ALBERT

Description: Spatial and temporal trends in stream chemistry have been used to provide insights into the scale dependencies of streamflow generation processes in small catchments. However, these scale dependencies have not been thoroughly investigated at large watershed scales (defined as drainage areas greater than 1000 km2). Quantifying these scale dependencies is critical to understanding how large watersheds will respond to future perturbations; e.g., the long-term streamflow response to climate change and/or changes in land-cover and land-use. Here we investigate the spatial and temporal scaling relationships of all dominant streamflow generation processes in a large alpine watershed in the southern Rocky Mountains of Colorado. Observations in the watershed indicate that dominant streamflow processes are spatially and temporally variable. The relative strengths of dominant streamflow mechanisms vary as a function of internal watershed structure (i.e., spatial variability in topographic relief, soil development, groundwater flowpath development, and stream network structure) and external forcing such as timing and character of precipitation. This behavior coupled with previous observations that streamflow from the watershed contained a significant component of basin-scale groundwater, suggests that similar large watersheds may have internal buffering, at least initially, against rapid change.

Description: GOCE gravity gradient data of the entire science mission and data from LAGEOS-1/2 and GRACE were combined in the construction of a satellite-only gravity field model to maximum degree 300. When compared to EGM2008 it is more accurate at low to medium resolution thanks to GOCE and GRACE data. When compared to earlier releases of ESA GOCE models, it is more accurate at high degrees owing to the larger amount of data ingested, which was moreover taken at lower altitude. The impact of orbiting at lower altitude in the last year of the mission is large: a model based on data of the last 14 months is significantly more accurate than the Release 4 model constructed with the first 28 months. The (calibrated) cumulated geoid error estimate at 100 km resolution is 1.7 cm. The optimal resolution of the GOCE model for oceanographic application is between 100 and 125 km.

Description: ABSTRACT Twenty-first century snow depth and snow water equivalent (SWE) changes are assessed for three time periods (2020–2049, 2045–2079 and 2070–2099) at 11 stations in Switzerland with the physics-based snow model SNOWPACK and meteorological input data perturbed by the output from ten regional climate models (RCMs) through the delta change method. Unlike in previous studies, incoming long-wave radiation has also been modified for future climatic conditions. We thus show the range of future snow simulations assuming different RCM projections. Model validation yields satisfying results for simulating snow depth and SWE for the reference period with errors in the order of 9% and 15%, respectively. For the end of the century, the stations between 1000–1700 m a.s.l. show no pronounced elevation dependence but surprisingly react quite similarly in terms of the relative magnitude of snow cover decrease, which may reach 90%. The projected small increase in winter precipitation has almost no effect at these stations, but incoming long-wave radiation has an important effect. At the high-elevation station Weissfluhjoch (2540 m a.s.l.) however, the precipitation increase is partly able to compensate for the increased temperature. This would imply that the snow cover at mid-elevation stations becomes temperature and radiation dominated and will react similarly to the spatially small differences in the projected temperature change. The low-elevation stations already show a strong decrease in the near future, and the inclusion of modified incoming long-wave radiation has almost no effect on the decrease of future snow depth and SWE because the temperatures are already close to the melting point in the reference period. At the end of the century, mean snow depth/SWE are reduced by 35/32%, 83/86% and 96/97% at high-, mid- and low-elevations, respectively.

Description: [1]  Reprocessed GOCE gravity gradient data were combined with data from LAGEOS-1/2 and GRACE to generate a satellite-only gravity field model to degree 260 using the direct approach, named DIR-R4. When compared to EGM2008 it is more accurate at low to medium resolution thanks to GOCE and GRACE data. When compared to earlier releases of ESA GOCE models, it is more accurate at high degrees owing to the larger amount of data ingested. It is also slightly more accurate than ESA's fourth release of the Time-Wise model (TIM-R4), as demonstrated by GPS/leveling, orbit determination tests, and an oceanographic evaluation. According to the formal, probably too optimistic by a factor 2 to 2.5, cumulated geoid (1.3 cm) and gravity anomaly (0.4 mGal) errors at 100 km resolution, the GOCE mission objectives have been reached.

Description: Springs are integral components of the unique web of life in desert ecosystems of the western United States. Many desert springs would not exist without local mountains to intercept and store water from rainfall and snowmelt, and many desert aquatic ecosystems would not exist without the springs, illustrating the connectivity between landscape processes (the realm of geoscientists) and ecosystem functioning (the realm of ecologists). On a human scale, early exploration, inhabitation, and survival in the arid and semiarid western United States would not have been feasible without springs. People living there today continue to value springs as dependable sources of water for irrigation, livestock, drinking, and recreational and economic uses (e.g., hot springs). Unfortunately, some desert springs may be less resistant to the effects of climate change than others. How can this resistance be quantified?

