Sedimentation and continental slope processes in the vicinity of an ocean waste‐disposal site,southeastern Tasmania

Digital echo sounding, SeaBeam swath bathymetry data and sediment cores were collected on the continental slope (1500–3700 m water depth) off southeastern Tasmania in order to study sedimentary processes in the vicinity of an ocean disposal site. The new bathymetry data show that the shallower limits of the disposal site are positioned on the seaward edge of a gently dipping (3°) mid‐slope shoulder, between 1200 and 2100 m water depth. The slope below the disposal site is relatively steep (6.5°) and is cut by submarine canyons which lead into the adjacent East Tasman Saddle. The SeaBeam bathymetry data show a small submarine canyon traversing the slope in 2400 m water depth directly downslope from the disposal site, with local slopes of up to 22°. The canyon feeds into a perched basin at 2450 m, which could be acting as a local sediment trap. Short (<90 cm) gravity cores indicate that indurated erosional surfaces characterise the slope environment. The cores contain Upper Cretaceous (upper Campanian) sandstones and siltstones, which in places crop out on the sea floor where they are locally draped by a thin (0–30 cm), modern layer of hemipelagic calcareous ooze. Five cores collected from the vicinity of the disposal site had lead and zinc concentrations in the surface 1 cm of 10.3 ± 5.0 and 39.5 ± 19.6 mg/kg, respectively, significantly greater than the background values (2.9 ± 1.4 for lead and 21.2 ± 5.4 for zinc) which characterise the underlying unit that is composed of the same hemipelagic calcareous ooze. Lead and zinc are constituents of the dumped material, jarosite, which, after mixing with slope sediments, can be used as sediment tracers. One core contains a fining‐upwards bed which is also elevated in lead and zinc. This is interpreted as evidence for dispersal of the jarosite from the disposal site downslope to depths >3000 m via turbidity flows sometime during the past 24 years. Current meter data collected from 30 m above the sea floor over one year at the disposal site show that bottom currents attain speeds of up to 0.46 m/s. The current events are attributed to eddies shed by the East Australia Current. The measured bottom currents are capable of transporting fine‐grained hemipelagic muds and could provide a trigger mechanism for turbidity flows.     

Seismic site characterization with shear wave (SH) reflection and refraction methods

Journal of Seismology - Reflection and critically refracted seismic methods use traveltime measurements of body waves propagating between a source and a series of receivers on the ground surface to...     

The formation of peridotitic suite inclusions in diamonds

Olivine, orthopyroxene and garnet grains belonging to the peridotitic suite of mineral inclusions in natural diamonds typically show compositions poorer in Ca and Al and richer in Mg and Cr than the same minerals in peridotite nodules in kimberlite. Other features suggest the crystallisation of diamonds from magmas of kimberlitic affinities, and it is suggested that the genesis of peridotitic suite diamonds is linked with that of a CO₂-bearing magma. It is shown that the generation of kimberlitic magma from common garnet-peridotite (with 5 wt.% clinopyroxene) in the presence of CO₂ may rapidly remove by melting all Ca-rich solid phases (clinopyroxene and/or carbonate). Further melting may form liquids in equilibrium with olivine, orthopyroxene, and garnet with the distinctive compositions of the diamond inclusions. The amount of melting and CO₂ necessary for the loss of clinopyroxene (and/or carbonate) are estimated at approximately 5.0 wt.% and 0.5 wt.% respectively.     

The drying up of Britain? A national estimate of changes in seasonal river flows from 11 Regional Climate Model simulations

As climate change may modify the hydrological cycle significantly, understanding the impact on river flow is important because it affects long‐term water resources planning. Here, we describe a high‐resolution British assessment of changes in river flows in the 2050s under 11 different realisations of HadRM3. In winter, river flows may either increase or decrease, with a wide range of possible decreases in summer flow. These results should encourage adaptation that copes with a broad range of future hydrological conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

From SARS to pandemic influenza: the framing of high-risk populations

Natural Hazards - The 2003 global outbreak of severe acute respiratory syndrome (SARS) was a wake-up call for health systems in Canada, with realization of occupational health risks faced by health...     

