Thematic Map Analysis Using Multiple Regression

Thematic maps can be analyzed by multiple regression for (1) forward prediction where a younger geological structural map is written as a least-squares function of older maps for information on historical perspectives or (2) by backward prediction where an older map is regressed stepwise on a series of younger ones to aid in prospecting. The technique was evaluated by a series of structure maps on different geological horizons from the U.S. Midcontinent (Kansas) where the forward prediction proved more effective than backward. In forward prediction, the first map entered into a multiple regression is invariably the immediately underlying one as expected. On the other hand, the first map in a backward prediction is not necessarily related to stratigraphy which limits the utility of the technique for prospecting.     

The DAV and Periadriatic fault systems in the Eastern Alps south of the Tauern window

Alpine deformation of Austroalpine units south of the Tauern window is dominated by two kinematic regimes. Prior to intrusion of the main Periadriatic plutons at ~30 Ma, the shear sense was sinistral in the current orientation, with a minor north-side-up component. Sinistral shearing locally overprints contact metamorphic porphyroblasts and early Periadriatic dykes. Direct Rb-Sr dating of microsampled synkinematic muscovite gave ages in the range 33-30 Ma, whereas pseudotachylyte locally crosscutting the mylonitic foliation gave an interpreted ⁴⁰Ar-³⁹Ar age of ~46 Ma. The transition from sinistral to dextral (transpressive) kinematics related to the Periadriatic fault occurred rapidly, between solidification of the earlier dykes and of the main plutons. Subsequent brittle-ductile to brittle faults are compatible with N-S to NNW-SSE shortening and orogen-parallel extension. Antithetic Riedel shears are distinguished from the previous sinistral fabric by their fine-grained quartz microstructures, with local pseudotachylyte formation. One such pseudotachylyte from Speikboden gave a ⁴⁰Ar-³⁹Ar age of 20 Ma, consistent with pseudotachylyte ages related to the Periadriatic fault. The magnitude of dextral offset on the Periadriatic fault cannot be directly estimated. However, the jump in zircon and apatite fission-track ages establishes that the relative vertical displacement was ~4-5 km since 24 Ma, and that movement continued until at least 13 Ma.     

Impact of the Montreal protocol and its amendments on the rate of change of global radiative forcing

Increases in chlorinated and brominated halocarbons are believed to be responsible for the depletion of stratospheric ozone observed over much of the globe in the past decade or so. Ozone depletion is in turn believed to lead to a negative radiative forcing, tending to cool the stratosphere and the surface. We show that the increasing atmospheric concentrations of ozone-depleting halocarbons and onset of related ozone depletion likely led to a negative forcing of the climate system in the 1980s that slowed significantly the rate of change of total anthropogenic radiative forcing due to the combined effect of all greenhouse gases over that decade. Within the next decade, emissions of these halocarbons are expected to rapidly decrease, with corresponding impacts on ozone and radiative forcing. As the emissions of ozone-depleting gases are reduced and eventually phased out, the rate of ozone depletion is expected to decrease and eventually reverse. All other things being equal, we show that the change from deepening ozone depletion in the 1980s to ozone increases in the future should lead to a pronounced increase in the decadal rate of change of anthropogenic greenhouse forcing of the next few decades, perhaps to levels unprecedented in this century.     

Calibration of regional pollen data to construct maps of former forest types in southern Sweden

A method was developed to construct maps of former forest types based on regional pollen data in southern Sweden. The considered species were Alnus, Betula, Carpinus, Corylus, Fagus, Fraxinus, Juniperus, Picea, Pinus, Populus, Quercus, Salix, Tilia and Ulmus. A network of 37 regional pollen sites with high data quality from lakes and peat deposits were selected from Sweden south of 60 ° N. Pollen percentage values were calculated and converted into estimates of tree composition. For controlling the reliability of the reconstruction, the estimates from the core-tops were compared with present day forest inventory data, and local pollen diagrams were compared with the regional pollen diagrams. An inverse distance weighted interpolation algorithm was used to generate maps for each tree species distribution at 2000 BP, 1500 BP, 1000 BP, 500 BP and 0 BP. A supervised classification routine was implemented to generate nine different forest types common to the five studied time intervals. The maps show that the amounts and patterns of distribution of the species and the forest types have varied in a significant but systematic manner through time. The changes are due to human activities, migrational patterns and changes in climate. These maps will be of value as a basis for future landscape planning, forestry and conservation of biodiversity.This is the 20th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.     

