Rain Shadow Effect Research Articles

New evidence on the age of the Taklimakan Desert

Research Article| February 01, 2009 New evidence on the age of the Taklimakan Desert Jimin Sun; Jimin Sun * 1Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China *E-mail: jmsun@mail.igcas.ac.cn Search for other works by this author on: GSW Google Scholar Zhenqing Zhang; Zhenqing Zhang 1Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Liyuan Zhang Liyuan Zhang 1Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Geology (2009) 37 (2): 159–162. https://doi.org/10.1130/G25338A.1 Article history received: 13 Jul 2008 rev-recd: 03 Oct 2008 accepted: 13 Oct 2008 first online: 12 Oct 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jimin Sun, Zhenqing Zhang, Liyuan Zhang; New evidence on the age of the Taklimakan Desert. Geology 2009;; 37 (2): 159–162. doi: https://doi.org/10.1130/G25338A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Taklimakan Desert is the world's second-largest shifting sand desert, located in the rain shadow of the Tibetan Plateau. The initiation of desert formation in the Asian interior is one of the most prominent climate changes in the Northern Hemisphere during the Cenozoic Era. Dating the earliest formation of this desert is important for understanding the climatic effects of the uplifted Tibetan Plateau. Here we report 1071-m-thick Neogene deposits with intercalated eolian dune sands from the only outcrop in the central Taklimakan Desert. Based on paleomagnetic measurements, biostratigraphic age control, and previous electron spin resonance dating results, the oldest in situ eolian dune sands were confirmed to be ca. 7 Ma, much older than the previous reported wind-blown siltstone from the southern edge of the Taklimakan Desert. This new result indicates that desert conditions initiated ca. 7 Ma in the center of the Tarim Basin. We attribute this event to the late Cenozoic climatic deterioration and/or to the rain-shadow effect caused by late Miocene uplift of the northern Tibetan margin. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The influence of emergent trees on rainfall distribution in a cacao agroforest (Sulawesi, Indonesia)

Emergent trees may have an influence on the volume and the spatial distribution of water input into agroforestry stands and may thus affect water availability for the main crops. Our goal was to analyze the influence of such trees on rainfall distribution in a cacao agroforest area in the rainforest margin zone of Central Sulawesi, Indonesia. The emergent trees studied belong to the species Bischofia javanica (Phyllanthaceae) and were 15 m high remnants from the natural forest. A set of 96 throughfall gauges was systematically distributed underneath canopies of cacao only, and underneath canopies of cacao plus emergent trees (cacao plus trees). From an earlier study we knew that stemflow can safely be estimated with less than 1% of gross precipitation (Pg). Median throughfall tended to be lower in gauges underneath cacao plus trees than under cacao only ( p⩽0.1), and the estimated rainfall interception loss was 4% and 16% of Pg in cacao only and cacao plus trees plots, respectively. This difference was most likely caused by a tree-induced enhancement of the canopy water storage capacity and an increase in canopy roughness. Underneath the canopy of emergent trees (cacao plus trees), throughfall exceeded gross precipitation east of the tree stems (113%) and was significantly lower ( p⩽0.05) west and north of the tree stems (67–77% of Pg). Significant effects of trees on throughfall did not extend beyond their canopy area. We assume that wind-driven rain was stripped out east of the stems causing an increase in throughfall, while rain-shadow effects led to a decrease in throughfall west and north of the tree stems. Thus, at our study site emergent trees tended to reduce rain water input, and produced clear spatial patterns in throughfall distribution. A reduced water availability may lead to reduced cacao bean yields in times of water scarcity but a more complete assessment of the hydrological function of shade trees in agroforestry systems may also reveal positive influences of shade trees on cacao trees. Such an advanced analysis of hydrological functions still remains to be done.

