bluuebunny/crossref_metadata_2025 huggingface dataset:
Dendroecological Evidence of Lake-Level Changes during the Last Three Centuries in Subarctic Québec
Authors: Bégin Yves , Payette Serge
Published: December 2004

Dendroecological analysis of black spruces (Picea mariana (Mill.) BSP.) near the shore of Clearwater Lake in the eastern Canadian subarctic yielded information on water level over the past three centuries. Tree positions, growth froms, layering, tree ring patterns, and ice scars provide direct evidence of a major rise in lake level. From the 17th century to the present, trees on the lake shore were progressively submerged by the increasing water level, which reached a maximum in this century. Higher levels began around the mid-18th century when shoreline spruce trees started to lean because extensive wave erosion caused landward shore displacement. High mortality of leaning spruce and abundant ice scar formation occurred during this century. The rise in water level in inferred to have been caused by snowier winters occurring parallel to climatic warming.
A Reevaluation of the Timing and Causes of High Lake Phases in the Lake Michigan Basin
Authors: Hansel Ardith K. , Mickelson David M.
Published: December 2004

Radiocarbon age control on the type Glenwood, Calumet, and Toleston shoreline features and on the abandoned Chicago outlet at the south end of the Lake Michigan basin provides a basis for reevaluating the timing and causes of high lake phases in the basin. Radiocarbon dates suggest that Glenwood-level (195 m) shoreline features formed between 14,100 and 12,700 yr B.P. (Glenwood I and II phases), Calumet-level (189 m) between 12,700 and 11,000 yr B.P. (Calumet I and II phases), and Toleston-level (184.5 m) between 5000 and 4000 yr B.P. (Nipissing phase), and that the Chicago outlet was cut to its present level (180 m) on bedrock while the lake was at the Glenwood level. This new chronology is inconsistent with J H. Bretz' hypothesis ((1951) American Journal of Science 249 , 401–429) that the progressive lowering of lake level resulted from episodic down-cutting of the outlet. Instead, the changes in lake level appear to relate to changes in the amount of glacial meltwater and precipitation entering the basin. We hypothesize that the Glenwood phases correspond with times when discharge from the Huron and Erie basins also entered the Lake Michigan basin (Lake Border and early Port Huron glacial phases), the Calumet phases with times when drainage was from the Lake Michigan basin alone (late Port Huron and Two Rivers glacial phases), and the Nipissing phase with the postglacial middle Holocene transgression caused by differential uplift in the basin. Estimates of relative net inputs to the basin during the Glenwood, Calumet, and Nipissing lake phases are consistent with estimates of relative outputs (i.e., discharge through the Chicago outlet); the magnitude of relative differences in inputs and outputs between phases is sufficient to explain lake-level changes of 4.5 to 6 m.
Origin and Consequences of Cyclic Ice Rafting in the Northeast Atlantic Ocean During the Past 130,000 Years
Authors: Heinrich Hartmut
Published: December 2004

Deep-sea sediment cores recovered from the Northeast Atlantic Ocean were examined in order to elucidate the influence of the Earth's orbital parameters on major ice rafting. Analyses of coarse-grained ice-rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal. Since 130,000 yr B.P., dropstone layers have been deposited each half period of a precessional cycle (11,000 ± 1000 yr). Ice rafting occurs during times of winter minimum/summer maximum insolation and summer minimum/winter maximum insolation. In the first case, high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter. In the second case, growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater. Both situations result in a southward penetration of polar water. Thus, the marine record of dropstones documents ice rafting not only during Weichselian stades but also during cold events within interstades. The regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes, not only in the region of the North Atlantic Ocean but also in remote areas such as the Pacific Ocean and the Antarctic.
Ice-Wedge Casts and Relict Patterned Ground in Central Illinois and their Environmental Significance
Authors: Johnson W. Hilton
Published: December 2004

Sediment features and soil patterns indicate that permafrost developed beyond the late Wisconsinan (Woodfordian) ice margin in Illinois. Vertical wedge-shaped bodies in Woodfordian glacigenic deposits and buried by Woodfordian loess are interpreted to be ice-wedge casts. Large-scale patterned ground, common on the late Wisconsinan drift plain and on the Illinoian drift plain to the south and west, also is interpreted to be the result of ice-wedge formation. Permafrost extended to about 38° 30′ N latitude and formed during the interval from about 21,000 to 16,000 yr B.P. Formation and degradation of permafrost was time-transgressive, directly related to the ice-marginal climate, and probably restricted temporally to less than 1000 years at a site. The following environmental conditions are suggested near the ice margin: mean annual ground temperature −3°C; mean annual air temperature −6 ± 2°C; less precipitation than modern, particularly in winter; strong and likely dry wind systems; and relatively open vegetation with few woody plants.
Early Holocene pinyon (Pinus monophylla) in the northeastern Great Basin
Authors: Madsen David B. , Rhode David
Published: December 2004

