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USGS2016

Long period seismicity and very long period infrasound driven by shallow magmatic degassing at Mount Pagan, Mariana Islands

Long period (LP) seismicity and very long period infrasound (iVLP) were recorded during continuous degassing from Mount Pagan, Mariana Islands, in July 2013 to January 2014. The frequency content of the LP and iVLP events and delay times between the two arrivals were remarkably stable and indicate nearly co-located sources. Using phase-weighted stacking over similar events to dampen noise, we find that the LP source centroid is located 60 m below and 180 m west of the summit vent. The moment tensor reveals a volumetric source modeled as resonance of a subhorizontal sill intersecting a dike. We model the seismoacoustic wavefields with a coupled earth-air 3-D finite difference code. The ratios of pressure to velocity measured at the infrasound arrays are an order of magnitude larger than the synthetic ratios, so the iVLP is not the result of LP energy transmitting into the atmosphere at its epicenter. Based on crater shape and dimensions determined by structure from motion, we model the iVLP as acoustic resonance of an exponential horn. The source of the continuous plume from gas analysis is shallow magmatic degassing, which repeatedly pressurized the dike-sill portion of the conduit over the 7 months of observation. Periodic gas release caused the geologically controlled sill to partially collapse and resonate, while venting of gas at the surface triggered resonance in the crater. LP degassing only accounts for ~12% of total degassing, indicating that most degassing is relatively aseismic and that multiple active pathways exist beneath the vent.

Mount Pagan↗

USGS2008

Columbia Hills, Mars: aeolian features seen from the ground and orbit

Abundant wind-related features occur along Spirit's traverse into the Columbia Hills over the basaltic plains of Gusev Crater. Most of the windblown sands are probably derived from weathering of rocks within the crater, and possibly from deposits associated with Ma'adim Vallis. Windblown particles act as agents of abrasion, forming ventifacts, and are organized in places into various bed forms. Wind-related features seen from orbit, results from atmospheric models, and considerations of topography suggest that the general wind patterns and transport pathways involve: (1) winter nighttime winds that carry sediments from the mouth of Ma'adim Vallis into the landing site area of Spirit, where they are mixed with locally derived sediments, and (2) winter daytime winds that transport the sediments from the landing site southeast toward Husband Hill; similar patterns occur in the summer but with weaker winds. Reversals of daytime flow out of Gusev Crater and nighttime wind flow into the crater can account for the symmetry of the bed forms and bimodal orientations of some ventifacts.

Journal of Geophysical Research E: Planets↗

USGS2022

New craters on Mars: An updated catalog

We present a catalog of new impacts on Mars. These craters formed in the last few decades, constrained with repeat orbital imaging. Crater diameters range from 58 m down to <1 m. For each impact, we report whether it formed a single crater or a cluster (58% clusters); albedo features of the blast zone (88% halos; 64% linear rays; 10% arcuate rays; majority dark-toned; 4% light-toned; 14% dual-toned); and exposures of ice (4% definite; 2% possible). We find no trends in the occurrences of clusters with latitude, elevation, or impact size. Albedo features do not depend on atmospheric fragmentation. Halos are more prevalent at lower elevations, indicating an atmospheric pressure dependence; and around smaller impacts, which could be an observational bias. Linear rays are more likely to form from larger impacts into more consolidated material and may be enhanced by lower atmospheric pressure at higher elevations. Light- and dual-toned blast zones occur in specific regions and more commonly around larger impacts, indicating excavation of compositionally distinct material. Surfaces covered with bright dust lacking cohesion are favored to form detectable surface features. The slope of the cumulative size frequency distribution for this data set is 2.2 for diameters >8 m (differential slope 2.9), significantly shallower than the slope of new lunar craters. We believe that no systematic biases exist in the Martian data set sufficient to explain the discrepancy. This catalog is complete at the time of writing, although observational biases exist, and new discoveries continue.

