History and variability of Asian interior aridity recorded by eolian flux in the Chinese Loess Plateau during the past 7 Ma

Eolian flux in the Chinese Loess Plateau was reconstructed by measuring the dry bulk density and CaCO3 content of the late Cenozoic loess-paleosol-red clay sequences in the Lingtai profile. Comparison of eolian flux variation between the Lingtai profile and the ODP sites 885/886 in the North Pacific shows a significant wet-dry variability in addition to a gradual drying trend in the dust source regions in interior Asia. Especially, the increase of eolian fluxes from both continental and pelagic eolian sediments indicates a sharp drying of the dust source regions between 3.6 and 2.6 MaBP, which might be attributed to the tectonic uplift of the Tibetan Plateau, which cut down the moisture input to the interior Asia. The average value and variability of eolian flux are higher after 2.6 MaBP than before, which may be related to the Quaternary climatic fluctuations on the glacial-interglacial timescale after the commencement of major Northern Hemisphere Glaciations. The eolian fluxes of the Lingtai profile and Core V21-146 in northwest Pacific show a synchronous variation on the 104-105 a timescale, indicating that the flux variations from both continental and marine records are closely correlated to the Quaternary climatic fluctuation forced by the ice volume changes on a global scale.     

Loess accumulation and soil formation in central kansas,United States,during the past 400 000 years

Based on interpolation of thermoluminescence dates and the mean accumulation rate of 0.034 mm yr^?1, four cycles of pedogenic CaCO₃ accumulation are found within the Loveland Loess: 415–325 ka, 325–250 ka, 250–195 ka and 195–95 ka. The four CaCO₃ peaks correspond chronologically to marine oxygen isotope stages 11, 9, 7 and 5, respectively. The early Wisconsin (95–70 ka) was characterized by sand dune activity. The reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very slow rate of silt accumulation (0·016 mm yr^?1). The Gilman Canyon pedocomplex, enriched in organic matter and dated at 35–20 ka, was formed under a strong physical weathering regime and a relatively high rate of silt accumulation (0·15 mm yr^?1), indicating a windy, relatively moist, probably cool environment. It developed when the Laurentide ice sheet was advancing and dust content in Greenland ice core was low. The Peoria Loess was accumulated at a rate of 0·3 mm yr^?1 in central Kansas under cold dry conditions when the ice sheet fluctuated around its maximum position and the dust content in the Greenland ice core was the highest. Even the warm substage around 13 ka has some corresponding evidence in the central Great Plains. The well-developed Brady Soil, dated at 10·5–8·5 ka, indicates that the early Holocene was the optimal time for soil development since 20 ka. The poorly weathered Bignell Loess might have been deposited during the Altithermal Period from 8·5 to 6 ka.     

Carbon isotopic composition of modern soil and paleosol as a response to vegetation change on the Chinese Loess Plateau

The relationship between the carbon isotopic composition of paleosols and pale-ovegetation on the Loess Plateau is still unclear. One of the main reasons is that we are short of knowledge about the characteristics of the carbon isotopic composition of modern soil in this area. A preliminary investigation of the carbon isotopic compositions of the modern soil and the loess/paleosol sequence on the Loess Plateau shows that the carbon isotopic composition of modern soil is consistent with the distribution of modern plants on the Loess Plateau, where the ecosystem is dominated by a mixture of C4 and C3 plants. Comparing the δ13C values of modern soil and loess-paleosol sequences from the Xunyi profile, we conclude that C3 plants dominated the landscape during loess sediment stages, while C4 plants expanded during paleosol stages.     

Implications of correlated Nd and Sr isotopic variations for the chemical evolution of the crust and mantle

