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At least 1,459 records · Page 81Linked to original sources
USGS1981

Significant results from using earth observation satellites for mineral and energy resource exploration

A large number of Earth-observation satellites orbit our world several times each day, providing new information about the land and sea surfaces and the overlying thin layer of atmosphere that makes our planet unique. Meteorological satellites have had the longest history of experimental use and most are now considered operational. The geologic information collected by the Landsat, Polar Orbiting Geophysical Observatory (POGO), Magsat, Heat Capacity Mapping Mission (HCMM) and Seasat land and ocean observation systems is being thoroughly tested, and some of these systems are now approaching operational use. Landsat multispectral images provide views of large areas of the Earth under uniform lighting conditions and can be obtained at a variety of scales and formats. Not only do the Landsat data provide highly useful images showing surficial materials and structures such as folds and faults, but also measurements and computer-derived ratios of the brightness of different rock types, alteration zones, and mineral associations. These data have led to the finding of a variety of new ore deposits. In addition, the combination of Landsat digital data and aeromagnetic data has extended the use of Landsat as an exploration tool which can be used to readily relate surface features to subsurface anomalies. Magsat data, now being collected, are helping refine information on major crustal anomalies that were first recognized during the analysis of POGO data. The more nearly circular orbit, lower altitude, and increased sophistication of its vector magnetometer enable Magsat to provide more precise information than POGO. Information of this type is required to develop crustal models. Although Magsat is designed to operate for only 4–8 months, the number of orbits that it should be able to make will be sufficient to accomplish its mission and to record a major magnetic storm expected in 1980. HCMM is a two-band visible to near-IR (0.55–1.1 μm) and thermal infrared (10.2–12.5 μm) system designed to measure reflected solar energy, determine the heat capacity of rocks and to monitor soil moisture, thermal effluents, plant canopy temperatures and snow cover. Launched in April 1978, it is in sun-synchronous, circular orbit at an altitude of 620 km. It is a relatively low-resolution system with an instantaneous field of view (IFOV) of 500–600 m and a swath width of 716 km. However, the system is designed to detect objects in the range of 260°–340° K with a sensitivity (NEδT) of 0.4°K at 280°. Recording the thermal radiation of urban heat islands and high thermal inertia of quartzite strata in the Appalachian region are two examples of its land applications. Launched in June 1978, Seasat operated for only 100 days, but successfully acquired much information over both sea and land. The collection of synthetic aperture radar (SAR) imagery and radar altimetry was particularly important to geologists. Although there are difficulties in processing and distributing these data in a timely manner, initial evaluations indicate that the radar imagery supplements Landsat data by increasing the spectral range and offering a different look angle. The radar altimeter provides accurate profiles over narrow strips of land (1 km wide) and has demonstrated usefulness in measuring icecap surfaces (Greenland, Iceland, and Antarctica). The Salar of Uyuni in southern Bolivia served as a calibration site for the altimeter and has enabled investigators to develop a land-based smoothing algorithm that is believed to increase the accuracy of the system to 10 cm. Data from the altimeter are currently being used to measure subsidence resulting from ground water withdrawal in the Phoenix-Tucson area.

Advances in Space Research↗
USGS2020

The water-year water balance of the Colorado River Basin

Model‐estimated monthly water balance components (i.e., potential evapotranspiration, actual evapotranspiration, and runoff ( R )) for 146 United States (U.S.) Geological Survey 8‐digit hydrologic units located in the Colorado River Basin (CRB) are used to examine the temporal and spatial variability of the CRB water balance for water years 1901 through 2014 (a water year is the period from October 1 of one year through September 30 of the following year). Results indicate that the CRB can be divided into six subregions with similar temporal variability in monthly R . The water balance analyses indicated that approximately 75% of total water‐year R is generated by just one CRB subregion and that most of the R in the basin is derived from surplus ( S ) water generated during the months of October through April. Furthermore, the analyses show that temporal variability in S is largely controlled by the occurrence of negative atmospheric pressure anomalies over the northwestern conterminous U.S. (CONUS) and positive atmospheric pressure anomalies over the southeastern CONUS. This combination of atmospheric pressure anomalies results in an anomalous flow of moist air from the North Pacific Ocean into the CRB, particularly the Upper CRB. Additionally, the occurrence of extreme dry and wet periods in the CRB appears to be related to variability of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2017

