Investigation of a eutrophic tidal basin: part 2nutrients and environmental aspects

The eutrophication of Langstone Harbour, a large tidal basin, has been studied by statistically designed nutrient surveys. Rates of input of nutrients from the sea, from effluent discharges and from other sources, have been estimated. Sediment/water interactions have been shown to be important in the phosphate budget of the basin, but they are less important in the nitrogen budget. Deductions were made about the relative importance of the various inputs and processes affecting concentrations of nutrients in the water column.It is concluded that ecologically or aesthetically detrimental growths of macroalgae are unlikely to occur in Langstone Harbour in the foreseeable future and that the removal of nutrient inputs, formerly thought to be necessary, will not, in fact, be required.The principles of the experimental design and of interpreting the data are of general applicability to tidal waters where the ratio of natural to man-made inputs needs to be known, where eutrophication is, or is expected to become, a problem, or where the progressive accumulation of nutrients by recycling is suspected.     

A laboratory study of baroclinic instability

Abstract

Experimental and theoretical results are presented for a simple system which exhibits baroclinic instability. We consider the motion of two immiscible fluids with densities ρ ₁ and ρ ₂ contained in a cylinder rotating with angular frequency ω. The motion is driven by a contact lid rotating with frequency ω + ω. In this paper ω, ω, 2(ρ ₂ – ρ ₁)/(ρ ₂ + ρ ₁), and the geometry are such that the interface does not intersect the “ground” (e.g. an almost horizontal boundary). The motions are described by two-layer quasi-geostrophic equations which are identical, except perhaps for the presence of interfacial friction and tension, with those used in meteorology and oceanography. For small enough internal Froude number F = 4ω² L ²/(g(Δρ/ρ)H) or small enough Rossby number ? = ω/2ω the flow is steady and axisymmetric, the velocity field in each layer being determined primarily by frictional effects in top, bottom, and interfacial Ekman layers. For certain (F, ?) the flow becomes non-axisymmetric. The transition points for the case where the basic potential vorticity gradient is due to interface slope alone have been carefully measured and are in very good agreement with a linear instability theory which neglects sidewall effects. Some preliminary observations of supercritical motion, which include repeatable amplitude and wavenumber vacillation, are reported.     

A call for increased public engagement in geology higher education

Rising fees are forcing higher education institutions to think critically about what students are offered for their money. In geology courses there appears to be a lack of guidance for alternative careers in academia or industry, and even a lack of education about wider social, political and economic impacts of the discipline. It is possible to detect a lack of high‐impact geoscience among the popular science communication communities, such as online multidisciplinary blogging platforms. In order to enhance the student experience and the impact of geoscience on the wider public, universities need to look inwards at what they can do to help inspire and educate students to have broader career horizons and bigger public impacts through their research.     

The Wide Field Spectrograph (WiFeS)

This paper describes the Wide Field Spectrograph (WiFeS) under construction at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) for the ANU 2.3 m telescope at the Siding Spring Observatory. WiFeS is a powerful integral field, double-beam, concentric, image-slicing spectrograph designed to deliver excellent throughput, wavelength stability, spectrophotometric performance and superb image quality along with wide spectral coverage throughout the 320–950 nm wavelength region. It provides a 25×38 arcsec field with 0.5 arcsec sampling along each of twenty five 38×1 arcsec slitlets. The output format is optimized to match the 4096×4096 pixel CCD detectors in each of two cameras individually optimized for the blue and the red ends of the spectrum, respectively. A process of “interleaved nod-and-shuffle” will be applied to permit quantum noise-limited sky subtraction. Using VPH gratings, spectral resolutions of 3000 and 7000 are provided. The full spectral range is covered in a single exposure at R=3000, and in two exposures in the R=7000 mode. The use of transmissive coated optics, VPH gratings and optimized mirror coatings ensures a throughput (including telescope atmosphere and detector) >30% over a wide spectral range. The concentric image-slicer design ensures an excellent and uniform image quality across the full field. To maximize scientific return, the whole instrument is configured for remote observing, pipeline data reduction, and the accumulation of calibration image libraries.     

