Large sand waves on the Atlantic Outer Continental Shelf around Wilmington Canyon,off Eastern United States

New seismic-reflection data show that large sand waves near the head of Wilmington Canyon on the Atlantic Outer Continental Shelf have a spacing of 100–650 m and a relief of 2–9 m. The bedforms trend northwest and are asymmetrical, the steeper slopes being toward the south or west. Vibracore sediments indicate that the waves apparently have formed on a substrate of relict nearshore sediments. Although the age of the original bedforms is unknown, the asymmetry is consistent with the dominant westerly to southerly drift in this area which has been determined by other methods; the asymmetry, therefore, is probably modern. Observations in the sand-wave area from a submersible during August 1975, revealed weak bottom currents, sediment bioturbation, unrippled microtopography, and lack of scour. Thus, the asymmetry may be maintained by periodic water motion, possibly associated with storms or perhaps with flow in the canyon head.     

Limited differences among habitats in deep‐sea macro‐infaunal communities off New Zealand: implications for their vulnerability to anthropogenic disturbance

The spread of human activities into the deep sea may pose a high risk to benthic communities and affect ecosystem integrity. The deep sea is characterized by physical and biological heterogeneity and different habitat types are likely to differ in their vulnerability to anthropogenic impacts. However, across‐habitat comparisons are rare, and no comprehensive ecological risk assessment has yet been developed. To address this gap in our knowledge, we compared macro‐infaunal community structure in four habitats (slope, canyons, seamounts and methane seeps) at depths between 700 and 1500 m in the Hikurangi Margin and Bay of Plenty regions off New Zealand. The most striking contrast in community structure was between the two study regions, due to an order of magnitude difference in macro‐infaunal abundance that we believe was caused by differences in surface productivity and food availability at the sea bed. We found differences in structural and functional attributes of macro‐infaunal communities among some habitats in the Hikurangi Margin (slope, canyon and seep), but not in the Bay of Plenty. We posit that differences between canyon and slope communities on the Hikurangi Margin are due to enhanced food availability inside canyons compared with adjacent slope habitats. Seep communities were characterized by elevated abundance of both symbiont‐bearing and heterotrophic taxa, and were the most distinct, and variable, among the habitats that we considered on the Hikurangi Margin. Communities of seamounts were not distinct from slope or canyon communities on the Hikurangi Margin, probably reflecting similar environmental conditions in these habitats. The communities of deep‐sea canyon and seep habitats on the Hikurangi Margin were sufficiently dissimilar from each other and from slope habitats to warrant separate management consideration. By contrast, the low dissimilarity between communities of canyon and slope habitats in the Bay of Plenty suggests that habitat‐based management is not required in this region, for macro‐infauna at least. Although the two study regions share similar species pools, populations of the Hikurangi Margin region may be less vulnerable than the sparser populations of the Bay of Plenty due to the higher availability of potential colonizers and faster population growth. Thus regions, and habitats in some regions, should be subject to separate ecological risk assessment to help identify the key risks and consequences of human activities, and to inform options for reducing or mitigating impacts.     

A Method for Installing Piezometers in Large Cobble Bed Rivers

An impact drive point method is described for emplacing piezometers in a cobble river bottom where this has previously been difficult without the use of drilling rigs. To force the drive point piezometers through coble, the vibrational impact of an air-powered hammer was carried directly to the drive point by the use of an internal drive rod. After insertion to depth, the drive rod was removed from the lower portion of the piezometer and a standpipe was added to extend the piezometer above the river level. Piezometers installed in this way have permitted water quality analysis and dynamic measurement of vertical potentials in cobble sediments ranging in size from 2.5 to >30 cm and the method has been successfully used in the Columbia River, USA, and Töss River, Switzerland. This innovative method provides information on the hydrodynamics of pore water in highly permeable, cobble deposits that are common in high-energy river and lake bottoms. Piezometers installed using the internal drive rod method facilitate the assessment of the temporal and spatial dynamics of recharge and discharge at the ground water/surface water interface and analyses of the ecological connectivity between the hyporheic zone and surface water of rivers and streams. This information will lead to improved management decisions related to our nation's ground water and surface water supplies.     