Monitoring storm tide and flooding from Hurricane Matthew along the Atlantic coast of the United States, October 2016

Introduction Hurricane Matthew moved adjacent to the coasts of Florida, Georgia, South Carolina, and North Carolina. The hurricane made landfall once near McClellanville, South Carolina, on October 8, 2016, as a Category 1 hurricane on the Saffir-Simpson Hurricane Wind Scale. The U.S. Geological Survey (USGS) deployed a temporary monitoring network of storm-tide sensors at 284 sites along the Atlantic coast from Florida to North Carolina to record the timing, areal extent, and magnitude of hurricane storm tide and coastal flooding generated by Hurricane Matthew. Storm tide, as defined by the National Oceanic and Atmospheric Administration, is the water-level rise generated by a combination of storm surge and astronomical tide during a coastal storm. The deployment for Hurricane Matthew was the largest deployment of storm-tide sensors in USGS history and was completed as part of a coordinated Federal emergency response as outlined by the Stafford Act (Public Law 92–288, 42 U.S.C. 5121–5207) under a directed mission assignment by the Federal Emergency Management Agency. In total, 543 high-water marks (HWMs) also were collected after Hurricane Matthew, and this was the second largest HWM recovery effort in USGS history after Hurricane Sandy in 2012. During the hurricane, real-time water-level data collected at temporary rapid deployment gages (RDGs) and long-term USGS streamgage stations were relayed immediately for display on the USGS Flood Event Viewer ( https://stn.wim.usgs.gov/FEV/#MatthewOctober2016 ). These data provided emergency managers and responders with critical information for tracking flood-effected areas and directing assistance to effected communities. Data collected from this hurricane can be used to calibrate and evaluate the performance of storm-tide models for maximum and incremental water level and flood extent, and the site-specific effects of storm tide on natural and anthropogenic features of the environment.

Florida, Georgia, North Carolina, South Carolina↗
USGS2018

Analysis of multi-decadal wetland changes, and cumulative impact of multiple storms 1984 to 2017

Land-cover classification analysis using Landsat satellite imagery acquired between 1984 and 2017 quantified short- (post-Hurricane Sandy) and long-term wetland-change trends along the Maryland and Virginia coasts between Metompkin Bay, VA and Ocean City, MD. Although there are limited options for upland migration of wetlands in the study area, regression analysis showed that wetland area increased slightly between 1984 and 2011, indicating that marsh aggradation rates were sufficient to maintain wetland elevation relative to mean sea level. Following Hurricane Irene (August 2011), the Halloween Nor’Easter (October 2011), and Hurricane Sandy (October 2012), wetland area decreased by more than 7 km 2 compared with average pre-storm extents. We assume that Hurricane Sandy had the greatest impact due to the size and intensity of the storm. However, the cumulative effects of multiple storms within a short time period likely contributed to the greater observed losses in coastal wetlands relative to earlier periods. Five years after Hurricane Sandy, wetland area had not significantly recovered, but more time may be necessary to assess if the observed wetland losses will persist or if new growth within flooded marsh areas will be sufficient for the wetlands to recover to pre-storm extents. Comparisons of long-term and storm-driven wetland changes can lead to improved accuracy of habitat vulnerability models and greater understanding of potential impacts of future storms and SLR to coastal wetlands.

Wetlands Ecology and Management↗
USGS2015

Accuracy assessment of NOAA gridded daily reference evapotranspiration for the Texas High Plains

The National Oceanic and Atmospheric Administration (NOAA) provides daily reference evapotranspiration (ET ref ) maps for the contiguous United States using climatic data from North American Land Data Assimilation System (NLDAS). This data provides large-scale spatial representation of ET ref , which is essential for regional scale water resources management. Data used in the development of NOAA daily ET ref maps are derived from observations over surfaces that are different from short (grass — ET os ) or tall (alfalfa — ET rs ) reference crops, often in nonagricultural settings, which carries an unknown discrepancy between assumed and actual conditions. In this study, NOAA daily ET os and ET rs maps were evaluated for accuracy, using observed data from the Texas High Plains Evapotranspiration (TXHPET) network. Daily ET os , ET rs and the climatic data (air temperature, wind speed, and solar radiation) used for calculating ET ref were extracted from the NOAA maps for TXHPET locations and compared against ground measurements on reference grass surfaces. NOAA ET ref maps generally overestimated the TXHPET observations (1.4 and 2.2 mm/day ET os and ET rs , respectively), which may be attributed to errors in the NLDAS modeled air temperature and wind speed, to which reference ET ref is most sensitive. Therefore, a bias correction to NLDAS modeled air temperature and wind speed data, or adjustment to the resulting NOAA ET ref , may be needed to improve the accuracy of NOAA ET ref maps.

