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At least 1,675 records · Page 93Linked to original sources

USGS1999

Mercury concentration in coal — Unraveling the puzzle

Based on data from the US Geological Survey's COALQUAL database, the mean concentration of mercury in coal is approximately 0.2 μg g −1 . Assuming the database reflects in-ground US coal resources, values for conterminous US coal areas range from 0.08 μg g −1 for coal in the San Juan and Uinta regions to 0.22 μg g −1 for the Gulf Coast lignites. Recalculating the COALQUAL data to an equal energy basis unadjusted for moisture differences, the Gulf Coast lignites have the highest values (36.4 lb of Hg/10 12 Btu) and the Hams Fork region coal has the lowest value (4.8 lb of Hg/10 12 Btu). Strong indirect geochemical evidence indicates that a substantial proportion of the mercury in coal is associated with pyrite occurrence. This association of mercury and pyrite probably accounts for the removal of mercury with the pyrite by physical coal cleaning procedures. Data from the literature indicate that conventional coal cleaning removes approximately 37% of the mercury on an equal energy basis, with a range of 0% to 78%. When the average mercury reduction value is applied to in-ground mercury values from the COALQUAL database, the resulting `cleaned' mercury values are very close to mercury in `as-shipped' coal from the same coal bed in the same county. Applying the reduction factor for coal cleaning to eastern US bituminous coal, reduces the mercury input load compared to lower-rank non-cleaned western US coal. In the absence of analytical data on as-shipped coal, the mercury data in the COALQUAL database, adjusted for cleanability where appropriate, may be used as an estimator of mercury contents of as-shipped coal.

Fuel↗

USGS2002

Towards a sediment budget for the Santa Cruz shelf

A conceptual model is presented for the northern Monterey Bay continental shelf in which coarse sediment moves southward along the coast in the littoral zone while fine sediment moves to the north by advection and diffusion along the midshelf. Data from measurements and estimates of various sediment sources and sinks show that the midshelf mudbelt is the dominant sink for fine-grained sediment introduced into Monterey Bay. The principal sources of the fine sediment are the three rivers that enter Monterey Bay: the San Lorenzo, Pajaro and Salinas rivers. Accumulation rates in the midshelf mudbelt are high relative to documented yields of rivers and cliff erosion, and also are high relative to other documented mud accumulations of the west coast continental shelves. ?? 2002 Elsevier Science B.V. All rights reserved.

Marine Geology↗

USGS1997

Mass-mortality of guillemots ( Uria aalge ) in the Gulf of Alaska in 1993

During the first six months of 1993, about 3500 dead and moribund guillemots ( Uria aalge ) were observed throughout the northern Gulf of Alaska coast ( ca 1800 km range). Mortality peaked during March. Highest numbers were observed in western Prince William Sound and along the south coast of the Kenai Peninsula. Large flocks of live guillemots gathered in nearshore waters, in contrast to most winters when guillemots reside offshore. Most guillemots recovered were extremely emaciated ( ca 60% of normal weight) and sub-adult (80%). Based on carcass deposition and persistence experiments, we calculate that about 10 900 birds eventually came ashore on beaches that were surveyed. Even if most birds killed made it to shore, only a fraction of beaches in the Gulf of Alaska were surveyed and we estimate that a minimum total of 120 000 guillemots died. Results of other investigations on potential causes of mortality (biotoxins, pathogens, parasites, metals, etc.) were either negative or inconclusive, and necropsies lead us to believe that starvation was the proximate cause of death. Reduced food availability could have been related to anomalous sea conditions found during the prolonged 1990–1995 El Niño-Southern Oscillation event.