Description: We investigate the relationship between sulfur degassing and oxygen fugacity at Erta Ale and Masaya volcanoes. Oxygen fugacity was assessed utilizing Fe 3+ /∑Fe ratios and major element compositions measured in olivine-hosted melt inclusions and matrix glasses. Erta Ale melts have Fe 3+ /∑Fe of 0.15 to 0.16, reflecting f O 2 of ΔQFM 0.0±0.3, which is indistinguishable from f O 2 calculated from CO 2 /CO ratios in high temperature gases. Masaya is more oxidized at ΔQFM +1.7±0.4, typical of arc settings. Sulfur isotope compositions of gases and scoria at Erta Ale (δ 34 S gas -0.5‰; δ 34 S scoria +0.9‰) and Masaya (δ 34 S gas +4.8‰; δ 34 S scoria +7.4‰) reflect distinct sulfur sources, as well as isotopic fractionation during degassing (equilibrium and kinetic fractionation effects). Sulfur speciation in melts plays an important role in isotope fractionation during degassing and S 6+ /∑S is 〈0.07 in Erta Ale melt inclusions compared to 〉0.67 in Masaya melt inclusions. No change is observed in Fe 3+ /∑Fe or S 6+ /∑S with extent of S degassing at Erta Ale, indicating negligible effect on f O 2 , and further suggesting that H 2 S is the dominant gas species exsolved from the S 2- -rich melt (i.e. no redistribution of electrons). High SO 2 /H 2 S observed in gas emissions is due to gas re-equilibration at low pressure and fixed f O 2. Sulfur budget considerations indicate that the majority of S injected into the systems is emitted as gas, which is therefore representative of the magmatic S isotope composition. The composition of the Masaya gas plume (+4.8‰) cannot be explained by fractionation effects but rather reflects recycling of high δ 34 S sulfate through the subduction zone.

Description: [1]  Residence times provide vital information on hydrological, geochemical, and ecological processes in watersheds. The common perception is that mean residence times in watersheds are very short, on the order of days to years. However, there is growing concern that longer residence times of centuries to millennia are not being captured by traditional surface water age-dating methods. We hypothesize that if mean residence times are biased short, then weathering rates calculated from mean residence times will be forced unrealistically high to match observed solute concentrations. We test this hypothesis by calculating weathering rates from springs based upon residence times estimated using three different age-dating methods. Observed solute concentrations require unrealistically large weathering rates if typical short residence times are employed as compared to rates derived from longer residence times. Residence-time distributions in watersheds have substantially longer tails than previously thought, with implications for age-dating methods and their interpretation to infer process behavior.

Description: [1]  Adsorption of noble gases into solids is often posited to account for their abundance patterns in meteorites, terrestrial rocks, and planetary atmospheres. Since these elements present isotope variations among geochemical reservoirs, we have experimentally tested the possibility that adsorption of neutral noble gases could result in isotopic fractionation. Our experiment consists of a cycle of adsorption/desorption processes in which xenon is progressively lost from a reservoir by equilibrium adsorption on kerogen and on montmorillonite. Any isotopic fractionation would then be amplified by the Rayleigh-like distillation experiment. The fractionation factors α are extrapolated to be -0.18 ± 0.08 ‰ per u and -0.22 ± 0.07 ‰ per u (both at the 2 σ level) for kerogen and montmorillonite, respectively. Thus, adsorption of neutral noble gases alone cannot account for the specific isotopic composition of noble gases trapped in meteorites, nor for the isotopic composition of xenon in the terrestrial and martian atmospheres.

Description: [1]  A long-term perspective on Mars’ exosphere variability at 405 km is provided by merging together density data derived from precise orbit determination of the Mars Global Surveyor (MGS) and Mars Odyssey (MO) satellites extending from 2001 to 2010. Thesedata are heavily weighted towards afternoon local times at high latitudes in the Southern Hemisphere. Clear long-term solar and annual variations are well-captured by empirical formulas. Residuals from the empirical fit show evidence for relative depletions in exosphere density around Mars’ closest approach to Earth, which would be consistent with a scavenging mechanism that is dependent on solar wind dynamic pressure. Superimposed on this variation with Mars-Sun distance are positive density residuals during MY25, MY27 and MY 29 that are apparently due to elevated dust levels in Mars’ middle atmosphere. However, during MY24, MY26 and MY28 there are dust level increases without any corresponding increase in exosphere density. We suspect that this inconsistency is related to a variable ability to sense the response to dust-related effects, imposed by the high-latitude limitations of our measurements combined with interference between the mechanisms that translate middle atmosphere heating to an exosphere response. Evidence also supports the hypothesis that winter Helium bulge effects contributed to the inferred inter-annual density variability during the 2007-2009 solar minimum period, when the O-He transition height likely resided near the ∼ 405 km orbit of MO.