Texas↗
USGS2009

Gas hydrate drilling transect across northern Cascadia margin - IODP Expedition 311

A transect of four sites (U1325, U1326, U1327 and U1329) across the northern Cascadia margin was established during Integrated Ocean Drilling Program Expedition 311 to study the occurrence and formation of gas hydrate in accretionary complexes. In addition to the transect sites, a fifth site (U1328) was established at a cold vent with active fluid flow. The four transect sites represent different typical geological environments of gas hydrate occurrence across the northern Cascadia margin from the earliest occurrence on the westernmost first accreted ridge (Site U1326) to the eastward limit of the gas hydrate occurrence in shallower water (Site U1329). Expedition 311 complements previous gas hydrate studies along the Cascadia accretionary complex, especially ODP Leg 146 and Leg 204 by extending the aperture of the transect sampled and introducing new tools to systematically quantify the gas hydrate content of the sediments. Among the most significant findings of the expedition was the occurrence of up to 20 m thick sand-rich turbidite intervals with gas hydrate concentrations locally exceeding 50% of the pore space at Sites U1326 and U1327. Moreover, these anomalous gas hydrate intervals occur at unexpectedly shallow depths of 50-120 metres below seafloor, which is the opposite of what was expected from previous models of gas hydrate formation in accretionary complexes, where gas hydrate was predicted to be more concentrated near the base of the gas hydrate stability zone just above the bottom-simulating reflector. Gas hydrate appears to be mainly concentrated in turbidite sand layers. During Expedition 311, the visual correlation of gas hydrate with sand layers was clearly and repeatedly documented, strongly supporting the importance of grain size in controlling gas hydrate occurrence. The results from the transect sites provide evidence for a structurally complex, lithology-controlled gas hydrate environment on the northern Cascadia margin. Local shallow occurrences of high gas hydrate concentrations contradict the previous model of gas hydrate formation at an accretionary prism. However, long-lived fluid flow (part of the old model) is still required to explain the shallow high gas hydrate concentrations, although it is most likely not pervasive throughout the entire accretionary prism, but rather localized and focused by the tectonic processes. Differences in the fluid flow regime across all of the transect drill sites indicate site-specific and probably disconnected (compartmented) deeper fluid sources in the various parts of the accretionary prism. The data and future analyses will yield a better understanding of the geologic controls, evolution and ultimate fate of gas hydrate in an accretionary prism as an important contribution to the role of gas hydrate methane gas in slope stability and possibly in climate change. ?? The Geological Society of London 2009.

Geological Society Special Publication↗
USGS2020

Alkalinity in tidal tributaries of the Chesapeake Bay

Despite the important role of alkalinity in estuarine carbon cycling, the seasonal and decadal variability of alkalinity, particularly within multiple tidal tributaries of the same estuary, is poorly understood. Here we analyze more than 26,000 alkalinity measurements, mostly from the 1980s and 1990s, in the major tidal tributaries of the Chesapeake Bay, a large, coastal-plain estuary of eastern North America. The long-term means of alkalinity in tidal-fresh waters vary by a factor of 6 among seven tidal tributaries, reflecting the alkalinity of non-tidal rivers draining to these estuaries. At 25 stations, mostly in the Potomac River Estuary, we find significant long-term increasing trends that exceed the trends in the non-tidal rivers upstream of those stations. Box model calculations in the Potomac River Estuary indicate that the main cause of the estuarine trends is a declining alkalinity sink. The magnitude of this sink is consistent with a simple model of calcification by the invasive bivalve Corbicula fluminea. More generally, in tidal tributaries fed by high-alkalinity non-tidal rivers, alkalinity is consumed, with sinks ranging from 8 to 27% of the upstream input. In contrast, tidal tributaries that are fed by low-alkalinity non-tidal rivers have sources of alkalinity amounting to 34 to 171% of the upstream input. For a single estuarine system, the Chesapeake Bay has diverse alkalinity dynamics and can thus serve as a laboratory for studying the numerous processes influencing alkalinity among the world’s estuaries.

