North-south Variation Research Articles

Responses of diatom assemblages and life cycle to sea ice variation in the eastern Indian sector of the Southern Ocean during austral summer 2018/2019

In the Southern Ocean, rapid environmental changes (warming, freshening, and poleward shifts of the physiological fronts) are underway. These changes affect the distribution, abundance, and life cycle of protists. However, the spatial distribution of protists is not well understood in the eastern Indian sector of the Southern Ocean. We, therefore, evaluated the effects of environmental factors at the community level (abundance and species composition) and species-specific level (life cycle in diatoms) based on field sampling during the austral summer of 2018/2019. High chlorophyll levels and protist cell densities were observed in the eastern area from 120°E, in contrast to the distribution reported in the 1996 BROKE (The Baseline Research on Oceanography, Krill and the Environment) survey. This inter-annual variation was caused by differences in the sampling periods, nutrients, and zooplankton grazing pressures. North–south variation in protist abundance was well explained by silicate distribution, whereas sea ice variation did not influence it explicitly. The clustering of protist groups was well associated with nutrients, but locally, offshore groups were extended southward by currents and eddies. The cell size of the two dominant Fragilariopsis curta and F. kerguelensis exhibited similar significant relationships with sea ice variation and decreased 60 days after sea ice melted. Our findings demonstrate that sea ice changes do not clearly affect the protist community level but potentially affect the life cycle level of diatoms.

Annual sea level variations off Atlantic Canada from satellite altimetry

Annual cycle of sea level off Atlantic Canada has been investigated based on a merged satellite altimetry dataset and a monthly temperature and salinity dataset. The altimetric results were compared with coastal tide-gauge data and steric height calculated from the temperature and salinity dataset. There was a general north-south variation in the amplitude of the altimetric annual cycle, increasing from 4 cm in the Labrador Sea to 15 cm in the Gulf Stream and the North Atlantic Current Region. The annual cycle in the deep ocean can approximately be accounted for by the steric height variability relative to 700 m, in which the thermosteric effect was the dominant contributor. The halosteric effect over the continental slope, especially over the northern Labrador Slope was also important. While the thermosteric effect occurred dominantly at the top 100 m water column, there was substantial halosteric variation in the 100–300 m water column. The annual sea level cycle along the Canadian Atlantic coast showed a complicated pattern in amplitude, but the phase was highly coherent with the highest sea level in fall. The steric height accounts for a substantial portion of the coastal annual cycle, but other factors such as wind forcing may be equally important.

Variation model of north-south plant species diversity in the Qinling-Daba Mountains in China

Understanding the variation patterns of mountain plant species diversity is becoming increasingly important in forest ecosystem management and protection. However, the research on plant species diversity has mainly focused on changes in whole plant species. Therefore, an in-depth study of the change mode of plant species via different classification methods and its impact on the overall change in plant diversity is very important for forestland restoration and biodiversity protection. In this study, the Qinling-Daba Mountains, a major feature of China's north–south transitional zone, were selected as the study area. Based on the floristic data of 58 nature reserves in the Qinling-Daba Mountains and its adjacent areas, the north–south change patterns of plant orders, families, genera and species diversity were first analyzed. Second, plant species were divided into different groups according to taxonomic group (orders, families and genera), life form (trees, shrubs and herbs) and endemism (species endemic and nonendemic to China). The change patterns of each group in the north–south direction were analyzed. Finally, the effects of different groups on the north–south change patterns of whole species are discussed. The species diversity of orders, genera and species exhibited a typical latitudinal gradient pattern, specifically, it gradually decreases from south to north, but the species diversity is relatively scattered. According to the north–south variation in species diversity in each order, families and genus, 5% of the orders, 2% of the families and 6% of the genera were positively correlated with latitude, and the rest were negatively correlated or uncorrelated. According to the north–south variation patterns of different life forms, the diversity of trees and shrubs showed a bimodal Gaussian distribution with latitude. According to the north–south variation patterns of plant endemism, the diversity of endemic species showed a Gaussian distribution with latitude, but the diversity of nonendemic species was negatively correlated with latitude. The dispersion of whole species diversity is caused by species in a few orders, families and genera, trees and shrubs, and endemic species. They may be more strongly affected by the vertical zonality of the mountains, which is inconsistent with the typical latitude gradient model. Our research will provide a basis for forestland management, nature reserve establishment and biodiversity conservation. • We examined a latitudinal gradient model of plant diversity in the Qinling-Daba Mountains. • The latitudinal gradient patterns of a few taxa are inconsistent with the typical patterns. • The relationships between tree and shrub diversity and latitude have Gaussian distributions. • Qinling-Daba Mountains is one of distribution areas of species endemic to China.