Scales of nutrient-limited phytoplankton productivity in Chesapeake Bay

The scales on which phytoplankton biomass vary in response to variable nutrient inputs depend on the nutrient status of the plankton community and on the capacity of consumers to respond to increases in phytoplankton productivity. Overenrichment and associated declines in water quality occur when phytoplankton growth rate becomes nutrient-saturated, the production and consumption of phytoplankton biomass become uncoupled in time and space, and phytoplankton biomass becomes high and varies on scales longer than phytoplankton generation times. In Chesapeake Bay, phytoplankton growth rates appear to be limited by dissolved inorganic phosphorus (DIP) during spring when biomass reaches its annual maximum and by dissolved inorganic nitrogen (DIN) during summer when phytoplankton growth rates are highest. However, despite high inputs of DIN and dissolved silicate (DSi) relative to DIP (molar ratios of N∶P and Si∶P>100), seasonal accumulations of phytoplankton biomass within the salt-intruded-reach of the bay appear to be limited by riverine DIN supply while the magnitude of the spring diatom bloom is governed by DSi supply. Seasonal imbalances between biomass production and consumption lead to massive accumulations of phytoplankton biomass (often>1,000 mg Chl-a m^?2) during spring, to spring-summer oxygen depletion (summer bottom water <20% saturation), and to exceptionally high levels of annual phytoplankton production (>400 g m^?2 yr^?1). Nitrogen-dependent seasonal accumulations of phytoplankton biomass and annual production occur as a consequence of differences in the rates and pathways of nitrogen and phosphorus cycling within the bay and underscore the importance of controlling nitrogen inputs to the mesohaline and lower reaches of the bay.     

Anomalous structural evolution of the Shimanto Accretionary Prism at Murotomisaki, Shikoku Island, Japan

Abstract The Late Oligocene-Early Miocene Nabae Sub-belt of the Shimanto Accretionary Prism was created coevally (ca 25-15 Ma) with the opening of the Shikoku back-arc basin, located to the south of the southwest Japan convergent margin. The detailed geology of the sub-belt has been controversial and the interaction of the Shimanto accretionary prism and the opening of the Shikoku Basin has been ambiguous. New structural analysis of the sub-belt has led to a new perception of its structural framework and has significant bearing on the interpretation of the Neogene tectonics of southwest Japan. The sub-belt is divided into three units: the Nabae Complex; the Shijujiyama Formation; and the Maruyama Intrusive Suite. The Nabae Complex comprises coherent units and mélange, all of which show polyphase deformation. The first phase of deformation appears to have involved landward vergent thrusting of coherent units over the mélange terrane. The second phase of deformation involved continued landward vergent shortening. The Shijujiyama Formation, composed mainly of mafic volcanics and massive sandstone, is interpreted as a slope basin deposited upon the Nabae Complex during the second phase of deformation. The youngest deformational pulse involved regional flexing and accompanying pervasive faulting. During this event, mafic rocks of the Maruyama Intrusive Suite intruded the sub-belt. Fossil evidence in the Nabae Complex and radiometric dates on the intrusive rocks indicate that this tectonic scheme was imprinted upon the sub-belt between ～23 and ～14 Ma. The timing of accretion and deformation of the sub-belt coincides with the opening of the Shikoku Basin; hence, subduction and spreading operated simultaneously. Accretion of the Nabae Sub-belt was anomalous, involving landward vergent thrusting, magmatism in newly accreted strata and regional flexing. It is proposed that this complex and anomalous structural history is largely related to the subduction of the active Shikoku Basin spreading ridge and associated seamounts.     

Sr-Isotope record of Quaternary marine terraces on the California coast and off Hawaii

Strontium-isotopic ratios of dated corals have been obtained from submerged reefs formed during Quaternary glacial periods off the Hawaiian islands. These data, combined with data from deep-sea sediments, tightly constrain the secular variation of marine ⁸⁷Sr/⁸⁶Sr for the past 800,000 yr. Although long-term trends are apparent, no significant (>0.02‰), rapid (<100,000 yr) excursions in ⁸⁷Sr/⁸⁶Sr were resolved nor did we observe any samples with ⁸⁷Sr/⁸⁶Sr greater than that of modern seawater. Strontium in mollusks from elevated marine terraces formed during interglacial periods on the southern California coast show resolvable and consistent variations in ⁸⁷Sr/⁸⁶Sr which, when compared to the trend of Quaternary marine ⁸⁷Sr/⁸⁶Sr, can be used to infer uplift rates and define approximate ages for the higher terraces. The Sr-isotope age estimates indicate that uplift rates vary among crustal blocks and were not necessarily constant with time. No contrast in Sr-isotopic ratios between similar-age Hawaiian and California fossils was observed, confirming that any change in marine ⁸⁷Sr/⁸⁶Sr from glacial to interglacial periods must be small. A realistic appraisal of the potential of Sr-isotope stratigraphy for chronometric applications in the Quaternary suggests that the technique will be limited to relatively coarse distinctions in age.     

Mountains,nations, parks,and conservation

Between 1985 and 1991, two new mountain protected areas (MTNPA) covering more than 35,000 km² and based on participatory management models — the Makalu-Barun National Park and Conservation Area, Nepal, and Qomolangma Nature Preserve, Tibet Autonomous Region — were successfully established through the collaborative efforts of Woodlands Mountain Institute and conservationists in China and Nepal. Characteristics common to both projects include the importance of establishing (1) effective rationales, (2) local support constituencies, (3) a senior advisory group, (4) a task force, (5) linkages between conservation and development, and (6) fund raising mechanisms. The lessons derived from the experiences of Woodlands Mountain Institute are of significant value to others in preserving MTNPA. Increased collaboration and communication between all interested in conservation, however, will remain a critical component for expanding mountain protected area coverage to throughout the world.