On predicting the response of forests in eastern North America to future climatic change

Our ability to accurately predict the response of forests in eastern North America to future climatic change is limited by our knowledge of how different tree species respond to climate. When the climatic response of eastern hemlock is modeled across its range, we find that the assumed climatic response used in simulation models is not sufficient to explain how this species is presently responding to climate. This is also the case for red spruce growing in the northern Appalachian Mountains. Consequently, simulations of future change to forests that include eastern hemlock and red spruce may need to be improved. We suspect that similar findings will be made when other tree species are studied in detail using tree-ring analysis. If so, our present understanding of how individual tree species respond to climate may not be adequate for accurately predicting future changes to these forests. Tree-ring analysis can increase our understanding of how climate affects tree growth in eastern North America and, hence, provide the knowledge necessary to produce more accurate predictions.     

A unified earthquake-resistant design method for steel frames using arma models

The objective of this paper is to develop a unified earthquake-resistant design method for moment-resisting steel frames, including the design earthquake via a dynamic ARMA model. Important features of this design method are: (i) to make it possible to incorporate inherent uncertain features of design earthquakes into the design process itself through the dynamic ARMA model, (ii) to provide a simplified design formula for a preliminary design of moment-resisting steel frames based upon the concept of stiffness-oriented design and (iii) to facilitate the formulation of a new probabilistic multi-objective optimal design problem aimed at finding the design with the minimum level of designer's dissatisfaction. In this optimal design problem, constraints and objectives are handled in a unified manner after a feasible design is obtained. A design example is presented to demonstrate the validity of this unified design method and to examine the convergence of response statistics. Finally, the generality and practicality of this design method are assessed.     

Hydrocarbon contamination on the Antarctic peninsula: III. The Bahia Paraiso—Two years after the spill

Two years after the release of 600 000 l of diesel fuel arctic into Arthur Harbor, little spill-related contamination can be detected in intertidal limpets (Nacella concinna) and subtidal sediments. Periodic releases of small amounts of material from the ship oil nearby islands, in particular the intertidal areas of Christine, Limitrophe and Humble Islands. Subtidal sediment contamination is primarily due to other local inputs such as ship, boating and station activities. Beaches were unusually contaminated after 2 yr, but quiescent weather conditions, occasional releases from the wreck, and prevailing currents may concentrate hydrocarbon contamination in relatively low energy areas. Intertidal limpets (N. concinna) collected along these beaches were also contaminated. The volatility of the fluid, the amount spilled, and the dynamic weather and current conditions in Arthur Harbor tended to minimize long-term contamination of the area.     

Bulk sampling of coarse clastic sediments for particle-size analysis

A guide is provided to the minimum sample masses required to obtain reproducible measures of the particle-size distributions of coarse sediments. This is based on studies of the actual particle-size distributions of a range of clastic deposits. Procedures are given to enable representative bulk samples of tills, fluvial gravels and beach gravels to be taken.     

Long-term landscape evolution in Australia

The main features of the Australian physical landscape are of the order of 10⁷-10⁸ years old. This contradicts the widely held view that little of the Earth's topography predates the Quaternary and that erosion cycles are carried to planation within tens of millions of years. Much of the Australian landscape must have developed over similar timescales to that of the tectonic evolution of the continent itself. The study of the geomorphology of such ancient terrains may therefore be seriously deficient unless it is considered within the context of continental-scale tectonic development. Application of this approach shows that there are strong links between the geomorphology of Australia and plate movements, ocean spreading, plate convergence, tectonostratigraphic terranes, orogenesis and epeirogenesis. The most important factor contributing to the survival of ancient landscapes in Australia is the low rate of denudation which the continent has experienced during the Mesozoic and Cenozoic. This is largely a consequence of orogenic stability, although the absence of significant Quaternary glaciation may also be of importance. However, in order for landforms to have survived over such timespans, denudation must not only have been low, but must also have been highly localized over space and time. This has been the case both on a regional scale, with long-term denudation rates of 0-2 m Ma^?1 in central Australia contrasting with higher rates along the continental margins, and on a local scale, with denudation confined to valleys, leaving divides and interfluves almost unscathed.     