Throughfall in an evergreen-dominated forest stand in northern Thailand: Comparison of mobile and stationary methods

Throughfall determined by stationary and mobile methods in a disturbed evergreen-dominated forest stand in northern Thailand was 82% of rainfall (1134 mm) during a 4-month study period in the monsoon rain season of 2002. Associated coefficients of variation and standard errors were ≤10% and 2%, respectively, for both methods. Agreement between four stationary trough collectors and 20 mobile standard gauge collectors was achieved only after 35 sampling occasions, having a total rainfall depth >700 mm, and included one storm event >100 mm. Several canopy trees contributed to points with throughfall > rainfall by channeling stemflow to common drip points on the trunk and large limbs. However, no significant correlation was observed between throughfall point measurements and corresponding canopy cover. Although 180-point measurements of throughfall provided a realistic representation of the spatial variability within the 500-m 2 forest stand, it is questionable that they duplicated the basin-scale variability, which would be affected both by tree gaps and variable topographically related rain shadow effects.

Late Quaternary glaciation of Tibet and the bordering mountains: a review

Lehmkuhl, F. & Owen, L. A. 2005 (May): Late Quaternary glaciation of Tibet and the bordering mountains: a review. Boreas, Vol. 34, pp. 87–100. Oslo. ISSN 0300–9483. Abundant glacial geologic evidence present throughout Tibet and the bordering mountains shows that glaciers have oscillated many times throughout the late Quaternary. Yet the timing and extent of glacial advances is still highly debated. Recent studies, however, suggest that glaciation was most extensive prior to the last glacial cycle. Furthermore, these studies show that in many regions of Tibet and the Himalaya glaciation was generally more extensive during the earlier part of the last glacial cycle and was limited in extent during the global Last Glacial Maximum (marine oxygen isotope stage 2). Holocene glacial advances were also limited in extent, with glaciers advancing just a few kilometers from their present ice margins. In the monsoon-influenced regions, glaciation appears to be strongly controlled by changes in insolation that govern the geographical extent of the monsoon and consequently precipitation distribution. Monsoonal precipitation distribution strongly influences glacier mass balances, allowing glaciers in high altitude regions to advance during times of increased precipitation, which are associated with insolation maxima during glacial times. Furthermore, there are strong topographic controls on glaciation, particular in regions where there are rainshadow effects. It is likely that glaciers, influenced by the different climatic systems, behaved differently at different times. However, more detailed geomorphic and geochronological studies are needed to fully explore regional variations. Changes in glacial ice volume in Tibet and the bordering mountains were relatively small after the global LGM as compared to the Northern Hemisphere ice sheets. It is therefore unlikely that meltwater draining from Tibet and the bordering mountains during the Lateglacial and early Holocene would have been sufficient to affect oceanic circulation. However, changes in surface albedo may have influenced the dynamics of monsoonal systems and this may have important implications for global climate change. Drainage development, including lake level changes on the Tibetan plateau and adjacent regions has been strongly controlled by climatic oscillations on centennial, decadal and especially millennial timescales. Since the Little Ice Age, and particularly during this century, glaciers have been progressively retreating. This pattern is likely to continue throughout the 21st century, exacerbated by human-induced global warming.

A Miocene to Pleistocene climate and elevation record of the Sierra Nevada (California)

Orographic precipitation of Pacific-sourced moisture creates a rain shadow across the central part of the Sierra Nevada (California) that contrasts with the southern part of the range, where seasonal monsoonal precipitation sourced to the south obscures this rain shadow effect. Orographic rainout systematically lowers the hydrogen isotope composition of precipitation (deltaD(ppt)) and therefore deltaD(ppt) reflects a measure of the magnitude of the rain shadow. Hydrogen isotope compositions of volcanic glass (deltaD(glass)) hydrated at the earth's surface provide a unique opportunity to track the elevation and precipitation history of the Sierra Nevada and adjacent Basin and Range Province. Analysis of 67 well dated volcanic glass samples from widespread volcanic ash-fall deposits located from the Pacific coast to the Basin and Range Province demonstrates that between 0.6 and 12.1 Ma the hydrogen isotope compositions of meteoric water displayed a large (>40 per thousand) decrease from the windward to the leeward side of the central Sierra Nevada, consistent with the existence of a rain shadow of modern magnitude over that time. Evidence for a Miocene-to-recent rain shadow of constant magnitude and systematic changes in the longitudinal climate and precipitation patterns strongly suggest that the modern first-order topographic elements of the Sierra Nevada characterized the landscape over at least the last 12 million years.