Detrital Zircon U-Pb Geochronology of Upper Devonian and Lower Carboniferous Strata of Western Laurentia (North America): A Record of Transition from Passive to Convergent Margin

Abstract The Late Devonian-Early Carboniferous (DC) Antler orogeny in southwestern Laurentia is contemporaneous with influx of clastic sediments, unconformities, and volcanism across much of western Laurentia (WL), suggesting the demise of the Paleozoic passive margin. However beyond the type Antler orogeny in southwestern Laurentia, the DC tectonic setting is still unclear. Westerly sediment provenance has been suggested as evidence of a convergent margin setting in a foreland basin. However, there is a gap in our understanding in central WL (Alberta and Montana) despite the fact that paleogeographic reconstructions place this area at the centre of WL. We provide detrital zircon (DZ) U-Pb geochronological data from strata in Alberta, Montana, and Nevada that are synchronous with the Antler orogeny to constrain sediment dispersal patterns and test the westerly sediment sourcing hypothesis. We show three DZ facies specific to particular geographic locations: DZ facies 1 in southern Nevada has a prominent subpopulation of early to mid-Mesoproterozoic (mode at 1430 Ma), DZ facies 2 in northeastern Nevada has a late Paleoproterozoic population (mode at 1823 Ma), and DZ facies 3 in Alberta and Montana displays Mesoproterozoic to Neoproterozoic (mode at 1036 Ma), mid-Paleozoic (mode at 411 Ma), and depositional (ca. 360-340 Ma) ages. North-south variation in DZ facies indicates that WL basins were locally sourced from various tectonic fragments having different signatures. Comparing our data with published data, we show that WL is dominated by DZ recycled from uplifted older strata with input from mid-Paleozoic arc terrane (s) to the west. Westerly sourcing is evidenced by the presence of near-depositional ages and affinities of this study’s DZ facies with strata located to the west. Our results and geological evidence from other studies suggest that the Antler orogeny triggered a depositional shift and controlled sediments dispersal in WL, signaling the demise of the Paleozoic passive margin.

Variation in the Positioning of the Asian Summer Monsoon Boundary in the Tibetan Plateau and Potential Drivers

Studying the variation in the boundary position of the Asian summer monsoon in the Tibetan Plateau (TP) region and its potential drivers is important for understanding the climate in this region. Three sets of mean monthly precipitation data from 1980 to 2019 were sourced from the Global Precipitation Climatology Centre, the Climate Research Unit, and China Meteorological Information Service Centre. Several indicators that represent the Asian summer monsoon boundary (ASMB) were selected to compare their applicability to the TP region and elucidate the changes in the location of the ASMB in the TP over the last four decades. The results showed that the ASMB in the TP region extends in a southwest-northeast direction, with a clear north-south variation. It reaches as far north as the Kunlun Mountains and as far south as the Himalayas. The largest amplitude in spatial fluctuation occurs in the middle of the TP, and the smallest amplitude occurs at both ends of the region. A “small-large-small” fluctuation pattern was observed from west to east. The water vapor mainly originates from the South Asian region. The South Asian summer monsoon can move the ASMB position northward, whereas the westerly wind moves the ASMB position southward. Variation in the ASMB in the TP region is closely associated with the South Asian monsoon and westerly wind.

