The Vema Transverse Ridge (Central Atlantic)

Transverse ridges are elongate reliefs running parallel and adjacent to transform/fracture zones offsetting mid-ocean ridges. A major transverse ridge runs adjacent to the Vema transform (Central Atlantic), that offsets the Mid-Atlantic Ridge by 320 km. Multibeam morphobathymetric coverage of the entire Vema Transverse ridge shows it is an elongated (300 km), narrow (<30 km at the base) relief that constitutes a topographic anomaly rising up to 4 km above the predicted thermal contraction level. Morphology and lithology suggest that the Vema Transverse ridge is an uplifted sliver of oceanic lithosphere. Topographic and lithological asymmetry indicate that the transverse ridge was formed by flexure of a lithospheric sliver, uncoupled on its northern side by the transform fault. The transverse ridge can be subdivided in segments bound by topographic discontinuities that are probably fault-controlled, suggesting some differential uplift and/or tilting of the different segments. Two of the segments are capped by shallow water carbonate platforms, that formed about 3–4 m.y. ago, at which time the crust of the transverse ridge was close to sea level. Sampling by submersible and dredging indicates that a relatively undisturbed section of oceanic lithosphere is exposed on the northern slope of the transverse ridge. Preliminary studies of mantle-derived ultramafic rocks from this section suggest temporal variations in mantle composition. An inactive fracture zone scarp (Lema fracture zone) was mapped south of the Vema Transverse ridge. Based on morphology, a fossil RTI was identified about 80 km west of the presently active RTI, suggesting that a ridge jump might have occurred about 2.2 m.a. Most probable causes for the formation of the Vema Transverse ridge are vertical motions of lithospheric slivers due to small changes in the direction of spreading of the plates bordering the Vema Fracture Zone.     

AzTEC millimetre survey of the COSMOS field – I. Data reduction and source catalogue

We present a 1.1 mm wavelength imaging survey covering 0.3 deg² in the COSMOS field. These data, obtained with the AzTEC continuum camera on the James Clerk Maxwell Telescope, were centred on a prominent large-scale structure overdensity which includes a rich X-ray cluster at z ≈ 0.73. A total of 50 mm-galaxy candidates, with a significance ranging from 3.5 to 8.5σ, are extracted from the central 0.15 deg² area which has a uniform sensitivity of ∼1.3 mJy beam⁻¹. 16 sources are detected with S/N ≥ 4.5, where the expected false-detection rate is zero, of which a surprisingly large number (9) have intrinsic (deboosted) fluxes ≥5 mJy at 1.1 mm. Assuming the emission is dominated by radiation from dust, heated by a massive population of young, optically obscured stars, then these bright AzTEC sources have far-infrared luminosities  >6 × 10¹² L_⊙  and star formation rates  >1100 M_⊙ yr⁻¹  . Two of these nine bright AzTEC sources are found towards the extreme peripheral region of the X-ray cluster, whilst the remainder are distributed across the larger scale overdensity. We describe the AzTEC data reduction pipeline, the source-extraction algorithm, and the characterization of the source catalogue, including the completeness, flux deboosting correction, false-detection rate and the source positional uncertainty, through an extensive set of Monte Carlo simulations. We conclude with a preliminary comparison, via a stacked analysis, of the overlapping MIPS 24-μm data and radio data with this AzTEC map of the COSMOS field.     

Carbon disulfide in the estuarine, coastal, and oceanic environments

The concentration of carbon disulfide (CS₂) in surface water and relevant hydrographic parameters were determined in coastal waters of the eastern USA (Delaware Bay and Chesapeake Bay, including the Potomac River; 7–11 September 1986). The CS₂ concentration varied extensively along the cruise track, from 4 to 510 pmol S(CS₂) l⁻¹ (n = 103). The average values in estuarine, shelf, and oceanic waters were found to be 118 ± 100 pmol S(CS₂) l⁻¹ (n = 54), 51 ± 34 pmol S(CS₂) l⁻¹ (n = 14), and 28 ± 12 pmol S(CS₂) l⁻¹ (n = 35), respectively. To help interpret the geochemical behavior of CS₂, we analyzed the depth distribution of CS₂ in the North Atlantic Ocean during an earlier cruise (23 April–2 May 1986). In most cases, these depth profiles show a near-surface maximum at about 10–20 m depth and a relatively steep gradient below this maximum. Based on the distribution pattern in the water column and evidence provided by earlier workers, we propose that diffusion of CS₂ from bottom sediments may contribute to CS₂ levels in surface seawater. The atmospheric concentration of CS₂ was also investigated at some locations during the September cruise. Except during periods when there was a significant anthropogenic input, the concentration of CS₂ in air was generally in the range of 4–15 pptv (parts per trillion by volume) with a mean of 10.4 ± 4.0 pptv (n = 10). The calculated sea-to-air emission rates of CS₂ at each of our sampling stations show a decreasing trend across estuarine, shelf, and oceanic areas, in agreement with the trend in surface water concentrations.     