Volcán Las Navajas,a Pliocene-Pleistocene trachyte/peralkaline rhyolite volcano in the northwestern Mexican volcanic belt

Volcán Las Navajas, a Pliocene-Pleistocene volcano located in the northwestern portion of the Mexican volcanic belt, erupted lavas ranging in composition from alkali basalt through peralkaline rhyolite, and is the only volcano in mainland Mexico known to have erupted pantellerites. Las Navajas is located near the northwestern end of the Tepic-Zacoalco rift and covers a 200-m-thick pile of alkaline basaltic lavas, one of which has been dated at 4.3 Ma. The eruptive history of the volcano can be divided into three stages separated by episodes of caldera formation. During the first stage a broad shield volcano made up of alkali basalts, mugearites, benmoreites, trachytes, and peralkaline rhyolites was constructed. Eruption of a chemically zoned ash flow then caused collapse of the structure to form the first caldera. The second stage consisted of eruptions of glassy pantellerite lavas that partially filled the caldera and overflowed its walls. This stage ended about 200 000 years ago with the eruption of pumice falls and ash flows, which led to the collapse of the southern portion of the volcano to form the second caldera. During the third stage, two benmoreite cinder cones and a benmoreite lava flow were emplaced on the northwestern flank of the volcano. Finally, the calc-alkaline volcano Sanganguey was built on the southern flank of Las Lavajas. Alkaline volcanism continued in the area with eruptions of alkali basalt from cinder cones located along NW-trending fractures through the area. Although other mildly peralkaline rhyolites are found in the rift zones of western Mexico, only Las Navajas produced pantellerites. Greater volumes of basic alkaline magma have erupted in the Las Navajas region than in the other areas of peralkaline volcanism in Mexico, a factor which may be necessary to provide the initial volume of material and heat to drive the differentiation process to such extreme peralkaline compositions.     

Grassland biogeochemistry: Links to atmospheric processes

Regional modeling is an essential step in scaling plot measurements of biogeochemical cycling to global scales for use in coupled atmosphere-biosphere studies. We present a model of carbon and nitrogen biogeochemistry for the U.S. Central Grasslands region based on laboratory, field, and modeling studies. Model simulations of the geography of C and N biogeochemistry adequately fit observed data. Model results show geographic patterns of cycling rates and element storage to be a complex function of the interaction of climatic and soil properties. The model also includes regional trace gas simulation, providing a link between studies of atmospheric geochemistry and ecosystem function. The model simulates nitrogenous trace gas emission rates as a function of N turnover and indicates that they are variable across the grasslands. We studied effects of changing climate using information from a global climate model. Simulations showed that increases in temperature and associated changes in precipitation caused increases in decomposition and long-term emission of Co₂ from grassland soils. Nutrient release associated with the loss of soil organic matter caused increases in net primary production, demonstrating that nutrient interactions are a major control over vegetation response to climate change.     

Evolution of the Miocene Tejeda magmatic system,Gran Canaria,Canary Islands

This paper is a companion to Clark (1988; hereafter Part I) which described the evolution of the Tejeda Magmatic System (TMS), a Miocene caldera complex, Gran Canaria, Spain, based on geochronologic, paleomagnetic and field data. In this study, petrochemical data are used to corroborate the history out-lined in Part I. Geochemical discriminant analysis shows that whereas the Extra-Caldera (EC) Mogan/Fataga volcanics are separated by a composition gap, no composition gap exists within the Intra-Caldera (IC) sequence. IC ignimbrites change rapidly but progressively from pantellerites and comendites to comenditic trachytes and finally to trachytes in a 0.47 Ma time interval. Significantly, the lower pantelleritic part of the IC series is similar to the EC pantellerites (units B, C and D) as expected based on results from Part I. The appearance of a compositional gap in the EC sequence is the result of flows having been trapped within the caldera during the 0.47 Ma Mogan-Fataga transition interval. The transitional IC sequence may be geochemically modelled by mixing of Mogan comendites and Fataga trachytes. The mixing was most probably induced by the high discharge of magma from the compositionally-zoned Tejeda magma body. The rate of change in erupted composition is best explained by imagining a continuous influx of Fataga or parental Fataga magma into a chamber whose previous silicic component (Mogan composition) was no longer being replenished and that the two magmas did not convectively mix prior to eruption. Repose times between successive eruptions in the lower to middle Mogan (from P1/T1 to A) were of order 30 000 a; the upper Mogan pantellerites and comendites/comenditic trachytes (B to F?) erupted once every 125 000 years or so. The longer repose time for the upper units is consistent with their more differentiated character.