Mean Annual Precipitation Values Research Articles

Modern Abies, Picea, and Tsuga pollen distribution along the elevation gradient in East Asia

Sub-alpine dark coniferous forests (SCFs) exhibit distinct latitudinal and longitudinal elevation distributions in East Asia. The SCF genera Abies, Picea, and Tsuga produce distinctive pollen and have specific elevation and climate requirements, allowing for the reconstruction of paleo-climatic and paleo-elevational changes from fossil pollen sequences. However, the relationship between SCF elevational distribution and the percentage of coniferous pollen has not been elucidated at the continental scale. In this study, we determined the relationship between Abies, Picea, and Tsuga pollen percentages and SCF elevation distributions in East Asia using an integrated pollen dataset comprising 4863 modern samples. The total percentage of these pollen types showed bimodal patterns with elevation and unimodal patterns with climate. Maximum pollen percentages occurred at elevations of 0–1000 and 2000–4600 m, mean annual temperatures of −5–10 ℃, and mean annual precipitation values of 100–1500 mm. The elevation with the highest proportion of Abies + Picea + Tsuga pollen increased with decreasing latitude: from 500 m (>43°N) to 2300 m (37–43°N), to 3500 m (30–37°N), and to 4000 m (18–30°N). Elevation also exhibited non-monotonic variations with longitude, first increasing from 2500 m (<93°E) to 3500 m (93–102°E), and then decreased to 2500 m (102–113°E) and 500 m (>113°E). The spatial patterns of Abies, Picea, and Tsuga pollen abundance were closely correlated with modern SCF distributions, which are largely modulated by climate and elevation. This study lays the foundation for reconstructing paleo-climate and paleo-elevation variations across East Asia.

Weak precipitation δ2H response to large Holocene hydroclimate changes in eastern North America

In eastern North America, annual precipitation increased by >40% over the Holocene, largely in response to melting of the Laurentide Ice Sheet. The change substantially raised lake levels and transformed conifer-dominated ecosystems into mesic deciduous forests. δ2H values of terrestrially derived leaf-wax n-alkanes can facilitate diagnoses of the climate dynamics involved by reconstructing δ2H values of mean annual precipitation (δ2HMAP). However, competing influences on δ2HMAP values in the mid-latitudes, such as changes in moisture sources and in the seasonal distribution of precipitation, can generate confounding effects. To test δ2HMAP sensitivity to potential changes associated with the final Holocene phases of deglaciation in eastern North America, we used 14 fossil-pollen records to reconstruct monthly precipitation changes and to model δ2HMAP values during the Holocene. The pollen-inferred precipitation increased by 100–200 mm during both cold and warm seasons, but modeled δ2HMAP values changed by only ∼10‰, because isotopically-heavy summer precipitation increased by nearly as much as the cold-season isotopically-light winter precipitation. Three new leaf wax n-C29-alkane (δ2HC29) records spanning the Holocene from Vermont, Pennsylvania, and Massachusetts closely follow modeled δ2HMAP trends and confirm only a small decline in δ2HMAP values over the Holocene. Because the shifts in precipitation seasonality accurately predict the n-alkane records, changes in moisture sources or pathways appear to play only a minor role in the regional δ2HMAP history despite the effects of deglaciation on atmospheric circulation. Soil evaporation also did not significantly alter δ2HC29 values from the values predicted using the pollen-derived reconstructions. The results affirm that δ2HC29 values faithfully detected anticipated isotopic changes in δ2HMAP values, but that important paleoclimate events may not always yield strong changes in δ2HMAP values.

How does climate affect the topography in tectonically active orogens

AbstractA central theme in geomorphology is the quantitative determination of the relationship between topography and its controlling factors, such as tectonics, lithology, and climate. However, rather than relief and slope, channel steepness (ksn) is a more effective metric for topography, and together with the abundance of beryllium‐10 (10Be) erosion rate data, it provides a more convenient means of quantitatively revealing the relationship between topography and its driving factors. A power‐law relationship between ksn and 10Be erosion rates has been widely demonstrated, which indicates the dominant control of tectonics on topography, while the dominant control of climate has not been clearly revealed. In this study we selected nine tectonically active regions, comprising 241 catchments, covering a wide range of mean annual precipitation values, and by extracting ksn values and hypsometric curves, we obtained the relationship between ksn and erosion rates. The results show that the power‐law relationship differs between regions, largely due to differences in the erosion coefficient, K. After separating the influences of lithology and climate, we found that although soft sedimentary rocks will increase the erosion coefficient, precipitation plays the main role in controlling the erosion coefficient, resulting in a linear relationship between precipitation and K. This relationship clearly demonstrates the occurrence of higher relief under a drier climate, even with similar rates of tectonic uplift.

