Local Spring Research Articles

Urea distribution and uptake in the Atlantic Ocean between 50°N and 50°S

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 368:53-63 (2008) - DOI: https://doi.org/10.3354/meps07586 Urea distribution and uptake in the Atlantic Ocean between 50°N and 50°S Stuart C. Painter1,*, Richard Sanders1, Howard N. Waldron2, Michael I. Lucas1,3, Sinhue Torres-Valdes1 1Ocean Biogeochemistry and Ecosystems, National Oceanography Centre, Southampton, European Way, Southampton, SO14 3ZH, UK 2Department of Oceanography, University of Cape Town, Private Bag, Rondebosch 7701, Cape Town, South Africa 3Present address: Department of Zoology, University of Cape Town, Private Bag, Rondebosch 7701, Cape Town, South Africa *Email: scp@noc.soton.ac.uk ABSTRACT: We investigate the distribution of urea and its uptake by phytoplankton during 3 meridional transects of the Atlantic Ocean between 50°N and 50°S. Significant relationships were identified between urea uptake and Prochlorococcus abundance (p < 0.01) in the northern subtropical Atlantic, where Prochlorococcus appears likely to dominate urea uptake, and between urea concentration and the <200 µm microplankton biomass fraction (p < 0.005) in the South Atlantic, which may be associated with the production of urea. These results suggest that the distribution of urea in the subtropical ocean may be controlled by regional imbalances between urea consumption and urea production. In parallel with these simple relationships significant spring-autumn seasonal changes in the distribution of urea were identified in southern subtropical and tropical latitudes. Urea was twice as abundant during local spring than during local autumn in the subtropical South Atlantic but 2.5 times more abundant in equatorial waters during the boreal autumn period. Euphotic zone integrated urea uptake rates also varied seasonally, being considerably higher in the North Atlantic temperate and subtropical latitudes during the boreal spring whilst in the subtropical South Atlantic urea uptake peaked in local autumn. KEY WORDS: Urea concentration · Prochlorococcus · Seasonal variability · Atlantic Meridional Transect · Urea uptake Full text in pdf format PreviousNextCite this article as: Painter SC, Sanders R, Waldron HN, Lucas MI, Torres-Valdes S (2008) Urea distribution and uptake in the Atlantic Ocean between 50°N and 50°S. Mar Ecol Prog Ser 368:53-63. https://doi.org/10.3354/meps07586 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 368. Online publication date: September 25, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

The impact of tunneling construction on the hydrogeological environment of “Tseng-Wen Reservoir Transbasin Diversion Project” in Taiwan

Groundwater flow and the associated surface water flow are potential negative factors on underground tunnels. Early detection of environmental impacts on water resources is of significant importance to planning, design and construction of tunnel projects, as early detection can minimize accidents and project delays during construction. The groundwater modeling software package Groundwater Modeling System (GMS), which supports the groundwater numerical codes MODFLOW and FEMWATER, was utilized to determine the impact of tunneling excavation on the hydrogeological environment in a regional area around the tunnel and a local hot springs area, at the “Tseng-Wen Reservoir Transbasin Diversion Project”, in Taiwan. A hydrogeological conceptual model was first developed to simplify structures related to the site topography, geology and geological structure. The MODFLOW code was then applied to simulate groundwater flow pattern for the hydrogeological conceptual model in the tunnel area. The automated parameter estimation method was applied to calibrate groundwater level fluctuation and hydrogeological parameters in the region. Calibration of the model demonstrated that errors between simulated and monitored results are smaller than allowable errors. The study also observed that tunneling excavation caused groundwater to flow toward the tunnel. No obvious changes in the groundwater flow field due to tunnel construction were observed far away in the surrounding regions. Furthermore, the FEMWATER code for solving 3-D groundwater flow problems, in which hydrogeological characteristics are integrated into a geographic information system (GIS), is applied to evaluate the impact of tunnel construction on an adjacent hot spring. Simulation results indicated that the groundwater drawdown rate is less than the groundwater recharge rate, and the change to the groundwater table after tunnel construction was insignificant for the hot spring area. Finally, the groundwater flow obtained via the GMS indicated that the hydrogeological conceptual model can estimate the possible quantity of tunnel inflow and the impact of tunnel construction on the regional and local groundwater resources regime of the transbasin diversion project.

