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USGS2013

Working with strainmeter data

The Plate Boundary Observatory (PBO), the geodetic component of the U.S. National Science Foundation–funded Earthscope program, includes 75 borehole and 6 laser strainmeters ( http://pbo.unavco.org ). The strainmeters are installed at several locations: on the Cascadia forearc in Washington state and on Vancouver Island, Canada; in arrays of two to nine instruments along the North American–Pacific plate boundary in California; at Mount St. Helens; and in Yellowstone National Park. For deformation signals seconds to weeks in duration, strainmeters have a resolution and a signal-to-noise ratio superior to those of seismometers and GPS. However, this high sensitivity can introduce nontectonic signals into strain data, presenting data interpretation challenges, especially for borehole strainmeters.

Eos, Earth and Space Science News↗

USGS2014

Science is the first step to siting nuclear waste repositories

As Shaw [2014] notes, U.S. research on shale as a repository host was halted before expending anything close to the effort devoted to studying crystalline rock, salt, and - most notably - tuff at Yucca Mountain. The new political reality regarding Yucca Mountain may allow reconsideration of the decision to abandon research on shale as a repository host.

Eos, Earth and Space Science News↗

USGS2014

Geophysical advances triggered by 1964 Great Alaska Earthquake

A little more than 50 years ago, on 27 March 1964, the Great Alaska earthquake and tsunami struck. At moment magnitude 9.2, this earthquake is notable as the largest in U.S. written history and as the second-largest ever recorded by instruments worldwide. But what resonates today are its impacts on the understanding of plate tectonics, tsunami generation, and earthquake history as well as on the development of national programs to reduce risk from earthquakes and tsunamis.

Alaska↗

USGS2014

Magnetic storms and induction hazards

Magnetic storms are potentially hazardous to the activities and technological infrastructure of modern civilization. This reality was dramatically demonstrated during the great magnetic storm of March 1989, when surface geoelectric fields, produced by the interaction of the time-varying geomagnetic field with the Earth's electrically conducting interior, coupled onto the overlying Hydro-Québec electric power grid in Canada. Protective relays were tripped, the grid collapsed, and about 9 million people were temporarily left without electricity [ Bolduc , 2002].

Eos, Earth and Space Science News↗

USGS2014

Elders recall an earlier tsunami on Indian Ocean shores

Ten years on, the Indian Ocean tsunami of 26 December 2004 still looms large in efforts to reduce coastal risk. The disaster has spurred worldwide advances in tsunami detection and warning, tsunami-risk assessment, and tsunami awareness [Satake, 2014]. Nearly a lifetime has passed since the northwestern Indian Ocean last produced a devastating tsunami. Documentation of this tsunami, in November 1945, was hindered by international instability in the wake of the Second World War and, in British India, by the approach of independence and partition. The parent earthquake, of magnitude 8.1, was widely recorded, and the tsunami registered on tide gauges, but intelligence reports and newspaper articles say little about inundation limits while permitting a broad range of catalogued death tolls. What has been established about the 1945 tsunami falls short of what's needed today for ground-truthing inundation models, estimating risk to enlarged populations, and anchoring awareness campaigns in local facts. Recent efforts to reduce coastal risk around the Arabian Sea include a project in which eyewitnesses to the 1945 tsunami were found and interviewed (Fig. 1), and related archives were gathered. Results are being made available through UNESCO's Indian Ocean Tsunami Information Center in hopes of increasing scientific understanding and public awareness of the region's tsunami hazards.

Eos, Earth and Space Science News↗

USGS2015

Variability and trends in global drought

Monthly precipitation ( P ) and potential evapotranspiration (PET) from the CRUTS3.1 data set are used to compute monthly P minus PET (PMPE) for the land areas of the globe. The percent of the global land area with annual sums of PMPE less than zero are used as an index of global drought (%drought) for 1901 through 2009. Results indicate that for the past century %drought has not changed, even though global PET and temperature ( T ) have increased. Although annual global PET and T have increased, annual global P also has increased and has mitigated the effects of increased PET on %drought.