Structural characterization of the Phitsanulok basin, onshore Thailand, and regional tectonic implications

The Phitsanulok basin is the largest onshore rift basin in Thailand and has been a major hydrocarbon producer for over 30 years. The basin formed in the mid-Cenozoic and was episodically reactivated after the early Miocene from nearby active tectonics, including the India-Asia collision. The basin is formed near a key tectonic transition between north and south Thailand between 16°N and 18°N. Previous studies recognized a north-south variation in structural styles across the Phitsanulok basin that may express deeper basement structures. The northern Phitsanulok basin is predominantly extensional whereas the southern basin shows unconformities, folding, and reverse faults from stronger inversion. Here we systematically characterize structural domains within the Phitsanulok basin from a basin-wide 2D and 3D petroleum industry seismic dataset and examine our observations within the context of regional tectonics. Our analysis includes time structure and isochron maps, spatial fault patterns, fault dip angles, fault throws, and fault azimuths. We find the most dramatic structural changes occur between the northern and southern Phitsanulok basin across 16°50′N latitudes. North of 16°50′N, the Phitsanulok basin has near-planar, steeply-dipping normal faults; arrays of low displacement, cross-cutting synthetic and antithetic extensional faults; and, a thickened and relatively undeformed Sukhothai depression that had up to 1700 ms two-way time (TWT) thickness (~2.3 km) between the Pliocene to Upper Early Miocene strata. In contrast, south of 16°50′N the basin has listric extensional faults; an abruptly thinner stratigraphic section (~400 ms TWT between the Pliocene to Upper Early Miocene strata; ~0.4 km), more gently-dipping faults, and larger fault throws. Our interpreted 16°50′N structural transition occurs near the southern limit of major earthquakes, changes in regional fault trends, and ENE-WSW magnetic lineaments and may highlight deep basement fabrics.

Multiple movement characteristics of the Meiyu rain belt in East Asia: reconstructing historical data on the southern margin from 1861 to 2017

The location of the Meiyu belt has an important influence on the summer precipitation pattern in East Asia. In this study, historical diary-recorded data and modern instrument-measured data were used to reconstruct the Meiyu sequence at its southern margin from 1861 to 2017. Combining with the variation of Meiyu intensity in the middle and lower Yangtze River Valley (YRV) and the Huai River Valley (HRV), this study discussed the change characteristics of the Meiyu rain belt. The overall shift of the Meiyu belt is basically the same as the change to the southern margin of the rain belt which has interdecadal and multidecadal north-south shifts. The northward shift of the rain belt after 2000 occurred only as an interdecadal fluctuation. The summer monsoon is the main factor for the shift of the Meiyu belt on a multidecadal-centennial scale, AMO (Atlantic Multidecadal Oscillation) has a certain role in modulation, and PDO (Pacific Decadal Oscillation) is the decisive factor for the interdecadal scale of the Meiyu belt position. When PDO is in a positive (negative) phase, the whole Meiyu belt tends to be strong (weak) and shifts to the South (North). AMO and IOBM (Indian Ocean Basin Mode) play a particular role in modulation. The shift of the Meiyu belt is usually consistent with the north-south variation of the main rain belt of eastern China. Its location may play a role in predicting summer precipitation in North China.

Development of surface ruptures by hanging-wall extension over a thrust ramp along the Ragged Mountain fault, Katalla, Alaska, USA: Applications of high-resolution three-dimensional terrain models