Published data showing a linear correlation between initial Nd and Sr isotope compositions in young basalts indicate the existence of a spectrum of isotopically distinct reservoirs in the mantle which represent either (1) mixtures of two homogeneous endmember reservoirs, one of which may be undifferentiated material or (2) fractionated reservoirs all derived from a homogeneous initial reservoir with the same ratio of enrichment factors for Sm/Nd and Rb/Sr. The slope of the correlation, which can be described approximately by (⁸⁷Sr/⁸⁶Sr) = ?3.74114 (¹⁴³Nd/¹⁴⁴Nd) + 2.61935orε_Nd = ?2.7 ε_Sr, places constraints on the origin of these reservoirs and hence on the chemical evolution of the crust-mantle system. The reservoirs could be residual regions of the mantle left after ancient partial melting events. If so, the requirement of constant relative fractionation of Sm/Nd and Rb/Sr in refractory residues is a strong constraint on partial melting models. Calculations suggest that batch melting models are more compatible with this constraint than are fractional melting models, but models incorporating currently accepted distribution coefficients and residual phase assemblages cannot reproduce the observed isotope effects except under highly specific conditions. The slope of the correlation is not consistent with the hypotheses that chemical structure in the mantle is due to accretional heterogeneity or variable loss of elements to the core. If the mantle reservoirs are complementary in composition to the continental crust, and if the crust + mantle has ε_Nd = 0andε_Sr = 0 and chondritic Sr/Nd, then Rb/Sr in the crust is calculated to be less than 0.10, suggesting that the crust may be more mafic in composition and contain a smaller proportion of the earth's Rb and heat-producing elements than previously estimated.     

Oxygen isotope compositions of quartz grains (4—16μm) from Chinese eolian deposits and their implications for provenance

In recent years, the researches of inland Asia aridification since late Cenozoic have attracted much attention in the paleoclimate community. Rea et al.[1] studied a 12 Ma eolian record in North Pacific and associated it with the aridification of northwes…     

The Vendian record of Sr and C isotopic variations in seawater: Implications for tectonics and paleoclimate

New Sr and C isotopic data, both obtained on the same samples of marine carbonates, provide a relatively detailed record of isotopic variation in seawater through the latest Proterozoic and allow, for the first time, direct correlation of these isotopic changes in the Vendian ( 540–610 Ma). The strong isotope variations determined in this study record significant environmental and tectonic changes. Together with a fairly poorly constrained Nd isotopic record, the Sr and C isotopic records can be used to constrain rates of erosion, hydrothermal alteration and organic C burial. Further, comparison of these records with those of the Cenozoic permit investigation of the general relationship between global tectonics and continental glaciation. In particular, results of this study show a very large change in the ⁸⁷Sr/⁸⁶Sr of marine carbonates from low pre-Vendian ( > 610 Ma) values ( 0.7066) to high Middle Cambrian values ( 0.7090). This change is greater in magnitude than the significant increase in seawater ⁸⁷Sr/⁸⁶Sr through the Cenozoic. Both changes are attributed to high erosion rates associated with continent-continent collisions (Pan-African and Himalayan-Tibetan). In the latest Proterozoic these high erosion rates, probably coupled with high organic productivity and anoxic bottom-water conditions, contributed to a significant increase in the burial rate of organic C. Ice ages mark both the Neoproterozoic and Cenozoic, but different stratigraphic relationships between the Sr isotopic increase and continental glaciation indicate that uplift-driven models proposed to explain Cenozoic climatic change cannot account for the latest Proterozoic ice ages.     

Sources and genesis of the Chinkuashih Au-Cu deposits in northern Taiwan: constraints from Os and Sr isotopic compositions of sulfides

The Chinkuashih district at northern Taiwan hosts one of the largest Au deposits in the western Pacific gold province. Gold were precipitated from hydrothermal solutions as native gold or incorporated into sulfides at a temperature range of 200-350 °C. The sulfides in ore mines have ¹⁸⁷Os/¹⁸⁸Os ratios varying from 0.139 to 0.249. The positive ¹⁸⁷Os/¹⁸⁸Os-1/Os correlation is consistent with derivation from the hybrid fluids containing various proportions of mantle and crustal components. The crustal component was the meteoric water that had acquired its Sr and Os isotopic signatures from the local sedimentary formations and dacitic intrusions. The mantle component was the magmatic fluid segregated from the dacitic magma by fractional crystallization. Based on the ¹⁸⁷Os/¹⁸⁸Os-1/Os correlation, the hybrid fluids forming the Chinkuashih sulfides contained less than 30% magmatic fluid, except for one sulfide sample from Hsumei, which required >40% magmatic fluid. Compared to meteoric water, the magmatic fluid contained a higher Os content (130 times higher) and was enriched in Os relative to Sr with an Os/Sr ratio two orders higher than that of the crustal fluid. Consequently, the Os budget in the hybrid fluids was controlled by the magmatic fluid, although the meteoric water was volumetrically dominated. If gold and Os behave similarly in chemistry, the Chinkuashih gold deposits are of mantle origin and the area where sulfides with the greatest mantle Os signature may host undiscovered gold deposits. Finally, the ¹⁸⁷Os/¹⁸⁸Os ratios of sulfides show no relationship with the mineral assemblages of sulfides, implying that the sulfide mineral assemblages reflect local surfacial redox conditions rather than the chemical characteristics of parental fluids.     