Stiffness analysis of overconstrained parallel manipulators

The paper presents a new stiffness modeling method for overconstrained parallel manipulators with flexible links and compliant actuating joints. It is based on a multidimensional lumped-parameter model that replaces the link flexibility by localized 6-dof virtual springs that describe both translational/rotational compliance and the coupling between them. In contrast to other works, the method involves a FEA-based link stiffness evaluation and employs a new solution strategy of the kinetostatic equations for the unloaded manipulator configuration, which allows computing the stiffness matrix for the overconstrained architectures, including singular manipulator postures. The advantages of the developed technique are confirmed by application examples, which deal with comparative stiffness analysis of two translational parallel manipulators of 3-PUU and 3-PRPaR architectures. Accuracy of the proposed approach was evaluated for a case study, which focuses on stiffness analysis of Orthoglide parallel manipulator.

Equinox transition at the magnetic equator in Africa: analysis of ESF ionograms

Abstract. We study equatorial night-time F layer behaviour from quarter-hourly ionograms at Korhogo/Ivory Coast (9.2° N, 5° W, dip lat. −2.4°) during local Spring March–April 1995, declining solar flux period, according to the magnetic activity. The height and thickness of the F-layer are found to vary intensely with time and from one day to the next. At time of the equinox transition, by the end of March, a net change of the nightly height-time variation is observed. The regime of a single height peak phase before 22 March changes to up to three main F-layer height phases after 30 March, each associated to a dominant mechanism. The first phase is identified to the post-sunset E×B pulse, the second phase associated to a change in the wind circulation phenomenon and the third one attributed to pre-sunrise phenomena. The influence of the magnetic activity is identified by the increase in the second peak amplitude. After the 21 April magnetic-equinox period, the height-time morphology becomes more irregular suggesting meridional wind abatement. The initiation, the growth and the maintenance of ESF are explored in relation to these nightly variations. The Rayleigh-Taylor instability is clearly identified as main precursor phenomenon. This is followed by the P-type (F-layer peak spread) structures, the whole with no specific dependence on the magnetic activity and on the F-layer phases, in contrast to further I and F-type (Inside and Frequency spread) ESFs. We discuss our results in the light of recent advanced experiments in Peru and the pacific.

Long-range cohesive interactions of non-local continuum faced by fractional calculus

A non-local continuum model including long-range forces between non-adjacent volume elements has been studied in this paper. The proposed continuum model has been obtained as limit case of two fully equivalent mechanical models: (i) A volume element model including contact forces between adjacent volumes as well as long-range interactions, distance decaying, between non-adjacent elements. (ii) A discrete point-spring model with local springs between adjacent points and non-local springs with distance-decaying stiffness connecting non-adjacent points. Under the assumption of fractional distance-decaying interactions between non-adjacent elements a fractional differential equation involving Marchaud-type fractional derivatives has been obtained for unbounded domains. It is shown that for unbounded domains the two mechanical models revert to Lazopoulos and Eringen model with fractional distance-decaying functions. It has also been shown that for a confined bar, the stress–strain relation is substantially different from that obtained simply using the truncated Marchaud derivatives since a double integral instead of convolution integral appears. Moreover, in the analysis of bounded domains, the governing equations turn out to an integro-differential equation including only the integral part of Marchaud fractional derivatives on finite interval. The mechanical boundary condition for the proposed model has been introduced consistently on the basis of mechanical considerations, and the constitutive law of the proposed continuum model has been reported by mathematical induction. Several numerical applications have been reported to show, verify and assess the concepts listed in this paper.

