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The hydrogen isotope composition of leaf wax biomarkers (δ2Hwax) is a valuable tool for reconstructing continental paleohydrology, as it serves as a proxy for the hydrogen isotope composition of precipitation (δ2Hpre). To yield robust palaeohydrological reconstructions using δ2Hwax in marine archives, it is necessary to examine the impacts of regional climate on δ2Hwax and assess the similarity between marine sedimentary δ2Hwax and the source of continental δ2Hwax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific, soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and δ2Hwax values. We find that apparent fractionation between leaf waxes and source water is relatively constant in humid/semiarid regions (average: −121 ‰). However, it becomes less negative in hyperarid regions (average: −86 ‰) as a result of evapotranspirative processes affecting soil and leaf water 2H enrichment. We also observed that along strong aridity gradients, the 2H enrichment of δ2Hwax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicated that δ2Hwax values in marine surface sediments largely reflect δ2Hwax values from the continent, confirming the robustness of marine δ2Hwax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of δ2Hwax values and pave the way for more quantitative paleohydrological reconstructions using δ2Hwax. [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]

Stable carbon (δ13C) and oxygen (δ18O) isotope measurements in lacustrine ostracodes are widely used as paleolimnological indicators of past climate change. Previous work has used individual ostracode valves to resolve seasonal and subdecadal paleohydrological signals, yet replicated assessments of co‐occurring specimens from modern samples are rare. Here we focus on ostracodes from sediments collected in 1979 from Lake Turkana, an alkaline desert lake in tropical eastern Africa. Sourced from the Ethiopian highlands, the Omo River is the dominant inflow into this lake. We present individual ostracode valve analyses (IOVA) of δ13C and δ18O measurements (n = 329) of the extant benthic ostracode Sclerocypris clavularis from 17 sites spanning the entire lake (navg = ∼19 specimens/site). We demonstrate that the pooled statistics of individual valve measurements at each site are shaped by lake hydrology, superimposed over inter‐individual isotopic variations. Within‐site variance in IOVA‐δ13C is larger (∼60%) than that of IOVA‐δ18O. Yet, site‐based averages exhibit a systematic pattern, with higher δ values toward the southern part of the lake, away from Omo River inflow. We suggest that the latitudinal δ13C gradient may arise from low riverine δ13C and low organic matter δ13C as a productivity response to nutrient‐rich Omo River inflow toward the north. The δ18O pattern may be explained by the diminishing influence of Omo River inflows and more evaporation driving higher IOVA‐δ18O values toward the windier, southern basin. We conclude that pooled IOVA statistics in Omo‐Turkana sediments can aid interpretations of past regional paleohydrology and its variability in this basin. Plain Language Summary: Ostracodes are microscopic, aquatic crustaceans that deposit shells ("valves") made of calcium carbonate. Retrieved from sediment cores, these valves are widely used to estimate past water conditions using their shell chemistry. Here we focus on stable oxygen and carbon isotopes in numerous individual valves in modern sediments taken from multiple sites across Lake Turkana, Kenya. This lake is located in a hot and arid region in tropical eastern Africa. The Omo River, which is sourced from rainfall in the Ethiopian Highlands region, is the major river that flows into Lake Turkana. We find that ostracode stable isotopes are useful recorders of lake hydrology in this basin and reveal a strong fingerprint of Omo River inflow as well as evaporation toward the windier southern part of Lake Turkana. Analyzing numerous individual valves at each site can help produce better estimates of average changes in past lakewater conditions versus changes arising from seasonal variations. Our results provide a modern baseline of ostracode stable isotopes at Lake Turkana. We suggest that both the average of, and variations within individual‐valve measurements of ostracode geochemistry can help characterize past hydrological variability and lake water conditions. Key Points: We present individual ostracode valve analyses (IOVA) of δ18O and δ13C in modern Sclerocypris clavularis specimens from Lake TurkanaPooled averages of IOVA‐δ18O and ‐δ13C at each site steadily increase from the northern to southern basin of the lakeWe suggest that riverine inflows and productivity drive IOVA‐δ13C whereas inflows, their δ18O values, and evaporation drive IOVA‐δ18O [ABSTRACT FROM AUTHOR]

