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At least 721 records · Page 40Linked to original sources

USGS1996

The initial cooling of pahoehoe flow lobes

In this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows. The accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation. This model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data. We find that the only significant processes are (a) heat loss by thermal radiation, (b) heat loss by atmospheric convection, (c) heat transport within the flow by conduction with temperature and porosity-dependent thermal properties, and (d) the release of latent heat during crystallization. The numerical model is better able to reproduce field measurements made in Hawai'i between 1989 and 1993 than other published thermal models. By adjusting one parameter at a time, the effect of each of the input parameters on the cooling rate was determined. We show that: (a) the surfaces of porous flows cool more quickly than the surfaces of dense flows, (b) the surface cooling is very sensitive to the efficiency of atmospheric convective cooling, and (c) changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures. These model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes (Jones 1992, 1993). The predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification, and the model provides a tool to begin studies of the dynamic crystallization of real lavas. Future versions of the model can also be made applicable to extraterrestrial, submarine, silicic, and pyroclastic flows.

Bulletin of Volcanology↗

USGS2013

On the twenty-first-century wet season projections over the Southeastern United States

This paper reconciles the difference in the projections of the wet season over the Southeastern United States (SEUS) from a global climate model (the Community Climate System Model Version 3 [CCSM3]) and from a regional climate model (the Regional Spectral Model [RSM]) nested in the CCSM3. The CCSM3 projects a dipole in the summer precipitation anomaly: peninsular Florida dries in the future climate, and the remainder of the SEUS region becomes wetter. The RSM forced with CCSM3 projects a universal drying of the SEUS in the late twenty-first century relative to the corresponding twentieth-century summer. The CCSM3 pattern is attributed to the “upped-ante” mechanism, whereby the atmospheric boundary layer moisture required for convection increases in a warm, statically stable global tropical environment. This criterion becomes harder to meet along convective margins, which include peninsular Florida, resulting in its drying. CCSM3 also projects a southwestward expansion of the North Atlantic subtropical high that leads to further stabilizing of the atmosphere above Florida, inhibiting convection. The RSM, because of its high (10-km grid) resolution, simulates diurnal variations in summer rainfall over SEUS reasonably well. The RSM improves upon CCSM3 through the RSM’s depiction of the diurnal variance of precipitation, which according to observations accounts for up to 40 % of total seasonal precipitation variance. In the future climate, the RSM projects a significant reduction in the diurnal variability of convection. The reduction is attributed to large-scale stabilization of the atmosphere in the CCSM3 projections.

Alabama;Arkansas;Florida;Georgia;Kentucky;Louisian↗

USGS2013

A 17-year record of environmental tracers in spring discharge, Shenandoah National Park, Virginia, USA: use of climatic data and environmental conditions to interpret discharge, dissolved solutes, and tracer concentrations

A 17-year record (1995–2012) of a suite of environmental tracer concentrations in discharge from 34 springs located along the crest of the Blue Ridge Mountains in Shenandoah National Park (SNP), Virginia, USA, reveals patterns and trends that can be related to climatic and environmental conditions. These data include a 12-year time series of monthly sampling at five springs, with measurements of temperature, specific conductance, pH, and discharge recorded at 30-min intervals. The monthly measurements include age tracers (CFC-11, CFC-12, CFC-113, CFC-13, SF 6 , and SF 5 CF 3 ), dissolved gases (N 2 , O 2 , Ar, CO 2 , and CH 4 ), stable isotopes of water, and major and trace inorganic constituents. The chlorofluorocarbon (CFC) and sulfur hexafluoride (SF 6 ) concentrations (in pptv) in spring discharge closely follow the concurrent monthly measurements of their atmospheric mixing ratios measured at the Air Monitoring Station at Big Meadows, SNP, indicating waters 0–3 years in age. A 2-year (2001–2003) record of unsaturated zone air displayed seasonal deviations from North American Air of ±10 % for CFC-11 and CFC-113, with excess CFC-11 and CFC-113 in peak summer and depletion in peak winter. The pattern in unsaturated zone soil CFCs is a function of gas solubility in soil water and seasonal unsaturated zone temperatures. Using the increase in the SF 6 atmospheric mixing ratio, the apparent (piston flow) SF 6 age of the water varied seasonally between about 0 (modern) in January and up to 3 years in July–August. The SF 6 concentration and concentrations of dissolved solutes (SiO 2 , Ca 2+ , Mg 2+ , Na + , Cl − , and HCO 3 − ) in spring discharge demonstrate a fraction of recent recharge following large precipitation events. The output of solutes in the discharge of springs minus the input from atmospheric deposition per hectare of watershed area (mol ha −1 a −1 ) were approximately twofold greater in watersheds draining the regolith of Catoctin metabasalts than that of granitic gneisses and granitoid crystalline rocks. The stable isotopic composition of water in spring discharge broadly correlates with the Oceanic Niño Index. Below normal precipitation and enriched stable isotopic composition were observed during El Niño years.