Fine-grained excavation and analysis of a stratigraphic column from Danger Cave, northeastern Great Basin, suggests prehistoric hunter-gatherers were collecting and using singleleaf pinyon (Pinus monophylla) near the site for at least the last 7500 yr. Human use of the cave began after the retreat of Lake Bonneville from the Gilbert level, shortly before 10,000 yr B.P. In stratum 9, culturally deposited pine nut hulls appear in the sequence by about 7900 yr B.P. and are continuously present thereafter. A hull fragment in stratum 10 is directly dated to 7410 ± 120 yr B.P. These dates are at least 2000 yr earlier than expected by extrapolation to macrofossil records from the east-central and central Great Basin, and necessitate some revision of current biogeographical models of late Quaternary pinyon migration.
Paleoenvironments and Human Occupation in Late-Glacial Panama
Authors: Piperno Dolores R. , Bush Mark B. , Colinvaux Paul A.
Published: December 2004

The first pollen and phytolith data covering the entire Pleistocene/Holocene transition from the lowlands of the Central American isthmus indicate that the forests of late-glacial Panama at an altitude of 650 m resembled those currently found at ca. 1500–1800 m. A temperature depression of ca. 5°C and reduced precipitation/evaporation ratios in the late-glacial period are suggested. Forest composition from ca. 14,000 to 10,500 yr B.P., although primarily montane in character, contained a low biomass of species today segregated in lowland forests and, hence, a floral assemblage with no modern analog. The sudden appearance of carbon and burnt, weedy plant material at ca. 11,000 yr B.P. is attributed to the earliest human impact yet recorded from tropical America and may perhaps have been associated with the first human occupation of the region.
Accelerator Dating of a Mixed Assemblage of Late Pleistocene Insect Fossils from the Lamb Spring Site, Colorado
Authors: Elias Scott A. , Toolin Laurence J.
Published: December 2004

Fossil insects from the late-glacial deposits at the Lamb Spring archaeological site, near Denver, Colorado, are relatively abundant and diverse, providing considerable paleoecological data for the site. The late Pleistocene insect fauna from the site comprises 72 identified taxa, principally beetles. However, the fauna presented an interpretive problem because it contained a mixture of prairie and alpine tundra species. This was initially considered to be the result of a mixing of faunal elements during the climatic transition of late-glacial times, a “no-modern-analog” fauna. Accelerator dating of insect fossil specimens from the two ecological groups helped resolve the paleoecological problem. Fossil specimens of the prairie-associated species were dated at 17,850 ± 550 yr B.P., while specimens of the tundra-associated species yielded an age of 14,500 ± 500 yr B.P. These dates reveal that what appeared to be an ecological mixing was probably a taphonomic problem, wherein full-glacial-age fossils were probably reworked into latest Wisconsin sediments. While both faunal assemblages reflect climatic conditions substantially colder than present, initial results suggest that the full-glacial fauna represents a cold, dry grassland or steppe environment, while the younger fauna suggests moister and more tundra-like conditions.
Late Weichselian Glacier Retreat in Kongsfjorden, West Spitsbergen, Svalbard
Authors: Lehman Scott J. , Forman Steven L.
Published: December 2004

The chronology of Late Weichselian to Holocene deglaciation of Kongsfjorden, west Spitsbergen has been reconstructed based on the geomorphic and stratigraphic record of ice retreat, relative sea-level relationships, and 14C dating of associated marine organic materials. The seaward extent of glacial drift and fjord bathymetry constrain a secure reconstruction for the ice sheet near the mouth of the fjord at ca. 13,000 yr B.P., but do not rule out the possibility that more extensive glaciation was achieved earlier during the Late Weichselian. Regional shoreline relations, rates of emergence, and radiocarbon dating of foraminifera deposited just above till indicate that deglaciation occurred in two steps: one beginning during or just prior to the Late Weichselian Marine Limit phase at 13,000–12,000 yr B.P. and another beginning at 10,000–9500 yr B.P. The fjord was completely deglaciated by 9440 ± 130 yr B.P. A period of stable relative sea level began 10,700 yr B.P. and ended between 10,000 and 9500 yr B.P., which we take to indicate renewed glacial loading during the Younger Dryas. Glacier readvance within Kongsfjorden at this time was diminutive, suggesting that most of the Younger Dryas ice-sheet growth was confined to the eastern part of the archipelago and/or to the Barents Shelf. The two-step deglaciation of Kongsfjorden occurred during intervals of accelerated global ice-sheet melting and rapid oceanic and atmospheric warming in more temperate latitudes of the circum-Atlantic region. This coincidence most likely resulted from contemporaneous increases in the poleward transport of oceanic heat.
Mictomys Borealis(Northern Bog Lemming) and the Wisconsin Paleoecology of the East-Central Great Basin
Authors: Mead Jim I. , Bell Christopher J. , Murray Lyndon K.
Published: December 2004

Teeth of northern bog lemming,Mictomys borealis, are reported from Cathedral and Smith Creek caves and represent the first Wisconsin remains of the genus from the Great Basin. Specimens from Cathedral Cave, Snake Range, are associated with U-series ages of 24,000 to 15,000 yr B.P. Previous work with pollen and packrat middens, dating to the same age as theMictomys, indicate that Smith Creek Canyon contained a riparian, locally mesic community, includingPicea engelmannii(spruce),Betulasp. (birch),Cercocarpussp. (mountain mahogany), andArtemisiasp. (sagebrush) among other species. Exposed canyon slopes and the adjacent valley apparently contained a more xeric steppe community including sagebrush and Chenopodiineae species; rocky outcrop permittedPinus flexilis(limber pine) andP. longaeva(bristlecone pine) to grow adjacent to Lake Bonneville or low in the canyon. The region apparently experienced a dry climate (not necessarily drier than today); however, Smith Creek Canyon was fed by glacial meltwater from Mt. Moriah. The northern bog lemming probably lived only in the riparian community and possibly on the north-facing slope below Cathedral Cave. Few canyons of the Snake Range would have had the unusually mesic conditions found in Smith Creek Canyon.
Circumpolar Distribution of Holocene Marine Fossils in Antarctic Beaches
Authors: Berkman Paul Arthur
Published: December 2004

