Search

The mountainous region of central Shandong Province in eastern China is renowned for its high frequency of rainstorms, which often result in devastating flood disasters and have profoundly affected the evolution of local ancient civilizations. To identify ancient flood disaster events, recognizing sediment signatures via multiple indices is important. Here, we investigated the 2018 flood deposits in the Danhe River Basin and sampled short core DH2, on which the grain size, total organic matter (TOM) content, carbonate content, magnetic susceptibility (MS) and pollen were measured. The fine grain size of the flood sedimentary layer reveals that the flood energy in the alluvial plain area is usually weak. The pollen species and concentration and the tree pollen content in the flood layer are significantly greater than those in the soil layer, suggesting that the flood sediment mainly originates from the mountainous areas in the upper reaches of the river, which provides more forest vegetation information. The MS of flood deposits is lower than that of the soil layer, which is mainly related to the intensity of pedogenesis. The research results indicate that the flood sediments in the downstream floodplain areas of small watersheds are predominantly composed of fine-grained components, with characteristics of high loss on ignition, low magnetic susceptibility, high pollen abundance and diverse species. These findings establish a multi-index identification system for paleoflood sedimentation, which has important reference significance for the study of paleoflood sedimentology and hydrology. [ABSTRACT FROM AUTHOR]

As was shown in Part I of this paper, a simple application of Sternberg's Law of downstream fining does not accommodate all the data included in this study. The study area includes the low-relief Great Plains and the high relief of the Rocky Mountains, good overall terrain for application of Sternberg's Law, but with some complications from isolated mountain ranges. Most of the study area exhibits evidence of glaciation, but diluvial planation surfaces are also present. Channelized flow, transport by ice, and sheet flow are all candidate processes for transport of gravel. Results from statistical analysis of 5,839 sieve analysis reports indicate a complex history for the surficial gravel deposits. [ABSTRACT FROM AUTHOR]

Freshwater mussels preserve valuable information about hydrology, climate, and population dynamics, but developing seasonal chronologies can be problematic. Using clumped isotope thermometry, we produced high-resolution reconstructions of modern and historic (~ 1900) temperatures and δ18Owater from mussel shells collected from an impounded river, the Brazos in Texas, before and after damming. We also performed high-resolution growth band analyses to investigate relationships between mussel growth rate, rainfall, and seasonal temperature. Reconstructed δ18Owater and temperature vary little between the modern (3R5) and historic shell (H3R). However, a positive relationship between reconstructed δ18Owater and growth rate in H3R indicates that aside from diminished growth in winter, precipitation and flow rate are the strongest controls on mussel growth in both modern and pre-dam times. Overall, our results demonstrate (1) the impact, both positive and negative, of environmental factors such as flow alteration and temperature on mussel growth and (2) the potential for clumped isotopes in freshwater mussels as a paleohydrology and paleoclimate proxies in terrestrial environments. [ABSTRACT FROM AUTHOR]

In the 150 years since Sternberg's Law of downstream fining was published, causes and complications have proliferated with research in many fluvial environments. The basic relationship is a first-order differential equation expressing an energy relationship, and the geologic causes and effects that fall under its umbrella are diverse. Grain size distributions of sands provide indications of modes of deposition, but gravels do not. However, while competence is seldom a limiting factor for sands, it is for gravels. The study area includes the low-relief Great Plains and the high relief of the Rocky Mountains. Island mountain ranges complicate this somewhat, but stream courses are sufficiently simple for Sternberg's Law. Most of the study area exhibits features generally believed to have resulted from Ice-Age glaciation. Catastrophic evidence in the form of planation surfaces is also present. Thus channelized flow, transport by ice, and sheet flow are all candidate processes for transport of gravel. Predictions of grain size distributions from these processes are compared with results from statistical analysis of 5,839 sieve analysis reports. The results indicate a complex history for the surficial gravel deposits. [ABSTRACT FROM AUTHOR]

Giant evaporite deposits formed during the Messinian Salinity Crisis (MSC) in the Mediterranean Sea during the upper Miocene. The primary cause is a restricted Atlantic-Mediterranean connection, but the detailed hydroclimate evolution of this event is still a matter of debate. Here we reconstruct the triple oxygen and hydrogen isotopic composition of paleo brines from structurally bonded water in Messinian gypsum from Cyprus. A two-stage evaporation model is constructed to best approximate the hydrological conditions at which Messinian gypsum formed in marginal basins of the Mediterranean Sea. Subsequently, hydroclimatic parameters like paleo relative humidity (RH) are modelled using an iterative curve fitting isotope model approach. The results of our limited dataset reveal a slightly lower RH during the third compared to the second stage of the MSC. This apparent drop in RH is consistent with previous observations from the literature. Besides absolute values of RH, our model allows reconstructing the triple oxygen and hydrogen isotopic composition of the open Mediterranean Sea. This provides an estimate for the proportions of continental water vs. Atlantic seawater flowing into the basin, serving as a proxy for the size of the strait of Gibraltar. The model implies a continental water fraction of around 75–81 % both for the second and third stage of the MSC. In addition, we determined the 87Sr/86Sr of our samples to: i) confirm their stratigraphy; and ii) estimate the relative proportion of continental water vs. Atlantic seawater entering the Mediterranean using Sr mass balance calculations. The combined oxygen and Sr isotope records indicate a persistent connection to the Atlantic supporting the hypothesis that the striking drop in 87Sr/86Sr at the beginning of MSC stage 3 is mainly related to an increased contribution of continental water with low 87Sr/86Sr and high Sr concentrations from the Paratethys. Our results show that the combination of triple oxygen, hydrogen, and Sr isotope data provides a powerful tool to disentangle paleo-hydroclimate even in such complicated hydrological settings as the Mediterranean Sea during the MSC. [ABSTRACT FROM AUTHOR]

Fundamental insight into the long-term 'geoecohydrological' dynamics of rivers and floodplains is required for their sustainable management. To study these dynamics, a multi-proxy approach is essential. While suitable proxies are available for reconstructing floodplain geomorphology and past vegetation, the suitability of the available proxies for past hydrology to reconstruct floodplain wetness has not yet been evaluated. In this study, we apply a multi-proxy analysis combining testate amoebae and several geochemical proxies for decomposition (humification, carbon and nitrogen stable isotopes), in comparison to sedimentological (stratigraphy, loss on ignition) and palaeobotanical records, to obtain independent hydrological reconstructions of alluvial floodplains in contrasting environmental settings to explore the suitability of the available proxies for past hydrology to reconstruct floodplain wetness. This study concludes that testate amoebae cannot provide a continuous and reliable hydrological reconstruction, as they are insufficiently preserved in alluvial peat deposits. In addition, mineral particles within the tests size range hamper the analysis in mineral-dominated sediment units. As organic matter decomposition is low when water tables are high and vice versa, we expected the decomposition proxies to reflect the hydrological conditions. While the amount of humic acids appears to depend mainly on the substrate rather than the decomposition of the organic matter in it, the analyses of carbon and nitrogen stable isotopes provide promising results, for both peat and non-peat deposits. [ABSTRACT FROM AUTHOR]

Speleothem δ13C in monsoonal China differs from speleothem δ18O, which is widely used as a climatic proxy for several complex control reasons. Nevertheless, δ13C records have the potential to reveal the implications of hydroclimatic changes. This study reports a speleothem δ13C record from Didonghe (DDH) Cave in central China spanning 34 to 13 kyr BP. After we investigated the factors that influence speleothem δ13C, we found that the δ13C record showed that DDH Cave can prompt directional shifts via local hydroclimatic changes, such as in vegetation types, biomass, and rock–water interaction processes, suggesting that δ13C is mainly controlled by the local hydroclimate. Ensemble empirical mode decomposition (EEMD) results revealed a coupling relationship between δ18O and δ13C on multiple timescales, which suggested that changes in precipitation caused by large-scale monsoonal circulation are controlled by regional hydrological conditions to a great extent. However, the hydrological conditions of the cave were relatively mild and humid during the last glacial maximum (LGM), which revealed the impact of evaporation on changes in the region's hydrological conditions. We also found that the δ18O and δ13C profiles decoupled when δ13C changed with a shift in the location of the westerly during HS1. The δ13C record correlates well with other paleoclimate records, suggesting that regional hydrological conditions are also modulated by the Earth's internal and external driving factors. [ABSTRACT FROM AUTHOR]

Freshwater mussels preserve valuable information about hydrology, climate, and population dynamics, but developing seasonal chronologies can be problematic. Using clumped isotope thermometry, we produced high-resolution reconstructions of modern and historic (~ 1900) temperatures and δ18Owater from mussel shells collected from an impounded river, the Brazos in Texas, before and after damming. We also performed high-resolution growth band analyses to investigate relationships between mussel growth rate, rainfall, and seasonal temperature. Reconstructed δ18Owater and temperature vary little between the modern (3R5) and historic shell (H3R). However, a positive relationship between reconstructed δ18Owater and growth rate in H3R indicates that aside from diminished growth in winter, precipitation and flow rate are the strongest controls on mussel growth in both modern and pre-dam times. Overall, our results demonstrate (1) the impact, both positive and negative, of environmental factors such as flow alteration and temperature on mussel growth and (2) the potential for clumped isotopes in freshwater mussels as a paleohydrology and paleoclimate proxies in terrestrial environments. [ABSTRACT FROM AUTHOR]