Virginia↗

USGS2020

Decadal-scale decoupling of soil phosphorus and molybdenum cycles by temperate nitrogen-fixing trees

Symbiotic nitrogen- (N) fixing trees can influence multiple biogeochemical cycles by fixing atmospheric N, which drives net primary productivity and soil carbon (C) and N accumulation, as well as by mobilizing soil phosphorus (P) and other nutrients to support growth and metabolism. The soil micronutrient molybdenum (Mo) is essential to N-fixation, yet surprisingly little is known of whether N-fixing trees alter soil Mo cycling, and if changes to soil Mo are coupled to soil C, N, and P. We compared how symbiotic N-fixing red alder and non-N-fixing Douglas-fir trees modified surface soil C, N, P, and Mo across variation in climate and other site factors in the Pacific Northwest. We found that after two decades, N-fixing trees drove coupled increases in surface soil C, N, total P, and organic P. Consistent with contributions of N-fixing trees to soil organic matter, increased soil C and N were accompanied by lower δ13C in all sites, and lower δ15N in sites where non-fixer plots exhibited elevated soil δ15N. However, N-fixing trees did not affect surface soil Mo concentrations or fractions, suggesting that different factors control the cycling of P versus Mo over decadal timescales. Random forest analysis revealed that surface soil P was most strongly influenced by factors related to soil C accumulation, whereas surface soil Mo was related primarily to environmental factors, including potential differences in atmospheric Mo deposition across sites. Ratios of surface soil P:Mo were higher in extractable pools than in total soil digests, reinforcing the idea of stronger biotic cycling of P than Mo. Overall, our multi-site, multi-decadal field study found surprisingly small effects of N-fixing trees on soil Mo, despite rapid increases in soil organic C, N, and P. We hypothesize that, rather than direct effects of N-fixing vegetation, abiotic or indirect biotic factors such as soil sorption of atmospheric Mo inputs can link C–N–P–Mo cycles in terrestrial ecosystems on longer timescales.

British Columbia, Washington↗

USGS2025

Seasonal synchronicity and multi-decadal stability of headwater biogeochemistry in the northern temperate zone

Temporal patterns in chemistry of headwater streams reflect responses of water and elemental cycles to perturbations occurring at local to global scales. We evaluated multi-scale temporal patterns in up to 32 y of monthly observations of stream chemistry (ammonium, calcium, dissolved organic carbon, nitrate, total dissolved phosphorus, and sulfate) in 22 reference catchments within the northern temperate zone of North America. Multivariate autoregressive state-space (MARSS) models were applied to quantify patterns at multi-decadal, seasonal, and shorter intervals during a period that encompassed warming climate, seasonal changes in precipitation, and regional declines in atmospheric deposition. Significant long-term trends in solute concentrations within a subset of the catchments were consistent with recovery from atmospheric deposition (e.g., calcium, nitrate, sulfate) and increased precipitation (e.g., dissolved organic carbon). Lack of evidence for multi-decadal trends in most catchments suggests resilience of northern temperate ecosystems or that subtle net effects of simultaneous changes in climate and disturbance regimes do not result in directional trends. Synchronous seasonal oscillations of solute concentrations occurred across many catchments, reflecting shared climate and biotic drivers of seasonality within the northern temperate zone. Despite shared patterns among catchments at a seasonal scale, multi-scale temporal patterns were statistically distinct among even adjacent headwater catchments, implying that local attributes of headwater catchments modify the signals imparted by atmospheric phenomena and regional disturbances. To effectively characterize hydrologic and biogeochemical responses to changing climate and disturbance regimes, catchment monitoring programs could include multiple streams with contributing areas that encompass regional heterogeneity in vegetation, topography, and elevation. Overall, detection of long-term patterns and trends requires monitoring multiple catchments at a frequency that captures periodic variation (e.g., seasonality) and a duration encompassing the perturbations of interest.

