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USGS2008

Mars Exploration Rover Navigation Camera in-flight calibration

The Navigation Camera (Navcam) instruments on the Mars Exploration Rover (MER) spacecraft provide support for both tactical operations as well as scientific observations where color information is not necessary: large-scale morphology, atmospheric monitoring including cloud observations and dust devil movies, and context imaging for both the thermal emission spectrometer and the in situ instruments on the Instrument Deployment Device. The Navcams are a panchromatic stereoscopic imaging system built using identical charge-coupled device (CCD) detectors and nearly identical electronics boards as the other cameras on the MER spacecraft. Previous calibration efforts were primarily focused on providing a detailed geometric calibration in line with the principal function of the Navcams, to provide data for the MER navigation team. This paper provides a detailed description of a new Navcam calibration pipeline developed to provide an absolute radiometric calibration that we estimate to have an absolute accuracy of 10% and a relative precision of 2.5%. Our calibration pipeline includes steps to model and remove the bias offset, the dark current charge that accumulates in both the active and readout regions of the CCD, and the shutter smear. It also corrects pixel-to-pixel responsivity variations using flat-field images, and converts from raw instrument-corrected digital number values per second to units of radiance (W m-2 nm-1 sr-1), or to radiance factor (I/F). We also describe here the initial results of two applications where radiance-calibrated Navcam data provide unique information for surface photometric and atmospheric aerosol studies. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2009

Measurement of soil carbon oxidation state and oxidative ratio by 13 C nuclear magnetic resonance

The oxidative ratio (OR) of the net ecosystem carbon balance is the ratio of net O 2 and CO 2 fluxes resulting from photosynthesis, respiration, decomposition, and other lateral and vertical carbon flows. The OR of the terrestrial biosphere must be well characterized to accurately estimate the terrestrial CO 2 sink using atmospheric measurements of changing O 2 and CO 2 levels. To estimate the OR of the terrestrial biosphere, measurements are needed of changes in the OR of aboveground and belowground carbon pools associated with decadal timescale disturbances (e.g., land use change and fire). The OR of aboveground pools can be measured using conventional approaches including elemental analysis. However, measuring the OR of soil carbon pools is technically challenging, and few soil OR data are available. In this paper we test three solid-state nuclear magnetic resonance (NMR) techniques for measuring soil OR, all based on measurements of the closely related parameter, organic carbon oxidation state (C ox ). Two of the three techniques make use of a molecular mixing model which converts NMR spectra into concentrations of a standard suite of biological molecules of known C ox . The third technique assigns C ox values to each peak in the NMR spectrum. We assess error associated with each technique using pure chemical compounds and plant biomass standards whose C ox and OR values can be directly measured by elemental analyses. The most accurate technique, direct polarization solid-state 13 C NMR with the molecular mixing model, agrees with elemental analyses to ??0.036 C ox units (??0.009 OR units). Using this technique, we show a large natural variability in soil C ox and OR values. Soil C ox values have a mean of -0.26 and a range from -0.45 to 0.30, corresponding to OR values of 1.08 ?? 0.06 and a range from 0.96 to 1.22. We also estimate the OR of the carbon flux from a boreal forest fire. Analysis of soils from nearby intact soil profiles imply that soil carbon losses associated with the fire had an OR of 1.09 1 (??0.00 3 ). Fire appears to be a major factor driving the soil C pool to higher oxidation states and lower OR values. Episodic fluxes caused by disturbances like fire may have substantially different ORs from ecosystem respiration fluxes and therefore should be better quantified to reduce uncertainties associated with our understanding of the global atmospheric carbon budget. Copyright 2009 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗

USGS2017

Methane fluxes from tropical coastal lagoons surrounded bymangroves, Yucatán, Mexico