Recent studies have shown that biosignatures of ancient microbial life exist in mineral coatings in deep bedrock fractures of Precambrian cratons, but such surveys have been few and far between. Here, we report results from southwestern Sweden in an area of 1.6–1.5 Ga Paleoproterozoic rocks heavily reworked by the 1.14–0.96 Ga Sveconorwegian orogeny, a terrane previously scarcely explored for ancient microbial biosignatures. Calcite‐pyrite‐adularia‐illite‐coated fractures were analyzed for stable isotopes via Secondary Ion Mass Spectrometry (δ13C, δ18O, δ34S) and in situ Rb/Sr geochronology via Laser‐ablation inductively coupled plasma mass spectrometry. The Rb/Sr ages for calcite‐adularia and calcite‐illite show that several fluid flow events can be discerned (797 ± 18–769 ± 7, 391 ± 5–387 ± 6, 356 ± 5–347 ± 4, and 301 ± 7 Ma). The δ13C, δ18O and 87Sr/86Sr values of different calcite growth zones further confirmed episodic fluid flow. Pyrite δ34S values down to −49.9‰V‐CDT, together with systematically increased δ34S from crystal core to rim, suggest formation following microbial sulfate reduction under semi‐closed conditions. Assemblages involving MSR‐related pyrite generally have Devonian to Permian Rb/Sr ages, indicating an association to extension‐related fracturing and fluid mixing during foreland‐basin formation linked to Caledonian orogeny in the northwest. An assemblage with an age of 301 ± 7 Ma is potentially related to Oslo Rift extension, whereas the Neo‐Proterozoic ages relate to post‐Sveconorwegian extensional tectonics. Remnants of short‐chained fatty acids in the youngest calcite coatings further indicate a biogenic origin, while the absence of organic molecules in older calcite is in line with thermal degradation, potentially related to heating during Caledonian foreland basin burial. Plain Language Summary: This study investigates mineral coatings in Proterozoic basement fractures of Southwestern Sweden, within the Precambrian Fennoscandian shield, to gain insights into ancient microbial life and paleo‐fluid flow. Isotopic signatures of these mineral coatings suggest that microbial sulfate reducers have been present in the system as also indicated by preserved organic molecules. Microanalytical geochronology determinations reveal that the fracture system has been activated several times in the Neoproterozoic, Devonian‐Early Carboniferous, and Late Carboniferous/Early Permian. These activations are associated with extension events following the Sveconorwegian and Caledonian orogenies as well as formation of the Oslo Rift. The signs of microbial activity are related to the youngest of these events, post‐dating burial in the Caledonian foreland basin, when bedrock temperatures became habitable. Key Points: Rb/Sr geochronology of calcite veins detects several generations of fracture activation and fluid flow in Paleoproterozoic basement rocksSubstantial δ34S variation and preserved fatty acids suggest that microbial sulfate reduction has been active in the fracture systemMicrobial activity relates to Paleozoic fracture activation in relation to Caledonian orogeny/foreland basin and later extensional events [ABSTRACT FROM AUTHOR]

Intense debate persists about the timing and magnitude of the wet phases in the East Asia deserts since the late Pleistocene. Here we show reconstructions of the paleohydrology of the East Gobi Desert since the last interglacial using satellite images and digital elevation models (DEM) combined with detailed section analyses. Paleolakes with a total area of 15,500 km2 during Marine Isotope Stage 5 (MIS 5) were identified. This expanded lake system was likely coupled to an 800–1000 km northward expansion of the humid region in East China, associated with much warmer winters. Humid climate across the Gobi Desert during MIS 5 likely resulted in a dustier MIS 4 over East Asia and the North Pacific. A second wet period characterized by an expanded, albeit smaller, lake area is dated to the mid-Holocene. Our results suggest that the East Asian Summer Monsoon (EASM) might have been much weaker during MIS 3. A Gobi Desert megalake system reconstruction enables a quantitative estimate of East Asian Monsoon climate for the last two interglacials and provides insights into dust flux variations across East Asia and northern Pacific [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]

New to archaeological studies is the field of paleohydrology characterized by the use of modern hydraulic engineering and computational fluid dynamics (CFD) analysis of ancient urban and agricultural water supply and distribution systems. Examples are presented in nine chapters of CFD investigations of old and new world archaeological sites (several of which are World Heritage sites) using FLOW-3D CFD software to bring forward new discoveries revealing the depth of ancient water engineers' knowledge and creativity not previously noted in the archaeological literature. As modern analysis methods reveal technical details of ancient water systems, equivalent ancient technologies exist that were used in the design and operation of ancient water systems, albeit in formats, texts, and origins yet to be discovered. The nine chapters to follow present brief summaries of ancient sites' water systems and the use of CFD and modern hydraulic engineering methods to discover the water engineering knowledge base used by ancient water engineers. Results are new revelations unknown in the current literature of ancient sites. Paleohydrology studies presented serve to add a further dimension to the history of ancient new and old world archaeological sites by bringing forward added details of water engineering projects accomplished by ancient engineers. [ABSTRACT FROM AUTHOR]

Numerous studies have focused on modern hydroclimate and the modulated mechanisms in the Tianshan Mountains (TMs), arid central Asia. However, the detailed information of hydroclimatic processes beyond the instrumental period is still scarce. This paper reconstructed a hydrology history from core sediments of the Dalongchi Lake in the Tianshan Mountains. The comparability between end-members (EMs) of grain size and ICP-AES based geochemical elements in the lake sediments highlighted their availability for hydrological reconstructions. Hydrodynamic forces (EM1, EM4, Ti/Al and Li/Al), chemical weathering intensity [(Mg+Ca+K)/Al], salinity proxy (Mg/Ca) and redox-sensitive proxy (Fe/Mn) highly correlated with the first principal component (P<0.01), whereas paleoproductivity proxies (TN, TOC, Ba/Al, Zn/Al and Cu/Al) and C/N showed high loadings on the second principal component (P<0.05). The inferred hydrology progress was nonlinearly responded to temperature, precipitation and climate-dictated glaciers. Specifically, the water level didn't always covary with the humidity because of glaciers. The maximum water level was the comprehensive result of glaciers melting and high humidity around 1830 CE. Thereafter, water level continually decreased with declining moisture at high temperature, implying a limited buffering capacity of glaciers in the Dalongchi Lake basin. EM3-indicated eolian activity intensity was caused by the behaviors of Siberian High because the latter intensified surface wind and the dust transportation. The hydrothermal patterns were characterized by warm/dry and cold/wet alternations in a long run although warm/wet pattern was identified from a short-term view. [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]