Journal of Geophysical Research E: Planets↗

USGS2006

Overview of the Spirit Mars Exploration Rover mission to Gusev Crater: Landing site to Backstay Rock in the Columbia Hills

Spirit landed on the floor of Gusev Crater and conducted initial operations on soil‐covered, rock‐strewn cratered plains underlain by olivine‐bearing basalts. Plains surface rocks are covered by wind‐blown dust and show evidence for surface enrichment of soluble species as vein and void‐filling materials and coatings. The surface enrichment is the result of a minor amount of transport and deposition by aqueous processes. Layered granular deposits were discovered in the Columbia Hills, with outcrops that tend to dip conformably with the topography. The granular rocks are interpreted to be volcanic ash and/or impact ejecta deposits that have been modified by aqueous fluids during and/or after emplacement. Soils consist of basaltic deposits that are weakly cohesive, relatively poorly sorted, and covered by a veneer of wind‐blown dust. The soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover. Mobilization of soluble species has occurred within at least two soil deposits examined. The presence of monolayers of coarse sand on wind‐blown bedforms, together with even spacing of granule‐sized surface clasts, suggests that some of the soil surfaces encountered by Spirit have not been modified by wind for some time. On the other hand, dust deposits on the surface and rover deck have changed during the course of the mission. Detection of dust devils, monitoring of the dust opacity and lower boundary layer, and coordinated experiments with orbiters provided new insights into atmosphere‐surface dynamics.

Journal of Geophysical Research E: Planets↗

USGS2016

Variation of energy and carbon fluxes from a restored temperate freshwater wetland and implications for carbon market verification protocols

Temperate freshwater wetlands are among the most productive terrestrial ecosystems, stimulating interest in using restored wetlands as biological carbon sequestration projects for greenhouse gas reduction programs. In this study, we used the eddy covariance technique to measure surface energy carbon fluxes from a constructed, impounded freshwater wetland during two annual periods that were 8 years apart: 2002–2003 and 2010–2011. During 2010–2011, we measured methane (CH 4 ) fluxes to quantify the annual atmospheric carbon mass balance and its concomitant influence on global warming potential (GWP). Peak growing season fluxes of latent heat and carbon dioxide (CO 2 ) were greater in 2002–2003 compared to 2010–2011. In 2002, the daily net ecosystem exchange reached as low as −10.6 g C m −2  d −1 , which was greater than 3 times the magnitude observed in 2010 (−2.9 g C m −2  d −1 ). CH 4 fluxes during 2010–2011 were positive throughout the year and followed a strong seasonal pattern, ranging from 38.1 mg C m −2  d −1 in the winter to 375.9 mg C m −2  d −1 during the summer. The results of this study suggest that the wetland had reduced gross ecosystem productivity in 2010–2011, likely due to the increase in dead plant biomass (standing litter) that inhibited the generation of new vegetation growth. In 2010–2011, there was a net positive GWP (675.3 g C m −2  yr −1 ), and when these values are evaluated as a sustained flux, the wetland will not reach radiative balance even after 500 years.

California↗

USGS2001

Mars Global Surveyor Thermal Emission Spectrometer experiment: Investigation description and surface science results

