Stadial subdivisions of early Pleistocene glaciations in central United States - a developing chronology

Recently recognized field evidence clearly indicates that both the Nebraskan and Kansan Glaciations are divisible into stades on the basis of a stratigraphic record of ice-margin fluctuations. Two Nebraskan stades and three Kansan stades have been identified; it is suggested that others will be found. Recognition of multiple stades requires a thorough review of all Early Pleistocene stratigraphic and paleontologic age assignments applied in the American Midwest.     

An integrated approach for assessing the relative significance of human pressures and environmental forcing on the status of Large Marine Ecosystems

An ecosystem approach to the management of the marine environment has received considerable attention over recent years. However, there are few examples which demonstrate its practical implementation. Much of this relates to the history of existing marine monitoring and assessment programmes which (for many countries) are sectoral, making it difficult to integrate monitoring data and knowledge across programmes at the operational level.To address this, a scientific expert group, under the auspices of the International Council for the Exploration of the Sea (ICES), prepared a plan for how ICES could contribute to the development of an Integrated Ecosystem Assessment (IEA) for the North Sea by undertaking a pilot study utilising marine monitoring data. This paper presents the main findings arising from the expert group and in particular it sets out one possible integrated approach for assessing the relative significance of environmental forcing and fishing pressure on the ecological status of the North Sea, it then compares the findings with assessments made of other Large Marine Ecosystems (LMEs).We define the North Sea ecosystem on the basis of 114 state and pressure variables resolved as annual averages between 1983 and 2003 and at the spatial scale of ICES rectangles. The paper presents results of integrated time-series and spatial analysis which identifies and explains significant spatial and temporal gradients in the data. For example, a significant shift in the status of the North Sea ecosystem (based upon 114 state-pressure variables) is identified to have occurred around 1993. This corresponds to previously documented shifts in the environmental conditions (particularly sea surface temperature) and changes in the distribution of key species of plankton (Calanus sp.), both reported to have occurred in 1989. The difference in specific timing between reported regime shifts for the North Sea may be explained, in part, by time-lag dependencies in the trophic structure of the ecosystem with shifts in higher trophic levels occurring later than 1989.By examining the connection (or relatedness) between ecosystem components (e.g. environment, plankton, fish, fishery and seabirds) for the identified regime states (1983–1993; 1993–2003) we conclude that both the North Sea pelagic and benthic parts of the ecosystem were predominantly top-down (fishery) controlled between 1983 and 1993, whereas between 1993 and 2003 the pelagic stocks shifted to a state responding mainly to bottom-up (environment) influences. However, for the demersal fish stocks between 1993 and 2003 top-down (fishery) pressure dominated even though over this period significant reductions in fishing pressure occurred. The present analysis, therefore, provides further evidence in support of the need for precautionary management measures taken in relation to setting fishery quotas.     

Coupling of deformation and reactions during mid-crustal shear zone development: an in situ frictional–viscous transition

A well preserved strain and reaction gradient records the progressive transformation of a megacrystic Kfs+Cpx+Opx+Bt₁±Qtz syenitic pluton to a strongly sheared Kfs+Act+Bt₂+Ab+Qtz tectonite within the exhumed Norumbega Fault System, Maine, USA. Detailed microstructural analysis indicates that fracturing and localized fluid infiltration initiated the deconstruction of the existing K-feldspar and two-pyroxene load-bearing framework, and that feedback among metamorphic reactions, fabric development and enhanced permeability during progressive shearing led to the development of an interconnected, biotite- and actinolite-rich foliation. The activation of dislocation creep in biotite and quartz, and dissolution–precipitation creep in actinolite and feldspar, with increasing strain ultimately resulted in a transition from dominantly frictional to dominantly viscous deformation processes. Petrological data show that various scales of geochemical disequilibrium exist across the strain and reaction gradient, and that reaction progress was limited by slow chemical diffusion during the early stages of deformation. Petrological modelling results indicate that the existing plutonic assemblage was metastable at mid-crustal conditions, and that fluid infiltration and deformation allowed the product assemblage to advance towards chemical equilibration. Comparison of the observed microstructures and deformation mechanisms with experimental and numerical modelling results suggest that the development of an interconnected biotite-dominated fabric probably caused a major (up to three fold) reduction in bulk rock strength and localization of strain into the foliated margin.     

MIT's Computer Resource Lab:

Abstract

The paper describes the curriculum on geographic information systems developed in the Department of Planning at the Massachusetts Institute of Technology for those studying for the Master in City Planning degree. Particular emphasis is given to the part played by the Computer Resources Lab in serving the needs of the architecture and planning departments, the interactions between teaching and research, and those between the course and professional practice. The required courses are outlined and the wide range of recommended courses, drawn from a number of departments in the Institute, are listed- The authors emphasize the necessity of their being at the forefront of research if they are lo maintain the flow of hardware and software from contacts and donations on which their research and teaching depend.     

CO2 in the Weddell Gyre and Antarctic Circumpolar Current: austral autumn and early winter

Quasi-continuous fugacity of CO₂ (fCO₂) data were collected in the eastern Weddell Gyre and southern Antarctic Circumpolar Current (ACC) of the Southern Ocean during austral autumn 1996. Full depth Total CO₂ (TCO₂) sections are presented for austral autumn and winter (1992) cruises. Pronounced fCO₂ gradients were observed at the Southern Ocean fronts. In the Weddell Gyre, fCO₂ regimes appeared to coincide with surface and subsurface hydrographic regimes. The southern ACC was supersaturated with respect to CO₂, as was part of the northern Weddell Gyre. The southern Weddell Gyre was markedly undersaturated. The great potential of autumn cooling for generating undersaturation and CO₂ uptake from the atmosphere was demonstrated. In the northeastern Weddell Gyre, upwelling of CO₂- and salt-rich deep water was shown to play a role as the horizontal fCO₂ distribution closely resembled that of the surface salinity. The total uptake of atmospheric CO₂ by the Weddell Gyre in autumn (45 days) was calculated to be 7·10¹² g C. The deep TCO₂ distribution noticeably reflected the different water masses in the region. A new deep TCO₂ maximum was detected in the ACC, which apparently characterizes the boundary between the equatorward flowing Antarctic Bottom Water (AABW) and the Circumpolar Deep Water (CDW). East of the Weddell Gyre, the AABW stratum is much thicker (>2000 m) than more to the west, on the prime meridian (<300 m).     

Sedimentologic,mineralogic, and geotechnical descriptions of fine-grained slope and basin deposits,Baffin Island Fiords

Sediments from Baffin Island fiords are graded, massive, laminated, or bioturbated. Plasticity indices vary with sediment type (lowest = laminated or graded; intermediate = massive; and highest = bioturbated). Graded and massive silty/sandy muds are most common on prodelta or proglacial slopes. Bioturbated graded and laminated muds, and rare massive pebbly muds occur more distally down-fiord from the deltas or glaciers. Clays are mostly mica, with only minor to moderate amounts of chlorite, kaolinite, and swelling clays. On the Casagrande plasticity chart, the sediments plot in fields for clay-size material of medium to high plasticity.