The Greenland and Antarctic ice sheets are covered in a layer of porous firn. Knowledge of firn structure improves our understanding of ice sheet mass balance, supra- and englacial hydrology, and ice core paleoclimate records. While macroscale firn properties, such as firn density, are relatively easy to measure in the field or lab, more intensive measurements of microstructural properties are necessary to reduce uncertainty in remote sensing observations of mass balance, model meltwater infiltration, and constrain ice age – gas age differences in ice cores. Additionally, as the duration and extent of surface melting increases, refreezing meltwater will greatly alter firn structure. Field observations of firn grain size and ice layer stratigraphy are required to test and validate physical models that simulate the ice-sheet-wide evolution of the firn layer. However, visually measuring grain size and ice layer distributions is tedious, is time-consuming, and can be subjective depending on the method. Here we demonstrate a method to systematically map firn core grain size and ice layer stratigraphy using a near-infrared hyperspectral imager (NIR-HSI; 900–1700 nm). We scanned 14 firn cores spanning ∼ 1000 km across western Greenland's percolation zone with the NIR-HSI mounted on a linear translation stage in a cold laboratory. We leverage the relationship between effective grain size, a measure of NIR light absorption by firn grains, and NIR reflectance to produce high-resolution (0.4 mm) maps of effective grain size and ice layer stratigraphy. We show the NIR-HSI reproduces visually identified ice layer stratigraphy and infiltration ice content across all cores. Effective grain sizes change synchronously with traditionally measured grain radii with depth, although effective grains in each core are 1.5 × larger on average, which is largely related to the differences in measurement techniques. To demonstrate the utility of the firn stratigraphic maps produced by the NIR-HSI, we track the 2012 melt event across the transect and assess its impact on deep firn structure by quantifying changes to infiltration ice content and grain size. These results indicate that NIR-HSI firn core analysis is a robust technique that can document deep and long-lasting changes to the firn column from meltwater percolation while quickly and accurately providing detailed firn stratigraphy datasets necessary for firn research applications. [ABSTRACT FROM AUTHOR]

The driving force of climate change in the monsoon margin is complex, making it a key area for regional and global climate change research. Palaeohydrological studies in the monsoon margin have increased the resolution of research in the long term, transitioning from qualitative to quantitative studies to comprehend climate change processes, patterns, and mechanisms. Testate amoebae (TA) in peat sediments are used as a proxy indicator organism for quantitative reconstruction of palaeohydrology. Thus, their community changes are directly related to precipitation, and widely used to reconstruct the patterns of summer precipitation globally. We investigated TA species and reconstructed palaeohydrological changes in the Greater Khingan Mountains' Hongtu (HT) peatland, located in the East Asian Summer Monsoon (EASM) margin. The result showed that the most abundant TA species were Assulina muscorum (12.4 ± 5.0%) and Nebela tincta (8.9 ± 4.9%) in the HT peat core. The increase in dry indicator species (e.g., A. muscorum and Alabasta militaris) indicated a drying pattern in the HT peatland since 150 cal yr BP. Principal component analysis (PCA) explained 47.6% of the variation in the selected TA assemblages. During 400 to 250 cal yr BP, PCA axis 1 scores ranged from 0.2 to −1.3 (reflecting a drier climate), associating with the Little Ice Age. The paleohydrology of the northern part of the Greater Khingan Mountains was mainly controlled by the EASM, which was associated with changes in North Atlantic Sea surface temperature and solar radiative forcing. The apparent drying pattern may be the result of the gradual intensification of anthropogenic activities and the increase in EASM intensity. [ABSTRACT FROM AUTHOR]

This study focuses on characterizing a discontinuity within the Seán stalagmite (4.75–7.75 cm) by means of two nondestructive techniques: (1) high-resolution micro-computed tomography (micro-CT) and (2) X-ray fluorescence (XRF) core scanning (XRFCS). Micro-CT was used to study the stalagmite density, and XRFCS was applied to obtain the qualitative elemental composition and colour measurements. The new data obtained from nondestructive techniques have been combined with previously published geochemical data and fabric determinations from the same stalagmite found in Sa Balma des Quartó cave in Mallorca. The two methodologies applied in the present study have improved the characterization of the distinctive horizon. The micro-CT images identified the layer as a minor event due the high air content. The distinctive horizon is characterized by a high Ti-content, indicating the arrival of terrigenous particles. Based on those observations, together with the fact that the micrite layer appears filling the gaps between the older columnar fabric, we argue that the micrite layer may represent a major flooding event inside the cave after the year 1616 ± 23 CE and before the year 1623 ± 28 CE, which can be related to an extreme rainfall event. This hypothesis is further supported by the observed cave flooding during the autumn of 2018. [ABSTRACT FROM AUTHOR]

Strata produced by fluvial dunes can provide insight into the hydrological regime of ancient rivers. Recent experiments indicate that conditions of disequilibrium between bedforms and formative flows may be inferred from the coefficient of variation of preserved dune cross‐set thickness, suggesting that this quantity may act as a proxy for the flashiness of river floods relative to the time required for full bedform translation. To assess whether this idea is applicable to interpretations of the stratigraphic record, this study examines published data relating to more than 2600 cross‐sets from 53 sedimentary units of 19 river systems. The presented analyses must not be over‐interpreted, because the considered rivers span different environmental settings, the data sources are heterogeneous in terms of type and dimensionality, and some variables were established by applying empirical relationships. Yet, significant findings are revealed. Larger rivers exhibit discharge and bedform characteristics that are more conducive to disequilibrium; however, a modest increase in the coefficient of variation of cross‐set thickness, CV(Dst), as opposed to the expected decrease, is seen as a function of river size. Crucially, smaller CV(Dst) values are not systematically associated with conditions that should favour dune disequilibrium. Meanwhile, only ca 25% of the studied examples demonstrate cross‐set thickness statistics compatible with quantitative formulations of the autogenic control by variable dune topography – the notion of 'variability‐dominated' preservation. These findings indicate that the variability in cross‐set thickness may be a poor predictor of discharge variability, perhaps because of the multiplicity of factors controlling dune preservation, such as bedform hierarchy, transport stage and depth‐dependent variations in dune disequilibrium. To improve interpretations of cross‐stratified deposits, further research is needed: (i) to establish the value of process‐to‐product models for reverse product‐to‐process interpretations; and (ii) to define representative samples for preserved dune deposits accounting for temporal and spatial variability in preservation potential. [ABSTRACT FROM AUTHOR]

Dynamics of the terrestrial water surface impact hydrological connectivity. Compared with traditionally deployed water surface parameters, changes in the water-boundary more effectively account for the dynamics of water surface and depth resulting from hydrological variations. However, previous studies of hydrological connectivity generally applied only connectivity length or width parameters using the center line of the water body and therefore fail to fully capture the impact of water boundary dynamics. In this study, optimized water body extraction indices based on data obtained from remote sensing imagery are used to develop a novel metric that indicates water surface boundary dynamics and reveal surface hydrological connectivity changes in the Yangtze River Delta from 1990 to 2020. Detailed inter-annual and seasonal changes in the evolution of water body boundaries from a water surface perspective indicate an overall decline in hydrological connectivity against the background of climate change, increased urbanization, and dam construction. The declining trend in connectivity occurs in three phases, viz. from 1990 to 2003, a gradual decline is exhibited but with a very marked degree of inter-seasonal variability; between 2003 and 2012, connectivity remains relatively constant but with a reduced amplitude between seasons; further reductions in the magnitude of seasonal variations characterize the third phase, to 2020. Meanwhile, the stability of hydrological connectivity, indicated by the coefficient of variation, also exhibits marked spatial heterogeneity. Parts of the delta with more tributaries, including the Huaihe and southeastern basins, have lower stability (7.33 and 6.59, respectively) than the Yangtze basin (6.22). This study presents a novel metric to achieve greater precision in the monitoring of hydrological connectivity. Such information can be harnessed to improve regional ecological and water resource management. [ABSTRACT FROM AUTHOR]

Slackwater deposits representing past flood events provide a robust means to extend systematic gage records further back in time, place historic floods in a longer-term context, and reduce uncertainties in flood hazard analysis. The identification and application of slackwater deposits in riverine paleoflood hydrology has traditionally been limited to arid bedrock-controlled environments and periglacial environments. In this study, we utilize methods developed in humid alluvial settings and apply them to slackwater deposits, one of the first studies to do so. This novel approach uses sediment texture and geochemistry to distinguish slackwater deposits from in situ material in a temperate alluvial setting. We identify multiple slackwater deposits in two rock shelters situated on bluffs adjacent to the lower Ohio River. Flood age estimates are based on optically stimulated luminescence (OSL) dating, and discharge estimates are based on a 1D HEC-RAS model. The uppermost slackwater deposit at both sites corresponds to the AD 1937 historic flood of record (∼31,400 m3/s), while another slackwater deposit identified only at the lower elevation site corresponds to a paleoflood that occurred around AD 1650 with a discharge of ∼23,900 m3/s. Our findings imply that the AD 1937 flood represents the largest magnitude flood on the lower Ohio River in at least the last 400 years. Inclusion of the paleoflood into a flood frequency analysis for the Ohio River at Louisville reduces uncertainties in large flood quantiles by ∼50%. [ABSTRACT FROM AUTHOR]

