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USGS2013

Applying UV cameras for SO 2 detection to distant or optically thick volcanic plumes

Ultraviolet (UV) camera systems represent an exciting new technology for measuring two dimensional sulfur dioxide (SO 2 ) distributions in volcanic plumes. The high frame rate of the cameras allows the retrieval of SO 2 emission rates at time scales of 1 Hz or higher, thus allowing the investigation of high-frequency signals and making integrated and comparative studies with other high-data-rate volcano monitoring techniques possible. One drawback of the technique, however, is the limited spectral information recorded by the imaging systems. Here, a framework for simulating the sensitivity of UV cameras to various SO 2 distributions is introduced. Both the wavelength-dependent transmittance of the optical imaging system and the radiative transfer in the atmosphere are modeled. The framework is then applied to study the behavior of different optical setups and used to simulate the response of these instruments to volcanic plumes containing varying SO 2 and aerosol abundances located at various distances from the sensor. Results show that UV radiative transfer in and around distant and/or optically thick plumes typically leads to a lower sensitivity to SO 2 than expected when assuming a standard Beer–Lambert absorption model. Furthermore, camera response is often non-linear in SO 2 and dependent on distance to the plume and plume aerosol optical thickness and single scatter albedo. The model results are compared with camera measurements made at Kilauea Volcano (Hawaii) and a method for integrating moderate resolution differential optical absorption spectroscopy data with UV imagery to retrieve improved SO 2 column densities is discussed.

Journal of Volcanology and Geothermal Research↗

USGS2013

Potential climate change impacts on temperate forest ecosystem processes

Large changes in atmospheric CO2, temperature and precipitation are predicted by 2100, yet the long-term consequences for carbon, water, and nitrogen cycling in forests are poorly understood. We applied the PnET-CN ecosystem model to compare the long-term effects of changing climate and atmospheric CO2 on productivity, evapotranspiration, runoff, and net nitrogen mineralization in current Great Lakes forest types. We used two statistically downscaled climate projections, PCM B1 (warmer and wetter) and GFDL A1FI (hotter and drier), to represent two potential future climate and atmospheric CO2 scenarios. To separate the effects of climate and CO2, we ran PnET-CN including and excluding the CO2 routine. Our results suggest that, with rising CO2 and without changes in forest type, average regional productivity could increase from 67% to 142%, changes in evapotranspiration could range from –3% to +6%, runoff could increase from 2% to 22%, and net N mineralization could increase 10% to 12%. Ecosystem responses varied geographically and by forest type. Increased productivity was almost entirely driven by CO2 fertilization effects, rather than by temperature or precipitation (model runs holding CO2 constant showed stable or declining productivity). The relative importance of edaphic and climatic spatial drivers of productivity varied over time, suggesting that productivity in Great Lakes forests may switch from being temperature to water limited by the end of the century.

Michigan;Minnesota;Wisconsin↗

USGS1986

Evaluation of gas data from high-temperature fumaroles at Mount St. Helens, 1980-1982

The Mount St. Helens fumarole gases show linear composition trends during periods of noneruptive degassing between September 1980 and October 1981. The trends are characterized by increasing H2O and decreasing CO2 and sulfur. Maximum fumarole temperatures also show a linear decrease during this period. High-temperature fumarole gases collected from the crater and dome between September 1980 and July 1982 are all H2O-rich (> 90%) with 1-10% CO2 and small amounts of H2S, SO2, H2, CO, HC, and HF. Trace amounts of COS and S2 are present, and occasional observations of minor CH4 appear to result from contamination or low-temperature reactions in sample vessels. The O2 fugacities of the gases remain near Ni-NiO during cooling. The low sulfur content of the gases obviates the need for extensive gas-rock oxygen exchange to maintain fO2's near Ni-NiO. A detailed thermodynamic analysis of 50 gas samples collected between September 1980 and December 1981 led to improved compositions for 22 samples. The gases were initially in a state of equilibrium, but disequilibrium modifications from atmospheric oxidation of H2 and, to a lesser extent, CO occurred within the upper portions of the fumarole vents. The last temperatures of equilibrium for the fumarole gases range from 800??C to 650??C and are nearly always higher than the collection temperatures. No evidence was found of disequilibrium admixture of surface waters; if such modifications of the fumarole gases occurred, the water must have been added at depth and have reequilibrated with the other gas species at magmatic or near-magmatic temperatures. The highest quality analytical data are obtained by field gas chromatograph measurements and from caustic soda bottle samples. Samples collected in evacuated bottles or by pumping through double stopcock tubes tend to be severely deficient in sulfur due to post-collection reactions between H2S and SO2. It is also necessary to infer the water content of the latter samples. ?? 1986.