Forensic Isotope Analysis to Refine a Hydrologic Conceptual Model

Water resources in the arid southwestern United States are frequently the subject of conflict from competing private and public interests. Legal remedies may remove impasses, but the technical analysis of the problem often determines the future success of legal solutions. In Owens Valley, California, the source of water for the Los Angeles Aqueduct (LAA) is flow diverted from the Owens River and its tributaries and ground water from valley aquifers. Future management of ground water delivered to the LAA needs technical support regarding quantity available, interconnection of shallow and confined aquifers, impact on local springs, and rate of recharge. Ground water flow models and ground water composition are tools already in use, but these have large uncertainty for local interpretations. This study conducted targeted sampling of springs and wells to evaluate the hydrologic system to corroborate conceptual and numerical models. The effort included measurement of intrinsic isotopic composition at key locations in the aquifers. The stable isotopic data of boron (delta(11)B), sulfur (delta(34)S), oxygen (delta(18)O), hydrogen (delta D), and tritium ((3)H) supported by basic chemical data provided rules for characterizing the upper and the lower aquifer system, confirmed the interpretation of ground water flow near faults and flow barriers, and detected hydraulic connections between the LAA and the perennial springs at key locations along the unlined reach of the LAA. This study exemplifies the use of forensic isotopic approaches as independent checks on the consistency of interpretations of conceptual models of a ground water system and the numerical hydrologic simulations.

Genealogical analysis of the diversity of spring barley cultivars released in former Czechoslovakia and modern Czech Republic

Genealogical analysis was employed in studying the time course of changes in genetic diversity of spring barley cultivars released in former Czechoslovakia and the modem Czech Republic. Cultivars from different regions proved to significantly differ in the distribution of dominant ancestor contributions, suggesting a specificity of original ancestors to different cultivation conditions. A comparison of cultivar groups differing in end use showed that the genetic diversity of malting cultivars was significantly lower than that of feed cultivars, although modern malting and feed cultivars of Czechia and Slovakia have virtually the same genetic basis. Temporal analysis showed that diversity tended to increase through decades. While new original ancestors were introduced in pedigrees, especially in the past 30 years, the number of local landraces and old cultivars gradually decreased. The losses accounted for about two-thirds of the local germplasm. Thus, a substantial increase in genetic diversity was accompanied by genetic erosion of the local spring barley gene pool of former Czechoslovakia. A cluster structure was observed for the set of spring barley cultivars released in the postwar period. The coefficient of parentage averaged overall possible pairs of cultivars introduced in the Czech National List was estimated at 0.11. It was concluded that the genetic diversity of modern spring barley cultivars in the Czech Republic is at an acceptable level.

Colline

First, a reprise for potentially new or actually forgetful readers. Published in 1929, Colline is a cautionary tale about the reluctant reawakening of a small peasant community to an awareness that humans and Nature are reciprocally cruel. In a semi-ruined hamlet, an old man, Janet, lies paralysed but rambling incessantly. When the local spring dries up, he withholds his water-divining skills. He becomes the focus of his neighbours' attention, which veers from fear to hatred. Could there be a connection between his flow of apparently crazy words and the loss of their water-supply? He is a Cassandra bellowing in the remote reaches of Upper Provence. Giono's pacifism, soon to be given full rein in his Le Grand Troupeau (1931), is active already in this pagan sermon on the mountain. Janet dies before Jaume and Gondran can kill him off as the fount of evil, which embraces his semi-magic knowledge. The spring restarts to flow. Forgetting what they have learnt — the need to live in respectful partnership with nature — Jaume shoots a boar. The novel ends with its corpse leaking tears of blood on to the grass. Perhaps, like Melville's Ahab, in pursuing evil, the villagers have become evil themselves.