Methane concentrations in the water column and emissions to the atmosphere were determined for three tropical coastal lagoons surrounded by mangrove forests on the Yucatán Peninsula, Mexico. Surface water dissolved methane was sampled at different seasons over a period of 2 years in areas representing a wide range of salinities and anthropogenic impacts. The highest surface water methane concentrations (up to 8378 nM) were measured in a polluted canal associated with Terminos Lagoon. In Chelem Lagoon, methane concentrations were typically lower, except in the polluted harbor area (1796 nM). In the relatively pristine Celestún Lagoon, surface water methane concentrations ranged from 41 to 2551 nM. Methane concentrations were negatively correlated with salinity in Celestún, while in Chelem and Terminos high methane concentrations were associated with areas of known pollution inputs, irrespective of salinity. The diffusive methane flux from surface lagoon water to the atmosphere ranged from 0.0023 to 15 mmol CH 4 m −2 d −1 . Flux chamber measurements revealed that direct methane release as ebullition was up to 3 orders of magnitude greater than measured diffusive flux. Coastal mangrove lagoons may therefore be an important natural source of methane to the atmosphere despite their relatively high salinity. Pollution inputs are likely to substantially enhance this flux. Additional statistically rigorous data collected globally are needed to better consider methane fluxes from mangrove-surrounded coastal areas in response to sea level changes and anthropogenic pollution in order to refine projections of future atmospheric methane budgets.

Yucatam↗

USGS2012

Coupled atmosphere-ocean-wave simulations of a storm event over the Gulf of Lion and Balearic Sea

The coastal areas of the North-Western Mediterranean Sea are one of the most challenging places for ocean forecasting. This region is exposed to severe storms events that are of short duration. During these events, significant air-sea interactions, strong winds and large sea-state can have catastrophic consequences in the coastal areas. To investigate these air-sea interactions and the oceanic response to such events, we implemented the Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System simulating a severe storm in the Mediterranean Sea that occurred in May 2010. During this event, wind speed reached up to 25 m.s-1 inducing significant sea surface cooling (up to 2°C) over the Gulf of Lion (GoL) and along the storm track, and generating surface waves with a significant height of 6 m. It is shown that the event, associated with a cyclogenesis between the Balearic Islands and the GoL, is relatively well reproduced by the coupled system. A surface heat budget analysis showed that ocean vertical mixing was a major contributor to the cooling tendency along the storm track and in the GoL where turbulent heat fluxes also played an important role. Sensitivity experiments on the ocean-atmosphere coupling suggested that the coupled system is sensitive to the momentum flux parameterization as well as air-sea and air-wave coupling. Comparisons with available atmospheric and oceanic observations showed that the use of the fully coupled system provides the most skillful simulation, illustrating the benefit of using a fully coupled ocean-atmosphere-wave model for the assessment of these storm events.

Journal of Geophysical Research↗

USGS2016

The role of crystallization-driven exsolution on the sulfur mass balance in volcanic arc magmas

The release of large amounts of sulfur to the stratosphere during explosive eruptions affects the radiative balance in the atmosphere and consequentially impacts climate for up to several years after the event. Quantitative estimations of the processes that control the mass balance of sulfur between melt, crystals, and vapor bubbles is needed to better understand the potential sulfur yield of individual eruption events and the conditions that favor large sulfur outputs to the atmosphere. The processes that control sulfur partitioning in magmas are (1) exsolution of volatiles (dominantly H 2 O) during decompression (first boiling) and during isobaric crystallization (second boiling), (2) the crystallization and breakdown of sulfide or sulfate phases in the magma, and (3) the transport of sulfur-rich vapor (gas influx) from deeper unerupted regions of the magma reservoir. Vapor exsolution and the formation/breakdown of sulfur-rich phases can all be considered as closed-system processes where mass balance arguments are generally easier to constrain, whereas the contribution of sulfur by vapor transport (open system process) is more difficult to quantify. The ubiquitous “excess sulfur” problem, which refers to the much higher sulfur mass released during eruptions than what can be accounted for by amount of sulfur originally dissolved in erupted melt, as estimated from melt inclusion sulfur concentrations (the “petrologic estimate”), reflects the challenges in closing the sulfur mass balance between crystals, melt, and vapor before and during a volcanic eruption. In this work, we try to quantify the relative importance of closed- and open-system processes for silicic arc volcanoes using kinetic models of sulfur partitioning during exsolution. Our calculations show that crystallization-induced exsolution (second boiling) can generate a significant fraction of the excess sulfur observed in crystal-rich arc magmas. This result does not negate the important role of vapor migration in sulfur mass balance but rather points out that second boiling (in situ exsolution) can provide the necessary yield to drive the excess sulfur to the levels observed for crystal-rich systems. In contrast, in crystal-poor systems, magma recharge that releases sulfur-rich bubbles is necessary and most likely the primary contributor to sulfur mass balance. Finally, we apply our model to account for the effect of sulfur partitioning during second boiling and its impact on sulfur released during the Cerro Galan supereruption in Argentina (2.08 Ma) and show the potential importance of second boiling in releasing a large amount of sulfur to the atmosphere during the eruption of large crystal-rich ignimbrites.

