Yearly changes in the seasonal frequency and duration of short-term acid pulses in some Nova Scotia, Canada streams

 The seasonal frequency and duration of low pH events at three sites located in southwestern Nova Scotia were analyzed using measured and synthetic daily pH data. The basins varied in size from 0.3 to 300 km² and were subject to frequent snowmelt events in winter and spring, as well as occasional runoff events during summer and fall. Results showed that, in order to fill in missing data from periods where collection was interrupted, statistical approximations using discharge were not totally acceptable, as generated data consistently missed the extreme values measured. Despite a lack of totally accurate event pH estimates for periods where daily data were missing, analysis showed that in this region, low pH episodes can occur year-round including summer. The highest probabilities of low pH episodes nevertheless occurred in the winter and spring when snowmelts were frequent. Received: 12 November 1999 · Accepted: 18 July 2000     

Age and paleoclimatic significance of the Stansbury shoreline of Lake Bonneville, Northeastern Great Basin

The Stansbury shoreline, one of the conspicuous late Pleistocene shorelines of Lake Bonneville, consists of tufa-cemented gravel and barrier beaches within a vertical zone of about 45 m, the lower limit of which is 70 m above the modern average level of Great Salt Lake. Stratigraphic evidence at a number of localities, including new evidence from Crater Island on the west side of the Great Salt Lake Desert, shows that the Stansbury shoreline formed during the transgressive phase of late Pleistocene Lake bonneville (sometime between about 22,000 and 20,000 yr B.P.). Tufa-cemented gravel and barrier beaches were deposited in the Stansbury shorezone during one or more fluctuations in water level with a maximum total amplitude of 45 m. We refer to the fluctuations as the Stansbury oscillation. The Stansbury oscillation cannot have been caused by basin-hypsometric factors, such as stabilization of lake level at an external overflow threshold or by expansion into an interior subbasin, or by changes in drainage basin size. Therefore, changes in climate must have caused the lake level to reverse its general rise, to drop about 45 m in altitude (reducing its surface area by about 18%, 5000 km²), and later to resume its rise. If the sizes of Great Basin lakes are controlled by the mean position of storm tracks and the jetstream, which as recently postulated may be controlled by the size of the continental ice sheets, the Stansbury oscillation may have been caused by a shift in the jetstream during a major interstade of the Laurentide ice sheet.     

Desert methane: Implications for life detection on Mars

Methane, a potential biosignature, has recently been detected in the martian atmosphere. This Note focuses on field investigations/operational simulations and laboratory studies which resulted in successful detection of methane within arid terrestrial soils, as distinct from the usual methanogen environment, but in at least partial analogy to martian conditions.     

Emerging coral diseases: a temperature‐driven process?

In the last few decades there has been a surge in research focusing on coral disease. While climate change, specifically rising sea surface temperature, has been proposed as a major and growing driver of the emergence of marine diseases, to date a solid connection between disease epizootics and elevated sea surface temperature has not been established. However, a wealth of data now exists, compiled from many different perspectives, that may support such a connection. In this work we provide a comprehensive review targeting one coral disease, black band disease, that spans the infection process, pathobiology, and epizootiology, and links specific mechanisms of the disease process to increasing temperatures. This temperature‐driven pattern of infection can be expanded to include similar processes associated with other temperature‐related coral diseases. The conclusions presented here are based upon the results of many studies using a diverse suite of approaches that have been synthesized to argue that the emergence and continuing spread of black band disease is linked to warming sea surface temperatures. In summary, as global ocean temperatures increase seasonally and over decades, the environment shifts to become more favorable for the growth of potentially pathogenic microorganisms endemic to the immediate environment of the reef. The increase in the relative number of potential pathogens in the microbial community produces microenvironments conducive to the growth of other potential pathogens, leading to infection by a polymicrobial consortium. This consortium is easily perturbed by a (seasonal) temperature decrease, but remains associated with the coral host and can be reactivated with a subsequent seasonal increase in temperature, resulting in a cycle of temperature‐dependent disease emergence.     

Physico-chemical phenomena in comets—III: The continuum of comet Burnham (1960 II)

The new model of the cometary head proposed in papers I and II is developed and applied to comet Burnham. It takes into account the likely existence of a halo of large icy particles surrounding the nucleus. These particles are steadily stripped from the nucleus by evaporating gases. Their terminal velocity and their rate of evaporation set the size of the halo. The existence of the icy halo influences in two ways the photometric characteristics of the coma. This paper establishes the photometric shape of the continuum as reflected by the icy grains, and compares it to the observed continuum of comet Burnham. Paper IV will compare the predictions of the model with the photometric profile of the molecular emission bands of C₂, in the same comet.     