The Thermal Emission Spectrometer (TES) investigation on Mars Global Surveyor (MGS) is aimed at determining (1) the composition of surface minerals, rocks, and ices; (2) the temperature and dynamics of the atmosphere; (3) the properties of the atmospheric aerosols and clouds; (4) the nature of the polar regions; and (5) the thermophysical properties of the surface materials. These objectives are met using an infrared (5.8- to 50-μm) interferometric spectrometer, along with broadband thermal (5.1- to 150-μm) and visible/near-IR (0.3- to 2.9-μm) radiometers. The MGS TES instrument weighs 14.47 kg, consumes 10.6 W when operating, and is 23.6×35.5×40.0 cm in size. The TES data are calibrated to a 1-σ precision of 2.5 −6 ×10 −8 W cm −2 sr −1 /cm −1 , 1.6×10 −6 W cm −2 sr −1 , and ∼0.5 K in the spectrometer, visible/near-IR bolometer, and IR bolometer, respectively. These instrument subsections are calibrated to an absolute accuracy of ∼4×10 −8 W cm −2 sr −1 /cm −1 (0.5 K at 280 K), 1–2%, and ∼1–2 K, respectively. Global mapping of surface mineralogy at a spatial resolution of 3 km has shown the following: (1) The mineralogic composition of dark regions varies from basaltic, primarily plagioclase feldspar and clinopyroxene, in the ancient, southern highlands to andesitic, dominated by plagioclase feldspar and volcanic glass, in the younger northern plains. (2) Aqueous mineralization has produced gray, crystalline hematite in limited regions under ambient or hydrothermal conditions; these deposits are interpreted to be in-place sedimentary rock formations and indicate that liquid water was stable near the surface for a long period of time. (3) There is no evidence for large-scale (tens of kilometers) occurrences of moderate-grained (>50-μm) carbonates exposed at the surface at a detection limit of ∼10%. (4) Unweathered volcanic minerals dominate the spectral properties of dark regions, and weathering products, such as clays, have not been observed anywhere above a detection limit of ∼10%; this lack of evidence for chemical weathering indicates a geologic history dominated by a cold, dry climate in which mechanical, rather than chemical, weathering was the significant form of erosion and sediment production. (5) There is no conclusive evidence for sulfate minerals at a detection limit of ∼15%. The polar region has been studied with the following major conclusions: (1) Condensed CO 2 has three distinct end-members, from fine-grained crystals to slab ice. (2) The growth and retreat of the polar caps observed by MGS is virtually the same as observed by Viking 12 Martian years ago. (3) Unique regions have been identified that appear to differ primarily in the grain size of CO 2 ; one south polar region appears to remain as black slab CO 2 ice throughout its sublimation. (4) Regional atmospheric dust is common in localized and regional dust storms around the margin and interior of the southern cap. Analysis of the thermophysical properties of the surface shows that (1) the spatial pattern of albedo has changed since Viking observations, (2) a unique cluster of surface materials with intermediate inertia and albedo occurs that is distinct from the previously identified low-inertia/bright and high-inertia/dark surfaces, and (3) localized patches of high-inertia material have been found in topographic lows and may have been formed by a unique set of aeolian, fluvial, or erosional processes or may be exposed bedrock.

Journal of Geophysical Research E: Planets↗

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↗

USGS2001

Rapid fluid disruption: A source for self-potential anomalies on volcanoes

Self-potential (SP) anomalies observed above suspected magma reservoirs, dikes, etc., on various volcanoes (Kilauea, Hawaii; Mount Unzen, Japan; Piton de la Fournaise, Reunion Island, Miyake Jima, Japan) result from transient surface electric fields of tens of millivolts per kilometer and generally have a positive polarity. These SP anomalies are usually attributed to electrokinetic effects where properties controlling this process are poorly constrained. We propose an alternate explanation that contributions to electric fields of correct polarity should be expected from charge generation by fluid vaporization/disruption. As liquids are vaporized or removed as droplets by gas transport away from hot dike intrusions, both charge generation and local increase in electrical resistivity by removal of fluids should occur. We report laboratory observations of electric fields in hot rock samples generated by pulses of fluid (water) through the rock at atmospheric pressure. These indicate the relative amplitudes of rapid fluid disruption (RFD) potentials and electrokinetic potentials to be dramatically different and the signals are opposite in sign. Above vaporization temperatures, RFD effects of positive sign in the direction of gas flow dominate, whereas below these temperatures, effects of negative sign dominate. This suggests that the primary contribution to observed self-potential anomalies arises from gas-related charge transport processes at temperatures high enough to produce vigorous boiling and vapor transport. At lower temperatures, the primary contribution is from electrokinetic effects modulated perhaps by changing electrical resistivity and RFD effects from high-pressure but low-temperature CO2 and SO2 gas flow ripping water molecules from saturated crustal rocks. If charge generation is continuous, as could well occur above a newly emplaced dike, positive static potentials will be set up that could be sustained for many years, and the simplest method for identifying these hot, active regions would be to identify the SP anomalies they generate.

