Geology topics

Research about California

Source-linked reports with geographic coverage including California.

At least 577 records · Page 32Linked to original sources

USGS2023

Bivalve effects on the food web supporting delta smelt—A spatially intensive study of bivalve recruitment, biomass, and grazing rate patterns with varying freshwater outflow in 2019

Phytoplankton are an important and limiting food source in the Sacramento-San Joaquin Delta and San Francisco Bay. The decline of phytoplankton biomass is one potential factor in the decline of the protected Hypomesus transpacificus (delta smelt) and other pelagic organisms. The bivalves Corbicula fluminea and Potamocorbula amurensis (hereafter C. fluminea and P. amurensis , respectively) have been shown to control phytoplankton biomass in several locations throughout the San Francisco Bay and the Sacramento-San Joaquin Delta; therefore, knowledge of their distribution and population dynamics are of great interest. Here, we describe the distribution and dynamics of bivalve biomass using samples collected by the California Department of Water Resources (DWR) as part of the benthic monitoring program in 2019. One element of DWR’s and the Bureau of Reclamation’s Environmental Monitoring Program—the Generalized Random Tessellation Stratified (GRTS) program—examines the spatial and temporal extent of C. fluminea and P. amurensis control on phytoplankton. Historically, the GRTS program sampled 175 benthic stations (50 stations that are monitored every year and 125 randomly selected new stations that are changed yearly) throughout the Sacramento-San Joaquin Delta and northern San Francisco Bay (San Pablo and Suisun Bays) during one week in May and October. In 2019, only the 50 annually replicated stations were sampled. Corbicula fluminea and P. amurensis biomass and grazing rates had similar trends; therefore, the conclusions regarding biomass are applied to grazing rate data as well. Corbicula fluminea biomass decreased from May to October, whereas P. amurensis average biomass (reported increased from May (1 g ash-free-dry-tissue mass/square meter (g AFDM/m 2 ) to October (2 g AFDM/m 2 ). Although C. fluminea ’s average biomass was lower in October (10 gAFDM/m 2 ) than in May (20 gAFDM/m 2 ), the highest single biomass value was also observed in October (300 gAFDM/m 2 ). In both May and October, most stations that recorded high C. fluminea biomass values were located in the deep water (≥3 m of depth between the surface of the water and the surface of the substrate on the bottom) and were sampled in either rivers or sloughs. A relation between depth and biomass was not observed for P. amurensis . Both C. fluminea and P. amurensis recruitment (recruits are considered animals ≤2.5mm in length in this study and recruitment is the process of recruits successfully settled to the bottom) increased from May to October. The total number of C. fluminea recruits more than doubled from May to October, whereas P. amurensis total recruitment increased by 8-fold during the same period. Most P. amurensis recruits in May can be attributed to one station, whereas the recruits in October were found at 14 stations. A relation between number of recruits and station depth was not evident for either C. fluminea or P. amurensis .

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USGS2023

Drought survival strategies differ between coastal and montane conifers in northern California

Increasingly severe and prolonged droughts are contributing to tree stress and forest mortality across western North America. However, in many cases, we currently have poor information concerning how drought responses in forests vary in relation to competition, climate, and site and tree characteristics. We used annual tree ring evidence of 13 C discrimination (Δ 13 C) and growth metrics to assess drought resistance and resilience for six conifer species at the intersection of several bioregions in northern California. Within each species' range in northern California, we collected competition and tree characteristics from 270 focal trees across sites that varied from wetter to drier habitat conditions (54 sites). Across sites, all six conifer species weathered the severe 2013–2015 drought with reasonably high resistance and post-drought resilience. However, we found important differences in drought responses between coastal and montane species based on annual growth and Δ 13 C metrics. Broadly, the two coastal species showed consistent declines in drought resistance across successive drought years, whereas the four montane species maintained high drought resistance across drought years. More specifically, we found lower Δ 13 C and growth during drought years in coastal species, suggesting stomatal closure during drought with the potential for vulnerability to carbon depletion during long-term drought. Conversely, Δ 13 C and growth were stable in montane species throughout the drought, which may contribute to hydraulic failure under increased drought frequency and/or severity. We also evaluated environmental factors that affect Δ 13 C using data from before and during the drought. These physiological models were consistent for the two coastal species, with a positive relationship between annual precipitation and Δ 13 C and a negative relationship between tree density and Δ 13 C. Conversely, the four montane models illustrated a greater importance of site conditions on drought responses for these species. Our findings show differential risk for drought stress across diverse conifers during severe drought. This work highlights the importance of site and tree characteristics in determining drought responses across cool, annually humid coastal habitats to seasonally dry montane habitats.