Role of abiotic factors in Nothofagus pumilio forest mortality: The sensitivity of ecotones

The world's forests are being affected by a changing climate. Recently, patches of dead trees have been found in forests of the Patagonian endemic species Nothofagus pumilio, which could not be related to insects or pathogenic fungi acting as primary agents. This study aimed to analyze environmental variables associated with N. pumilio mortality at a landscape scale. Dead patches were recorded from satellite image analysis and field trips throughout the distribution of N. pumilio forests in Chubut province (Argentina). The relation between forest mortality and environmental variables, including elevation, slope, aspect, recent volcanic ash deposits, precipitation, and temperature, was analyzed by contingency tables and chi-square analysis, and a risk model was developed using the Maximum Entropy (MaxEnt) algorithm. One hundred and seven dead patches were recorded only in the northern region of the study area (ca. −42.5°S to −44.5°S), where forests develop at higher elevations, slopes, precipitations, and temperatures than in the southern region. In the northern region, elevation, followed by precipitation, was the environmental variable most related to forest mortality. Nothofagus pumilio mortality was related to two ecotones: an altitudinal one, associated with middle-high mountainsides (1200 and 1400 m asl), and a longitudinal one, associated with intermediate values of mean annual precipitation within the west-east rainfall gradient. These results highlight the sensitivity of these transitional environments. According to the risk model based on abiotic features, more than 100,000 ha of forest (ca. 30%) are located under environmental variables favorable for decline and death. In the context of climate change and in the light of the results, abiotic factors seem to be the main predisposing factors of N. pumilio mortality.

Leaf Wax Hydrogen Isotopes as a Hydroclimate Proxy in the Tropical Pacific

AbstractHydrogen isotope ratios of sedimentary leaf waxes (δ2HWax values) are increasingly used to reconstruct past hydroclimate. Here, we add δ2HWax values from 19 lakes and four swamps on 15 tropical Pacific islands to an updated global compilation of published data from surface sediments and soils. Globally, there is a strong positive linear correlation between δ2H values of mean annual precipitation (δ2HP values) and the leaf waxes n‐C29‐alkane (R2 = 0.74, n = 665) and n‐C28‐acid (R2 = 0.74, n = 242). Tropical Pacific δ2HWax values fall within the predicted range of values based on the global calibration, and the largest residuals from the global regression line are no greater than those observed elsewhere, despite large uncertainties in δ2HP values at some Pacific sites. However, tropical Pacific δ2HWax values in isolation are not correlated with estimated δ2HP values from isoscapes or from isotope‐enabled general circulation models. Palynological analyses from these same Pacific sediment samples suggest no systematic relationship between any particular type of pollen distribution and deviations from the global calibration line. Rather, the poor correlations observed in the tropical Pacific are likely a function of the small range of δ2HP values relative to the typical residuals around the global calibration line. Our results suggest that δ2HWax values are currently most suitable for use in detecting large changes in precipitation in the tropical Pacific and elsewhere, but that ample room for improving this threshold exits in both improved understanding of δ2H variability in plants, as well as in precipitation.

Oligocene Desmanthus (Leguminosae) from the Qaidam Basin in northeastern Tibetan Plateau, China, and its implications for paleoclimate and paleoelevation

ABSTRACT Fossils are critical for understanding the environmental changes and uplift history of the Tibetan Plateau during the Cenozoic. As the largest inland basin located at the northeastern plateau, Qaidam Basin has been regarded as the key region to understand the climatic changes in the plateau during the Cenozoic. Herein, fossil legumes from the Oligocene Shangganchaigou Formation in northwestern Qaidam Basin have been reported and are assigned to Desmanthus cf. virgatus (L.) Willd. based on morphological comparison. Current materials represent the first megafossil record of this genus in the world. The living analogues of current fossils now live in regions with mean annual temperature values (MAT) ranging from 13.4 to 29.1°C and mean annual precipitation values (MAP) ranging from 36 to 2874 mm while the MAT and MAP of current northwestern Qaidam Basin is −1.03°C and 60.5 mm, respectively, and indicate that the Oligocene Qaidam was much warmer than today. We calculate that current fossils could grow no higher than 2492 m considering the climatic condition of the Oligocene Qaidam. The difference between estimated and modern elevation of the fossil site suggests that the elevation of the research area has increased by at least ≈1000 m since the Oligocene.