Hydraulic and sedimentary processes causing anastomosing morphology of the upper Columbia River, British Columbia, Canada

The upper Columbia River, British Columbia, Canada, shows typical anastomosing morphology — multiple interconnected channels that enclose floodbasins — and lateral channel stability. We analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper Columbia River is caused by sediment (bedload) transport inefficiency, in combination with very limited potential for lateral bank erosion because of very low specific stream power (≤ 2.3 W/m²) and cohesive silty banks. In a diagram of channel type in relation to flow energy and median grain size of the bed material, data points for the straight upper Columbia River channels cluster separately from the data points for braided and meandering channels. Measurements and calculations indicate that bedload transport in the anastomosing reach of the upper Columbia River decreases downstream. Because of lateral channel stability no lateral storage capacity for bedload is created. Therefore, the surplus of bedload leads to channel bed aggradation, which outpaces levee accretion and causes avulsions because of loss of channel flow capacity. This avulsion mechanism applies only to the main channel of the system, which transports 87% of the water and > 90% of the sediment in the cross-valley transect studied. Because of very low sediment transport capacity, the morphological evolution of most secondary channels is slow. Measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper Columbia River than in the relatively gentle lower anastomosing reach. With anastomosing morphology and related processes (e.g., crevassing) being best developed in the upper reach, this confirms the notion of upstream rather than downstream control of upper Columbia River anastomosis.     

Perceptions and costs of seal impacts on Atlantic salmon fisheries in the Moray Firth,Scotland: Implications for the adaptive co-management of seal-fishery conflict

The Moray Firth Seal Management Plan (MFSMP) was introduced in Scotland in 2005 as a pilot for resolving conflict between Atlantic salmon fisheries and conservation imperatives for protected harbour and grey seals. This adaptive co-management model is now being applied nationally through the Marine (Scotland) Act (2010). However, no information exists on salmon fishery stakeholders’ perceptions of seal predation impacts and related costs, which could influence the success of the MFSMP and other similar initiatives. In 2006 a questionnaire survey of the 95 salmon rod fisheries in seven major Moray Firth rivers was undertaken, and all 20 active salmon netting stations in the Firth. Forty-five fishery owners, 39 ghillies, 120 anglers and 11 netsmen (representing 17 netting stations) responded. The majority (81%) believed that seals had a significant or moderate impact on stocks and catches, 77% believed that all seals were responsible and 47% supported seal culling. Seals were sighted by 38% of rod fisheries, and 18% lost angler days from seal interference. Overall, 0.2% of total reported angler days were lost annually. The estimated direct cost of seal interference for responding rod fisheries was £14,960 annum⁻¹, and losses of catches and damage to nets was £16,500 annum⁻¹ for responding netsmen. Stakeholders’ perceptions were largely inconsistent with their low direct costs and the aims of the MFSMP. Possible reasons for this are discussed, and implications for the governance of future adaptive co-management initiatives for seal-fishery conflict.     

Ripple cross-laminated sediments on the East Antarctic Shelf: evidence for episodic bottom water production during the Holocene?

Biosiliceous sediments sampled from a submarine valley system on the continental shelf of East Antarctica contain intervals of ripple cross-lamination interspersed with massively bedded units. Based on radiocarbon dates from one core collected on the Mac.Robertson Shelf, the most intensely cross-laminated sediments were deposited between 6 and 3.5 kyr BP, with isolated cross-laminae deposited at other times in the Holocene. The cross-laminated sediments are interpreted here as a signal of episodic density currents flowing across the outer shelf, which result from the formation of high salinity shelf water (HSSW). This HSSW is formed in winter by brine rejection during sea ice formation and by the exchange and cooling of upwelled saline slope water, and it contributes to the bottom water produced along the continental margin of Antarctica. If this interpretation of the cross-laminae is correct, then bottom water formation and export from the East Antarctic shelf has exhibited temporal, and probably also spatial, variability throughout the Holocene. Such variability would have implications for oceanographers attempting to quantify Antarctic bottom water production rates based only on present day observations.