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USGS2023

Dense geophysical observations reveal a triggered, concurrent multi-fault rupture at the Mendocino Triple Junction

A central question of earthquake science is how far ruptures can jump from one fault to another, because cascading ruptures can increase the shaking of a seismic event. Earthquake science relies on earthquake catalogs and therefore how complex ruptures get documented and cataloged has important implications. Recent investments in geophysical instrumentation allow us to resolve increasingly complex, multi-fault ruptures for even moderate-sized earthquakes. We combine dense seismic and geodetic measurements to reveal an enigmatic rupture in late 2021 at the Mendocino Triple Junction in northern California. We show that rupture was dynamically triggered, yet concurrent, on two distinct faults roughly 30 km apart. Thus, this rupture combines features of complex ruptures usually considered to be single earthquakes, and triggered ruptures considered as multiple earthquakes. This event illustrates that moderate-sized earthquakes can exhibit similar complexity to that more commonly documented for large earthquakes.

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USGS2023

What controls suspended-sediment concentration and export in flooded agricultural tracts in the Sacramento-San Joaquin Delta?

We investigated wind-wave and suspended-sediment dynamics in Little Holland Tract and Liberty Island, two subsided former agricultural tracts in the Cache Slough complex in the northern Sacramento-San Joaquin Delta which were restored to tidal shallows to improve habitat. Turbidity, and thus suspended-sediment concentration (SSC), is important to habitat quality because some species of native fishes, including the Delta Smelt, are found preferentially in more turbid waters. Data from October 2015 to August 2016 show that average SSC was greater within Little Holland Tract than in the primary breach that connects the basin to surrounding channels: approximately twice as great at a shallower station farther from the breach and 15% greater at a deeper station closer to the breach. Suspended-sediment concentration within Little Holland Tract was directly related to wave shear stress and inversely related to water depth, based on linear regression. We used measurements of suspended-sediment flux (SSF) through the largest levee breaches to assess whether the enhanced SSC within Little Holland Tract is exported to surrounding waters, thus potentially increasing turbidity over a wider region. Cumulatively, sediment is exported through the Little Holland Tract breaches in winter and imported in summer, consistent with regional patterns in sediment flux, indicating that wind-wave re-suspension within the basin does not control sediment flux from Little Holland Tract on seasonal time-scales. Some sediment was exported during wind-wave events, and results show that sediment export is greater when primary breaches are located downwind of the basin rather than upwind.

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USGS2023

Observations and morphodynamic modeling of decadal-scale morphologic change in estuaries under sea level rise

Sea level rise is expected to affect coastal areas all around the world, including the estuarine environment. New bathymetry collected in 2014 provided a unique opportunity to test the modeling of Elmilady et al. (2019), who presented a morphodynamic DELFT3D model of San Pablo Bay, California, that included detailed tidal water movement, wind-wave action, sediment transport, and resulting bed level updates. Their hindcasts (1856–1983) showed significant skill in reproducing observed patterns and volumes of deposition and erosion in San Pablo Bay. Their forecasts (1983–2100) showed that sea level rise results in increased deposition, loss of intertidal flats because of drowning, and a greater channel volume. The model, in general, forecasted observed trends in change from 1983 to 2014. Morphodynamic modeling is a promising approach for identifying the effect of sea level rise on estuarine environments.

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USGS2023

Successful hindcast of 7 years of mud morphodynamics influenced by salt pond restoration in south San Francisco Bay

Alviso Slough in South San Francisco Bay has been experiencing restoration of adjacent former salt-production ponds into muted tidal ponds, tidal ponds, and salt marsh. As a result, tidal prism through Alviso Slough has increased and mercury-contaminated sediment has been remobilized. We developed a 2D, high-resolution, process-based model (Delft3D FM-wave) to hindcast observed morpho-dynamic developments and to investigate associated sediment flux in the slough and pond system. Our results contrastingly demonstrate that a successful hindcast of the observed morphodynamic trend is made while reproducing observed intratidal suspended sediment concentrations in Alviso Slough remains a challenge. Our explanation is that the model is able to capture spatial gradients in the tide-residual sediment transports as the result of the large-scale management actions in the system, i.e., the opening of the salt ponds. These tide-residual processes are generally difficult to measure over an entire domain, but are very relevant to model the morphodynamic development. Our model provides a promising tool to trace eroding contaminated sediments to the benefit of restoration project managers and to support planning and design phases of adaptive management measures.