Journal of Geophysical Research B: Solid Earth↗

USGS2012

Impact crater outflows on Venus: Morphology and emplacement mechanisms

Many of the 932 impact craters discovered by the Magellan spacecraft at Venus are associated with lobate flows that originate at or near the crater rim. They extend for several to several hundred kilometers from the crater, and they commonly have a strong radar backscatter. A morphologic study of all identifiable crater outflows on Venus has revealed that many individual flows each consist of two areas, defined by distinct morphologic features. These two areas appear to represent two stages of deposition for each flow. The part of the flow that is generally deposited closest to the crater tends to be on the downrange side of the crater, flows in the downrange direction, and it is interpreted to be a late-stage ejecta. In many cases, this proximal part of the flow is too thin to completely bury the large blocks in subjacent ejecta deposits. Dendritic channels, present in many proximal flows, appear to have drained liquid from the proximal part in the downhill direction, and they debouch to feed the outer part of the flows. This distal part flows downhill, fills small grabens, and is ponded by ridges, behavior that mimics that of volcanic lava flows. The meandering and dendritic channels and the relation of the distal flows to topography strongly suggest that the distal portion is the result of coalescence and slow drainage of impact melt from the proximal portion. Impact melt forms a lining to the transient crater and mixes turbulently with solid clasts, and part of this mixture may be ejected to form the proximal part of the flow during the excavation stage of crater development. A statistical study of the Venusian craters has revealed that, in general, large craters produced by impacts with relatively low incidence angles to the surface are more likely to produce flows than small craters produced by higher-angle impacts. The greater flow production and downrange focusing of the proximal flows with decreasing incidence angle indicate a strong control of the flows by the impactor flight direction, and a high downrange velocity imparted to the proximal flow material in lower angle impacts. On the Moon, small flows interpreted to be composed of impact melt are observed atop the ejecta of large, fresh craters; on Earth, melt-rich suevite deposits form the uppermost layer of ejecta of some fresh craters. These features, albeit much smaller, may be analogous to the flows on Venus. Numerical models have predicted that larger volumes of impact melt would be produced on Venus than on the cooler terrestrial bodies due to high atmospheric and target temperatures, perhaps 3 times the volume produced on the Moon for a given crater diameter.

Journal of Geophysical Research E: Planets↗

USGS2012

Use of weather types to disaggregate general circulation model predictions

General circulation models (GCMs) simulate climatic conditions with a grid cell resolution on the order of 100,000 km 2 . This resolution is inadequate to assess the effects of climatic change on water resources at a regional scale. A method has been developed that uses weather-type analysis as a tool to spatially disaggregate GCM predictions to make them useful for water resource studies. The method has been applied to the Delaware River basin to predict the effects of doubling atmospheric carbon dioxide on precipitation patterns in the region. An application of the technique to the Delaware River basin indicates that future climatic conditions will show minimal changes in weather-type frequency, implying that air circulation patterns will remain unchanged. Results of this study indicate that changes in regional precipitation patterns under a doubling of atmospheric carbon dioxide will be a result of within-type changes in weather characteristics.

Journal of Geophysical Research↗

USGS2009

Projected changes in atmospheric heating due to changes in fire disturbance and the snow season in the western Arctic, 2003–2100

In high latitudes, changes in climate impact fire regimes and snow cover duration, altering the surface albedo and the heating of the regional atmosphere. In the western Arctic, under four scenarios of future climate change and future fire regimes (2003–2100), we examined changes in surface albedo and the related changes in regional atmospheric heating due to: (1) vegetation changes following a changing fire regime, and (2) changes in snow cover duration. We used a spatially explicit dynamic vegetation model (Alaskan Frame-based Ecosystem Code) to simulate changes in successional dynamics associated with fire under the future climate scenarios, and the Terrestrial Ecosystem Model to simulate changes in snow cover. Changes in summer heating due to the changes in the forest stand age distributions under future fire regimes showed a slight cooling effect due to increases in summer albedo (mean across climates of −0.9 W m −2 decade −1 ). Over this same time period, decreases in snow cover (mean reduction in the snow season of 4.5 d decade −1 ) caused a reduction in albedo, and a heating effect (mean across climates of 4.3 W m −2 decade −1 ). Adding both the summer negative change in atmospheric heating due to changes in fire regimes to the positive changes in atmospheric heating due to changes in the length of the snow season resulted in a 3.4 W m −2 decade −1 increase in atmospheric heating. These findings highlight the importance of gaining a better understanding of the influences of changes in surface albedo on atmospheric heating due to both changes in the fire regime and changes in snow cover duration.