Triassic alkaline intrusives in the Yanliao-Yinshan area: their chronology, Sr, Nd and Pb isotopic characteristics and their implication

Dated isotopic ages for 15 alkaline intrusives in the Yanliao-Yinshan area, ranging from 268 to 190 Ma, ten of which are from 250 to 208 Ma, indicate that most of them were formed in the Triassic Epoch. All the E_Nd(t) ratios from - 17.19 to -3.21 averaging -7.09, the E_Sr(t) ratios fmm 11.7 to71.5 averaging 36.63, and the I_sr(t) ratios from 0.705 0 to 0.709 3 averaging 0.706 8, show their characteristics of enrichment. On the E_Nd (t) virus E_Sr(t) correlation diagram, the samples from these intmsives were plotted within the enriched mantle trend lines and just outside, demonstrating their close connection to materials from the enriched mantle reservoir, taking into account the same Pb isotopic composition as that of the mantle.     

Variations in chemical compositions of the eolian dust in Chinese Loess Plateau over the past 2.5 Ma and chemical weathering in the Asian inland

Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemical composition of AI phase of loess and paleosols is distinctive to the average composition of upper continental crust (UCC), characterized by depletion of mobile elements Na, Ca and Sr. The distribution pattern of elements in AI phase reveals that initial dust, derived from a vast area of Asian inland, has suffered from Na- and Ca-removed chemical weathering compared to UCC. Some geochemical parameters (such as CIA values, Na/K, Rb/Sr and⁸⁷Sr/⁸⁶Sr ratios) display a regular variation and evolution, reflecting that the chemical weathering in the source region of loess deposits has decreased gradually since 2.5 Ma with the general increase of global ice volume. This coincidence reflects that the aridity of Asian inland since the Quaternary is a possible regional response to the global climate change.     

Eolian evidence from the Chinese Loess Plateau: the onset of the Late Cenozoic Great Glaciation in the Northern Hemisphere and Qinghai-Xizang Plateau uplift forcing

On the basis of a newly-constructed record of magnetic susceptibility (SUS) and the depositional rate change of eolian loess-red clay sequences in the last 7.2 Ma BP from the hea Plateau, together with a cornperison of a record of °¹⁸O values from the equatorial East Pacific Ocean and eolian Quartz flux variations fmm the North Pacific Ocean, the evolutiomuy process of the Late Cenozoic Great Glaciation in the Northern Hemisphere can be divided into three stages: the arrival stage around 7.2–3.4 Ma BP, the initial stage at about 3.4—2.6 Ma BP, and the Great Ice Age since 2.6 Ma BP. The evolution of the East Asian monsoon is characterized by paid winter and summer monsoons, and it is basically composed of the initial stage of weak winter and summer monsoons, the transitional stage of simultaneous increase in intensity of winter and summer monsoons, and the prevailing stage of strong winter and week summer monsoons, or weak winter and strong summer monsoons. The Late Cenowic global tectonic uplift, paaicdarly the Qinghai-Xizang Plateau uplift and the associated CO₂ concentration variation, controls the dng processes of the onset of Great Glaciation and the long-term changes of East Asian monsoom climate in the Northern Hemisphere to a large extent. The accelerating uplift of the Qinghai-Xizang Plateau between 3.4 and 2.6 Ma BP provided an important driving force to global climiatic change. Project supported by the foundation of Chinese Academy of Sciences (Grant No. KZ951-A1-402), the State Science and Technology Committee (Grant No. 95-pre-40)and the Chinese Nature Science Foundation (Grant No. 49672140)     

Early Paleozoic ridge subduction in the Chinese Altai: Insight from the abrupt change in zircon Hf isotopic compositions

Zircons were separated from granitoids, gneisses, and sedimentary rocks of the Chinese Altai. Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma, recording a long history of magmatic activity in the region. Zircon Hf isotopic compositions show an abrupt change at ~420 Ma, indicating that prior to that time the magmas came from both ancient and juvenile sources, whereas younger magmas were derived mainly from juvenile material. This may imply that the lithosphere was signifi- cantly modified...     