Biogeochemistry↗

USGS2010

Mercury trends in fish from rivers and lakes in the United States, 1969-2005

A national dataset on concentrations of mercury in fish, compiled mainly from state and federal monitoring programs, was used to evaluate trends in mercury (Hg) in fish from US rivers and lakes. Trends were analyzed on data aggregated by site and by state, using samples of the same fish species and tissue type, and using fish of similar lengths. Site-based trends were evaluated from 1969 to 2005, but focused on a subset of the data from 1969 to 1987. Data aggregated by state were used to evaluate trends in fish Hg concentrations from 1988 to 2005. In addition, the most recent Hg fish data (1996–2005) were compared to wet Hg deposition data from the Mercury Deposition Network (MDN) over the same period. Downward trends in Hg concentrations in fish from data collected during 1969–1987 exceeded upward trends by a ratio of 6 to 1. Declining Hg accumulation rates in sediment and peat cores reported by many studies during the 1970s and 1980s correspond with the period when the most downward trends in fish Hg concentrations occurred. Downward Hg trends in both sediment cores and fish were also consistent with the implementation of stricter regulatory controls of direct releases of Hg to the atmosphere and surface waters during the same period. The southeastern USA had more upward Hg trends in fish than other regions for both site and state aggregated data. Upward Hg trends in fish from the southeastern USA were associated with increases in wet deposition in the region and may be attributed to a greater influence of global atmospheric Hg emissions in the southeastern USA. No significant trends were found in 62% of the fish species from six states from 1996 to 2005. A lack of Hg trends in fish in the more recent data was consistent with the lack of trends in wet Hg deposition at MDN sites and with relatively constant global emissions during the same time period. Although few significant trends were observed in the more recent Hg concentrations in fish, it is anticipated that Hg concentrations in fish will respond to changes in atmospheric Hg deposition, however, the magnitude and timing of the response is uncertain.

Environmental Monitoring and Assessment↗

USGS2014

A framework for the probabilistic analysis of meteotsunamis

A probabilistic technique is developed to assess the hazard from meteotsunamis. Meteotsunamis are unusual sea-level events, generated when the speed of an atmospheric pressure or wind disturbance is comparable to the phase speed of long waves in the ocean. A general aggregation equation is proposed for the probabilistic analysis, based on previous frameworks established for both tsunamis and storm surges, incorporating different sources and source parameters of meteotsunamis. Parameterization of atmospheric disturbances and numerical modeling is performed for the computation of maximum meteotsunami wave amplitudes near the coast. A historical record of pressure disturbances is used to establish a continuous analytic distribution of each parameter as well as the overall Poisson rate of occurrence. A demonstration study is presented for the northeast U.S. in which only isolated atmospheric pressure disturbances from squall lines and derechos are considered. For this study, Automated Surface Observing System stations are used to determine the historical parameters of squall lines from 2000 to 2013. The probabilistic equations are implemented using a Monte Carlo scheme, where a synthetic catalog of squall lines is compiled by sampling the parameter distributions. For each entry in the catalog, ocean wave amplitudes are computed using a numerical hydrodynamic model. Aggregation of the results from the Monte Carlo scheme results in a meteotsunami hazard curve that plots the annualized rate of exceedance with respect to maximum event amplitude for a particular location along the coast. Results from using multiple synthetic catalogs, resampled from the parent parameter distributions, yield mean and quantile hazard curves. Further refinements and improvements for probabilistic analysis of meteotsunamis are discussed.