AbstractHigh-resolution three-dimensional terrain models are used to evaluate the Ragged Mountain fault kinematics (Katalla, Alaska, USA). Previous studies have produced contradictory interpretations of the fault’s kinematics because surface ruptures along the fault are primarily steeply dipping, uphill-facing normal fault scarps. In this paper, we evaluate the hypothesis that these uphill-facing scarps represent extension above a buried thrust ramp. Detailed geomorphic mapping along the fault, using 20-cm-resolution aerial imagery draped onto a 1-m-resolution lidar (light detection and ranging) elevation model, was used to produce multiple topographic profiles. These profiles illustrate scarp geometries and prominent convex-upward topographic surfaces, indicating significant disturbance by active tectonics. A theoretical model is developed for fault-parallel flow over a thrust ramp that shows the geometric relationships between thrust displacement, upper-plate extension, and ramp dip. An important prediction of the model for this study is that the magnitude of upper-plate extension is comparable to, or greater than, the thrust displacement for ramps with dips greater than ∼45°. This model is used to analyze profile shapes and surface displacements in Move software (Midland Valley Ltd.). Analyses of scarp heights allow estimates of hanging-wall extension, which we then use to estimate slip on the underlying thrust via the model. Assuming a low-angle (30°) uniformly dipping thrust and simple longitudinal extension via normal faulting, variations in extension along the fault would require a slip gradient from ∼8 m in the north to ∼22 m in the south. However, the same north-south variation in extension with a constant slip of 8–10 m may infer an increase in fault dip from ∼30° in the north to ∼60° in the south. This model prediction has broader implications for active-fault studies. Because the model quantifies relationships between hanging-wall extension, fault slip, and fault dip, it is possible to invert for fault slip in blind thrust ramps where hanging-wall extension is the primary surface manifestation. This study, together with results from the St. Elias Erosion and Tectonics Project (STEEP), clarifies the role of the Ragged Mountain fault as a contractional structure within a broadly sinistral shear system in the western syntaxis of the St. Elias orogeny.

The relative influence of temperature and size‐structure on fish distribution shifts: A case‐study on Walleye pollock in the Bering Sea

AbstractResearch has estimated associations between water temperature and the spatial distribution of marine fishes based upon correlations between temperature and the centroid of fish distribution (centre of gravity, COG). Analysts have then projected future water temperatures to forecast shifts in COG, but often neglected to demonstrate that temperature explains a substantial portion of historical distribution shifts. We argue that estimating the proportion of observed distributional shifts that can be attributed to temperature vs. other factors is a critical first step in forecasting future changes. We illustrate this approach using Gadus chalcogrammus (Walleye pollock) in the Eastern Bering Sea, and use a vector‐autoregressive spatiotemporal model to attribute variation in COG from 1982 to 2015 to three factors: local or regional changes in surface and bottom temperature (“temperature effects”), fluctuations in size‐structure that cause COG to be skewed towards juvenile or adult habitats (“size‐structured effects”) or otherwise unexplained spatiotemporal variation in distribution (“unexplained effects”). We find that the majority of variation in COG (including the north‐west trend since 1982) is largely unexplained by temperature or size‐structured effects. Temperature alone generates a small portion of primarily north–south variation in COG, while size‐structured effects generate a small portion of east–west variation. We therefore conclude that projections of future distribution based on temperature alone are likely to miss a substantial portion of both the interannual variation and interdecadal trends in COG for this species. More generally, we suggest that decomposing variation in COG into multiple causal factors is a vital first step for projecting likely impacts of temperature change.

Mountain Waves, Downslope Winds, and Low-Level Blocking Forced by a Midlatitude Cyclone Encountering an Isolated Ridge

Abstract The interaction of a midlatitude cyclone with an isolated north–south mountain barrier is examined using numerical simulation. A prototypical cyclone develops from an isolated disturbance in a baroclinically unstable shear flow upstream of the ridge, producing a cold front that interacts strongly with the topography. The structure and evolution of the lee waves launched by the topography are analyzed, including their temporal and their north–south variation along the ridge. Typical mountain wave patterns are generated by a 500-m-high mountain, but these waves often exhibit significant differences from the waves produced in 2D or 3D simulations with steady large-scale-flow structures corresponding to the instantaneous conditions over the mountain in the evolving flow. When the mountain height is 2 km, substantial wave breaking occurs, both at low levels in the lee and in the lower stratosphere. Despite the north–south uniformity of the terrain profile, large north–south variations are apparent in wave structure and downslope winds. In particular, for a 24-h period beginning after the cold front passes the upstream side of the ridge toward the south, strong downslope winds occur only in the northern half of the lee of the ridge. Just prior to this period, the movement of the cold front across the northern lee slopes is complex and accompanied by a burst of strong downslope winds and intense vertical velocities.