The composite frequency of radiocarbon ages for Holocene marine fossils from beaches around Antarctica is significantly different than random. Variations in the frequency of fossil ages coincide with the timing of Holocene climate changes inferred from Antarctic ice cores, sub-Antarctic lakes, polar and alpine moraines, and sea level. Extant Antarctic marine species that occur as fossils in beaches may reflect coastal meltwater impacts associated with ice sheet marginal fluctuations that were circumpolar during the Holocene.
Functional properties of the alternative NADH:ubiquinone oxidoreductase from E. coli through comparative 3‐D modelling
Authors: Schmid Ralf , Gerloff Dietlind L.
Published: December 2004

The alternative NADH:ubiquinone oxidoreductase (NDH‐2) from Escherichia coli is a membrane protein playing a prominent role in respiration by linking the reduction of NADH to the quinone pool. Remote sequence similarity reveals an evolutionary relation between alternative NADH:quinone oxidoreductases and the SCOP‐family “FAD/NAD‐linked reductases”. We have created a structural model for NDH‐2 from E. coli through comparative modelling onto a template from this family. Combined analysis of our model and sequence conservation allowed us to include the cofactor FAD and the substrate NADH in atomic detail. Furthermore, we propose the most plausible orientation of NDH‐2 relative to the membrane and specify a region of the protein potentially involved in ubiquinone binding.
Post‐transcriptional effects of phorbol 12‐myristate 13‐acetate on transcriptome of U937 cells
Authors: Kitamura Hiroshi , Nakagawa Tomoko , Takayama Michiyo , Kimura Yayoi , Hijika Atsushi , Ohara Osamu
Published: December 2004

To identify post‐transcriptionally modulated genes at the translational level by phorbol 12‐myristate 13‐acetate (PMA), we investigated mRNA profiles in the polysomal and the cytoplasmic fractions of U937 cells before and after PMA stimulation using microarrays with 15 017 oligonucleotide probes. Global comparison of the profiles showed that the cytoplasmic distribution of mRNAs was considerably modulated upon PMA stimulation. The results also indicate that PMA post‐transcriptionally regulated at least 0.7% of detectable genes in U937 cells. Thus, besides transcriptional modulation by PMA, changes in the translational state of transcripts seem to play a critical role in PMA‐induced differentiation of U937 cells.
Circulating and synovial levels of IGF‐I, cytokines, physical function and anthropometry differ in women awaiting total knee arthroplasty when compared to men
Authors: Pagura Sonia M. C. , Thomas Scott G. , Woodhouse Linda J. , Ezzat Shereen , Marks Paul
Published: December 2004

Purpose: Determine if gender differences in osteoarthritis relate to cytokine and growth factor levels.

Methods: Cross‐sectional comparison of serum and synovial concentrations of cytokines (IL‐1αβ, TNF‐α, IL‐6), growth factors (IGF‐I, TGF‐β, IRAP), physical performance and perceived function in total knee arthroplasty candidates (TKAC) (n = 17) and healthy controls (n = 21) was done.

Results: Serum IGF‐I values were reduced in female (TKAC 137.6 ± 7.2; Controls 160.2 ± 26.2) but not male TKAC (TKAC 182.6 ± 18.4; Controls 184.0 ± 18.4) (p < 0.05). Serum and synovial levels of cytokines and growth factors did not differ significantly by group or gender. Physical performance testing (SPW, TUG) revealed significant group and gender differences (p = 0.001) with women demonstrating greater functional impairment.

Discussion: A systemic, not local component to OA pathophysiology may exist for female TKAC. Male TKAC were less impaired, and their IGF‐I levels differ little from Control values. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
In vivo assessment of regenerate axial stiffness in distraction osteogenesis
Authors: Aarnes Gudrun Trøite , Steen Harald , Ludvigsen Per , Waanders Nicholas A. , Huiskes Rik , Goldstein Steven A.
Published: December 2004

This paper presents an in vivo test for assessment of regenerate axial stiffness after the distraction phase of lengthening therapy. The test result supplements radiography in evaluating bone healing and assists in determining when the regenerate stiffness is sufficient for removal of the external fixator. The test is non‐invasive and does not require fixator removal. The theoretical basis for the method is that an externally applied load is shared between the fixator and the regenerating bone. The amount of load carried by the regenerate depends on its axial stiffness, which increases with advanced mineralization. By measuring the force in the fixator while applying a known external load to the limb, the load‐share ratio between fixator and limb can be assessed. A load‐share ratio of 100% indicates that the entire load is carried by the fixator. The ratio decreases as the regenerate structure gradually stiffens. In a clinical trial of 22 individuals with tibial lengthening, the fixator was removed when the load‐share ratio dropped below 10%. None of the patients experienced fracture after removal of the fixator. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Parity conditions and the efficiency of the Australian 90‐ and 180‐day forward markets
Authors: Felmingham Bruce , Leong SuSan
Published: December 2004