Maryland, Virginia↗
USGS2024

Juvenile coho salmon growth differences track biennial pink salmon spawning patterns

1. Spawning Pacific salmon ( Oncorhynchus spp.) provide marine-derived resources (MDR) to freshwater food webs in the form of eggs, flesh and maggots that consume salmon carcasses, all of which positively impact stream-dwelling fish growth. Pink salmon ( O. gorbuscha ) are widely distributed throughout coastal catchments along the North Pacific Ocean and display increased spawning abundances in odd years, owing to a fixed 2-year life history. While many studies have found that foraging and growth of stream-dwelling salmonids are improved by increased adult salmon spawning abundance, few studies have investigated the importance of alternating pink salmon spawning abundance between years. 2. Here, we examined how patterns of pink salmon spawning abundance impact the foraging and growth of juvenile coho salmon ( O. kisutch ). First, we used bioenergetic simulations to generate a hypothesis that coho salmon growth would increase during odd relative to even years. We then collected empirical juvenile coho salmon diet and growth data from a Southeast Alaska catchment in 2021 (pink salmon spawning) and 2022 (no pink salmon spawning). Field data were compared against simulation predictions to understand impacts of biennial pink salmon spawning patterns on juvenile coho salmon growth. 3. Empirical growth data revealed similar patterns to bioenergetic simulations. Age-1 coho salmon grew 16.6 mm longer and 5.5 g heavier on average in 2021 compared to 2022. Age-0 coho salmon displayed minor growth differences between years. 4. These results support bioenergetic model predictions and suggest that patterns of pink salmon spawning abundance can impart interannual growth disparities to juvenile coho salmon. Moreover, we show that distinct spawning characteristics of Pacific salmon species are important when understanding patterns of MDR transfer and growth responses in stream fishes.

Alaska↗
USGS2015

Hydrogeology, hydrologic effects of development, and simulation of groundwater flow in the Borrego Valley, San Diego County, California

Executive Summary The Borrego Valley is a small valley (110 square miles) in the northeastern part of San Diego County, California. Although the valley is about 60 miles northeast of city of San Diego, it is separated from the Pacific Ocean coast by the mountains to the west and is mostly within the boundaries of Anza-Borrego Desert State Park. From the time the basin was first settled, groundwater has been the only source of water to the valley. Groundwater is used for agricultural, recreational, and municipal purposes. Over time, groundwater withdrawal through pumping has exceeded the amount of water that has been replenished, causing groundwater-level declines of more than 100 feet in some parts of the basin. Continued pumping has resulted in an increase in pumping lifts, reduced well efficiency, dry wells, changes in water quality, and loss of natural groundwater discharge. As a result, the U.S. Geological Survey began a cooperative study of the Borrego Valley with the Borrego Water District (BWD) in 2009. The purpose of the study was to develop a greater understanding of the hydrogeology of the Borrego Valley Groundwater Basin (BVGB) and to provide tools to help evaluate the potential hydrologic effects of future development. The objectives of the study were to (1) improve the understanding of groundwater conditions and land subsidence, (2) incorporate this improved understanding into a model that would assist in the management of the groundwater resources in the Borrego Valley, and (3) use this model to test several management scenarios. This model provides the capability for the BWD and regional stakeholders to quantify the relative benefits of various options for increasing groundwater storage. The study focuses on the period 1945–2010, with scenarios 50 years into the future. This report documents and presents (1) an analysis of the conceptual model, (2) a description of the hydrologic features, (3) a compilation and analysis of water-quality data, (4) the measurement and analysis of land subsidence by using geophysical and remote sensing techniques, (5) the development and calibration of a two-dimensional borehole-groundwater-flow model to estimate aquifer hydraulic conductivities, (6) the development and calibration of a three-dimensional (3-D) integrated hydrologic flow model, (7) a water-availability analysis with respect to current climate variability and land use, and (8) potential future management scenarios. The integrated hydrologic model, referred to here as the “Borrego Valley Hydrologic Model” (BVHM), is a tool that can provide results with the accuracy needed for making water-management decisions, although potential future refinements and enhancements could further improve the level of spatial and temporal resolution and model accuracy. Because the model incorporates time-varying inflows and outflows, this tool can be used to evaluate the effects of temporal changes in recharge and pumping and to compare the relative effects of different water-management scenarios on the aquifer system. Overall, the development of the hydrogeologic and hydrologic models, data networks, and hydrologic analysis provides a basis for assessing surface and groundwater availability and potential water-resource management guidelines.