Hypogene Zn carbonate ores in the Angouran deposit, NW Iran

The world-class Angouran nonsulfide Zn–Pb deposit is one of the major Zn producers in Iran, with resources estimated at about 18 Mt at 28% Zn, mainly in the form of the Zn carbonate smithsonite. This study aims to characterize these carbonate ores by means of their mineralogy and geochemistry, which has also been extended to the host rocks of mineralization and other local carbonate rock types, including the prominent travertines in the Angouran district, as well as to the local spring waters. Petrographical, chemical, and stable isotope (O, H, C, Sr) data indicate that the genesis of the Zn carbonate ores at Angouran is fairly distinct from that of other “classical” nonsulfide Zn deposits that formed entirely by supergene processes. Mineralization occurred during two successive stages, with the zinc being derived from a preexisting sulfide ore body. A first, main stage of Zn carbonates (stage I carbonate ore) is associated with both preexisting and subordinate newly formed sulfides, whereas a second stage is characterized by supergene carbonates (Zn and minor Pb) coexisting with oxides and hydroxides (stage II carbonate ore). The coprecipitation of smithsonite with galena, pyrite and arsenopyrite, as well as the absence of Fe- and Mn-oxides/hydroxides and of any discernible oxidation or dissolution of the sphalerite-rich primary sulfide ore, shows that the fluids responsible for the main, stage I carbonate ores were relatively reduced and close to neutral to slightly basic pH with high fCO2. Smithsonite δ18OVSMOW values from stage I carbonate ore range from 18.3 to 23.6‰, while those of stage II carbonate ore show a much smaller range between 24.3 and 24.9‰. The δ13C values are fairly constant in smithsonite of stage I carbonate ore (3.2–6.0‰) but show a considerable spread towards lower δ13CVPDB values (4.6 to −11.2‰) in stage II carbonate ore. This suggests a hypogene formation of stage I carbonate ore at Angouran from low-temperature hydrothermal fluids, probably mobilized during the waning stages of Tertiary–Quaternary volcanic activity in an environment characterized by abundant travertine systems throughout the whole region. Conversely, stage II carbonate ore is unambiguously related to supergene weathering, as evidenced by the absence of sulfides, the presence of Fe-Mn-oxides and arsenates, and by high δ18O values found in smithsonite II. The variable, but still relatively heavy carbon isotope values of supergene smithsonite II, suggests only a very minor contribution by organic soil carbon, as is generally the case in supergene nonsulfide deposits.

Climatic effects on arrival and laying dates in a long‐distance migrant, the Collared Flycatcher Ficedula albicollis

Long‐distance migrants may respond to climate change in breeding, wintering or staging area by changing their phenology. The geographical variation in such responses (e.g. coastal vs. continental Europe) and the relative importance of climate at different spatial scales remain unclear. Here we analysed variation in first arrival dates (FADs) and laying dates of the Collared Flycatcher Ficedula albicollis in a central European population, from 1973 to 2002. The North Atlantic Oscillation (NAO) index correlated weakly with local temperature during the laying period. Decreasing spring temperatures until 1980 were associated with a trend towards later laying. The rate of warming (0.2 °C per year) and laying advancement (0.4 days per year) since 1980 are amongst the highest values reported elsewhere. This long‐term trend in laying date was largely explained by the change in climatic factors. The negative effect of local spring temperature on laying was relatively stronger than that of NAO. The number of clutches initiated on a particular day was marginally affected by the temperature 3 days prior to laying and the response of females to daily variation in temperature did not change over years. Correspondence between the average population‐level and the individual‐level responses of laying date to climate variation suggests that the advancement of laying was due to phenotypic plasticity. Despite warmer springs and advanced laying, FADs did not change over years and were not correlated with local spring temperature. Marginal evidence suggests later departure from wintering grounds and faster migration across staging areas in warmer conditions. Advancement of arrival was probably constrained by low local temperatures in early spring just before arrival that have not changed over years. The interval between first arrival and laying has declined since 1980 (0.5 days per year), but the increasing temperature during that period may have kept the food supply approximately unchanged.

Seasonal water use patterns of Juniperus ashei on the Edwards Plateau, Texas, based on stable isotopes in water

Summary Naturally occurring stable isotopes of oxygen and hydrogen were used to determine the seasonal water sources of Juniperus ashei and its relationship with soil water content on the Edwards Plateau of central Texas, Honey Creek State Natural Area. The patchy nature of juniper stands rooting in the thin soils over karstified carbonate bedrock imparts large spatial heterogeneity in soil water content and isotopic composition largely by differential shading, but also by canopy interception. There is a seasonal decrease in the oxygen isotope composition of juniper xylem water by ∼2‰ during the transition from hot, dry summer conditions to the cool, moist winter. Prior to this shift, the xylem water isotope composition is similar to local springs, presumed to represent local groundwater; after this shift, the xylem water composition is similar to soil water below 10 cm. These results suggest a change in juniper water use from a dominantly deep water source during the summer to a dominantly soil source during the winter over the study period, but the timing of this transition will likely vary from year to year.