Factors affecting severe weather threat index in urban areas of Turkey and Iran

BackgroundDistinguishing dynamic variations of the climate from the physical urban indicators is a challenge to assess the factors affecting weather severity. Hence, the time-series of the severe weather threat index (SWEAT) were considered in the four urban areas of Turkey and Iran to identify its affecting factors among the climatic variables and urban indicators in 2018. The SWEAT data were obtained from the upper-air sounding database of the University of Wyoming. The climatic variables were extracted from the Asia Pacific data research center (APDRC). The spatial statistics for urban expansion were collected from global human built-up and settlement extent (HBASE) data sets. A quantitative measuring of the Pearson correlation test was used to expose the relationships between dependent index (SWEAT) and independent variables (climatic and anthropogenic).ResultsResults revealed that the high and extreme severity classes of the weather condition in the Ankara, Istanbul, Mashhad, and Tehran are estimated as 7.7% (28 days), 15.3% (56 days), 1.1% (4 days), and 4.4% (16 days), respectively. The strongest values of the annual SWEAT index, exposing the unstable and severe weather conditions, were observed for Istanbul and Ankara urban regions. This result may be corresponding to the highest values of mean annual precipitation and relative humidity in addition to the largest values of urban expansion and sprawl index. The statistical correlation tests in annual scale confirmed the effective role of climatic elements of precipitation, relative humidity, and cloudiness (R from 0.94 to 0.99) and the urban expansion indicators (R from 0.86 to 0.91) in increasing annual severe weather index of SWEAT at above 85–95% of confidence level.ConclusionsThe correlations between the urban expansion indicators and outcome SWEAT index can be strengthened by some climatic elements (e.g., precipitation, humidity, and cloudiness), revealing the mediator and magnifier task. However, the mentioned correlations can be weakened by another climatic variable (i.e., air temperature), revealing a moderator and modifier task. Ultimately, investigation of the weather severity indices (e.g., SWEAT index) could be applied to identify the local and regional evidence of climate change in the urban areas.

An Assessment of Plant Species Differences on Cellulose Oxygen Isotopes From Two Kenai Peninsula, Alaska Peatlands: Implications for Hydroclimatic Reconstructions

Peat cores are valuable archives of past environmental change because they accumulate plant organic matter over millennia. While studies have primarily focused on physical, ecological, and some biogeochemical proxies, cores from peatlands have increasingly been used to interpret hydroclimatic change using stable isotope analyses of cellulose preserved in plant remains. Previous studies indicate that the stable oxygen isotope compositions (δ18O) preserved in alpha cellulose extracted from specific plant macrofossils reflect the δ18O values of past peatland water and thereby provide information on long-term changes in hydrology in response to climate. Oxygen isotope analyses of peat cellulose (δ18Ocellulose) have been successfully developed from peat cores that accumulate the same species for millennia. However, to fully exploit the potential of this proxy in species-diverse fens, studies are needed that account for the isotopic variations caused by changes in dominant species composition. This study assesses variation in δ18O values among peatland plant species and how they relate to environmental waters in two fens informally named Horse Trail and Goldfin, located on the leeward (dry) and windward (wet) side, respectively, of the climatic gradient across the Kenai Peninsula, Alaska. Environmental water δ18O values at both fens reflect unmodified δ18O values of mean annual precipitation, although at Goldfin standing pools were slightly influenced by evaporation. Modern plant (mosses and Carex (sedges)) δ18Ocellulose values indicate that all Carex are higher (~2.5 ‰) than those of mosses, likely driven by their vascular structure and ecophysiological difference from non-vascular mosses. Moss δ18Ocellulose values within each peatland are similar among the species, and differences appear related to evaporation effects on environmental waters within hummocks and hollows. The plant taxa-environmental water δ18O differences are applied to the previously determined Horse Trail Fen untreated bulk δ18O record. Results include significant changes to inferred millennial-to-centennial scale hydroclimatic trends where dominant taxa shift from moss to Carex, indicating that modern calibration datasets are necessary for interpreting stable isotopes from fens, containing a mix of vascular and nonvascular plants. Accounting for isotopic offsets through macrofossil analysis and modern plant-water isotope measurements opens new opportunities for hydroclimatic reconstructions from fen peatlands.