California↗
USGS1980

Current-controlled, abyssal microtopography and sedimentation in Mozambique Basin, southwest Indian Ocean

The Antarctic Bottom Water (AABW) activity and the variations in the abundance and grain size of the terrigenous sediments, derived from Africa and Madagascar land masses, are reflected in different types of microtopography in the Mozambique Basin. In southerly areas, where the sediment supply is much less, the bottom-current activity has resulted in the presence of manganese nodules, a thin veneer of sediments, and the absence of sediment waves. Farther north, along the marginal areas of the basin where the fine-grained sediments from the Africa—Madagascar source have been supplied in abundance, wavy bedforms have been generated by AABW. Wavy bedforms do not exist even in the northerly areas if coarse-grained, turbidite sediments are present on the sea floor. The continuation of acoustic reflectors from the zone of turbidites in the central areas of the basin into the zone of sediment waves along the margins, and the lithology and structures in sediment cores from these zones suggest that the turbidity-current-fed, fine-grained sediments were deposited as wavy bedforms by AABW flow. Thus, sediment waves formed readily during Pleistocene times. The enrichment of quartz and displaced Antarctic diatoms, and the relatively low kaolinite/chlorite ratios in the sediments, the north-pointing current lineations on the sea floor, the lack of any perceptible sedimentary fill in the troughs of waves, and the dense nepheloid layer in the westerly areas of the Mozambique Basin, attest to the current-controlled sedimentation and generation of wavy bedforms during Holocene time also. The formation of sediment waves in the Mozambique Basin can be modeled after a fluvial antidune mechanism. This model envisages that internal waves, focused on a benthic boundary layer cap, have been locked in phase with sediment waves in the presence of an 8–10 cm/sec current in the Mozambique Basin. A density contrast of 2·10 −6 g/cm 3 appears to exist at the tops of benthic boundary layers in the Mozambique Basin and is quite sufficient for supporting the internal waves. The densiometric Froude number calculated for a 60–280 m thick boundary layer in the basin is close to unity or greater, and is compatible with the antidune model.

Marine Geology↗
USGS2013

Assessing factors affecting the thermal properties of a passive thermal refuge using three-dimensional hydrodynamic flow and transport modeling

Everglades restoration activities may cause changes to temperature and salinity stratification at the Port of the Islands (POI) marina, which could affect its suitability as a cold weather refuge for manatees. To better understand how the Picayune Strand Restoration Project (PSRP) may alter this important resource in Collier County in southwestern Florida, the USGS has developed a three-dimensional hydrodynamic model for the marina and canal system at POI. Empirical data suggest that manatees aggregate at the site during winter because of thermal inversions that provide warmer water near the bottom that appears to only occur in the presence of salinity stratification. To study these phenomena, the environmental fluid dynamics code simulator was used to represent temperature and salinity transport within POI. Boundary inputs were generated using a larger two-dimensional model constructed with the flow and transport in a linked overland-aquifer density-dependent system simulator. Model results for a representative winter period match observed trends in salinity and temperature fluctuations and produce temperature inversions similar to observed values. Modified boundary conditions, representing proposed PSRP alterations, were also tested to examine the possible effect on the salinity stratification and temperature inversion within POI. Results show that during some periods, salinity stratification is reduced resulting in a subsequent reduction in temperature inversion compared with the existing conditions simulation. This may have an effect on POI’s suitability as a passive thermal refuge for manatees and other temperature-sensitive species. Additional testing was completed to determine the important physical relationships affecting POI’s suitability as a refuge.