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USGS2023

2019 M7.1 Ridgecrest earthquake slip distribution controlled by fault geometry inherited from Independence dike swarm

Faults often form through reactivation of pre-existing structures, developing geometries and mechanical properties specific to the system’s geologic inheritance. Competition between fault geometry and other factors (e.g., lithology) to control slip at Earth’s surface is an open question that is central to our knowledge of fault processes and seismic hazards. Here we use remote sensing data and field observations to investigate the origin of the 2019 M 7.1 Ridgecrest, California, earthquake rupture geometry and test its impact on the slip distribution observed at Earth’s surface. Common geometries suggest the fault system evolved through reactivation of structures within the surrounding Independence dike swarm (IDS). Mechanical models testing a range of fault geometries and stress fields indicate that the inherited rupture geometry strongly controlled the M 7.1 earthquake slip distribution. These results motivate revisiting the development of other large-magnitude earthquake ruptures (1992 M 7.3 Landers, 1999 M 7.1 Hector Mine) and tectonic provinces within the IDS.

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USGS2023

Fault roughness at seismogenic depths and links to earthquake behavior

Fault geometry affects the initiation, propagation, and cessation of earthquake rupture, as well as, potentially, the statistical behavior of earthquake sequences. We analyze 18,250 (−0.27 < M < 4.4) earthquakes of the 2016–2019 Cahuilla, California, swarm and, for the first time, use these high‐resolution earthquake locations to map, in detail, the roughness across an active fault surface at depth. We find that the strike‐slip fault is 50% rougher in the slip‐perpendicular direction than parallel to slip. 3D mapping of fault roughness at seismogenic depths suggests that roughness varies by a factor of 8 for length scales of 1 km. We observe that the largest earthquake ( M 4.4) occurred where there is significant fault complexity and the highest measured roughness. We also find that b ‐values are weakly positively correlated with fault roughness. Following the largest earthquake, we observe a distinct population of earthquakes with comparatively low b ‐values occurring in an area of high roughness within the rupture area of the M 4.4 earthquake. Finally, we measure roughness at multiple scales and find that the fault is self‐affine with a Hurst exponent of 0.52, consistent with a Brownian surface.

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USGS2023

Hydrodynamics structure plankton communities and interactions in a freshwater tidal estuary

Drivers of phytoplankton and zooplankton dynamics vary spatially and temporally in estuaries due to variation in hydrodynamic exchange and residence time, complicating efforts to understand controls on food web productivity. We conducted approximately monthly (2012–2019; n = 74) longitudinal sampling at 10 fixed stations along a freshwater tidal terminal channel in the San Francisco Estuary, California, characterized by seaward to landward gradients in water residence time, turbidity, nutrient concentrations, and plankton community composition. We used multivariate autoregressive state space (MARSS) models to quantify environmental (abiotic) and biotic controls on phytoplankton and mesozooplankton biomass. The importance of specific abiotic drivers (e.g., water temperature, turbidity, nutrients) and trophic interactions differed significantly among hydrodynamic exchange zones with different mean residence times. Abiotic drivers explained more variation in phytoplankton and zooplankton dynamics than a model including only trophic interactions, but individual phytoplankton–zooplankton interactions explained more variation than individual abiotic drivers. Interactions between zooplankton and phytoplankton were strongest in landward reaches with the longest residence times and the highest zooplankton biomass. Interactions between cryptophytes and both copepods and cladocerans were stronger than interactions between bacillariophytes (diatoms) and zooplankton taxa, despite contributing less biovolume in all but the most landward reaches. Our results demonstrate that trophic interactions and their relative strengths vary in a hydrodynamic context, contributing to food web heterogeneity within estuaries at spatial scales smaller than the freshwater to marine transition.

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USGS2023

Field assessment of Naled and its primary degradation product (dichlorvos) in aquatic ecosystems following aerial ultra-low volume application for mosquito control

Naled, an organophosphate insecticide, is applied aerially at ultra-low volumes over aquatic ecosystems near Sacramento, California, USA, during summer months for mosquito control. Two ecosystem types (rice fields and a flowing canal) were sampled in 2020 and 2021. Naled and its primary degradation product (dichlorvos) were measured in water, biofilm, grazer macroinvertebrates, and omnivore/predator macroinvertebrates (predominantly crayfish). Maximum naled and dichlorvos concentrations detected in water samples one day after naled application were 287.3 and 5647.5 ng/L, respectively, which were above the U.S. Environmental Protection Agency’s aquatic life benchmarks for invertebrates. Neither compound was detected in water more than one day after the application. Dichlorvos, but not naled, was detected in composite crayfish samples up to 10 days after the last aerial application. Detections in water from the canal showed that the compounds were transported downstream of the target application area. Factors such as vector control flight paths, dilution, and transport through air and water likely affected concentrations of naled and dichlorvos in water and organisms from these aquatic ecosystems.