Journal of Volcanology and Geothermal Research↗

USGS2023

Vulnerability to climate change of managed stocks in the California Current large marine ecosystem

Introduction: Understanding how abundance, productivity and distribution of individual species may respond to climate change is a critical first step towards anticipating alterations in marine ecosystem structure and function, as well as developing strategies to adapt to the full range of potential changes. Methods: This study applies the NOAA (National Oceanic and Atmospheric Administration) Fisheries Climate Vulnerability Assessment method to 64 federally-managed species in the California Current Large Marine Ecosystem to assess their vulnerability to climate change, where vulnerability is a function of a species’ exposure to environmental change and its biological sensitivity to a set of environmental conditions, which includes components of its resiliency and adaptive capacity to respond to these new conditions. Results: Overall, two-thirds of the species were judged to have Moderate or greater vulnerability to climate change, and only one species was anticipated to have a positive response. Species classified as Highly or Very Highly vulnerable share one or more characteristics including: 1) having complex life histories that utilize a wide range of freshwater and marine habitats; 2) having habitat specialization, particularly for areas that are likely to experience increased hypoxia; 3) having long lifespans and low population growth rates; and/or 4) being of high commercial value combined with impacts from non-climate stressors such as anthropogenic habitat degradation. Species with Low or Moderate vulnerability are either habitat generalists, occupy deep-water habitats or are highly mobile and likely to shift their ranges. Discussion: As climate-related changes intensify, this work provides key information for both scientists and managers as they address the long-term sustainability of fisheries in the region. This information can inform near-term advice for prioritizing species-level data collection and research on climate impacts, help managers to determine when and where a precautionary approach might be warranted, in harvest or other management decisions, and help identify habitats or life history stages that might be especially effective to protect or restore.

California, Oregon, Washington↗

USGS1998

Cruise report for a seismic investigation of gas hydrates in the Mississippi Canyon region, northern Gulf of Mexico: Cruise M1-98-GM

During June 1998, the U.S. Geological Survey (USGS) and the University of Mississippi Marine Minerals Technology Center (MMTC) conducted a 12-day cruise in the Mississippi Canyon region of the Gulf of Mexico (Fig. 1). The R/V Tommy Munro, owned by the Marine Research Institute of the University of Southern Mississippi, was chartered for the cruise. The general objective was to acquire very high resolution seismic-reflection data across of the upper and middle continental slope (200-1200-m water depths) to study the acoustic character, distribution and potential effects of gas hydrates within the shallow subsurface, extending from the sea floor down to the base of the gas-hydrate stability zone. The Gulf of Mexico is well known for hydrocarbon resources that include petroleum and related gases. Areas of the Gulf that lie in waters deeper than about 250 m potentially have conditions (e.g., pressure, temperature, near-surface gas content, etc.) that are right for the shallow-subsurface formation of the ice-like substance (gas and water) known as gas hydrate (Kvenvolden, 1993). Gas hydrates have previously been sampled in sea-floor cores and observed as massive mounds in several parts of the northern Gulf, including the Mississippi Canyon region (e.g., Anderson et al., 1992). Extensive seismic data have been recorded in the Gulf, in support of commercial drilling efforts, but few very high resolution data exist in the public domain to aid in gas-hydrate studies. Studies of long-term interest include those on the resource potential of gas hydrates, the geologic hazards associated with dissociation and formation of hydrates, and the impact, if any, of gas-hydrate dissociation on atmospheric warming (i.e., via release of methane, a "greenhouse" gas). Several very high resolution seismic systems (surface-towed, deep-towed, and sea-floor) were used during the cruise to test the feasibility of using such data for detailed structural (geometric) and stratigraphic (physical property) analyses based on the acoustic data. The cruise was conducted in two regions, on opposite flanks of the Mississippi Canyon, where gas hydrates are known and suspected from prior coring and seismic operations (e.g., Neurauter and Bryant, 1989). The regions are also characterized by thick surficial, relatively young (Pleistocene and younger) sediments. Swath-bathymetry data (Fig. 2) show extensive sea-floor faults, piercement features, and slumps—features whose development could potentially be related to gas hydrates. The specific objectives of the cruise were (a) to image the gas-hydrate stability zone across the continental margin to document bottom-simulating reflections (BSRs) and changes in geometry of the hydrate stability zone; (b) to image known hydrate features (with several seismic systems) to estimate physical properties for hydrate and non-hydrate areas; (c) to outline the shallow structures of the hydrate stability zone to ascertain their potential effects on the formation/distribution of hydrates and on stability of the sea floor; and (d) to estimate, if possible, the amounts of hydrates present in the shallow sub surface. During the cruise about 850 km of multichannel and single-channel seismic data were recorded. Seismic measurements at nine ocean-bottom seismometer (OBS) stations were recorded for several of the multichannel tracklines (see Fig. 3 in report). The following report describes the field operations and equipment systems employed, gives two examples of ship-board seismic records, and outlines a few preliminary results.