Three-dimensional calculations of high- and low-mass planets embedded in protoplanetary discs

We analyse the non-linear, three-dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from 1 Earth mass (1 M_⊕) to 1 Jupiter mass (1 M_J) by using the zeus hydrodynamics code. We determine the gas flow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a fixed circular orbit about the central star. It is also assumed to be able to accrete gas without expansion on the scale of its Roche radius. Only planets with masses   M _p≳ 0.1 M_J  produce significant perturbations in the surface density of the disc. The flow within the Roche lobe of the planet is fully three-dimensional. Gas streams generally enter the Roche lobe close to the disc mid-plane, but produce much weaker shocks than the streams in two-dimensional models. The streams supply material to a circumplanetary disc that rotates in the same sense as the orbit of the planet. Much of the mass supply to the circumplanetary disc comes from non-coplanar flow. The accretion rate peaks with a planet mass of approximately 0.1 M_J and is highly efficient, occurring at the local viscous rate. The migration time-scales for planets of mass less than 0.1 M_J, based on torques from disc material outside the Roche lobes of the planets, are in excellent agreement with the linear theory of type I (non-gap) migration for three-dimensional discs. The transition from type I to type II (gap) migration is smooth, with changes in migration times of about a factor of 2. Starting with a core which can undergo runaway growth, a planet can gain up to a few M_J with little migration. Planets with final masses of the order of 10 M_J would undergo large migration, which makes formation and survival difficult.     

Evaluating a process‐based model for use in streambank stabilization: insights on the Bank Stability and Toe Erosion Model (BSTEM)

Streambank retreat is a complex cyclical process involving subaerial processes, fluvial erosion, seepage erosion, and geotechnical failures and is driven by several soil properties that themselves are temporally and spatially variable. Therefore, it can be extremely challenging to predict and model the erosion and consequent retreat of streambanks. However, modeling streambank retreat has many important applications, including the design and assessment of mitigation strategies for stream revitalization and stabilization. In order to highlight the current complexities of modeling streambank retreat and to suggest future research areas, this paper reviewed one of the most comprehensive streambank retreat models available, the Bank Stability and Toe Erosion Model (BSTEM), which has recently been integrated with several popular hydrodynamic and sediment transport models including the Hydrologic Engineering Center's River Analysis System (HEC‐RAS). The objectives of this paper were to: (i) comprehensively review studies that have utilized BSTEM and report their findings, (ii) address the limitations of the model so that it can be applied appropriately in its current form, and (iii) suggest directions of research that will help make the model a more useful tool in future applications. The paper includes an extensive overview of peer reviewed studies to guide future users of BSTEM. The review demonstrated that the model needs further testing and evaluation outside of the central United States. Also, further development is needed in terms of accounting for spatial and temporal variability in geotechnical and fluvial erodibility parameters, incorporating subaerial processes, and accounting for the influence of riparian vegetation on streambank pore‐water pressure dynamics, applied shear stress, and erodibility parameters. Copyright © 2016 John Wiley & Sons, Ltd.     

Consequences of change and variability in sea ice on marine ecosystem and biogeochemical processes during the 2007–2008 Canadian International Polar Year program

Change and variability in the timing and magnitude of sea ice geophysical and thermodynamic state have consequences on many aspects of the arctic marine system. The changes in both the geophysical and thermodynamic state, and in particular the timing of the development of these states, have consequences throughout the marine system. In this paper we review the ??consequences?? of change in sea ice state on primary productivity, marine mammal habitats, and sea ice as a medium for storage and transport of contaminants and carbon exchange across the ocean-sea-ice-atmosphere interface based upon results from the International Polar Year. Pertinent results include: 1) conditions along ice edges can bring deep nutrient-rich ??pacific?? waters into nutrient-poor surface waters along the arctic coast, affecting local food webs; 2) both sea ice thermodynamic and dynamic processes ultimately affect ringed seal/polar bear habitats by controlling the timing, location and amount of surface deformation required for ringed seal and polar bear preferred habitat 3) the ice edges bordering open waters of flaw leads are areas of high biological production and are observed to be important beluga habitat. 4) exchange of climate-active gases, including CO₂, is extremely active in sea ice environments, and the overall question of whether the Arctic Ocean is (or will be) a source or sink for CO₂ will be dependent on the balance of competing climate-change feedbacks.