Excess 3He in deep water on the East Pacific Rise

Helium isotope measurements show that water on the crest and flanks of the East Pacific Rise has the highest enrichment in ³He so far observed in the oceans; the ³He/⁴He ratio anomaly relative to atmospheric helium is + 32% at the mid-depth maximum in the profiles. The corresponding ³He solubility anomaly relative to saturation with atmospheric helium is +50%. These data indicate that active sea-floor spreading sites on the crests of the mid-ocean rises are the sources of primordial helium injected into the ocean from the earth's interior. The ³He/⁴He ratio in this flux is approximately 1.6 × 10^?5, about 11 times the atmospheric ratio of 1.4 × 10^?6. The total flux of ³He into the atmosphere is 4.6 atoms cm^?2 earth-surface sec^?1, most of which (4.0 atoms cm^?2 sec^?1) is supplied by the oceanic flux. The corresponding atmospheric residence time for ³He is 10⁶ years, which, within the large uncertainties of supply and demand (thermal escape), is consistent with the requirement for a steady state.     

Stratigraphy,paleontology, and age of Lake Algonquin sediments in southwestern Ontario,Canada

Molluscs, ostracodes, diatoms, pollen, plant macrofossils, peat, and wood have been found in glacial Lake Algonquin sediments, and estuarine-alluvial sediments of the same age, in southern Ontario. Molluscs and ostracodes are particularly abundant and widespread. Pollen analysis of Lake Algonquin sediments, bogs on the Algonquin terrace, and upland bogs above the Algonquin terrace, indicate that Lake Algonquin was still in existence at the time of the spruce-pine pollen transition, previously dated at an average of 10,600 yr BP at a number of sites in Michigan, Ohio, and southern Ontario. Wood in estuarine-alluvial sediments graded to the Algonquin level is of similar radiocarbon age. Evidence from several sites in the eastern Great Lakes area suggests the presence of a preceding low-water stage (Kirkfield outlet stage); drowned and alluviated valleys and fining-upward sediment sequences have been identified in this study as further supporting evidence. Lake Algonquin drained from the southern sites by isostatic tilting and eventual opening of the “North Bay outlet” some time shortly after 10,400 yr BP.Our radiocarbon dates suggest the low-water stage has an age of about 11,000 yr BP, and that Lake Algonquin drained 10,000–15,000 y. a. Dates previously published for the Lake Michigan basin are generally too young in comparison with ours, and dates on the Champlain Sea are generally too old. More critical evaluation of all dating results is desirable.From fossil remains we suggest a rapidly expanding fauna in the waters of Lake Algonquin. The spruce pollen period was a time of rapid faunal and floral migration, when the ice front was retreating from Kirkfield to North Bay, Ontario. Diversity of some species and fossil numbers increased substantially at the transition from spruce to pine just before Lake Algonquin drained.     

Defining a Digital Earth System

In a 1998 speech before the California Science Center in Los Angeles, then US Vice‐President Al Gore called for a global undertaking to build a multi‐faceted computing system for education and research, which he termed “Digital Earth.” The vision was that of a system providing access to what is known about the planet and its inhabitants’ activities – currently and for any time in history – via responses to queries and exploratory tools. Furthermore, it would accommodate modeling extensions for predicting future conditions. Organized efforts towards realizing that vision have diminished significantly since 2001, but progress on key requisites has been made. As the 10 year anniversary of that influential speech approaches, we re‐examine it from the perspective of a systematic software design process and find the envisioned system to be in many respects inclusive of concepts of distributed geolibraries and digital atlases. A preliminary definition for a particular digital earth system as: “a comprehensive, distributed geographic information and knowledge organization system,” is offered and discussed. We suggest that resumption of earlier design and focused research efforts can and should be undertaken, and may prove a worthwhile “Grand Challenge” for the GIScience community.     

The July 2007 rock and ice avalanches at Mount Steele, St. Elias Mountains, Yukon, Canada

A large rock and ice avalanche occurred on the north face of Mount Steele, southwest Yukon Territory, Canada, on July 24, 2007. In the days and weeks preceding the landslide, several smaller avalanches initiated from the same slope. The ice and rock debris traveled a maximum horizontal distance 5.76 km with a maximum vertical descent of 2,160 m, leaving a deposit 3.66 km² in area on Steele Glacier. The seismic magnitude estimated from long-period surface waves (M _s) is 5.2. Modeling of the waveforms suggests an estimated duration of approximately 100 s and an average velocity of between 35 and 65 m/s. This landslide is one of 18 large rock avalanches known to have occurred since 1899 on slopes adjacent to glaciers in western Canada. We describe the setting, reconstruct the event chronology and present a preliminary characterization of the Mount Steele ice and rock avalanches based on field reconnaissance, analysis of seismic records and an airborne LiDAR survey. We also present the results of a successful dynamic simulation for the July 24 event.     