Open-File Report↗

USGS2002

Tracing and quantifying magmatic carbon discharge in cold groundwaters: Lessons learned from Mammoth Mountain, USA

A major campaign to quantify the magmatic carbon discharge in cold groundwaters around Mammoth Mountain volcano in eastern California was carried out from 1996 to 1999. The total water flow from all sampled cold springs was ??? 1.8 ?? 107 m3/yr draining an area that receives an estimated 2.5 ?? 107 m3/yr of recharge, suggesting that sample coverage of the groundwater system was essentially complete. Some of the waters contain magmatic helium with 3He/4He ratios as high as 4.5 times the atmospheric ratio, and a magmatic component in the dissolved inorganic carbon (DIC) can be identified in virtually every feature sampled. Many waters have a 14C of 0-5 pmC, a ??13C near -5???, and contain high concentrations (20-50 mmol/1) of CO2(aq); but are otherwise dilute (specific conductance = 100-300 ??S/cm) with low pH values between 5 and 6. Such waters have previously escaped notice at Mammoth Mountain, and possibly at many other volcanoes, because CO2 is rapidly lost to the air as the water flows away from the springs, leaving neutral pH waters containing only 1-3 mmol/1 HCO-3. The total discharge of magmatic carbon in the cold groundwater system at Mammoth Mountain is ~ 20 000 t/yr (as CO2), ranging seasonally from about 30 to 90 t/day. Several types of evidence show that this high discharge of magmatic DIC arose in part because of shallow dike intrusion in 1989, but also demonstrate that a long-term discharge possibly half this magnitude (~ 10 000 t/yr) predated that intrusion. To sustain a 10 000 t/yr DIC discharge would require a magma intrusion rate of 0.057 km3 per century, assuming complete degassing of magma with 0.65 wt% CO2 and a density of 2.7 t/m3. The geochemical data also identify a small ( < 1 t/day) discharge of magmatic DIC that can be traced to the Inyo Domes area north of Mammoth Mountain and outside the associated Long Valley caldera. This research, along with recent studies at Lassen Peak and other western USA volcanoes, suggests that the amount of magmatic carbon in cold groundwaters is important to constraining rates of intrusion and edifice weathering at individual volcanoes and may even represent a significant fraction of the global carbon discharge from volcanoes. ?? 2002 Elsevier Science B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗

USGS2014

HiRISE observations of new impact craters exposing Martian ground ice

Twenty small new impact craters or clusters have been observed to excavate bright material inferred to be ice at mid and high latitudes on Mars. In the northern hemisphere, the craters are widely distributed geographically and occur at latitudes as low as 39°N. Stability modeling suggests that this ice distribution requires a long-term average atmospheric water vapor content around 25 precipitable microns, more than double the present value, which is consistent with the expected effect of recent orbital variations. Alternatively, near-surface humidity could be higher than expected for current column abundances if water vapor is not well-mixed with atmospheric CO 2 , or the vapor pressure at the ice table could be lower due to salts. Ice in and around the craters remains visibly bright for months to years, indicating that it is clean ice rather than ice-cemented regolith. Although some clean ice may be produced by the impact process, it is likely that the original ground ice was excess ice (exceeding dry soil pore space) in many cases. Observations of the craters suggest small-scale heterogeneities in this excess ice. The origin of such ice is uncertain. Ice lens formation by migration of thin films of liquid is most consistent with local heterogeneity in ice content and common surface boulders, but in some cases nearby thermokarst landforms suggest large amounts of excess ice that may be best explained by a degraded ice sheet.