In situ uptake of mercury by the intertidal mussel,Mytilus californianus

The in situ uptake of mercury in tissues of Mytilus californianus was studied by exposing control specimens to waters at four depths near a submarine wastewater discharge for a period of 24 weeks. The response patterns observed for digestive gland, adductor muscle and gonadal tissues were strikingly different. Digestive gland concentrations increased rapidly to the heightened levels found for indigenous specimens. On the other hand, changes in the mercury content of adductor muscle were not statistically significant, and gonadal tissues generally exhibited a low rate of increase. No correlation with depth was observed.     

Solution of H2O in diopside melts: a thermodynamic model

Structural similarities between dry diopside melt and superhydrous albite melt (X _w >0.5) — both lack three-dimensional silicate units — suggest that thermodynamic relations may be similar. A model based on that assumption successfully predicts diopside melting relations and H₂O solubilities. For the model, the three partial differential equations describing solution of H₂O in albite melt for X _w >0.5 have been integrated for diopside melt from X _w =0 to X _w at least as large as 0.76, with two exceptions: an alternative partial differential equation for Henrian solution of H₂O in dilute melts was applied for X _w <0.20, and an alternative differential equation for the pressure dependence of a _w at pressures below 2 kbar was developed. The latter alternative equation yields relatively small ¯V_w's at low pressures rather than the large ¯V_w's calculated from the equation from the albite system. Available experimental solubility data are not precise enough to offer a choice between the small-¯V_w and large-¯V_w equations. Integration of all the partial differential equations was constrained solely by the P and T of a single experimentally-determined point on the H₂O-saturated solidus.Solubilities calculated by a Henrian-analogue solution model (a _di=X _di ² ) from the experimental H₂O saturated solidus lie outside experimental solubility constraints for dilute melts. On the other hand, a Henrian model (a _di=X_di) successfully predicts solubilities in dilute melts. The formulation of the Henrian model and magnitudes of model molar entropies of solution are consistent with the hypothesis that H₂O dissolves in diopside melt as an essentially undissociated species with little ordering on melt structural sites. That species could in turn be consistently, if not uniquely, interpreted to be molecular H₂O or a hydroxylation (OH^–) complex formed from nonbridging oxygens.     

Generalised formulation of composite filters and their application to earthquake engineering test systems

This paper addresses the problem of generating unmeasured kinetic data—and/or providing improvements in existing data—for the enhancement of performance characteristics of earthquake engineering test systems, such as shaking tables, reaction walls and other custom‐made test rigs. The approach relies upon the use of composite filters (CF), a method of data fusion that was originally conceived via transfer function formulation. The current work generalises the CF concept and extends its formulation into the state‐space domain, thereby providing a wider basis for application to test systems and their controllers, including those of a multivariable (coupled, multi‐axis) nature. Comparative simulation studies of shaking table control are presented that demonstrate the design techniques for state‐space CF and also their effectiveness for signal synthesis, noise suppression and performance improvement. Specific examples include the use of CF for displacement demand signal generation, velocity feedback generation and acceleration control. In each case, the essential principles behind CF—output signals with zero bias and zero drift—are consistently upheld. Copyright © 2017 John Wiley & Sons, Ltd.     

Climatology of extratropical cyclones over the South American–southern oceans sector

A climatology of extratropical cyclones is presented. Extratropical cyclones, their main characteristics and their predominant tracks, as well as their interannual variability, affect weather in South America. For that purpose, a storm track database has been compiled by applying a cyclone tracking scheme to six-hourly sea level pressure fields, available from the National Center for Environmental Prediction–National Center for Atmospheric Research reanalyses II for the 1979–2003 period. The spatial distribution of the cyclogenesis frequency shows two main centers: one around Northern Argentina, Uruguay, and Southern Brazil in all seasons and the other near to the North Antarctic Peninsula. The lifetime of extratropical cyclones in the South American sector exhibits small seasonality, being typically of the order of 3.0 days during most of the year and slightly higher (3.5 days) in austral summer. The distance travelled by the cyclones formed in the South American sector tends to be smaller than the total paths found in other areas of the Southern Hemisphere. A k-mean clustering technique is used to summarize the analysis of the 25-year climatology of cyclone tracks. Three clusters were found: one storm-track cluster in Northeast Argentina; a second one west of the Andes Cordillera; and a third cluster located to the north of the Antarctic Peninsula (around the Weddell Sea). The influence of the Antarctic Oscillation (AAO) in the variability of extratropical cyclones is explored, and some signals of the impacts of the variability of the AAO can be observed in the position of the extratropical cyclones around 40°S, while the impacts on the intensity is detected around 55°S.     

