Timescales of melt generation and the thermal evolution of the Himalayan metamorphic core,Everest region,eastern Nepal

In the Everest region of the Nepalese Himalaya, ⁴⁰Ar/³⁹Ar and U-Pb geochronology provide evidence for a complex thermal history marked by multiple episodes of granite intrusion. The oldest mobilized melt formed syn-deformational granitic sills that have U-Pb crystallization ages of 21.33±0.03 and 21.80±0.05 Ma. Preserved in these same granites is a record of earlier magmatic crystallization of xenotime, zircon and monazite between ca. 26 Ma and ca. 23 Ma. This pattern of accessory phase crystallization is interpreted to reflect incremental melting and crystallization in the source region of the sills before ultimate melt migration, and provides the earliest evidence for anatexis in the Everest region. The beginning of crustal melting in the Everest region predates the earliest known movement on both the Main Central Thrust and the South Tibetan fault systems, but is temporally associated with the implied pressure decrease between Eohimalayan and Neohimalayan metamorphism.     

Experiences and perspective in compiling long-term remote sensing data sets on landscapes and biospheric processes

Remote sensing has been employed to study the Earth's landscapes for more than a century. Over the last thirty years major changes in all aspects of the technology, as well as scientific understanding of the measurements, have revolutionized use of these data for terrestrial research. The emergence of biophysical interpretations of land remotely sensed data has created great interest in the potential of these data to study the dynamics of landscapes and biospheric processes as contributors to global change. However, the evolutionary history of land remote sensing, particularly in the Landsat era, has in many ways worked against this use of the data. Until recently, there was little appreciation of the need to compile long-term historical records of these observations. There are currently no formal scientific institutional systems dedicated to preserving and distributing the long-term record of Earth observations acquired by Landsat, AVHRR or other land observing systems. As the International Geosphere-Biosphere Program begins, this issue should be one of the first priorities of the participants.     

Climate change in southern Illinois, USA, based on the age and δC of organic matter in cave sediments

Matrix-supported diamicton and uniform to laminated, silty, fine-grained sediment deposited from about 42,500 to 27,600 cal yr B.P. under slackwater conditions nearly filled two caves in southwestern Illinois. At some point, most of the sediment was flushed from the caves and from about 22,700 to 4000 cal yr B.P., floods deposited a drape of sandy and silty sediment on remnant slackwater successions, cobbly alluvium, and bedrock (especially from 7700 to 4000 cal yr B.P.). Clay mineral analyses of the slackwater cave sediment reveal a provenance of chiefly Petersburg Silt, a smectite- and illite-rich proglacial lacustrine unit present in the overlying Illinois Episode glacial succession. Today, remnants of the ancient subterranean slackwater deposits nearly fill several secondary passages and, in at least two locations, cover a cobble-mantled strath terrace 1.3 to 1.5 m above active stream channels. Slumping and sinkhole formation appear to have been important mechanisms for deposition of the ancient subterranean deposits. Slumping of these surficial deposits and associated vegetation can occur along the flanks of sinkholes (in addition to sinkhole formation) and enter caves; however, the finer organics, some of them comminuted during transport into the caves, become part of the cave alluvium. This finer organic fraction is the modern analog of the humified organic matter disseminated in slackwater sediment dated in this investigation by radiocarbon methods. Twenty-four ¹⁴C ages on humified organic matter provide chronologic control. The δ¹³C values of the organic matter reflect the proportion of C₄-type to C₃-type vegetation growing in and around swallets and sinkholes at the time of redeposition. Drought-tolerant C₄-type vegetation was more prevalent relative to C₃-type vegetation from 42,500 to 31,200 cal yr B.P. compared to conditions from 28,800 cal yr B.P. to the present. The δ¹³C values are consistent with the results from other investigations of speleothems and organic matter from loessial paleosols.     

Spatial Patterns of Migration and Income Change in the Mountain West: The Dominance of Service‐Based,Amenity‐Rich Counties

One of the most recognizable and important changes occurring in the West is rapid population growth. This article intends to address questions associated with whether patterns of population growth and income migration are associated with “new” and “old” West economies. Rural restructuring in the U.S. has created a group of counties with service‐based economies. In the Mountain West, a number of counties with service‐based economies are located in areas with high levels of environmental or natural amenities, creating what has been termed the “New West.” Migration to the rural parts of the Mountain West, and the income transfers associated with migration, are increasingly concentrated within these New West counties. Rapid population growth, the changing characteristics of in‐migrants, and their spatial concentration in New West counties provide a basis for conflicts over what the rural West is becoming.     