Journal of Geophysical Research E: Planets↗

USGS2021

Evaluation of SWIR crop residue bands for the Landsat Next mission

This research reports the findings of a Landsat Next expert review panel that evaluated the use of narrow shortwave infrared (SWIR) reflectance bands to measure ligno-cellulose absorption features centered near 2100 and 2300 nm, with the objective of measuring and mapping non-photosynthetic vegetation (NPV), crop residue cover, and the adoption of conservation tillage practices within agricultural landscapes. Results could also apply to detection of NPV in pasture, grazing lands, and non-agricultural settings. Currently, there are no satellite data sources that provide narrowband or hyperspectral SWIR imagery at sufficient volume to map NPV at a regional scale. The Landsat Next mission, currently under design and expected to launch in the late 2020’s, provides the opportunity for achieving increased SWIR sampling and spectral resolution with the adoption of new sensor technology. This study employed hyperspectral data collected from 916 agricultural field locations with varying fractional NPV, fractional green vegetation, and surface moisture contents. These spectra were processed to generate narrow bands with centers at 2040, 2100, 2210, 2260, and 2230 nm, at various bandwidths, that were subsequently used to derive 13 NPV spectral indices from each spectrum. For crop residues with minimal green vegetation cover, two-band indices derived from 2210 and 2260 nm bands were top performers for measuring NPV (R 2 = 0.81, RMSE = 0.13) using bandwidths of 30 to 50 nm, and the addition of a third band at 2100 nm increased resistance to atmospheric correction residuals and improved mission continuity with Landsat 8 Operational Land Imager Band 7. For prediction of NPV over a full range of green vegetation cover, the Cellulose Absorption Index, derived from 2040, 2100, and 2210 nm bands, was top performer (R 2 = 0.77, RMSE = 0.17), but required a narrow (≤20 nm) bandwidth at 2040 nm to avoid interference from atmospheric carbon dioxide absorption. In comparison, broadband NPV indices utilizing Landsat 8 bands centered at 1610 and 2200 nm performed poorly in measuring fractional NPV (R 2 = 0.44), with significantly increased interference from green vegetation.

Remote Sensing↗

USGS1997

Estimation of directional surface wave spectra from a towed research catamaran

During the High-Resolution Remote Sensing Main Experiment (1993), wave height was estimated from a moving catamaran using pitch-rate and roll-rate sensors, a three-axis accelerometer, and a capacitive wave wire. The wave spectrum in the frequency band ranging roughly from 0.08 to 0.3 Hz was verified by independent buoy measurements. To estimate the directional frequency spectrum from a wave-wire array, the Data-Adaptive Spectral Estimator is extended to include the Doppler shifting effects of a moving platform. The method is applied to data obtained from a fixed platform during the Risø Air–Sea Experiment (1994) and to data obtained from a moving platform during the Coastal Ocean Processes Experiment (1995). Both results show that the propagation direction of the peak wind waves compares well with the measured wind direction. When swells and local wind waves are not aligned, the method can resolve the difference of propagation directions. Using the fixed platform data a numerical test is conducted that shows that the method is able to distinguish two wave systems propagating at the same frequency but in two different directions.

Journal of Atmospheric and Oceanic Technology↗

USGS2019

The dependence of hydroclimate projections in snow‐dominated regions of the western United States on the choice of statistically downscaled climate data