Reactions of aqueous iron-DFOB (desferrioxamine B) complexes with flavin mononucleotide in the absence of strong iron(II) chelators

The mechanisms controlling microbial uptake of Fe^III-siderophore complexes and subsequent release of the metal for cellular use have been extensively studied in recent years. Reduction of the Fe^III center is believed to be necessary to labilize the coordinated Fe and facilitate exchange with cellular ligands. Previous studies report reduction of Fe^III-DFOB by various reducing agents in solutions containing Fe^II-chelating colorimetric agents for monitoring reaction progress, but the importance of these findings is unclear because the colorimetric agents themselves stabilize and enhance the reactions being monitored. This study examines the reduction of Fe^III complexes with DFOB (desferrioxamine B), a trihydroxamate siderophore, by the fully reduced hydroquinone form of flavin mononucleotide (FMN_HQ) in the absence of strong Fe^II-chelating agents, and Fe redox cycling in solutions containing DFOB and oxidized and reduced FMN species. Experimental results demonstrate that the rate and extent of Fe^III-DFOB reduction is strongly dependent on pH and FMN_HQ concentration. At pH ? 5, incomplete Fe^III reduction is observed due to two processes that re-oxidize Fe^II, namely, the autodecomposition of Fe^II-DFOB complexes (Fe^II oxidation is coupled with reduction of a protonated hydroxamate moiety) and reaction of Fe^II-DFOB complexes with the fully oxidized flavin mononucleotide product (FMN_OX). Chemical speciation-dependent kinetic models for the forward reduction process and both reverse Fe^II oxidation processes are developed, and coupling kinetic models for all three Fe redox processes leads to successful predictions of steady-state Fe^II concentrations observed over a range of pH conditions in the presence of excess FMN_HQ and FMN_OX. The observed redox reactions are also in agreement with thermodynamic constraints imposed by the combination of Fe^III/Fe^II and FMN_OX/FMN_HQ redox couples. Quantitative comparison between kinetic trends and changing Fe speciation reveals that FMN species react predominantly with diprotonated Fe^III-DFOB and Fe^II-DFOB complexes, where protonation of one hydroxamate group opens up two Fe coordination positions. This finding suggests that ternary complex formation (FMN-Fe-DFOB) facilitates inner-sphere electron transfer reactions between the flavin and Fe center.     

Submarine groundwater discharge revealed by aerial thermal infrared imagery: a case study on Jeju Island,Korea

Submarine groundwater discharge (SGD) is a global phenomenon that carries large volumes of groundwater and dissolved chemical species such as nutrient, metals, and organic compounds to coastal zones. We report the influence of SGD on the coastal waters of Jeju Island, Korea, using high‐resolution aerial thermal infrared (TIR) mapping techniques and field investigations. An aircraft‐based system was implemented using a cost‐effective TIR camera for aerial TIR mapping. Ground‐based calibrations and system integration with GPS/IMU (global positioning system/inertial measurement unit) were performed for the aerial systems. The aerial surveys showed distinct low‐temperature signatures of SGD along the coasts of Jeju Island, revealing large groundwater inputs from the coastal aquifers to the ocean. Multiple aerial surveys over a range of seasons and tidal stages revealed that SGD rates dynamically affect the sea surface temperature (SST) of the coastal zone. The in‐situ measurements supported that SGD has a substantial influence on the coastal water chemistry as well as SST. Our observations highlight the extent to which aerial‐based TIR mapping can serve as a powerful tool for studying SGD and other coastal processes. Copyright © 2016 John Wiley & Sons, Ltd.     

The modifiable areal unit problem in hedonic house-price models

When geographically aggregated data are included in hedonic models, the resulting coefficients are biased by the spatial scale and spatial configuration of variable measurement. We explore the effects of this modifiable areal unit problem (MAUP) within the context of hedonic price models with an individual-level dependent variable. Specifically, we developed standard and spatial hedonic regression models in order to examine the effects of the MAUP on model fit and coefficient estimates. Our empirical analysis documents several significant scale and zoning effects in the hedonic modeling framework. First, neighborhood characteristics are clearly important in efforts to improve model fit—and they are more significant contributors in the standard model than in the spatial hedonic model. For aggregation scale, the model fit change of the standard model is relatively large, whereas the change is more modest for spatial models. The patterns of change in model fit for standard and spatial hedonic models clearly diverge from one another, implying the existence of a scale level showing a maximum functional range of the submarket on which scale dependencies are expected to have an impact. Regarding the zoning effect, the model fits for both standard and spatial hedonic models vary according to the submarket systems.     