The early to middle Holocene was marked by considerable variability in lake levels in the Lake Superior Basin due to a combination of meltwater runoff, isostatic adjustment, shifting glacial margins, and climate change. These processes likely had a large impact on the preservation and visibility of coastal archaeological sites dating from the Early Period (Paleoindian) to the Middle Period (Shield Archaic). Of particular interest is the brief interval after 9300 cal. B.P. when ancestral Lake Superior dropped to its lowest level (Houghton) and human populations may have made incursions deeper into the basin. Elsewhere in the Upper Great Lakes, this period is associated with offshore archaeological sites submerged by rising water levels later in the Holocene. New geological data from the Thunder Bay, ON, region yield exceptional insight into the paleohydrology of the Houghton phase and, hence, the underwater archaeological prospects of this low water phase in the northern Lake Superior Basin. These data indicate that the lake reached its lowest level by at least ~9100 cal. B.P. but was highly unstable, at least initially, due to a combination of climate and meltwater runoff. Early underwater sites may be confined to two short, hydrologically closed, lowstands between ~9100 and 8700 cal. B.P. and would have been impacted by at least one lake transgression. Such sites, however, may still hold better potential for organic preservation and the visibility of large cultural features compared to their terrestrial counterparts. Coastal sites occupied when the lake was hydrologically closed may be especially well‐preserved due to rapid inundation before the gradual, and generally erosional, Nipissing transgression occurred. [ABSTRACT FROM AUTHOR]

We developed a new approach to identify vulnerabilities to water insecurity across entire archaeological culture areas by combining a paleohydrological model of the sensitivites of hydrological systems to droughts with least-cost analyses of the costs to acquire domestic water. Using a custom Python script integrated into ArcGIS Pro software, we calculated the pairwise one-way cost in time for walking between 225 water sources and 5,446 Ancestral Pueblo cultural sites across the Jemez and Pajarito Plateaus of the Jemez Mountains, New Mexico. This allowed us to identify whether periodic hydrological droughts occurring between AD 1100 and 1700 increased water acquisition costs across these regions.We found that hydrological droughts increased travel times in both regions to durations exceeding modern standards for water insecurity. Beginning in the fourteenth century, greater underlying hydrogeological sensitivities to droughts and the decline of a dual-residence pattern caused by population losses made the remaining aggregated communities of the Pajarito Plateau much more vulnerable to water insecurity than those on the Jemez Plateau. This would have upended long-standing relationships between communities and water on the Pajarito Plateau during a time when socioeconomic integration across the northern Rio Grande Valley pulled people toward valley bottoms. [ABSTRACT FROM AUTHOR]

An increasing, but spatially inhomogeneous, trend in Tibetan Plateau (TP) precipitation, and especially the precipitation anomalies in southeastern TP (TPSE), has become the subject of major scientific concern. The Indian summer monsoon (ISM) is one of the TPSE's most important moisture sources, and its characteristics are therefore key for precipitation changes. Here we present the ISM activities (ISM onset/retreat date, ISM duration, and ISM intensity) and the percentages of varied moisture sources in TPSE, using OLR datasets and Hysplit modeling with gbl reanalysis. The recent precipitation anomalies in TPSE are analyzed with CMFD reanalysis. Major findings: (1) The ISM in TPSE generally begins later, retreats earlier, is of shorter duration, and weaker in intensity. (2) Uniformly decreasing (increasing) precipitation trends are found in TPSE for periods 1979 − 2018 and 1999 − 2018 (1979 − 1998). (3) Moistures along with the ISM are the primary controls of TPSE precipitation (~ 85% in summer); these are also verified by the generally same linear trends observed in ISM moistures and TPSE precipitation in summer. (4) The precipitation anomalies in TPSE are closely related with the ISM activities: the ISM onset date (retreat date) and its variabilities affect precipitation during May − June (September − October); precipitation during July − August correlates positively with the ISM duration and its intensity. The ISM activities impact the percentages of ISM moistures and finally affect the precipitation amount and their trends. These results will contribute to precipitation-related studies as hydrology, ecology, and paleoclimate reconstructions in TP. [ABSTRACT FROM AUTHOR]

The recognition of meandering rivers in Earth's prevegetation stratigraphic record is hindered by an absence of depositional models specifically tailored to unvegetated single‐channel rivers. As a result, their abundance on the early Earth is currently unknown. Here, sedimentological studies of two modern meandering river reaches with unvegetated banks were conducted. Both reaches are located in arid basins of Nevada, USA. Stratigraphy was analysed in conjunction with satellite imagery and high‐resolution topographic data to understand how channels and floodplains record past flow conditions. Analyses of point‐bar and channel‐fill deposits showed that lateral accretion sets are not heterolithic but, rather, composed of mixed sand and sand‐sized mud aggregates (clumps of clay and silt) interpreted to have formed through flocculation. Levées are present but subdued. Notably, downstream‐migrating outer‐bank‐attached bars are prominent architectural features that may be common in unvegetated meandering rivers in arid landscapes elsewhere. The identification of such depositional elements in the stratigraphic record may enhance recognition of ancient unvegetated meandering rivers and improve reconstructions of palaeohydrology on early Earth and Mars. [ABSTRACT FROM AUTHOR]

Establishing accurate palaeo‐hydroclimatic reconstructions from lacustrine and marine archives is a long‐standing challenge in palaeoenvironment studies. Closed‐basin evaporites, and especially halite, record episodes of extremely arid conditions during rapid climate change. However, the complex limnological behaviour of deep hypersaline water bodies and the stochastic nature of the hydroclimatic regime and its variations limit detailed palaeo‐hydroclimatic interpretations from such records. Therefore, a mass‐balance model was developed to explore hydrology–limnology–sedimentology relationships in hypersaline environments under both deterministic and stochastic approaches that generates synthetic halite–mud sequences. Applying the model to the Holocene Dead Sea halites yields novel insights into palaeoenvironmental conditions in the Levant. The deterministic framework indicates that: (i) under a series of similar hydroclimatic cycles, the thickness of each subsequent halite interval decreases, due to the depletion of dissolved‐ions storage in the brine; (ii) halite deposition requires lake levels to drop below the minimal lake level of the preceding cycle; (iii) the time interval between halite deposition and the hydrological minimum is increasingly longer in subsequent cycles. Thus, counter‐intuitively, halite deposition mostly takes place as water discharge increases, providing that the water balance is still negative. The stochastic approach produced random sequences comparable to the observed Dead Sea sedimentary record. It demonstrates that some hydrological minima are not represented by halite deposition at all. Furthermore, the thickness and number of halite beds at each hydrological cycle vary substantially, depending on the specific hydrological conditions realized. Finally, these results imply that the major Dead Sea level drop at the pre‐Holocene deglaciation (ca 14 ka bp), previously assumed to be a record minimum, could not have been as pronounced as suggested, and must have been milder than the subsequent drop at the early Holocene (ca 11–10 ka bp). [ABSTRACT FROM AUTHOR]

During the Roman domain of the Iberian Peninsula (from 201 BCE to 460 CE) water management infrastructures were built to satisfy high water demand. However, whether the Roman activities affected the hydrological balance of Iberian wetlands remains unclear. Here, we investigate the paleo-hydrology of Lake Zóñar (southern Iberia) by using the stable isotopes (16O, 17O, 18O, 1H and 2H) of its gypsum (CaSO4·2H2O) sediments and reconstruct the isotopic composition of the lake water during Roman times. A period of recurrent lake low stand occurred between 2120 and 1890 cal. yr BP (ca. 170 BCE to 60 CE), coinciding with a relatively dry climate stage recorded by most regional paleoclimate archives. The stable isotopes and hydrochemistry of the lake water during gypsum precipitation are consistent with a shallow saline lake that evaporated under relative humidity ~ 10% lower than the present annual mean and at least 20% less rainfall amount. Our analytical and archeological findings support lake level lowering during the Roman period was probably caused by combined arid climate conditions and diversion of the inlets feeding the lake. Spring capturing was likely necessary to satisfy the high water demand of nearby Roman settlements, in the framework of a period of persistent droughts. [ABSTRACT FROM AUTHOR]

