Identification and Assessment of Confined and Perched LNAPL Conditions

Although confined and perched light nonaqueous phase liquids (LNAPLs) have previously been recognized, the majority of technical LNAPL literature focuses on unconfined LNAPL. Little information exists regarding the appropriate use of LNAPL distribution and transmissivity data to distinguish between confined, perched, and unconfined LNAPL hydrogeological scenarios. This paper describes three case histories that illustrate how the observed behavior of LNAPL can be used to identify the hydrogeologic condition of LNAPL at a given site and improved methods for calculating LNAPL drawdown based on these hydrogeologic conditions. The assessment methodology uses routinely available data such as fluid gauging, boring lo, laser‐induced fluorescence, visual observations of soil cores, and LNAPL baildown testing. Identification of the correct LNAPL hydrogeologic condition results in more accurate LNAPL conceptual site models, improved estimates of LNAPL recovery rates and volumes, more appropriate technology applications, and improved accuracy of LNAPL remediation metrics such as LNAPL transmissivity.     

Tropical harmful algal blooms: An emerging threat to coral reef communities?

Tropical harmful algal blooms (HABs) are increasing in frequency and intensity and are substantially affecting marine communities. In October/November 2008 a large-scale HAB event (> 500 km², dinoflagellate Cochlodinium polykrikoides) in the Gulf of Oman caused the complete loss of the branching corals, Pocillopora and Acropora spp., and substantial reductions in the abundance, richness and trophic diversity of the associated coral reef fish communities. Although the causative agents of this C. polykrikoides bloom are unknown, increased coastal enrichment, natural oceanographic mechanisms, and the recent expansion of this species within ballast water discharge are expected to be the main agents. With rapid changes in oceanic climate, enhanced coastal eutrophication and increased global distribution of HAB species within ballast water, large-scale HAB events are predicted to increase dramatically in both intensity and distribution and can be expected to have increasingly negative effects on coral reef communities globally.     

An Acetic Acid‐Based Extraction Protocol for the Recovery of U,Th and Pb from Calcium Carbonates for U‐(Th)‐Pb Geochronology

A new method for the simultaneous recovery of U, Th and Pb from ca. 0.5 g calcium carbonate samples for the purpose of U‐(Th)‐Pb geochronometry is presented. The protocol employs ion‐exchange chromatography. Standard anion exchange resin (AG 1‐X8 100–200 mesh) was used as the static phase, and 90% acetic acid was used as the mobile phase to elute the unwanted matrix components; dilute nitric acid was used to elute the U, Th and Pb. Blanks of 1.8 pg Th, 6.4 pg Pb and 8.4 pg U were obtained. The protocol was evaluated by determining the isotopic composition of U‐Th‐Pb separates obtained from an in‐house reference material (prepared from a natural speleothem) by MC‐ICP‐MS. An independently dated speleothem was also reanalysed. Based on these tests, the extraction protocol had an acceptable blank and produced a Pb separate sufficiently free of matrix‐induced instrumental biases to be appropriate for U‐Th‐Pb chronology.     

Environmental tracers as indicators of karst conduits in groundwater in South Dakota,USA

Environmental tracers sampled from the carbonate Madison aquifer on the eastern flank of the Black Hills, South Dakota, USA indicated the approximate locations of four major karst conduits. Contamination issues are a major concern because these conduits are characterized by direct connections to sinking streams, high groundwater velocities, and proximity to public water supplies. Objectives of the study were to estimate approximate conduit locations and assess possible anthropogenic influences associated with conduits. Anomalies of young groundwater based on chlorofluorocarbons (CFCs), tritium, and electrical conductivity (EC) indicated fast moving, focused flow and thus the likely presence of conduits. δ¹⁸O was useful for determining sources of recharge for each conduit, and nitrate was a useful tracer for assessing flow paths for anthropogenic influences. Two of the four conduits terminate at or near a large spring complex. CFC apparent ages ranged from 15 years near conduits to >50 years in other areas. Nitrate-N concentrations >0.4 mg/L in groundwater were associated with each of the four conduits compared with concentrations ranging from <0.1 to 0.4 mg/L in other areas. These higher nitrate-N concentrations probably do not result from sinking streams but rather from other areas of infiltration.     