Journal of Geophysical Research: Biogeosciences↗

USGS2007

Dust deposition on the Mars Exploration Rover Panoramic Camera (Pancam) calibration targets

The Panoramic Camera (Pancam) on the Mars Exploration Rover mission has acquired in excess of 20,000 images of the Pancam calibration targets on the rovers. Analysis of this data set allows estimates of the rate of deposition and removal of aeolian dust on both rovers. During the first 150-170 sols there was gradual dust accumulation on the rovers but no evidence for dust removal. After that time there is ample evidence for both dust removal and dust deposition on both rover decks. We analyze data from early in both rover missions using a diffusive reflectance mixing model. Assuming a dust settling rate proportional to the atmospheric optical depth, we derive spectra of optically thick layers of airfall dust that are consistent with spectra from dusty regions on the Martian surface. Airfall dust reflectance at the Opportunity site appears greater than at the Spirit site, consistent with other observations. We estimate the optical depth of dust deposited on the Spirit calibration target by sol 150 to be 0.44 ?? 0.13. For Opportunity the value was 0.39 ?? 0.12. Assuming 80% pore space, we estimate that the dust layer grew at a rate of one grain diameter per ???100 sols on the Spirit calibration target. On Opportunity the rate was one grain diameter per ???125 sols. These numbers are consistent with dust deposition rates observed by Mars Pathfinder taking into account the lower atmospheric dust optical depth during the Mars Pathfinder mission. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2003

Imaging spectroscopy: Earth and planetary remote sensing with the USGS Tetracorder and expert systems

Imaging spectroscopy is a tool that can be used to spectrally identify and spatially map materials based on their specific chemical bonds. Spectroscopic analysis requires significantly more sophistication than has been employed in conventional broadband remote sensing analysis. We describe a new system that is effective at material identification and mapping: a set of algorithms within an expert system decision‐making framework that we call Tetracorder. The expertise in the system has been derived from scientific knowledge of spectral identification. The expert system rules are implemented in a decision tree where multiple algorithms are applied to spectral analysis, additional expert rules and algorithms can be applied based on initial results, and more decisions are made until spectral analysis is complete. Because certain spectral features are indicative of specific chemical bonds in materials, the system can accurately identify and map those materials. In this paper we describe the framework of the decision making process used for spectral identification, describe specific spectral feature analysis algorithms, and give examples of what analyses and types of maps are possible with imaging spectroscopy data. We also present the expert system rules that describe which diagnostic spectral features are used in the decision making process for a set of spectra of minerals and other common materials. We demonstrate the applications of Tetracorder to identify and map surface minerals, to detect sources of acid rock drainage, and to map vegetation species, ice, melting snow, water, and water pollution, all with one set of expert system rules. Mineral mapping can aid in geologic mapping and fault detection and can provide a better understanding of weathering, mineralization, hydrothermal alteration, and other geologic processes. Environmental site assessment, such as mapping source areas of acid mine drainage, has resulted in the acceleration of site cleanup, saving millions of dollars and years in cleanup time. Imaging spectroscopy data and Tetracorder analysis can be used to study both terrestrial and planetary science problems. Imaging spectroscopy can be used to probe planetary systems, including their atmospheres, oceans, and land surfaces.

Journal of Geophysical Research E: Planets↗

USGS2009

The source of infrasound associated with long-period events at mount St. Helens

During the early stages of the 2004-2008 Mount St. Helens eruption, the source process that produced a sustained sequence of repetitive long-period (LP) seismic events also produced impulsive broadband infrasonic signals in the atmosphere. To assess whether the signals could be generated simply by seismic-acoustic coupling from the shallow LP events, we perform finite difference simulation of the seismo-acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere. The effects of topography, velocity structure, wind, and source configuration are considered. The simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of P/SV and Rayleigh wave energy converted locally along the propagation path, and acoustic energy originating from , the source epicenter. Although the horizontal acoustic velocity of the latter is consistent with our data, the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations, and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source. The observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic LP events. The observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated, highly permeable material. Heating by magmatic activity causes pressure to rise, periodically reaching the pressure threshold for rupture of the "valve" sealing the crack. Sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack, initiating resonance of the remaining fluid. Subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13.4 km to the NW of the volcano are attributed primarily to atmospheric boundary layer propagation effects, superimposed upon amplitude changes at the source.

