Further assessment of flood‐ and drought‐dominated regimes in south‐eastern Australia

Kirkup et al. (1998) [Australian Geographer 29, pp. 241–55] criticise our theory of alternating flood regimes and question its application to river management. A brief but critical appraisal of their work shows many errors and misrepresentations. When these are corrected, their challenge is found deficient.     

Carbon isotopic fractionation between CO2 vapour,silicate and carbonate melts: an experimental study to 30 kbar

The carbon isotopic fractionation between CO₂ vapour and sodamelilite (NaCaAlSi₂O₇) melt over a range of pressures and temperatures has been investigated using solid-media piston-cylinder high pressure apparatus. Ag₂C₂O₄ was the source of CO₂ and experimental oxygen fugacity was buffered at hematite-magnetite by the double capsule technique. The abundance and isotopic composition of carbon dissolved in sodamelilite (SM) glass were determined by stepped heating and the ¹³C of coexisting vapour was determined directly by capsule piercing. CO₂ solubility in SM displays a complex behavior with temperature. At pressures up to 10 kbars CO₂ dissolves in SM to form carbonate ion complexes and the solubility data suggest slight negative temperature dependence. Above 20 kbars CO₂ reacts with SM to form immiscible Na-rich silicate and Ca-rich carbonate melts and CO₂ solubility in Na-enriched silicate melt rises with increasing temperature above the liquidus. Measured values for carbon isotopic fractionation between CO₂ vapour and carbonate ions dissoived in sodamelilite melt at 1200°–1400° C and 5–30 kbars average 2.4±0.2, favouring¹³C enrichment in CO₂ vapour. The results are maxima and are independent of pressure and temperature. Similar values of 2 are obtained for the carbon isotopic fractionation between CO₂ vapour and carbonate melts at 1300°–1400° C and 20–30 kbars.     

Age and structure of the southern Rockall Trough new evidence

The Rockall Trough separates the Rockall Plateau microcontinent from the shelf and slope west of the British Isles. The structure and age of the trough has been the source of considerable discussion. Although widely considered to be of oceanic origin, postulated ages for the spreading range from Permian to Cretaceous. New seismic profiles linked to the IPOD sites in the Bay of Biscay and to oceanic anomalies of known age are used to present a new assessment of the age and structure of the southern Rockall Trough. It is concluded that about 120 km of ocean crust is present in the trough and that spreading took place in the Albian-Maastrichtian interval.     

Permian volcanism in the Central Western Carpathians (Slovakia): Basin-and-Range type rifting in the southern Laurussian margin

The 1,500- to 2,000-m-thick Permian volcano-sedimentary Malu?iná Formation of the uppermost nappe of the Central Western Carpathians (a segment of the Alpine-Carpathian orogenic belt) occurs in several fault blocks distributed across Slovakia. This unit is a part of a post-Variscan overstep suite that followed accretion of the Gothic terranes to Laurussia. It consists of three upward-fining megacycles of semi-arid/arid, fluvial-lacustrine clastic redbeds and local dolomites and evaporites. Abundant intercalated volcanic rocks are predominantly mafic lava flows; volcaniclastic rocks and dykes are subordinate. Felsic rocks are represented by rare volcaniclastics and dykes. Compositionally, the mafic rocks are rift-related continental tholeiites with enriched light REE patterns having (La/Yb)_n ratios between 2 and 5.5 and with mantle-normalized patterns characterized by negative Nb-Ta anomalies. The rocks were derived from subcontinental lithospheric mantle and were affected by crustal contamination. It is inferred that the volcanism of the Malu?iná Formation formed in a Basin and Range tectonic setting in which rifting followed collision of the Palaeo-Tethys ridge with the trench bordering southern Laurussia. This model can be applied to other Permian volcanic suites of rift basins in the Eastern Alps and Carpathians over a strike-length of about 1,000 km, which indicates the width of the slab window.     

Application of the Genetic Algorithm to the Problem of Reconstruction of Missing Data

We study the problem of reconstruction (interpolation and extrapolation) of the vertical profiles of hydrochemical and hydrobiological elements according to incomplete sets of data with simultaneous filtration of short-period components based on expansions in empirical orthogonal functions. The genetic algorithm is used to compute the coefficients of expansion of profiles with missing data. We present the results of processing the data arrays on oxygen, chlorophyll A, and biogenic elements collected in the Black Sea in 1982–1993. The mean error of reconstruction of the profiles enables us to conclude that the proposed method has considerable advantages over the conventional approaches.     