Florida↗
USGS2002

Porometric properties of siliciclastic marine sand: A comparison of traditional laboratory measurements with image analysis and effective medium modeling

During the 1999 sediment acoustics experiment (SAX99), porometric properties were measured and predicted for a well sorted, medium sand using standard laboratory geotechnical methods and image analysis of resin-impregnated sediments. Sediment porosity measured by laboratory water-weight-loss methods (0.372 ?? 0.0073 for mean ??1 standard deviation) is 0.026 lower than determined by microscopic image analysis of resin-impregnated sediments (0.398 ?? 0.029). Values of intrinsic permeability (m2) determined from constant-head permeameter measurements (3.29 ?? 10-11 ?? 0.60 ?? 10-11) and by microscopic image analysis coupled with effective medium theory modeling (2.78 ?? 10-11 ?? 1.01 ?? 10-11) are nearly identical within measurement error. The mean value of tortuosity factor measured from images is 1.49 ?? 0.09, which is in agreement with tortuosity factor determined from electrical resistivity measurements. Slight heterogeneity and anisotropy are apparent in the top three centimeters of sediment as determined by image-based porometric property measurements. However, the overall similarity for both measured and predicted values of porosity and permeability among and within SAX99 sites indicates sediments are primarily homogeneous and isotropic and pore size distributions are fairly uniform. The results indicate that an effective medium theory technique and two-dimensional image analysis accurately predicts bulk permeability in resin-impregnated sands.

IEEE Journal of Oceanic Engineering↗
USGS2022

Environmental drivers of demography and potential factors limiting the recovery of an endangered marine top predator

Understanding what drives changes in wildlife demography is fundamental to the conservation and management of depleted or declining populations, though making inference about the intrinsic and extrinsic factors that influence survival and reproduction remains challenging. Here we use mark–resight data from 2000 to 2018 to examine the effects of environmental variability on age-specific survival and natality for the endangered western distinct population segment (wDPS) of Steller sea lions ( Eumetopias jubatus ) in Alaska, USA. Though this population has been studied extensively over the last four decades, the causes of divergent abundance trends that have been observed across the wDPS range remain unknown. We developed a Bayesian multievent mark–resight model that accounts for female reproductive state uncertainty. Annual survival probabilities for male pups (0.44; 0.36–0.53), female yearlings (0.63; 0.49–0.73), and male yearlings (0.62; 0.51–0.71) born in the western portion of the wDPS range, estimated here for the first time, were lower than those in the eastern portion of the wDPS range, estimated as: male pups (0.69; 0.65–0.74), female yearlings (0.76; 0.71–0.81), and male yearlings (0.71; 0.65–0.78). There was a higher proportion of young female breeders in the western portion of the range, but overall natality was lower (0.69; 0.47–0.96) than in the eastern portion of the range (0.80; 0.74–0.84). Additionally, pup mass had a positive effect on pup survival in the eastern portion of the range and a negative effect in the western portion of the range, potentially due to earlier weaning of heavier pups. Local- and basin-scale oceanographic features such as the Aleutian Low, the Arctic Oscillation Index, the North Pacific Gyre Oscillation, chlorophyll concentration, upwelling, and wind in certain seasons were correlated with vital rates. However, drawing strong inferences from these correlations is challenging given that relationships between ocean conditions and an adaptive top predator in a dynamic ecosystem are exceedingly complex. This study provides the first demographic rate estimates for the western portion of the range where abundance estimates continue to decline. These results will advance efforts to identify factors driving regionally divergent abundance trends, with implications for population-level responses to future climate variability.

Alaska↗
USGS2023

Carbon sequestration and subsidence reversal in the Sacramento-San Joaquin Delta and Suisun Bay: Management opportunities for climate mitigation and adaptation