Covered Interest Parity (CIP) holds in the 90 and 180 forward market for the AUD/USD spot exchange rate provided fully modified least absolute deviation model (FM‐LAD) procedures are applied to daily data for the period from December 2, 1985 to December 29, 2000. CIP fails if corrected ordinary least squares (OLS) and fully modified OLS (FM‐OLS) procedures are applied. However, UIP fails in both markets on early data: December 2, 1985 to December 31, 1991, but holds in the 90‐day market in a later subperiod: January 2, 1992 to December 29, 2000 FM. UIP is modified (M) to accommodate a potential risk premium. The MUIP model does not provide strong evidence suggesting the presence of a time‐varying risk premium (TRP).
Economic Growth as Environmental Policy? Reconsidering the Environmental Kuznets Curve
Authors: RAYMOND LEIGH
Published: December 2004

Some research has posited that while initially damaging to the environment, continued economic growth eventually leads to superior environmental quality. This relationship is often described as an ‘Environmental Kuznets Curve’ (EKC), after a similar hypothesis regarding income inequality made by economist Simon Kuznets. Following such findings, the EKC is sometimes offered as a rationale for encouraging economic growth as the best environmental policy option. This paper reconsiders the policy-relevance of the EKC idea, drawing on a wide range of international data collected in the Environmental Sustainability Index (ESI) project. Specifically, it tests the theoretical arguments advanced by Arrow and others (1995) that EKC relationships are unlikely to hold for environmental problems that are intergenerational in time or spread across national boundaries. The results of this research substantially confirm those arguments, providing more evidence that the EKC idea is an inadequate guide for environmental policy makers around the globe.
The Will and Authority of the Security Council after Iraq
Authors: WHITE NIGEL D.
Published: December 2004

One year after the invasion of Iraq, what lessons are to be drawn about the role of the Security Council in peace and security? This article looks at the issue by considering the nature of the Security Council in its dual functions as a forum for diplomacy and a corporate body for executive action. The idea of the Security Council's possessing a separate will in its executive function is developed. The article stresses the importance for the authority of the Council of that organ expressing its will within the legal parameters of the Charter and international law. It is argued that similar legal parameters are also applicable to the permanent members in exercising their power of veto and in interpreting resolutions. Further, when interpreting resolutions member states should not misconstrue the will of the Council. The Iraq crisis of 2003 raised all these issues and, further, necessitated a reappraisal of the rules of international law governing the use of force. This article considers the relationship between diminution in Council authority and erosion of the rules of the UN Charter governing the threat or use of force in international relations.
The First MOX Plant Award: The Need to Harmonize Competing Environmental Regimes and Dispute Settlement Procedures
Authors: SHANY YUVAL
Published: December 2004

The MOX Plant award, rendered on 3 July 2003, contributes to elucidation of the right of access to environmental information under the OSPAR Convention. However, the ‘self-contained’ vision of the OSPAR Convention embraced by the majority on the panel – rejecting in effect the relevance of competing international environmental regimes and dispute settlement procedures – deserves criticism. First of all, it leads to the establishment of a more limited right of access to environmental information under the OSPAR Convention than is recognized under other arrangements. It also represents an approach which might exacerbate the fragmentation of an increasingly complex body of international law.
A statistical study of the global structure of the ring current
Authors: Jorgensen A. M. , Spence H. E. , Hughes W. J. , Singer H. J.
Published: December 2004

In this paper we derive the average configuration of the ring current as a function of the state of the magnetosphere as indicated by the Dst index. We sort magnetic field data from the Combined Release and Radiation Effects Satellite (CRRES) by spatial location and by the Dst index in order to produce magnetic field maps. From these maps we calculate local current systems by taking the curl of the magnetic field. We find both the westward (outer) and the eastward (inner) components of the ring current. We find that the ring current intensity varies linearly with Dst as expected and that the ring current is asymmetric for all Dst values. The azimuthal peak of the ring current is located in the afternoon sector for quiet conditions and near midnight for disturbed conditions. The ring current also moves closer to the Earth during disturbed conditions. We attempt to recreate the Dst index by integrating the magnetic perturbations caused by the ring current. We find that we need to multiply our computed disturbance by a factor of 1.88 ± 0.27 and add an offset of 3.84 ± 4.33 nT in order to get optimal agreement with Dst. When taking into account a tail current contribution of roughly 25%, this agrees well with our expectation of a factor of 1.3 to 1.5 based on a partially conducting Earth. The offset that we have to add does not agree well with an expected offset of approximately 20 nT based on solar wind pressure.
A new technique for the estimation of sea surface salinity in the tropical Indian Ocean from OLR
Authors: Murty V. S. N. , Subrahmanyam Bulusu , Tilvi V. , O'Brien James J.
Published: December 2004