We assess monthly temperature and precipitation data produced by four statistically based techniques that were used to downscale general circulation models (GCMs) in the Climate Model Intercomparison Program Phase 5 (CMIP5) (Taylor et al., 2012). We drive a simple water-balance model with the downscaled data to demonstrate the effect of the methods on the cold season hydrology of three, snow dominated regions in the western U.S. Independent of substantial variation among the GCM simulations over the regions (maximum range of ~3.5 °C and 50% change in precipitation), the four methods produce disparate high resolution representations of the magnitude and spatial patterns of future temperature and precipitation simulated by the models that range for up to ~3 °C and 30% change in precipitation that propagate into the hydrologic simulations. Temperature-dependent snowfall, accumulation, and melt in the model are sensitive to how atmospheric lapse rates are applied in the gridded observations that are used to remove the bias in raw GCM temperatures. By the end of the century the same downscaling method (Bias Corrected Spatial Disaggregation) yields a loss of cold-season snowpack of 34% over the Greater Yellowstone Area under a constant lapse rate ( 6.5°C km-1), whereas spatially variable lapse rates nearly double the loss to 66%, highlighting the roll of both lapse rates and high elevation stations in the bias correction dataset. The two newest downscaling methods (Multivariate Adaptive Constructed Analogs and Localized Constructed Analogs) preserve the magnitude of change simulated GCMs better than the other methods and the produce comparable hydrologic projections. Because the downscaled data from the methods vary spatially and by GCM, the downscaled data should be evaluated carefully as part of the process of using downscaled climate products to drive hydrological models over the area of interest.

Arizona, California, Colorado, Idaho, Montana,Neva↗

USGS2024

A conceptual framework to assess post-wildfire water quality: State of the science and knowledge gaps

Wildfire substantially alters aquatic ecosystems by inducing moderate to catastrophic physical and chemical changes. However, the relations of environmental and watershed variables that drive those effects are complex. We present a Driver-Factor-Stressor-Effect (DFSE) conceptual framework to assess the current state of the science related to post-wildfire water-quality. We reviewed 64 peer-reviewed papers using the DFSE framework to identify drivers, factors, stressors, and effects associated with each study. A total of five drivers were identified and ranked according to their frequency of occurrence in the literature: atmospheric processes > fire characteristics > ecologic processes and characteristics > land surface characteristics > soil characteristics. Commonly reported stressors include increased nutrients, runoff, and sediment transport. Furthermore, although several different factors have been used at least once to explain water-quality effects, relatively few factors outside of precipitation and fire characteristics are frequently studied. We identified several gaps indicating the need for long-term monitoring, multi-factor studies, consideration of organic contaminants, consideration of groundwater, and inclusion of soil characteristics. This assessment expands on other reviews and meta-analyses by exploring causal linkages between influential variables and overall effects in post-wildfire watersheds. Information gathered from our assessment and the framework itself can be used to inform future monitoring plans and as a guide for modeling efforts focused on better understanding specific processes or to mitigate potential risks of post-wildfire water quality.

Water Resources Research↗

USGS2010

Development of a global land cover characteristics database and IGBP DISCover from 1 km AVHRR data

Researchers from the U.S. Geological Survey, University of Nebraska-Lincoln and the European Commission's Joint Research Centre, Ispra, Italy produced a 1 km resolution global land cover characteristics database for use in a wide range of continental-to global-scale environmental studies. This database provides a unique view of the broad patterns of the biogeographical and ecoclimatic diversity of the global land surface, and presents a detailed interpretation of the extent of human development. The project was carried out as an International Geosphere-Biosphere Programme, Data and Information Systems (IGBP-DIS) initiative. The IGBP DISCover global land cover product is an integral component of the global land cover database. DISCover includes 17 general land cover classes defined to meet the needs of IGBP core science projects. A formal accuracy assessment of the DISCover data layer will be completed in 1998. The 1 km global land cover database was developed through a continent-by-continent unsupervised classification of 1 km monthly Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) composites covering 1992-1993. Extensive post-classification stratification was necessary to resolve spectral/temporal confusion between disparate land cover types. The complete global database consists of 961 seasonal land cover regions that capture patterns of land cover, seasonality and relative primary productivity. The seasonal land cover regions were aggregated to produce seven separate land cover data sets used for global environmental modelling and assessment. The data sets include IGBP DISCover, U.S. Geological Survey Anderson System, Simple Biosphere Model, Simple Biosphere Model 2, Biosphere-Atmosphere Transfer Scheme, Olson Ecosystems and Running Global Remote Sensing Land Cover. The database also includes all digital sources that were used in the classification. The complete database can be sourced from the website: http://edcwww.cr.usgs.gov/landdaac/glcc/glcc.html.