Earth and Space Science↗

USGS2016

GOES-derived fog and low cloud indices for coastal north and central California ecological analyses

Fog and low cloud cover (FLCC) changes the water, energy, and nutrient flux of coastal ecosystems. Easy-to-use FLCC data are needed to quantify the impacts of FLC on ecosystem dynamics during hot, dry Mediterranean climate summers. FLCC indices were generated from 26,000 hourly night and day FLCC maps derived from Geostationary Environmental Operational Satellite (GOES) data for June, July, August, and September, 1999- 2009 for coastal California, latitude 34.50°N, south of Monterey Bay, to latitude 41.95°N, north of Crescent City. Monthly FLCC average hours per day (h/d) range from < 2 to 18. Average FLCC over the ocean increases from north (9 h/d) to south (14 h/d) whereas FLCC over land is reversed. Over land, FLCC is highest where land juts into the prevailing NW winds and is lowest in the lee of major capes. FLCC advects furthest inland through low-lying NW ocean-facing valleys. At night hours of FLCC is higher more frequently on land than over the ocean. Interannual FLCC coefficient of variation shows long term geographic stability strongly associated with landform position. Contours delineating homogeneous zones of FLCC, derived from average decadal h/d FLCC, provide data to refine the commonly used term ‘fog belt.’ FLCC indices are available for download from the California Landscape Conservation Cooperative Climate Commons website. FLCC indices can be used to improve analyses of biogeographic and bioclimatic species distribution models, meteorological mechanisms driving FLCC patterns, ecohydrological investigations of evapotranspiration, solar energy feasibility studies, agricultural irrigation demand and viticultural ripening models.

Earth and Space Science↗

USGS2017

Downscaling wind and wavefields for 21st century coastal flood hazard projections in a region of complex terrain

While global climate models (GCMs) provide useful projections of near-surface wind vectors into the 21st century, resolution is not sufficient enough for use in regional wave modeling. Statistically downscaled GCM projections from Multivariate Adaptive Constructed Analogues provide daily averaged near-surface winds at an appropriate spatial resolution for wave modeling within the orographically complex region of San Francisco Bay, but greater resolution in time is needed to capture the peak of storm events. Short-duration high wind speeds, on the order of hours, are usually excluded in statistically downscaled climate models and are of key importance in wave and subsequent coastal flood modeling. Here we present a temporal downscaling approach, similar to constructed analogues, for near-surface winds suitable for use in local wave models and evaluate changes in wind and wave conditions for the 21st century. Reconstructed hindcast winds (1975–2004) recreate important extreme wind values within San Francisco Bay. A computationally efficient method for simulating wave heights over long time periods was used to screen for extreme events. Wave hindcasts show resultant maximum wave heights of 2.2 m possible within the Bay. Changes in extreme over-water wind speeds suggest contrasting trends within the different regions of San Francisco Bay, but 21th century projections show little change in the overall magnitude of extreme winds and locally generated waves.

California↗

USGS2017

The Mars Science Laboratory Curiosity rover Mastcam instruments: Preflight and in-flight calibration, validation, and data archiving

The NASA Curiosity rover Mast Camera (Mastcam) system is a pair of fixed-focal length, multispectral, color CCD imagers mounted ~2 m above the surface on the rover's remote sensing mast, along with associated electronics and an onboard calibration target. The left Mastcam (M-34) has a 34 mm focal length, an instantaneous field of view (IFOV) of 0.22 mrad, and a FOV of 20° × 15° over the full 1648 × 1200 pixel span of its Kodak KAI-2020 CCD. The right Mastcam (M-100) has a 100 mm focal length, an IFOV of 0.074 mrad, and a FOV of 6.8° × 5.1° using the same detector. The cameras are separated by 24.2 cm on the mast, allowing stereo images to be obtained at the resolution of the M-34 camera. Each camera has an eight-position filter wheel, enabling it to take Bayer pattern red, green, and blue (RGB) “true color” images, multispectral images in nine additional bands spanning ~400–1100 nm, and images of the Sun in two colors through neutral density-coated filters. An associated Digital Electronics Assembly provides command and data interfaces to the rover, 8 Gb of image storage per camera, 11 bit to 8 bit companding, JPEG compression, and acquisition of high-definition video. Here we describe the preflight and in-flight calibration of Mastcam images, the ways that they are being archived in the NASA Planetary Data System, and the ways that calibration refinements are being developed as the investigation progresses on Mars. We also provide some examples of data sets and analyses that help to validate the accuracy and precision of the calibration.