Natural Hazards↗

USGS2005

Sources of nitrate in snowmelt discharge: Evidence from water chemistry and stable isotopes of nitrate

To determine whether NO 3 − concentration pulses in surface water in early spring snowmelt discharge are due to atmospheric NO 3 − , we analyzed stream δ 15 N-NO 3 − and δ 18 O-NO 3 − values between February and June of 2001 and 2002 and compared them to those of throughfall, bulk precipitation, snow, and groundwater. Stream total Al, DOC and Si concentrations were used to indicate preferential water flow through the forest floor, mineral soil, and ground water. The study was conducted in a 135-ha subcatchment of the Arbutus Watershed in the Huntington Wildlife Forest in the Adirondack Region of New York State, U.S.A. Stream discharge in 2001 increased from 0.6 before to 32.4 mm day −1 during snowmelt, and element concentrations increased from 33 to 71 μmol L −1 for NO 3 − , 3 to 9 μmol L −1 for total Al, and 330 to 570 μmol L −1 for DOC. Discharge in 2002 was variable, with a maximum of 30 mm day −1 during snowmelt. The highest NO 3 − , Al, and DOC concentrations were 52, 10, and 630 μmol L −1 , respectively, and dissolved Si decreased from 148 μmol L −1 before to 96 μmol L −1 during snowmelt. Values of δ 15 N and δ 18 O of NO 3 − in stream water were similar in both years. Stream water, atmospherically-derived solutions, and groundwaters had overlapping δ 15 N-NO 3 − values. In stream and ground water, δ 18 O-NO 3 − values ranged from +5.9 to +12.9‰ and were significantly lower than the +58.3 to +78.7‰ values in atmospheric solutions. Values of δ 18 O-NO 3 − indicating nitrification, increase in Al and DOC, and decrease in dissolved Si concentrations indicating water flow through the soil suggested a dilution of groundwater NO 3 − by increasing contributions of forest floor and mineral soil NO 3 − during snowmelt.

Water, Air, & Soil Pollution↗

USGS2008

Origins of sediment-associated contaminants to the Marais Vernier, the Seine Estuary, France

The Marais Vernier is the largest freshwater wetland in the Seine Estuary in northern France. It is in a heavily urbanized and industrialized region and could be affected by atmospheric deposition and by fluvial input of contaminants in water diverted from the Seine River. To evaluate contaminant histories in the wetland and the region, sediment cores were collected from two open-water ponds in the Marais Vernier: the Grand-Mare, which was connected to the Seine by a canal from 1950 to 1996, and the Petite Mare, which has a small rural watershed. Diversions from the Seine to the Grand-Mare increased sedimentation rates but mostly resulted in low contaminant concentrations and loading rates, indicating that the sediment from the Seine was predominantly brought upstream by tidal currents from the estuary and was not from the watershed. Atmospheric sources of metals dominate inputs to the Petite Mare; however, runoff of metals from vehicle-related sources in the watershed might contribute to the upward trends in concentrations of Cr, Cu, and Zn. Estimates of atmospheric deposition using the Petite Mare core are consistent with measured deposition in the region and are mixed (similar for Hg and Pb; larger for Cd, Cu, and Zn) compared with deposition estimated from sediment cores in the northeastern United States. A local source of PAHs in the watershed of the Petite Mare is indicated by higher concentrations, higher accumulation rates, and a different, more petrogenic, PAH assemblage than in the Grand-Mare. The study illustrates how diverse sources and transport pathways can affect wetlands in industrial regions and can be evaluated using sediment cores from the wetland ponds. ?? 2008 Springer Science+Business Media B.V.

