Seagrass population dynamics and water quality in the Great Barrier Reef region: a review and future research directions

Seagrasses in the Great Barrier Reef region, particularly in coastal habitats, act as a buffer between catchment inputs and reef communities and are important habitat for fisheries and a food source for dugong and green turtle. Within the Great Barrier Reef region there are four different seagrass habitat types now recognised. The spatial and temporal dynamics of the different types of seagrass habitat is poorly understood. In general seagrass growth is limited by light, disturbance and nutrient supply, and changes to any or all of these limiting factors may cause seagrass decline. The capacity of seagrasses to recover requires either recruitment via seeds or through vegetative growth. The ability of seagrass meadows to recover from large scale loss of seagrass cover observed during major events such as cyclones or due to anthropogenic disturbances such as dredging will usually require regeneration from seed bank. Limited research into the role of pollutants on seagrass survival suggests there may be ongoing impacts due to herbicides, pesticides and other chemical contaminants. Further research and monitoring of seagrass meadow dynamics and the influence of changing water quality on these is needed to enhance our ability to manage seagrasses on the Great Barrier Reef.     

Athabasca Glacier,Canada – a field example of subglacial ice and till erosion?

The Athabasca Glacier, resting on a rigid bed, provides an excellent example of subglacial ice and till erosion. The presence of a thin mobile till layer is shown by the presence of flutes, saturated till layer, push moraines and ploughed boulders. Cross‐cutting striations, v‐shaped striations and reversed stoss‐and‐lee clasts are indicative of clasts rotating within this layer. As the till moves it erodes the bedrock and clasts within it. A combination of erosion by ice and till produces stoss‐and‐lee‐clasts and generates striations on flutes and embedded clasts, as well as eroding the bedrock into a continuum of smoothed, rounded and streamlined forms. Copyright © 2005 John Wiley & Sons, Ltd.     

Resolving archaeological populations with Sr-isotope mixing models

Strontium isotope analysis of tooth enamel is a useful provenancing technique to investigate the childhood origins and residential mobility of ancient people. However, where different geographical target regions have similar biosphere ⁸⁷Sr/⁸⁶Sr it is often difficult to resolve the ⁸⁷Sr/⁸⁶Sr ranges of two different groups of people and establish what constitutes the local range at each site. Here a multi-period study is presented from the Outer Hebrides, Scotland and an investigation of Neolithic and Early Bronze Age populations from the Yorkshire Wolds, NE England. The aim is to demonstrate that, despite complex human dietary strategies, simple mixing systems with only two end-members do occur in archaeological human populations in certain geological provinces and, despite overlapping ⁸⁷Sr/⁸⁶Sr ranges, it is possible to separate two populations based on the structure within the data set.     

An unusual modern silica–carbonate sinter from Pavlova spring, Ngatamariki, New Zealand

ABSTRACT A silica–carbonate deposit is forming from the dilute alkali chloride waters of Pavlova spring, a small thermal pool and outflow channel (85 to <40 °C), situated at the northern extent of the South Orakonui area of the Ngatamariki geothermal field, Taupo Volcanic Zone (TVZ), New Zealand. It is one of a small but growing number of thermal spring features known to yield deposits of mixed mineralogy. At Pavlova, a distinctive, crustose, chalk‐white, meringue‐like sinter, comprising non‐crystalline opal‐A silica with subordinate calcite, is actively precipitating both around the margins of and as small islets within the spring, with an average accumulation rate of ≈ 2 mm year^?1. Both emergent and partly submerged substrates host the sinter, including fallen pine branches, twigs, needles and cones, gum leaves, grass blades, bracken fronds, pumice, sediment and microbial mats. The sinter is thin (25–35 mm thickness), finely laminated and contains three distinct types of stacked horizons. Submerged basal layers constitute stratiform to undulatory microstromatolites with pseudocolumns, which grew outwards and upwards on narrow twig nuclei. Emergent middle layers comprise discontinuous, spicular microstromatolites (to 10 mm height), with prostrate and erect microbial filaments, silica spheres and silicified mucus, overlain by silicified structures of probable fungal origin. In places, lower and middle sinter layers are capped by white, smooth, convex surfaces that coalesce into subdued, curved ridges, resembling laterally continuous peaks of egg‐white meringue. The meringue is internally laminated, with fossilized microbes preserved in thin horizons. Small lensoid masses of calcite crystals nestle between silica laminae throughout the sinter. The near‐neutral (pH ≈ 7·2) spring water is a dilute chloride‐carbonate type (HCO≈ 470 µg g^?1, Cl^–≈ 600 µg g^?1) with low (≈ 50 µg g^?1), typical of TVZ thermal fields where deep chloride fluid mixes with CO₂‐rich, steam‐heated shallow waters before discharge. The hot water changed little in composition from 1993 to 1999 and, despite dilution by meteoric waters, contains sufficient SiO₂ (≈ 220 µg g^?1) for opal‐A to deposit at the surface upon cooling. However, the concentration of Ca²⁺ (≈ 6 µg g^?1) is such that the precipitation of calcite is not expected without modification of spring waters. Precipitation occurs by evaporation of thin water films at exposed substrate surfaces, via meniscoid as well as capillary creep (wicking), through porous sinter horizons and across emergent vegetative surfaces in contact with spring water or steam. The height of the deposit above the water surface is restricted by the upper limit of moisture bathing these substrates. Splash and spray are not involved in the formation of Pavlova spicular microstromatolites, as is the case for other texturally similar deposits from hotsprings elsewhere. This young (< 15 years), mineralogically and morphologically complex hot‐spring deposit exhibits > 10 times lower accumulation rates than typical siliceous sinters in the TVZ, and deposition of both silica and calcite is controlled by microchemical conditions and local temperature gradients, rather than by bulk spring water chemistry.     