For decades, diatoms have been recognized as powerful bio-indicators of modern water quality. They have also been utilized in the design of transfer functions, which can be applied to diatom assemblages in lake sediment cores to infer aspects of past lake hydrochemistry and estimate variables that can be incorporated into paleohydrology models. The Ounianga lakes, in the heart of the Chadian Sahara, possess unique and well-preserved sediment records that extend back beyond the middle Holocene. Today, the lakes display a range of hydrochemical conditions, from fresh to hypersaline. Mainly fed by fossil groundwater that originates in the Nubian Sandstone Aquifer System, measured conductivity across these lakes varies from 217 to 352,000 µS cm−1, values that are influenced by factors such as hydrology, local geomorphology (e.g., depth and area), and aquatic vegetation. Although these lakes have been on the UNESCO World Heritage List since 2012, they have never been studied in detail because they are located on the fringes of the Chadian Sahara. The distribution of diatom taxa in the lakes today is closely linked to water-column physical and chemical conditions, especially conductivity. Whereas each lake has particular features that influence its diatom flora, diatoms across a conductivity gradient enabled identification of three distinct waterbody types, freshwater lakes, meso-saline to hyper-saline lakes, and freshwater springs. Relationships between diatom species distributions and environmental variables were examined using multivariate analysis, which revealed that conductivity is the variable that explains most of the variance in the diatom flora. We used modern diatom assemblages from the lakes to develop a predictive model (transfer function) for conductivity, using the weighted averaging method. Our conductivity prediction model is strong, with a coefficient of determination (R2) of 0.89 between estimated and measured values, and a value of 0.78 using jackknife estimates of prediction. This study better constrained conductivity optima and tolerance values for diatom species found in the Ounianga lakes, thereby enabling development of a model that will yield better inferences for past conductivity, using diatoms from lake sediment records in the region. [ABSTRACT FROM AUTHOR]

Global climate models with coarse horizontal resolution are largely unable to reproduce the monsoonal precipitation pattern over North Africa during the mid-Holocene. Here we present the first regional, storm-resolving simulations with an idealized but reasonable mid-Holocene vegetation cover. In these simulations, the West African monsoon expands farther north by about 4–5 ∘ , and the precipitation gradient between the Guinea coast and the Sahara decreases compared to simulations with a barren Sahara as it is today. The northward shift of monsoonal precipitation is caused by land surface–atmosphere interaction, i.e., the coupling of soil moisture and precipitation, as well as interactions of the land surface with the large-scale monsoon circulation (e.g., the African easterly jet). The response of the monsoon circulation to an increased vegetation cover is qualitatively similar but more pronounced in parameterized convection simulations. We attribute the differences in monsoonal precipitation to differences in soil moisture that are strongly controlled by runoff and precipitation characteristics. If precipitation is intense and falls over a spatially small region, as in our storm-resolving simulations, about 35 % of all precipitation water goes into runoff instead of filling soil moisture storage. In contrast, in light and spatially more homogeneous precipitation, as produced in our parameterized convection simulations, only some 20 % leaves the grid cell as runoff. Therefore, much more water is available to maintain high soil moisture content. We confirm the significant role of soil moisture and runoff by performing simulations with the same constant soil moisture field in both storm-resolving and parameterized convection simulations. These constant soil moisture simulations cancel the effect of lower soil moisture on the land–atmosphere feedback cycle in our storm-resolving simulations. We show that precipitation strongly increases in the storm-resolving simulations, especially in moisture-controlled regions, such as the northern Sahel and Sahara, and reaches equally high values as in parameterized convection simulations. Our study highlights how the type of rainfall (e.g., local and intense or widespread and light) impacts soil moisture and thus land–atmosphere feedbacks. This is contrary to many studies that focus mainly on the amount of rainfall and how it modifies land–atmosphere feedbacks. Moreover, this study suggests that comprehensive land-surface schemes, which appropriately respond to varying precipitation characteristics, are needed for studying land surface–atmosphere interaction. [ABSTRACT FROM AUTHOR]

The hydrological regime of large meandering rivers of the West Siberian Plain in the Late Pleniglacial/Late Glacial was reconstructed from the hydraulic geometry of palaeochannels. The main tools for the reconstruction were the power law relationship between channel bankfull width and mean maximum discharge, taken in the downstream direction, and relationships between peak flood discharge and the contributing basin area. Reconstructed values of daily maximum surface runoff depth during the snow thaw period in the Late Pleniglacial/Late Glacial were 60–75 mm/day in the north of the plain with tundra and sparse forest and 20–40 mm/day in the south with periglacial steppe. The mean daily maximum surface runoff depth for the entirety of West Siberia was about 46 mm, which is more than five times greater than the modern value. Annual river runoff was calculated with the ratio between mean annual and mean maximum runoff depths, estimated for the modern region's analogues of ancient periglacial landscapes and climates. Total annual flow of the Ob into the ocean was about 1000 km3. This is three times the current flow from the same basin, so the river was a significant source of fresh water to the Arctic Ocean during the last deglaciation. [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]

