Oxygen isotopes in calcite grown under cave-analogue conditions

Speleothem oxygen isotopes and growth rates are valuable proxies for reconstructing climate history. There is debate, however, about the conditions that allow speleothems to grow in oxygen isotope equilibrium, and about the correct equilibrium fractionation factors. We report results from a series of carbonate growth experiments in karst-analogue conditions in the laboratory. The setup closely mimics natural processes (e.g. precipitation driven by CO₂-degassing, low ionic strength solution, thin solution film) but with a tight control on growth conditions (temperature, pCO₂, drip rate, calcite saturation index and the composition of the initial solution). Calcite is dissolved in water in a 20,000 ppmV pCO₂ environment. This solution is dripped onto glass plates (coated with seed-carbonate) in a lower pCO₂ environment (<2500 ppmV), where degassing leads to calcite growth. Experiments were performed at 7, 15, 25 and 35 °C. At each temperature, calcite was grown at three drip rates (2, 6 and 10 drips per minute) on separate plates. The mass of calcite grown in these experiments varies with temperature (T in K) and drip rate (d_r in drips min⁻¹) according to the relationship daily growth mass = 1.254 + 1.478 ∗ 10⁻⁹ ∗ e^0.0679T + (e^0.00248T − 2) ∗ (−0.779d_r² + 10.05d_r + 11.69). This relationship indicates a substantial increase of growth mass with temperature, a smaller influence of drip rate on growth mass at low temperature and a non-linear relationship between drip rate and growth mass at higher temperatures. Low temperature, fast dripping conditions are found to be the most favourable for reducing effects associated with evaporation and rapid depletion of the dissolved inorganic carbon reservoir (rapid DIC-depletion). The impact of evaporation can be large so caves with high relative humidity are also preferable for palaeoclimate reconstruction. Even allowing for the maximum offsets that may have been induced by evaporation and rapid DIC-depletion, δ¹⁸O measured in some of our experiments remain higher than those predicted by Kim and O’Neil (1997). Our new results are well explained by equilibrium at a significantly higher α_{calcite-water}, with a kinetic-isotope effect that favours ¹⁶O incorporation as growth rate increases. This scenario agrees with recent studies by [Coplen, 2007] and [Dietzel et al., 2009]. Overall, our results suggest that three separate processes cause δ¹⁸O to deviate from true isotope equilibrium in the cave environment. Two of these drive δ¹⁸O to higher values (evaporation and rapid DIC-depletion) while one drives δ¹⁸O to lower values (preferential incorporation of ¹⁶O in the solid carbonate at faster growth rates). While evaporation and DIC-depletion can be avoided in some settings, the third may be inescapable in the cave environment and means that any temperature to δ¹⁸O relationship is an approximation. The controlled conditions of the present experiments also display limitations in the use of the Hendy test to identifying equilibrium growth.     

Geochemical and stratigraphic evidence against an oceanic crust interpretation for the Tumut ‘greenstone’ occurrence

Evidence is presented to show that the Tumut ‘greenstone’ occurrence is unlikely to be an example of Palaeozoic oceanic crust. First, new rare‐earth element analyses are unlike those obtained from oceanic tholeiites. Second, the published major‐ and trace‐element analyses of the metabasalts are not definitive of an oceanic magma type. Third, the juxtaposition of mafic volcanic rocks and ultramafic intrusives is not considered to be diagnostic of an oceanic crustal section. Fourth, the sulphide mineralization is not similar to that found in typical ophiolites such as those at Troodos in Cyprus.

In the light of the presently available data the basalts could have formed in a variety of environments including island‐arc, continental‐marginal or continental.     

Use of probiotic bacteria to improve growth and survivability of farmed New Zealand abalone (Haliotis iris)

The effects of two probiotic feeds containing two and three bacterial isolates were evaluated on the growth performance of New Zealand abalone (Haliotis iris). Probiotic bacteria were isolated from the guts of healthy adult abalone. The isolates were screened qualitatively and quantitatively according to their ability to hydrolyse nutrients (i.e. proteins, starch and alginate), produce acid and resist bile salts. Based on the screening results, we developed a multi-strain conglomerate of 2- and 3- probiotic bacterial strains that were supplemented into a commercial abalone feed to use in our experiments. The 2-probiotic conglomerate consisted of Exiguobacterium JHEb1 and Vibrio JH1, and the 3-probiotic conglomerate consisted of Exiguobacterium JHEb1, Vibrio JH1 and Enterococcus JHLDc. The probiotic feeding trial involved abalone juveniles (20–30 mm in maximum shell length). Both probiotic feeds significantly improved abalone growth compared to that of the unsupplemented feed. The 3-probiotic supplemented feed produced a significant shell length increase of 20.9%, a wet weight gain of 19.8% and a five-fold reduction in mortality compared to the controls. The 2-probiotic supplemented feed resulted in significant increases in shell length (15.4%) and reduced mortality (five-fold), but not in weight gain, compared to controls.     