Water, Air, & Soil Pollution↗

USGS1985

Sulphur in char and char desulphurization by acid leaching and hydropyrolysis

Sulphur compounds volatilized during pyrolysis of acid-leached char were measured to determine characteristics of char desulphurization reactions. Pyrolysis of char in a hydrogen atmosphere (hydropyrolysis) produced a much higher concentration of thiophenic organics compared with that produced during pyrolysis in a nitrogen atmosphere. Hydrogen sulphide gas evolution, at progressively increasing pyrolysis temperature in a helium atmosphere, was measured on five char samples: untreated char, hydrochloric acid-leached char, and three model chars: a demineralized char and two demineralized chars incorporated with sulphur via reactions with elemental sulphur. Hydrogen sulphide gas evolution in untreated char and acid-leached char was found to peak in three temperature regions; the maxima are thought to relate to sulphur in different bonding environments. The amounts of hydrogen sulphide volatilized were much higher for acid-leached char than for untreated char. The gas evolved from each of the remaining three samples showed a single peak region corresponding closely to one of the three peak regions observed for the first two chars. The results of this study indicate that elemental sulphur was produced during hydrochloric acid leaching of the untreated char and suggested that the improved rate of desulphurization observed in the char that had been acid-leached before hydropyrolysis was due in part to the conversion of strongly bound mineral sulphur forms to more weakly bound sulphur forms that are predominantly elemental sulphur in character, and are more easily removed by hydrogen.

Fuel↗

USGS1976

Studies of quaternary saline lakes-II. Isotopic and compositional changes during desiccation of the brines in Owens Lake, California, 1969-1971

Owens Lake is an alkaline salt lake in a closed basin in southeast California. It is normally nearly dry, but in early 1969, an abnormal runoff from the Sierra Nevada flooded it to a maximum depth of 2·4 m. By late summer of 1971, the lake was again nearly dry and the dissolved salts recrystallized. Changes in the chemistry, pH, and deuterium content were monitored during desiccation. During flooding, salts (mostly trona, halite, and burkeite) dissolved slowly from the lake floor. Their concentration in the lake waters increased as evaporation removed water and salts again crystallized, but winter temperatures caused precipitation of some salts and the following summer warming caused their solution, resulting in seasonal variations in the concentration patterns of some ions. The pH values (9·4–10·4) changed with time but showed no detectable diurnal pattern. The deuterium concentration increased during evaporation and appeared to be in equilibrium with vapor leaving the lake according to the Rayleigh equation. The effective α(D/H in liquid/D/H in vapor) decreased as salinity increased; the earliest measured value was 1·069 [as total dissolved solids (TDS) of lake waters changed from 136,200 to 250,400 mg/1]and the last value (calc.) was 1·025 (as TDS changed from 450,000 to 470,300 mg/1). Deuterium exchange with the atmosphere was apparently small except during late desiccation stages when the isotopic contrast became great. Eventually, atmospheric exchange, combined with decreasing α and lake size and increasing salinity, stopped further deuterium concentration in the lake. The maximum contrast between atmospheric vapor and lake deuterium contents was about 110%.

Geochimica et Cosmochimica Acta↗

USGS1995

The geochemical cycling of stable Pb, 210Pb, and 210Po in seasonally anoxic Lake Sammamish, Washington, USA

The geochemical processes controlling the behavior of stable Pb, 210 Pb, and 210 po in seasonally anoxic Lake Sammamish, Washington were identified from water column distributions and box model calculations. Total (sum of dissolved and particulate) inventories of stable Pb, 210 Pb, and 210 Po increased in the whole lake during the latter part of the oxic stage of the lake and were attributed to diffusion from sediments. Large decreases in the total inventories of these elements occurred during the transition from oxic to anoxic conditions, and the lowest inventories were observed during the sulfidic stage of stratification. The cycling of stable Pb and 210 Pb during oxic periods appeared to be linked to Fe cycling while 210 Po cycling was more closely linked to the cycling of Mn. The behavior of stable and radioactive Pb and, possibly, 210 Po during anoxia was influenced by sulfur cycling. Thermodynamic calculations indicated that dissolved Pb concentrations might be controlled by PbS precipitation during anoxia. Flux balance calculations during stratification indicated that atmospheric deposition was the major source of both 210 Pb and 210 Po to the lake and fluvial input was more important for 210 Po than for 210 Pb. 210 Pb and 210 Po supplied by atmospheric deposition were scavenged and removed by sedimentation from the epilimnion. Residence times with respect to scavenging and sedimentation in the epilimnion were 1–3 and 617 days, respectively, for 210 Pb and 9–22 and 9–26 days for 210 Po. Model results in the hypolimnion indicated that at certain times the radionuclides diffused out of the sediments and at other times into the sediments. Residence times with respect to sedimentation of particulate nuclides in the hypolimnion were 2–124 days for 210 Pb and 8–48 days for 210 Po. The behavior of 210 Pb and 210 Po in Lake Sammamish was compared to that in B~' kford Reservoir, Massachusetts. Although the comparison indicated similarities (e.g., links to Fe and Mn cycling, larger scavenging rates for 210 Pb than for 210 Po), the major differences between the systems were that atmospheric inputs were greater than fluvial inputs, activities of the radionuclides were lower, and the presence of sulfide in the hypolimnion during anoxia affected the cycling of stable Pb, 210 Pb, and 210 Po in Lake Sammamish.