Evidence for enhanced aridity in the Tarim Basin of China since 5.3 Ma

Thick Cenozoic deposits formed from the erosion of the northern evolving edge of the Tibetan Plateau provide opportunities to study the exhumation history and climatic changes within the region. Such deposits are important because they are located in an actively deforming mountain belt as well as in a rain shadow of the Tibetan Plateau. Multi-proxy studies indicate that hyperarid climate has prevailed since 5.3 Ma ago within the basin. This information, together with the geometry analysis of syntectonic deposits of the Sanju Anticline, which indicate tectonic deformation at 5.3 Ma, enable us to better understand the interlay between climatic changes and tectonic uplift. Our results suggest that the tectonic uplift of the Kunlun Mountains at 5.3 Ma must have been one of the significant regional tectonic events, and the uplifted elevation of the Kunlun Mountains more effectively blocks the penetration of moisture from the Indian monsoon into the Tarim Basin and thus enhances the rain shadow effect. This can account for the increasing aridity as well as the formation of the world's second largest active sand desert (the Taklimakan Desert) in the Tarim Basin initiated at 5.3 Ma ago.

Evolution of the great river systems of southern Asia during the Cenozoic India–Asia collision: Rivers draining north from the Pamir syntaxis

Abstract During uplift of the Tibetan plateau and surrounding ranges, tectonic processes have interacted with climatic change and with local random effects (such as landslides) to determine the development of the major river systems of Asia. Rivers draining northward from the Pamir syntaxis have three distinctive patterns that are controlled by different tectonic and climatic regimes. West of the Pamir, the rivers have moderate but irregular gradients and drain northwards to disappear into arid depressions. Relatively steady uplift of the Hindu Kush in northern Afghanistan allowed rivers to cut across the rising ranges, modified by the shear along the Harirud fault zone, local faulting, and by increasing rain-shadow effects from the rising Makran. In the transition to the Pamir the rivers have steeper but more even gradients suggesting more even flow and downcutting during uplift, possibly related to larger glacial sources. In the central Pamir, only one antecedent river, the Pyandzh appears to have kept its northward course with compression and uplift of the indenter, and its course strangely corresponds with a major geophysical boundary (a distorted subducted slab) but not a geological boundary: the other rivers are subsequent rivers developed along deformation fronts during development and northward displacements of the Pamir structural units. The above areas have sources north of the Cretaceous Karakorum–South Pamir Andean margin. On the eastern flank of the Pamir, in the Kunlun and northern Tibetan plateau, the rivers rise similarly north of the Cretaceous Andean margin of southern Tibet, but then flow with low gradients across the plateau, before cutting and plunging steeply down across the Kunlun to disappear into the arid Tarim. These steep profiles are the result of late Neogene uplift of the northern Tibetan plateau and Kunlun possibly modified by glacial diversion and river capture. The drainage history of the Pamir indenter can be reconstructed by restoring the gross movements of the plates and the tectonic displacements, uplift, and erosion of individual tectonic units. Most important changes in drainage took place in the last 10 million years, late Miocene to Quaternary times, as the Pamir syntaxis developed.