Geochemical processes controlling arsenic mobility in groundwater: A case study of arsenic mobilization and natural attenuation

The behavior of As in the subsurface environment was examined along a transect of groundwater monitoring wells at a Superfund site, where enhanced reductive dechlorination (ERD) is being used for the remediation of groundwater contaminated with chlorinated solvents. The transect was installed parallel to the groundwater flow direction through the treatment area. The ERD technology involves the injection of organic C (OC) to stimulate in situ microbial dechlorination processes. A secondary effect of the ERD treatment at this site, however, is the mobilization of As, as well as Fe and Mn. The concentrations of these elements are low in groundwater collected upgradient of the ERD treatment area, indicating that, in the absence of the injected OC, the As that occurs naturally in the sediment is relatively immobile. Batch experiments conducted using sediments from the site inoculated with an Fe(III)- and As(V)-reducing bacterium and amended with lactate resulted in mobilization of As, Fe and Mn, suggesting that As mobilization in the field is due to microbial processes.     

Climate,environment, and humans in North America’s Great Basin during the Younger Dryas, 12,900–11,600 calendar years ago

Global climate change associated with the onset of the Younger Dryas chronozone affected different regions of the northern hemisphere in different ways. In the Great Basin of western North America, the effect was positive for human populations. Relatively cool temperatures causing effectively wetter conditions filled some pluvial basins with shallow but permanent lakes and other basins with well-watered marshes or meadows. Vegetation communities dominated by sagebrush and grasses promoted healthy and diverse animal populations. Ten archaeological sites from the region have been dated to the Younger Dryas chronozone. Evidence from these sites indicates that Paleoindians with skull shapes and mitochondrial DNA similar to modern western North American Indians occupied the region. These early humans produced a material culture characterized predominantly by large stemmed bifacial points, although one site contained a small fluted point. Curated tool forms and technological activities represented in analyzed lithic assemblages suggest a highly mobile settlement strategy, and redundant short-term occupations of sites indicate frequent and long-distance residential moves across territories spanning distances of up to 400 km. Paleoindian subsistence pursuits focused on artiodactyls (primarily mule deer, bighorn sheep, and pronghorn antelope), leporids (chiefly jackrabbits), birds (sage grouse and waterfowl), insects (grasshoppers), and possibly fish. Easy-to-process plants like cactus pads were also eaten, but small seeds do not seem to have been an important part of Great Basin human diets until long after the Younger Dryas, closer to 9500 cal BP. The Great Basin record contains no evidence for natural catastrophe at the onset of the chronozone. Instead, the Younger Dryas appears to have been among the best of times for human foragers in this region of North America.     

Spatially explicit measures of production of young alewives in Lake Michigan: Linkage between essential fish habitat and recruitment

The identification and protection of essential habitats for early life stages of fishes are necessary to sustain fish stocks. Essential fish habitat for early life stages may be defined as areas where fish densities, growth, survival, or production rates are relatively high. To identify critical habitats for young-of-year (YOY) alewives (Alosa pseud oharengus) in Lake Michigan, we integrated bioenergetics models with GIS (Geographic Information Systems) to generate spatially explicit estimates of potential population production (an index of habitat quality). These estimates were based upon YOY alewife bioenergetic growth rate potential and their salmonine predators’ consumptive demand. We compared estimates of potential population production to YOY alewife yield (an index of habitat importance). Our analysis suggested that during 1994–1995, YOY alewife habitat quality and yield varied widely throughout Lake Michigan. Spatial patterns of alewife yield were not significantly correlated to habitat quality. Various mechanisms (e.g., predator migrations, lake circulation patterns, alternative strategies) may preclude YOY alewives from concentrating in areas of high habitat quality in Lake Michigan.