths. Sea otters usually rest at sea, and when they rest on shore, they usually haul out on offshore rocks, reefs, and small islands—possibly a behavioral response to terrestrial predators (brown bears and wolves can kill non-vigilant sea otters on shore). In areas where many sea otters haul out together, group vigilance may be important in detecting an approaching threat. Along the coast of central California, white sharks are a significant source of sea otter mortality, and the only antipredator strategy is avoidance or crypsis by resting in kelp beds. Despite the threat, sea otters still forage in open water, so the perception of risk may be low. In the western Aleutian Islands, killer whale predation is believed to be the cause of a > 90% decline in sea otters. As a result, sea otters perceive killer whales as a threat and limit their movements to shallow, complex habitats where the risk of attack is low. This behavioral response is so strong in the western Aleutian Islands that it may it limit sea otter dispersal among islands, with implications for the connectivity and genetic health of the small, isolated populations that remain.

Book chapter↗
USGS2022

A review of the exploration, discovery, and characterization of highly concentrated gas hydrate accumulations in coarse-grained reservoir systems along the Eastern Continental Margin of India

The analysis of 3-D seismic data has become one of the most powerful ways to identify sand-rich gas hydrate reservoir systems and to directly identify highly concentrated gas hydrate prospects. Scientific drilling programs have shown that the occurrence of highly concentrated gas hydrate accumulations in coarse-grained, sand-rich, reservoir systems has a significant impact on the physical properties of sediments, allowing gas hydrates to be “directly detected” by conventional seismic analysis techniques. One of the most diagnostic responses of a gas hydrate-bearing sand reservoir is that of a high-velocity sedimentary section and an associated high-amplitude seismic response with a reflection polarity matching that of the seafloor. Knowledge of this physical relationship guided the Indian National Gas Hydrate Program Expedition 02 (NGHP-02) in their pre-drill site review and selection effort along the eastern continental margin of India in 2016. Within the planning, operational and post-operational data analysis phases of the NGHP-02 Expedition, scientists relied heavily on the analyses of the (1) pre-expedition acquired 3-D seismic data from offshore India, (2) downhole logging data acquired during NGHP-02 and (3) core samples and data obtained from NGHP-02 conventional- and pressure-cores to identify gas hydrates and assess the geologic controls on the formation and stability of these accumulations. Data analysis has confirmed the presence of extensive sand-rich depositional systems throughout the deepwater portions of the Krishna-Godavari and Mahanadi Basins in the Bay of Bengal. Two areas of the Krishna-Godavari Basin contain substantial gas hydrate accumulations in sand-rich systems, representing candidate sites for future potential energy exploitation.

Bay of Bengal, Krishna-Godavari Basin, Mahanadi Ba↗
USGS2022

Northern Cascadia Margin gas hydrates — Regional geophysical surveying, IODP drilling leg 311, and cabled observatory monitoring

This article reviews extensive geophysical survey data, ocean drilling results and long-term seafloor monitoring that constrain the distribution and concentration of gas hydrates within the accretionary prism of the northern Cascadia subduction margin, located offshore Vancouver Island in Canada. Seismic surveys and geologic studies conducted since the 1980s have mapped the bottom simulating reflector (BSR), detected gas hydrate occurrence and estimated gas hydrate and free gas concentrations. Additional constraints were obtained from seafloor-towed, controlled-source electromagnetic surveying. A component of these studies has been the examination of low-temperature seafloor vents and seeps that emit gas and fluids into the ocean. These features are identified seismically as chimney-like zones of reduced acoustic reflectivity within the sediment stratigraphy, functioning as conduits for gas and fluid migration from below the BSR to the seafloor. Gas hydrates have been recovered from the seafloor and from sediment cores at vent sites, mostly in massive (nodular) form and as a vein-like fracture filling. The Ocean Networks Canada cabled NEPTUNE observatory has gathered extensive continuous, long-term observations on gas hydrate dynamics at the seafloor and in boreholes at two nodes on the continental slope featuring high gas hydrate concentrations. Measurements taken at the observatory include a time-series of gas bubble emission rates, changes in the near-seafloor electromagnetic structure and seafloor compliance linked to gas hydrate formation and dissociation. Two Integrated Ocean Drilling Program (IODP) expeditions collected cores, measured downhole properties and deployed downhole instruments within the central accretionary prism. At IODP Site U1364, pore pressures are being monitored above and below the base of the gas hydrate stability zone at a slope setting using an “Advanced Circulation Obviation Retrofit Kit” (A-CORK). Downhole pore pressures, temperatures and electrical resistivities also are being monitored at IODP Site U1416 using the “Simple Cabled Instrument for Measuring Parameters In Situ” (SCIMPI) tool at a vent site from near-seafloor to just above the base of the gas hydrate stability zone.

British Columbia↗
USGS2026

Beach nourishment morphodynamics in a high-energy U.S. West Coast environment

Dredged sediment from engineered inlets can be used to nourish coastlines adjacent to these inlets, serving as a beneficial alternative to offshore disposal. Effective strategies for beneficial use of dredged sediment, however, rely on understanding of local sediment transport. A beach nourishment project utilizing dredged sand was carried out at a highly energetic beach north of the Columbia River mouth (Washington, USA). Within two weeks of placement, during a moderately energetic period, a large part of the beach nourishment had eroded. To predict local hydro- and morphodynamics there, a XBeach model was used, validated with field observations of nearshore hydrodynamics and morphology. It showed that while the subaerial nourishment eroded rapidly, it is likely that the sediment is deposited around the inner bar and is still available to the morphological system of Benson Beach. Additionally, model simulations suggest the nourishment provided a buffer against erosion of the local dune system during its presence.

Washington↗