Earth and Space Science↗

USGS2020

Sphalerite oxidation in seawater with covellite: Implications for seafloor massive sulfide deposits and mine waste

Metal sulfide minerals exist in several marine environments and are in thermodynamic disequilibrium with oxygenated seawater from the time of their formation. Oxidation is both ubiquitous and heterogeneous, as observational and experimental evidence demonstrates that sulfide minerals may oxidize completely on decadal timescales (hydrothermal plumes) or incompletely in billions of years (mineral deposits); however, the processes, rates, and interactions among minerals as oxidative dissolution occurs are not well understood. Added impetus to understanding these processes exists due to the potential for mining of seafloor massive sulfide deposits and potential environmental impacts of that activity. Here, we present a laboratory-based experimental study on the galvanic oxidation of sphalerite and synthesized zinc sulfide and coupled to covellite. We find that, in contrast to single-mineral reactions, coupled mineral reactions are at least 2 orders of magnitude more rapid, light independent, and have a lower apparent activation energy for oxidation. These results begin to provide insight into observed differences between laboratory and environmentally observed oxidation rates and are a step in the direction of more accurately predicting environmental rates as well as any changes to those rates from anthropogenic disturbances.

ACS Earth and Space Chemistry↗

USGS2021

Isotope fractionation from In Vivo methylmercury detoxification in waterbirds

The robust application of stable mercury (Hg) isotopes for mercury source apportionment and risk assessment necessitates the understanding of mass-dependent fractionation (MDF) due to internal transformations within organisms. Here, we used high energy-resolution XANES spectroscopy and isotope ratios of total mercury (δ202THg) and methylmercury (δ202MeHg) to elucidate the chemical speciation of Hg and the resultant MDF due to internal MeHg demethylation in waterbirds. In three waterbirds (Clark’s grebe, Forster’s tern, south polar skua), between 17-86% of the MeHg was demethylated to inorganic mercury (iHg) species primarily in the liver and kidneys as Hg-tetraselenolate (Hg(Sec)4) and minor Hg-dithiolate (Hg(SR)2) complexes. Tissular differences between δ202THg and δ202MeHg correlated linearly with %iHg (Hg(Sec)4 + Hg(SR)2), and were interpreted to reflect a kinetic isotope effect during in vivo MeHg demethylation. The product-reactant isotopic enrichment factor (εp/r) for the demethylation of MeHg  Hg(Sec)4 was −2.2 ± 0.1‰. δ202MeHg values were unvarying within each bird regardless of Hg(Sec)4 abundance, indicating fast internal cycling or replenishment of MeHg relative to demethylation. Our findings document a universal selenium-dependent demethylation reaction in birds, provide new insights on the internal transformations and cycling of MeHg and Hg(Sec)4, and allow for mathematical correction of δ202THg values due to the MeHg  Hg(Sec)4 reaction.