Isotope-based records provide valuable information on past climate changes. However, it is not always trivial to disentangle past changes in the isotopic composition of precipitation from possible changes in evaporative enrichment, and seasonality may need to be considered. Here, we analyzed δ2H on n-alkanes and δ18O on hemicellulose sugars in sediments from Bichlersee, Bavaria, covering the Late Glacial and Early Holocene. Our δ2Hn-C31 record documents past changes in the isotopic composition of summer precipitation and roughly shows the isotope pattern known from Greenland. Both records show lower values during the Younger Dryas, but at Bichlersee the signal is less pronounced, corroborating earlier suggestions that the Younger Dryas was mainly a winter phenomenon and less extreme during summer. δ18Ofucose records the isotopic composition of the lake water during summer and is sensitive to evaporative enrichment. Coupling δ2Hn-C31 and δ18Ofucose allows calculating lake water deuterium-excess and thus disentangling changes in the isotopic composition of precipitation and evaporative enrichment. Our deuterium-excess record reveals that the warm Bølling–Allerød and Early Holocene were characterized by more evaporative enrichment compared to the colder Younger Dryas. Site-specific hydrological conditions, seasonality, and coupling δ2H and δ18O are thus important when interpreting isotope records. [ABSTRACT FROM AUTHOR]

Deep Springs Valley (DSV) is a hydrologically isolated valley between the White and Inyo mountains that is commonly excluded from regional paleohydrology and paleoclimatology. Previous studies showed that uplift of Deep Springs ridge (informal name) by the Deep Springs fault defeated streams crossing DSV and hydrologically isolated the valley sometime after eruption of the Pleistocene Bishop Tuff (0.772 Ma). Here, we present tephrochronology and clast counts that reaffirms interruption of the Pliocene--Pleistocene hydrology and formation of DSV during the Pleistocene. Paleontology and infrared stimulated luminescence (IRSL) dates indicate a freshwater lake inundated Deep Springs Valley from ca. 83-61 ka or during Late Pleistocene Marine Isotope Stages 5a (MIS 5a; ca. 82 ka peak) and 4 (MIS 4; ca. 71-57 ka). The age of pluvial Deep Springs Lake coincides with pluvial lakes in Owens Valley and Columbus Salt Marsh and documents greater effective precipitation in southwestern North America during MIS 5a and MIS 4. In addition, we hypothesize that Deep Springs Lake was a balanced-fill lake that overflowed into Eureka Valley via the Soldier Pass wind gap during MIS 5a and MIS 4. DSV hydrology has implications for dispersal and endemism of the Deep Springs black toad (Anaxyrus exsul). [ABSTRACT FROM AUTHOR]

Antarctica is of great importance in terms of global warming, the sustainability of resources, and the conservation of biodiversity. However, due to 99.66% of the continent being covered in ice and snow, geological research and geoscientific study in Antarctica face huge challenges. Geophysical surveys play a crucial role in enhancing comprehension of the fundamental structure of Antarctica. This study used bibliometric analysis to analyze citation data retrieved from the Web of Science for the period from 1982 to 2022 with geophysical research on Antarctica as the topic. According to the analysis results, the amount of Antarctic geophysical research has been steadily growing over the past four decades as related research countries/regions have become increasingly invested in issues pertaining to global warming and sustainability, and international cooperation is in sight. Moreover, based on keyword clustering and an analysis of highly cited papers, six popular research topics have been identified: Antarctic ice sheet instability and sea level change, Southern Ocean and Sea Ice, tectonic activity of the West Antarctic rift system, the paleocontinental rift and reorganization, magmatism and volcanism, and subglacial lakes and subglacial hydrology. This paper provides a detailed overview of these popular research topics and discusses the applications and advantages of the geophysical methods used in each field. Finally, based on keywords regarding abrupt changes, we identify and examine the thematic evolution of the nexus over three consecutive sub-periods (i.e., 1990–1995, 1996–2005, and 2006–2022). The relevance of using geophysics to support numerous and diverse scientific activities in Antarctica becomes very clear after analyzing this set of scientific publications, as is the importance of using multiple geophysical methods (satellite, airborne, surface, and borehole technology) to revolutionize the acquisition of new data in greater detail from inaccessible or hard-to-reach areas. Many of the advances that they have enabled be seen in the Antarctic terrestrial areas (detailed mapping of the geological structures of West and East Antarctica), ice, and snow (tracking glaciers and sea ice, along with the depth and features of ice sheets). These valuable results help identify potential future research opportunities in the field of Antarctic geophysical research and aid academic professionals in keeping up with recent advances. [ABSTRACT FROM AUTHOR]

Variations in lake-levels and hydrology are connected to climatic dynamics over the Trans-Himalaya and Tibetan Plateau (TP). Pangong Tso, a ~140 km long hypersaline lake, is sensitive to changes in air temperature, precipitation and snow-glacier melt over the southwestern TP. The incised tributaries entering the lake expose deltaic sequences constituting topset, foreset and bottomset. Sedimentology, chronology and diatom analysis of delta sediments; and stable isotopic and sclerochronological analysis of gastropods helped delineate the Late-Holocene variation in lake levels, surface temperature and salinity. The elevation of the topsets is considered as representing past lake high-stands from where molluscs were also recovered. Three phased lake level changes are observed during the past 3 ka. The first high-stand (+1.4–3.0 m) was at ~2.8–2.0 ka when lake surface salinity and temperature were 4.67–6.01 ppt (parts per thousand) and 5°C–7°C, respectively, against the modern average values of 7.7 ± 0.09 ppt and 16.1°C ± 2.0°C. Followed by a brief decline, another high-stand (+3.0–3.6 m) is observed at 1.1 ka when the salinity is reduced to 4.03–5.72 ppt and lake surface temperature to 5°C–8°C. A corresponding increase in freshwater diatom concentration is also observed here. The third phase over the past 1 ka witnessed a fall of ~3.6–6 m in lake level that is attributed to an abrupt rise in aridity over the TP. We demonstrate that lake level variation in the region is a function of the variability of the Indian Summer Monsoon (ISM) and the westerlies, however during the high-stand, the hydrology of the lake was dominated by ISM precipitation. [ABSTRACT FROM AUTHOR]

It is commonly assumed that the gradients of pre-vegetation fluvial systems were greater than those of modern rivers. If the measured thickness of crossbeds is first corrected for post-depositional compaction, using thin-section-based observations, the corrected thickness data can be applied to a new suite of formulae, based on observations of >4000 modern rivers, to provide more realistic paleohydrological reconstructions of ancient river systems. Using this approach, after correction for 36% compaction, the average slope of the rivers that deposited the Mississagi Formation was calculated as 0.0013 m/m (0.0005–0.0026), with an average bankfull channel depth of 2.67 m. The slope of Serpent Formation rivers, after correction for 33.5% compaction, averaged 0.0007 m/m (0.0003–0.0016), with an average bankfull channel depth of 5.85 m. The calculation of slopes using this approach on these Paleoproterozoic and other Precambrian systems indicates that primary river gradients were similar to modern rivers, falling well below the "depositional gap", of 0.007–0.026 m/m, between modern rivers and arid-region fans, negating the long-held idea that pre-vegetation rivers had higher slopes than their modern counterparts. [ABSTRACT FROM AUTHOR]

Long‐term hydroclimate change can provide reliable reference for water resources management in Central Asia. However, only a few palaeohydrological records exist in Tajikistan. To obtain a long‐term perspective on hydrological changes in Tajikistan, we developed, for the first time, a streamflow reconstruction from September of the previous year to June of the current one in the Kafirnigan River basin, based on Juniperus semiglobosa tree‐ring width indices from the Iskanderkul area in northern Tajikistan. The streamflow reconstruction explains 40% of the actual streamflow variance during the period 1939–1993. Spatial correlation analyses with gridded precipitation data indicate that our streamflow reconstruction contains a strong regional hydroclimatic signal for southern Central Asia. The high and low intervals of our streamflow reconstruction are closely related to the interdecadal variations of El Niño‐Southern Oscillation (ENSO). Our reconstructed streamflow is significantly correlated with sea surface temperatures in the eastern equatorial Pacific Ocean and northern Indian Ocean, indicate the existence of remarkable 11‐, 5.6–5.7‐, 4.3‐, 2.6‐, 2.3‐ and 2.0‐year cycles, and suggest a relationship between southern Central Asian streamflow variations and ENSO activity. [ABSTRACT FROM AUTHOR]

