Arctic versus temperate comparison of risk assessment metrics for 2-methyl-naphthalene

Reliable risk assessment approaches for Arctic environments are requested to manage potential impacts associated with increased activities in Arctic regions. We performed toxicity tests on Arctic and temperate species exposed to the narcotic acting oil component, 2-methyl naphthalene. The experimental results were used to quantify concentration causing lethality to 50% of exposed individuals and no-effect concentration (individual level). For estimates at community level, the hazardous concentrations affecting 5% and 50% of the species were calculated from sensitivity distribution curves. These survival metrics were then used to elucidate whether temperate toxicity data used in risk assessment are sufficiently representative for the Arctic. Taking data uncertainty into consideration, we found no regional difference in tolerances to 2-methyl naphthalene either at the species level or at the community level. Hence these data support a conclusion that values of survival metrics for temperate regions are transferrable to the Arctic for the chemical 2-methyl naphthalene, as long as extrapolation techniques are properly applied and uncertainties are taken into consideration.     

Vertical concentration gradients of heavy metals in cultured mussels

Cultured mussels, Perna canaliculus (Gmelin), from two widely separated locations in New Zealand have been analysed for variation in heavy metal content with depth. The mussels, which are grown on vertically suspended ropes to a depth of 9 m, have been analysed for cadmium, lead, iron, and zinc at 1‐m intervals. At the first location (Kenepuru Sound), cadmium, lead, and iron increased with depth, while zinc decreased with depth. At the second location (Waiheke Island), concentrations of the four metals all remained essentially constant with depth. The differences in vertical concentration gradients between these two locations must result from differences in mixing of the water column. The differences in mixing may cause variations in the type of food organisms with depth, or variations in the ratio of particulate v. dissolved metal levels with depth. Either or both of these conditions could result in differences in the bioavailability of these metals with depth.     

Response of Coastal Groundwater Table to Offshore Storms

Large groundwater table fluctuations were observed in a coastal aquifer during an offshore storm. The storm induced significant changes of the mean shoreline elevation, characterized by a pulse-like oscillation. This pulse propagated in the aquifer, resulting in the water table fluctuations. A general analytical solution is derived to quantify this new mechanism of water table fluctuation. The solution is applied to field observations and is found to be able to predict reasonably well the observed storm-induced water table fluctuations. Based on the analytical solution, the damping characteristics and phase shift of the oscillation as it propagates inland are examined.     

Downward transfer of momentum by wind-driven waves

A model for the downward transfer of wind momentum is derived for growing waves. It is shown that waves, which grow due to an uneven pressure distribution on the water surface or a wave-coherent surface shear stress have horizontal velocities out of phase with the surface elevation. Further, if the waves grow in the x-direction, while the motion is perhaps time-periodic at any fixed point, the Reynolds stresses associated with the organized motion are positive. This is in agreement with several field and laboratory measurements which were previously unexplained, and the new theory successfully links measured wave growth rates and measured sub-surface Reynolds stresses. Wave coherent air pressure (and/or surface shear stress) is shown to change the speed of wave propagation as well as inducing growth or decay. From air pressure variations that are in phase with the surface elevation, the influence on the waves is simply a phase speed increase. For pressure variations out of phase with surface elevation, both growth (or decay) and phase speed changes occur. The theory is initially developed for long waves, after which the velocity potential and dispersion relation for linear waves in arbitrary depth are given. The model enables a sounder model for the transfer to storm surges or currents of momentum from breaking waves in that it does not rely entirely on ad-hoc turbulent diffusion. Future models of atmosphere-ocean exchanges should also acknowledge that momentum is transferred partly by the organized wave motion, while other species, like heat and gasses, may rely totally on turbulent diffusion. The fact that growing wind waves do in fact not generally obey the dispersion relation for free waves may need to be considered in future wind wave development models.     

Transformation of South African industrial fisheries

South African industrial fisheries have been dominated by a few large companies. The Marine Living Resources Act (MLRA) of 1998 emphasised that equity was to be achieved by redistribution through co-operative strategies among stakeholders. Instead, the reallocation of fishing rights has been treated as a resource management issue rather than a socio-economic challenge. Further, the institutional structures for transformation have been inappropriate. This paper investigates the institutional dynamics and discrepancies associated with transformation and concludes that the process became locked in a path dependency, which will eventually undermine the intentions of transformation.     