Abandoned channels are essential in the Quaternary floodplains, and their infill contains different paleoenvironment recorders. Grain-size distribution (GSD) is one proxy that helps characterize the alluviation and associated sedimentological processes of the abandoned channels. The classic statistical methods of the grain-size analysis provide insufficient information on the whole distribution; this necessitates a more comprehensive approach. Grain-size endmember modeling (EMM) is one approach beyond the traditional procedures that helps unmix the GSDs. This study describes the changes in the depositional process by unmixing the GSDs of a Holocene abandoned channel through parameterized EMM integrated with lithofacies, age–depth model, loss-on-ignition (LOI), and magnetic susceptibility (MS). This approach effectively enabled the quantification and characterization of up to four endmembers (EM1-4); the characteristics of grain-size endmembers imply changes in sedimentary environments since 8000 BP. EM1 is mainly clay and very fine silt, representing the fine component of the distribution corresponding to the background of quiet water sedimentation of the lacustrine phase. EM2 and EM3 are the intermediate components representing the distal overbank deposits of the flood. EM4 is dominated by coarse silt and very fine sand, representing deposition of overbank flow during the flood periods. This paper demonstrates that the parametrized grain-size EMM is reasonable in characterizing abandoned channel infill sedimentary depositional and sedimentation history. [ABSTRACT FROM AUTHOR]

We evaluate the efficacy of the stable isotope composition of precipitation and plant waxes as proxies for paleoaltimetry and paleohydrology in the northern tropical Andes. We report monthly hydrogen (δ2Hp) and oxygen (δ18Op) isotope values of precipitation for an annual cycle, and hydrogen isotope values of plant waxes (δ2Hwax) obtained from modern soils along the eastern and western flanks of the Eastern Cordillera of Colombia. δ2Hp, δ18Op, as well as the unweighted mean δ2Hwax values of n‐C29, n‐C31, and n‐C33n‐alkanes in the eastern flank show a dependence on elevation (R2 = 0.90, 0.82, and 0.65, respectively). In stark contrast, the stable isotope compositions of neither precipitation nor plant waxes from the western flank correlate with elevation (R2 < 0.23), on top of a negligible (p‐value >0.05) correlation between δ2Hwax and δ2Hp. In general, δ2Hwax values along the eastern flank of the Eastern Cordillera seem to follow the trend of a simple Rayleigh distillation process that is consistent with studies elsewhere on the eastern side of the Andes in South America. Neither δ2Hp nor δ18Op, and therefore δ2Hwax, offer reliable estimates of past elevations in the western flank, due perhaps to water vapor source mixing, evaporation overprint, contrasting plant communities, and/or differences in evapotranspiration. Thus, δ2Hwax is only reliable for paleohydrology and paleoaltimetry reconstructions on the eastern flank of the Andes, whereas interpretations based on δ2Hp and/or δ18Op west of the highest point of the Eastern Cordillera need to consider mixing of moisture sources in addition to precipitation amount. Plain Language Summary: As air rises over mountainous terrain, heavy isotopes of hydrogen and oxygen preferentially enter the condensate and rain out during ascent leaving remaining vapor depleted in the heavy isotopes. Previous studies have shown that stable isotope values of both precipitation and plant waxes correlate with elevation, and therefore, can be used to reconstruct past surface elevations. This correlation with elevation is clear on the eastern flank of the Eastern Cordillera of Colombia in the northern tropical Andes. On the western flank, however, no correlation was found for either precipitation or plant waxes. Complex atmospheric circulation and the topographic configuration of inter‐Andean valleys pose a challenge for simple isotope signals. It follows that geologists carrying out paleoaltimetry and paleohydrology studies using stable isotopes should be wary of mixed moisture sources and/or complex evaporation paths and be more confident in paleoelevation and paleoclimate estimates if moisture sources are simple. Key Points: The stable isotope composition of precipitation and plant waxes in the eastern flank of the Eastern Cordillera record an elevation‐dependent signalThe stable isotope composition of neither precipitation nor plant waxes from the western flank correlate with elevationStable isotopes are unreliable paleoaltimeters when multiple water vapor sources and/or evaporation overprint simple Rayleigh distillation [ABSTRACT FROM AUTHOR]

Planning and management of water resource infrastructure requires a depth of knowledge on the characteristics of hydrological extremes, floods and droughts. Infrastructure design is traditionally based upon historically observed extreme events, assuming that they are independent and identically distributed (i.i.d.) and stationary, i.e. they fluctuate within a fixed envelope of variability. Information on historical hydroclimate provides a limited range of hydrological extremes, which rarely includes long-term worst droughts. This study demonstrates the application of a paleo-environmental dataset, 900 years of weekly streamflow stochastically derived from a tree-ring reconstruction of annual streamflow, to assess the hydrological drought risk. The historic and prehistoric hydrological drought characteristics, i.e. severity–duration–frequency (SDF) relationships, are evaluated. The results indicate that the severity and duration of hydrological drought with the same recurrence interval is substantially larger and longer than those observed over the 100-year historical period. Historic and prehistoric drought SDF relationships established in this study demonstrate the implications of non-stationary climate in the analysis of extreme droughts. Therefore, projected droughts of the 21st century may not exceed the drought severity found in the prehistoric record to the same extent that they exceed historical droughts in the instrumental record. This study emphasizes the importance of paleohydrology in comprehending the region's drought. HIGHLIGHTS The results from the study indicate that the drought characteristics over the past millennium differed substantially from those which occurred over the past century.; Defining drought response triggers based on the historical data alone could underestimate the potential drought severity.; Our results also indicate that it is irrational to assume stationary climate in determining the frequency of severe droughts.;