Unstable hydrological cycles and water resource instability over and around the Tibetan Plateau (TP) are topics of wide concern. The Indian summer monsoon (ISM) is one of the TP's most important moisture sources; as such, its behavior is key to any changes in precipitation and water-related environments. However, there have been relatively few thorough investigations into ISM activities. Here we primarily explore ISM activities using outgoing longwave radiation (OLR) datasets in TP, and precipitation isotopes recorded at Lhasa, for the period 1975–2020. Our major findings are that 1) the ISM onset (retreat date) is between ∼31 May and 19 July (∼8 August–27 September), with ISM duration of ∼40–110 days; 2) significant spatial inhomogeneous patterns are evident in ISM activities, i.e., the western part of our study area experiences earlier ISM onset, delayed retreat, longer duration, and greater intensity and strength, and the inverse is true in the eastern sector of the study area; 3) the ISM activities that dominate the 1975–98 period determine their general patterns over the entire 1975–2020 period, taking into account evident discrepancies in subperiods; and 4) the negative relations between precipitation δ18O and ISM intensity/strength at Lhasa confirm the ISM activities defined using OLR. These results will improve our understanding of hydrological cycles in TP and provide insights into hydrological studies in the "Asian Water Tower" region. Significance Statement: Over the recent decades, the Tibetan Plateau (TP) (Asian Water Tower) has undergone dramatic environmental changes, evinced by the instabilities of hydrological cycles. As one of TP's most important moisture sources, the Indian summer monsoon (ISM) is key to changes in precipitation and water-related environments. To get thorough investigations into ISM activities, we primarily explore ISM activities using outgoing longwave radiation (OLR) datasets in TP and precipitation isotopes at Lhasa. Significant spatial inhomogeneous patterns are evident in ISM activities: the western part experiences earlier ISM onset, delayed retreat, longer duration, and stronger intensity and strength, and the inverse occurs in the eastern sector. These results will improve our understanding of hydrology, meteorology, ecology, and paleoclimate reconstructions in the Asian Water Tower region. [ABSTRACT FROM AUTHOR]

Alluvial rivers aggrade, incise, and adjust their sediment‐transport rates in response to changing sediment and water supply. Fluvial landforms, such as river terraces, and downstream stratigraphic archives may therefore record information about past environmental change. Using a physically based model describing sediment transport and long‐profile evolution of alluvial rivers, we explore how their responses to environmental change depend on distance downstream, forcing timescales, and whether sediment or water supply is varied. We show that amplitudes of aggradation and incision, and therefore the likelihood of terrace formation, are greater upstream and in shorter and/or wetter catchments. Aggradation and incision, and therefore terrace ages, may also lag behind environmental change. How sediment‐transport rates evolve depends strongly on whether water or sediment supply is varied. Diverse responses to environmental change could arise in natural alluvial valleys, controlled by their geometry and hydrology, with important implications for paleo‐environmental interpretations of fluvial archives. Plain Language Summary: Rivers carry sediment from upland regions, where it is produced by weathering and erosion, to low‐lying areas where it is deposited and stored. This process is sensitive to climate: for example, wetter conditions enhance rivers' capacity to transport sediment, causing rivers to cut into their beds, which in turn remobilizes sediment that is transported downstream. Changing climate may also lead to enhanced sediment production and supply to rivers, causing them to accumulate sediment in their beds. Climate cycles can therefore produce alternating periods of sediment accumulation and removal, resulting in ancient floodplains being abandoned and preserved alongside modern rivers ("terraces"), and in variations in the amounts of sediment delivered downstream. Terraces and patterns of sediment accumulation downstream could therefore provide valuable records of past climatic change. We develop a mathematical model that describes the effects of climatic change on river‐bed height and sediment‐transport rates. We show how the amount and timing of river in‐filling and down‐cutting, and the timescales over which they occur, depend on the rate of climatic change, on river length and associated drainage‐basin area, and on the amount of water it carries. These predictions will facilitate more detailed interpretations of terrace records along rivers and of the sedimentary deposits that they leave behind. Key Points: Alluvial rivers respond in diverse ways to cyclical climatic change depending on their geometry and hydrology and on the forcing frequencyTerrace formation is favored upstream and in shorter and wetter catchments and may lag appreciably behind environmental changeVariation in sediment output lags variation in sediment supply but can lead and be amplified with respect to variation in water supply [ABSTRACT FROM AUTHOR]

There are very few records of past terrestrial environmental change of any time period for the Australian tropical savannas. Here we document the hydrological development of Sanamere Lagoon, north Queensland, from a 1.72 m sediment sequence with a basal age of ca. 33 ka. We measure a variety of proxies reflecting environmental change within and around the lagoon, including grain size, elemental and diatom abundance, and carbon and nitrogen isotope composition. By integrating the interpretation of multiple proxies, we show that regional climatic events, such as the reactivation of the monsoon at 15 ka and sea-level rise ending at 7 ka, are reflected in local ecosystem change and a diversity of biogeochemical responses in Sanamere Lagoon. This record makes a significant contribution to the development of records of environmental change from an under-studied region in tropical Australia through the Holocene to the LGM and beyond—a step towards enabling a more detailed understanding of regional monsoon (paleo)dynamics. In particular, this study highlights nuances in the effect of Indonesian-Australian Summer monsoon dynamics in a region less affected by sea level and continental shelf drowning complexities. [ABSTRACT FROM AUTHOR]

The fluvial geomorphology and stratigraphy on the middle Snake River at Bancroft Springs, Idaho, provide evidence for numerous episodes of Snake River aggradation and incision since the Bonneville Flood at ca. 18 ka. A suite of seven terraces ranging from 20–1 m above modern bankfull elevation records multiple cut-and-fill cycles during the latest Pleistocene and Holocene in response to local base-level controls, variations in sediment supply, and hydroclimate change. Radiocarbon and luminescence dating show that the ages of fluvial aggradation generally coincide with increased sediment supply and likely wetter hydroclimate during onset of the Younger Dryas stadial (ca. 13.2 ka), deglaciation and termination of the Younger Dryas stadial (ca. 11.3 ka), Early Holocene cooling (ca. 8.8 ka), and Neoglacial (ca. 4.5, 2.9, 1.1 ka). Six intervening periods of incision and channel stability may also reflect either reduced sediment supply, drier hydroclimate, or both. The terrace chronology can be correlated to a variety of local and regional paleoclimate proxy records and corresponds well with periods of continental- and global-scale rapid climate change during the Holocene. The fluvial record demonstrates the geomorphic response and sensitivity of large river systems to changes in hydroclimate variability, which has important implications for inferring paleoenvironmental conditions in the region. [ABSTRACT FROM AUTHOR]

Triassic strata of the Tecovas and Trujillo formations in the Palo Duro Canyon of West Texas record deposition dominated throughout by upper‐flow‐regime channel flow. These strata provide an opportunity for new insights into the architecture, floodplain/channel processes, vertical profiles, palaeohydrology and taphonomy typical of broader upper‐flow‐regime‐dominated fluvial systems. Thicker channel‐fills (ca 2 m, aspect ratio ca 24) host upper‐plane‐bed, symmetrical antidune, breaking‐antidune, chute‐and‐pool, and cyclic‐step structures. The thinner channel‐fill population (<1 m, aspect ratio ca 35) comprises upper‐plane‐bed and some antidune structures. Some of the larger channel fills developed low‐angle downstream‐accreting bars, with rare examples of laterally accreting side‐attached bars. This appears to be the first documentation of an ancient upper‐flow‐regime side‐attached bar. Lamina orientation of structures parallel accretion surfaces because these followed the original bed surface, and structures drop in flow regime down the bar surfaces as formative Froude numbers also declined. A generalized vertical sequence for large upper‐flow‐regime channel storeys has upper‐plane‐bed structures above the basal scour, transitioning upward into higher flow regime structures (for example, antidunes, cyclic steps, etc.), then back to a mix of upper‐plane‐bed and antidunes or lower‐flow‐regime structures towards the top. The Tecovas Formation and overlying Trujillo Sandstone both bear layers of cross‐cutting laterally amalgamated valley fills, multivalleys, and are separated by a regional sequence boundary. Calculated palaeodischarges for Tecovas (ca 90 m3/s) and Trujillo (ca 76 m3/s) rivers record flow at the stage where symmetrical antidunes were deposited. These discharges occurred at some point on the falling limb of a flood hydrograph of currently unknown shape. Slopes for the rivers were on the order of 10−4 to 10−5, consistent with typical continental‐interior rivers. Large and flashy discharge was, thus, the likely cause for supercritical‐flow conditions instead of excessive slopes. Rivers in both the Tecovas and Trujillo formations record a fluvial system developed in a tropical to subtropical megamonsoonal environment. The tendency for preservation of metre‐scale channel‐fills and catastrophic inundations of floodplains and lakes in single floods has also made the Dockum Group a prolific preserver of large Triassic vertebrates. [ABSTRACT FROM AUTHOR]

Pseudobeaconiidae is a South American endemic actinopterygian family recorded in the Middle-Late Triassic Cuyana and Ischigualasto-Villa Unión rift basins. This family has been studied for more than seven decades by several authors. In spite of that, the morphological information about their scales is not complete, especially the one related to micromorphology, which has remained unknown until now. The main goal of this contribution is to provide new macro- and micromorphological information of scales from new material of Pseudobeaconiidae, including a brief revision of the scales of the family based on our own observations from material collections. The new studied specimens were recovered from the center lake facies of the Santa Clara Abajo Formation with detailed stratigraphic control. The macromorphology of isolated scales confirms a peg-and-socket articulation in this newly studied material. New features described also include the squamation general pattern, including the scales of the lateral line, the ventral margin, that is characterized by round or angular scales, and the presence of ganoine ornamentations covering preanal and postanal scutes. Regarding micromorphology, paleohistology shows lepidosteoidtype ganoid scales and; also, possible transitional ganoid scales between lepidosteoid and palaeoniscoid-type. Detailed morphological studies on Triassic fish faunas are necessary to obtain clearer patterns that contribute to the understanding of the evolution of Actinopterygii from Gondwana. [ABSTRACT FROM AUTHOR]