Alaska↗

USGS2003

A 38,000-year record of floods and debris flows in the Ilo region of southern Peru and its relation to El Niño events and great earthquakes

Previous work throughout the Ilo region of south coastal Peru has documented the existence of flood and debris-flow deposits produced by two El Niño events evidently much more severe than any in recent history. These two events have been dated to ca. AD 1300–1400 and AD 1607–08. The Late Pleistocene to Holocene record of older sedimentary deposits in this region is dominated by flood and debris-flow deposits of similar scale. These older deposits have been described and dated from three coastal, alluvial-fan sites. These deposits, which are as old as 38 200 years, are dominated by massive debris-flow deposits, several tens of cm thick, typically composed of cobble- and boulder-sized clasts in a matrix of silty sand, with characteristics indicating generation by heavy rainfall in an arid environment. Twenty-two radiocarbon dates and a single infrared-stimulated luminescence date show that particularly severe El Niño events occurred throughout the Late Pleistocene and two of three divisions of the Holocene with significantly different frequencies. The period of greatest activity was during the Early Holocene when at least six such events took place during a period of ca. 3600 years, beginning near the end of the Younger Dryas ca. 12 000 years ago. One of these events produced a debris flow that may have caused abandonment of the Paleo-Indian site at Quebrada Tacahuay, one of the oldest on the Andean coast. No severe events took place during the Middle Holocene between ca. 8400 and 5300 years ago, when a wide variety of other paleoclimate proxy records indicate that the El Niño–Southern Oscillation regime was particularly weak. Since ca. 5300 years ago, four of these severe events have taken place. The Late Pleistocene sequence is constrained by only two dates, which indicate that at least ten severe events took place between ca. 38 200 and 12 900 years ago. Mechanisms probably responsible for generating these large-scale deposits include: (1) ‘Mega-Niños’ that produced anomalously heavy rainfall along most or all of the central Andean coast; (2) El Niños that occurred shortly after great earthquakes that produced large amounts of sediment; or (3) El Niños that produced anomalously heavy local rainfall. The existence of these large-scale deposits in the Ilo region implies a level of hazard much higher than indicated by the historical record alone

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS1997

Reinterpretation of the peninsular Florida Oligocene: An integrated stratigraphic approach

A very thick (> 300 m) nearly continuous Oligocene section exists in southern peninsular Florida, as revealed by lithostratigraphic, biostratigraphic (mollusks and dinocysts), chronostratigraphic (Sr isotopes) and petrographic analyses of twelve cores and two quarries. The Oligocene deposits in the subsurface of southern Florida are the thickest documented in the southeastern U.S., and they also may represent the most complete record of Oligocene deposition in this region. No major unconformities within the Oligocene section are detected in the southern portion of the peninsula; hiatuses at the Eocene-Oligocene boundary, the early Oligocene-late Oligocene boundary, and the late Oligocene-Miocene boundary, are of limited duration if they exist at all. No significant disconformity is recognized between the Suwannee Limestone and the Arcadia Formation in southern Florida. However, on the east coast of Florida a hiatus of more than 12 m.y., spanning from at least the middle of the early Oligocene to early Miocene is present. The Suwannee Limestone was deposited during the early Oligocene. The top of the Suwannee Limestone appears to be diachronous across the platform. The 'Suwannee' Limestone, previously identified incorrectly as a late Oligocene unit, is herein documented to be early Oligocene and is encompassed in the lower Oligocene Suwannee Limestone. An unnamed limestone, found on the east coast of the peninsula is, at least in part, correlative with the Suwannee Limestone. The Arcadia Formation, basal Hawthorn Group, accounts for a large portion of the Oligocene deposition in southern Florida, spanning the interval from the middle of the early Oligocene to at least the early Miocene. Comparisons of the depositional patterns, and the distribution of dolomite and phosphate within the Suwannee Limestone and the Arcadia Formation, suggest fluctuating sea levels and that the paleo-Gulf Stream played a role in determining the nature and extent of Oligocene deposition in peninsular Florida.

