The clustering of colour-selected galaxies

We present measurements of the angular correlation function of galaxies selected from a B _J ∼23.5 multicolour survey of two 5°×5° fields located at high galactic latitudes. The galaxy catalogue of ∼4×10⁵ galaxies is comparable in size to catalogues used to determine the galaxy correlation function at low redshift. Measurements of the z ∼0.4 correlation function at large angular scales show no evidence for a break from a power law, although our results are not inconsistent with a break at ≳15 h⁻¹ Mpc. Despite the large fields-of-view, there are large discrepancies between the measurements of the correlation function in each field, possibly caused by dwarf galaxies within z ∼0.11 clusters near the South Galactic Pole.
Colour selection is used to study the clustering of galaxies from z ∼0 to z ∼0.4. The galaxy correlation function is found to depend strongly on colour, with red galaxies more strongly clustered than blue galaxies by a factor of ≳5 at small scales. The slope of the correlation function is also found to vary with colour, with γ∼1.8 for red galaxies and γ∼1.5 for blue galaxies. The clustering of red galaxies is consistently strong over the entire magnitude range studied, although there are large variations between the two fields. The clustering of blue galaxies is extremely weak over the observed magnitude range, with clustering consistent with r ₀∼2 h⁻¹ Mpc. This is weaker than the clustering of late-type galaxies in the local Universe, and suggests that galaxy clustering is more strongly correlated with colour than morphology. This may also be the first detection of a substantial low-redshift galaxy population with clustering properties similar to faint blue galaxies.     

Uranium and thorium isotope concentrations in foraminiferal calcite

Uranium and thorium isotope activities were measured by isotope dilution alpha spectrometry in four late Pleistocene and Holocene foraminiferal calcite samples. Sample cleaning methods were utilized to separate calcite tests from contaminating clay and surface oxide coatings. The maximum concentration of lattice bound uranium is 0.023 ppm (10 × 10^?9 moles U/mole Ca), consistent with the lowest reported value, 0.025 ppm [1].²³⁰Th/²³⁴U activity ratios in samples cleaned as described above are much greater than one, indicating that the cleaning methods used do not effectively remove²³⁰Th from the surfaces of the calcite. The upper limit for lattice bound²³²Th is 0.039 ppm (17 × 10^?9 moles Th/mole Ca).     

Aspects of the ecology of a littoral chiton,Sypharochiton pellisekpentis (Mollusca: Polyplacophora)

On several Auckland shores, a littoral chiton, Sypharochiton pelliserpentis (Quoy and Gaimard, 1835), was widely distributed and common. At Castor Bay it was the commonest chiton, and its density equalled or exceeded that of the commonest limpet (Cellana spp.) over most of the inter‐tidal range. Spot measurements of population density were made at other sites including exposed and sheltered shores. The smallest animals were restricted to the lower shore in pools or on areas of rock which were slow to drain. Exclusive of these small animals, the population structure was similar in pools and water‐filled crevices situated either high or low on the shore. This was also true for populations of animals from drained surfaces, but, at both shore levels, the population structure in the two micro‐habitats (pools and drained surfaces) was distinct.

Single measurements of salinity in the very small volumes of water in which chitons were living gave a range of 13.3–45.8‰. In laboratory experiments at normal temperatures this species could survive these fluctuations for the maximum time possible between tides. Desiccation experiments, in which weight loss was expressed as a percentage of total water content, showed weight loss to depend on size. No significant differences in weight loss were found between populations from the two shore levels and the two micro‐habitats considered, though there were slight survival differences. Desiccation is probably an important factor influencing population structure, but loss of up to 75% of water content could be tolerated before 50% mortality occurred. Osmotic and desiccation stress evoked a characteristic behaviour pattern.     

Winter cyclone frequencies in thirteen models participating in the Atmospheric Model Intercomparison Project (AMIP1)

Various aspects of the simulated behaviour of cyclones in thirteen models participating in the AMIP1 exercise are presented. In the simulation of the winter climatological mean sea level pressure field for the Northern Hemisphere, the models produce reasonable simulations of the "semi-permanent" features of the climatology. The greatest departures from the observed climatology occur near the exit regions of the oceanic storm tracks; i.e., over northwestern North America, over and to the west of the British Isles and in the Mediterranean. The departures in the three geographical areas are very systematic in that at least eleven of the models exhibit similar departures from observations. In the Southern Hemisphere the intensity of the circumpolar trough is generally well simulated but positioned slightly too far north. Most models exhibit errors south of Africa, New Zealand, and South America. The simulations of the cyclone events show that the models are reasonably successful in reproducing the large-scale aspects of observed cyclone events but deficiencies in the details of the simulations are apparent. The paucity of simulated events to the south of the Alps and to the east of the Rockies suggests that the models have difficulty simulating lee cyclogenesis. Over much of North America, the models have difficulty simulating the correct level of synoptic activity as demonstrated by the low numbers of both cyclone events and anticyclone events. The models have difficulty simulating the distribution of cyclone events as a function of central pressure. The most common problem is that the models exhibit an ever increasing deficit of events with decreasing central pressure. This problem is more apparent in the Southern Hemisphere than in the Northern Hemisphere and does not appear to be resolution dependent. There is an apparent ENSO signal in the observed Northern Hemisphere interannual variability of intense winter cyclone events. With the exception of ECMWF, the models fail to reproduce this phenomenon. There is some evidence that the models do indeed respond to the interannual variability in the SSTs, but the response tends to be negatively correlated with that of the real atmosphere. In the Southern Hemisphere, there does not appear to be ENSO-induced interannual variability in the observed numbers of cyclone events. Consequently, it could be argued that the models have been reasonably successful in the Southern Hemisphere since they, like the observations, do not exhibit any ENSO-induced interannual variability.     