The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modeled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modeled water isotopologues, as well as the diversity of their representation in different models, are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable terrestrial paleoclimate archives and provide well-preserved (semi-)continuous multivariate isotope time series in the lower latitudes and mid-latitudes and are therefore well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationships of speleothem oxygen and carbon isotopes to climate variables are influenced by site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and Analysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850–1850 CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of variability for modeled isotopes and compare them to those of measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modeled surface temperature. At low latitudes, precipitation amount is the dominant driver for stable water isotope variability; however, at cave locations the agreement between modeled temperature variability is higher than for precipitation variability. While modeled isotopic signatures at cave locations exhibited extreme events coinciding with changes in volcanic and solar forcing, such fingerprints are not apparent in the speleothem isotopes. This may be attributed to the lower temporal resolution of speleothem records compared to the events that are to be detected. Using spectral analysis, we can show that all models underestimate decadal and longer variability compared to speleothems (albeit to varying extents). We found that no model excels in all analyzed comparisons, although some perform better than the others in either mean or variability. Therefore, we advise a multi-model approach whenever comparing proxy data to modeled data. Considering karst and cave internal processes, e.g., through isotope-enabled karst models, may alter the variability in speleothem isotopes and play an important role in determining the most appropriate model. By exploring new ways of analyzing the relationship between the oxygen and carbon isotopes, their variability, and co-variability across timescales, we provide methods that may serve as a baseline for future studies with different models using, e.g., different isotopes, different climate archives, or different time periods. [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]

In reconstructing past changes in precipitation or evaporation from the geologic record, paleoclimatologists sometimes employ the dual‐biomarker isotope method. This method requires that two co‐occurring sedimentary lipids are derived from different biological sources, and that their compound‐specific 2H/1H ratios record different aspects of the hydrologic cycle. Several studies have used this approach, typically by comparing the 2H/1H ratios of n‐alkyl lipids (δ2Hwax) thought to be sourced from aquatic versus terrestrial plants that gain their hydrogen atoms from lake water and soil water, respectively. Yet confidently fingerprinting n‐alkyl lipid sources continues to be a challenge because the wax inputs of different plant types vary across biomes, lake types, and time. New research in the Journal of Geophysical Research‐Biogeosciences by Hollister et al. (2022, https://doi.org/10.1029/2022jg006903) utilizes a combination of three independent metrics to demonstrate that for Arctic lakes, mid‐chain n‐alkanoic acids can be sourced principally from aquatic plants whereas long‐chain n‐alkanoic acids derive from a mixture of aquatic and terrestrial plants. By cataloging wax compound distributions and compound‐specific H and C isotopes of many new plant species, their efforts will strengthen future biomarker paleoclimatology and reinforce previous applications of the dual‐biomarker approach in high‐latitude lakes. The identification of a lake system with a strong aquatic plant wax signal in the sediments should motivate future targeting of similar lakes for reconstructing past moisture with the dual‐biomarker method. Plain Language Summary: Lake sediments accumulate leaf wax molecules made by plants that climate scientists can use to reconstruct past changes in precipitation and evaporation, key climate variables in the Earth system. For scientists to leverage information from these chemical fossils, they need to understand which plants are producing the waxes, and whether those plants gain their water from soils, from lakes, or from another water source. While land plants using soil water can dominate sedimentary wax signals, a recently published study indicates that exceptions occur in Arctic lakes with abundant aquatic plant growth. These advances support paleoclimate research and demonstrate an approach for fingerprinting the source of plant waxes in Arctic lakes. Key Points: Comparison of 2H/1H among differing sedimentary lipids can reveal paleohydrologic insights that single compounds cannotThe biological sources of mid‐chain n‐alkyl lipids to Arctic lake sediments remains debated because of variations between study sitesA new article by Hollister et al. (2022, https://doi.org/10.1029/2022jg006903) documents the contribution of aquatic plants to sedimentary waxes in Qaupat Lake, Baffin Island [ABSTRACT FROM AUTHOR]

Karst landscapes are characterized by intermittent and sinking streams. The most common method used to study underground hydrological connections in karst is tracing tests. However, a more biologically oriented approach has been suggested: analysis of the genetic structure of aquatic organisms. Biological tracers can be sought among trogloxenes, that is, surface species that occasionally enter caves and groundwater. One such example is the fish genus Phoxinus, which exhibits high genetic diversity and complex phylogeography in the Balkan Peninsula. In the north‐western Dinaric Karst, the complex hydrological network was digitalized in 2020. Contemporaneously, Phoxinus lumaireul populations in the Slovenian Dinaric Karst were intensively sampled and analysed for fragments of two mitochondrial genes and one nuclear gene. The derived phylogeographic structure and data on hydrological connections were compared to evaluate support for three alternative scenarios: The genetic structure (1) is a consequence of the ongoing geneflow through underground connections, (2) reflects a previous hydrological network or (3) is an outcome of anthropogenic translocations. The results suggest that the first two scenarios seem to have played a major role, while the third has not had profound effects on the genetic composition. Comparison between the genetic structure of Slovenian Dinaric Karst sampling sites and that of hydrologically isolated reference sampling sites indicated a greater genetic connectivity in the former. Moreover, the range of Adriatic (1a) and Black Sea (1c) haplotypes does not correspond to the Adriatic–Black Sea basin divide but is shifted northwards. [ABSTRACT FROM AUTHOR]