Changes in grain-size and sedimentation rate of the Neogene Red Clay deposits along the Chinese Loess Plateau and implications for the palaeowind system

In recent years, the Red Clay deposits underlying Quaternary loess on the Chinese Loess Plateau (north China) have attracted more attention because they show a direct and continuous record of past atmos- pheric circulation and palaeoclimatic change. Investiga- tions on Red Clay deposits through multidisciplinary methods have demonstrated an aeolian origin for the Red Clay, like the overlying Quaternary loess. The Red Clay formed during the Miocene and Pliocene[1―13]. However, the type o…     

The Shabogamo Intrusive Suite,Labrador: Sr and Nd isotopic evidence for contaminated mafic magmas in the Proterozoic

The Shabogamo Intrusive Suite comprises numerous bodies of variably metamorphosed gabbro which intrude Archean and Proterozoic sequences at the junction of the Superior, Churchill, and Grenville structural provinces in western Labrador. Combined Sm-Nd and Rb-Sr systematics in two bodies, ranging from unmetamorphosed to lightly metamorphosed, document a crystallization age of about 1375 m.y., and suggest that both bodies crystallized from magmas with similar Nd and Sr isotopic compositions. This age is in accordance with the existence of a regional magmatic event in the Churchill Province at approximately 1400 m.y.Rb-Sr systematics in two bodies of amphibolite-grade gabbro suggest a regional metamorphic event at about 950 m.y., corresponding to the waning stages of Grenville activity. Sm-Nd systematics in these high-grade bodies are affected to a much lesser degree than Rb-Sr.Initial ratios for¹⁴³Nd/¹⁴⁴Nd and⁸⁷Sr/⁸⁶Sr are lower and higher, respectively, than bulk earth values at 1375 m.y. Both these displacements are in the direction of older crustal material at 1375 m.y., and a model is proposed to produce the Shabogamo magma by mixing a mantle-derived magma with a partial melt of crustal rocks (approximately 4: 1 by volume). Young volcanic rocks with anomalous Nd and Sr isotopic ratios, which have previously been taken as evidence for “enriched” mantle, may be interpreted similarly.     

Mapping long-term terrace change in the Chinese Loess Plateau: A new approach by decision tree model with digital elevation model (DEM) and land use

Human-created terraces are distributed extensively in the Chinese Loess Plateau, which play key roles in soil conservation, agricultural production and sustainable development. However, large-scale and long-term terrace mapping remains a big challenge due to the complexity of topography, land cover and the deficiency of high-quality historical spatial data. Facing this task, our study aims to develop a new approach for capturing 30 years (from 1990 to 2020) of terrace patterns at macroscales (the whole Loess Plateau, with an area of 6.4 × 10⁵ km²). The decision tree model (DTM) was integrated with digital elevation model (DEM) and land use data to detect terrace change, and terraced samples were extracted from existing findings for spatial validation. Our study confirmed that this new approach can work successfully on identifying cultivated and grassy terraces, as evidenced by receiver operating characteristic (ROC) curves and area under curve (AUC) values. More notably, a decreasing trend was detected in cultivated terraces with continued uneven distribution from 1990 to 2020, while the areas of grassy terraces increased markedly with more-concentrated larger patches. This finding indicated that huge areas of terrace abandonment may have already occurred in this region. More attention thus should be paid to the rising risks of cropland utilization and food security. Since it is the first time to get long-term reliable terrace maps on the Loess Plateau, our efforts can help to better take stock of terrace resources for wiser land use managements and agricultural policy adjustments, finally benefiting socio-ecological sustainability.     

Pb, Nd, and Sr isotopic constraints on the origin of Miocene basaltic rocks from northeast Hokkaido, Japan: Implications for opening of the Kurile back-arc basin