Washington↗

USGS2012

Laboratory studies of volcanic jets

The study of the fluid dynamics of violent volcanic eruptions by laboratory experiment is described, and the important fluid-dynamic processes that can be examined in laboratory models are discussed in detail. In preliminary experiments, pure gases are erupted from small reservoirs. The gases used are Freon 12 and Freon 22, two gases of high molecular weight and high density that are good analogs of heavy and particulate-laden volcanic gases; nitrogen, a moderate molecular weight, moderate density gas for which the thermodynamic properties are well known; and helium, a low molecular weight, lowdensity gas that is used as a basis for comparison with the behavior of the heavier gases and as an analog of steam, the gas that dominates many volcanic eruptions. Transient jets erupt from the reservoir into the laboratory upon rupture of a thin diaphragm at the exit of a convergent nozzle. The gas accelerates from rest in the reservoir to high velocity in the jet. Reservoir pressures and geometries are such that the fluid velocity in the jets is initially supersonic and later decays to subsonic. The measured reservoir pressure decreases as the fluid expands through repetitively reflecting rarefaction waves, but for the conditions of these experiments, a simple steady-discharge model is sufficient to explain the pressure decay and to predict the duration of the flow. Density variations in the flow field have been visualized with schlieren and shadowgraph photography. The observed structure of the jet is correlated with the measured pressure history. The starting vortex generated when the diaphragm ruptures becomes the head of the jet. Though the exit velocity is sonic, the flow head in the helium jet decelerates to about one-third of sonic velocity in the first few nozzle diameters, the nitrogen head decelerates to about three-fourths of sonic velocity, while Freon maintains nearly sonic velocity. The impulsive acceleration of reservoir fluid into the surrounding atmosphere produces a compression wave. The strength of this wave depends primarily on the sound speed of the fluid in the reservoir but also, secondarily with opposite effect, on the density: helium produces a relatively strong atmospheric shock while the Freons do not produce any optically observable wave front. Well-formed N waves are detected with a microphone far from the reservoir. Barrel shocks, Mach disks, and other familiar features of steady underexpanded supersonic jets form inside the jet almost immediately after passage of the flow head. These features are maintained until the pressure in the reservoir decays to sonic conditions. At low pressures the jets are relatively structureless. Gas-particle jets from volcanic eruptions may behave as pseudogases if particle concentrations and mass and momentum exchange between the components are sufficiently small. The sound speed of volcanic pseudogases can be as large as 1000 m s −1 or as small as a few tens of meters per second depending on the mass loading and initial temperature. Fluids of high sound speed produce stronger atmospheric shock waves than do those of low sound speed. Therefore eruption of a hot gas lightly laden with particulates should produce a stronger shock than eruption of a cooler or heavily laden fluid. An empirical expression suggests that the initial velocity of the head of supersonic volcanic jets is controlled by the sound speed and the ratio of the density of the erupting fluid to that of the atmosphere. The duration of gas or pseudogas eruptions is controlled by the sound speed of the fluid and the ratio of reservoir volume to vent area.

Journal of Geophysical Research Solid Earth↗

USGS2018

Flooding alters plant-mediated carbon cycling independently of elevated atmospheric CO2 concentrations

Plant‐mediated processes determine carbon (C) cycling and storage in many ecosystems; how plant‐associated processes may be altered by climate‐induced changes in environmental drivers is therefore an essential question for understanding global C cycling. In this study, we hypothesize that environmental alterations associated with near‐term climate change can exert strong control on plant‐associated ecosystem C cycling and that investigations along an extended hydrologic gradient may give mechanistic insight into C cycling. We utilize a mesocosm approach to investigate the response of plant, soil, and gaseous C cycling to changing hydrologic regimes and elevated atmospheric carbon dioxide (CO 2) concentrations expected by 2100 in a coastal salt marsh in Louisiana, USA. Although elevated CO 2 had no significant effects on C cycling, we demonstrate that greater average flooding depth stimulated C exchange, with higher rates of labile C decomposition, plant CO 2 assimilation, and soil C respiration. Greater average flooding depth also significantly decreased the soil C pool and marginally increased the aboveground biomass C pool, leading to net losses in total C stocks. Further, flooding depths along an extended hydrologic gradient garnered insight into decomposition mechanisms that was not apparent from other data. In C‐4 dominated salt marshes, sea‐level rise will likely overwhelm effects of elevated CO 2 with climate change. Deeper flooding associated with sea‐level rise may decrease long‐term soil C pools and quicken C exchange between soil and atmosphere, thereby threatening net C storage in salt marsh habitats. Manipulative studies will be indispensable for understanding biogeochemical cycling under future conditions.