Hamilton Harbour, Ontario: 8300 years of limnological and environmental change inferred from microfossil and isotopic analyses

Limnological changes in Hamilton Harbour, Lake Ontario, over the Holocene were investigated by using proxy evidence from diatoms and other siliceous microfossils in a radiometrically dated sediment core (HH26comp), together with environmental data derived from sediment pollen and oxygen and carbon isotope analyses. The evidence demonstrates that the site of Hamilton Harbour has changed over the past 8300 y from a shallow, separate waterbody, to a deep embayment of Lake Ontario. The earliest evidence, from 8300 BP to 7000 BP, is of a mesotrophic pond of moderate alkalinity, warmer than present, and probably with an extensive marginal wetland. An initial transitory connection with the rising water level of Lake Ontario was established at c. 7000 BP, possibly via a deep outlet channel. This connection is 2000 y earlier then previously estimated. Permanent confluence with Lake Ontario was established at c. 6200 BP, causing a decline in inferred trophic level and water temperatures. Microfossils reach a minimum at 4400 BP coincident with the Nipissing Flood. Decreased mixing of Lake Ontario water from about 4000 BP following the Nipissing Flood highstand is evidenced in isotopic and diatom data. Three isolated shifts in the diatom spectrum at c. 4900 BP, 4500 BP, and 3500 BP may be associated with extreme turbidity or storm deposit events. Between 3200 BP and 280 BP, Hamilton Harbour was evidently a moderately alkaline embayment of Lake Ontario, oligotrophic to mesotrophic, and relatively cooler than present. The final 280 y sedimentary record reveals the magnitude of anthropogenically induced changes to the harbour, including eutrophication and organic pollution.     

Using a Thermal Proxy to Examine Sediment–Water Exchange in Mid-Continental Shelf Sandy Sediments

Fluid exchange across the sediment–water interface in a sandy open continental shelf setting was studied using heat as a tracer. Summertime tidal oscillation of cross-shelf thermal fronts on the South Atlantic Bight provided a sufficient signal at the sediment–water interface to trace the advective and conductive transport of heat into and out of the seabed, indicating rapid flushing of ocean water through the upper 10–40 cm of the sandy seafloor. A newly developed transport model was applied to the in situ temperature data set to estimate the extent to which heat was transported by advection rather than conduction. Heat transported by shallow 3-D porewater flow processes was accounted for in the model by using a dispersion term, the depth and intensity of which reflected the depth and intensity of shallow flushing. Similar to the results of past studies in shallower and more energetic nearshore settings, transport of heat was greater when higher near-bed velocities and shear stresses occurred over a rippled bed. However, boundary layer processes by themselves were insufficient to promote non-conductive heat transport. Advective heat transport only occurred when both larger boundary layer stresses and thermal instabilities within the porespace were present. The latter process is dependent on shelf-scale heating and cooling of bottom water associated with upwelling events that are not coupled to local-scale boundary layer processes.     

Zero-offset P–S energy in horizontally layered media

The existence of non‐zero reflectivity for zero‐offset PS waves in horizontally layered media is discussed. Field measurements have suggested the occurrence of this phenomenon. We show that, in some cases, if anisotropy is considered in the problem, this reflectivity can be predicted. By using an approximated formulation to determine the coefficient of reflection in arbitrarily anisotropic media, it is clear that, for some elastic arrangements of the subsurface, reflected energy is associated with the converted wave resulting from normal P‐wave incidence.     

Cross inoculation studies: Response of Vigna mungo to inoculation with rhizobia from tree legumes growing under arid Environment

Cross-inoculation experiments were conducted in the greenhouse to test the rhizobia isolated from nodules of seven tree legumes for their effectiveness in Vigna mungo plants. The tree legumes included Albizia lebbeck, Dalbergia sissoo, Leucaena leucocephala, Pithecellobium dulce, Prosopis cineraria, Prosopis glandulosa and Prosopis juliflora, all growing under arid environment. Rhizobia from these legumes formed nodules on the roots of Vigna mungo except isolates from Albizia lebbeck. Dry weight and nitrogen contents of Vigna mungo plants increased significantly (P<0.05) in response to cross inoculation as compared to uninoculated control. Rhizobia from Leucaena leucocephala and Prosopis glandulosa showed significant increase in dry weight (P<0.05) and nitrogen contents (P<0.05) than other inoculated treatments. The natural rhizobia of wild tree legumes growing under arid environment show higher tolerance to prevailing adverse conditions like salt stress, elevated temperatures and drought. These rhizobia may be used to inoculate wild as well as crop legumes cultivated in reclaimed desert lands. These rhizobia may have specific traits that can be transferred to other rhizobia through genetic engineering tools. The cross infection of agriculturally important legumes with isolates from wild legumes may prove a useful means of increasing nitrogen contents within these plants.