Bioluminescence potential during polar night: impact of behavioral light sensitivity and water mass pathways

During polar nights of 2012 and 2017, bioluminescence (BL) potential surveys demonstrated high emissions at depths around and below 100 m at offshore stations to the north of a Svalbard fjord (Rijpfjorden). We demonstrated that the highest bioluminescent emissions for offshore stations are located at depths below depths of modelled/ambient light intensities corresponding to the reported irradiance thresholds for the behavioral light sensitivity of krill and copepods, and suggest that behavioral light sensitivity is one of the reasons for high values of BL potential observed below 100 m at offshore stations. In order to understand sources of bioluminescent taxa responsible for the observed high values of BL potential in offshore waters, we have investigated the origin and pathways of water masses circulating to the north, offshore of the fjord Rijpfjorden by using a hydrodynamic model. For both 2012 and 2017, the model water masses mostly originate from the west, where the Atlantic water is flowing northward, then along the shelf and shelf slope of northern Svalbard, and to the offshore of the fjord. This indicates that the advection of zooplankton by North Atlantic Water is one possible source of bioluminescent organisms offshore of northern Svalbard. In 2012, water masses also originated from the inflow through Hinlopen trench and strait, while, in 2017, the offshore water was advected and upwelled into the fjord on time scales less than 10 days, and after that there was a recirculation back from the fjord to offshore on time scales larger than 10 days. This recirculation from the fjord might be another source of bioluminescent organisms in the offshore waters.

     

Multi-frequency synthetic-aperture imaging with a lightweight ground penetrating radar system

The detection of buried objects, particularly hazardous waste containers and unexploded ordnance (UXO), has gained significant interest in the Unites States in the late 1990s. The desire to remediate the thousands of sites worldwide has become an increasing concern and the application of radar to this problem has received renewed attention. The US Department of Energy's Special Technologies Laboratory (STL), operated by Bechtel Nevada, has developed several frequency-modulated, continuous-wave (FM-CW) ground penetrating radar (GPR) units. To meet technical requirements for higher-resolution data, STL and the University of California, Santa Barbara (UCSB) is investigating advanced GPR hardware, signal processing, and synthetic-aperture imaging with the development of an innovative system. The goal is to design and fabricate a lightweight, battery-operated unit that does not require surface contact, can be operated by a novice user, and can achieve improved resolution. The latter is accomplished by using synthetic-aperture imaging, which forms the subsurface images by fully utilizing the data sequences collectively along a scan path. We also present the backward propagation algorithm as the basic structure of the multiple-frequency tomographic imaging technique, and the conventional fast Fourier transform (FFT) method which can be described as a degenerated case of the model where the computation procedure is approximated under the narrow-beam assumption.     

A Review of “Urban Climate Change Crossroads”

This article examines the former location-based social medium Brightkite, over its three-year life span, based on the concept of natural cities. The term natural cities refers to spatially clustered geographic events, such as the agglomerated patches aggregated from individual social media users’ locations. We applied the head/tail division rule to derive natural cities, based on the fact that there are far more low-density areas than high-density areas on the Earth's surface. More specifically, we generated a triangulated irregular network, made up of individual unique user locations, and then categorized small triangles (smaller than an average) as natural cities for the United States (mainland) on a monthly basis. The concept of natural cities provides a powerful means to develop new insights into the evolution of real cities, because there are virtually no data available to track the history of cities across their entire life spans and at very fine spatial and temporal scales. Therefore, natural cities can act as a good proxy of real cities, in the sense of understanding underlying interactions, at a global level, rather than of predicting cities, at an individual level. Apart from the data produced and the contributed methods, we established new insights into the structure and dynamics of natural cities; for example, the idea that natural cities evolve in nonlinear manners at both spatial and temporal dimensions.     