The effect of mineralogy on the mobility of heavy metals in mine tailings: a case study in the Samsanjeil mine,Korea

This study examined the chemical speciation and mobility of As and heavy metals in a tailings impoundment in Samsanjeil mine located in Gosung, Korea, as well as the factors affecting them. XRD, SEM, and 5-step sequential extraction were used to examine the samples at two sampling sites (NN and SN sites). The pH of the tailings decreased with increasing depth at the NN site (from 7.2 to 2.8), whereas no significant differences were observed at the SN site (8.1–8.8). The samples at the SN site showed a larger amount of calcite than those at the NN site, indicating that calcite plays an important role buffering the pH in the study sites. Jarosite was found only at the lower part of the NN site, where calcite was not found. The mineralogical observation of jarosite and calcite was also confirmed by SEM. The concentrations of As and heavy metals in the tailings were as follows: Cu > As > Zn > > Pb > Co > Cr > Ni > Cd. The total concentrations of Ni, Zn, Co, and Cd were higher at the SN site than those at the NN site. On the other hand, the concentrations of As and Cr existing as oxyanions were higher at the NN site, which can be explained by the mobility changes of those elements affected by pH variations. At the NN site, the fractions of heavy metals bound to the Fe/Mn oxides, except for As and Cr, decreased, and Cu, Zn, and Co showed an increasing fraction of exchangeable metals with increasing depth. This suggests that the pH and resulting surface charge of minerals, such as goethite and jarosite, are the dominant factors controlling the chemical speciation of metals. These results highlight the importance of mineralogy in controlling the mobility and possible bioavailability of heavy metals in tailings.     

Mechanical Characteristics of Light-Weighted Soils Using Dredged Materials

This study investigates the mechanical characteristics of light-weighted soils (LWS) consisting of expanded polystyrene (EPS), dredged clays, and cement through both unconfined and triaxial compression tests. The mechanical characteristics of the compressive strength of LWS are analyzed with varying initial water contents of dredged clays, EPS ratio, cement ratio, and curing pressure. In the triaxial compression test, it is found that the compressive strength of LWS associated with EPS is independent on the effective confining pressure. When both EPS ratio is less than 2% and cement ratio is more than 2%, the compressive strength rapidly decreases after the ultimate value. This signifies that the compressive strength-strain behavior is quite similar to that of the cemented soil. The ground improved by LWS has the compressive strength of 200 kPa associated with the optimized EPS ratio of 3–4% and initial water content of 165–175%. The ultimate compressive strength under both triaxial and unconfined compression tests is almost constant for a cement ratio of up to 2%.     

Generic 3D interpolation of Holocene base‐level rise and provision of accommodation space,developed for the Netherlands coastal plain and infilled palaeovalleys

We present an interpolation model that describes Holocene groundwater level rise and the creation of accommodation space in 3D in the Rhine‐Meuse delta – the Netherlands. The model area (ca. 12 400 km²) covers two palaeovalleys of Late Pleistocene age (each 30 km wide) and the overlying Holocene deposits of the Rhine‐Meuse delta, the Holland coastal plain, and the Zuiderzee former lagoon. Water table rise is modelled from 10 800 to 1000 cal. BP, making use of age‐depth relations based on 384 basal peat index points, and producing output in the form of stacked palaeo groundwater surfaces, groundwater age‐depth curves, and voxel sets. These products allow to resolve (i) regional change and variations of inland water table slopes, (ii) spatial differences in the timing and pacing of transgression, and (iii) analysis of interplay of coastal, fluvial and subsidence controls on the provision of accommodation space. The interpolation model is a multi‐parameter trend function, to which a 3D‐kriging procedure of the residuals is added. This split design deploys a generic approach for modelling provision of accommodation space in deltas and coastal lowlands, aiming to work both in areas of intermediate data availability and in the most data‐rich environments. Major provision of accommodation space occurred from 8500 cal BP onwards, but a different evolution occurred in each of the two palaeovalleys. In the northern valley, creation of accommodation space began to stall at 7500 cal BP, while in the southern valley provision of new accommodation space in considerable quantities continued longer. The latter is due to the floodplain gradient that was maintained by the Rhine, which distinguishes the fluvial deltaic environment from the rest of the back‐barrier coastal plain. The interpolation results allow advanced mapping and investigation of apparent spatial differences in Holocene aggradation in larger coastal sedimentary systems. Furthermore, they provide a means to generate first‐order age information with centennial precision for 3D geological subsurface models of Holocene deltas and valley fills. As such, the interpolation is of use in studies into past and present land subsidence and into low land sedimentation.