Long-term human-environmental interactions in naturally fragile drylands are a focus of geomorphological and geoarchaeological research. Furthermore, many dryland societies were also affected by seismic activity. The semi-arid Shiraki Plain in the tectonically active southeastern Caucasus is currently covered by steppe and largely devoid of settlements. However, numerous Late Bronze to Early Iron Age city-type settlements suggest early state formation between ca. 3.2-2.5 ka that abruptly ended after that time. A paleolake was postulated for the lowest plain, and nearby pollen records suggest forest clearcutting of the upper altitudes under a more humid climate during the Late Bronze/Early Iron Ages. Furthermore, also an impact of earthquakes on regional Early Iron Age settlements was suggested. However, regional paleoenvironmental changes and paleoseismicity were not systematically studied so far. We combined geomorphological, sedimentological, chronological and paleoecological data with hydrological modelling to reconstruct regional Holocene paleoenvironmental changes, to identify natural and human causes and to study possible seismic events during the Late Bronze/Early Iron Ages. Our results show a balanced to negative Early to Mid-Holocene water balance probably caused by forested upper slopes. Hence, no lake but a pellic Vertisol developed in the lowest plain. Following, Late Bronze/Early Iron Age forest clear-cutting caused lake formation and the deposition of lacustrine sediments derived from soil erosion. Subsequently, regional aridification caused slow lake desiccation. Remains of freshwater fishes indicate that the lake potentially offered valuable ecosystem services for regional prehistoric societies even during the desiccation period. Finally, colluvial coverage of the lake sediments during the last centuries could have been linked with hydrological extremes during the Little Ice Age. Our study demonstrates that the Holocene hydrological balance of the Shiraki Plain was and is situated near a major hydrological threshold, making the landscape very sensitive to small-scale human or natural influences with severe consequences for local societies. Furthermore, seismites in the studied sediments do not indicate an influence of earthquakes on the main and late phases of Late Bronze/Early Iron Age settlement. Altogether, our study underlines the high value of multi-disciplinary approaches to investigate human-environmental interactions and paleoseismicity in drylands on millennial to centennial time scales.

This paper presents the first Lateglacial/Holocene (the last 13 500 cal a bp) ostracod δ18O record to infer hydroclimate variability in the Southern French Alps. Cytherissa lacustris (δ18Osp) shells extracted from the sediments of Lake Allos allowed a reconstruction of δ18Olake water (δ18Olw) except for the interval 5800–2800 cal a bp. The shape of the Younger Dryas (YD) clearly differed from records documented in the northern Alps. First, δ18Olw values remained close to modern values before a marked drop ca. 12 000 cal a bp. Then, after several oscillations, δ18Olw values increased, reaching the highest value of the record ca. 6100 cal a bp during a thermal optimum for this latitude. Finally, low δ18Olw values occurred from 450 to 100 cal a bp during the Little Ice Age (LIA) following the Medieval Climate anomaly. At the beginning of the YD, δ18Olw probably reflected changes in local glacier dynamics and precipitation sources. The following decrease in δ18Olw values was associated with higher freshwater inputs during the second half of the YD. During the LIA, the low δ18O values are consistent with a higher torrential activity and lower air temperatures. [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]

A submillennial‐resolution record of lake water oxygen isotope composition (δ18O) from chironomid head capsules is presented from Burial Lake, northwest Alaska. The record spans the Last Glacial Maximum (LGM; ~20–16k cal a bp) to the present and shows a series of large lake δ18O shifts (~5‰). Relatively low δ18O values occurred during a period covering the LGM, when the lake was a shallow, closed‐basin pond. Higher values characterize deglaciation (~16–11.5k cal a bp) when the lake was still closed but lake levels were higher. A rapid decline between ~11 and 10.5k cal a bp indicates that lake levels rose to overflowing. Lake δ18O values are interpreted to reflect the combined effects of changes in lake hydrology, growing season temperature and meteoric source water as well as large‐scale environmental changes impacting this site, including opening of the Bering Strait and shifts in atmospheric circulation patterns related to ice‐sheet dynamics. The results indicate significant shifts in precipitation minus evaporation across the late Pleistocene to early Holocene transition, which are consistent with temporal patterns of vegetation change and paludification. This study provides new perspectives on the paleohydrology of eastern Beringia concomitant with human migration and major turnover in megafaunal assemblages. [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]

Significant evolutionary stages of Selinitsa Cave (SW Peloponnese, Greece) were revealed by 3D mapping, as well as geomorphological study of the cave and the nearby landscape. Four marine terraces were identified in the area of the coastal cave at 6, 10.7, 16.6, and 30–32 m above sea level (asl), with the terrace at 16.6 m representing Marine Isotope Stage (MIS) 5. The widest karstified space of Selinitsa Cave clusters between 15.73 and 18.05 m above sea level (asl), with the peak lying at 16.4 m asl, corresponding to the level where the phreatic/epiphreatic zone was stable for a sufficient period of time. A tidal notch at 16.4 m asl at the cave entrance is correlated to the marine terrace at 16.6 m. Both features correspond to the sea-level stand at which intense karstification occurred. The tidal notch bears a horizontal arrangement of Lithophaga borings at the vertex. Sedimentological investigation of the Selinitsa fine-grained deposit revealed the paleohydrologic regime of the cave. It is characterized by "slack-water" facies, indicating very low water flow speeds, whereas the thickness of the deposit points to stable hydrological conditions for prolonged periods. The cave sediment height of 18.8 m asl indicates a flooding level higher than sea level. The overlying Plattenkalk flysch is most probably the major source of detritus, and the predominance of authigenic dolomite (>98% modal in the carbonate fraction) indicates a hyposaline environment related to mixing of sea water with percolating fresh water. The approach of this study shows the significance of 3D mapping, bio-geo-Relative Sea Level (RSL) indicators, and sedimentology in deciphering the paleogeographic evolution of coastal karstic systems and subsequently defining the paleoclimate regime of coastal areas in Greece and the eastern Mediterranean during the Late Quaternary. [ABSTRACT FROM AUTHOR]