A comparison of the NW European glaciated margin with other glaciated margins

The present paper provides an overview of glacial related seabed features and sedimentary sequences found along the formerly glaciated NW European margin and compare it with those found on contemporary glaciated margins from both the Southern and Northern Hemispheres. A brief review of the seabed physiography and strata architecture of the margins under consideration is followed by comparison of the most relevant similarities and differences. Comparison of the present-day bathymetric setting of both former and contemporary glaciated margins reveals no clear link to the effect of neither ice sheet or sediment load. Three different types of glacially eroded shelf transverse troughs have been identified, while marginal troughs seem connected to similar geological settings everywhere. Beyond the shelf edge interaction between downslope and alongslope processes has occurred resulting, amongst others, in the formation of large sedimentary mounds on the rise. More frequent large-scale mass wasting occurs on the former glaciated NW European margin than the Greenland and Antarctic margins in the latest Neogene to recent times. A two-stage evolution of the shelf prograding wedges is observed on all margins under consideration, which may reflect a general development of an ice cover from an initial phase of non- to restricted glaciation, evolving to a mature stage of expansive glaciation.     

Compound response of marine and terrestrial ecosystems to varying climate: pre-anthropogenic perspective from bivalve shell growth increments and tree-rings

Annual growth increments were examined from shells of the ocean quahog (Arctica islandica L.) from northwest Norway and from tree-ring samples of the Scots pine (Pinus sylvestris L.) from nearby coastal areas. The reconstructed annual growth increments were used to compare growth variability in marine and terrestrial ecosystems. Spatiotemporal comparison of the growth records showed statistically significant correlation during the 19th century A.D., indicative of ecosystem-independent response to pre-anthropogenic climate variations. Geographical correlation between marine and terrestrial records was only observed at the local scale. Years with particularly low winter or high summer North Atlantic Oscillation (NAO) indices showed the best synchronization of marine and terrestrial growth. Despite strong correlation during historical time, our palaeoecological evidence suggests that marine and terrestrial ecosystems may show dissimilar growth reaction to recently observed positive winter-NAO phases.     

Numerical prediction of green water incidents

Green water loads on moored or sailing ships occur when an incoming wave significantly exceeds the freeboard and water runs onto the deck. In this paper, a Navier–Stokes solver with a free surface capturing scheme (i.e. the VOF model; [Hirt and Nichols, 1981]) is used to numerically model green water loads on a moored FPSO exposed to head sea waves. Two cases are investigated: first, green water on a fixed vessel has been analysed, where resulting waterheight on deck, and impact pressure on a deck mounted structure have been computed. These results have been compared to experimental data obtained by [Greco, 2001] and show very favourable agreement. Second, a full green water incident, including vessel motions has been modelled. In these computations, the vertical motion has been modelled by the use of transfer functions for heave and pitch, but the rotational contribution from the pitch motion has been neglected. The computed water height on deck has been compared to the experimental data obtained by [Buchner, 1995a] and it also shows very good agreement. The modelling in the second case was performed in both 2-D and 3-D with very similar results, which indicates that 3-D effects are not dominant.     

Advances in monitoring vegetation and land use dynamics in the Sahel

Vegetation dynamics of the West African Sahel has attracted great scientific interest over the last 40?years because of the dramatic inter-decadal variability observed in the resource base of the region directly impacting on the livelihoods of the West African population. From farmers to pastoralists, agro-pastoralists and forest-users, all depend on the availability of vegetation resources and are affected by fluctuations in the available vegetation resource. Vegetation dynamics are controlled by both natural and human factors, including climate change and variability, increased concentration of CO₂ in the atmosphere, grazing pressure, bush fires and agricultural expansion or contraction. The use of satellite data in combination with field data played a major role in the monitoring of vegetation dynamics and land use in the Sahel, since the mega drought of the 1970s and the 1980s. This paper briefly reviews the advance of satellite-based monitoring of vegetation dynamics over these 40?years. We discuss the promises of current and likely future data sources and analysis tools, as well as the need to strengthen in situ data collection to support and validate satellite-based vegetation and land use monitoring and modelling.