Springs of Great Britain

Predictably, in a country such as Britain, with its preponderance of consolidated, sedimentary, mainly fissure-flow aquifers, there is a very large number of springs, many of which are, or have been, used for public supply. Migratory springs are a feature of the British (Ur. Cretaceous) Chalk, the most important British aquifer. The Chalk's low specific yield and high capillary moisture retention together give rise to very considerable fluctuations (more than 33 m in some areas) of the unconfined water table. Along the gentle dip slopes of the Chalk (North and South Downs of southern and southeastern England) springs may migrate laterally for several miles, giving rise to seasonal streams locally known as bournes or lavants. However, springs such as at Duncton, West Sussex, at the base of the much steeper scarp slopes of the Chalk, form point sources, the flows from which tend to be relatively steady; such springs commonly supply and are the original reason for the existence of many of the small towns and villages which nestle along the bases of the chalk scarps of Sussex and Kent.Where the Chalk forms coastal cliffs, a number of springs break out at the base of the cliff between high and low tide levels; there are major chalk coastal springs, for instance, at St. Margaret's Bay (Kent) and at Arish Mells, east of Lulworth Cove, Dorset. Such springs are not used for direct supply (their salinity is usually too high) but are indicators of the presence of local reserves of groundwater for possible future development.     

Temperature evolution in the presence of anisotropic stresses

In a recent paper by Das et al. (Astrophys. Space Sci. 361:99, 2016) it was shown that the sign of the anisotropy parameter plays a pivotal role in determining the time of formation of the horizon of a collapsing radiating star. Spurred on by this observation we investigate the impact of the (an)isotropy featured in the (Das et al. in Astrophys. Space Sci. 361:99, 2016) collapsing model on the temperature profiles of the evolving system. We show that the temperature within the stellar interior is increased as the anisotropy in the pressure grows. Relaxational effects due to heat dissipation within the core further enhances the temperature at each interior point of the stellar distribution.     

Short-term sedimentation dynamics in the Rhône River Delta. France: The importance of riverine pulsing

Short-term sedimentation patterns were evaluated from August 1992 to May 1993 in different wetland habitats characteristic of the Rhône Delta, including impounded and seasonally-dry saline Arthrocnemum marshes, brackish Juncus, Phragmites, and Scirpus riverine wetlands directly connected to the Rhône River, and Arthrocnemum-dominated marine marshes influenced by the Mediterranean. Short-term sedimentation was measured as sediment accumulation on paper filters which had been placed on the soil surface for several weeks. Total sedimentation and material lost on ignition was significantly related to individual sampling periods, reflecting the importance of short-term processes. High sedimentation at riverine sites (up to 22 g m^?2 d^?1) was related to a combination of river stage and wind events. Marine and impounded wetlands of the Rhône Delta experienced low sedimentation throughout the period of study. Sedimentation rates averaged over the study period were 0.8 g m^?2 d^?1, 1.8 g m^?2 d^?1, and 5.4 g m^?2 d^?1 for marine, impounded, and riverine sites, respectively. Percent material lost on ignition was low in all habitats (average 15%) and followed a seasonal trend with a minimum in late fall and winter (1%). Soil percent organic matter was also low in the top several centimeters (13%), suggesting that inorganic sedimentation is very important for accretion on these wetland surfaces. Coastal flooding was not a significant mechanism for sedimentation in the marine sites during the period of study. Sedimentation is an important factor in elevation change, and this study shows that impounded habitats, the most common “natural environment“ left in the delta, may become vulnerable to sea-level rise in the future if management practices continue to isolate these wetlands from riverine sources of sediment.     

Oxygen isotope heterogeneity of the mantle beneath the Canary Islands: a discussion of the paper of Gurenko et al.

Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) report laser-assisted fluorination (LF) and secondary ionization mass spectrometry (SIMS) ¹⁸O/¹⁶O datasets for olivine grains from the Canary Islands of Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro. As with prior studies of oxygen isotopes in Canary Island lavas (e.g. Thirlwall et al. Chem Geol 135:233–262, 1997; Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010), these authors find variations in δ¹⁸O_ol (~4.6–6.0 ‰) beyond that measured for mantle peridotite olivine (Mattey et al. Earth Planet Sci Lett 128:231–241, 1994) and interpret this variation to reflect contributions from pyroxenite-peridotite mantle sources. Furthermore, Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) speculate that δ¹⁸O_ol values for La Palma olivine grains measured by LF (Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) may be biased to low values due to the presence of altered silicate, possibly serpentine. The range in δ¹⁸O_ol values for Canary Island lavas are of importance for constraining their origin. Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) took a subset (39 SIMS analyses from 13 grains from a single El Hierro lava; EH4) of a more extensive dataset (321 SIMS analyses from 110 grains from 16 Canary Island lavas) to suggest that δ¹⁸O_ol is weakly correlated (R ² = 0.291) with the parameter used by Gurenko et al. (Earth Planet Sci Lett 277:514–524, 2009) to describe the estimated weight fraction of pyroxenite-derived melt (Xpx). With this relationship, end-member δ¹⁸O values for HIMU-peridotite (δ¹⁸O = 5.3 ± 0.3 ‰) and depleted pyroxenite (δ¹⁸O = 5.9 ± 0.3 ‰) were defined. Although the model proposed by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) implicates similar pyroxenite-peridotite mantle sources to those proposed by Day et al. (Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) and Day and Hilton (Earth Planet Sci Lett 305:226–234, 2011), there are significant differences in the predicted δ¹⁸O values of end member components in the two models. In particular, Day et al. (Geochim Cosmochim Acta 74:6565–6589, 2010) proposed a mantle source for La Palma lavas with low-δ¹⁸O (<5 ‰), rather than higher-δ¹⁸O (c.f. the HIMU-peridotite composition of Gurenko et al. in Contrib Mineral Petrol 162:349–363, 2011). Here we question the approach of using weakly correlated variations in δ¹⁸O_ol and the Xpx parameter to define mantle source oxygen isotope compositions, and provide examples of why this approach appears flawed. We also provide reasons why the LF datasets previously published for Canary Island lavas remain robust and discuss why LF and SIMS data may provide complementary information on oxygen isotope variations in ocean island basalts (OIB), despite unresolved small-scale uncertainties associated with both techniques.     

Supercritical gas sorption on moist coals

The effect of moisture on the CO₂ and CH₄ sorption capacity of three bituminous coals from Australia and China was investigated at 55 °C and at pressures up to 20 MPa. A gravimetric apparatus was used to measure the gas adsorption isotherms of coal with moisture contents ranging from 0 to about 8%. A modified Dubinin–Radushkevich (DR) adsorption model was found to fit the experimental data under all conditions. Moisture adsorption isotherms of these coals were measured at 21 °C. The Guggenheim–Anderson–de Boer (GAB) model was capable of accurately representing the moisture isotherms over the full range of relative pressures.Moist coal had a significantly lower maximum sorption capacity for both CO₂ and CH₄ than dry coal. However, the extent to which the capacity was reduced was dependent upon the rank of the coal. Higher rank coals were less affected by the presence of moisture than low rank coals. All coals exhibited a certain moisture content beyond which further moisture did not affect the sorption capacity. This limiting moisture content was dependent on the rank of the coal and the sorbate gas and, for these coals, corresponded approximately to the equilibrium moisture content that would be attained by exposing the coal to about 40–80% relative humidity. The experimental results indicate that the loss of sorption capacity by the coal in the presence of water can be simply explained by volumetric displacement of the CO₂ and CH₄ by the water. Below the limiting moisture content, the CO₂ sorption capacity reduced by about 7.3 kg t^− 1 for each 1% increase in moisture. For CH₄, sorption capacity was reduced by about 1.8 kg t^− 1 for each 1% increase in moisture.The heat of sorption calculated from the DR model decreased slightly on addition of moisture. One explanation is that water is preferentially attracted to high energy adsorption sites (that have high energy by virtue of their electrostatic nature), expelling CO₂ and CH₄ molecules.     

Evidence for distinct proportions of subducted oceanic crust and lithosphere in HIMU-type mantle beneath El Hierro and La Palma, Canary Islands