Journal of Geophysical Research: Biogeosciences↗

USGS2012

Coupling of volatile transport and internal heat flow on Triton

Recently Brown et al. (1991) showed that Triton's internal heat source could amount to 5–20% of the absorbed insolation on Triton, thus significantly affecting volatile transport and atmospheric pressure. Subsequently, Kirk and Brown (1991a) used simple analytical models of the effect of internal heat on the distribution of volatiles on Triton's surface, confirming the speculation of Brown et al. that Triton's internal heat flow could strongly couple to the surface volatile distribution. To further explore this idea, we present numerical models of the permanent distribution of nitrogen ice on Triton that include the effects of sunlight, the two‐dimensional distribution of internal heat flow, the coupling of internal heat flow to the surface distribution of nitrogen ice, and the finite viscosity of nitrogen ice. From these models we conclude that: (1) The strong vertical thermal gradient induced in Triton's polar caps by internal heat‐flow facilitates viscous spreading to lower latitudes, thus opposing the poleward transport of volatiles by sunlight, and, for plausible viscosities and nitrogen inventories, producing permanent caps of considerable latitudinal extent; (2) It is probable that there is a strong coupling between the surface distribution of nitrogen ice on Triton and internal heat flow; (3) Asymmetries in the spatial distribution of Triton's heat flow, possibly driven by large‐scale, volcanic activity or convection in Triton's interior, can result in permanent polar caps of unequal latitudinal extent, including the case of only one permanent polar cap; (4) Melting at the base of a permanent polar cap on Triton caused by internal heat flow can significantly enhance viscous spreading, and, as an alternative to the solid‐state greenhouse mechanism proposed by Brown et al. (1990), could provide the necessary energy, fluids, and/or gases to drive Triton's geyser‐like plumes; (5) The atmospheric collapse predicted to occur on Triton in the next 20 years (Spencer, 1990) may be plausibly avoided because of the large latitudinal extent expected for permanent polar caps on Triton.

Journal of Geophysical Research E: Planets↗

USGS2010

Infrasonic harmonic tremor and degassing bursts from Halema'uma'u Crater, Kilauea Volcano, Hawaii

The formation, evolution, collapse, and subsequent resurrection of a vent within Halema'uma'u Crater, Kilauea Volcano, produced energetic and varied degassing signals recorded by a nearby infrasound array between 2008 and early 2009. After 25 years of quiescence, a vent-clearing explosive burst on 19 March 2008 produced a clear, complex acoustic signal. Near-continuous harmonic infrasonic tremor followed this burst until 4 December 2008, when a period of decreased degassing occurred. The tremor spectra suggest volume oscillation and reverberation of a shallow gas-filled cavity beneath the vent. The dominant tremor peak can be sustained through Helmholtz oscillations of the cavity, while the secondary tremor peak and overtones are interpreted assuming acoustic resonance. The dominant tremor frequency matches the oscillation frequency of the gas emanating from the vent observed by video. Tremor spectra and power are also correlated with cavity geometry and dynamics, with the cavity depth estimated at ~219 m and volume ~3 x 10 6 m 3 in November 2008. Over 21 varied degassing bursts were observed with extended burst durations and frequency content consistent with a transient release of gas exciting the cavity into resonance. Correlation of infrasound with seismicity suggests an open system connecting the atmosphere to the seismic excitation process at depth. Numerous degassing bursts produced very long period (0.03-0.1 Hz) infrasound, the first recorded at Kilauea, indicative of long-duration atmospheric accelerations. Kilauea infrasound appears controlled by the exsolution of gas from the magma, and the interaction of this gas with the conduits and cavities confining it.