A composite solution method for physical equations and its application in the Nea Kessani geothermal field (Greece)

We propose a method for solving physical equations under conditions of uncertainty and we use it to study the Nea Kessani (Greece) geophysical system formed by a thermal reservoir of arcosic sandstones. The method is based on the Bayesian maximum entropy theory and generates temperature solutions that are (1) composite, in the sense that apart from being consistent with the physical model, they also account for the multisourced uncertainty of the model parameters and the site‐specific information at a set of vertical drill holes indicating that hot fluids rising from depth enter the reservoir in a restricted area and flow toward local thermal springs; and (2) complete, in the sense that the whole temperature probability density is generated at each spatial location. From these densities, different temperature maps can be derived (most probable, error minimizing, etc., maps), depending on the study objectives. The proposed composite solution is distinguished from the standard (direct) physical model solution in a formal mathematical sense. By means of comparative analysis, it is shown that the numerical composite solution is more informative than the direct temperature solution as well as the analytical solution obtained using simplified boundary conditions (the composite solution offers a more realistic representation of the real‐world phenomenon, and unlike the previous methods, it is in agreement with empirical quartz geothermometry analyses). The composite method can be a valuable contribution for scientists and engineers working on incorporating secondary information for improving the quality of the solutions obtained from a physical model in general.

Spatial and seasonal variations of elemental composition in Mt. Everest (Qomolangma) snow/firn

In May 2005, a total of 14 surface snow (0–10 cm) samples were collected along the climbing route from the advanced base camp to the summit (6500–8844 m a.s.l.) on the northern slope of Mt. Everest (Qomolangma). A 108 m firn/ice core was retrieved from the col of the East Rongbuk Glacier (28.03°N, 86.96°E, 6518 m a.s.l.) on the north eastern saddle of Mt. Everest in September 2002. Surface snow and the upper 3.5 m firn samples from the core were analyzed for major and trace elements by inductively coupled plasma mass spectroscopy (ICP-MS). Measurements show that crustal elements dominated both surface snow and the firn core, suggesting that Everest snow chemistry is mainly influenced by crustal aerosols from local rock or prevalent spring dust storms over southern/central Asia. There are no clear trends for element variations with elevation due to local crustal aerosol inputs or redistribution of surface snow by strong winds during the spring. Seasonal variability in snow/firn elements show that high elemental concentrations occur during the non-monsoon season and low values during the monsoon season. Ca, Cr, Cs, and Sr display the most distinct seasonal variations. Elemental concentrations (especially for heavy metals) at Mt. Everest are comparable with polar sites, generally lower than in suburban areas, and far lower than in large cities. This indicates that anthropogenic activities and heavy metal pollution have little effect on the Mt. Everest atmospheric environment. Everest firn core REE concentrations are the first reported in the region and seem to be comparable with those measured in modern and Last Glacial Maximum snow/ice samples from Greenland and Antarctica, and with precipitation samples from Japan and the East China Sea. This suggests that REE concentrations measured at Everest are representative of the background atmospheric environment.

Divergent origins of sympatric herring population components determined using genetic mixture analysis

The origin and reproductive interactions of sympatric, spatially separated spawning components of Atlantic herring Clupea harengus have received long-standing interest. In the west- ern Baltic most herring spawn in spring, with smaller components spawning in winter. We used microsatellite DNA analysis and a novel Bayesian genetic mixture analysis approach to compare the genetic relationships of 2 western Baltic winter-spawning aggregations with those of their sympatric spring-spawning components, and combined information for genetic markers and morphological traits (otolith-determined hatching time and growth relationships) to test alternative hypotheses for the origin of winter spawners. We show that genetic relationships between sympatric components differ greatly between the 2 locations; the results indicate that winter spawning has arisen via 2 fundamentally different processes: (1) as a result of 'spawning-time switching' in a local spring- spawning component and (2) via 1 or more founder events from an extant winter-spawning popula- tion into an area otherwise dominated by spring spawners.