A survey of relationship between urbanization and climate change for major cities in Iran

The present study aims to investigate the urbanization characteristic of population growth during five time windows from 1976 to 2016, which can represent the evidence of climate change. For this purpose, seven major urbanized regions of Iran were chosen to study, which have the population greater than one million in 2016. Three main climatic data called as mean annual temperature, upward long-wave radiation (ULR), and precipitation, by monthly scale, were considered averagely to five aforementioned annual time scales from 1976 to 2016 then were extracted spatially with coordination of 1°N × 1°E around each urbanized region. Temporal change of climatic variables within five time windows indicated the average values of + 2.09 °C, + 11.2 W/m2, and − 21 mm for mean annual temperature, ULR, and precipitation in whole study areas. The most increase for mean annual temperature and ULR values were observed in Mashhad and Tehran-Karaj urbanized regions, respectively. In vice versa, the most decrease for mean annual precipitation values was observed in Ahwaz and Shiraz urbanized regions. A parallel increasing trend for temperature and ULR and a parallel declining trend for precipitation were observed adjusted by increasing urban population in all urbanized regions. In addition, the significant and strong relationships (R2 = + 0.814 to + 0.998) between temperature and ULR variations and urban population were observed in each urbanized region indicating as important signals of climate change affected by urbanization in Iran.

Leaf and infructescence fossils of Alnus (Betulaceae) from the late Eocene of the southeastern Qinghai–Tibetan Plateau

AbstractPlant fossils from the Qinghai–Tibetan Plateau (QTP), China are critical to understand not only the diversification history of plants there, but also the paleoenvironmental conditions. Alnus are deciduous trees, mainly distributed in temperate and subtropical regions of Eurasia and North America, and they are well known in the fossil records throughout the Cenozoic in the Northern Hemisphere. We collected numerous well‐preserved Alnus leaf and infructescence fossils from the Lawula Formation (∼34.6 Ma with 40Ar/39Ar dating) at the present elevation of 3910 m a.s.l. in the southeastern QTP. Based on detailed morphological comparisons with existing and fossil species, these fossils show closest affinity to Alnus ferdinandi‐coburgii C. K. Schneid., and we refer to these fossils as A. cf. ferdinandi‐coburgii. These specimens comprise the oldest megafossil record of Alnus in the QTP, and provide solid evidence for the distribution of Alnus there as early as the late Eocene. Extant A. ferdinandi‐coburgii is distributed in areas with mean annual temperature values between 9.7 °C and 16.9 °C, and mean annual precipitation values ranging from 896.2 mm to 1161.2 mm; therefore, fossils of A. cf. ferdinandi‐coburgii suggest a much warmer and wetter climate during the late Eocene than today in the southeastern QTP. This finding is consistent with other evidence for continued uplift of the southeastern QTP after the late Eocene that might be due to the eastward extension of the QTP.

Isotope Investigation of Nitrate in Soils and Agricultural Drains of the Lower Yakima Valley, Washington

Nitrate in the groundwater of the lower Yakima Valley, Washington frequently exceeds the Environmental Protection Agency (EPA) maximum contaminant level standard for potable water (10 mg/L), impacting communities with disadvantaged socioeconomic status. Nitrogen and oxygen isotopic signatures were determined for nitrate in soil leachates and irrigation return flow. Isotope signatures for nitrate from soil leachate had significant overlap with both the isotope signatures of naturally occurring soil nitrate at the nearby Hanford site, Washington and of groundwater nitrate attributed to manure and fertilizer application in a local EPA study. A mass balance calculation using Δ17O data suggests that there is a consistent ∼9% atmospheric contribution to nitrate in soil accumulations below caliche layers at several locations. This agrees with other research on the atmospheric contribution to naturally occurring soil nitrates in areas with similar mean annual precipitation values. We argue that this consistent ∼9% atmospheric component indicates that soil nitrate at depth is dominated by naturally occurring, biologically fixed nitrate across multiple sites. We suggest the flushing of naturally occurring soil nitrate to groundwater during land use conversion to irrigated agriculture may represent a previously overlooked significant nitrate input to aquifers in this region.