The effects of sample scheduling and sample numbers on estimates of the annual fluxes of suspended sediment in fluvial systems

Since the 1970s, there has been both continuing and growing interest in developing accurate estimates of the annual fluvial transport (fluxes and loads) of suspended sediment and sediment‐associated chemical constituents. This study provides an evaluation of the effects of manual sample numbers (from 4 to 12 year^?1) and sample scheduling (random‐based, calendar‐based and hydrology‐based) on the precision, bias and accuracy of annual suspended sediment flux estimates. The evaluation is based on data from selected US Geological Survey daily suspended sediment stations in the USA and covers basins ranging in area from just over 900 km² to nearly 2 million km² and annual suspended sediment fluxes ranging from about 4 Kt year^?1 to about 200 Mt year^?1. The results appear to indicate that there is a scale effect for random‐based and calendar‐based sampling schemes, with larger sample numbers required as basin size decreases. All the sampling schemes evaluated display some level of positive (overestimates) or negative (underestimates) bias. The study further indicates that hydrology‐based sampling schemes are likely to generate the most accurate annual suspended sediment flux estimates with the fewest number of samples, regardless of basin size. This type of scheme seems most appropriate when the determination of suspended sediment concentrations, sediment‐associated chemical concentrations, annual suspended sediment and annual suspended sediment‐associated chemical fluxes only represent a few of the parameters of interest in multidisciplinary, multiparameter monitoring programmes. The results are just as applicable to the calibration of autosamplers/suspended sediment surrogates currently used to measure/estimate suspended sediment concentrations and ultimately, annual suspended sediment fluxes, because manual samples are required to adjust the sample data/measurements generated by these techniques so that they provide depth‐integrated and cross‐sectionally representative data. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Geographically weighted methods and their use in network re-designs for environmental monitoring

Given an initial spatial sampling campaign, it is often of importance to conduct a second, more targeted campaign based on the properties of the first. Here a network re-design modifies the first one by adding and/or removing sites so that maximum information is preserved. Commonly, this optimisation is constrained by limited sampling funds and a reduced sample network is sought. To this extent, we demonstrate the use of geographically weighted methods combined with a location-allocation algorithm, as a means to design a second-phase sampling campaign in univariate, bivariate and multivariate contexts. As a case study, we use a freshwater chemistry data set covering much of Great Britain. Applying the two-stage procedure enables the optimal identification of a pre-specified number of sites, providing maximum spatial and univariate/bivariate/multivariate water chemistry information for the second campaign. Network re-designs that account for the buffering capacity of a freshwater site to acidification are also conducted. To complement the use of basic methods, robust alternatives are used to reduce the effect of anomalous observations on the re-designs. Our non-stationary re-design framework is general and provides a relatively simple and a viable alternative to geostatistical re-design procedures that are commonly adopted. Particularly in the multivariate case, it represents an important methodological advance.     

Accretion-driven core collapse and the collisional formation of massive stars

We consider the conditions required for a cluster core to shrink, by adiabatic accretion of gas from the surrounding cluster, to densities such that stellar collisions are a likely outcome. We show that the maximum densities attained, and hence the viability of collisions, depend on the balance between core shrinkage (driven by accretion) and core puffing up (driven by relaxation effects). The expected number of collisions scales as     , where N _core is the number of stars in the cluster core and     is the free-fall velocity of the parent cluster (gas reservoir). Thus, whereas collisions are very unlikely in a relatively low-mass, low-internal-velocity system such as the Orion Nebula Cluster, they become considerably more important at the mass and velocity scales characteristic of globular clusters. Thus, stellar collisions in response to accretion-induced core shrinkage remain a viable prospect in more massive clusters, and may contribute to the production of intermediate-mass black holes in these systems.     

A 2000 year record of climatic change at Ongoke Lake,southwest Alaska

We analyzed sediments of the past 2000 years from Ongoke Lake, southwest Alaska, for organic carbon, organic nitrogen, biogenic silica (BSi), and diatom assemblages at decadal to centennial resolution to infer limnological changes that may be related to climatic variation in southwestern Alaska. The chronology is based on a ²¹⁰Pb profile from bulk sediments and nine AMS ¹⁴C ages from terrestrial plant macrofossils. Four of the ¹⁴C ages span a core depth interval of 60.5 cm but are statistically indistinguishable from one another with a mean of ~1300 AD, which compromises the determination of temporal trends at Ongoke Lake and comparison with other paleoclimate records. The diatom record suggests changes in the duration of ice cover and strength of thermal stratification that are probably related to temperature variation. This variation includes a cold interval around the first millennium cooling (FMC) and a warm interval spanning the medieval climate anomaly (MCA). However, the lake-sediment record shows no clear signals of temperature variation for the period of the Little Ice Age (LIA) or the twentieth century. Climatic changes during these periods may have been manifested through effective-moisture (precipitation minus evapotranspiration) variation in the Ongoke Lake area. We estimate water depths and infer effective-moisture fluctuations by applying a regional transfer function to our diatom record. Together with inferences from diatom autecologies, this water-depth reconstruction suggests that effective moisture increased steadily from 50 BC to 350 AD, which was followed by relatively dry conditions between 550 and 750 AD and relatively wet conditions between 750 and 1450 AD. Effective moisture was low from ~1450 to 1850 AD, coinciding with the LIA; an alternative age model places this interval between ~1315 and 1850 AD. During the past 150 years, effective moisture increased, with estimated water depths reaching peak values in the second half of the twentieth century. This study offers the first paleolimnological record for inferring centennial-scale climatic variation over the past two millennia from southwestern Alaska.

Doing interdisciplinarity: motivation and collaboration in research for sustainable agriculture in the UK

This paper studies knowledge production in complex, collaborative research projects that brought together academics from different disciplines, research users and agricultural businesses. It takes a comparative approach, studying the interactions within interdisciplinary research teams from ten case studies, considering the process of collaboration from initial idea through to publication. The research developed a typology of participants in these projects, and identified the motivations and challenges of each. Our results analyse the process of research teams coming together and the relationships that are built up during the research. A particular challenge identified was the building of cooperation and trust. This issue is explored alongside issues of communication, methodology, data analysis and the process of drawing and publicising conclusions.