ACS Earth and Space Chemistry↗

USGS2022

Crystal chemistry of thallium in marine ferromanganese deposits

Our understanding of the up to 7 orders of magnitude partitioning of thallium (Tl) between seawater and ferromanganese (FeMn) deposits rests upon two foundations: (1) being able to quantify the Tl(I)/Tl(III) ratio that reflects the extent of the oxidative scavenging of Tl by vernadite (δ-MnO 2 ), the principle manganate mineral in oxic and suboxic environments, and (2) being able to determine the sorption sites and bonding environments of the Tl(I) and Tl(III) complexes on vernadite. We investigated these foundations by determining the oxidation state and chemical form of Tl in FeMn crusts and nodules from the global oceans at a Tl concentration ranging from several hundred ppm (mg/kg) down to the low ppm level. Seventeen hydrogenetic crusts and eleven nodules from the Pacific, Atlantic, Arctic, and Indian Oceans and Baltic Sea were characterized by chemical analysis, X-ray diffraction, Raman spectroscopy, Mn K-edge X-ray absorption near-edge structure (XANES) spectroscopy, Tl L 3 -edge high energy-resolution XANES (HR-XANES) spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The Tl concentration increases linearly from 1.5 to 319 ppm with the Mn/Fe ratio in Fe-vernadite from hydrogenetic crusts, whereas the percentage of Tl(III) to total Tl varies between 62 and 100% independent of both the Mn/Fe and Mn(III)/Mn(IV) ratios. The data, complemented by molecular modeling of the Tl(III) coordination and by XANES calculations, suggest that the enrichment of Tl in Fe-vernadite is driven by (1) the oxidative uptake of octahedrally coordinated Tl(III) above the vacant Mn(IV) sites and on the layer edges of the vernadite layers, and (2) the sorption of Tl(I) on the crystallographic site of Ba at the surface of the vernadite layers, which is an analogue to the surface site of K. Thus, Tl has a high affinity for vernadite regardless of its oxidation state, and the lack of correlation between Tl(III) and the Mn/Fe ratio in FeMn crusts is explained by the affinity of Tl(I) for the Ba site. The Tl concentration varies between 2 and 112 ppm in surface and buried nodules independent of the Mn/Fe ratio, and the percentage of Tl(III) varies between 0 and 100%. Nodules subjected to sediment diagenesis with replacement of layered vernadite by tunneled todorokite are depleted in Tl and have more reduced thallium. Knowledge of the complex interplay of mineralogy, surface chemical processes, and crystallographic siting is required to understand the variability of Tl concentrations, redox state, and acquisition processes by marine FeMn deposits.

ACS Earth and Space Chemistry↗

USGS2023

Attenuation of barium, strontium, cobalt, and nickel plumes formed during microbial iron-reduction in a crude-oil-contaminated aquifer

We assessed the spatial distribution of 35 elements in aquifer sediments and groundwater of a crude-oil-contaminated aquifer and show evidence of the dissolution of barium (Ba), strontium (Sr), cobalt (Co), and nickel (Ni) during hydrocarbon oxidation coupled to historic microbial Fe(III)-reduction near the oil. Trace element plumes occur in the crude-oil-contaminated aquifer, where 50% Co, 47% Ni, 24% Ba, and 15% Sr have been mobilized from the sediment near the oil into groundwater, resulting in dissolved masses >33, 18, three, and two times greater than estimated dissolved masses prior to contamination, respectively. Ba 2+ and Ni 2+ concentrations exceeded the World Health Organization’s drinking-water guidelines of 700 and 20 μg/L, respectively. Sediments attenuate trace element plumes in two geochemically distinct zones, resulting in <0.01% total trace element masses dissolved in groundwater, despite the substantial mobilization near the oil body. Geochemical modeling of the modern Fe(III)-reducing zone suggests trace elements are likely attenuated via coprecipitation with/without sorption on iron carbonate precipitates. In the suboxic transition zone at the leading edge of the plume, Fe(III)-hydroxides sorb Ba 2+ , Sr 2+ , Co 2+ , and Ni 2+ . This study emphasizes that slow but persistent biogeochemical activity can substantially alter aquifer chemistry over decadal timeframes, a phenomenon we term biogeochemical gradualism.