Florida↗

USGS2000

Characterization and speciation of mercury-bearing mine wastes using X-ray absorption spectroscopy

Mining of mercury deposits located in the California Coast Range has resulted in the release of mercury to the local environment and water supplies. The solubility, transport, and potential bioavailability of mercury are controlled by its chemical speciation, which can be directly determined for samples with total mercury concentrations greater than 100 mg kg-1 (ppm) using X-ray absorption spectroscopy (XAS). This technique has the additional benefits of being non-destructive to the sample, element-specific, relatively sensitive at low concentrations, and requiring minimal sample preparation. In this study, Hg L(III)-edge extended X-ray absorption fine structure (EXAFS) spectra were collected for several mercury mine tailings (calcines) in the California Coast Range. Total mercury concentrations of samples analyzed ranged from 230 to 1060 ppm. Speciation data (mercury phases present and relative abundances) were obtained by comparing the spectra from heterogeneous, roasted (calcined) mine tailings samples with a spectral database of mercury minerals and sorbed mercury complexes. Speciation analyses were also conducted on known mixtures of pure mercury minerals in order to assess the quantitative accuracy of the technique. While some calcine samples were found to consist exclusively of mercuric sulfide, others contain additional, more soluble mercury phases, indicating a greater potential for the release of mercury into solution. Also, a correlation was observed between samples from hot-spring mercury deposits, in which chloride levels are elevated, and the presence of mercury-chloride species as detected by the speciation analysis. The speciation results demonstrate the ability of XAS to identify multiple mercury phases in a heterogeneous sample, with a quantitative accuracy of ??25% for the mercury-containing phases considered. Use of this technique, in conjunction with standard microanalytical techniques such as X-ray diffraction and electron probe microanalysis, is beneficial in the prioritization and remediation of mercury-contaminated mine sites. (C) 2000 Elsevier Science B.V.

Science of the Total Environment↗

USGS2011

Fire in Chile

The mediterranean-type climate (MTC) in Chile (Fig. 6.1) is distributed from La Serena (30° S; Región IV, see Appendix 6.1) in the north to Concepción (37° S; Región X) in the south. It is constrained to the west side of the Andean mountain range, although as the height of this range decreases in the south, a MTC is observed at least as far eastward as Bariloche, Argentina. Although a pattern of winter rains and summer droughts extends northward into the Atacama Desert, this area falls outside our definition of MTC because winter evaporation exceeds rainfall in these areas of extremely low precipitation. The northern border of the MTC region is the transition from desert communities to shrubby matorral, while the southern border corresponds to the point of transition from sclerophyll woodlands to Valdivian evergreen forests (Gajardo 1994; Amigo & Ramirez 1998; Rundel et al . 2007). The landforms of central Chile can be divided into three north–south trending geomorphic zones (Fig. 6.1): the Coastal Cordillera, the Central Valley, and the high Andean Cordillera (Armesto et al . 2007). The Coastal Cordillera rises relatively sharply from the coast, with little extent of coastal terraces, and reaches elevations as high as 2222 m at Cerro Roble and 1880 m at Cerro Campana, which lie between Valparaíso (Región V) on the coast and Santiago (Región Metropolitana) at the base of the Andes. The Central Valley is a structural basin filled to great depth by sediments from the surrounding mountains. North of Santiago, spurs from the Andes extend west across the valley and connect with the Coastal Cordillera, separating individual river basins such as that of the Río Aconcagua (Región V). From Santiago to the south, however, the valley extends uninterrupted for a distance of 900 km to Puerto Montt (Región X), with typical elevations of 400–700 m. The Andean Cordillera marks the eastern boundary of the MTC zone of central Chile. It is the product of complex tectonic activity beginning in the Cretaceous (see Fig. 9.1), but with major uplift in the late Tertiary. Paleobotanical evidence suggests that the central Andes had not attained more than half their current elevation by 10 Ma (Gregory-Wodzicki 2000), but was close to the present height by the end of the Miocene (Reynolds et al . 1990). Elevations reach from 4000 m to nearly 7000 m. To the north of Santiago the Andes are largely composed of metamorphosed sedimentary rock, but a major volcanic zone extends from south of Santiago through the Lake District (Los Lagos Región X).