The aquatic landscapes of the Sacramento–San Joaquin Delta (hereafter, the Delta) and Suisun Bay represent both a significant past and future soil carbon stock. Historical alterations of hydrologic flows have led to depletion of soil carbon stocks via emissions of carbon dioxide (CO2), and loss of elevation as a result of subsidence. Optimizing ecosystem hydrology in the Delta and Suisun Bay could both reduce and reverse subsidence while also providing significant opportunities for climate mitigation and adaptation. Emissions of greenhouse gases (GHGs)—notably CO2, methane (CH4 ), and nitrous oxide (N2O)—contribute to global warming at different rates and intensities, requiring GHG accounting and modeling to assess the relative benefits of management options. Decades of data collection, model building, and map development suggest that past and current management actions have both caused—and can mitigate—losses of soil carbon. We review here the magnitude of potential GHG offsets, management options that may be achievable, and trade-offs of carbon storage under different land management. Using a land-use/land-cover framework to assess these management options, we describe the potential of three interventions (impoundment to reverse subsidence, agricultural management, and tidal reintroduction and/or maintained connectivity), both in acreage and radiative balance to clarify their relative influence on the region’s GHG balance today and in relation to its millennial history. From floodplains to farming to floating aquatic vegetation, we find specific scalable strategies to manage hydrology that can alter regional GHG balance. Preservation of soil carbon stocks and restoration of net atmospheric CO2 fluxes into soils are the primary route to net negative emissions in the Delta and Suisun Bay, with CH4 emission management occurring in a supporting role. Over a 40-year horizon of climate-mitigation markets, the resilience of different aquatic habitats introduces the most uncertainty, from expected and unexpected hydrologic changes associated with land, ocean, and operational water flows.

California↗
USGS2023

Constraints on the composition and thermal structure of Ariel’s icy crust as inferred from its largest observed impact crater

The large graben-like troughs and smooth plains visible on the surface of Ariel are indicative of a period of high heat flow in the Uranian moon's past. High heat flows on icy moons like Ariel can also enable viscous flow that removes impact crater topography, a process called viscous relaxation. Here we use numerical modeling to investigate the conditions necessary to viscously relax Ariel's largest impact crater, Yangoor, which is 80 km in diameter and unusually shallow. If we assume that Ariel's crust consists of non-porous water ice, heat fluxes ≥60 mW m −2 are required to reduce an initially deep Yangoor-like crater to its current observed depth. Lower fluxes are required if a high-porosity (30%), low-conductivity surface layer several kilometers thick is assumed to exist, but in any case, fluxes in excess of 30 mW m −2 are necessary to substantially reduce Yangoor's topography. The inclusion of ammonia dihydrate has a negligible effect on our results despite decreasing the viscosity of Ariel's deep ice. Our results are consistent with previous inferences of high heat fluxes on Ariel, but exceed both expected radiogenic heat fluxes and known equilibrium tidal heat fluxes by an order of magnitude. If Yangoor's shallow depth is the result of tidal heating, then short-lived non-equilibrium tidal dissipation or some other source of energy is required. Notably, although our results do not require the presence of an ocean within Ariel, the thermal conditions necessary to viscously relax Yangoor also imply a relatively thin ice shell (∼10-km thick) if conductive heat transport is assumed.

Icarus↗
USGS2010

Remagnetization and northward coastwise transport of Franciscan Complex rocks, northern California: A reinterpretation of the paleomagnetic data

Previous paleomagnetic studies of accreted oceanic rocks within the Franciscan Complex of northern California have concluded that these rocks originated far to the south of their present positions with respect to the North American continent. Based on positive “fold” tests, the characteristic remanent magnetizations were inferred to predate accretion-related deformation and metamorphism, and to have been acquired during or soon after deposition of these rocks. Thus, the paleomagnetic data were thought to provide direct information on ancient oceanic plate motions. However, the plate motions implied by some of these paleomagnetic data are problematic (e.g., exceptional plate velocities), and uniform-polarity magnetizations in almost all of these rocks indicate the possibility of remagnetization. Recent work on oceanic rocks in similar subduction complexes of Japan and Mexico have shown that they were most likely chemically remagnetized during accretion prior to disruption of the original stratigraphic sequences. Modern analogs indicate that the oceanic rocks in Mexico were probably remagnetized while still part of a shallow-dipping subducting slab (<10°) at the base of an accretionary prism. Assuming these rocks were near horizontal at the time of remagnetization, paleolatitudes at which these rocks were subducted and subsequent arc-parallel displacements along the western margin of North America can be inferred. In this paper, Franciscan rocks in northern California are reinterpreted as also having been remagnetized prior to accretion-related deformation. This scenario satisfies both geologic and paleomagnetic constraints for these rocks, and resolves conflicts between data indicating both remagnetization and tectonic displacement. Transport of the Laytonville Limestone from the southern hemisphere is not required. Paleolatitudes of subduction and remagnetization in the northern hemisphere (12° to 33°) appear to be inversely proportional to age of accretion (middle Cretaceous to Oligocene) for the Franciscan rocks. Subsequent northward diplacements (800 to 3700 km) and clockwise rotations (56° and 154°) of these rocks inferred from the paleomagnetic data are consistent with potential displacements along the western margin of North America during late Mesozoic and Cenozoic time calculated using examples of modern subduction zones and current plate reconstruction models.

