Rapid, oxygen-dependent microbial Mn(II) oxidation kinetics at sub-micromolar oxygen concentrations in the Black Sea suboxic zone

Microbial Mn(II) oxidation kinetics in response to oxygen concentration were assessed in suboxic zone water at six sites throughout the Black Sea. Mn(II) oxidation rates increased asymptotically with increasing oxygen concentration, consistent with Michaelis-Menten enzyme kinetics. The environmental half-saturation constant, K_E, of Mn(II) removal (oxidation) varied from 0.30 to 10.5 μM dissolved oxygen while the maximal environmental rate, V_E−max, ranged from 4 to 50 nM h⁻¹. These parameters varied spatially and temporally, consistent with a diverse population of enzymes catalyzing Mn oxide production in the Black Sea. Coastally-influenced sites produced lower K_E and higher V_E−max constants relative to the Western and Eastern Gyre sites. In the Bosporus Region, the Mn(II) residence time calculated using our K_E and V_E−max values with 0.1 μM oxygen was 4 days, 25-fold less than previous estimates. Our results (i) indicate that rapid Mn(II) oxidation to solid phase Mn oxides in the Black Sea’s suboxic zone is stimulated by oxygen concentrations well below the 3-5 μM concentration reliably detected by current oceanographic methods, (ii) suggest the existence of multiple, diverse Mn(II)-oxidizing enzymes, (iii) are consistent with shorter residence times than previously calculated for Mn(II) in the suboxic zone and (iv) cast further doubt on the existence of proposed reactions coupling solid phase Mn oxide production to electron acceptors other than oxygen.     

Evaluating the potential of the red edge channel for C3 (Festuca spp.) grass discrimination using Sentinel-2 and Rapid Eye satellite image data

Integrating the Red Edge channel in satellite sensors is valuable for plant species discrimination. Sentinel-2 MSI and Rapid Eye are some of the new generation satellite sensors that are characterized by finer spatial and spectral resolution, including the red edge band. The aim of this study was to evaluate the potential of the red edge band of Sentinel-2 and Rapid Eye, for mapping festuca C3 grass using discriminant analysis and maximum likelihood classification algorithms. Spectral bands, vegetation indices and spectral bands plus vegetation indices were analysed. Results show that the integration of the red edge band improved the festuca C3 grass mapping accuracy by 5.95 and 4.76% for Sentinel-2 and Rapid Eye when the red edge bands were included and excluded in the analysis, respectively. The results demonstrate that the use of sensors with strategically positioned red edge bands, could offer information that is critical for the sustainable rangeland management.     

Effect of climate change on corrosion rates of structures in Australia

As structures built now will be expected to last well past 2064 (50 years) it is vital that the effect of climate change be considered in their design and material selection. In particular changes in the rate of corrosion of metal components must be considered. To this end this study estimates the maximum likely change in the corrosion rate for the year 2070 so it can be included in current design. Changes in corrosion are estimated for 11 coastal and inland locations in Australia. For each station the climatic data (3-hourly) in 2070 is estimated by modifying current data with probable changes based on two climate change models (CSIRO: CSIRO-Mk 3.5 and MRI: MRI-CGCM 3.2.2). The former is for high global warming rate and the later the A1FI scenario. This climatic data is then run the Corrosion “predictor” (a multi-scale process model) to predict corrosion at each location. It is found that significant changes occur with corrosion in coastal locations increasing substantially, in contrast the corrosion at inland locations will decrease moderately. The increase in coastal locations is associated with a greater build up of salt due to less frequent rain evens while the reduction in inland locations is associated with a reduction in RH and thus surface wetness.     

Tilting of active folds and drainage asymmetry on the Manawatu anticlines,New Zealand: a preliminary investigation

The apparent southward tilting of five anticlines in the Manawatu, North Island, New Zealand, is investigated using two drainage basin analysis techniques: the transverse topographic symmetry factor (T) and the asymmetry factor (AF). The techniques are used to determine whether westward‐flowing trunk streams on the gentle western limbs of five anticlines are migrating southwards across their drainage basins, concomitant with down‐tilting of the fold axes. While results show potential for the techniques to be applied in such a tectonic setting, our findings are inconclusive. This could be due to the incipient nature of the folds (c. 0·5 Ma in age), and it would seem more appropriate to apply the techniques in concert with detailed field analyses of river migration patterns. Copyright © 2008 John Wiley & Sons, Ltd.     

Asthenospheric counterflow: a kinematic model

Summary. Present-day plate motions imply that about 240 km³ of oceanic lithosphere is created by sea-floor spreading and destroyed by subduction per year. A greater volume of asthenosphere will be dragged along by plate motions. Given the fluxes generated at plate boundaries, the horizontal direction and net rate of counterflow required to maintain mass balance is determined globally by a simple analytical model. Time-dependent calculations indicate that the motions are approximately valid in the hotspot reference frame over the past 5 Myr. Under most plates, the model return flow is opposite to the lithospheric motion in the hotspot frame. The counterflow dominates the resisting stresses to plate motion, so driving force models based on plate drag alone are not valid where the directions of plate motion and counterflow differ. The most marked departure of the two directions is under the North American plate. The model counterflow directions indicate that the sources of mantle hotspots are not located within the asthenosphere. Model flux balances demonstrate exchange of material between asthenospheric reservoirs located beneath different plates. Suggestions of southward asthenospheric motion under the North Atlantic, based on physical features around Iceland and strontium isotope geochemistry, are consistent with the direction of flow predicted by the model.