A multiscale spatio-temporal framework to regionalize annual precipitation using k-means and self-organizing map technique

Determination of homogenous precipitation-based regions is a very important task in effective management of water resources. The present study tried to propose an effective precipitation-based regionalization methodology by conjugating both temporal pre-processing and spatial clustering approaches in a way to take advantage of multiscale properties of precipitation time series. Annual precipitation data of 51 years (1960-2010) for 31 rain gauges (RGs) were collected and used in proposed clustering approaches. Discreet wavelet transform (DWT) was used to capture the time-frequency attributes of the time series and multiscale regionalization was performed by using k-means and Self Organizing Maps (SOM) clustering techniques. Daubechies function (db) was selected as mother wavelet to decompose the precipitation time series. Also, proper boundary extensions and decomposition level were applied. Different combinations of the approximation (A) and detail (D) coefficients were used to determine the input dataset as a basis of spatial clustering. The proposed model’s efficiency in spatial clustering stage was verified using three different indexes namely, Silhouette Coefficient (SC), Dunn index and Davis Bouldin index (DB). Results approved superior performance of k-means technique in comparison to SOM. It was also deduced that DWT-based regionalization methodology showed improvements in comparison to historical-based models. Cross mutual information was used to investigate the RGs of cluster 3’s homogeneousness in DWT-k-means approach. Results of non-linear correlation approach verified homogeneity of cluster 3. Verifications based on mean annual precipitation values of rain gauges in each cluster also approved the capability of multiscale approach in precipitation regionalization.

Exploring Mean Annual Precipitation Values (2003–2012) in a Specific Area (36°N–43°N, 113°E–120°E) Using Meteorological, Elevational, and the Nearest Distance to Coastline Variables

Gathering very accurate spatially explicit data related to the distribution of mean annual precipitation is required when laying the groundwork for the prevention and mitigation of water-related disasters. In this study, four Bayesian maximum entropy (BME) models were compared to estimate the spatial distribution of mean annual precipitation of the selected areas. Meteorological data from 48 meteorological stations were used, and spatial correlations between three meteorological factors and two topological factors were analyzed to improve the mapping results including annual precipitation, average temperature, average water vapor pressure, elevation, and distance to coastline. Some missing annual precipitation data were estimated based on their historical probability distribution and were assimilated as soft data in the BME method. Based on this, the univariate BME, multivariate BME, univariate BME with soft data, and multivariate BME with soft data analysis methods were compared. The estimation accuracy was assessed by cross-validation with the mean error (ME), mean absolute error (MAE), and root mean square error (RMSE). The results showed that multivariate BME with soft data outperformed the other methods, indicating that adding the spatial correlations between multivariate factors and soft data can help improve the estimation performance.

Use of artificial neural network for spatial rainfall analysis

In the present study, the precipitation data measured at 23 rain gauge stations over the Achaia County, Greece, were used to estimate the spatial distribution of the mean annual precipitation values over a specific catchment area. The objective of this work was achieved by programming an Artificial Neural Network (ANN) that uses the feed-forward back-propagation algorithm as an alternative interpolating technique. A Geographic Information System (GIS) was utilized to process the data derived by the ANN and to create a continuous surface that represented the spatial mean annual precipitation distribution. The ANN introduced an optimization procedure that was implemented during training, adjusting the hidden number of neurons and the convergence of the ANN in order to select the best network architecture. The performance of the ANN was evaluated using three standard statistical evaluation criteria applied to the study area and showed good performance. The outcomes were also compared with the results obtained from a previous study in the area of research which used a linear regression analysis for the estimation of the mean annual precipitation values giving more accurate results. The information and knowledge gained from the present study could improve the accuracy of analysis concerning hydrology and hydrogeological models, ground water studies, flood related applications and climate analysis studies.