Late Miocene (7–9 Ma) basaltic rocks from the Monbetsu‐Kamishihoro graben in northeast Hokkaido have chemical affinities to certain back‐arc basin basalts (referred to herein as Hokkaido BABB). Pb‐, Nd‐ and Sr‐isotopic compositions of the Hokkaido BABB and arc‐type volcanic rocks (11–13 Ma and 4–4.5 Ma) from the nearby region indicate mixing between the depleted mantle and an EM II‐like enriched component (e.g. subducted pelagic sediment) in the magma generation. At a given ⁸⁷Sr/⁸⁶Sr, Hokkaido BABB have slightly lower ¹⁴³Nd/¹⁴⁴Nd and slightly less radiogenic ²⁰⁶Pb/²⁰⁴Pb compared with associated arc‐type lavas, but both these suites are difficult to distinguish solely on the basis of isotopic compositions. These isotopic data indicate that while generation of the Hokkaido BABB involves smaller amounts of the EM II‐like enriched component than do associated arc lavas, Hokkaido BABB are isotopically distinct from basalts produced at normal back‐arc basin spreading centers. Instead, northeast Hokkaido BABB are more similar to basalts erupted during the initial rifting stage of back‐arc basins. The Monbetsu‐Kamishihoro graben may have developed in association with extension that formed the Kurile Basin, suggesting that opening of the basin continued until late Miocene (7–9 Ma).     

Effects of precipitation and landuse on runoff during the past 50 years in a typical watershed in the Loess Plateau, China

In the past century, great progress has been made worldwide in our understanding of forest-water relationship. The successful forestation programs implemented in China-which have improved the ecological environmental conditions-have gained the attention of many researchers and highlighted the relationship between forestation and water yields. The arid and semi-arid Loess Plateau has received attention from water engineers and eco-hydrological researchers in China because of a shortage in water resources. We selected one of the oldest stations conducting soil and water conservation experiments, the Xifeng soil and water conservation station, and chose the Nanxiaohe catchment and its paired catchments （Yangjiagou catchment and Dongzhuanggou catchment） as our research areas. Trends in precipitation, air temperature, streamflow over the past 50 years, and the effect of changing land use on streamflow were analyzed. The Mann-Kendall test showed that precipitation had a negative trend （downward trend）, whereas air temperature showed a positive trend （upward trend） from the past to present in the Nanxiaohe catchment. However, the trends seen in precipitation, air temperature did not contain any ＂jumping points.＂ The paired catchment approach is used to detect the effects of land cover change on hydrology in the Yangjiagou and the contrast catchment, i.e., Dongzhuanggou catchment in our study. The results showed a large change in land use in the Yangjiagou catchment from 1954 to 2008. An increase in forested land （from 0% to 40.08% from 1954 to 2008） and a reduction of bare land （from 51.26% to 5.50% from 1954 to 2008） accounted for a large part of the change in land use. However, the land use changed little in the contrast catchment. The comparison of streamfiow in the paired catchments showed that forestation reduced streamflow by 49.63% （or 6.5 mm） each year.     

Cosmogenic nuclide burial ages and provenance of Late Cenozoic deposits in the Sichuan Basin: Implications for Early Quaternary glaciations in east Tibet

Collision between the Indian and the Eurasian plates since the early Cenozoic produces one of the world’s most remarkable continental escarpments between the Tibetan Plateau and the adjacent Sichuan Basin. Yet Tertiary sediments are rare in the Sichuan Basin; the oldest preserved Late Cenozoic deposits called Dayi conglomerates directly overlie the Cretaceous or Jurassic red beds. Using cosmogenic ¹⁰Be and ²⁶Al burial dating, we obtain deposition ages of ～2.0 Ma and catchment erosion rates of ～400 mm/ka for the Dayi conglomerates. Zircon U–Pb age distributions suggest derivation of these conglomerates from the Songpan-Ganzi flysch, the Pengguan complex and Late Permian and Triassic granite plutons in the headwater regions of the Min Jiang (Jiang, a Chinese term, means river). The formation of the poorly-sorted, sub-angular to sub-rounded and tens-centimeter-sized deposits in the western margin of the Sichuan Basin, after long distance transportation, is best explained by glacial activity ～2.0 Ma ago in east Tibet.     