Paleoaltimetry from Stable Isotope Compositions of Fossils

Stable isotope systematics of phosphatic (vertebrate) and carbonate (invertebrate) fossils are reviewed, emphasizing external vs. biological controls on isotope compositions and their variation. External controls include elevation and isotopic lapse rates, temperature, atmospheric circulation patterns, aridity, and changes to precipitation seasonality, e.g., development of monsoons. Biological controls include temperature regulation and temperature-dependent biological activity, water balance, behavior, and rates of hard-part secretion and maturation. Some key factors include what sources of water an animal samples, how those sources respond isotopically to elevation, and the isotopic sensitivity of a biologic tissue to environmental changes. General research design criteria are enumerated, including numbers of fossils and analyses required, as well as uncertainties in the interpretability of isotopic shifts. Isotope zoning from fossil teeth and shells from the Indian foreland demonstrate comparable seasonal monsoon signals at ~11 Ma vs. today, implying a high and broad plateau at that time. Mean isotope compositions of fossil teeth from the lee of the Cascade Range, central Oregon, show a pronounced decrease in δ 18 O initiating ~7 Ma, signaling topographic rise associated with impingement of Basin and Range extension on the arc. Mean compositions and zoning in fossil shells from the northern Rocky Mountains indicate high elevations and topographic relief in the late Cretaceous and early Paleogene. Paleoaltimetry will principally benefit from better estimates of temperature, because temperature lapse rates are less variable than isotopic lapse rates, and because the combination of temperature and isotopic studies may help distinguish between local isotopic changes and distal ones caused by catchment or rain shadow effects.

Precipitation and Circulation Covariability in the Extratropics

Abstract Extratropical precipitation is primarily produced by cold and warm fronts associated with surface cyclones and upper-level troughs. The growth of these midlatitude storms is partially controlled by the dry baroclinicity of the troposphere, which in turn can be roughly quantified by the intensity of the upper-level zonal flow. Orographic rainfall, an important component of the precipitation in several midlatitude regions, is also partially determined by the intensity of the cross-mountain midlevel winds. Thus, at monthly and longer time scales, variations of precipitation and zonal flow aloft (as well as wind shear) at a given location should exhibit some degree of coherence. In this work the local covariability of these variables is documented over intermonthly and interannual time scales, using global precipitation products and atmospheric reanalysis from 1979 to 2004. The spatial correspondence between the precipitation and two indices of synoptic activity in the extratropics is also documented. The local correlation (r0) between monthly anomalies of precipitation and upper-level (300 hPa) zonal flow varies in space, from moderately and even highly significant values (r0 ∼ 0.3 to 0.7) over the midlatitude oceans to near zero over the interior of continental areas. Broadly similar results are found when considering the monthly variance of the high-pass-filtered meridional wind (an index of eddy activity) or the midlevel Eady growth rate. The local correlation map between precipitation and low-level (850 hPa) zonal flow is similar to its upper-level counterpart, but the correlations over open ocean are somewhat weaker, while orographic effects show up more clearly. The correlations are positive and large upstream of the major north–south-oriented mountain ranges, as strong westerlies promote upslope rain in addition to storm-related precipitation. In contrast, the correlation tends to be negative downstream of the ranges, as strong westerlies enhance the rain shadow effects over the lee side.

屋久島河川水にあらわれる同位体高度効果と流出特性

Isotopic compositions were analyzed to grasp the altitude effect observed in and the discharge characteristics of river water in Yakushima Island, southwestern Japan. The isotopic characteristics of the river water are similar to those of precipitation in summer; a regression line for the river water is δ D = 7.68 δ18O + 10.06 and d values are in a range of 6.5 ∼ 16.1‰. Moreover, the altitude effects are -0.17‰/100 m for δ18O and-1.3‰/100 m for δ D irrespective of river drainage size. These altitude effects are well concordant with the values in the previous report in Japan, strongly indicating that the river water in Yakushima Island is scarcely affected by the processes of evaporation and mixing with groundwater having long residence time. This idea is not contradict with verifications using mass ratio of potential evapotranspiration in precipitation as an index. Such discharge characteristics of the river might be attributed to hydrological setting of Yakushima Island, i.e., lower permeability of granite and high amounts of precipitation up to 10,000 mm/yr in the mountainous area. Some river water samples in central-northern and western parts of the Island have apparently light isotopic compositions against the average altitudes of drainage basin. Considering landforms of Yakushima Island and meteoric conditions, such isotopic data would be caused by rain shadow effect in which vapor mass as a source of these river water samples has been brought across a ridge by seasonal southern wind.