Minnesota↗

USGS2023

Competition between dissolved organic matter and freshwater plankton control methylmercury isotope fractionation during uptake and photochemical demethylation

Isotope fractionation related to photochemical reactions and planktonic uptake at the base of the food web is a major uncertainty in the biological application of mercury (Hg) stable isotopes. In freshwater systems, it is unclear how competitive interactions among methylmercury (MeHg), dissolved organic matter (DOM), and phytoplankton govern the magnitude of mass-dependent and mass-independent fractionation. This study investigated how DOM alters rates of planktonic MeHg uptake and photodegradation and corresponding Hg isotope fractionation in the presence of freshwater phytoplankton species, Raphidocelis subcapitata . Outdoor sunlight exposure experiments utilizing R. subcapitata were performed in the presence of different DOM samples using environmentally relevant ratios of MeHg-DOM thiol groups. The extent of Δ 199 Hg in phytoplankton incubations (2.99‰ St. Louis River HPOA, 1.88‰ Lake Erie HPOA) was lower compared to paired abiotic control experiments (4.29 and 2.86‰, respectively) after ∼30 h of irradiation, resulting from cell shading or other limiting factors reducing the extent of photodemethylation. Although the Δ 199 Hg/Δ 201 Hg ratio was uniform across experiments (∼1.4), Δ 199 Hg/δ 202 Hg slopes varied dramatically (from −0.96 to 15.4) across incubations with R. subcapitata and DOM. In addition, no evidence of Hg isotope fractionation was observed within R. subcapitata cells. This study provides a refined examination of Hg isotope fractionation markers for key processes occurring in the lower food web prior to bioaccumulation, critical for accurately accounting for the photochemical processing of Hg isotopes across a wide spectrum of freshwater systems.

ACS Earth and Space Chemistry↗

USGS2024

Methane clumped isotopologue variability from ebullition in a mid-latitude lake

Methane is a greenhouse gas and is an important component of carbon cycling in freshwater environments. Isotope ratios of methane ( 13 C/ 12 C and D/H) are used extensively as tracers to identify methane sources. Recent advances in the measurement of clumped methane isotopologues ( 13 CH 3 D, 12 CH 2 D 2 ) offer new opportunities to constrain sources and sinks of atmospheric methane. Previous measurements of clumped methane isotopologues from freshwater environments have been spatially and temporally limited. The abundance of 13 CH 3 D and methane flux from ebullition in the deep basin of Upper Mystic Lake were measured from May to November 2021 to characterize the source isotopologue signatures and methane fluxes for mid-latitude lakes. The trends in δ 13 C and δD values support decreased methane oxidation in the early summer compared to fall. The Δ 13 CH 3 D values from this study range from 2.0 to 4.2‰, reflecting methane oxidation occurring anaerobically in lake sediments and euxinic bottom waters at sample sites. The relatively large variation in the Δ 13 CH 3 D values observed within this lake basin aligns with previous observations of bubbles from arctic lakes. The values of Δ 13 CH 3 D do not correlate with methane flux, suggesting that Δ 13 CH 3 D measurements from background ebullition are not sensitive as a proxy for ebullition rates. This study presents a uniquely large ( n = 40) set of freshwater Δ 13 CH 3 D values from a single lake basin, which we use to recommend a sampling strategy of ≥9 samples to constrain the Δ 13 CH 3 D source signal within ∼0.5‰ from similar environments. This data demonstrates the utility of clumped methane isotopologues to gain insights into local biogeochemical processes from field studies and points to the challenge of using clumped isotopologue measurements to constrain global freshwater–methane sources to the atmosphere.