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USGS2023

Increased salinity decreases annual gross primary productivity at a Northern California brackish tidal marsh

Tidal marshes sequester 11.4–87.0 Tg C yr −1 globally, but climate change impacts can threaten the carbon capture potential of these ecosystems. Tidal marshes occur across a wide range of salinity, with brackish marshes (0.5–18 ppt (parts per thousand)) dominating global tidal marsh extents. A diverse mix of freshwater- and saltwater-tolerant plant and microbial communities has led researchers to predict that carbon cycling in brackish wetlands may be less sensitive to changes in salinity than fresh- or saltwater wetlands. Rush Ranch, a well-monitored brackish tidal wetland of the San Francisco Bay National Estuarine Research Reserve, experiences highly variable annual salinity regimes. Within a five-year period (2014–2018), Rush Ranch experienced particularly extreme drought-induced salinization during the 2014 and 2015 growing seasons. During drought years, tidal channel salinity rose from a 15 year baseline of 4.7 ppt to growing season peaks of 10.3 ppt and 12.5 ppt. Continuous eddy covariance data from 2014 to 2018 demonstrate that during drought summers, gross primary productivity (GPP) decreased by 24%, whereas ecosystem respiration remained similar among all five years. Stepwise linear regression revealed that salinity, not air temperature or tidal height, was the dominant driver of annual GPP. A random forest model trained to predict GPP based on environmental data from low salinity years (i.e. naive to salinization) significantly over predicted GPP in drought years. When growing season salinities were doubled, annual estimates of net ecosystem exchange of CO 2 decreased by up to 30%. These results provide ecosystem-scale evidence that increased salinity influences CO 2 fluxes dominantly through reductions in GPP. This relationship provides a starting point for incorporating the effect of changes in salinity in wetland carbon models, which could improve wetland carbon forecasting and management for climate resilience.

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USGS2023

Food caching by a solitary large carnivore reveals importance of intermediate-sized prey

Pumas ( Puma concolor ) are solitary large carnivores that exhibit high energetic investments while hunting prey that often take multiple days to consume. Therefore, pumas should behave in a way to maximize their energetic gains, including using caching, which is a behavior used by many mammal species to preserve and store food or to conceal it from conspecifics and scavengers to limit their losses. Yet pumas do not always cache their kills. In order to understand caching behavior, we used variables associated with the kills such as prey mass, search time, climate, and habitat to test 20 ecological models (representing four a priori hypotheses: food perishability, resource pulse, consumption time, and kleptoparasitism deterrence) in an information-theoretic approach of model selection to explore factors related to the caching behavior. Models were run with information from tracked radio-collared pumas in California over a 2.5-year period and identified a total of 352 kills. Overall, we documented pumas caching 61.5% of their kills, including 71.6% of Black-tailed Deer ( Odocoileus hemionus columbianus ), their primary prey in the study area. The model with a quadratic effect of adjusted mass of prey on puma caching probability had all of the empirical support ( w = 1.00). Specifically, pumas were most likely to cache intermediate-sized prey, such as yearling and adult female deer, and also fed from cached kills for longer periods of time. Larger prey may be too large to easily cache, making it less energetically efficient—while small prey can often be consumed quickly enough to not require caching. This suggests that intermediate-sized prey may be the optimal size for caching, allowing a puma to feed for multiple days while not greatly increasing energetic output. The hypotheses we tested were not mutually exclusive and pumas caching their prey may occur for several reasons; nevertheless, our study demonstrated that pumas use caching to extend their foraging time and maximize energetic gains when preying on intermediate-sized prey.