Resolving the source and mixing proportions of modern leakage to the Memphis aquifer in a municipal well field using geochemical and 3H/3He data, Memphis, Tennessee, USA

The Memphis aquifer in southwestern Tennessee is a confined to semi-confined unconsolidated sand aquifer and is the primary municipal water source for the Memphis metropolitan area. Leakage of modern water from shallow unconfined aquifers through the upper Claiborne confining unit locally degrades water quality in the Memphis aquifer and makes the aquifer more vulnerable to contamination. Major solute chemistry, tritium, and ³H/³He data were used to investigate the source and mixing proportions of modern water in the Memphis aquifer in the Davis well field, Memphis, Tennessee. Water quality in several production wells in the Davis well field has declined over the past 30 years, mainly through increased total dissolved solids, iron, alkalinity, and hardness. Trends in chemical data, tritium, and other hydrogeologic data support a source for the leakage from the Mississippi River Valley Alluvial aquifer. Mixing proportions of alluvial water in production well water obtained by inverse chemical modeling with PHREEQCi range from 7 to 45%. For two of the production wells, MLGW 414 and 432, ³H/³He data yield mixing ratios similar to those obtained from PHREEQCi in three of four cases; the dissimilar ratio is likely due to a poor solution from the PHREEQCi inverse modeling. Modeling of the age distribution obtained from MLGW 414 and 432 using an exponential-piston flow model (EPM) with an inverse solution computer code yielded mixed results. The EPM solution obtained for MLGW 414 converged with difficulty only for a 5-year transit time in the shallow aquifer and is consistent with a source from the Mississippi River Valley Alluvial aquifer; however, the modeled age of the water is greater than that observed. In comparison, the EPM solution for MLGW 432 converged for the 5- and 7-year transit periods in the shallow aquifer and yielded model ages consistent with observed ³H/³He ages; however, the extent of the maximum radii for infiltration source is not consistent with a Mississippi River Valley Alluvial aquifer source. Other potential sources for leakage to MLGW 432 include water from the Fluvial-terrace aquifer migrating along a fault east of the well field or infiltration of water from a lake south of the well field.     

Evaluating TCE Abiotic and Biotic Degradation Pathways in a Permeable Reactive Barrier Using Compound Specific Isotope Analysis

A pilot‐scale zero valent iron (ZVI) Permeable Reactive Barrier (PRB) was installed using an azimuth‐controlled ‐vertical hydrofracturing at an industrial facility to treat a chlorinated Volatile Organic Compound (VOC) plume. Following ZVI injection, no significant reduction in concentration was observed to occur with the exception of some multilevel monitoring wells, which also showed high levels of total organic carbon (TOC). These patterns suggested that the zero valent iron was not well distributed in the PRB creating leaky conditions. The geochemical data indicated reducing conditions in these areas where VOC reduction was observed, suggesting that biotic processes, associated to the guar used in the injection of the iron, could be a major mechanism of VOC degradation. Compound‐Specific Isotope Analysis (CSIA) using both carbon and chlorine stable isotopes were used as a complementary tool for evaluating the contribution of abiotic and biotic processes to VOC trends in the vicinity of the PRB. The isotopic data showed enriched isotope values around the PRB compared to the isotope composition of the VOC source confirming that VOC degradation is occurring along the PRB. A batch experiment using site groundwater collected near the VOC source and the ZVI used in the PRB was performed to evaluate the site‐specific abiotic isotopic fractionation patterns. Field isotopic trends, typical of biodegradations were observed at the site and were different from those obtained during the batch abiotic experiment. These differences in isotopic trends combined with changes in VOC concentrations and redox parameters suggested that biotic processes are the predominant pathways involved in the degradation of VOCs in the vicinity of the PRB.     

Real-time PCR and NASBA for rapid and sensitive detection of Vibrio cholerae in ballast water

Transport of ballast water is one major factor in the transmission of aquatic organisms, including pathogenic bacteria. The IMO-guidelines of the Convention for the Control and Management of Ships' Ballast Water and Sediments, states that ships are to discharge <1 CFU per 100 ml ballast water of toxigenic Vibrio cholerae, emphasizing the need to establish test methods. To our knowledge, there are no methods sensitive and rapid enough available for cholera surveillance of ballast water. In this study real-time PCR and NASBA methods have been evaluated to specifically detect 1 CFU/100ml of V. cholerae in ballast water. Ballast water samples spiked with V. cholerae cells were filtered and enriched in alkaline peptone water before PCR or NASBA detection. The entire method, including sample preparation and analysis was performed within 7 h, and has the potential to be used for analysis of ballast water for inspection and enforcement control.     