Shield-stage high-MgO alkalic lavas from La Palma and El Hierro (Canary Islands) have been characterized for their O-Sr-Nd-Os-Pb isotope compositions and major-, trace-, and highly siderophile-element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundances. New data are also reported for associated evolved rocks, and entrained xenoliths. Clear differences in Pd/Ir and isotopic ratios for high Os (>50 ppt) lavas from El Hierro (δ¹⁸O_olivine = 5.17 ± 0.08‰; ⁸⁷Sr/⁸⁶Sr = 0.7029 to 0.7031; ε_Nd = +5.7 to +7.1; ¹⁸⁷Os/¹⁸⁸Os = 0.1481 to 0.1750; ²⁰⁶Pb/²⁰⁴Pb = 19.1 to 19.7; Pd/Ir = 6 ± 3) versus those from La Palma (δ¹⁸O_olivine = 4.87 ± 0.18‰; ⁸⁷Sr/⁸⁶Sr = 0.7031 to 0.7032; ε_Nd = +5.0 to +6.4; ¹⁸⁷Os/¹⁸⁸Os = 0.1421 to 0.1460; ²⁰⁶Pb/²⁰⁴Pb = 19.5 to 20.2; Pd/Ir = 11 ± 4) are revealed from the dataset.Crustal or lithospheric assimilation during magma transport cannot explain variations in isotopic ratios or element abundances of the lavas. Shallow-level crystal-liquid fractionation of olivine, clinopyroxene and associated early-crystallizing minerals (e.g., spinel and HSE-rich phases) controlled compatible element and HSE abundances; there is also evidence for sub-aerial degassing of rhenium. High-MgO lavas are enriched in light rare earth elements, Nb, Ta, U, Th, and depleted in K and Pb, relative to primitive mantle abundance estimates, typical of HIMU-type oceanic island basalts. Trace element abundances and ratios are consistent with low degrees (2-6%) of partial melting of an enriched mantle source, commencing in the garnet stability field (?110 km). Western Canary Island lavas were sulphur undersaturated with estimated parental melt HSE abundances (in ppb) of 0.07 ± 0.05 Os, 0.17 ± 0.16 Ir, 0.34 ± 0.32 Ru, 2.6 ± 2.5 Pt, 1.4 ± 1.2 Pd, 0.39 ± 0.30 Re. These estimates indicate that Canary Island alkali basalts have lower Os, Ir and Ru, but similar Pt, Pd and Re contents to Hawai’ian tholeiites.The HIMU affinities of the lavas, in conjunction with the low δ¹⁸O_olivine and high ²⁰⁶Pb/²⁰⁴Pb for La Palma, and elevated ¹⁸⁷Os/¹⁸⁸Os for El Hierro implies melting of different proportions of recycled oceanic crust and lithosphere. Our preferred model to explain isotopic differences between the islands is generation from peridotitic mantle metasomatised by <10% pyroxenite/eclogite made from variable portions of similar aged recycled oceanic crust and lithosphere. The correspondence of radiogenic ²⁰⁶Pb/²⁰⁴Pb, ¹⁸⁷Os/¹⁸⁸Os, elevated Re/Os and Pt/Os, and low-δ¹⁸O in western Canary Island lavas provides powerful support for recycled oceanic crust and lithosphere to generate the spectrum of HIMU-type ocean island basalt signatures. Persistence of geochemical heterogeneities throughout the stratigraphies of El Hierro and La Palma demonstrate long-term preservation of these recycled components in their mantle sources over relatively short-length scales (∼50 km).     

MoisturEC: A New R Program for Moisture Content Estimation from Electrical Conductivity Data

Noninvasive geophysical estimation of soil moisture has potential to improve understanding of flow in the unsaturated zone for problems involving agricultural management, aquifer recharge, and optimization of landfill design and operations. In principle, several geophysical techniques (e.g., electrical resistivity, electromagnetic induction, and nuclear magnetic resonance) offer insight into soil moisture, but data‐analysis tools are needed to “translate” geophysical results into estimates of soil moisture, consistent with (1) the uncertainty of this translation and (2) direct measurements of moisture. Although geostatistical frameworks exist for this purpose, straightforward and user‐friendly tools are required to fully capitalize on the potential of geophysical information for soil‐moisture estimation. Here, we present MoisturEC, a simple R program with a graphical user interface to convert measurements or images of electrical conductivity (EC) to soil moisture. Input includes EC values, point moisture estimates, and definition of either Archie parameters (based on experimental or literature values) or empirical data of moisture vs. EC. The program produces two‐ and three‐dimensional images of moisture based on available EC and direct measurements of moisture, interpolating between measurement locations using a Tikhonov regularization approach.     

Deep events in U.K. South Western Approaches

Summary. Apparently planar dipping events are observed in seismic data off south-west Britain within otherwise essentially transparent upper and middle crust. These are believed to represent Variscan thrusts, some of which were re-activated during the post-Carboniferous phase of extension that affected the southern U.K. They can be seen in two extensive commercial seismic surveys recorded to 6 s two-way-time (TWT) and, where laterally persistent, they have been mapped to reveal their essentially planar nature. Commonly these dipping events are associated with deeper, near-horizontal, or gently convex upwards events with which they often appear to converge. Where 'real', these are thought to indicate a complex fault system or possibly the top of the reflective lower crust. The thrusts are seen over the whole area except where granite is known to occur, and commonly exert a major control on the position and subsequent deformation of overlying sedimentary basins.