California↗
USGS2010

Dacite petrogenesis on mid-ocean ridges: Evidence for oceanic crustal melting and assimilation

Whereas the majority of eruptions at oceanic spreading centers produce lavas with relatively homogeneous mid-ocean ridge basalt (MORB) compositions, the formation of tholeiitic andesites and dacites at mid-ocean ridges (MORs) is a petrological enigma. Eruptions of MOR high-silica lavas are typically associated with ridge discontinuities and have produced regionally significant volumes of lava. Andesites and dacites have been observed and sampled at several locations along the global MOR system; these include propagating ridge tips at ridge-transform intersections on the Juan de Fuca Ridge and eastern Gal??pagos spreading center, and at the 9??N overlapping spreading center on the East Pacific Rise. Despite the formation of these lavas at various ridges, MOR dacites show remarkably similar major element trends and incompatible trace element enrichments, suggesting that similar processes are controlling their chemistry. Although most geochemical variability in MOR basalts is consistent with low-pressure fractional crystallization of various mantle-derived parental melts, our geochemical data for MOR dacitic glasses suggest that contamination from a seawater-altered component is important in their petrogenesis. MOR dacites are characterized by elevated U, Th, Zr, and Hf, low Nb and Ta concentrations relative to rare earth elements (REE), and Al2O3, K2O, and Cl concentrations that are higher than expected from low-pressure fractional crystallization alone. Petrological modeling of MOR dacites suggests that partial melting and assimilation are both integral to their petrogenesis. Extensive fractional crystallization of a MORB parent combined with partial melting and assimilation of amphibole-bearing altered crust produces a magma with a geochemical signature similar to a MOR dacite. This supports the hypothesis that crustal assimilation is an important process in the formation of highly evolved MOR lavas and may be significant in the generation of evolved MORB in general. Additionally, these processes are likely to be more common in regions of episodic magma supply and enhanced magma-crust interaction such as at the ends of ridge segments. ?? The Author 2010. Published by Oxford University Press. All rights reserved.

Journal of Petrology↗
USGS2018

Inland waters

1. The total flux of carbon—which includes gaseous emissions, lateral flux, and burial—from inland waters across the conterminous United States (CONUS) and Alaska is 193 teragrams of carbon (Tg C) per year. The dominant pathway for carbon movement out of inland waters is the emission of carbon dioxide gas across water surfaces of streams, rivers, and lakes (110.1 Tg C per year), a flux not identified in the First State of the Carbon Cycle Report (SOCCR1; CCSP 2007). Second to gaseous emissions are the lateral fluxes of carbon through rivers to coastal environments (59.8 Tg C per year). Total carbon burial in lakes and reservoirs represents the smallest flux for CONUS and Alaska (22.5 Tg C per year) (medium confidence). 2. Based on estimates presented herein, the carbon flux from inland waters is now understood to be four times larger than estimates presented in SOCCR1. The total flux of carbon from inland waters across North America is estimated to be 507 Tg C per year based on a modeling approach that integrates high-resolution U.S. data and continental-scale estimates of water area, discharge, and carbon emissions. This estimate represents a weighted average of 24 grams of carbon per m2 per year of continental area exported and removed through inland waters in North America (low confidence). 3. Future research can address critical knowledge gaps and uncertainties related to inland water carbon fluxes. This chapter, for example, does not include methane emissions, which cannot be calculated as precisely as other carbon fluxes because of significant data gaps. Key to reducing uncertainties in estimated carbon fluxes is increased temporal resolution of carbon concentration and discharge sampling to provide better representations of storms and other extreme events for estimates of total inland water carbon fluxes. Improved spatial resolution of sampling also could potentially highlight anthropogenic influences on the quantity and quality of carbon fluxes in inland waters and provide information for land-use planning and management of water resources. Finally, uncertainties could likely be reduced if the community of scientists working in inland waters establishes and adopts standard measurement techniques and protocols similar to those maintained through collaborative efforts of the International Ocean Carbon Coordination Project and relevant governmental agencies from participating nations.

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