Holocene sediments at Emerald Lake in central Utah (3090 m asl) document the paleohydroclimatic history of the western Upper Colorado River headwater region. Multi-proxy analyses of sediment composition, mineralogy, and stable isotopes of carbonate (δ18O and δ13C) show changes in effective moisture for the past ca. 10,000 years at millennial to decadal timescales. Emerald Lake originated as a shallow, closedbasin cirque pond during the Early Holocene. By ca. 7000 cal yr BP, higher lake levels and carbonate δ18O values indicate rising effective moisture and higher proportions of summer precipitation continued at least until ca. 5500 cal yr BP when a landslide entered the lake margin. Between ca. 4500 and 2400 cal yr BP dry conditions at Emerald Lake envelop the timing of the ‘Late Holocene Dry Period’ identified at lower elevations. For the past ca. 2500 years, Emerald Lake δ18O values were relatively low, indicating wetter conditions and higher snow input (compared to rain), except for dry periods at ca. 2000 cal yr BP and during the Medieval Climate Anomaly at ca. 1000 and ca. 500 cal yr BP. Results provide a long-term perspective on precipitation extremes that influence regional water supplies from a snow-dominated catchment typical of the predominant source region for the Upper Colorado River. [ABSTRACT FROM AUTHOR]

Holocene environmental and climate change on the Tibetan Plateau is intensively studied and discussed with the aim to better understand the factors controlling the hydrology of individual river catchments and especially the availability of water which is of utmost significance for the communities downstream in times of rapid climate change. Thus, a late glacial and Holocene sediment record from Lake Heihai in the Kunlun-Pass region was investigated using ostracod and geochemical analyses. Cold and dry conditions were inferred between ca. 12.9 and 12.3 cal ka BP and higher temperatures before and afterwards. The cold spell probably corresponds to the Younger Dryas (YD) event in the North Atlantic region. Warmer and wetter conditions with highest lake levels and decreased lake-water salinity were recorded from ca. 10.8 to 7.0 cal ka BP when the summer monsoon was strengthened. The cold 8.2 cal ka BP event is not significantly recorded in the region probably due to the predominance of the summer monsoon over the westerlies. A declined lake level and increased lake-water salinity as the result of cold and dry conditions are inferred from ca. 7.0 to 4.5 cal ka BP when the strengthening of the mid-latitude westerly circulation probably triggered glacier advances in the catchment. An even lower lake level existed during cold conditions with glacier advances from ca. 4.5 to 1.2 cal ka BP. The level of Lake Heihai rose again after ca. 1.2 cal ka BP due to warmer conditions, causing the retreat of glaciers and higher runoff. Our record from the Kunlun Pass region provides further evidence for the catchment-specific response of hydrographical systems which are partly controlled by glaciers as major water sources. [ABSTRACT FROM AUTHOR]

To study the geological environmental records of alpine-karst-type tufa deposits in the eastern margin of the Tibetan Plateau, the calcareous tufa profile exposed by the "8.8" Jiuzhaigou earthquake was taken as the research object and combined with a field geological investigation. Further, the petrography, sedimentology, chronology, and elemental geochemistry of the calcareous tufa were studied and analyzed. The results show the following. (1) The Sparkling Lake calcareous tufa profile was deposited under the background of a warm and humid climate during the Holocene. The growth pattern follows a bottom-to-top deposition. (2) At 750 ± 30–300 ± 30 aB.P., the calcareous tufa layers were gray-black as a whole, and the changes in mineral composition and elemental geochemistry indicate a fluctuating upward trend for temperature and precipitation during this period. (3) The formation of two sets of black peat layers in the upper part of the tufa calcareous profile is due to the synergistic action of multiple factors caused by strong tectonic activity. In conclusion, the deposition mechanism of the calcareous tufa in Jiuzhaigou was controlled by paleoclimate hydrology and glaciation for a long time, while strong tectonic activity over a short period of time considerably changed the color, structure, element content, and mineral composition of the calcareous tufa. [ABSTRACT FROM AUTHOR]

Alluvial landscapes have long been considered optimal locations for Neolithic settlement because of the availability of water and nutrient-bearing silts. However, the dynamics of these landscapes have often been underestimated in relation to the interactions of precipitation, temperature and vegetation at catchment scale, along with flow and geomorphic processes in the channel and adjacent areas. In this paper we employ a multi-method approach to model the alluvial landscape around Çatalhöyük in central Turkey to develop a more nuanced understanding of the potential interactions between the Neolithic population and its environment. Starting from detailed sedimentological reconstructions of the area surrounding the site, we use climate and vegetation proxies to estimate past climate scenarios. Four temperature and five precipitation scenarios and two vegetation endmember scenarios were constructed for the Neolithic. These scenarios are coupled with a stochastic weather generator to simulate past flows using the HEC-HMS rainfall-runoff model. Impacts and extents of past flooding are then estimated using bankfull flow estimates from the modelled time series. The model results suggest that crops at Çatalhöyük were less vulnerable to flooding than has previously been supposed, with flooding spread more evenly through the year and with relatively unerosive flows. Spatial variability suggests a range of wet and dry conditions would have been available at different times of the year near the site. Interannual and decadal variability was important and so resilience against drought is also a significant consideration and so subsistence patterns must have been resilient to this variability to enable the settlement to continue for over a millennium. This interpretation of the riverscape of Neolithic Çatalhöyük as a mosaic of wet and dry conditions is compatible with the range of plant and animal remains excavated from the site. [ABSTRACT FROM AUTHOR]

This study compares the paleohydrologic variability in two California regions over the last 2000 years – Sierra Nevada region and southern California region. Both regions show significant and reproducible proxy evidence for multi-decadal wet/dry intervals that are synchronous between the two regions. The overall durations of individual cycles (wet-wet or dry-dry) average ~130 years, but the cycles are closer to 90–100 year duration for the last 500 years and more than 200 years in duration 1500–2000 years ago. This pattern of varying cyclicity is ongoing today and appears to be related to the intrinsic regional climate variability of the Pacific/California margin. [ABSTRACT FROM AUTHOR]

It is crucially important to estimate unknown parameters in process-based models by integrating observation and numerical simulation. For many applications in earth system sciences, a parameter estimation method which allows parameters to temporally change is required. In the present paper, an efficient and practical method to estimate time-varying parameters of relatively low dimensional models is presented. In the newly proposed method, called Hybrid Offline Online Parameter Estimation with Particle Filtering (HOOPE-PF), an inflation method to maintain the spread of ensemble members in a Sampling-Importance-Resampling Particle Filter (SIRPF) is improved using a non-parametric posterior probabilistic distribution of time-invariant parameters obtained by comparing simulated and observed climatology. HOOPE-PF outperforms the original SIRPF in synthetic experiments with toy models and a real-data experiment with a conceptual hydrological model when an ensemble size is small. The advantage of HOOPE-PF is that its performance is not greatly affected by the size of perturbation to be added to ensemble members to maintain their spread while it is important to get the optimal performance in the original particle filter. Since HOOPE-PF is the extension of the existing particle filter which has been extensively applied to many models in earth system sciences such as land, ecosystem, hydrology, and paleoclimate reconstruction, HOOPE-PF can be applied to improve the simulation of these process-based models by considering time-varying model parameters. Plain Language Summary Computer simulation is widely used to understand earth systems such as atmosphere, ocean, land, ecosystem, and society. Many computer simulation models in earth system sciences inevitably have unknown coefficients of equations, which are called model parameters. It is important for accurate simulation of earth systems to tune these model parameters by comparing the results of computer simulation with observation. Although many previous works assumed that model parameters do not change over time, it is necessary to allow them to change over time in some applications, which makes it more difficult to estimate model parameters. In this study, a new method to estimate time-varying model parameters is proposed. The key idea of this paper is to combine two existing methods which integrate observations into computer simulation models. It is found that the proposed method works better than the existing method in three case studies. The proposed method can contribute to improving many simulations in earth system sciences by efficiently tuning time-varying model parameters. [ABSTRACT FROM AUTHOR]

The data set represents the Regional Meteoric Water Line (RMWL) for the Yucatan Peninsula (Mexico), a region with karstic aquifers but little knowledge of the isotopic composition of meteoric water. This data paper comprises the isotopic composition of meteoric water collected from November 2018 to November 2019 as monthly composite samples expressed as weighted monthly mean precipitation from 16 locations across the Yucatan Peninsula. The RMWL was δ2H = 7.803 δ18O + 12.075, with a slope and intercept suggesting precipitation from air that has undergone condensation, air masses with variable moisture or recycled moisture. The average δ18O is −2.57‰ (−12.23 to 1.2‰) and δ2H is −7.94‰ (−83.39 to 18.32‰). This data set was collected by the implementation of an isotopic monitoring network, gathering information useful as a tool for better understanding of the hydrology and hydrogeochemistry of karstic aquifers, and to develop proxies for paleohydrology, ecohydrology, climate change and paleoclimate studies in the Gulf of Mexico and the Great Caribbean Area. [ABSTRACT FROM AUTHOR]