Neurophysiological control of swimming behaviour,attachment and metamorphosis in black-footed abalone (Haliotis iris) larvae

Experiments were conducted to test the effect of a range of chemicals on larval responses in swimming behaviour, attachment and metamorphosis of the black-footed abalone (Haliotis iris). The effect of antibiotics on larval survival was first tested within negative (filtered seawater) and positive (GABA at 10^?5, 10^?4 and 10^?3 mol L^?1) control assays over 3 days. This experiment corroborated the effectiveness of using antibiotics to improve survival of larvae without obvious synergistic interactions with the GABA inducer or confounding effects of potential bacterial interactions. Chemical treatments (acetylcholine, potassium chloride, dopamine and glutamine) were then tested at various concentrations for their ability to modulate swimming behaviour and induce larval attachment and metamorphosis over 14 days. Generally, larval state shifted from swimming to attached, and from attached to metamorphosed, in the control and treatments over time. However, the peak percentage of attached and metamorphosed larvae varied in time among chemicals and concentrations. While overall percent metamorphosis was minimally enhanced after 14 days of exposure to some chemical treatments at certain concentrations, all treatments displayed significant capacities to down-regulate larval swimming and induce early attachment and metamorphosis. Mortality was recorded throughout the duration of the experiment, and was generally low (<20%) across controls and most treatments for exposures of less than 12 days. Interpretations of specific results from this study are used to elucidate neurophysiological control of larval activities for this abalone species. Comparisons with other marine invertebrates highlight the specificities of chemical cues and endogenous regulatory mechanisms across relatively closely related taxa.     

Discharge responses associated with rapid snow cover ablation events in the Susquehanna and Wabash River basins

ABSTRACT

In the mid-latitudes, snow plays a critical role in regional hydroclimate, with snow ablation variability in ephemeral regions representing an area of essential research. Due to a lack of historical snow-water-equivalent data in the eastern United States, recent research has substituted daily snow depth changes for ablation. These studies, however, do not explicitly examine if such a substitution yields a snowmelt hydrological signal, an important component of water resource management. As such, this study evaluates if ablation events, as defined as a daily snow depth decrease, subsequently result in increased river discharge within two similarly sized watersheds in the eastern United States: the Wabash and Susquehanna River basins. For both basins, >75% of snow ablation events resulted in a positive river discharge response (increase in discharge) at a 3-day lag. Furthermore, results show a significant and positive relationship between ablation event frequency and seasonal discharge response, such that an increase (decrease) in seasonal snow ablation event frequency yields an increase (decrease) in associated seasonal river discharge at a 3-day lag. These relationships indicate that inter-diurnal decreases in snow depth do carry hydrological implications, adding confidence that such a definition of ablation is appropriate for climatological applications.     

Modelling wetland connectivity during overbank flooding in a tropical floodplain in north Queensland,Australia

Hydrological connectivity between floodplain wetlands and rivers is one of the principal driving mechanisms for the diversity, productivity and interactions of the major biota in river–floodplain systems. This article describes a method of quantifying flood‐induced overbank connectivity using a hydrodynamic model (MIKE 21) to calculate the timing, the duration and the spatial extent of the connections between several floodplain wetlands and rivers in the Tully–Murray catchment, north Queensland, Australia. Areal photogrammetry and field surveyed stream cross data were used to reproduce floodplain topography and rivers in the model. Laser altimetry (LiDAR)–derived fine resolution elevation data, for the central floodplain, were added to the topography model to improve the resolution of key features including wetlands, flow pathways and natural and artificial flow barriers. The hydrodynamic model was calibrated using a combination of in‐stream and floodplain gauge records. A range of off‐stream wetlands including natural and artificial, small and large were investigated for their connectivity with two main rivers (Tully and Murray) flowing over the floodplain for flood events of 1‐, 20‐ and 50‐year recurrence intervals. The duration of the connection of individual wetlands varied from 1 to 12 days, depending on flood magnitude and location in the floodplain, with some wetlands only connected during large floods. All of the wetlands studied were connected to the Tully River for shorter periods than they were to the Murray River because of the higher bank heights and levees on the Tully River and wetland proximity to the Murray River. Other than hydrology, land relief, riverbank elevation and levee banks along the river were found key factors controlling the degree of connectivity. These variations in wetland connectivity could have important implications for aquatic biota that move between rivers and off‐stream habitats during floods. Copyright © 2011 John Wiley & Sons, Ltd.     