Algorithms are developed for the estimation of sea surface salinity (SSS) in the tropical Indian Ocean from the space‐borne satellite measurements of outgoing longwave radiation (OLR). The algorithms are based on the interrelationships between OLR, the effective oceanic layer (EOL), climatological SSS (World Ocean Atlas 1998 (WOA98)), and freshwater flux (P‐E). Coupling between the atmospheric convection (OLR) and the geopotential thickness of the oceanic near‐surface stratified layer (EOL) forms the main relationship for the estimation of SSS, followed by the relationships between EOL and WOA98 SSS and between OLR and P‐E. The SSS has been estimated using 16 years (1979–1994) of OLR data and the algorithms for the tropical Indian Ocean. The estimated SSS at 2.5° × 2.5° grid on monthly scale is nearer to the WOA98 SSS with lower differences within ±0.5–0.8 away from the coastal region. The estimated SSS also agrees reasonably with the observed SSS along the trans‐Indian zonal sections occupied during World Ocean Circulation Experiment (WOCE) and also other sections. The SSS differences bring out clearly the impact of the strong 1997–1998 El Niño on the rainfall in the southeastern Indian Ocean and the eastern equatorial region. On the basis of the results, the seasonal and interannual variability of SSS in the tropical Indian Ocean are discussed. Through a physical model, phase lags between P‐E and SSS and between OLR and P‐E are estimated and their incorporation into the algorithms is suggested for improvement in the estimation of SSS. This SSS information is useful to the studies on coupled models, El Niño‐Southern Oscillation forecast models, and Ocean Global Circulation Models or regional scale circulation models.
Regional water quality mapping through the assimilation of spaceborne remote sensing data to ship‐based transect observations
Authors: Pulliainen Jouni , Vepsäläinen Jenni , Kaitala Seppo , Hallikainen Martti , Kallio Kari , Fleming Vivi , Maunula Petri
Published: December 2004

Satellite observations and surface‐observed transect data are combined to assess the spatial characteristics of water quality in the Baltic Sea, northern Europe. The technique that optimally assimilates the two data sources is based on Bayes' theorem. The method considers the spatial accuracy characteristics of both transect and satellite data. The mathematical formulation of the method is generally applicable. Hence it can be applied to other environmental monitoring problems as well. This investigation demonstrates its feasibility for water quality mapping. The characteristic under investigation is chlorophyll (chl a) concentration, which is currently operationally monitored in the Baltic Sea at shipborne Alg@line transects, using flow‐through fluorometer sampling systems. In order to optimally extrapolate transect observations the developed method benefits from the full spatial coverage of spaceborne optical spectroradiometer data. The results show that the estimation accuracy of regional chl a concentration during the spring bloom period substantially improves as satellite observations are assimilated to transect data. The assimilation results show significantly higher accuracies than those obtained using either extrapolated transect data or stand‐alone retrieval algorithms for satellite data.
Significance of the Nova Brasilândia metasedimentary belt in western Brazil: Redefining the Mesoproterozoic boundary of the Amazon craton
Authors: Tohver Eric , van der Pluijm Ben , Mezger Klaus , Essene Eric , Scandolara Jaime , Rizzotto Gilmar
Published: December 2004

The Nova Brasilândia metasedimentary belt (NBMB) of western Brazil marks a fundamental crustal boundary in the Amazon craton. The metasedimentary rocks of the NBMB (calc‐silicates, metapelites, quartzites, metabasites) contrast strongly with the older, polycyclic granitoid rocks of the adjacent Amazon craton. Aeromagnetic anomalies indicate that the belt is continuous for at least 1000 km in an E‐W direction, although the easternmost extent of the NBMB is covered by the Cretaceous sediments of the Parecis Formation. Additional geologic evidence suggests that the belt extends along an E‐W trend for ∼2000 km. The northern portion of the NBMB preserves vestiges of an early high pressure‐temperature (P‐T) assemblage (kyanite + staurolite) overprinted by sillimanite during prograde metamorphism. A higher metamorphic grade is observed in the southern portion of the belt, with peak conditions calculated to be 800 MPa and 800°C for granulitic assemblages. The combined P‐T path demonstrates that the competing processes of imbrication (northern domain) and magma generation (southern domain) are responsible for regional metamorphism and crustal thickening. Cooling from peak metamorphic conditions is recorded by U‐Pb monazite ages of 1090 Ma and titanite ages of ∼1060 Ma. Integrated cooling rates of 2°–3°C/Myr from regional metamorphism are calculated from these U/Pb ages combined with 40Ar/39Ar ages of hornblende (∼970 Ma) and biotite (∼910 Ma). The NBMB marks the Mesoproterozoic limit of the SW Amazon craton. The discordance of the NBMB to the NNW structural trend of the younger Aguapeí belt (200 km SE of NBMB), together with marked differences between the two belts in sedimentary environment, metamorphic grade, and timing of deformation, signify that these two belts are not geologically continuous. The “Grenvillian” deformation recorded by the NBMB belt marks the final docking of the Amazon craton and Paragua craton within the Rodinia framework. The Aguapeí belt, in contrast, seems to record only limited deformation internal to the Paragua craton.
Climate variability in central equatorial Africa: Influence from the Atlantic sector
Authors: Todd Martin C. , Washington Richard
Published: December 2004

We document a strong teleconnection between Central Equatorial African (CEA) rainfall (and Congo River discharge) and the large‐scale circulation over the North Atlantic, throughout the boreal winter/spring season. Positive rainfall anomalies over CEA (at interannual and multi‐annual timescales) are related to anomalous westerly mid‐tropospheric zonal winds over the CEA/Atlantic region. These anomalies appear to be part of a coherent structure of zonal wind anomalies extending to the polar regions of the North Atlantic, similar to that associated with the NAO pattern. Idealised model simulations suggest that at least over the tropical and subtropical latitudes of the Atlantic/African sector such a signal may be associated with SST forcing from the Tropical North Atlantic (TNA) region. We conclude that TNA SSTs may force these circulation anomalies over CEA at multi‐annual timescales but at interannual timescales they may be relatively independent of TNA SSTs.
A potential thermal erosion lava channel on Io
Authors: Schenk Paul M. , Williams David A.
Published: December 2004