Hawai'i↗

USGS2024

Source, migration pathways, and atmospheric release of geologic methane associated with the complex permafrost regimes of the outer Mackenzie River Delta, Arctic, Canada

Sources and fluxes of methane to the atmosphere from permafrost are significant but poorly constrained in global climate models. We present data collected from the variable permafrost setting of the outer Mackenzie River Delta, including observations of aquatic methane seepage, core determinations of in situ methane occurrence and seep gas isotope geochemistry. The sources and locations of in situ geologic methane occurrence and aquatic and atmospheric gas release appear to be controlled by the regional geology and permafrost conditions. Where permafrost is >250 m thick, thermogenic gas deposits at depth are isolated by laterally continuous, low permeability ice-bearing sediments with few through-going thawed taliks. Thus, the observed in situ methane and aquatic gas seepage appears to be dominated by microbial methane. In contrast, where permafrost is <80 m thick, taliks are more likely to be through-going, providing permeable conduits from depth and migration pathways for both thermogenic and biogenic gas. Continuous annual fluid sampling of two lakes and a river channel documents aquatic methane flux from microbial sources, more deeply buried thermogenic sources, and mixtures of both. Using estimates of in situ methane concentration from deep core samples and observations of in situ free gas occurrences, we conclude that the reservoir of in situ geologic methane within ice bonded permafrost is substantial and that this methane is presently migrating with ongoing atmospheric release. It is our assessment that the permafrost setting, and processes described are sensitive to future climate change as the permafrost warms.

Mackenzie River Delta↗

USGS2012

Water-soluble material on aerosols collected within volcanic eruption clouds

In February and March of 1978, filter samplers mounted on an aircraft were used to collect the aerosol fraction of the eruption clouds from three active Guatemalan volcanoes (Fuego, Pacaya, and Santiaguito). The samples were collected on Teflon (Fluoropore) filters with a nominal pore diameter of 0.5μm. The mass of air sampled by the filters ranged from 0.15 to 6.6 kg. The particulate material collected consisted of fragments of angular silicate ash and droplets of what is interpreted as dilute H 2 SO 4 and HCl. After collection of the samples, each filter was rinsed with 60 ml of distilled-deionized water. Splits of each extract were centrifuged to remove particles greater than or equal to 0.1 μm in diameter, acidified, and analyzed for B, Ba, Be, Ca, Cd, Co, Cu, Fe, Li, Mg, Mn, Mo, Na, Pb, Si, Sr, V, and Zn by inductively coupled plasma—optical emission spectroscopy. Separate splits were analyzed for F and Cl by specific-ion-electrode methods and for U by a fission track technique. The elements dissolved in the aqueous extracts represent components of water-soluble material either formed directly in the eruption cloud or derived from interaction of ash particles and aerosol components of the plume. Calculations of enrichment factors, based upon concentration ratios, showed the elements most enriched in the extracts relative to bulk ash composition were Cd, Cu, V, F, Cl, Zn, and Pb. These elements represent a subset (with the addition of Cl and F) of elements previously reported enriched in atmospheric aerosols in remote regions as well as in volcanic areas. This suggests that some of the enriched elements were widely dispersed as volatile halides emitted from a volcanic source.

Journal of Geophysical Research - Oceans↗

USGS2014

Differential response of carbon fluxes to climate in three peatland ecosystems that vary in the presence and stability of permafrost

Changes in vegetation and soil properties following permafrost degradation and thermokarst development in peatlands may cause changes in net carbon storage. To better understand these dynamics, we established three sites in Alaska that vary in permafrost regime, including a black spruce peat plateau forest with stable permafrost, an internal collapse scar bog formed as a result of thermokarst, and a rich fen without permafrost. Measurements include year-round eddy covariance estimates of carbon dioxide (CO 2 ), water, and energy fluxes, associated environmental variables, and methane (CH 4 ) fluxes at the collapse scar bog. The ecosystems all acted as net sinks of CO 2 in 2011 and 2012, when air temperature and precipitation remained near long-term means. In 2013, under a late snowmelt and late leaf out followed by a hot, dry summer, the permafrost forest and collapse scar bog were sources of CO 2 . In this same year, CO 2 uptake in the fen increased, largely because summer inundation from groundwater inputs suppressed ecosystem respiration. CO 2 exchange in the permafrost forest and collapse scar bog was sensitive to warm air temperatures, with 0.5 g C m −2 lost each day when maximum air temperature was very warm (≥29°C). The bog lost 4981 ± 300 mg CH 4 m −2 between April and September 2013, indicating that this ecosystem acted as a significant source of both CO 2 and CH 4 to the atmosphere in 2013. These results suggest that boreal peatland responses to warming and drying, both of which are expected to occur in a changing climate, will depend on permafrost regime.

Alaska↗