Washington↗

USGS2016

Iron oxide minerals in dust-source sediments from the Bodélé Depression, Chad: Implications for radiative properties and Fe bioavailability of dust plumes from the Sahara

Atmospheric mineral dust can influence climate and biogeochemical cycles. An important component of mineral dust is ferric oxide minerals (hematite and goethite) which have been shown to influence strongly the optical properties of dust plumes and thus affect the radiative forcing of global dust. Here we report on the iron mineralogy of dust-source samples from the Bodélé Depression (Chad, north-central Africa), which is estimated to be Earth’s most prolific dust producer and may be a key contributor to the global radiative budget of the atmosphere as well as to long-range nutrient transport to the Amazon Basin. By using a combination of magnetic property measurements, Mössbauer spectroscopy, reflectance spectroscopy, chemical analysis, and scanning electron microscopy, we document the abundance and relative amounts of goethite, hematite, and magnetite in dust-source samples from the Bodélé Depression. The partition between hematite and goethite is important to know to improve models for the radiative effects of ferric oxide minerals in mineral dust aerosols. The combination of methods shows (1) the dominance of goethite over hematite in the source sediments, (2) the abundance and occurrences of their nanosize components, and (3) the ubiquity of magnetite, albeit in small amounts. Dominant goethite and subordinate hematite together compose about 2% of yellow-reddish dust-source sediments from the Bodélé Depression and contribute strongly to diminution of reflectance in bulk samples. These observations imply that dust plumes from the Bodélé Depression that are derived from goethite-dominated sediments strongly absorb solar radiation. The presence of ubiquitous magnetite (0.002–0.57 wt%) is also noteworthy for its potentially higher solubility relative to ferric oxide and for its small sizes, including PM < 0.1 μm. For all examined samples, the average iron apportionment is estimated at about 33% in ferric oxide minerals, 1.4% in magnetite, and 65% in ferric silicates. Structural iron in clay minerals may account for much of the iron in the ferric silicates. We estimate that the mean ferric oxides flux exported from the Bodélé Depression is 0.9 Tg/yr with greater than 50% exported as ferric oxide nanoparticles (<0.1 μm). The high surface-to-volume ratios of ferric oxide nanoparticles once entrained into dust plumes may facilitate increased atmospheric chemical and physical processing and affect iron solubility and bioavailability to marine and terrestrial ecosystems.

Aeolian Research↗

USGS2017

Terrestrial subaqueous seafloor dunes: Possible analogs for Venus

Dunes on Venus, first discovered with Magellan Synthetic Aperture Radar (SAR) in the early 1990s, have fueled discussions about the viability of Venusian dunes and aeolian grain transport. Confined to two locations on Venus, the existence of the interpreted dunes provides evidence that there could be transportable material being mobilized into aeolian bedforms at the surface. However, because of the high-pressure high-temperature surface conditions, laboratory analog studies are difficult to conduct and results are difficult to extrapolate to full-sized, aeolian bedforms. Field sites of desert dunes, which are well-studied on Earth and Mars, are not analogous to what is observed on Venus because of the differences in the fluid environments. One potentially underexplored possibility in planetary science for Venus-analog dune fields could be subaqueous, seafloor dune fields on Earth. Known to the marine geology communities since the early 1960s, seafloor dunes are rarely cited in planetary aeolian bedform literature, but could provide a necessary thick-atmosphere extension to the classically studied aeolian dune environment literature for thinner atmospheres. Through discussion of the similarity of the two environments, and examples of dunes and ripples cited in marine literature, we provide evidence that subaqueous seafloor dunes could serve as analogs for dunes on Venus. Furthermore, the evidence presented here demonstrates the usefulness of the marine literature for thick-atmosphere planetary environments and potentially for upcoming habitable worlds and oceanic environment research program opportunities. Such useful cross-disciplinary discussion of dune environments is applicable to many planetary environments (Earth, Mars, Venus, Titan, etc.) and potential future missions.