We have discovered a prominent >190 km long, ∼0.5–6 km wide lava channel on Io. The channel is sinuous with interior islands and may be associated with the active Tawhaki Patera hotspot. Photoclinometric analysis of the Galileo images indicates that this channel, provisionally named Tawhaki Vallis, is ∼40–65 m deep. Although a constructional contribution cannot be ruled out, the depth, morphology, and sinuosity of the channel is consistent with erosion by lava. Erosion of flowing silicate over silicate substrate or flowing sulfur over sulfur substrate likely requires eruption durations of days to months to form an ∼50 m deep channel, whereas flowing silicate over a sulfur substrate or flowing sulfur over a frozen SO2 substrate would likely require only hours to days. Future spacecraft observation of actively forming lava channels on Io are possible and desirable.
Field evidence for geophysical detection of subsurface zones of enhanced microbial activity
Authors: Atekwana Eliot A. , Atekwana Estella , Legall Franklyn D. , Krishnamurthy R. V.
Published: December 2004

Geochemical data from closely spaced vertical intervals in a hydrocarbon‐impacted aquifer were used to assess the relationship between bulk conductivity and zones of enhanced microbial activity. The bulk conductivity was measured using in situ vertical resistivity probes. Microbial activity was verified using terminal electron acceptors (nitrate, sulfate, iron, and manganese), dissolved inorganic carbon (DIC), and major ion chemistry. Peaks in bulk conductivity in the aquifer overlapped with zones where nitrates and sulfates were depleted, total petroleum hydrocarbon, iron, manganese, dissolved ions, and DIC were elevated, suggesting a link between higher electrical conductivity and zones of enhanced microbial activity stimulated by the presence of hydrocarbon. Thus the subsurface expression of microbial activity is apparently recorded in the bulk conductivity measurements. Our results argue for combining geophysics with biogeochemistry studies to delineate subsurface zones of enhanced microbial activity.
An ultrasonic frequency sweep interferometer for liquids at high temperature: 2. Mechanical assembly, signal processing, and application
Authors: Ai Yuhui , Lange Rebecca
Published: December 2004

The design and application of a frequency sweep (FS) interferometer for sound speed measurements on high‐temperature silicate liquids, with the potential to be applied to liquids at high pressure, are presented. FS interferometry differs from variable path length interferometry in that no mechanical movement of a buffer rod is required. Instead, a wideband pulse spanning 1–2 MHz is transmitted down the upper buffer rod, which allows maxima/minima in the returned signal to be evaluated as a periodic function of frequency. Measurements may be made at several different centered frequencies (from 3 to 7 MHz with the transducer used in this apparatus) in order to test whether the liquid sound speed is frequency‐independent and thus relaxed. This paper describes the mechanical assembly and the algorithms for signal and data processing, which are based on the solutions to the wave equations in a rod‐liquid‐rod interferometer. The precision and accuracy of the FS interferometer is demonstrated by measuring the relaxed sound velocities in six liquids (NaCl, a sodium silicate, two sodium aluminosilicates, CaMgSi2O6, and Fe2SiO4) with well‐known sound speeds from the literature.
Three‐dimensional viscoelastic finite element model for postseismic deformation of the great 1960 Chile earthquake
Authors: Hu Y. , Wang K. , He J. , Klotz J. , Khazaradze G.
Published: December 2004

We develop a three‐dimensional viscoelastic finite element model to study postseismic deformation associated with the 1960 great Chile earthquake. GPS observations 35 years after the earthquake show that, while all coastal sites are moving landward, a group of inland sites 200–400 km from the trench are moving seaward and that coastal velocities in the 1960 rupture area are distinctly smaller than those to the north. We explain these observations in terms of mantle stress relaxation. The earthquake stretches the upper plate to move seaward, but elastic stresses coseismically induced in the upper mantle resist this motion. Stress relaxation allows seaward motion to take place in the inland area for several decades following the earthquake. With a viscosity of 2.5 × 1019 Pa s for the continental upper mantle, the model well explains the GPS observations. Numerical tests suggest that the continental mantle viscosity value is reasonably well constrained. The model shows the prolonged postseismic seaward motion of the inland area to be a unique feature of earthquakes with very long rupture along strike and large coseismic fault slip. For short rupture and small coseismic slip, the motion will stop very quickly after the earthquake, explaining why this phenomenon is not more commonly observed. With an oceanic mantle viscosity of 1020 Pa s, the model also provides an explanation for tide‐gauge constrained postseismic uplift 200 km from the trench that had previously been explained using a model of prolonged afterslip of a deep segment of the Chile subduction fault.
Seasonal variations of precipitation δ18O in eastern Asia
Authors: Posmentier Eric S. , Feng Xiahong , Zhao Meixun
Published: December 2004

