Abstract Soil waters are a central component of the terrestrial water cycle. Their δ2H, δ18O, and d‐excess values contain rich information about hydroclimate, including the source of moisture and its evaporative history. Paleoclimate workers seek to investigate ancient hydroclimates via triple oxygen isotope geochemistry, termed Δ′17O, which is analogous to d‐excess but can be measured in oxygen‐bearing minerals in paleosols. Observations of Δ′17O in soil water across climates, seasons, and depths are needed to establish a framework for applying Δ′17O to paleohydrology. We measured the δ18O, δ2H, and Δ′17O values in soil waters (0–1 m) and precipitation in the Mojave, Great Basin, and Chihuahuan Deserts and in a temperate forest in Michigan. Evaporation drives covariation in Δ′17O and d‐excess in soil waters. The range of Δ′17O values in soil waters (−148 to 44 per meg) spans the heretofore observed range of Δ′17O in the water cycle. The uppermost 20 cm of the soil profiles experience the greatest isotopic variation as soil water is subject to infiltration and evaporation. Each environment displays a distinct pattern in δ18O, d‐excess, and Δ′17O of soil water. Soil water at the forested site has isotope values that closely adhere to meteoric waters. In contrast, at the dryland sites, evaporation causes soil waters to deviate from meteoric waters along site‐specific trajectories. The Δ′17O patterns in soil waters adhere to expectations based on d‐excess, strongly affirming the utility of Δ′17O in fossilized soil sediments and in modern soil waters to investigate the water cycle.

South American summer monsoon (SASM) strength tracks insolation on orbital timescales, linking global climate and continental hydrology. However, whether local water availability also responds to global climate forcings is unclear. Here, we present water balance records from Lake Jun & iacute;n, an Andean lake within the SASM domain. Local water balance and SASM strength is inferred from triple oxygen isotopes of lake carbonates during two interglacial periods (Marine Isotope Stage (MIS) 15, 621-563 ka; the Holocene, 11.7-0 ka). We find SASM strength and water balance both follow the precession-pacing of local summer insolation, with the driest conditions occurring at Lake Jun & iacute;n under weakened SASM conditions (and vice versa). Further, the largest variations occurred during MIS 15, when insolation was more variable than the Holocene. These results suggest that global climate influences South American hydrology on both the local and continental scales, with implications for tropical water resources, the atmospheric greenhouse effect, and ecosystem dynamics.

In humid, continental Michigan, we identified pedogenic carbonate in a soil profile developed on glacial drift sediments, as rinds, rhizoliths, and filaments (at depths >50 cm). Given that the climate setting is unusual for pedogenic carbonate, we investigated its formation with environmental monitoring and isotope analyses of carbonate (delta C-13, delta O-18, Delta(47), and C-14) and waters (delta O-18 and delta H-2). We found covariation in delta C-13 and Delta(47) amongst the carbonate types (rhizoliths, rinds, filaments, bulk soil, and detrital clasts), and C-14 ages of rinds that predate plausible formation ages. The delta C-13 and Delta(47) values of the bulk carbonate and some of the pedogenic morphologies are not fully compatible with pedogenic formation in the modern environment. The delta O-18 data from precipitation and river waters and from carbonates are not uniquely identifying; they are compatible with the soil carbonate being pedogenic, detrital, or a mix. We conclude that the soil carbonate is likely a physical mix of pedogenic and detrital carbonate. Pedogenic carbonate is forming in this humid setting, likely because seasonal cycles in soil respiration and temperature cause cycles of dissolution and re-precipitation of detrital and pedogenic carbonate. The pedogenic carbonate may be a transient feature as carbonate-rich till undergoes post-glacial chemical weathering.