Hawai'i↗

USGS1999

Overview of the Mars Pathfinder Mission: Launch through landing, surface operations, data sets, and science results

Mars Pathfinder successfully landed at Ares Vallis on July 4, 1997, deployed and navigated a small rover about 100 m clockwise around the lander, and collected data from three science instruments and ten technology experiments. The mission operated for three months and returned 2.3 Gbits of data, including over 16,500 lander and 550 rover images, 16 chemical analyses of rocks and soil, and 8.5 million individual temperature, pressure and wind measurements. Path‐finder is the best known location on Mars, having been clearly identified with respect to other features on the surface by correlating five prominent horizon features and two small craters in lander images with those in high‐resolution orbiter images and in inertial space from two‐way ranging and Doppler tracking. Tracking of the lander has fixed the spin pole of Mars, determined the precession rate since Viking 20 years ago, and indicates a polar moment of inertia, which constrains a central metallic core to be between 1300 and ∼2000 km in radius. Dark rocks appear to be high in silica and geochemically similar to anorogenic andesites; lighter rocks are richer in sulfur and lower in silica, consistent with being coated with various amounts of dust. Rover and lander images show rocks with a variety of morphologies, fabrics and textures, suggesting a variety of rock types are present. Rounded pebbles and cobbles on the surface as well as rounded bumps and pits on some rocks indicate these rocks may be conglomerates (although other explanations are also possible), which almost definitely require liquid water to form and a warmer and wetter past. Air‐borne dust is composed of composite silicate particles with a small fraction of a highly magnetic mineral, interpreted to be most likely maghemite; explanations suggest iron was dissolved from crustal materials during an active hydrologic cycle with maghemite freeze dried onto silicate dust grains. Remote sensing data at a scale of a kilometer or greater and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catstrophic floods, which are relatively dust free. The surface appears to have changed little since it formed billions of years ago, with the exception that eolian activity may have deflated the surface by ∼3–7 cm, sculpted wind tails, collected sand into dunes, and eroded ventifacts (fluted and grooved rocks). Pathfinder found a dusty lower atmosphere, early morning water ice clouds, and morning near‐surface air temperatures that changed abruptly with time and height. Small scale vortices, interpreted to be dust devils, were observed repeatedly in the afternoon by the meteorology instruments and have been imaged.

Journal of Geophysical Research E: Planets↗

USGS2020

Surface methane concentrations along the mid-Atlantic bight driven by aerobic subsurface production rather than seafloor gas seeps

Relatively minor amounts of methane, a potent greenhouse gas, are currently emitted from the oceans to the atmosphere, but such methane emissions have been hypothesized to increase as oceans warm. Here, we investigate the source, distribution, and fate of methane released from the upper continental slope of the U.S. Mid-Atlantic Bight, where hundreds of gas seeps have been discovered between the shelf-break and ~1600 m water depth. Using physical, chemical, and isotopic analyses, we identify two main sources of methane in the water column: seafloor gas seeps and in situ aerobic methanogenesis which primarily occurs at 100 – 200 m depth in the water column. Stable isotopic analyses reveal that water samples collected at all depths were significantly impacted by aerobic methane oxidation, the dominant methane sink in this region, with more than 50% of the methane being oxidized, on average. Due to methane oxidation in the deeper water column, below 200 m depth, surface concentrations of methane are influenced more by methane sources found near the surface (0 – 10 m depth) and in the subsurface (10 - 200 m depth), rather than seafloor emissions at greater depths.