Statoliths

Statoliths, in modern cephalopods, are the paired calcareous ‘stones’ that lie in two adjacent cavities (or statocysts) within the cartilage of the head. The stones are generally 0.5–2.0 mm in length and appear to be formed of aragonite. Statoliths often co‐occur with fish otoliths, and being of similar appearance, size, colour, etc., this has caused confusion in the past. It was only towards the latter part of the twentieth century that it was recognized that statoliths could occur as fossils.     

Snowmelt variability in Polar Bear Pass,Nunavut, Canada,from QuikSCAT: 2000–2009

Snowmelt onset and end date estimates are made from QuikSCAT scatterometer measurements in the Canadian High Arctic wetland of Polar Bear Pass (PBP) and the surrounding region of Bathurst Island, Nunavut. In situ data within PBP is used to validate QuikSCAT snowmelt onset/end date estimates. Results indicate that within PBP from 2000 to 2009, the mean snowmelt onset date was Year Day (YD) 162, the mean snowmelt end date was YD179, and the mean snowmelt duration was 17 days. More interannual variability was apparent in snowmelt end date and duration compared with onset, and only snowmelt end date was significantly correlated with mean June air temperature at ?0.78. Cooler air temperatures in 2004 contributed to a long snowmelt duration of 24 days, and the very short snowmelt duration in 2007 of just 11 days was caused by rapid and sustained increases in air temperature. For snowmelt end date and duration the mean spatial pattern revealed two centres of later snowmelt end date/longer snowmelt duration over Bathurst Island. They were separated by early snowmelt end date/short snowmelt duration in PBP. These patterns are in agreement with the spatial distribution of mean May to July air temperature over Bathurst Island and are likely influenced by the local‐scale topography of Bathurst Island. Given the correlation between air temperature and snowmelt end date, we might expect quicker snowmelt under increased warming. The latter process may have implications for the sustainability of the PBP wetland under a warmer climate. Copyright © 2011 John Wiley & Sons, Ltd.     

Public support for carbon dioxide removal strategies: the role of tampering with nature perceptions

Climatic Change - Carbon dioxide removal (CDR) describes a suite of controversial approaches to mitigating climate change that involve removing existing carbon dioxide from the atmosphere. Through...     

Variation of Mo isotopes from molybdenite in high-temperature hydrothermal ore deposits

Measurable molybdenum isotope fractionation in molybdenites from different ore deposits through time provides insights into ore genesis and a new technique to identify open-system behavior of Re–Os in molybdenites. Molybdenite samples from six porphyry copper deposits, one epithermal polymetallic vein deposit, four skarns, and three Fe-oxide Cu–Au deposits were analyzed. The δ⁹⁷Mo‰ (where ) for all samples varied from 1.34 ± 0.09‰ to −0.26 ± 0.04‰. This is the largest molybdenum isotopic variation in molybdenite from high-temperature ore deposits recorded to date. δ⁹⁷Mo‰ of molybdenite varies as a function of the deposit type and the rhenium and osmium concentrations of the samples. Isotope values for Mo also vary within the individual deposits. In general, molybdenites from porphyry copper deposits have the lightest values averaging 0.07 ± 0.23‰ (1σ). Molybdenites from the other deposit types average 0.49 ± 0.26‰ (1σ). The variations could be related to the fractionation of Mo into different mineral phases during the ore-forming processes. A comparison of the Mo isotope ratios and the Re–Os ages obtained from the same aliquot may possess a geochronological evaluation tool. Samples that yielded robust ages have different Mo isotopic compositions in comparison to samples that yielded geologically unreasonable ages. Another observed relationship between the Re–Os and Mo isotope data reveals a weak correspondence between Re concentration and Mo isotope composition. Molybdenites with higher concentrations of Re correspond to lighter Mo isotope values.