Albedos and diameters of three Mars Trojan asteroids

We observed the Mars Trojan Asteroids (5261) Eureka and (101429) 1998 VF₃₁ and the candidate Mars Trojan 2001 FR₁₂₇ at 11.2 and 18.1 microns using Michelle on the Gemini North telescope. We derive diameters of 1.28, 0.78, and <0.52 km, respectively, with corresponding geometric visible albedos of 0.39, 0.32, and >0.14. The albedos for Eureka and 1998 VF₃₁ are consistent with the taxonomic classes and compositions (S(I)/angritic and S(VII)/achondritic, respectively) and implied histories presented in a companion paper by Rivkin et al. Eureka's surface likely has a relatively high thermal inertia, implying a thin regolith that is consistent with predictions and the small size that we derive.     

Vent temperature trends at the Vulcano Fossa fumarole field: the role of permeability

Between 1994 and 2010, we completed 16 thermal surveys of Vulcano’s Fossa fumarole field (Aeolian Islands, Italy). In each survey, between 400 and 1,200 vent temperatures were collected using a thermal infrared thermometer from distances of ～1?m. The results show a general decrease in average vent temperature during 1994–2003, with the average for the entire field falling from ～220°C in 1994 to ～150°C by 2003. However, between 2004 and 2010, we witnessed heating, with the average increasing to ～190°C by 2010. Alongside these annual-scale field-wide trends, we record a spatial re-organisation of the fumarole field, characterised by shut down of vent zones towards the crater floor, matched by rejuvenation of zones located towards the crater rim. Heating may be expected to be associated with deflation because increased amounts of vaporisation will remove volume from the hydrothermal system Gambino and Guglielmino (J Geophys Res 113:B07402, 2008). However, over the 2004–2010 heating period, no ground deformation was observed. Instead, the number of seismic events increased from a typical rate of 37 events per month during 1994–2000 to 195 events per month during 2004–2010. As part of this increase, we noticed a much greater number of high-frequency events associated with rock fracturing. We thus suggest that the heating event of 2004–2010 was the result of changed permeability conditions, rather than change in the heat supply from the deeper magmatic source. Within this scenario, cooling causes shut down of lower sectors and re-establishment of pathways located towards the crater rim, causing fracturing, increased seismicity and heat flow in these regions. This is consistent with the zone of rejuvenation (which lies towards and at the rim) being the most favourable location for fracturing given the stress field of the Fossa cone Sch?pa et al. (J Volcanol Geotherm Res 203:133–145, 2011); it is also the most established zone, having been active at least since the early twentieth century. Our data show the value of deploying multi-disciplinary geophysical campaigns at degassing (fumarolic) hydrothermal systems. This allows more complete and constrained understanding of the true heat loss dynamics of the system. In the case study presented here, it allows us to distinguish true heating from apparent heating phases. While the former are triggered from the bottom-up, i.e. they are driven by increases in heat supply from the magmatic source, the latter are triggered from the top-down, i.e. by changing permeability conditions in the uppermost portion of the system to allow more efficient heat flow over zones predisposed to fracturing.     

Postshield stage transitional volcanism on Mahukona Volcano, Hawaii

Age spectra from ⁴⁰Ar/³⁹Ar incremental heating experiments yield ages of 298 ± 25 ka and 310 ± 31 ka for transitional composition lavas from two cones on submarine Mahukona Volcano, Hawaii. These ages are younger than the inferred end of the tholeiitic shield stage and indicate that the volcano had entered the postshield alkalic stage before going extinct. Previously reported elevated helium isotopic ratios of lavas from one of these cones were incorrectly interpreted to indicate eruption during a preshield alkalic stage. Consequently, high helium isotopic ratios are a poor indicator of eruptive stage, as they occur in preshield, shield, and postshield stage lavas. Loihi Seamount and Kilauea are the only known Hawaiian volcanoes where the volume of preshield alkalic stage lavas can be estimated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.