The effects of seasonal variability and weather on microbial fecal pollution and enteric pathogens in a subtropical estuary

The Charlotte Harbor estuary in southwest Florida was sampled monthly for one year at twelve stations, in the lower reaches of the Myakka and Peace Rivers. The objectives of the study were to address the distribution and seasonal changes in microbial indicators and human pathogen levels in Charlotte Harbor shellfish and recreational waters, and to determine those factors that may be important in the transport and survival of pathogens. Monthly water samples and quarterly sediment samples were analyzed for fecal coliform bacteria, enterococci,Clostridium perfringens, and coliphage. Quarterly samples also were analyzed for the enteric human pathogens,Cryptosporidium spp.,Giardia spp., and enteroviruses. Fecal indicator organisms were generally concentrated in areas of low salinity and high densities of septic systems; however, pollution became widespread during wet weather in, the late fall and winter of 1997–1998, coincident with a strong El Nino event. Between, December 1997 and February 1998, enteroviruses were detected at 75% of the sampling stations; none were detected in other months. Enteric protozoa were detected infrequently and were not related to seasonal influences. Fecal indicators and enteroviruses were each significantly associated with rainfall, streamflow, and temperature. Regression models suggest that temperature and rainfall can predict the occurrence of enteroviruses in 93.7% of the cases. Based on findings in this watershed, factors such as variability in precipitation, streamflow, and temperature show promise in modeling and forecasting periods of poor coastal water quality.     

Continental origin and industrial sources of trace metals in the Northwest Atlantic troposphere

Trace metals (Mn, Fe, Ni, Cu, Zn, Cd, Pb and stable lead isotopes) have been analyzed in precipitation and total aerosols collected in the northwest Atlantic troposphere in April and November 1989. According to stable lead isotope signatures we encountered two main air mass sources, Mediterranean easterlies (206Pb/207Pb=1.131) and US westerlies (206Pb/207Pb=1.195–1.205). The phasing out of leaded gasoline has been invoked to explain the decrease of the 206Pb/207Pb ratios from 1.22 to 1.20 for the past 10 years in North America. Based on trajectory analyses, intermediate 206Pb/207Pb ratios are explained by a mixing of pure US westerlies with Canadian air masses (206Pb/207Pb=1.190–1.195) or Mediterranean air masses (206Pb/207Pb=1.18–1.19). Isentropic trajectories are very useful in explaining the variability of trace metal concentrations, a result of the fluctuating transport range of anthropogenic aerosols to remote marine areas of the North Atlantic. Lead concentrations appear to be closely correlated to the air mass transport patterns as defined from the meteorological analyses. For instance oceanic air masses transported over remote marine areas for more than three days were characterized by lead concentrations 2 to 10 times lower (Pb=0.5 to 2 ng/scm) than coastal air masses (Pb=3 to 10 ng/scm).Anthropogenic trace metal concentrations are generally in good agreement with the air mass signatures which display Pb and Cu, Ni, Zn concentrations higher than 2 and 10 ng/scm respectively in aerosol samples for the US source. Trace metal elemental ratios and soil enrichment factors were used to define industrial sources. Aerosol originating from the US exhibits the distinct industrial signature of Cu/Ni production and coal-oil combustion, while steel metallurgy could account for more than 50% of the overall Mn input into the Northwest Atlantic ocean.     

The global distribution of long-term total ozone variations during the period 1957–1975

Total ozone observations in the international network have been used as a basis for the analysis of the mean monthly ozone distribution over the globe for the period 1957–75. It has been found that during the period 1961–70 the total ozone amount increased in the Northern Hemisphere by about 12 percent and that this increase seems to be significant at all latitudes. Although the data were sparse for the Southern Hemisphere, there did not appear to be any significant ozone changes during the 10 year period. Relatively large geographic variations were found in the ozone trends and it is suggested that these variations are related to large scale changes in the atmospheric circular pattern.