Paleoenvironmental context of the Middle Stone Age record from Karungu, Lake Victoria Basin, Kenya, and its implications for human and faunal dispersals in East Africa

The opening and closing of the equatorial East African forest belt during the Quaternary is thought to have influenced the biogeographic histories of early modern humans and fauna, although precise details are scarce due to a lack of archaeological and paleontological records associated with paleoenvironmental data. With this in mind, we provide a description and paleoenvironmental reconstruction of the Late Pleistocene Middle Stone Age (MSA) artifact- and fossil-bearing sediments from Karungu, located along the shores of Lake Victoria in western Kenya. Artifacts recovered from surveys and controlled excavations are typologically MSA and include points, blades, and Levallois flakes and cores, as well as obsidian flakes similar in geochemical composition to documented sources near Lake Naivasha (250 km east). A combination of sedimentological, paleontological, and stable isotopic evidence indicates a semi-arid environment characterized by seasonal precipitation and the dominance of C4 grasslands, likely associated with a substantial reduction in Lake Victoria. The well-preserved fossil assemblage indicates that these conditions are associated with the convergence of historically allopatric ungulates from north and south of the equator, in agreement with predictions from genetic observations. Analysis of the East African MSA record reveals previously unrecognized north–south variation in assemblage composition that is consistent with episodes of population fragmentation during phases of limited dispersal potential. The grassland-associated MSA assemblages from Karungu and nearby Rusinga Island are characterized by a combination of artifact types that is more typical of northern sites. This may reflect the dispersal of behavioral repertoires—and perhaps human populations—during a paleoenvironmental phase dominated by grasslands.

Subsurface Zonal and Meridional Flow Derived from GONG and SDO/HMI: A Comparison of Systematics

We study the subsurface flows in the near-surface layers of the solar convection zone from the surface to a depth of 16 Mm derived from Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) Dopplergrams using a ring-diagram analysis. We characterize the systematic east–west and north–south variations present in the zonal and meridional flows and compare flows derived from GONG and HMI data before and after the correction. The average east–west variation with depth of one flow component resembles the average north–south variation with depth of the other component. The east–west variation of the zonal flow together with the north–south variation of the meridional flow can be modeled as a systematic radial velocity. This indicates a solar center-to-limb variation as the underlying cause. The north–south variation of the zonal flow and the east–west variation of the meridional flow require two separate functions. The east–west variation of the meridional flow consists mainly of an annual variation with the B0 angle, while the north–south trend of the zonal flow consists of a constant non-zero component in addition to an annual variation. This indicates a geometric projection artifact. After compensating for these systematic effects, the meridional and zonal flows derived from HMI data agree well with those derived from GONG data. An offset remains between the zonal flow derived from GONG and HMI data. The equatorward meridional flows at high latitude that appear episodically depending on the B0 angle are absent from the corrected flows.

Harmonic and statistical analyses of the gravity and topography of Vesta

We examine the gravity and topography of the asteroid 4 Vesta, as recently revealed by the Dawn mission. The observed gravity is highly correlated with the observed topography, and suggests little lateral variation in density. The variance spectra of both gravity and topography follow power laws which are very similar to those seen for the Moon, Mars, Venus, and Earth. A significant way in which Vesta differs from these larger silicate bodies is that both gravity and topography are significantly anisotropic, with more north–south variation than east–west variation. Rapid rotation plausibly contributes to this anisotropy, but only at harmonic degree two. The remainder of the anisotropy appears related to the large impacts which formed the Rheasilvia and Veneneia basins. We note that, as usual, gravitational inverse problems are non-unique. While the observed gravity and topography of Vesta do not preclude existence of a metallic core, they certainly do not require it.

Strain rate tensor in Iran from a new GPS velocity field

The aim of this paper is to determine the strain rate tensor (SRT) for the Iranian region. In this study, (1) we apply a method of computation of the SRT never used for the Iranian area and (2) we use a new GPS velocity field obtained from several previously published velocity fields. First, the method is described and tested on a synthetic case, which mimics the real Iranian case. The synthetic tests confirm that the method allows us to both retrieve high gradients of the strain rate field and reduce the effect of an erroneous velocity vector. Second, the method is applied to a real data set covering the Arabia-Eurasia collision zone in Iran.We particularly focus on the Zagros-Makran transition zone, the Central Iran region and the northernmost part of the Arabia-Eurasia collision zone (NW Iran-Caucasus-East Turkey).Whereas themain characteristics of the obtained SRT are consistent with known tectonic features, important new results are found in the Central Iran, with the strike-slip style along the Anar and Deshir faults, and the Zagros-Makran transition zone, with a north-south variation of the SRT along the Zendan-Minab-Palami fault system. We link these results to recent active tectonic studies.