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USGS2023

Comparison of nonergodic ground-motion components from CyberShake and NGA-West2 datasets in California

In this study, we compare the Southern California Earthquake Center CyberShake platform against the Next Generation Attenuation‐West2 empirical datasets. Because the CyberShake and empirical datasets cover very different magnitude ranges and site conditions, we develop ground‐motion models (GMMs) for CyberShake datasets to compare trends with empirical GMMs and decompose the residuals for further analysis. We apply mixed effects regression to four CyberShake datasets in southern, central, and northern California at 2, 3, 5, and 10 s periods, and compare the results with the empirical datasets using the same approach. CyberShake captures the total variability of ground motions in the empirical datasets but tends to predict larger median ground motions relative to the empirical GMMs. We then calculate and compare the repeatable source‐specific location, site, and path effects between CyberShake and empirical datasets. We find that the correlations of site effects between the CyberShake and empirical datasets are generally satisfactory, but the variability of site effects is slightly smaller for CyberShake datasets. There is no apparent correlation of source‐specific location effects between the CyberShake and empirical datasets. Comparison of path effects shows a wide range of correlation coefficients. Finally, we investigate the source of observed differences between the CyberShake and empirical datasets. We attribute the larger median ground‐motion levels in CyberShake to a combination of the homogeneous slip patterns of the earthquake ruptures, the low resolution of near‐surface materials in the velocity models, and strong reflections at high‐contrast boundaries in the velocity models. These factors also impact the correlations of site and path effects between the CyberShake and empirical datasets. Moreover, the leakage from location effects into site and path terms further weakens the correlations. In summary, we find that CyberShake could be improved, but it is still very useful to supplement empirical datasets for ground‐motion studies, especially to inform their nonergodic components.

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USGS2023

South San Francisco Bay Salt Pond Restoration Project—A synthesis of Phase-1 mercury studies

The South Bay Salt Pond Restoration Project (SBSPRP) encompasses over 6,000 hectares of former salt production ponds along the south edge of the San Francisco Bay and represents the largest wetland restoration effort on the west coast of North America. A series of studies associated with Phase 1 (2010–2018) restoration activities that are focused on a historically mercury contaminated slough and series of ponds within the restoration area have recently been completed. This report brings together the key findings of these loosely coordinated studies and integrates the results into a more comprehensive and holistic product that informs future restoration activities associated with the SBSPRP and elsewhere. This report documents key findings associated with the breach of pond A6: (1) a short-term spike in slough fish (Mississippi silverside) total mercury concentration in lower Alviso Slough; (2) a short-term spike in surface-water particulate total mercury in lower Alviso Slough; (3) significant sediment scour in Alviso Slough adjacent to and downstream of the breach points; (4) a decrease in surface-sediment methylmercury (as a percentage of total mercury) in lower Alviso Slough; (5) the transport of 70 kilograms per year of sediment-associated total mercury into pond A6 during the first 2 years following the breach but with much of this coming from outside of Alviso Slough, presumably from the nearby shallows, Guadalupe Slough, and the larger southern San Francisco Bay area; and (6) a slowing of bed sediment erosion in lower Alviso Slough 3–5 years after the breaching of pond A6. Although this report is not intended to be prescriptive in terms of the next steps the SBSPRP should or should not take, the totality of the findings presented provide critical process-level information regarding the extent and the duration of spikes in mercury levels in water, sediment, fish, and birds, which appeared to result from the two management actions under study. Thus, these results can be used to anticipate similar ecosystem responses associated with similar management actions that may be considered in the future. We also conclude this report by highlighting unanswered questions associated with mercury dynamics as it relates to the restoration project, and possible future directions for research.

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USGS2023

Spatial and temporal analysis of geologic slip rates, Cucamonga Fault, California, USA: Implications for along-strike applications and multi-fault rupture

To constrain fault processes and hazard, fault slip rates may be extrapolated over different fault lengths or time intervals. Here, we investigate slip rates for the Cucamonga Fault (CF). The CF is located at the junction of the Transverse Range fault system with the San Andreas and San Jacinto Faults, and it is hypothesized to connect with these faults, promoting the propagation of large, multi-fault earthquakes. Previous work has shown that CF displacements on late Quaternary alluvial fan surfaces are highly variable along strike. We present two new 10 Be surface exposure ages from depth profiles on the alluvial fans. Slip rates are consistent with a rate of 1.4 ± 0.3 m/kyr over time intervals of ∼20, ∼30, and ∼40 kyr. If the CF participates in multi-fault ruptures, then these earthquakes occur either rarely or with sufficient regularity to maintain apparently steady rates over multiple intervals. We also explore along-strike fault displacement variability using a calibrated morphological model. The model successfully reproduces scarp profiles and indicates that fault displacement variability can be explained in part by scarp age but not uplift rate. We infer that both erosion by ephemeral gullying and distributed deformation contribute to fault displacement variability, although both are difficult to detect confidently without excavations across the scarp. These investigations show that better characterization of cumulative-slip variability along strike may improve accuracy and precision of slip rates. Slip rates that do not consider epistemic uncertainties may not be suitable for extrapolation over longer fault sections.