International Journal of Remote Sensing↗

USGS2026

Precipitation intensity increased across the South Pacific Convergence Zone in the Industrial Age

The position, strength, and variability of precipitation in the South Pacific Convergence Zone (SPCZ) remain challenging for coupled ocean-atmosphere climate models to represent, leaving future rainfall projections in this dynamically important region uncertain. Here, we present quantitative records of mean annual precipitation (MAP) spanning the past 1,000 years using sediment cores from five freshwater lakes on different islands in the western portion of the SPCZ. Precipitation reconstructions are based on the hydrogen isotope composition of the dinoflagellate biomarker dinosterol, which is inversely correlated with MAP. We show that MAP in the western tropical Pacific increased over the past ∼300 years, with a significant increase beginning in 1,820 ± 75 C.E., coincident with a warming trend in the Western Pacific Warm Pool. These results contrast with the expected drying associated with reduced Pacific Walker Circulation as global temperatures increase in many climate models. Future warming may promote more intense SPCZ precipitation.

Geophysical Research Letters↗

USGS1996

Research-derived insights into surface geochemical hydrocarbon exploration

Research studies based on foreland basins (mainly in eastern Colorado) examined three surface geochemical exploration (SGE) methods as possible hydrocarbon (HC) exploration techniques. The first method, microbial soil surveying, has high potential as an exploration tool, especially hi development and enhanced recovery operations. Integrative adsorption, the second technique, is not effective as a quantitative SGE method because water, carbon dioxide, nitrous oxide, unsaturated hydrocarbons, and organic compounds are collected by the adsorbent (activated charcoal) much more strongly than covalently bonded microseeping Q-Cs thermogenic HCs. Qualitative comparisons (pattern recognition) of C8+ mass spectra cannot gauge HC gas microseepage that involves only the Q-Cs HCs. The third method, soil cakite surveying, also has no potential as an exploration tool. Soil calcite concentrations had patterns with pronounced areal contrasts, but these patterns had no geometric relationship to surface traces of established or potential production, that is, the patterns were random. Microscopic examination of thousands of soils revealed that soil calcite was an uncrystallized caliche coating soil particles. During its precipitation, caliche captures or occludes any gases, elements, or compounds in its immediate vicinity. Thus, increased signal intensity of some SGE methods should depend on increasing soil calcite concentrations. Analyses substantiate this hypothesis. Because soil calcite has no utility as a surface exploration tool, any surface method that depends on soil calcite has a diminished utility as an SGE tool. Isotopic analyses of soil calcites revealed carbonate carbon ??13C values of -4.0 to +2.07co (indicating a strong influence of atmospheric CO2) as opposed to expected values of-45 to -30%c if the carbonate carbon had originated from microbial oxidation of microseeping HC gases. These analyses confirm a surface origin for this soil calcite (caliche), which is not necessarily related to HC gas microseepage. This previously unappreciated pivotal role of caliche is hypothesized to contribute significantly to the poor and inconsistent results of some SGE methods.

AAPG Memoir↗

USGS2000

Mercury in Long Island Sound sediments

Mercury (Hg) concentrations were measured in 394 surface and core samples from Long Island Sound (LIS). The surface sediment Hg concentration data show a wide spread, ranging from <50 ppb Hg in eastern LIS to >600 ppb Hg in westernmost LIS. Part of the observed range is related to variations in the bottom sedimentary environments, with higher Hg concentrations in the muddy depositional areas of central and western LIS. A strong residual trend of higher Hg values to the west remains when the data are normalized to grain size. Relationships between a tracer for sewage effluents (C. perfringens) and Hg concentrations indicate that between 0-50 % of the Hg is derived from sewage sources for most samples from the western and central basins. A higher percentage of sewage-derived Hg is found in samples from the westernmost section of LIS and in some local spots near urban centers. The remainder of the Hg is carried into the Sound with contaminated sediments from the watersheds and a small fraction enters the Sound as in situ atmospheric deposition. The Hg-depth profiles of several cores have well-defined contamination profiles that extend to pre-industrial background values. These data indicate that the Hg levels in the Sound have increased by a factor of 5-6 over the last few centuries, but Hg levels in LIS sediments have declined in modern times by up to 30 %. The concentrations of C. perfringens increased exponentially in the top core sections which had declining Hg concentrations, suggesting a recent decline in Hg fluxes that are unrelated to sewage effluents. The observed spatial and historical trends show Hg fluxes to LIS from sewage effluents, contaminated sediment input from the Connecticut River, point source inputs of strongly contaminated sediment from the Housatonic River, variations in the abundance of Hg carrier phases such as TOC and Fe, and focusing of sediment-bound Hg in association with westward sediment transport within the Sound.