Seasonal and Monthly Variation of Vertical Structure of Temperature, Salinity and Heat Flux of the Bay of Bengal

Seasonal and monthly variations of heat flux have been investigated in this study using the Modular Ocean Model of version 3 (MOM 3) simulations and 52 years Simple Ocean Data Assimilation (SODA) products. These variations of the heat flux in different boxes of the Bay of Bengal (BOB) in different depths show the different behavior of the boxes. It is seen that the model and SODA results are comparable. The basin shows north-south variation in the surface from winter to spring whereas there is east-west variation in the mixed layer throughout the year except winter. The remote effect caused by warm water penetration from Pacific Ocean through the Strait of Malacca and coastal Kelvin waves keeps the basin warm most of the year. This article addresses the mechanisms of the seasonal variation of the vertical structure of the temperature and heat flux components.

Syncollisional extension along the India–Asia suture zone, south-central Tibet: Implications for crustal deformation of Tibet

Crustal deformation models of the Tibetan plateau are assessed by investigating the nature of Neogene deformation along the India–Asia suture zone through geologic mapping in south-central Tibet (84°30′E). Our mapping shows that the suture zone is dominated by a system of 3 to 4 ENE-striking, south-dipping thrust faults, rather than strike-slip faults as predicted by models calling upon eastward extrusion of the Tibetan plateau. Faults along the suture zone are not active, as they are cut by a system of NNW-striking oblique slip normal faults, referred to herein as the Lopukangri fault system. Fault-slip data from the Lopukangri fault system shows that the mean slip direction of its hanging wall is N36W. We estimate the net slip on the Lopukangri fault by restoring components of the thrust system. We estimate that the fault has accommodated ∼ 7 km of right-slip and ∼ 8 km of normal dip-slip, yielding a net slip of ∼ 10.5 km, and 6 km of horizontal east–west extension. The Lopukangri fault system is active and geomorphic offsets indicate right separations and westside-down dip-separation. The mapview curviplanar geometry and geomorphic expression of the Lopukangri fault system is similar to faults and rift basins to its east and west. These extensional faults are en echelon in map view and encompass a region that is 200 km long (east–west) and 95 km wide (north–south). Assuming our results for the Lopukangri fault are applicable to the entire system, we estimate a maximum of 18% extension across the zone. All active faults in the system terminate southward adjacent to the India–Asia suture zone. Because the individual rift geometries are similar and suggest a common kinematic relationship, we propose that the extensional system formed as a trailing extensional imbricate fan at the southern termination of the central Tibet conjugate fault zone. Alternatively, the extensional system may terminate to the north and represent a group of isolated crustal tears. Both kinematic interpretations imply a semi-smooth north–south variation in the magnitude of east–west extension in southern Tibet, with higher magnitudes in the north along the Bangong–Nujiang suture zone than in the south along the India–Asia suture zone. Our results from southern Tibet show that deformation between southern Tibet and the Himalayas is broad (95 km wide) and best described as a continuum possibly since the Late Miocene. Conversely, the structural boundary between western Tibet and the Himalayas, which is defined by the Karakoram fault, is presently a discrete boundary, and probably has been since the Middle Miocene. We think this variation in the displacement gradient and age of these structural boundaries within the interior of Tibet is best explained by the fault patterns and strain history describing wholesale E–W stretching and N–S shortening of the Tibetan crust.