Continental basalts in the accretionary complexes of the South-west Japan Arc: Constraints from geochemical and Sr and Nd isotopic data of metadiabase

Abstract The Ryoke Belt is one of the important terranes in the South‐west Japan Arc (SJA). It consists mainly of late Cretaceous granitoid rocks, meta‐sedimentary rocks (Jurassic accretionary complexes) and mafic rocks (gabbros, metadiabases; late Permian–early Jurassic). Initial ?_Sr (+ 25– + 59) and ?_Nd (? 2.1–?5.9) values of the metadiabases cannot be explained by crustal contamination but reflect the values of the source material. These values coincide with those of island arc basalt (IAB), active continental margin basalt (ACMB) and continental flood basalt (CFB). Spiderdiagrams and trace element chemistries of the metadiabases have CFB‐signature, rather than those of either IAB or ACMB. The Sr–Nd isotope data, trace element and rare earth element chemistries of the metadiabases indicate that they result from partial melting of continental‐type lithospheric mantle. Mafic granulite xenoliths in middle Miocene volcanic rocks distributed throughout the Ryoke Belt were probably derived from relatively deep crust. Their geochemical and Sr–Nd isotopic characteristics are similar to the metadiabases. This suggests that rocks, equivalent geochemically to the metadiabases, must be widely distributed at relatively deep crustal levels beneath a part of the Ryoke Belt. The geochemical and isotopic features of the metadiabases and mafic granulites from the Ryoke Belt are quite different from those of mafic rocks from other terranes in the SJA. These results imply that the Ryoke mafic rocks (metadiabase, mafic granulite) were not transported from other terranes by crustal movement but formed in situ. Sr–Nd isotopic features of late Cretaceous granitoid rocks occurring in the western part of the Japanese Islands are coincident with those of the Ryoke mafic rocks. Such an isotopic relation between these two rocks suggests that a continental‐type lithosphere is widely represented beneath the western part of the Japanese Islands.     

In situ zircon Hf isotopic, U-Pb age and trace element study of monzonite xenoliths from Pingquan and Fuxin basalts:Tracking the thermal events of 169 Ma and 107 Ma in Yanliao area

K-Ar ages of the Mesozoic (92-100 Ma) Fuxin alkalic basalts (western Liaoning Province) and the Tertiary (23-45 Ma) Pingquan alkalic basalts (eastern Hebei Province), and the results of in situ zircon U-Pb dating, Hf isotope and the trace elements from three monzonite xenoliths carried in the alkalic basalts are reported. The crust-mantle interaction occurring in the Yanshan intracontinental orogenic belt is also discussed. Fuxin zircons show highly uniform U-Pb age ((169±3) Ma). More than 95% Pingquan zircons display the age of (107±10) Ma except two are 2491 Ma and 513 Ma respectively. Zircons with the ages of (169±3) Ma have εHf close to zero. εHf of the zircons with the ages of (107±10) Ma are mainly at -11.5--16.3, showing the crustal derivation. Fuxin zircons contain low Nb, Ta, Sr, Th, U contents, low and narrow Hf model ages (0.87-1.00 Ga), which reflect that the source materials of the monzonite xenoliths are young to Pingquan (focus at (1.28±0.08) Ga). High contents of the incompatible elements, and wide range of Hf model ages (0.89-2.56 Ga) in Pingquan zircons suggest a more complex source and the highly crustal maturity in their petrogenesis. Comprehensive information including the published data indicates that J3-K1 is the key period of the deep processes and shallow tectonic reverse in the Yanliao area. However, the processes were highly heterogeneous in spatial and in temporal.     

Spatio‐temporal variability of the isotopic input signal in a partly forested catchment: Implications for hydrograph separation

The isotopic composition of precipitation (D and ¹⁸O) has been widely used as an input signal in water tracer studies. Whereas much recent effort has been put into developing methodologies to improve our understanding and modelling of hydrological processes (e.g., transit‐time distributions or young water fractions), less attention has been paid to the spatio‐temporal variability of the isotopic composition of precipitation, used as input signal in these studies. Here, we investigated the uncertainty in isotope‐based hydrograph separation due to the spatio‐temporal variability of the isotopic composition of precipitation. The study was carried out in a Mediterranean headwater catchment (0.56 km²). Rainfall and throughfall samples were collected at three locations across this relatively small catchment, and stream water samples were collected at the outlet. Results showed that throughout an event, the spatial variability of the input signal had a higher impact on hydrograph separation results than its temporal variability. However, differences in isotope‐based hydrograph separation determined preevent water due to the spatio‐temporal variability were different between events and ranged between 1 and 14%. Based on catchment‐scale isoscapes, the most representative sampling location could also be identified. This study confirms that even in small headwater catchments, spatio‐temporal variability can be significant. Therefore, it is important to characterize this variability and identify the best sampling strategy to reduce the uncertainty in our understanding of catchment hydrological processes.