Climate change often occurs through changes in seasonal influences, but paleoclimate records rarely have intra‐annual resolution. The precipitation δ18O, either directly measured or indirectly inferred from other datable materials, is one of the most widely used proxies for paleoclimate studies. It is important, therefore, that we understand the seasonal distribution of meteoric δ18O in relation to climate dynamics. In most midlatitude and high‐latitude land areas, the precipitation is 18O enriched in the summer and depleted in the winter. However, this isotopic seasonality is reversed in the coastal regions of east Asia, while farther inland it returns to a summer‐enriched/winter‐depleted seasonal distribution. This spatial distribution of the isotopic seasonality in east Asia has been previously observed, but the mechanisms causing it have not been adequately explained. In this paper, we discuss nine climatic factors that influence isotopic seasonality, either summer‐enriched or the reverse. Using a simple two‐dimensional δ18O model, we show that one of the important mechanisms for the observed isotopic pattern in Asia may be interseasonal variations in vertical atmospheric stability. These variations are reflected in the large‐scale vertical advection of the Walker circulation and in small‐scale diffusional mixing, both of which are modulated by the greater stability of air above land relative to that above the ocean in the winter and the opposite in the summer. Our results indicate that the complex causes of interseasonal, interannual, and interepochal variations of meteoric δ18O require considerable caution in the attribution of records of past δ18O variations to changes in specific climate variables.
Conditional nonlinear optimal perturbations as the optimal precursors for El Nino–Southern Oscillation events
Authors: Duan Wansuo , Mu Mu , Wang Bin
Published: December 2004

We used the approach of conditional nonlinear optimal perturbation (CNOP) to investigate optimal precursors for El Nino–Southern Oscillation (ENSO) events with a theoretical coupled ocean‐atmosphere model. The CNOPs of the annual cycle of the coupled system were computed for different time periods, and the derived CNOPs were compared with the linear singular vectors (LSVs). The results show the existence of the CNOPs of annual cycle and local CNOPs. These CNOPs have the robust optimal patterns, which have opposite polarities in sea surface temperature and thermocline depth anomalies in the eastern equatorial Pacific. We demonstrate that the CNOP (local CNOP), rather than LSVs, has the highest likelihood to develop into an El Nino (La Nina) event; thus the CNOPs (local CNOPs) can be regarded as the optimal precursors for El Nino (La Nina) events. These optimal precursors agrees qualitatively well with the observations of period of 1980–2002. On the basis of the nonlinear oscillation described by the model, the physical mechanism of the optimal precursors for ENSO is discussed.
A principal component noise filter for high spectral resolution infrared measurements
Authors: Antonelli P. , Revercomb H. E. , Sromovsky L. A. , Smith W. L. , Knuteson R. O. , Tobin D. C. , Garcia R. K. , Howell H. B. , Huang H.‐L. , Best F. A.
Published: December 2004

This paper describes the application of principal component analysis to reduce the random noise present in the hyperspectral infrared observations. Within a set of spectral observations the number of components needed to characterize the atmosphere is far less than the number of wavelengths observed, typically by a factor between 50 and 70. The higher‐order components, which mainly serve to characterize noise, can be eliminated along with the noise that they characterize. The results obtained depend on the variability of the selected sets of observations and on specific instrument characteristics such as spectral resolution and noise statistics. For a set of 10,000 Fourier transform spectrometer (FTS) simulated spectra, whose standard deviation is about 10% of the mean, we were able to obtain noise reduction factors between 5 and 8. Results obtained from real FTS, with standard deviation of about 10% of the mean, indicated practical noise reduction between 5 and 6. To avoid loss of information in the presence of highly deviant observations, it is necessary to use a conservative number of principal components higher than the optimum to maximum noise reduction. However, even then, noise reduction factors of 4 are still achievable.
Definitions and sharpness of the extratropical tropopause: A trace gas perspective
Authors: Pan L. L. , Randel W. J. , Gary B. L. , Mahoney M. J. , Hintsa E. J.
Published: December 2004

Definitions of the extratropical tropopause are examined from the perspective of chemical composition. Fine‐scale measurements of temperature, ozone, carbon monoxide, and water vapor from approximately 70 aircraft flights, with ascending and descending tropopause crossings near 40°N and 65°N, are used in this analysis. Using the relationship of the stratospheric tracer O3 and the tropospheric tracer CO, we address the issues of tropopause sharpness and where the transitions from troposphere to stratosphere occur in terms of the chemical composition. Tracer relationships indicate that mixing of stratospheric and tropospheric air masses occurs in the vicinity of the tropopause to form a transition layer. Statistically, this transition layer is centered on the thermal tropopause. Furthermore, we show that the transition is much sharper near 65°N (a region away from the subtropical jet) but spans a larger altitude range near 40°N (in the vicinity of the subtropical jet). This latter feature is consistent with enhanced stratosphere‐troposphere exchange and mixing activity near the tropopause break.
Comparison of atmospheric temperatures obtained through infrared sounding and radio occultation by Mars Global Surveyor
Authors: Hinson D. P. , Smith M. D. , Conrath B. J.
Published: December 2004