Connecticut;New York↗

USGS2012

Ash3d: A finite-volume, conservative numerical model for ash transport and tephra deposition

We develop a transient, 3-D Eulerian model (Ash3d) to predict airborne volcanic ash concentration and tephra deposition during volcanic eruptions. This model simulates downwind advection, turbulent diffusion, and settling of ash injected into the atmosphere by a volcanic eruption column. Ash advection is calculated using time-varying pre-existing wind data and a robust, high-order, finite-volume method. Our routine is mass-conservative and uses the coordinate system of the wind data, either a Cartesian system local to the volcano or a global spherical system for the Earth. Volcanic ash is specified with an arbitrary number of grain sizes, which affects the fall velocity, distribution and duration of transport. Above the source volcano, the vertical mass distribution with elevation is calculated using a Suzuki distribution for a given plume height, eruptive volume, and eruption duration. Multiple eruptions separated in time may be included in a single simulation. We test the model using analytical solutions for transport. Comparisons of the predicted and observed ash distributions for the 18 August 1992 eruption of Mt. Spurr in Alaska demonstrate to the efficacy and efficiency of the routine.

Journal of Geophysical Research↗

USGS2018

Time-dependent pore filling

Capillarity traps fluids in porous media during immiscible fluid displacement. Most field situations involve relatively long time scales, such as hydrocarbon migration into reservoirs, resource recovery, nonaqueous phase liquid remediation, geological CO 2 storage, and sediment‐atmosphere interactions. Yet laboratory studies and numerical simulations of capillary phenomena rarely consider the impact of time on these processes. We use time‐lapse microphotography to record the evolution of saturation in air‐ or hydrocarbon‐filled capillary tubes submerged in water to investigate long‐term pore filling phenomena beyond imbibition. Microphotographic sequences capture a lively pore filling history where various concurrent physical phenomena coexist. Dissolution and diffusion play a central role. Observations indicate preferential transport of the wetting liquid along corners, vapor condensation, capillary flow induced by asymmetrical interfaces, and interface pinning that defines the diffusion length. Other processes include internal snap‐offs, fluid redistribution, and changes in wettability as fluids dissolve into each other. Overall, the rate of pore filling is diffusion‐controlled for a given interfacial configuration; diffusive transport takes place at a constant rate for pinned interfaces and is proportional to the square root of time for free interfaces where the diffusion length increases with time.

Water Resources Research↗

USGS2023

Regional variability in peatland burning at mid-to high-latitudes during the Holocene

Northern peatlands store globally-important amounts of carbon in the form of partly decomposed plant detritus. Drying associated with climate and land-use change may lead to increased fire frequency and severity in peatlands and the rapid loss of carbon to the atmosphere. However, our understanding of the patterns and drivers of peatland burning on an appropriate decadal to millennial timescale relies heavily on individual site-based reconstructions. For the first time, we synthesise peatland macrocharcoal records from across North America, Europe, and Patagonia to reveal regional variation in peatland burning during the Holocene. We used an existing database of proximal sedimentary charcoal to represent regional burning trends in the wider landscape for each region. Long-term trends in peatland burning appear to be largely climate driven, with human activities likely having an increasing influence in the late Holocene. Warmer conditions during the Holocene Thermal Maximum (∼9–6 cal. ka BP) were associated with greater peatland burning in North America's Atlantic coast, southern Scandinavia and the Baltics, and Patagonia. Since the Little Ice Age, peatland burning has declined across North America and in some areas of Europe. This decline is mirrored by a decrease in wider landscape burning in some, but not all sub-regions, linked to fire-suppression policies, and landscape fragmentation caused by agricultural expansion. Peatlands demonstrate lower susceptibility to burning than the wider landscape in several instances, probably because of autogenic processes that maintain high levels of near-surface wetness even during drought. Nonetheless, widespread drying and degradation of peatlands, particularly in Europe, has likely increased their vulnerability to burning in recent centuries. Consequently, peatland restoration efforts are important to mitigate the risk of peatland fire under a changing climate. Finally, we make recommendations for future research to improve our understanding of the controls on peatland fires.

Quaternary Science Reviews↗