The paleoclimate since the late Pleistocene has gained substantial attention due to its profound effects on hydrology, ecosystems, and landforms, particularly in regions experiencing permafrost thawing. Northeast China is acknowledged for exhibiting distinctive yet contentious paleoclimate, which has been elucidated through various proxies. In this case, we emphasize the significance of stable isotopes within the northern Songnen Plain as complementary proxies for paleoclimate interpretation, bolstered by radiocarbon dating. The Cretaceous sandstone confined aquifer (CSA) is designated as the reference aquifer, based on the hydrogeochemical and isotopic characteristics. The 14C results indicate that the CSA preserves groundwater from the late Pleistocene to the modern. These findings, in conjunction with isotope variations, delineate specific climate events, which are aligning with results derived from conventional proxies. The late Pleistocene-early Holocene showed a climate shift from cold to warm. The middle Holocene was warm and humid. Then the late Holocene entered the Neoglacial, which characterized by a cold climate environment. Our analysis also reveals fluctuations in the age and TDS concentration along the groundwater runoff. The paleo groundwater exhibits simultaneous lower TDS concentration, maximum δ 18O depletion and minimum recharge temperature. Neither latitude nor altitude effects could account for the sufficient isotopic depletion, instead, we found that the humid climate and permafrost meltwater also contributed to the isotope depletion. Simultaneously, the paleoclimatic environment such as freeze-thaw cycles of permafrost exerts a significant influence on the groundwater. The formation of permafrost hinders groundwater recharge, while its thawing dilutes the solute content of groundwater. Additionally, the recharge gaps also potentially result from arid climate, inadequate samples, and the effects of mixing water. The study substantiates the reliability of confined aquifers in permafrost thawing regions as robust paleoclimatic archives and emphasizes the utility of stable isotopes in combination with radiocarbon dating as ideal climate proxies. • Confined aquifers in permafrost thawing region are ideal paleoclimatic archives. • Groundwater isotopes are significant proxies for paleoclimatic reconstruction. • Groundwater salinity is sensitive to climate change in the permafrost region. [ABSTRACT FROM AUTHOR]

Here we explore the results and differences of two methods for reconstructing climatic and paleohydrological conditions from two sites in central North America during the Last Glacial Maximum. The Clementsian assemblage-based Mutual Climate Range (MCR) and Gleasonian species-range-based Mutual Ostracod Temperature Range (MOTR) methods are featured. We use autecological data from the North American Ostracode Database (NACODe) that includes water chemistry, physical data, location, and ambient climatic information from 7328 sites and the presence of 108 ostracode species. Reconstructions of last glacial average temperatures for January and July means, average mean annual temperature, mean total annual precipitation, and total dissolved solids of the host water are provided for records at Bellefontaine Quarry (Missouri) and Prides Creek (Indiana). The successions collectively date from about 25,100 to 18,300 cal yr BP. Our novel python program enables MCR calculations with results that fall within the envelope of values determined by MOTR. The program enables the user to determine the critical number of species that yield data less influenced by data structure and tending toward redundant but representative environmental and hydrochemical paleo-conditions. Data from sites with common species below the critical number are controlled by the biogeographic structure of NACODe; above the critical number, analog data reflect physiochemical attributes operating under a range of climatic conditions. The greater mean species richness of the Prides Creek record (x ‾ = 12) compared to Bellefontaine (x ‾ = 6) results in smoother profiles of mean Clementsian Mutual Climate Range values. We have modified an analog selection and ranking routine by favoring sites with sensitive species as defined by an environmental tolerance index. For average mean July temperature and mean total dissolved solids, the Prides Creek MCR-ETI profiles have approximately the same value as average values given by the Gleasonian Mutual Ostracod Temperature Range procedure. For average mean annual temperature and average mean January temperatures, MCR-ETI values plot on the cooler side of the MOTR envelopes, but still entirely within the envelope. For both records, mean total annual precipitation MCR-ETI profiles are on the arid side of the Gleasonian envelope. These results likely reflect the location of analog sites with the largest number of environmentally sensitive ostracodes and matching species located in southern Minnesota and Wisconsin at or near the edge of the prairie-forest transition where potential evapotranspiration is about equal to mean annual precipitation. • Reconstructed values of full glacial average mean temperature (January, July, and annual), mean total annual precip., and TDS are presented. • Sites are Prides Ck, IN (38.481°N, -87.287°W) and Bellefontaine Quarry, MO (38.841°N, -90.241°W); records span collectively 25.3 to 18.3 cal ka. • The mean values calculated using assemblage-based MCR-ETI generally fit within the envelope of values provided by species-based MOTR. • For Prides Creek, MCR-ETI average mean July temperatures range from 19.7 to 22.9 °C (x ‾ = 21.4 ± 0.4 °C) which is about 3.6 °C cooler than modern. • For Bellefontaine Quarry, MCR-ETI average mean July temperatures range from 20.1 to 22.1 °C (x ‾ = 21.1 ± 0.8 °C), about 4.9 °C cooler than modern. [ABSTRACT FROM AUTHOR]

Outburst flood sediments are studied on the upper course of the Yangtze River (known as the Jinsha River) where is a key region for the development of hydroelectric power. As the history and magnitude of outburst flooding in this stretch of the Jinsha River during historic times has remained largely undocumented, we have endeavored as part of this study to conduct field investigations into, and provide numerical dating (using OSL and 14C dating techniques) of outburst flood evidence found in the First Bend area of the Yangtze River. Carbonized nutshells and charcoal from the ancient settlement yielded 14C ages that precisely pinpointed an outburst flood event ∼1200–1300 cal yr BP, during China's Tang Dynasty (618–907 CE). However, OSL ages using the minimum age model for all outburst flood samples ranged from 9.1 to 1.8 ka, which was ∼0.5–7.8 ka older than the 14C-dated outburst flood. This discrepancy suggests a potential overestimation of quartz age when dating outburst flood sediments from the Holocene period. Furthermore, using 2D hydraulic modeling, we estimated the magnitude of the aforementioned outburst flood, revealing a reconstructed peak flow discharge of 51,000–55,300 m3/s. This discharge was three times greater than the 10,000-year flood for the hydroelectric power station nearest to the study area. Our study underscores the significant role of combining archaeological and geological evidence in enhancing paleoflood hydrology research. Through a multidisciplinary approach, our findings emphasize the importance of paleoflood hydrology studies in comprehending both the latent and catastrophic flood risks in alpine mountain areas amid the context of global warming. • A series of outburst flood sediments was identified in the First Bend area of the Yangtze River, with a maximum flood water surface ∼86 m high above modern river level. • The obtained 14C ages would suggest that the outburst flood occurred at ∼1200–1300 cal yr BP in the Tang Dynasty (618–907 CE) of China. • The reconstructed peak flow discharge (51,000–55,300 m3/s) is larger than the three times of the 10,000-yr flood for the nearest hydropower station to the study site. • Outburst floods were identified in the First Bend of the Yangtze River. • The 14C ages (∼1200–1300 cal yr BP) suggest the flood was in the Tang Dynasty. • The peak discharge is larger than triple the 10,000-flood of the nearest dam. [ABSTRACT FROM AUTHOR]

During the last deglaciation and middle Holocene, rapid climatic changes occurred repeatedly. Previous research has primarily focused on investigating these periods in East Asia's coastal and inland regions of the Eurasian continent. In contrast, a limited number of studies have reported on climate change and its environmental impacts in island areas near the Pacific Ocean. This study aims to reconstruct paleosol drainage conditions and lake water level fluctuations in the Suwa Basin, an inland basin in central Japan, after the last deglaciation. We utilize the identification of paleosols and the geochemistry of lacustrine sediments to discuss climate change and its impacts on terrestrial environments in the East Asian coastal region. During the Last Glacial Maximum, the basin experienced a lowstand period; meandering fluvial systems led to the development of dry and well-drained paleosols. The lacustrine environment expanded between ca. 16 cal kyr BP and 5 cal kyr BP during a transgressive period. Short-term lake-level fluctuations were reconstructed by examining repeated paleosol development and changes in the bulk SiO 2 content originating from biogenic silica in lacustrine sediments. Our data suggest that the lake's water level fell at ca. 12 cal kyr BP, 8 cal kyr BP, and 7 cal kyr BP. After 5 cal kyr BP, thin paleosols repeatedly formed during short exposure times due to the rapid sedimentation rate in the delta system, which corresponds to the highstand period. Short-term fluctuations between 16 kyr BP and 5 kyr BP, in the lake water level in the inland basin of the Japanese Islands was influenced by drying and cooling trends in the East Asian coastal region, as well as declines in sea surface temperatures in the western tropical Pacific Ocean. These fluctuations roughly synchronize with the Younger Dryas stadial and an 8.2 ka cooling event. Changes in precipitation, which responded to fluctuations in the East Asian summer monsoon intensity and tropical depressions, likely regulated the lake water level. These findings imply the predominant influence of paleoclimate fluctuations over thousands of years on the hydrological regime of lake systems across the island area of the East Asia. • Changes in lake water levels in central Japan in last 16 kyr were clarified. • 1000-yrs scale lake level changes occurred after the last deglaciation. • The lake level declines coincided with the Younger Dryas and an 8.2 ka event. • It shows effect of high latitude climate changes on lake systems in coastal East Asia. [ABSTRACT FROM AUTHOR]