Mars Global Surveyor monitors temperatures in the Martian atmosphere through infrared sounding by the Thermal Emission Spectrometer (TES) as well as Radio Science (RS) occultation experiments. We report results from extensive comparisons of TES nadir and RS temperature profiles, focusing on data obtained under conditions that allow nearly simultaneous measurements at the same location and local time. We analyzed data from 13 intervals with durations of 7–19 sols that sample latitudes of 62°–85°N during midspring through early autumn. Our results generally confirm the accuracy and reliability of both sets of observations. We find particularly good agreement between the zonal variations of temperature observed by the two instruments. Zonally averaged temperature profiles agree to within ∼2 K at pressures <400 Pa. Results are less satisfactory at 610 Pa, where the TES retrievals are persistently warmer by a margin of 2–8 K. These discrepancies arise primarily from a wide disparity in vertical resolution. The RS measurements reveal subtle but significant vertical variations of temperature, particularly at low altitudes, that the TES is unable to resolve. For the range of latitudes and seasons considered here, the most serious consequence is that vertical gradients of temperature deduced from TES profiles are unreliable in the lowest scale height above the surface. Our analysis also shows that the RS profiles from selected intervals might contain a low‐altitude bias due to the unmodeled effect of water vapor. These results should contribute to a more confident characterization of Martian climate.
Semianalytical solutions for fluid flow in rock joints with pressure‐dependent openings
Authors: Murphy Hugh , Huang Cunkui , Dash Zora , Zyvoloski George , White Andrew
Published: December 2004

If fluid is injected into joints in rock masses, the pressure required might result in changes in the joint space between rock blocks that accommodate the fluid transport. At one extreme, very low injection rate and pressure, the joint space is unaffected, and the fluid pressure follows the usual law of linear diffusion. At the opposite extreme, very high injection rates, as used, for example, during hydraulic fracturing, the pressure is so high as to overcome the original Earth stress holding the rock blocks in contact. They “lift off,” resulting in huge changes in joint space, and the flow equation then becomes so nonlinear that pressure pulses are no longer transmitted in a smooth, diffusive manner but more like a propagating shock wave. In between these extremes, at more modest pressure, the result is not liftoff, but nevertheless, the effective stress tending to close the joint space is reduced; this space dilates, and the effective permeability and storativity of the joint will increase. While the pressure wave will not propagate quite as sharply as it does for liftoff, nonlinearities greatly influence the results, exhibiting behavior far from that predicted by linear diffusion.
Interannual variability of summer mean soil moisture conditions in Switzerland during the 20th century: A look using a stochastic soil moisture model
Authors: Calanca Pierluigi
Published: December 2004

The interannual variability of summer mean soil moisture conditions in Switzerland during the 20th century was studied using a stochastic soil moisture model. The model was validated against high‐quality observations of the water balance at a representative location. The summer mean degree of saturation was found to fluctuate around the point of stomatal closure at low elevations to the north of the Alps, clearly above this threshold at higher elevations and to the south of the Alps, and systematically below this limit in the inner‐Alpine domain. In addition, the results indicated that the largest interannual variability occurs at low elevations. A linearization of the model revealed that interannual variations of summer mean soil moisture are driven in order of importance by variations in the rate of storm arrivals, joint variations in the rate of storm arrivals and maximum evapotranspiration, and variations in mean rainfall depth. This was explained in terms of the sensitivities of seasonal mean soil moisture with respect to the driving parameters.
Relationship between the optical gap and the optical-absorption tail breadth in amorphous GaAs
Authors: Dias da Silva J. H. , Campomanes R. R. , Leite D. M. G. , Orapunt Farida , O’Leary Stephen K.
Published: December 2004

We study the relationship between the optical gap and the optical-absorption tail breadth for the case of amorphous gallium arsenide (a-GaAs). In particular, we analyze the optical-absorption spectra corresponding to some recently prepared a-GaAs samples. The optical gap and the optical-absorption tail breadth corresponding to each sample is determined. Plotting the optical gap as a function of the corresponding optical-absorption tail breadth, we note that a trend, similar to that found for the cases of the hydrogenated amorphous silicon and hydrogenated amorphous germanium, is also found for the case of a-GaAs. The impact of alloying on the optical-absorption spectrum associated with a-GaAs is also briefly examined.
Optical and magnetic properties of Mn+-implanted GaAs
Authors: Shon Yoon , Park Y. S. , Chung K. J. , Fu D. J. , Kim D. Y. , Kim H. S. , Kim H. J. , Kang T. W. , Kim Yongmin , Fan X. J. , Park Y. J.
Published: December 2004

Neutron-transmutation-doped GaAs samples were prepared by irradiating the middle-level neutrons into the semi-insulating GaAs grown by a liquid encapsulated Czochralski method and subsequently implanted with Mn+. The characteristics of the Mn+-implanted neutron-transmutation-doped GaAs (namely, the implantation of Mn+ subsequent to neutron-transmutation-doping) were investigated by various measurements. The result of the energy dispersive x-ray peak displayed an injected Mn concentration of 9.65%. The photoluminescence peaks related to carbon and germanium acceptors were resolved, and the peaks related to Mn due to a neutral Mn acceptor were evidently observed. It is found that the proper activation for the neutral Mn acceptor starts from a relatively low annealing temperature of 600°C for 15min. The atomic force microscopy and magnetic forcemicroscopy images showed that magnetic clusters were well formed. The ferromagnetic hysteresis loop measured at 10K was observed, and the temperature-dependent magnetization revealed that the two different phases exist at 135 and 360K. The Curie temperature (Tc∼360K) is caused by MnAs, which agrees with the clusters of the magnetic force microscopy image.