Atlantic margin↗

USGS2013

Identification of unrecognized tundra fire events on the north slope of Alaska

Characteristics of the natural fire regime are poorly resolved in the Arctic, even though fire may play an important role cycling carbon stored in tundra vegetation and soils to the atmosphere. In the course of studying vegetation and permafrost-terrain characteristics along a chronosequence of tundra burn sites from AD 1977, 1993, and 2007 on the North Slope of Alaska, we discovered two large, previously unrecognized tundra fires. The Meade River fire burned an estimated 500 km 2 and the Ketik River fire burned an estimated 1200 km 2 . Based on radiocarbon dating of charred twigs, analysis of historic aerial photography, and regional climate proxy data, these fires likely occurred between AD 1880 and 1920. Together, these events double the estimated burn area on the North Slope of Alaska over the last ~100 to 130 years. Assessment of vegetation succession along the century-scale chronosequence of tundra fire disturbances demonstrates for the first time on the North Slope of Alaska that tundra fires can facilitate the invasion of tundra by shrubs. Degradation of ice-rich permafrost was also evident at the fire sites and likely aided in the presumed changes of the tundra vegetation postfire. Other previously unrecognized tundra fire events likely exist in Alaska and other Arctic regions and identification of these sites is important for better understanding disturbance regimes and carbon cycling in Arctic tundra.

Alaska↗

USGS2013

Representing the effects of alpine grassland vegetation cover on the simulation of soil thermal dynamics by ecosystem models applied to the Qinghai-Tibetan Plateau

Soil surface temperature is a critical boundary condition for the simulation of soil temperature by environmental models. It is influenced by atmospheric and soil conditions and by vegetation cover. In sophisticated land surface models, it is simulated iteratively by solving surface energy budget equations. In ecosystem, permafrost, and hydrology models, the consideration of soil surface temperature is generally simple. In this study, we developed a methodology for representing the effects of vegetation cover and atmospheric factors on the estimation of soil surface temperature for alpine grassland ecosystems on the Qinghai-Tibetan Plateau. Our approach integrated measurements from meteorological stations with simulations from a sophisticated land surface model to develop an equation set for estimating soil surface temperature. After implementing this equation set into an ecosystem model and evaluating the performance of the ecosystem model in simulating soil temperature at different depths in the soil profile, we applied the model to simulate interactions among vegetation cover, freeze-thaw cycles, and soil erosion to demonstrate potential applications made possible through the implementation of the methodology developed in this study. Results showed that (1) to properly estimate daily soil surface temperature, algorithms should use air temperature, downward solar radiation, and vegetation cover as independent variables; (2) the equation set developed in this study performed better than soil surface temperature algorithms used in other models; and (3) the ecosystem model performed well in simulating soil temperature throughout the soil profile using the equation set developed in this study. Our application of the model indicates that the representation in ecosystem models of the effects of vegetation cover on the simulation of soil thermal dynamics has the potential to substantially improve our understanding of the vulnerability of alpine grassland ecosystems to changes in climate and grazing regimes.

Qinghai;Tibet↗

USGS2020

Linking mesoscale meteorology with extreme landscape response: Effects of narrow cold frontal rainbands (NCFR)

Landscapes evolve in response to prolonged and/or intense precipitation resulting from atmospheric processes at various spatial and temporal scales. Whereas synoptic (large‐scale) features (e.g., atmospheric rivers and hurricanes) govern regional‐scale hydrologic hazards such as widespread flooding, mesoscale features such as thunderstorms or squall lines are more likely to trigger localized geomorphic hazards such as landslides. Thus, to better understand relations between hydrometeorological drivers and landscape response, a knowledge of mesoscale meteorology and its impacts is needed. Here we investigate the extreme geomorphic response associated with one type of mesoscale meteorological feature, the narrow cold frontal rainband (NCFR). Resulting from low‐level convergence and shallow convection along a cold front, NCFRs are narrow bands of high‐intensity rainfall that occur in midlatitude areas of the world. Our study examines an NCFR impacting the Sierra Nevada foothills (California, USA) that initiated over 500 landslides, mobilized ~360,000 metric tons of sediment to the fluvial system (as much as 16 times the local annual sediment yield), and severely damaged local infrastructure and regional water transport facilities. Coupling geomorphological field investigations with meteorological analyses, we demonstrate that precipitation associated with the NCFR was both intense (maximum 15 min intensity of 70 mm/hr) and localized, resulting in a highly concentrated band of shallow landsliding. This meteorological phenomenon likely plays an important role in landscape evolution and hazard initiation. Other types of mesoscale meteorological features also occur globally and offer new avenues for understanding the effects of storms on landscapes.