Warm climate in the late Miocene of the south coast of Alaska and the occurrence of Podocarpaceae pollen

A study of the Homerian type section in the upper Beluga Formation (Upper Miocene) of the Kenai Group of southern Alaska has yielded two surprising discoveries: (1) warmth‐loving taxa and (2) the presence in Alaska of a ‘new’ gymnosperm family, Podocarpaceae. A well‐preserved pollen and spore flora is present in Upper Miocene coal beds of the Kenai lowland, near Homer, Alaska. Stump horizons, abundant wood fragments, wood grain, and amber within the coal attest to a forested swamp. Pollen assemblages from the Homerian type section include elements of both Mixed Northern Hardwood and warm‐temperate Mesophytic forests and are far richer than the flora previously defining the Homerian type section, which had suggested a less diverse, cooler assemblage. Within the Homerian type section, the flora exhibits no definite taxonomic chronology; in general, Alnus dominates, with up to 45% of the total counts, followed by Pinaceae and Taxodiaceae pollen types (30 to 35%) and thermophiles (c. 14%). At least 36 genera are represented, including Carya type, Corylus, Ilex, Juglans, Myrica, Ostrya/Carpinus, Pterocarya, Quercus/Quercus‐type, and Ulmus/Zelkova, eight dicot genera have not previously been reported from the type Homerian. Presence of these hardwoods in moderate to minor amounts suggests that the climate during the Homerian (Late Miocene) was only slightly cooler than that of the Seldovian (Early to Middle Miocene). Unexpectedly, Dacrydium and Podocarpus are present as minor elements in most of the samples. They apparently coexisted with the other Miocene taxa, because the pre‐Paleogene Kenai‐Chugach terrane to the southeast, which supplied sediments to the Kenai Group, is mostly of oceanic plate provenance and is unlikely to have been the source of the pollen. A uniform orange fluorescence of all the pollen, including the podocarps and any potentially reworked pollen, also suggests a contemporaneous origin for all the taxa. The flora from the Homerian type section may precede or coincide with uplift of the Alaska Range to the north. Thus, further comparison with Homerian taxa at localities north and south of the Alaska Range will be important as it may reveal a possible rain shadow effect.

Remnants of a fossil alluvial fan landscape of Miocene age in the Atacama Desert of northern Chile using cosmogenic nuclide exposure age dating

We have used cosmogenic nuclides to estimate limits on the surface exposure durations and erosion rates of alluvial fans and bedrock surfaces in the Atacama Desert in Chile. The oldest landforms we studied are extensive alluvial fans referred to as “Atacama gravels”. With the exception of samples collected in Antarctica, the cobbles collected on these alluvial surfaces have the lowest erosion rates of any samples, as determined by cosmogenic nuclides, analyzed to date. The oldest cobble has a model surface exposure age of 9 Myr, based on combined measurements of cosmogenic 10Be, 26Al, and 21Ne concentrations. Cobbles from the alluvial fans are eroding slower than the surrounding steep mountainous bedrock surfaces. Maximum erosion rates for cobbles on alluvial surfaces are uniformly < 0.1 m/Myr. The survival of these gravels, specifically, and more generally, the stability of landform features in this geographic area is made possible by the attainment of hyperarid conditions in the Atacama Desert resulting from global climatic cooling about 15 Myr ago combined with the rain shadow effect caused by uplift of the Central Andes. The landform features observed presently in the Atacama Desert are remarkably stable and, despite the inevitable erosion that is detectable using cosmogenic nuclides, undoubtedly bear considerable resemblance to conditions as they existed in the Miocene. Over geologic time, the Atacama landscape is evolving in such a manner as to erode the higher bedrock ridges relative to the more stable, but stratigraphically lower depositional surfaces through which clastic detritus now travels occasionally along the floors of incised drainage systems leaving the older permeable alluvial fan surfaces largely intact as widespread remnants of a Miocene fossil landscape.