New record, geographic variation and redescription of Apedilum elachistus Townes (Diptera: Chironomidae: Chironominae)

Apedilum elachistus Townes 1945 is recorded from Argentina, representing the southernmost record of this species. Due to dissimilarities found between South and North American specimens a Principal Component Analysis and Minimum Spanning Tree were performed in order to determine if these differences reflect a geographic differentiation. The results show North–South variation in the number of acrostichal setae, number of dorsocentral setae, number of prealar setae, wing length, VR, length of thorax, and length of abdomen for males, and number of gonocoxite IX setae, length of thorax, number of temporal setae, length of palpomere III, wing length, BV2, length of notum, BV1, number of dorsocentral setae, length of palpomere IV, length of abdomen, VR, and length of palpomere V for females. Consequently, Apedilum elachistus is redescribed as larva, pupa, male, and female.

Seasonal and geographical variations in lung cancer prognosis in Norway: Does Vitamin D from the sun play a role?

Seasonal and geographical variations in lung cancer prognosis in Norway: Does Vitamin D from the sun play a role?

The geochemistry of groundwater resources in the Jordan Valley: The impact of the Rift Valley brines

The chemical composition of groundwater in the Jordan Valley, along the section between the Sea of Galilee and the Dead Sea, is investigated in order to evaluate the origin of the groundwater resources and, in particular, to elucidate the role of deep brines on the chemical composition of the regional groundwater resources in the Jordan Valley. Samples were collected from shallow groundwater in research boreholes on two sites in the northern and southern parts of the Jordan Valley, adjacent to the Jordan River. Data is also compiled from previous published studies. Geochemical data (e.g., Br/Cl, Na/Cl and SO 4/Cl ratios) and B, O, Sr and S isotopic compositions are used to define groundwater groups, to map their distribution in the Jordan valley, and to evaluate their origin. The combined geochemical tools enabled the delineation of three major sources of solutes that differentially affect the quality of groundwater in the Jordan Valley: (1) flow and mixing with hypersaline brines with high Br/Cl (>2 × 10 −3) and low Na/Cl (<0.8) ratios; (2) dissolution of highly soluble salts (e.g., halite, gypsum) in the host sediments resulting in typically lower Br/Cl signal (<2 × 10 −3); and (3) recharge of anthropogenic effluents, primarily derived from evaporated agricultural return flow that has interacted (e.g., base-exchange reactions) with the overlying soil. It is shown that shallow saline groundwaters influenced by brine mixing exhibit a north–south variation in their Br/Cl and Na/Cl ratios. This chemical trend was observed also in hypersaline brines in the Jordan valley, which suggests a local mixing process between the water bodies.

Socio-Demographic Variation of Dementia Subtypes in China: Methodology and Results of a Prevalence Study in Beijing, Chengdu, Shanghai, and Xian

Objective: To characterize sociodemographic variations in the prevalence of AD and VaD in China. Methods: Data were collected in a 1997–1998, cross-sectional, door-to-door prevalence survey of 34,807 community residents ages ≧55 years in Beijing, Shanghai, Chengdu and Xian. Initial diagnoses of AD and VaD were assessed by clinicians using standardized protocols, according to the NINCDS-ADRDA and NINDS-AIREN criteria; diagnoses were confirmed after 6 months by repeating neuropsychological evaluations. Prevalence odds ratios were estimated in logistic models adjusting for survey design, age, and other sociodemographic factors. Results: We identified 732 prevalent cases of AD and 295 cases of VaD. Adjusting for all sociodemographic factors concurrently, prevalence odds of AD and VaD were higher in northern versus southern China. Age trends for AD appeared different in western and eastern China. AD also showed an age-adjusted elevation among women and, in the fully adjusted model, a gender education interaction indicating a female preponderance in the highest education group. North-south variation for VaD was age-dependent. In the fully adjusted model, for AD, widowed had significantly higher prevalence odds; for VaD, widowed persons and minorities had significantly lower prevalence odds; professionals had statistically significant and borderline lower prevalence odds for both VaD and AD; sales-service occupations had significantly lower odds for AD only. Conclusion: We observed variations in prevalence for AD and VaD in different regions and demographic groups in China that persisted after controlling for potential confounding factors. Sociodemographic factors are probable surrogates for conditions such as lifestyle, environment, comorbidities, and life expectancy.