California↗

USGS2004

The new GFDL global atmosphere and land model AM2-LM2: Evaluation with prescribed SST simulations

The configuration and performance of a new global atmosphere and land model for climate research developed at the Geophysical Fluid Dynamics Laboratory (GFDL) are presented. The atmosphere model, known as AM2, includes a new gridpoint dynamical core, a prognostic cloud scheme, and a multispecies aerosol climatology, as well as components from previous models used at GFDL. The land model, known as LM2, includes soil sensible and latent heat storage, groundwater storage, and stomatal resistance. The performance of the coupled model AM2-LM2 is evaluated with a series of prescribed sea surface temperature (SST) simulations. Particular focus is given to the model's climatology and the characteristics of interannual variability related to El Nin??o-Southern Oscillation (ENSO). One AM2-LM2 integration was perfor med according to the prescriptions of the second Atmospheric Model Intercomparison Project (AMIP II) and data were submitted to the Program for Climate Model Diagnosis and Intercomparison (PCMDI). Particular strengths of AM2-LM2, as judged by comparison to other models participating in AMIP II, include its circulation and distributions of precipitation. Prominent problems of AM2-LM2 include a cold bias to surface and tropospheric temperatures, weak tropical cyclone activity, and weak tropical intraseasonal activity associated with the Madden-Julian oscillation. An ensemble of 10 AM2-LM 2 integrations with observed SSTs for the second half of the twentieth century permits a statistically reliable assessment of the model's response to ENSO. In general, AM2-LM2 produces a realistic simulation of the anomalies in tropical precipitation and extratropical circulation that are associated with ENSO. ?? 2004 American Meteorological Society.

Journal of Climate↗

USGS2010

Silica in a Mars analog environment: Ka u Desert, Kilauea Volcano, Hawaii

Airborne Visible/Near-Infrared Imaging Spectrometer (AVIRIS) data acquired over the Ka u Desert are atmospherically corrected to ground reflectance and used to identify the mineralogic components of relatively young basaltic materials, including 250-700 and 200-400 year old lava flows, 1971 and 1974 flows, ash deposits, and solfatara incrustations. To provide context, a geologic surface units map is constructed, verified with field observations, and supported by laboratory analyses. AVIRIS spectral endmembers are identified in the visible (0.4 to 1.2 ??m) and short wave infrared (2.0 to 2.5 ??m) wavelength ranges. Nearly all the spectral variability is controlled by the presence of ferrous and ferric iron in such minerals as pyroxene, olivine, hematite, goethite, and poorly crystalline iron oxides or glass. A broad, nearly ubiquitous absorption feature centered at 2.25 ??m is attributed to opaline (amorphous, hydrated) silica and is found to correlate spatially with mapped geologic surface units. Laboratory analyses show the silica to be consistently present as a deposited phase, including incrustations downwind from solfatara vents, cementing agent for ash duricrusts, and thin coatings on the youngest lava flow surfaces. A second, Ti-rich upper coating on young flows also influences spectral behavior. This study demonstrates that secondary silica is mobile in the Ka u Desert on a variety of time scales and spatial domains. The investigation from remote, field, and laboratory perspectives also mimics exploration of Mars using orbital and landed missions, with important implications for spectral characterization of coated basalts and formation of opaline silica in arid, acidic alteration environments. Copyright 2010 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2021

Hydrate formation on marine seep bubbles and the implications for water column methane dissolution