Book chapter↗

USGS2026

Importance of fish in the diet of Adélie penguins across multiple life stages

Over recent decades, the Adélie penguin ( Pygoscelis adeliae ) population has grown across most of its range, the exception being the northern coast of the western Antarctic Peninsula (WAP). In the Ross Sea, the very large Cape Crozier colony grew to reach ~9% of the global population. Demographic factors driving the Cape Crozier trend have yet to be identified. However, low chick fledging mass - a negative influence in the northern WAP where the diet is mostly less-energy-dense krill - is not showing an effect in the Cape Crozier colony. Previously, we hypothesized that Cape Crozier fledglings, and post-breeding adults, must be finding sufficient higher-quality prey once free of the prey-depleted colony foraging area, with subsequent higher survival. Here we explore penguin diet within and outside the colony foraging area using stable isotope analysis (SIA) of feathers: those grown by post-breeding adults outside the foraging area, prior to moult, compared to those of near-fledged chicks raised on meals obtained within the foraging area. Second, we explore whether a major difference occurs between breeding and post-breeding diet of adults from a small, nearby colony (Cape Royds) that exploits a smaller, little-depleted preyscape. Finally, we compare the results to SIA analyses published by others to explore whether the pre-moult diet of Ross Island adults, mostly foraging within the north-eastern Ross Sea, compares with that of adults nesting in the southern WAP (Bellingshausen Sea coast). At the latter, populations are not decreasing, with diet containing an appreciable contribution of fish. The results confirmed that fish contributed greatly to chick diets at both Ross Island colonies (δ 15 N 10.6–11.4). Once adults were released from central-place foraging, SIA levels (δ 15 N 9.7–12.9) were similar to those of the southern WAP. Foraging on energy-dense fish in coastal Antarctic waters could be one reason Adélie penguins are among the most abundant and therefore most ecologically successful penguin species.

Antarctic Science↗

USGS2010

New technique for quantification of elemental hg in mine wastes and its implications for mercury evasion into the atmosphere

Mercury in the environment is of prime concern to both ecosystem and human health. Determination of the molecular-level speciation of Hg in soils and mine wastes is important for understanding its sequestration, mobility, and availability for methylation. Extended X-ray absorption fine structure (EXAFS) spectroscopy carried out under ambient P-T conditions has been used in a number of past studies to determine Hg speciation in complex mine wastes and associated soils. However, this approach cannot detect elemental (liquid) mercury in Hg-polluted soils and sediments due to the significant structural disorder of liquid Hg at ambient-temperature. A new sample preparation protocol involving slow cooling through the crystallization temperature of Hg(0) (234 K) results in its transformation to crystalline α-Hg(0). The presence and proportion of Hg(0), relative to other crystalline Hg-bearing phases, in samples prepared in this way can be quantified by low-temperature (77 K) EXAFS spectroscopy. Using this approach, we have determined the relative concentrations of liquid Hg(0) in Hg mine wastes from several sites in the California Coast Range and have found that they correlate well with measured fluxes of gaseous Hg released during light and dark exposure of the same samples, with higher evasion ratios from samples containing higher concentrations of liquid Hg(0). Two different linear relationships are observed in plots of the ratio of Hg emission under light and dark conditions vs % Hg(0), corresponding to silica−carbonate- and hot springs-type Hg deposits, with the hot springs-type samples exhibiting higher evasion fluxes than silica−carbonate type samples at similar Hg(0) concentrations. Our findings help explain significant differences in Hg evasion data for different mine sites in the California Coast Range.

Environmental Science & Technology↗

USGS1999

Three-dimensional velocity structure of Siletzia and other accreted terranes in the Cascadia forearc of Washington

