Comparison of results from several AOGCMs for global and regional sea-level change 1900–2100

 Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need for detailed analysis and intercomparison in order to understand and reduce the disagreements. Received: 1 September 2000 / Accepted: 20 April 2001     

Chemical denudation rates in Kärkevagge, Swedish Lapland

This study examines the spatial and temporal variability of chemical denudation rates in Kärkevagge, northern Sweden. The chemical flux rates within the valley are strongly influenced by the local geology. Chemical denudation rates determined for the study period are more than double those previously reported in the literature for this valley. Rates of greater than 46t km⁻² a⁻¹ were measured at the valley mouth over the course of the melt season. This difference is likely due to differences in measurement technique compared to that used by past researchers. This rate is also much higher than for other arctic and alpine watersheds. Chemical denudation in Kärkevagge is comparable to larger temperate rivers. The rapid chemical denudation in Kärkevagge is likely due to sulfide weathering creating acid solutions.     

Enigmatic Efflorescence in Kärkevagge, Swedish Lapland: The Key to Chemical Weathering?

The second marvel to catch the eye of the visitor to Kärkevagge, after the impressive boulder deposit on the floor of the valley, is the series of prominent white stripes running down the valley's dark cliffs. Streams and springs descending the eastern flank of Kärkevagge are marked by the presence of whitish coatings on the black rock surfaces and on cobbles lining ephemeral waterways. These were referred to as 'lime crusts' by early investigators, but they are not reactive to HCl. We believe that they are a precipitate resulting from acid attack on the local rocks. Pyrite is common in many of the rocks in the valley and its oxidation produces sulfuric acid. As the dissolved mineral elements are carried in the drainage water, efflorescence forms on the surfaces where the water flows due to evaporation or to changes in temperature. The exact mineralogy of the white crusts is unknown, but the crusts are dominated by Al, S, and O, and in some cases by Ca, depending on the substrate and local conditions. Gypsum, illite, and chlorite have been identified by X–ray diffraction of some scrapings of white–coated rocks. However, we believe that some unidentified oxy–hydroxy aluminum sulfates make up the bulk of the precipitates.     

Groundwater vulnerability mapping: A GIS and fuzzy rule based integrated tool

Contamination of groundwater has become a major concern in recent years. Since testing of water quality of all domestic and irrigation wells within large watersheds is not economically feasible, one frequently used monitoring strategy is to develop contamination potential maps of groundwater, and then prioritize those wells located in the potentially highly contaminated areas for testing of contaminants. However, generation of contamination potential maps based on groundwater sensitivity and vulnerability is not an easy task due inherent uncertainty. Therefore, the overall goal of this research is to improve the methodology for the generation of contamination potential maps by using detailed landuse/pesticide and soil structure information in conjunction with selected parameters from the DRASTIC model. The specific objectives of this study are (i) to incorporate GIS, GPS, remote sensing and the fuzzy rule-based model to generate groundwater sensitivity maps, and (ii) compare the results of our new methodologies with the modified DRASTIC Index (DI) and field water quality data. In this study, three different models were developed (viz. DI_fuzz, VI_fuzz and VI_{fuzz_ped}) and were compared to the DI. Once the preliminary fuzzy logic-based (DI_fuzz) was generated using selected parameters from DI, the methodology was further refined through VI_fuzz and VI_{fuzz_ped} models that incorporated landuse/pesticide application and soil structure information, respectively. This study was conducted in Woodruff County of the Mississippi Delta region of Arkansas. Water quality data for 55 wells were used to evaluate the contamination potential maps. The sensitivity map generated by VI_{fuzz_ped} with soil structure showed significantly better coincidence results when compared with the field data.     