Potential ecological impact of climate change on the water quality of an intensively managed agricultural watershed in Quebec, Canada

This study investigated the effects of climate change (CC) on water redistribution in a micro-watershed of a lowland agricultural area of the Bras d'Henri River in the temperate cold climate of Quebec, Canada. A Water Flow and Balance Simulation Model (WaSiM-ETH) was used to simulate the hydrology using current climatic conditions and land use characteristics, applying Richards’ equation. A one-day temporal resolution was used with a spatial resolution of 2 × 2 m. The CC scenarios Coupled Global Climate Model, version 1 (CGCM1) and Hadley Centre Coupled Model, version 3.1 (HadCM3.1) were downscaled to the regional level and integrated into WaSiM-ETH and evaluated for both current and modified climatic conditions. Mean annual precipitation values (P) increased from 15–33%, evapotranspiration from 7–26%, and discharge (Q) from 16–45%. The identification of the significant water quality problem represented by average value of total suspended solids (TSS) 265.29 (kg ha−1), nutrients: nitrogen (NO3-N) 16.83 (kg ha−1) and total phosphorus (TP) 0.59 (kg ha−1) for the whole evaluated period; and (TSS) 148.09 (kg ha−1), (NO3-N) 5.65 (kg ha−1) and (TP) 0.31 (kg ha−1) during the days with surface runoff, in relation to water quantity and CC creates the basis for erosion risk assessment.

Spatial distribution of climatic conditions from the Middle Eocene to Late Miocene based on palynoflora in Central, Eastern and Western Anatolia

The continental climatic evolution of Anatolia has been reconstructed quantitatively for the last 45 million years using the coexistence approach. Although there were some regional effects, the Anatolian Cenozoic continental climate record correlated with the European climatic condition and the global oxygen isotope record from marine environments. From middle Eocene to late Miocene, continental warming in Anatolia was pronounced for inferred winter temperature and mean annual temperature as in Europe. Generally, the palaeoclimatic property of Anatolia resembles the European climatic changing and marine temperature changing based on the oxygen isotope record; however, climatic values of the terrestrial area in Anatolia are higher from Lutetian to Aquitanian and these values are lower than European values from Aquitanian to Tortonian. Correspondingly, Cenozoic climatic cooling in Anatolia is directly associated with an increase of seasonality, palaeogeographic position and terrestrial condition. Furthermore, mean annual precipitation values of Anatolia remained relatively stable during the Eocene–Oligocene; however, these values indicated changing throughout middle–late Miocene. Moreover, in this study, decline of abundance and variables for the mangrove and back mangrove palaeocommunities during the last 45 million years is recorded because of the decreasing of humidity, temperature and increasing of terrestrial condition.

Ungulate diets reveal patterns of grassland evolution in North America

Equids from the late Miocene (Hemphillian North American Land Mammal Age) of Texas evolved C4 dominated diets earlier than their Nebraska counterparts, leading researchers to hypothesize a northward expansion of C4 grasses between 8 and 6Ma. However, competing hypotheses from multiple paleoecological proxies support one of three hypotheses: that northward C4 expansion occurred at the expense of C3 woodlands, C3 grasslands, or was not occurring during the Hemphillian. We test these alternative hypotheses by comparing the ecosystems of Hemphillian Texas and Nebraska (6.3–7.5Ma) using hoofed mammal dietary reconstruction (hypsodonty and digestive strategy) and by incorporating published tooth enamel isotopes, paleosol isotopes, and phytolith assemblage data. We also use hypsodonty, mesowear, and microwear in a detailed comparison of two localities that are roughly contemporary (Cambridge, Nebraska at 7Ma and Coffee Ranch, Texas at 6.6Ma) to rule out time averaging as an explanatory variable. Through analogy with modern African communities, we reconstruct Texas and Nebraska ecosystems as bushland and woodland, respectively. Using the proportions of hypsodont taxa we estimate mean annual precipitation values of 1217mm/year for Nebraska and 1368mm/year for Texas. Using rarefaction we also do not find differences in the richness of brachydont, hypsodont, and hindgut fermenting taxa. We therefore conclude that both ecosystems were largely similar in hoofed mammal faunal structure during the late Miocene. When compared to published paleosol and phytolith data, which show no differences in C3/C4 biomass among latitudes, our results allow us to reject hypotheses of northward C4 expansion during the late Miocene. We therefore suggest that the equid enamel isotopes may have been biased by two potential factors: the primary reliance on a single locality of appropriate age and possible behavioural lag in C4 feeding among Nebraska equids. These results suggest that the formation of a modern C3/C4 latitudinal gradient occurred later than is previously suggested by equid enamel carbon isotopes.