The Yangtze River is a major component of the 'Asian Water Tower' and it provides freshwater resources for hundreds of millions of people in East Asia. Hence, climatic and environmental changes in the source region of the Yangtze River (SRYR) are of major significance for understanding changes in the status of its freshwater resources. However, due to the contradictory results shown by the available paleoclimatic records from the SRYR and neighboring regions, it remains unclear how the regional climate and hydrology have evolved since the middle Holocene. Here, we present records of hydrological variations based on multiple proxies (grain size, scanned micro-scale X-ray fluorescence (XRF) element composition, and loss on ignition (LOI)) of the sediments of alpine lake Saiyong Co, with the aim of reconstructing hydrological changes in the SRYR since 5.8 ka. The first principal component (PC1) of the XRF scanned element record is dominated by Ti, Fe and K, representing terrigenous inputs from the catchment. The LOI profile shows an inverse pattern of variation to that of PC1, suggesting that the sedimentary organic matter is primarily derived from aquatic plants. Since 5.8 ka the overall decrease in sample scores on PC1 and the increasing LOI, together with the grain-size based lake-level record, indicate an overall drying trend in SRYR. Furthermore, several major droughts are recorded, at ∼4.0 ka, ∼2.8 ka and ∼1.8 ka. The hydrological variations at Saiyong Co are supported by multiple records from the SRYR, suggesting that millennial-scale environmental variations were regionally synchronous and were influenced by Northern Hemisphere summer insolation and movement of the intertropical convergence zone. [ABSTRACT FROM AUTHOR]

Over the past century, the Red River of the North has been the least stationary river in the continental United States. In Canada, historical and paleoenvironmental evidence indicates severe floods were common during the early 1800s, with the record ce 1826 flood having an estimated peak discharge 50% higher than the second-most severe flood ever observed. Unfortunately, the recorded history of flooding upstream in the United States does not begin until seven decades after this event. If 1826 was an equally exceptional flood on American reach of the river, then current flood-frequency curves for the river underestimate significantly the risks posed by future flooding. Alternatively, if the American stretch did not produce a major flood in 1826, then the recent spate of flooding that has occurred over the past two decades is exceptional within the context of the past 200 years. Communities in the Fargo-Moorhead metropolitan area are building a 58-km long, $2.75 billion (USD) diversion channel that would redirect floodwaters westward around the two cities before returning it to the main channel. Because this and other infrastructure in North Dakota and Minnesota is intended to provide protection against low-probability, high-magnitude floods, new paleoflood investigations in the region would help local, state, and federal policy-makers better understand the true flood threats posed by the Red River of the North. [ABSTRACT FROM AUTHOR]

The paper presents a new local meteoric water line (LMWL) of stable oxygen and hydrogen isotopes in precipitation from Inuvik in the western Canadian Arctic. Data were obtained over 37 months between August 2015 and August 2018 resulting in 134 measurements of the isotopic composition of both types of precipitation, snow and rain. For 33 months of the sampling period each month is represented at least two times from different years. The new LMWL from Inuvik is characterized by a slope of 7.39 and an intercept of - 6.70 and fills a data gap in the western Arctic, where isotopic composition data of precipitation are scarce and stem predominantly from before the year 1990. Regional studies of meteorology, hydrology, environmental geochemistry and paleoclimate will likely benefit from the new Inuvik LMWL. Data are available on the PANGAEA repository under 10.1594/PANGAEA.935027 (Fritz et al., 2021). [ABSTRACT FROM AUTHOR]

The Las Vegas Formation (LVF) is a well-characterized sequence of groundwater discharge (GWD) deposits exposed in and around the Las Vegas Valley in southern Nevada. Nearly monolithologic bedrock surrounds the valley, which provides an excellent opportunity to test the hypothesis that GWD deposits include an aeolian component. Mineralogical data indicate that the LVF sediments are dominated by carbonate minerals, similar to the local bedrock, but silicate minerals are also present. The median particle size is ~35 μm, consistent with modern dust in the region, and magnetic properties contrast strongly with local bedrock, implying an extralocal origin. By combining geochemical data from the LVF sediments and modern dust, we found that an average of ~25% of the LVF deposits were introduced by aeolian processes. The remainder consists primarily of authigenic groundwater carbonate as well as minor amounts of alluvial material and soil carbonate. Our data also show that the aeolian sediments accumulated in spring ecosystems in the Las Vegas Valley in a manner that was independent of both time and the specific hydrologic environment. These results have broad implications for investigations of GWD deposits located elsewhere in the southwestern U.S. and worldwide. [ABSTRACT FROM AUTHOR]

Quantitative reconstruction of palaeohydrology from fluvial stratigraphy provides sophisticated insights into the response, and relative impact, of tectonic and climatic drivers on ancient fluvial landscapes. Here, field measurements and a suite of quantitative approaches are used to develop a four‐dimensional (space and time) reconstruction of palaeohydrology in Late Cretaceous palaeorivers of central Utah, USA – these rivers drained the Sevier mountains to the Western Interior Seaway. Field data include grain‐size and cross‐set measurements and span five parallel fluvial systems, two of which include up‐dip to down‐dip transects, across seven stratigraphic intervals through the Blackhawk Formation, Castlegate Sandstone and Price River Formation. Reconstructed palaeohydrological parameters include fluvial morphologies (flow depths, palaeoslopes, palaeorelief and planform morphologies) and various hydrodynamic properties (flow velocities, water discharges and sediment transport modes). Results suggest that fluvial morphologies were similar in space and time; median flow depths spanned 2 to 4 m with marginally greater flow depths in southerly systems. Meanwhile palaeoslopes spanned 10−3 to 10−4, decreasing downstream by an order of magnitude. The most prominent spatio‐temporal change is an up to four‐fold increase in palaeoslope at the Blackhawk–Castlegate transition; associated alluvial palaeorelief is tens of metres during Blackhawk deposition and >100 m during Castlegate Sandstone deposition. This study observed no change in unit water discharges at the Blackhawk–Castlegate transition, which argues against a climatically driven increase in palaeoslope and channel steepness. These findings instead point to a tectonically driven palaeoslope increase, although one limitation in this study is uncertainty in palaeochannel widths, which directly influences total water discharges. These reconstructions complement and expand on extensive previous work in this region, which enables the efficacy of quantitative reconstruction tools to be tested. Comparison of results with facies‐based interpretations indicates that quantitative tools work well, but inconsistencies in more complex reconstructions (for example, planform morphologies) highlight the need for further work. [ABSTRACT FROM AUTHOR]

Modern and ancient lacustrine carbonate build‐ups provide uniquely sensitive sedimentary and geochemical records for understanding the interaction between tectonics, past climates, and local and regional scale basin hydrology. Large (metre to decametre), well‐developed carbonate mounds in the Green River Formation have long been recognized along the margins of an Eocene lake, known as Lake Gosiute. However, their mode of origin and significance with respect to palaeohydrology remain controversial. Here, new sedimentological, Sr isotope data and structural evidence show that significant spring discharge led to the formation of a decametre size complex of shoreline carbonate mounds in the upper Wilkins Peak Member of the Green River Formation at Little Mesa and adjacent areas in the Bridger Basin, Wyoming, USA. Sedimentological evidence indicates that spring discharge was predominantly subaqueous but was, at times, also subaerial, which produced tufa cascades and micro‐rimstone dam structures. The 87Sr/86Sr ratios measured from these subaerial spring deposits are less radiogenic (87Sr/86Sr = 0.71040 to 0.71101) than contemporaneous palaeolake carbonates (87Sr/86Sr = 0.71195 to 0.71561) because their parent groundwaters likely interacted with less‐radiogenic Palaeozoic carbonate. Calcite‐cemented sandstone cones and spires (87Sr/86Sr = 0.71037 to 0.71057) in the Wasatch Formation directly below the spring deposits suggest that groundwaters derived from Palaeozoic carbonates preferentially flowed along thrust faults. These results imply that high spring discharge coincided with lake high stands of the upper Wilkins Peak Member, suggesting that recharge at the north‐west margin of the Bridger Basin contributed to Lake Gosiute's water budget and lowered the salinity of an underfilled, evaporative lake basin. The findings of this study provide criteria for the recognition of groundwater discharge in palaeolake systems which may lead to the discovery of palaeospring systems in other ancient lake deposits. [ABSTRACT FROM AUTHOR]