High-resolution multi-proxy records from two lakes on the southern Tibetan Plateau, Nam Co and Tangra Yumco, are used to infer long-term variations in the Asian monsoon system with a novel set of ostracod shell chemistry proxies. We track the moisture evolution since the Last Glacial Maximum using the trace element, rare earth element (REE) and stable isotope composition of ostracod shells. The sediment records covering the past 18.8 cal. ka BP and 17.4 cal. ka BP, respectively, demonstrate the suitability of REEs as indicators of weathering intensity and thus hydrological changes and moisture sources in the catchment. In Nam Co, high concentrations of light REEs between 14 and 13 cal. ka BP suggest an increased drainage from the glaciated Nyainqêngtanglha Mountains in the south, pointing to meltwater input. REEs in ostracod shells therefore provide additional information on water sources critical for the interpretation of stable isotope records. Mg/Ca, Sr/Ca, and Ba/Ca ratios reflect salinity and thus changes in effective moisture. Asynchronous behavior of Mg/Ca, Sr/Ca, and Ba/Ca ratios are controlled by changes in dominance of precipitating carbonate minerals in the lake. Synchronous behavior reflects calcite precipitation, indicating low-Mg/Ca warm-wet conditions. Constantly low Sr/Ca ratios reflect aragonite precipitation, indicating high-Mg dry conditions. Increased Sr/Ca and Ba/Ca relative to Mg/Ca ratios show monohydrocalcite precipitation, indicating high-Mg/Ca cold-dry conditions. Furthermore, Fe/Ca, Mn/Ca and U/Ca ratios in ostracods reflect changes in oxygen saturation in lake bottom waters controlled by lake level and microbial activity. The paleoclimate histories reconstructed from Nam Co and Tangra Yumco show high similarity throughout the late Quaternary. We identified two major dry periods, corresponding to Heinrich 1 and the Younger Dryas, followed by strengthening in Indian summer monsoon precipitation. The early Holocene is characterized by a moisture maximum, reflecting abundant water supply by a strong ISM. A time-delayed shift to dry conditions occurred at 2.6 cal. ka BP at Tangra Yumco, and at 2 cal. ka BP at Nam Co, resulting in decreasing lake levels, caused by weakened monsoon intensity due to a southeastward migration of the ISM-Westerly boundary with an estimated velocity of approximately 600 m per year.

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]

New to archaeological studies is the field of paleohydrology characterized by the use of modern hydraulic engineering and computational fluid dynamics (CFD) analysis of ancient urban and agricultural water supply and distribution systems. Examples are presented in nine chapters of CFD investigations of old and new world archaeological sites (several of which are World Heritage sites) using FLOW-3D CFD software to bring forward new discoveries revealing the depth of ancient water engineers’ knowledge and creativity not previously noted in the archaeological literature. As modern analysis methods reveal technical details of ancient water systems, equivalent ancient technologies exist that were used in the design and operation of ancient water systems, albeit in formats, texts, and origins yet to be discovered. The nine chapters to follow present brief summaries of ancient sites’ water systems and the use of CFD and modern hydraulic engineering methods to discover the water engineering knowledge base used by ancient water engineers. Results are new revelations unknown in the current literature of ancient sites. Paleohydrology studies presented serve to add a further dimension to the history of ancient new and old world archaeological sites by bringing forward added details of water engineering projects accomplished by ancient engineers.

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 Houghton phase was a brief period of low water in the glacial Lake Minong (ancestral Lake Superior) basin during the early-mid Holocene. Previous lake-level reconstructions link the onset of the Houghton phase to the cessation of meltwater inflow and the formation of a stable lake level controlled by the St. Marys River bedrock sill. New stratigraphic evidence and radiocarbon dates from the Thunder Bay (Ontario, Canada) region point to a more complex paleohydrological history during this time. Specifically, we reconstruct a lowstand from > 9100 to 8900 cal yr BP that was followed by an increase in sedimentation and base level between ~ 8900 and 8700 cal yr BP, and a second low water period beginning ~ 8700 cal yr BP. Although in need of further testing, these rapid oscillations in the lake level likely reflect the varying contributions of meltwater inflow and high rates of evaporation to the water budget of glacial Lake Minong. Strandline evidence of the first lowstand may have been eroded or buried by the 8900 cal yr BP transgression, and the second lowstand was synchronous with closed basin conditions in the other Laurentian Great Lakes. Paleoecological (pollen, wood identification, plant macrofossil) analyses of organic deposits formed during the lowstands also yield exceptionally detailed 'snapshots' of the earliest biological communities that colonized the lake margin. [ABSTRACT FROM AUTHOR]