Habitat tracking, range dynamics and palaeoclimatic significance of Eurasian giant salamanders (Cryptobranchidae) — indications for elevated Central Asian humidity during Cenozoic global warm periods

Environmental fluctuations are a driving force in vertebrate evolution, but cryptobranchids (giant salamanders) show little morphologic change since the Jurassic. Here we analyze their fossil distribution in the Cenozoic of Eurasia and show that morphologic stasis is also maintained by stable environments, making giant salamanders an ideal proxy-group for environmental and palaeoclimatic studies. The climate space of recent and fossil cryptobranchids is best characterized by high humidity with mean annual precipitation values over 900mm. The recorded patchiness of their fossil record can be explained by habitat tracking and/or range expansion from higher altitudes into lowland settings during humid periods with increased basinal relief. In Central Asia cryptobranchids are recorded from five intervals, four of them are global warm periods: Paleocene–Eocene Thermal Maximum, Late Oligocene warming, Miocene Climate Optimum, and Mio-Pliocene transition. This distribution suggests that during global warmth the Asian cold high pressure zone during winter months may be weak or absent, thus moist westerly winds penetrate far into the continent. The presence of cryptobranchids also indicates that the aridification across the Eocene–Oligocene boundary as reported from Mongolia and northwestern China, does not occur in the Zaysan Basin, probably due to increased upslope precipitation in the rising Altai Mountains.

Magnetic susceptibility as a proxy for rainfall: Worldwide data from tropical and temperate climate

The magnetic susceptibility of soils has been linked with climate, mainly through rainfall, by numerous investigators. For this study we assembled a worldwide dataset of 272 samples, both published and new, to determine the nature of the relationship between MS and rainfall. On a worldwide basis there is a crude relationship ( r 2 = 0.265) between MS and rainfall. MS increases with increasing rainfall from about 200 mm/yr to 1000–1200 mm/yr. Above 1200 mm/yr, MS decreases as rainfall increases up to about 2000 mm/yr. Under arid and semi-arid conditions, below about 200 mm/yr of rainfall, MS and rainfall exhibit no relationship, likely the result of limited pedogenic activity. When tropical and temperate localities are analyzed separately, the correlation between MS and rainfall exhibits a dramatic improvement, r 2 = 0.568 and 0.520, respectively. For similar amounts of rainfall tropical localities generally exhibit lower MS values which may be related to differences in the seasonal variation of rainfall. Because the soil environment is highly variable, it is unlikely that a global or even regional equation could accurately estimate rainfall from MS. Using data from Morocco and Mali we demonstrate that local equations using only MS to estimate rainfall produce reasonable results, r 2 = 0.700 for Morocco and 0.611 for Mali. However, a single independent variable is unlikely to capture the variability of the complex soil system. To the local equations described above we experimented with adding several independent variables in addition to MS including diffuse reflectance spectral data (DRS), x-ray diffraction (XRD), and x-ray fluorescence (XRF). For DRS data, % reflectance and red, yellow, and near-infrared wavelengths appear important; for XRD illite and kaolinite counts are important whereas for XRF Fe 2O 3 is important. The addition of these other independent variables dramatically improves prediction quality. In the case of the Mali transect, estimating rainfall from these variables produces an r 2 that exceeds 0.9. Based on these data we conclude that MS has the potential to be a reasonable proxy of rainfall for mean annual precipitation values from 200 to 2000 mm/yr, especially if local equations are used. Predictions can be improved by including other independent variables that show sensitivity to climate and are related to MS through the chemistry of the weathering process; we included DRS, XRD, and XRF data with good results.

Carbon accumulation in Umbrisols under Quercus pyrenaica forests: Effects of bedrock and annual precipitation

The objective of this study was to determine the effect of bedrock, mean annual precipitation and slope orientation on soil organic carbon (SOC) accumulation of Quercus pyrenaica Willd forests. Twelve different oak stands, along a rainfall gradient over two bedrock types (granites and schists), were selected for this study. Properties of the diagnostic soil horizons were determined. Bedrock type was the principal factor affecting soil development and fertility. Accumulated SOC varied between 33 and 185 Mg C ha− 1, the amounts of C accumulated over schists being significantly higher than over granites because of higher soil acidity, ‘silt + clay’ content and metal complexation. The SOC content in the entire profile was over 125 times higher than the C accumulated in the stand forest litter at the schist sites and 50 times higher at the granite sites. Soil acidity and metal complexation hampered microbial decomposition of soil organic matter, producing SOC accumulation and forming thick umbric Ah/AB-horizons, being thicker at sites with high values of mean annual precipitation than at sites with low ones. Mineral N release was low in these soils.