Long-term trends in first arrival and first egg laying dates of some migrant and resident bird species in northern Italy

Climate change is affecting the phenology of seasonal events in Europe and the Northern Hemisphere, as shown by several studies of birds' timing of migration and reproduction. Here, we analyse the long-term (1982-2006) trends of first arrival dates of four long-distance migratory birds [swift (Apus apus), nightingale (Luscinia megarhynchos), barn swallow (Hirundo rustica), and house martin (Delichon urbicum)] and first egg laying dates of two migrant (swift, barn swallow) and two resident species [starling (Sturnus vulgaris), Italian sparrow (Passer italiae)] at a study site in northern Italy. We also addressed the effects of local weather (temperature and precipitation) and a climate index (the North Atlantic Oscillation, NAO) on the interannual variability of phenological events. We found that the swift and the barn swallow significantly advanced both arrival and laying dates, whereas all other species did not show any significant temporal trend in either arrival or laying date. The earlier arrival of swifts was explained by increasing local temperatures in April, whereas this was not the case for arrival dates of swallows and first egg laying dates of both species. In addition, arrival dates of house martins were earlier following high NAO winters, while nightingale arrival was earlier when local spring rainfall was greater. Finally, Italian sparrow onset of reproduction was anticipated by greater spring rainfall, but delayed by high spring NAO anomalies, and swift's onset of reproduction was anticipated by abundant rainfall prior to reproduction. There were no significant temporal trends in the interval between onset of laying and arrival in either the swift or the barn swallow. Our findings therefore indicate that birds may show idiosyncratic responses to climate variability at different spatial scales, though some species may be adjusting their calendar to rapidly changing climatic conditions.

On Balloon Drawings of Rooted Trees

Among various styles of tree drawing, balloon drawing, where each subtree is enclosed in a circle, enjoys a desirable feature of displaying tree structures in a rather balanced fashion. We first design an efficient algorithm to optimize angular resolution and aspect ratio for the balloon drawing of rooted unordered trees. For the case of ordered trees for which the center of the enclosing circle of a subtree need not coincide with the root of the subtree, flipping the drawing of a subtree (along the axis from the parent to the root of the subtree) might change both the aspect ratio and the angular resolution of the drawing. We show that optimizing the angular resolution as well as the aspect ratio with respect to this type of rooted ordered trees is reducible to the perfect matching problem for bipartite graphs, which is solvable in polynomial time. Aside from studying balloon drawing from an algorithmic viewpoint, we also propose a local magnetic spring model for producing dynamic balloon drawings with applications to the drawings of galaxy systems, H-trees, and sparse graphs, which are of practical interest.

Influence of groundwater flow on thermochronometer-derived exhumation rates in the central Nepalese Himalaya

Research Article| September 01, 2007 Influence of groundwater flow on thermochronometer-derived exhumation rates in the central Nepalese Himalaya David M. Whipp, Jr.; David M. Whipp, Jr. 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Todd A. Ehlers Todd A. Ehlers 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (9): 851–854. https://doi.org/10.1130/G23788A.1 Article history received: 09 Feb 2007 rev-recd: 27 Apr 2007 accepted: 03 May 2007 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David M. Whipp, Todd A. Ehlers; Influence of groundwater flow on thermochronometer-derived exhumation rates in the central Nepalese Himalaya. Geology 2007;; 35 (9): 851–854. doi: https://doi.org/10.1130/G23788A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Mountain topography creates variations in water-table elevation that drive groundwater flow. Consequently, advective heat transport by topography-driven fluid flow can modify the crustal thermal field and bias exhumation rates calculated from thermochronometer data. Although previous studies have considered the thermal effects of fluid flow, none has quantified the influence on thermochronometer ages. We use a steady-state three-dimensional coupled hydraulic thermokinematic finite-element model to simulate the influence of fluid flow on exhumation rates derived from thermochronometer data in the Nepalese Himalaya. Local hot springs suggest substantial heat transport by fluid flow and are adjacent to apatite fission-track samples. Model hydraulic conductivity controls the rate of fluid flow, and values characteristic of fractured rock (>>10−9 m/s) yield a fluid advection–dominated thermal field. Hydraulic conductivity is estimated by minimizing the misfit between predicted and observed hot spring thermal power. The best-fit hydraulic conductivity value of ∼5 × 10−7 m/s produces a fluid advection–dominated thermal field and older predicted apatite fission-track ages. To fit the observed age-elevation relationship, model-predicted ages require denudation rates that are ∼5 mm/yr, ∼200% higher than predictions from thermal models that do not simulate fluid flow. Thus, true exhumation rates can be substantially underestimated in orogenic systems where fluid advection is significant. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Moisture source in the Hyblean Mountains region (south-eastern Sicily, Italy): Evidence from stable isotopes signature