Eocene mafic crust with high seismic velocities underlies much of the Oregon and Washington forearc and acts as a backstop for accretion of marine sedimentary rocks from the obliquely subducting Juan de Fuca slab. Arc-parallel migration of relatively strong blocks of this terrane, known as Siletzia, focuses upper crustal deformation along block boundaries, which are potential sources of earthquakes. In a three-dimensional velocity model of coastal Washington, we have combined surface geology, well data, and travel times from earthquakes and controlled source seismic experiments to resolve the major boundaries of the Siletz terrane with the adjacent accreted sedimentary prism and volcanic arc. In southern Washington and northern Oregon the Siletz terrane appears to be a thick block (???20 km) that extends west of the coastline and makes a high-angle contact with the offshore accreted sedimentary prism. On its east flank the high-velocity Siletz terrane boundary coincides with an en echelon zone of seismicity in the arc. In northern Washington the western edge of Siletzia makes a lower-angled, fault-bound contact with the accretionary prism. In addition, alternating, east-west trending uplifts and downwarps of the Siletz terrane centered on the antiformal Olympic Mountains may reflect focusing of north-south compression in the northern part of the Siletz terrane. This compressional strain may result from northward transport and clockwise rotation of the Siletz terrane into the relatively fixed Canadian Coast Mountains restraining bend along the coast.

Oregon, Washington↗

USGS2004

Paleomagnetic correlation of late Holocene earthquakes among estuaries in Washington and Oregon

Paleomagnetic directions of estuarine mud provide additional evidence that individual earthquakes, or rapid series of earthquakes, caused widespread coseismic land-level changes during the past 2000 years in western Washington and Oregon. Most of the paleomagnetic measurements were made on mud dating from the first decades after coseismic subsidence from plate-boundary earthquakes at the Cascadia subduction zone. Mud deposited soon after the A.D. 1700 Cascadia earthquake has similar remanent directions among all five sites ( k = 171) sampled along 80 km of Pacific coast between Grays Harbor and the mouth of the Columbia River. Likewise, internally consistent directions were obtained along this stretch of coast from mud deposited soon after a plate-boundary earthquake (or earthquake series) in A.D. 340–410 and soon after another such event in A.D. 680–720. Also analyzed were remanent magnetizations of mud deposited shortly before (or shortly after) land-level changes from seismicity in the North America plate beneath Puget Sound. A mean direction for sites on the Snohomish River delta, near Everett, from the time of an earthquake on the Seattle fault in A.D. 900–930 is statistically identical (95% confidence level) to a mean direction in mud that was uplifted in A.D. 800–1000 at potentially correlative sites near Tacoma and Olympia. The paleomagnetic direction from Everett for the upper-plate earthquake of A.D. 900–930 differs substantially from that for a plate-boundary earthquake in A.D. 810–1190. This difference implies that the upper-plate earthquake preceded the plate-boundary earthquake by a century or two on the basis of comparisons of their paleomagnetic poles with a previously reconstructed path of geomagnetic paleosecular variation in western North America.

Oregon, Washington↗

USGS2007

Bora event variability and the role of air-sea feedback

A two-way interacting high resolution numerical simulation of the Adriatic Sea using the Navy Coastal Ocean Model (NCOM) and Coupled Ocean/ Atmosphere Mesoscale Prediction System (COAMPS??) was conducted to improve forecast momentum and heat flux fields, and to evaluate surface flux field differences for two consecutive bora events during February 2003. (COAMPS?? is a registered trademark of the Naval Research Laboratory.) The strength, mean positions and extensions of the bora jets, and the atmospheric conditions driving them varied considerably between the two events. Bora 1 had 62% stronger heat flux and 51% larger momentum flux than bora 2. The latter displayed much greater diurnal variability characterized by inertial oscillations and the early morning strengthening of a west Adriatic barrier jet, beneath which a stronger west Adriatic ocean current developed. Elsewhere, surface ocean current differences between the two events were directly related to differences in wind stress curl generated by the position and strength of the individual bora jets. The mean heat flux bias was reduced by 72%, and heat flux RMSE reduced by 30% on average at four instrumented over-water sites in the two-way coupled simulation relative to the uncoupled control. Largest reductions in wind stress were found in the bora jets, while the biggest reductions in heat flux were found along the north and west coasts of the Adriatic. In bora 2, SST gradients impacted the wind stress curl along the north and west coasts, and in bora 1 wind stress curl was sensitive to the Istrian front position and strength. The two-way coupled simulation produced diminished surface current speeds of ???12% over the northern Adriatic during both bora compared with a one-way coupled simulation. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research C: Oceans↗