Late Holocene intermediate water variability in the northeastern Atlantic as recorded by deep-sea corals

The Nd isotopic composition of the aragonite skeleton of fossil deep-sea corals (Lophelia pertusa, Madrepora oculata and Desmophyllum dianthus) located in the northeastern Atlantic at water depths between 635 and 1300 m was investigated to reconstruct changes in the Atlantic mid-depth gyre circulation during the past millennium. The coral εNd values varied systematically from ? 11.8 to ? 14.4 during the past 1500 years, reflecting variations in seawater εNd and thus water mass provenance. Low εNd values (εNd = ? 14) occurred during the warm Medieval Climatic Anomaly (MCA) (between 1000 AD and 1250 AD) and during the most recent period (1950 AD to 2000 AD), interrupted by a period of significantly higher εNd values (~?12.5) during the Little Ice Age (LIA) (between 1350 AD and 1850 AD). One long-lived branching coral even recorded an abrupt systematic rise from low to high εNd values around 1250 AD over the course of its 10-year growth period.These variations are interpreted to result from variable contributions of the subpolar and subtropical Atlantic intermediate water masses, which today are characterized by εNd values of ? 15 and ~?11, respectively. The low εNd values observed during the warm MCA and during recent times imply a strong eastward extension of the mid-depth subpolar gyre (SPG) induced by a dominant positive phase of the North Atlantic oscillation (NAO). During the LIA, water from the subtropical gyre (STG) and potentially from the Mediterranean Sea Water (MSW) propagated further northward, as indicated by the higher coral εNd values. This pattern suggests a negative mean state of the NAO during the LIA, with weaker and more southerly located Westerlies and a westward contraction of the SPG. Variations in the contributions of the two gyres imply changes in the heat and salt budgets at intermediate depths during the past millennia that may have contributed to changes in the properties of North Atlantic inflow into the Nordic Seas and thus deep-water formation.     

Evolution in the discs and bulges of group galaxies since z= 0.4

We present quantitative morphology measurements of a sample of optically selected group galaxies at  0.3 < z < 0.55  using the Hubble Space Telescope ( HST ) Advanced Camera for Surveys (ACS) and the gim2d surface brightness fitting software package. The group sample is derived from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2) and follow-up Magellan spectroscopy. We compare these measurements to a similarly selected group sample from the Millennium Galaxy Catalogue (MGC) at  0.05 < z < 0.12  . We find that, at both epochs, the group and field fractional bulge luminosity (B/T) distributions differ significantly, with the dominant difference being a deficit of disc-dominated (B/T < 0.2) galaxies in the group samples. At fixed luminosity,   z = 0.4  groups have  ∼5.5 ± 2  per cent fewer disc-dominated galaxies than the field, while by   z = 0.1  this difference has increased to  ∼19 ± 6  per cent. Despite the morphological evolution we see no evidence that the group environment is actively perturbing or otherwise affecting the entire existing disc population. At both redshifts, the discs of group galaxies have similar scaling relations and show similar median asymmetries as the discs of field galaxies. We do find evidence that the fraction of highly asymmetric, bulge-dominated galaxies is  6 ± 3  per cent higher in groups than in the field, suggesting there may be enhanced merging in group environments. We replicate our group samples at   z = 0.4  and 0 using the semi-analytic galaxy catalogues of Bower et al. This model accurately reproduces the B/T distributions of the group and field at   z = 0.1  . However, the model does not reproduce our finding that the deficit of discs in groups has increased significantly since   z = 0.4  .     

Diadromy and longitudinal patterns of upstream penetration of freshwater fish in Taranaki,New Zealand

Diadromous fish species dominate the New Zealand freshwater fish fauna and make up 15 of the 17 native fish species found on the Taranaki Ring Plain. Trajectories of occurrence in relation to elevation and distance from the sea are described for 11 diadromous and 2 non‐diadromous species using data from the New Zealand Freshwater Fish Database and data collected over the summer of 1997/ 98. Distinctive distributions were found for most of the species related to their differing migratory strategies and abilities. The species were ranked based on components of these trajectories to compare their penetrative ability. Comparison of the ranking methods used revealed they produced similar results. The ranking of the 11 diadromous species in Taranaki relative to each other revealed similar rankings to those for the same species from the West Coast of the South Island. The non‐migratory native fish, Cran's bully (Gobiomorphus basalis), was not found on the western side of the mountain. This distribution is thought to be the result of the local extinction of non‐migratory species in high gradient or unstable streams.