Numerical Analysis to Investigate the Effects of the Design and Installation of Equilibrium Tension Plate Lysimeters on Leachate Volume

The composition and quantity of leachate as it moves down through the vadose zone is seldom measured directly because sampling in this unsaturated zone at the depths required has proven to be extremely difficult. A promising technique is the use of large porous plates known as equilibrium tension plate lysimeters (ETPLs), which have a controlled suction exerted on them that mimics the soil matric potential measured in the surrounding undisturbed soil profile. In the design phase for the installation of 15 ETPLs at five different depths (three replicates) around a central access chamber in the vadose zone in the Lake Taupo catchment of New Zealand, questions arose regarding the effects of the design and installation layout of the ETPLs on the measured leachate fluxes. To investigate the important design criteria and the spacing of the ETPLs, a numerical investigation using the HYDRUS‐2D software was conducted. This analysis showed that the distance between the tension plate and the base (lower boundary) of the ETPL needs to be large enough to ensure that the effect of the dry zone (rain shadow effect) created below the ETPL on the soil zone being sampled above the plate is minimized. The boundary condition between the ETPL and the central access chamber was also shown to be critical, requiring a free‐drainage condition in this location. The sampling efficiency of the ETPLs increases when the horizontal distance between adjacent ETPLs increases. Less obvious was the result that the sampling efficiency decreases with increasing vertical distance. This work demonstrates that the design and installation configuration of the ETPLs can significantly impact sampling efficiency. The relationships demonstrated in this work must be recognized and implemented in the design process, particularly when multiple ETPLs are installed at various depths through the vadose zone at other locations.

Late Paleozoic Sedimentation on the Northern Margin of the North China Block: Implications for Regional Tectonics and Climate Change

The Late Paleozoic collision between the North China continental block and the Altaid arc terranes of Mongolia represents one of the earliest and most fundamental tectonic events in the ongoing construction of Asia. New detrital zircon provenance data from Carboniferous-Permian nonmarine strata on the northern margin of North China imply that the northern margin of the North China block constituted a continental margin arc prior to this collision (~400-275 Ma) and that collision took place via south-directed subduction beneath North China. A significant and widespread climate change took place in North China in mid-Permian time, and is recorded by a change from Carboniferous and Lower Permian humid-climate, coal-bearing sedimentary facies to Upper Permian and Lower Triassic arid-climate redbeds. In northern North China, this climate change is accompanied by a paleocurrent reversal, which indicates the onset of uplift on the northern margin of the North China block. The temporal association of climate change and uplift suggests that aridification of North China may have been caused by a rainshadow effect from topography related to the convergence and ultimate collision between the North China block and the Altaid arc terranes of Mongolia. Alternatively, climate change may have occurred as a result of northward drift of the North China block through arid subtropical latitudes.

The TianShan Rain-shadow Influence on the Arid Climate Formation in Northwestern China

The role of mountain ranges upon the arid climate formation in northwestern China is investigated using regional climate model. Two kinds of numerical experiments are carried out with real topography and with modified topography which does not contain the TianShan Mountains. Simulated rainfall distribution with real topography shows maximum precipitation in upwind slope of the mountain and minimum precipitation in downwind side of it, which coincides with the features of rain-shadow in other regions of the world. However, numerical experiment without the TianShan Mountains also simulates the area of distinct minimum precipitation in the same location. The arid climate, therefore, is formed even though the rain shadow effect is absent. The difference in rainfall amount between these two experiments is very small around downwind arid region. On the other hand, more intense and frequent rainfall events tend to occur in upwind of the mountain range due to forced lifting of environmental flow, which just emphasizes the precipitation contrast between upwind and downwind side of the mountain. The precipitation accompanied with the synoptic scale disturbances is suppressed over the arid region whether the TianShan Mountains exist or not.