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USGS2023

Six years of fluvial response to a large dam removal on the Carmel River, California, USA

Measuring river response to dam removal affords a rare, important opportunity to study fluvial response to sediment pulses on a large field scale. We present a before–after/control–impact study of the Carmel River, California, measuring fluvial geomorphic and grain-size evolution over 8 years, six of which postdated removal of a 32 m-high dam (one of the largest dams removed worldwide) and included 11 flow events exceeding the 2-year flood magnitude. We find that the reservoir-sediment pulse following dam removal was relatively small (97 000 ± 24 000 t over 4 years), owing to deliberate reservoir-sediment stabilization. Scaled to the size of the Carmel River watershed and compared against long-term bedrock denudation rates, the post-dam-removal sediment release was slightly less than the annualized long-term sediment export from this basin. New sediment transited >30 km to the river mouth in less than 2 years, assisted by floods 2 and 4 years after dam removal. The sediment pulse fined the downstream riverbed while causing mostly low-magnitude bed-elevation changes: commonly 0.5 to 1 m or smaller, occurring as discontinuous sediment patches or interstitial deposits, aside from the filling and subsequent partial scour of deep pools. There was no major geomorphic reset downstream from the dam site. Geomorphic changes were driven almost entirely by flow rather than by the modest increase in sediment supply, in contrast to recent examples from other large dam removals. The relatively minor disturbance caused by dam removal on the Carmel River is likely analogous to many future dam removals: a relatively small sediment pulse after deliberate limitation of reservoir-sediment erosion, and with an upstream dam remaining in place. Thus, a large dam removal need not lead to major downstream impacts.

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USGS2023

Survival and establishment of captive-reared and translocated giant gartersnakes after release

Many imperiled species face increasing extinction risk that requires interventional management like translocation or captive rearing. The use of translocations to successfully restore or create populations requires that animals survive at recipient sites, information that is often lacking for imperiled species and that can be risky to acquire if not obtained before a species has dwindled in number. The giant gartersnake ( Thamnophis gigas ), a semiaquatic snake endemic to the Central Valley in California, USA, has declined after losing >90% of its historical habitat and may benefit from successful translocations to protected habitat. We released adult and captive-reared juvenile snakes from 2 donor sites into a recently restored wetland in 2019 and 2020 and compared their survival, movement, and activity using radio-telemetry through 2021. We monitored juvenile survival for 2 years in captivity after birth and then estimated post-release survival at the recipient site using radio-telemetry. Just 8% of translocated adult snakes survived >801 days (95% CI = 1–64%) compared with 39% of resident snakes at the donor sites surviving >1,154 days (95% CI = 23–68%). This equated to annualized survival rates of translocated adults ( x̄ = 0.32, 95% CI = 0.12–0.82) that were roughly half that of resident snakes ( x̄ = 0.74, 95% CI = 0.63–0.89). Translocation was negatively correlated with survival, but movement and activity received little support in models. Seventy-six percent of juvenile snakes survived captivity and, once released, juvenile survival was 60% (95% CI = 38–94%) for the 4-month monitoring period before winter. It is unclear why survival of translocated adult snakes was lower than that of resident snakes, but there was little evidence for differences in behavior (e.g., increased surface activity, average distance moved, emigration from the translocation site) that are commonly cited causes of mortality in other translocation studies. Our results suggest that, in the absence of a clear understanding as to what contributes to adult survival after release to a new site, future work using captive-rearing and juvenile translocation may be more promising for establishing and recovering populations than just translocating adults given the high survival of juveniles.

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USGS2023

Sediment gravity flow frequency offshore central California diminished significantly following the Last Glacial Maximum

A high-resolution multibeam survey from a portion of the San Simeon Channel (offshore Morro Bay, California) captured a zone of recurring troughs and ridges adjacent to prominent submarine meander bends. Through an integrated study using surveying data, sediment core analysis, radiocarbon dating, and stable isotope measurements, we hypothesize that turbidity current event frequency was higher during the late Pleistocene than at present conditions. We speculate that the rise in sea-level following the Last Glacial Maximum sequestered sedimentation largely to the shelf during the Holocene. This work suggests that the occurrence of sediment gravity flows in this region, particularly away from any submarine channels, is appreciably lower than at times of continental shelf subaerial exposure.

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