Lake ecosystem responses to catchment disturbance and airborne pollution: an 800-year perspective in southern Sweden

Sediment sequences spanning the last 800 years from two small lakes in the south Swedish uplands were explored for assessment of effects of changing human population, local land-use practices and airborne pollution on lake-ecosystem functioning and resilience. Variations in nutrient cycling and deposition of lithogenic elements were studied, using a multi-proxy stratigraphic approach. Carbon and nitrogen elemental and isotopic analyses were applied in combination with records of hydrocarbons (n-alkanes) to investigate the sources and depositional conditions of sediment organic matter. Changes in fluvial and airborne delivery of inorganic matter were based on X-ray fluorescence measurements. The results reveal that population growth and related increases in land-use pressure had a major impact on catchment erosion and input of terrestrial organic matter to the lakes from the 1500s to the end of the 1800s. Evidence also exists of a brief period of catchment disturbance at ca. 1200–1300, followed by recovery, likely connected to the Black Death pandemic. At ca. 1900 synchronous shifts in most of the proxy records suggest a marked change in external forcing common to the two lakes related to a major decrease in population density and the introduction of modern forestry following the industrial revolution. Interestingly, the two sediment records exhibit generally coherent trends in C/N ratio, organic C content and δ¹³C, both before and after 1900, indicating broadly similar sensitivities of the lake ecosystems to human impact. In contrast, deviating trends in total N content, δ¹⁵N and lithogenic element concentrations (K, Ti, Rb and Zr) reflect site-specific responses to local disturbances during the last century due to different nutrient conditions and catchment properties. Our companion sediment records highlight the importance of understanding long-term human impact on watersheds and demonstrate how regional versus local forcing of lake ecosystems, as well as site-specific responses related to catchment characteristics can be reconstructed.     

Groundwater sampling methodology for mineral exploration in glaciated terrain using reverse circulation overburden drilling

A technique to sample groundwaters in the basal sediment aquifers of regions characterized by thick glacial sediments using reverse circulation drilling has been developed together with a methodology for carrying out detailed groundwater hydrogeochemical surveys aimed at discovery of sub-outcropping and deep-seated ore deposits. The method consists essentially of five steps, namely: (1) overburden drilling using a stable tracer dye to monitor the effects of drill water input into the basal aquifer, (2) removal of the tricones from the drill bit to allow emplacement of the piezometer unit and injection of filter sand packs and bentonite seals, (3) development of groundwater in the basal aquifer to remove drill water inputs, (4) emplacement of the piezometer unit and injection of the filter sand pack and bentonite seal, and (5) further development of the piezometer installation followed by sampling of basal aquifer groundwater and measurement of piezometric heads. The piezometer installation and sampling procedures can be performed with a minimal amount of training by geological technicians either employed by mining companies or more generally by overburden drilling management companies as part of their contractual agreement with a mining company.     

Isotopic evidence for the source of lead in the North Pacific abyssal water

The absence of accurate measurements of lead (Pb) isotopic composition in the North Pacific abyssal water has made it difficult to assess the relative importance of what are believed to be the two major Pb sources: the natural Pb introduced during preindustrial time and recent anthropogenic Pb resulting from leaded gasoline combustion and high temperature industrial activities. Here we report a vertical profile of seawater ²⁰⁶Pb/²⁰⁷Pb ratio and a meridional section of Pb concentration in the North Pacific Ocean. We observe 2-3-fold increases in Pb concentration along the deep-water flow path and a deep-water ²⁰⁶Pb/²⁰⁷Pb ratio (∼1.188) substantially lower than the pre-industrial value (∼1.210). These data suggest that anthropogenic Pb has invaded the North Pacific abyssal water and become the predominant Pb source there. A simple model calculation based on these data indicates that the anthropogenic Pb is transported to the deep ocean by sinking particles and that this Pb vertical flux has a ²⁰⁶Pb/²⁰⁷Pb ratio that decreased during the past two centuries.