Streamflow in Australia's northern rivers has been steadily increasing since the 1970s, most likely due to increased intensity in the Indo‐Australian monsoon. However, because of limited data availability, it is hard to assess this recent trend and therefore contextualize potential future climatic changes. In this study, we used a network of 63 precipitation‐sensitive tree‐ring chronologies from the Indo‐Australian and Asian monsoon regions to reconstruct streamflow in the Daly catchment in the Northern Territory of Australia from 1413 to 2005 CE. We used a novel wavelet‐based method to transform the variance structure of the tree‐ring chronologies to better match the hydroclimate prior to reconstruction with a hierarchical Bayesian regression model. Our streamflow reconstruction accounts for 72%–78% of the variance in the instrumental period and closely matches both historical flood events and independent proxy records, increasing confidence in its validity. We find that while streamflow has been increasing since the 1800s, the most recent 40‐year period is unprecedented in the last ∼600 years. Comparison to an independent coral‐based streamflow record shows regional coherency in this trend. Extreme high flows were found to be linked to La Niña events, but we found no significant relationship between streamflow and El Niño events, or streamflow and other regional climatic drivers. More work is therefore needed to understand the drivers of the recent streamflow increase, but, regardless of the cause, water managers should be aware of the paleoclimatic context before making decisions on water allocations. Plain Language Summary: Large‐scale agricultural development has been proposed for the Daly catchment in the Northern Territory of Australia. Since the start of record keeping in the Daly catchment in the 1970s, streamflow has been steadily increasing, most likely due to increases in Australian monsoon rainfall. However, because of the limited amount of data, it is hard to assess whether this recent increase in streamflow is unusual, part of a longer trend, or a natural cycle in monsoon rainfall. In this study, we used rainfall‐sensitive tree growth and a statistical model to reconstruct Daly River streamflow over the past 592 years. Our streamflow reconstruction closely matches known past flood events, increasing confidence in its validity. We find that streamflow has increased since the 1800s but that the most recent 40‐year period is unprecedented in the last 600 years. More work is needed to understand the drivers of this increased streamflow but regardless of the cause, water managers should be aware of the Daly River's history before making decisions on allocating water to agriculture or other large users. Key Points: 592‐year annual streamflow reconstruction of the Daly River Catchment, Australia, derived using a tree‐ring networkWavelet‐based techniques to transform tree ring spectral characteristics improve the reconstruction abilityHigh streamflow in the twentieth Century is regionally coherent and unprecedented in the preceding five centuries [ABSTRACT FROM AUTHOR]

Lake sediments are a valuable archive to document past flood occurrence and magnitude, and their evolution over centuries to millennia. This information has the potential to greatly improve current flood design and risk assessment approaches, which are hampered by the shortness and scarcity of gauge records. For this reason, paleoflood hydrology from lake sediments received fast-growing attention over the last decade. This allowed an extensive development of experience and methodologies and, thereby, the reconstruction of paleoflood series with increasingly higher accuracy. In this review, we provide up-to-date knowledge on flood sedimentary processes and systems, as well as on state-of-the-art methods for reconstructing and interpreting paleoflood records. We also discuss possible perspectives in the field of paleoflood hydrology from lake sediments by highlighting the remaining challenges. This review intends to guide the research interest in documenting past floods from lake sediments. In particular, we offer here guidance supported by the literature in how: to choose the most appropriate lake in a given region, to find the best suited sedimentary environments to take the cores, to identify flood deposits in the sedimentary sequence, to distinguish them from other instantaneous deposits, and finally, to rigorously interpret the flood chronicle thus produced. [ABSTRACT FROM AUTHOR]

Floods are among the most destructive natural hazards on Earth. In paleohydrology, sediments are generally considered as one of the best archives to extend flood records to pre‐historical timescales. Doing so requires being able to identify flood deposits from sediment archives and decipher between flood types. The latter is particularly important in glacierized regions, where meteorological floods frequently co‐occur with glacial lake outburst floods (GLOFs). In Patagonia, results from a recent study suggest that GLOFs are recorded in downstream fjord sediments as fine‐grained and organic‐poor layers, representing the high amount of glacier rock flour transported during lake outbursts, whereas meteorological floods are represented by coarser and more organic deposits. However, not all fine‐grained organic‐poor deposits could be associated with historical GLOFs. Here, we reconstruct the provenance of these Baker River flood deposits using 87Sr/86Sr and εNd, taking advantage of the clear lithological differences that exist between both sides of the watershed. Our results show that both 87Sr/86Sr and εNd are suited to reconstruct sediment provenance in the Baker River watershed but that εNd is the most effective and the least affected by grain‐size variations. Our provenance results confirm that the 21st‐century fine‐grained and organic‐poor deposits represent GLOFs and that the largest winter meteorological flood on record has a distinct coarse and organic‐rich signature. However, our results show that rain‐on‐snow events that occur in summer, and therefore primarily affect the western glacierized part of the watershed, have the same fine‐grained organic‐poor signature as GLOFs. Therefore, this study shows that the sedimentary signature of rain‐on‐snow floods in partially glacierized watersheds depends on the season during which they occur. We anticipate that our findings will contribute to a better interpretation of flood records from partially glacierized watersheds. [ABSTRACT FROM AUTHOR]