Abstract Here the authors present results of an isotope study on precipitation collected during a 2-a period from a rain-gauge network consisting of 6 stations located at different elevations in the Hyblean Mountains (HM) region, in south-eastern Sicily. The slope of the local meteoric water line ( δD = 6.50 δ 18 O + 9.87) obtained for the region suggests that precipitation is affected by evaporation during rainfall events. The main variations in rainwater isotope composition are due to seasonal effects and elevation. An average 2 H excess value of +21.2‰ was found for precipitation events less affected by evaporation (i.e. when the rainfall was >65 mm/month). The spatial distribution of O isotope composition of precipitation shows a negative gradient from east and south to the inner areas. The depositional rate of Cl, used as a tracer of the origin of air masses, is highest at the coastal rain-gauges (SR and MRG stations) and lowest on the northern flank of the HM region (SC station). Based on these findings, a model is proposed for the origin of precipitation in the HM region, which assumes that a Mediterranean-derived component is the main source of moisture in the studied area. D/H and 18 O/ 16 O ratios of inferred meteoric recharge waters were also compared with the isotope composition of waters collected from the main local springs and wells. The best linear fit of the δ 18 O vs δD relationship for Hyblean groundwater is δD = 4.85 δ 18 O–2.01. The enrichment of heavy isotopes in Hyblean groundwater is probably due to evaporation occurring after precipitation events or to a recharging contribution from surface waters (lakes or rivers) enriched in heavy isotopes.

Evidence for long‐range transport of carbon monoxide in the Southern Hemisphere from SCIAMACHY observations

The SCIAMACHY satellite instrument shows enhanced carbon monoxide (CO) columns in the Southern Hemisphere during the local Spring. Chemistry‐transport model simulations using the new GFEDv2 biomass‐burning emission database show a similar temporal and spatial CO distribution, indicating that the observed enhancements are mainly due to biomass burning (BB). Large differences between the year 2003 and 2004 are observed in both the measurements and the model for South America and Australia. This study analyzes the origin of these observed enhancements in the Southern Hemisphere. The fact that SCIAMACHY is sensitive to surface CO allows for the observation of enhanced CO columns in both emission areas and in areas that are affected by long‐range transport of CO. Model results show a large contribution of South American BB CO over Australian BB regions during the 2004 BB season of up to ∼30–35% and up to 55% further south, with smaller contributions for 2003. BB CO transported from southern Africa contributes up to ∼40% in 2003 and ∼30% in 2004. The results indicate that differences between SCIAMACHY CO and the model simulations over Australian BB areas are probably not only caused by uncertainties in local emissions but also in overseas emissions.

Evaporation in the Atacama Desert: An empirical study of spatio-temporal variations and their causes

Summary The Atacama Desert is hyper-arid, and areas where adequate moisture exists for evaporation are spatially highly restricted. Nevertheless, water resources exist and their evaluation requires knowledge of this elusive but important component of the hydrological cycle. Evaporation may occur in four typical areas: rivers and associated riparian zones, localized springs, large playas and extensive areas of bare soil after infrequent precipitation events. Transpiration is locally possible where moisture is sufficiently close to the surface to allow phreatophytes or scarce grass cover to grow, but virtually no information is available for quantification. Pan evaporation data from 11 stations for the period 1977–1991 is analyzed and complemented by analysis of an evaporation study conducted in the Salar de Atacama during 1987/1988. The results show that pan evaporation, and hence maximum potential evaporation may be considered largely a function of maximum temperature and elevation as well as density of the evaporating fluid. Actual evaporation is limited by available moisture and diminishes rapidly as the level of soil moisture saturation drops below the soil surface, extinguishing at ca. 2 m depth. Evaporation is greatest during the summer, but at higher elevations convective cloudiness develops during January and February reducing evaporating rates at a time when significant precipitation may occur. Inter-annual variations in pan evaporation are considerable and weakly correlated with ENSO, but variations in actual evaporation are damped by comparison. Regression equations are developed which have widespread applicability and may be used to estimate evaporation in areas where no site-specific data exists.