ACS Earth and Space Chemistry↗

USGS2024

Simulated sea level rise in coastal peat oils stimulates mercury methylation

Coastal wetlands are vulnerable to sea level rise with unknown consequences for mercury (Hg) cycling, particularly the potential for exacerbating neurotoxic methylmercury (MeHg) production and bioaccumulation in food webs. Here, the effect of sea level rise on MeHg formation in the Florida Everglades was evaluated by incubating peat cores from a freshwater wetland for 0–20 days in the laboratory at five salinity conditions (0.16–6.0 parts-per-thousand; 0.20–454 mg L –1 sulfate (SO 4 2– )) to simulate the onset of sea level rise within coastal margins. Isotopically enriched inorganic mercury ( 201 Hg(II)) was used to track MeHg formation and peat-porewater partitioning. In all five salinity treatments, porewaters became anoxic within 1 day and became progressively enriched in dissolved organic matter (DOM) of greater aromatic composition over the 20 days compared to ambient conditions. In the four highest salinity treatments, SO 4 2– concentrations decreased and sulfide concentrations increased over time due to microbial dissimilatory SO 4 2– reduction that was concurrent with 201 Hg(II) methylation. Importantly, elevated salinity resulted in a greater proportion of produced Me 201 Hg observed in porewaters as opposed to bound to peat, interpreted to be due to the complexation of MeHg with aromatic DOM released from peat. The findings highlight the potential for enhanced production and mobilization of MeHg in coastal wetlands of the Florida Everglades due to the onset of saltwater intrusion.

Florida↗

USGS2025

Isotopic compositions of modern seawater at the Mariana and Yap trenches

The isotopic composition of ocean water is crucial in studying water masses and mixing in deep oceans, isotope mass balance in ocean water regulated by high-temperature and low-temperature hydrothermal alterations, and the exchange of water among crust-ocean-mantle reservoirs. We collected 40 water samples from Challenger Deep and the water column above at the Mariana Trench (down to 10,923 m) and 12 from the Yap Trench (down to 6,300 m) in the western Pacific Ocean in three hadal cruises from 2016 to 2018. The δ 2 H values at the Mariana and Yap Trenches average 0.1 ± 0.2 ‰ (1σ error). The δ 2 H records from this study, together with existing databases, manifest that deep waters have δ 2 H values varying between −2 and +2 ‰ (except for the Weddell Sea, the Greenland, Iceland, and Norwegian Seas, and the Mediterranean Sea), with increasing values from the Southern Ocean to the Pacific and Indian Oceans, and to the Atlantic Ocean. The average δ 18 O value of water samples from both trenches is –0.04 ± 0.03 ‰ (1σ error). The correlation between δ 18 O and salinity distinguishes abyssal water masses at the study region, UCDW (Upper Circumpolar Deep Water) and LCDW (Lower Circumpolar Deep Water). These water samples from the Mariana and Yap Trenches gave an average 17 O excess value of −6 ± 1 ppm (1σ error). Our 52 data records of 17 O excess expand the 38 existing records for the deep ocean. Both δ 2 H and 17 O excess of modern ocean have rolled as anchor points to reconstruct compositions of Earth’s early ocean.

ACS Earth and Space Chemistry↗

USGS2017

How could a freshwater swamp produce a chemical signature characteristic of a saltmarsh?

Reduction–oxidation (redox) reaction conditions, which are of great importance for the soil chemistry of coastal marshes, can be temporally dynamic. We present a transect of cores from northwest Florida wherein radical postdepositional changes in the redox regime has created atypical geochemical profiles at the bottom of the sedimentary column. The stratigraphy is consistent along the transect, consisting of, from the bottom upward, carbonate bedrock, a gray clay, an organic mud section, a dense clay layer, and an upper organic mud unit representing the current saltwater marsh. However, the geochemical signature of the lower organic mud unit suggests pervasive redox reactions, although the interval has been identified as representing a freshwater marsh, an unlikely environment for such conditions. Analyses indicate that this discrepancy results from postdepositional diagenesis driven by millennial-scale environmental parameters. Rising sea level that led to the deposition of the capping clay layer, created anaerobic conditions in the freshwater swamp interval, and isolated it hydrologically from the rest of the sediment column. The subsequent infiltration of marine water into this organic material led to sulfate reduction, the buildup of H 2 S and FeS, and anoxic conditions. Continued sulfidation eventually resulted in euxinic conditions, as evidenced by elevated levels of Fe, S, and especially Mo, the diagnostic marker of euxinia. Because this chemical transformation occurred long after the original deposition the geochemical signature does not reflect soil chemistry at the time of deposition and cannot be used to infer syn-depositional environmental conditions, emphasizing the importance of recognizing diagenetic processes in paleoenvironmental studies.

Florida↗