Growth and population dynamics of crayfish Paranephrops planifrons in streams within native forest and pastoral land uses

Population dynamics of crayfish (Paranephrops planifrons White) in streams draining native forest and pastoral catchments, Waikato, New Zealand, were investigated from September 1996 to July 1998. Crayfish densities were generally greater in native forest streams because of high recruitment over summer, but varied greatly between streams in both land uses. Peak densities in summer were 9 crayfish m^‐2 in native forest and 6 crayfish m^‐2 in pasture streams, but peak biomass in summer was much greater in pasture streams. Mark‐recapture data showed that crayfish, particularly juveniles, in pasture streams grew faster than in native forest streams, through both greater moult frequency and larger moult increments. Females reached reproductive size at c. 20 mm orbit‐carapace length (OCL) after their first year in pasture streams, but after 2 years in native forest streams. Annual degree days >10°C appeared to explain the differences in the timing of life cycles. Estimates of annual crayfish production (range = 0.8–3.4 g dry weight m^‐2 year^–1) were similar in both land uses, and P/B ratios were between 0.95 and 1.2. Despite deforestation and conversion to pasture, crayfish in these Waikato hill‐country streams have maintained similar levels of annual production to those in native forest streams, although juvenile growth rates have increased and longevity has decreased.     

Change and variability in sea ice during the 2007–2008 Canadian International Polar Year program

In this paper we describe sea ice change and variability during the Canadian International Polar Year (IPY) program and examine several regional and hemispheric causes of this change. In a companion paper (Barber et al., Climate Change 2012) we present an overview of the consequences of this observed change and variability on ecosystem function, climatically relevant gas exchange, habitats of primary and apex predators, and impacts on northern peoples. Sea ice-themed research projects within the fourth IPY were designed to be among the most diverse international science programs. They greatly enhanced the exchange of Inuit knowledge and scientific ideas across nations and disciplines. This interdisciplinary and cultural exchange helped to explain and communicate the impacts of a transition of the Arctic Ocean and ecosystem to a seasonally ice-free state, the commensurate replacement of perennial with annual sea ice types and the causes and consequences of this globally significant metamorphosis. This paper presents a synthesis of scientific sea ice research and traditional knowledge results from Canadian-led IPY projects between 2007 and 2009. In particular, a summary of sea ice trends, basin-wide and regional, is presented in conjunction with Inuit knowledge of sea ice, gathered from communities in northern Canada. We focus on the recent observed changes in sea ice and discuss some of the causes of this change including atmospheric and oceanic forcing of both dynamic and thermodynamic forcing on the ice. Pertinent results include: 1) In the Amundsen Gulf, at the western end of the Northwest Passage, open water persists longer than normal and winter sea ice is thinner and more mobile. 2) Large areas of summer sea ice are becoming heavily decayed during summer and can be broken up by long-period waves being generated in the now extensive open water areas of the Chukchi Sea. 3) Cyclones play an important role in flaw leads??regions of open water between pack ice and land-fast ice. They delay the formation of new ice and the growth of multi-year ice. 4) Feedbacks involving the increased period of open water, long-period wave generation, increased open-ocean roughness, and the precipitation of autumn snow are all partially responsible for the observed reduction in multiyear sea ice. 5) The atmosphere is observed as remaining generally stable throughout the winter, preventing vertical entrainment of moisture above the surface.     

Rhyolites at Kerlingarfjöll, Iceland: the evolution and lifespan of silicic central volcanoes

Kerlingarfjöll central volcano is Iceland’s second largest outcrop of Quaternary rhyolite and is part of the Icelandic Western Rift Zone. Geochemical and Ar/Ar age data show that at least 21 different rhyolite eruptions have taken place at Kerlingarfjöll over the last 350 ka. Ar/Ar dating was carried out on samples of obsidian which showed variable reproducibility, illustrating the difficulty in dating young Icelandic volcanics. Nevertheless, reasonable estimates of eruption age have been derived for a number of eruptive units that are consistent with observed stratigraphy, enabling an understanding of the temporal evolution of Kerlingarfjöll. Two rhyolite magma types are present. The first is an older, low-Nb rhyolite that was erupted episodically along a cryptic curved fracture system, to form a discontinuous ring of rhyolite mountains, between 350 and 250 ka. This discontinuous ring is similar to structures observed at other volcanoes in Iceland, suggesting that the development of a curved fracture that acts as a pathway for episodic silicic eruptions is a feature of central volcano development. The second magma is a younger, high-Nb rhyolite that was erupted episodically between 250 and 68 ka in the northern part of Kerlingarfjöll, forming two clusters, both of which have areas of intense hydrothermal activity. Repose periods for rhyolite volcanism are thought to be on the order of tens of thousands of years, and it is possible that Kerlingarfjöll will erupt rhyolite again in the future.