Aeolian Research↗

USGS2014

Hemispheric-scale wind selection facilitates bar-tailed godwit circum-migration of the Pacific

The annual 29 000 km long migration of the bar-tailed godwit, Limosa lapponica baueri, around the Pacific Ocean traverses what is arguably the most complex and seasonally structured atmospheric setting on Earth. Faced with marked variation in wind regimes and storm conditions across oceanic migration corridors, individuals must make critical decisions about when and where to fly during nonstop flights of a week's duration or longer. At a minimum, their decisions will affect wind profitability and thus reduce energetic costs of migration; in the extreme, poor decisions or unpredictable weather events will risk survival. We used satellite telemetry to track the annual migration of 24 bar-tailed godwits and analysed their flight performance relative to wind conditions during three major migration legs between nonbreeding grounds in New Zealand and breeding grounds in Alaska. Because flight altitudes of birds en route were unknown, we modelled flight efficiency at six geopotential heights across each migratory segment. Birds selected departure dates when atmospheric conditions conferred the greatest wind assistance both at departure and throughout their flights. This behaviour suggests that there exists a cognitive mechanism, heretofore unknown among migratory birds, that allows godwits to assess changes in weather conditions that are linked (i.e. teleconnected) across widely separated atmospheric regions. Godwits also showed adaptive flexibility in their response not only to cues related to seasonal changes in macrometeorology, such as spatial shifting of storm tracks and temporal periods of cyclogenesis, but also to cues associated with stochastic events, especially at departure sites. Godwits showed limits to their response behaviours, however, especially relative to rapidly developing stochastic events while en route. We found that flight efficiency depended significantly upon altitude and hypothesize that godwits exhibit further adaptive flexibility by varying flight altitude en route to optimize flight efficiency.

Animal Behaviour↗

USGS2012

Recent paleorecords document rising mercury contamination in Lake Tanganyika

Recent Lake Tanganyika Hg deposition records were derived using 14 C and excess 210 Pb geochronometers in sediment cores collected from two contrasting depositional environments: the Kalya Platform, located mid-lake and more removed from watershed impacts, and the Nyasanga/Kahama River delta region, located close to the lake’s shoreline north of Kigoma. At the Kalya Platform area, pre-industrial Hg concentrations are 23 ± 0.2 ng/g, increasing to 74 ng/g in modern surface sediment, and the Hg accumulation rate has increased from 1.0 to 7.2 μg/m 2 /a from pre-industrial to present, which overall represents a 6-fold increase in Hg concentration and accumulation. At the Nyasanga/Kahama delta region, pre-industrial Hg concentrations are 20 ± 3 ng/g, increasing to 46 ng/g in surface sediment. Mercury accumulation rate has increased from 30 to 70 μg/m 2 /a at this site, representing a 2–3-fold increase in Hg concentration and accumulation. There is a lack of correlation between charcoal abundance and Hg accumulation rate in the sediment cores, demonstrating that local biomass burning has little relationship with the observed Hg concentration or Hg accumulation rates. Examined using a sediment focusing-corrected mass accumulation rate approach, the cores have similar anthropogenic atmospheric Hg deposition profiles, suggesting that after accounting for background sediment concentrations the source of accumulating Hg is predominantly atmospheric in origin. In summary, the data document an increase of Hg flux to the Lake Tanganyika ecosystem that is consistent with increasing watershed sediment delivery with background-level Hg contamination, and regional as well as global increases in atmospheric Hg deposition.