USGS2011

Eruption of Alaska volcano breaks historic pattern

In the late morning of 12 July 2008, the Alaska Volcano Observatory (AVO) received an unexpected call from the U.S. Coast Guard, reporting an explosive volcanic eruption in the central Aleutians in the vicinity of Okmok volcano, a relatively young (~2000-year-old) caldera. The Coast Guard had received an emergency call requesting assistance from a family living at a cattle ranch on the flanks of the volcano, who reported loud "thunder," lightning, and noontime darkness due to ashfall. AVO staff immediately confirmed the report by observing a strong eruption signal recorded on the Okmok seismic network and the presence of a large dark ash cloud above Okmok in satellite imagery. Within 5 minutes of the call, AVO declared the volcano at aviation code red, signifying that a highly explosive, ash-rich eruption was under way.

Alaska↗

USGS2011

Forecasting hurricane impact on coastal topography: Hurricane Ike

Extreme storms can have a profound impact on coastal topography and thus on ecosystems and human-built structures within coastal regions. For instance, landfalls of several recent major hurricanes have caused significant changes to the U.S. coastline, particularly along the Gulf of Mexico. Some of these hurricanes (e.g., Ivan in 2004, Katrina and Rita in 2005, and Gustav and Ike in 2008) led to shoreline position changes of about 100 meters. Sand dunes, which protect the coast from waves and surge, eroded, losing several meters of elevation in the course of a single storm. Observations during these events raise the question of how storm-related changes affect the future vulnerability of a coast.

Eos, Transactions, American Geophysical Union↗

USGS2011

Complex mean circulation over the inner shelf south of Martha's Vineyard revealed by observations and a high-resolution model

Inner-shelf circulation is governed by the interaction between tides, baroclinic forcing, winds, waves, and frictional losses; the mean circulation ultimately governs exchange between the coast and ocean. In some cases, oscillatory tidal currents interact with bathymetric features to generate a tidally rectified flow. Recent observational and modeling efforts in an overlapping domain centered on the Martha's Vineyard Coastal Observatory (MVCO) provided an opportunity to investigate the spatial and temporal complexity of circulation on the inner shelf. ADCP and surface radar observations revealed a mean circulation pattern that was highly variable in the alongshore and cross-shore directions. Nested modeling incrementally improved representation of the mean circulation as grid resolution increased and indicated tidal rectification as the generation mechanism of a counter-clockwise gyre near the MVCO. The loss of model skill with decreasing resolution is attributed to insufficient representation of the bathymetric gradients (Δh/h), which is important for representing nonlinear interactions between currents and bathymetry. The modeled momentum balance was characterized by large spatial variability of the pressure gradient and horizontal advection terms over short distances, suggesting that observed inner-shelf momentum balances may be confounded. Given the available observational and modeling data, this work defines the spatially variable mean circulation and its formation mechanism—tidal rectification—and illustrates the importance of model resolution for resolving circulation and constituent exchange near the coast. The results of this study have implications for future observational and modeling studies near the MVCO and other inner-shelf locations with alongshore bathymetric variability.

Massachusetts↗

USGS2018

Neotectonics of the Big Sur Bend, San Gregorio‐Hosgri fault system, central California