WATER RELATIONS AND STOMATAL CONDUCTANCE IN NINE TREE SPECIES DURING A DRY PERIOD GROWN IN A HOT AND DRY VALLEY

The valleys along the rivers in southwestern China are hot and dry because of the rain shadow effect. The primary vegetation on the slopes in these valleys is savanna. However, due to heavy human disturbance, the vegetation on these slopes has been devastated or severely degraded, resulting in severe water and soil erosion. Rehabilitation or revegetation of these slopes is urgently needed. Some eucalypt and legume trees have been introduced for the purpose of revegetation, and these have shown fast growth during the first seven years. However, it is not known how these trees cope with the hot and dry stresses during the dry period. In the present study, we monitored the water status, stomatal conductance and osmotic regulation, and their seasonal changes of 9 tree species in a hot and dry valley. The height and diameter of these trees attained over 5 years of growth also were compared. The mean height of the 9 species ranged from 0.7 to 7.6 m, the diameter from 2.6 to 6.7 cm. Four species ( Eucalyptus dulebsis, Acacia leptocarpa, A. auriculiformis and A. cunninghamii ) showed fast growth, two species ( E. citriodora, Leucaena leucocephala ) had intermediate growth and the remaining species ( A. mangium and Robinia pseudoacacia ) had slow growth. The physiological measurements showed that as drought conditions progressed, all species decreased their leaf water potentials and stomatal conductance. However, the decrease was more rapid in A. leptocarpa, A. auriculiformis, A. cunninghamii and Eucalyptus dulebis. During the peak drought period (March and April), these species also reached the lowest water potentials (predawn water potential lower than -1.0 MPa) and nearly closed their stomata ( A. leptocarpa, A. auriculiformis, A. Cunninghamii ) or remained at low stomatal conductance ( Eucalyptus dulebsis, A. holosericea and Dodonaea wiscosa ) while the remaining species maintained relatively high water potentials and a low stomatal conductance ( Eucalyptus citriodora and Leucaena leucocephala ) or nearly closed stomata ( A. mangium). Nevertheless, during the drought period, no species showed leaf wilting, except R. pseudoacacia and the native species Vitex negundo and Terminalia franchetii, which were deciduous. All species increased osmoregulation capacity, as indicated by the decrease of osmotic potentials at full saturation, and the increase of osmoregulation substances. Osmoregulatory substances increased over time in the following sequence: K +, free Pro, other free amino acids and soluble sugars. It appeared that K + was important in osmoregulation at the beginning of the drought, while soluble sugars were important in the late drought period. E. dulebsis, A. auriculiformis and A. cunninghamii exhibited the highest osmoregulation capacities. Our results show that most of the introduced species are suitable to grow in these hot and dry habitats because of, among other things, they have strong capacities of water_absorption and water conservation.

The central Andean west‐slope rainshadow and its potential contribution to the origin of hyper‐aridity in the Atacama Desert

AbstractThe west slope of the central Andes exhibits a pronounced rainshadow effect. Precipitation between 15° and 27 °S is dominated by summer convective activity from Amazonia, and data analysis shows that the increase in precipitation with elevation due to the rainshadow effect best fits an exponential correlation. Coupling with limited data from high elevations suggests that the correlation is accurate to 4500 m above sea level (m a.s.l.) and perhaps to 5500 m a.s.l., suggesting that increased precipitation goes unrecorded over the peaks of the western Cordillera. South of 27 °S the precipitation is dominated by winter frontal sources and shows no well‐defined relationship with elevation. The core zone of hyper‐aridity in the Atacama Desert extends from 15 to 30 °S at elevations from sea level to 3500 m a.s.l. Although the Atacama Desert has existed since at least 90 Ma, it is considered that the initial onset of hyper‐aridity was most likely to have developed progressively with the uplift of the Andes as they reached elevations between 1000 to 2000 m a.s.l. coupled with the intensification of a cold, upwelling Peruvian Current between 15 and 10 Ma. Also apparent in the palaeogeographic record are subsequent fluctuations between (semi‐) arid to hyper‐arid conditions that were probably largely controlled by changes in orbital and oceanic forcing. Copyright © 2003 Royal Meteorological Society

Paleoclimate reconstruction based on the timing of speleothem growth and oxygen and carbon isotope composition in a cave located in the rain shadow in Israel