Tanzania, the Democratic Republic of the Congo , B↗

USGS2005

234Th, 210Pb, 210Po and stable Pb in the central equatorial Pacific: Tracers for particle cycling

Samples were collected during the 1992 US JGOFS EqPac Survey I and II cruises from 12??N to 12??S at 140??W in the central equatorial Pacific for water column profiles of dissolved, particulate and total 234Th, 210Pb and 210Po and total acid soluble stable Pb and sediment trap fluxes of 234Th, 210Pb and 210Po. Survey I occurred in February/March with moderate El Nino conditions while Survey II was conducted in September/October when there was a well developed cold-tongue. 234Th, 210Pb and 210Po are all particle reactive yet they partition differently between dissolved and particulate phases. Fractionation factors (the ratios of the distribution coefficients) show that the selectivity for suspended and sediment trap particles follows Th>Po>Pb. Scavenging residence times (??) for 234Th, 210Pb and 210Po ranged from 25 to 100 d, 3 to 8 years and 100 to 500 d, respectively. These particle reactive tracers have very different distributions in the water column, which reflect differences in their sources and sinks. The deficiency of 234Th relative to 238U was fairly uniformly distributed meridionally, though deficiencies were higher during Survey II when there was higher new production. Excess 210Pb relative to 226Ra was very asymmetrical with much higher excess values north of the equator. The distributions were similar for Surveys I and II. The deficiency of 210Po relative to 210Pb had a symmetrical distribution about the equator for both Survey I and II but the deficiencies were larger during Survey I when upwelling was smaller. Stable Pb was generally higher at the surface than at 250 m and there was no meridional trend from 12??N to 12??S. A mass balance for 210Pb was used to determine the atmospheric input of 210Pb. The average values for Surveys I and II were 0.12 and 0.32 dpm cm-2 year-1, respectively. There was no general increase in atmospheric input of 210Pb north of the equator but there was a strong maximum at 2-3??N during Survey I coincident with the location of the intertropical convergence zone (ITCZ), suggesting a large role for wet deposition. A mass balance for stable Pb was used to determine the atmospheric input of stable Pb. Results ranged from 110 to 140 pmol cm-2 year-1. This flux was low in the southern hemisphere and increased steadily north of the equator. We evaluated use of 210Po as a tracer for export of particulate organic matter during Survey I. Organic carbon and 210Po were highly correlated in suspended matter and sediment trap samples. Average values of organic carbon fluxes determined from the deficiencies of 210Po times the orgC/210Po ratio agreed well with those determined from the deficiencies of 234Th times the organic carbon/234Th ratio and 15N-new production, but had a much larger variability because of the more variable advection corrections. ?? 2005 Elsevier Ltd. All rights reserved.

Deep-Sea Research Part I: Oceanographic Research P↗

USGS2007

Application of a coupled ecosystem-chemical equilibrium model, DayCent-Chem, to stream and soil chemistry in a Rocky Mountain watershed

Atmospheric deposition of sulfur and nitrogen species have the potential to acidify terrestrial and aquatic ecosystems, but nitrate and ammonium are also critical nutrients for plant and microbial productivity. Both the ecological response and the hydrochemical response to atmospheric deposition are of interest to regulatory and land management agencies. We developed a non-spatial biogeochemical model to simulate soil and surface water chemistry by linking the daily version of the CENTURY ecosystem model (DayCent) with a low temperature aqueous geochemical model, PHREEQC. The coupled model, DayCent-Chem, simulates the daily dynamics of plant production, soil organic matter, cation exchange, mineral weathering, elution, stream discharge, and solute concentrations in soil water and stream flow. By aerially weighting the contributions of separate bedrock/talus and tundra simulations, the model was able to replicate the measured seasonal and annual stream chemistry for most solutes for Andrews Creek in Loch Vale watershed, Rocky Mountain National Park. Simulated soil chemistry, net primary production, live biomass, and soil organic matter for forest and tundra matched well with measurements. This model is appropriate for accurately describing ecosystem and surface water chemical response to atmospheric deposition and climate change. ?? 2006 Elsevier B.V. All rights reserved.

Ecological Modelling↗