The right‐lateral San Gregorio‐Hosgri fault system (SGHF) extends mainly offshore for about 400 km along the central California coast and is a major structure in the distributed transform margin of western North America. We mapped a poorly known 64‐km‐long section of the SGHF offshore Big Sur between Piedras Blancas and Point Sur using high‐resolution bathymetry, seismic reflection, and marine magnetic data. In this region, the SGHF is characterized by multiple strands, step overs, scarps and lineaments, shutter ridges, deflected drainages, and other geomorphic features consistent with strike‐slip faulting. Analysis of offset shelfbreak gullies suggest a lateral slip rate of about 3.35 mm/year. Vertical slip rates range as high as 0.8 to 1.2 mm/year. Lateral slip combined with high vertical slip rates result in a northwest decrease in shelf width, a northward increase in shelf and upper slope gradient, and progressive incision of submarine canyon heads. The SGHF between Point Sur and Piedras Blancas trends ~321° and forms a 105‐km‐long transpressive bend (the Big Sur Bend ) between more north trending transtensional fault sections to the south (120 km long, ~336° trend) and north (180 km long, ~337° trend). This transpressional bend and SGHF splay faults have had a significant role in shaping the modern geomorphology of the central California coast, controlling or influencing the locations of mountainous uplifts, large coastal headlands, embayments, and rivers.

California↗

USGS2020

Tidal wetland gross primary production across the continental United States, 2000–2019

We mapped tidal wetland gross primary production (GPP) with unprecedented detail for multiple wetland types across the continental United States (CONUS) at 16‐day intervals for the years 2000–2019. To accomplish this task, we developed the spatially explicit Blue Carbon (BC) model, which combined tidal wetland cover and field‐based eddy covariance tower data into a single Bayesian framework, and used a super computer network and remote sensing imagery (Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index). We found a strong fit between the BC model and eddy covariance data from 10 different towers ( r 2 = 0.83, p < 0.001, root‐mean‐square error = 1.22 g C/m 2 /day, average error was 7% with a mean bias of nearly zero). When compared with NASA's MOD17 GPP product, which uses a generalized terrestrial algorithm, the BC model reduced error by approximately half (MOD17 had r 2 = 0.45, p < 0.001, root‐mean‐square error of 3.38 g C/m 2 /day, average error of 15%). The BC model also included mixed pixels in areas not covered by MOD17, which comprised approximately 16.8% of CONUS tidal wetland GPP. Results showed that across CONUS between 2000 and 2019, the average daily GPP per m 2 was 4.32 ± 2.45 g C/m 2 /day. The total annual GPP for the CONUS was 39.65 ± 0.89 Tg C/year. GPP for the Gulf Coast was nearly double that of the Atlantic and Pacific Coasts combined. Louisiana alone accounted for 15.78 ± 0.75 Tg C/year, with its Atchafalaya/Vermillion Bay basin at 4.72 ± 0.14 Tg C/year. The BC model provides a robust platform for integrating data from disparate sources and exploring regional trends in GPP across tidal wetlands.

Global Biogeochemical Cycles↗

USGS2024

Incorporating intensity distance attenuation into PLUM ground-motion-based earthquake early warning in the United States: The APPLES configuration

We develop Attenuated ProPagation of Local Earthquake Shaking (APPLES), a new configuration for the United States West Coast version of the Propagation of Local Undamped Motion (PLUM) earthquake early warning (EEW) algorithm that incorporates attenuation into its ground-motion prediction procedures. Under APPLES, instead of using a fixed radius to forward-predict observed peak ground shaking to the area surrounding a seismic station, the forward-predicted intensity at a location depends on the distance from the station using an intensity prediction relationship. We conduct conceptual tests of maximum intensity distribution predictions in APPLES and PLUM using a catalog of ShakeMaps to confirm that the attenuation relationship in APPLES is appropriately modeling shaking distributions for West Coast earthquakes. Then, we run APPLES and PLUM in simulated real-time tests to determine warning time performance. Finally, we compare real-time alert behavior during the 2022 M 6.4 Ferndale, California, earthquake and other recent events. We find that APPLES presents two potential improvements to PLUM by reducing over-alerting during smaller magnitude earthquakes and by increasing warning times in some locations during larger earthquakes. APPLES can produce missed and late alerts in locations that experience shaking intensities close to the level used to issue alerts, so preferred alerting strategies with APPLES would use alert thresholds that are lower than the intensities targeted for EEW alerts. We find alerts using APPLES are also similar to those for the source-based approaches currently used in the ShakeAlert EEW system, which will make APPLES easier to integrate into the system.

California, Oregon, Washington↗