Potential Salinity and Temperature Futures for the Chesapeake Bay Using a Statistical Downscaling Spatial Disaggregation Framework

Estuaries are productive and ecologically important ecosystems, incorporating environmental drivers from watersheds, rivers, and the coastal ocean. Climate change has potential to modify the physical properties of estuaries, with impacts on resident organisms. However, projections from general circulation models (GCMs) are generally too coarse to resolve important estuarine processes. Here, we statistically downscaled near-surface air temperature and precipitation projections to the scale of the Chesapeake Bay watershed and estuary. These variables were linked to Susquehanna River streamflow using a water balance model and finally to spatially resolved Chesapeake Bay surface temperature and salinity using statistical model trees. The low computational cost of this approach allowed rapid assessment of projected changes from four GCMs spanning a range of potential futures under a high CO₂ emission scenario, for four different downscaling methods. Choice of GCM contributed strongly to the spread in projections, but choice of downscaling method was also influential in the warmest models. Models projected a ~2–5.5 °C increase in surface water temperatures in the Chesapeake Bay by the end of the century. Projections of salinity were more uncertain and spatially complex. Models showing increases in winter-spring streamflow generated freshening in the Upper Bay and tributaries, while models with decreased streamflow produced salinity increases. Changes to the Chesapeake Bay environment have implications for fish and invertebrate habitats, as well as migration, spawning phenology, recruitment, and occurrence of pathogens. Our results underline a potentially expanded role of statistical downscaling to complement dynamical approaches in assessing climate change impacts in dynamically challenging estuaries.     

Swelling capacity and permeability of an unprocessed and a processed bentonitic clay

Research on the longevity of potential bentonite-based barrier materials is an important part of the Canadian Nuclear Fuel Waste Management Program. Valuable information on the longterm effectiveness of bentonitic barriers can be obtained by examining the properties of unprocessed bentonites from natural deposits. This study compares the swelling capacity (P_s) and hydraulic conductivity (K) of an unprocessed (clay that has not been ground and dried by the supplier) and a processed bentonite from south-central Saskatchewan, Canada. The clay deposit is 75 to 85 Ma old. At a given clay density, the processed bentonite exhibits a greater P₃ and a lower K than the unprocessed clay. This can be at least partially attributed to the partial cementation of the unprocessed bentonite particles; this cementation is likely ruptured when the clay is ground during processing. Even though K for the unprocessed clay is higher than that of the processed clay, it is still low enough (< 10¹¹m/s) to meet the permeability requirements of a barrier material in a nuclear fuel waste disposal vault. The unprocessed clay also has the has the ability to self seal: exposure to water, the normalized flow rate of water through some samples was as high as 10^-5 m³/s, but the rate rapidly decreased to < 10^-10m³/s the clay absorbed water and swelled. The data indicate that the unprocessed bentonite clay maintains anacceptably high swelling capacity and low permeability millions of years after deposition.     

Yucatan after the wind: Human and environmental impact of hurricane Gilbert in the central and Eastern Yucatan Peninsula

Hurricane Gilbert made its landfall on the Yucatan peninsula on September 14, 1988, destroying valuable resort property in Cancun, Isla Mujeres, and Cozumel. Salt flats (salinas) in northern Quintana Roo and Yucatan were flooded by the storm surge and coastal marine ecosystem were devastated. Inland, the hurricane caused damages to houses, power lines, and farming land, but increased opportunities for garden hunting on destroyed fields. Twenty percent of tropical rain forest suffered losses of canopy and in the deciduous forests of north-central Yucatan noxiuous insects populations increased. Although damaging in its ultimate effects, hurricane Gilbert tested the resilience of Maya Indians and their readiness for post-disaster accommodation.     

Context and environment in taphonomic analysis: Examples from Alaska's Porcupine River Caves

Field investigations of caves along Alaska's Porcupine River document three major mechanisms which modify bone in patterns similar to alterations produced by man: (1) carnivore fracture; (2) rodent gnawing; and (3) rock fall and rubble scarring. A late Wisconsin faunal assemblage composed of Equus sp., Rangifer tarandus, Ovis dalli, Bison sp., proboscidean, numerous small mammal species, birds, and fish is well documented. This faunal assemblage suggests a mosaic environment of grassland-tundra-forest in the immediate vicinity of these caves and implies that the late Wisconsin environment in north-central Alaska may have been characterized by a number of microenvironments and colder, dryer, steppe conditions. Taphonomic data which have historically been interpreted to support human occupation of eastern Beringia during the Pleistocene are critically examined and the context of these discoveries (not the specimens themselves) provides the test essential to document the antiquity of man in North America prior to 12,000 yr ago.