Gender and physical geography in the United Kingdom

Summary This paper presents the results of a questionnaire survey of all higher education geography departments in the United Kingdom, in order to provide an overview of the current status of women employed in the discipline, particularly female physical geographers. The survey examined the position of female physical geographers of doctoral level and above, in terms of employment status, type of contract, career structure, research and teaching disciplines and successful grant applications. The publication records of female academic staff were also examined. The results of the survey demonstrate that women are under-represented in physical geography at all levels of the academic hierarchy and that the majority of female physical geography academic staff are below 40 years of age, and employed at the lecturer level on permanent contracts.     

The coastal ocean off Oregon from 1961 to 2000: is there evidence of climate change or only of Los Niños?

A zonal hydrographic section along 44.65°N, from the coast of Oregon to 300 km offshore, was occupied regularly (at least seasonally) from 1961 to 1971 and then sporadically until recently. Regular monitoring of this section to 160 km offshore resumed in July 1997 as part of the GLOBEC Long Term Observational Program; the recent data provide observations in Oregon coastal waters of El Niño 1997–98 and La Niña conditions that followed. The complete seasonal data from the decade 1961–1971 provide a basis for comparison with the recent temperature and salinity sections, steric height profiles, geostrophic velocity, and water mass characteristics. These data, and sporadic observations in intervening years, allow us to compare conditions during several ENSO events with the recent event and to search for evidence of climate change. The PFEL Coastal Upwelling Index, sea level from the University of Hawaii Sea Level Center, the Multivariate ENSO Index (MEI), the Pacific Decadal Oscillation (PDO), and outflow from the Columbia River are used to distinguish local and remote causes of variability in physical oceanographic conditions off Oregon. The sequence of El Niño/La Niña/El Niño in 1963–66, during a cool phase of PDO, provides a comparison to El Niño/La Niña of 1997–2000. El Niño in 1982–83 and 1997–98, during a warm phase of PDO, caused the largest oceanographic anomalies in the 40 years. The comparison indicates warming of the coastal ocean off Oregon and suggests a modulation of ENSO effects by PDO. Such modulation would mask evidence for secular climate change in our 40-year oceanographic data series.     

Variation in the Sizes of Chthamalid ­Barnacle Post-Settlement Cyprids on European Shores

Abstract. As part of a wider study on the settlement and recruitment of Chthamalus spp. in Europe, this study investigated whether chthamalid cyprids can be separated by length on a European scale. Variation in cyprid length with latitude and temporal variation at selected localities were also examined. The lengths of cyprids collected between 1996 – 1999 on nine rocky shores in Europe are reported. Elminius modestus cyprids were found only at Roscoff, NW France and could be distinguished due to their carapace shape and length. They showed a unimodal length distribution, measuring between 450 and 625 µm, with no variation in length between the two sampling dates (1997 and 1998). Based on carapace shape and length, the remaining cyprids in the collections were identified as one of three chthamalid species, Chthamalus montagui, Chthamalus stellatus or Euraphia depressa. Bimodal length distributions of chthamalid cyprids were seen on some shores, while others had a single small‐sized modal group (representing C. montagui on Atlantic shores and/or E. depressa in the Mediterranean) separated from a few distinctly larger cyprids (C. stellatus). Metamorphs collected simultaneously with cyprid collections were identified as C. stellatus or C. montagui, except at Roscoff, where E. modestus were also found. In southern Portugal, where all metamorphs collected were C. montagui and adult C. montagui were the dominant barnacles, most cyprids measured between 350 and 550 µm long and this size distribution coincides with the distribution expected for C. montagui. Cyprids collected on these four more southerly Portuguese shores had the same modal length class (475 µm) and this remained constant between successive years at Luz and Albufeira, Algarve. The smallest (350 µm long) wild chthamalid cyprids found were from southern Portugal and Italy. In Spain, France and Ireland the smallest chthamalid cyprid was 425 µm long. The results from the present study support the hypothesis that on Atlantic shores cyprids of C. montagui can be separated from those of C. stellatus based on size, although there is some variation in cyprid length with latitude as well as temporal variation at selected localities.     

Sedimentary diatom and pigment-inferred recent anthropogenic accelerated eutrophication of a Mediterranean lake (Lake Dojran,Republic of North Macedonia / Greece)

Journal of Oceanology and Limnology - Lake eutrophication is recognised as a serious global challenge, and many regional legislative programmes are being made to attempt to relieve nutrient...