High-resolution 230Th/ 234U ages and δ 18O and δ 13C compositions of speleothems in Ma’ale Efrayim Cave located to the east of the central mountain ridge of Israel enable us to examine the nature of the rain shadow aridity during glacial and interglacial intervals. Speleothem growth occurred during marine glacial isotopic periods, with no growth during the two last marine isotope interglacial intervals and during the peak of the Last Glacial Maximum. This contrasts with speleothem growth in caves located on the western flank of the central mountain ridge, in the Eastern Mediterranean semiarid climatic zone, which continued throughout the last 240,000 yr. Thus, during glacial periods water reached both sides of the central mountain ridge. A comparison of the present-day rain and cave water isotopic compositions and amounts at the Ma’ale Efrayim Cave site with those on the western flank shows that evaporation and higher temperatures on the eastern flank are major influences on isotopic composition and the lack of rainfall. The δ 18O and δ 13C profiles of the speleothems deposited between 67,000 and 25,000 yr B.P. match the general trends of the isotopic profiles of Soreq Cave speleothems, suggesting a similar source (eastern Mediterranean Sea) and similar climatic conditions. Thus, during glacial periods the desert boundary effectively migrated further south or east from its present-day location on the eastern flank, whereas interglacial periods appear to have been similar to the present, with the desert boundary at the same position. The decrease in overall temperature and a consequent reduction in the evaporation to precipitation ratios on the eastern flank are viewed as the major factors controlling the decay of the rain shadow effect during glacial periods.

Polychlorinated biphenyls and toxaphene in Pacific tree frog tadpoles (Hyla regilla) from the California Sierra Nevada, USA

Pacific tree frog (Hyla regilla) tadpoles were collected throughout the Sierra Nevada mountain range, California, USA, in 1996 and 1997 and analyzed for the presence of polychlorinated biphenyls (PCBs) and toxaphene. Whole-tadpole sigma PCB levels ranged from 244 ng/g (wet wt) at lower elevations on the western slope to 1.6 ng/g high on the eastern slope, whereas sigma toxaphene levels ranged from 15.6 to 1.5 ng/g. Linear regression of PCB and toxaphene residue levels versus elevation indicated a significant relationship, with an r2 value of 0.33 for PCB and 0.45 for toxaphene indicating a significant elevation effect on PCB and toxaphene bioaccumulation in Sierra Nevada H. regilla. Tadpole samples from sites in east-facing versus west-facing drainage basins showed significant differences in PCB and toxaphene residue levels, suggesting the possibility of a rain-shadow effect in the long-range atmospheric transport of these contaminants to the Sierra Nevada Mountains.

Stable isotopic evidence for a Pre‐Middle Miocene rain shadow in the western Basin and Range: Implications for the paleotopography of the Sierra Nevada

A recently proposed method for approximating the paleorelief of mountain belts makes use of the predictable relationship between the isotopic depletion of precipitation and the net elevation of an orographic barrier over which an air mass rises. This rain shadow effect often creates desert regions on the lee side of mountain belts in which precipitation is isotopically light. Changes in the isotopic composition of precipitation can be estimated from the isotopic composition of authigenic or pedogenic minerals, which can then be used to infer both the development of relief during orogenesis as well as the stability of a rain shadow formed by developing mountains. The δ18O of smectites formed from the weathering of Middle Miocene to Late Pliocene volcanic ashes currently exposed in the rain shadow of the modern Sierra Nevada of California show no indication of large‐scale Late Cenozoic surface uplift of the Sierra and corresponding regional rain shadow development. Rather smectite isotope data tentatively suggest that elevations may have decreased over this time by as much as 2000 m toward the southern end of the range and 700 m in regions farther north. This suggests that the modern rain shadow cast over the western Basin and Range has been in existence since pre‐Middle Miocene and that the Sierra Nevada have been a prominent orographic barrier since before this time. These interpretations are in accord with several recent studies also suggesting a possible Cenozoic elevation loss of an already developed Sierra Nevada mountain range.