Methane released from seafloor seeps contributes to a number of benthic, water column, and atmospheric processes. At seafloor seeps within the methane hydrate stability zone, crystalline gas hydrate shells can form on methane bubbles while the bubbles are still in contact with the seafloor or as the bubbles begin ascending through the water column. These shells reduce methane dissolution rates, allowing hydrate-coated bubbles to deliver methane to shallower depths in the water column than hydrate-free bubbles. Here, we analyze seafloor videos from six deepwater seep sites associated with a diverse range of bubble-release processes involving hydrate formation. Bubbles that grow rapidly are often hydrate-free when released from the seafloor. As bubble growth slows and seafloor residence time increases, a hydrate coating can form on the bubble's gas-water interface, fully coating most bubbles within ∼10 s of the onset of hydrate formation at the seafloor. This finding agrees with water-column observations that most bubbles become hydrate-coated after their initial ∼150 cm of rise, which takes about 10 s. Whether a bubble is coated or not at the seafloor affects how much methane a bubble contains and how quickly that methane dissolves during the bubble's rise through the water column. A simplified model shows that, after rising 150 cm above the seafloor, a bubble that grew a hydrate shell before releasing from the seafloor will have ∼5% more methane than a bubble of initial equal volume that did not grow a hydrate shell after it traveled to the same height.

Journal of Geophysical Research - Oceans↗

USGS2017

Influence of atmospheric rivers on vegetation productivity and fire patterns in the southwestern U.S.

In the southwestern U.S., the meteorological phenomenon known as atmospheric rivers (ARs) has gained increasing attention due to its strong connections to floods, snowpacks, and water supplies in the West Coast states. Relatively less is known about the ecological implications of ARs, particularly in the interior Southwest, where AR storms are less common. To address this gap, we compared a chronology of AR landfalls on the west coast between 1989 and 2011 and between 25°N and 42.5°N to annual metrics of the normalized difference vegetation index (NDVI; an indicator of vegetation productivity) and daily resolution precipitation data to assess influences of AR-fed winter precipitation on vegetation productivity across the southwestern U.S. We mapped correlations between winter AR precipitation during landfalling ARs and (1) annual maximum NDVI and (2) area burned by large wildfires summarized by ecoregion during the same year as the landfalls and during the following year. Interannual variations of AR precipitation strongly influenced both NDVI and area burned by wildfire in some dryland ecoregions. The influence of ARs on dryland vegetation varied significantly depending on the latitude of landfall, with those ARs making landfall below 35°N latitude more strongly influencing these systems, and with effects observed as far as 1300 km from the landfall location. As climatologists' understanding of the synoptic patterns associated with the occurrence of ARs continues to evolve, an increased understanding of how AR landfalls, in aggregate, influence vegetation productivity and associated wildfire activity in dryland ecosystems may provide opportunities to better predict ecological responses to climate and climate change.

Arizona, California, Nevada, Utah↗

USGS2011

Opportunity Mars Rover mission: Overview and selected results from Purgatory ripple to traverses to Endeavour crater

Opportunity has been traversing the Meridiani plains since 25 January 2004 (sol 1), acquiring numerous observations of the atmosphere, soils, and rocks. This paper provides an overview of key discoveries between sols 511 and 2300, complementing earlier papers covering results from the initial phases of the mission. Key new results include (1) atmospheric argon measurements that demonstrate the importance of atmospheric transport to and from the winter carbon dioxide polar ice caps; (2) observations showing that aeolian ripples covering the plains were generated by easterly winds during an epoch with enhanced Hadley cell circulation; (3) the discovery and characterization of cobbles and boulders that include iron and stony-iron meteorites and Martian impact ejecta; (4) measurements of wall rock strata within Erebus and Victoria craters that provide compelling evidence of formation by aeolian sand deposition, with local reworking within ephemeral lakes; (5) determination that the stratigraphy exposed in the walls of Victoria and Endurance craters show an enrichment of chlorine and depletion of magnesium and sulfur with increasing depth. This result implies that regional-scale aqueous alteration took place before formation of these craters. Most recently, Opportunity has been traversing toward the ancient Endeavour crater. Orbital data show that clay minerals are exposed on its rim. Hydrated sulfate minerals are exposed in plains rocks adjacent to the rim, unlike the surfaces of plains outcrops observed thus far by Opportunity. With continued mechanical health, Opportunity will reach terrains on and around Endeavour's rim that will be markedly different from anything examined to date.

Journal of Geophysical Research E: Planets↗