The naming of Australopithecus deyiremeda1 from Woranso-Mille (less than 3.59 to more than 3.33 million years) indicated the presence of a species contemporaneous with Australopithecus afarensis in the Ethiopian Afar Rift. A partial foot (BRT-VP-2/73)2 and several isolated teeth from two Burtele (BRT) localities, however, were not identified to the species level. Recently recovered dentognathic specimens clarify not only the taxonomic affinity of the BRT hominin specimens but also shed light on the diet and locomotion of A. deyiremeda. Here we present a comparative description of these specimens and show that they are attributable to A. deyiremeda. We also find it parsimonious to attribute the BRT foot to this species based on the absence of other hominin species at BRT. The new material demonstrates that overall, A. deyiremeda was dentally and postcranially more primitive than A. afarensis, particularly in aspects of canine and premolar morphology, and in its retention of pedal grasping traits. Furthermore, the low and less variable distributions of its dental enamel δ13C values are similar to those from Ardipithecus ramidus and Australopithecus anamensis, indicating a reliance on C3 foods. This suggests that A. deyiremeda had a dietary strategy similar to the earlier A. ramidus and A. anamensis. The BRT foot and its assignment to A. deyiremeda provides conclusive evidence that arboreality was a significant component of the positional behaviour of this australopith, further corroborating that some degree of arboreality persisted among Pliocene hominins1,3-7.

Global climate during the Holocene was relatively stable compared to the late Pleistocene. However, evidence from lacustrine records in South America suggests that tropical latitudes experienced significant water balance variability during the Holocene, rather than quiescence. For example, a tight coupling between insolation and carbonate delta 18O records from central Andean lakes (e.g., Lakes Jun & iacute;n, Pumacocha) suggest water balance is tied directly to South American summer monsoon (SASM) strength. However, lake carbonate delta 18O records also incorporate information about temperature and evaporation. To overcome this ambiguity, clumped and triple oxygen isotope records can provide independent constraints on temperature and evaporation. Here, we use clumped and triple oxygen isotopes to develop Holocene temperature and evaporation records from three central Andean lakes, Lakes Jun & iacute;n, Pumacocha, and Mehcocha, to build a more complete picture of regional water balance (P-E). We find that Holocene water temperatures at all three lakes were stable and slightly warmer than during the latest Pleistocene. These results are consistent with global data assimilations and records from the foothills and Amazon basin. In contrast, evaporation was highly variable and tracks SASM intensity. The hydrologic response of each lake to SASM depends greatly on the physical characteristics of the lake basin, but they all record peak evaporation in the early to mid-Holocene (11,700 to 4,200 years BP) when regional insolation was relatively low and the SASM was weak. These results corroborate other central Andean records and suggest synchronous, widespread water stress tracks insolation-paced variability in SASM strength. Lake carbonate Delta ' 17O and Delta 47 constrain lake temperature and water balance histories in ways that delta 18O records alone cannot resolve Carbonate Delta ' 17O records from three Andean lakes indicate that lake hydrology and regional water balance track insolation across the Holocene Low Delta ' 17O for reconstructed lake water indicates that greater evaporative conditions correspond to weakened early and mid-Holocene South American summer monsoon

The stable isotopic composition of pedogenic carbonates is central to many studies of past climate and topography, providing a basis for our understanding of Earth's terrestrial history. A core assumption of many applications of oxygen isotope values (δ18O) of pedogenic carbonate is that they reflect the δ18O value of precipitation (rain/snow). This assumption is violated if soil carbonates form in evaporated soil waters. In this work, we develop a means to identify evaporation in ancient soils using the triple oxygen isotope composition (16O-17O-18O) of pedogenic carbonates. Both theoretical predictions of isotope kinetics during evaporation and studies of triple oxygen isotopes in other geological materials show that the deviation in the relationship between δ17O and δ18O from a reference line, evaluated using the parameter Δ′17O, is sensitive to evaporation. As a first step in developing the use of Δ′17O in ancient pedogenic carbonates, we report Δ′17O values from 47 near-modern pedogenic carbonate samples from globally distributed environments that vary in aridity (hyper-arid to humid). The Δ′17O values of pedogenic carbonate range from −154 to −60 per meg (as CaCO3, measured via O2, VSMOW-SLAP), corresponding to calculated soil water values of −66 to +27 per meg (VSMOW-SLAP) (using a carbonate-water triple oxygen isotope fractionation exponent of 0.5250 and clumped isotope-derived carbonate growth temperatures). The Δ′17O values indicate that evaporative modification of soil water from which pedogenic carbonate forms is common, especially in arid environments. Arid environments host pedogenic carbonates formed from soil waters ranging from highly to minimally evaporated, while humid environments host pedogenic carbonates formed from waters that are only minimally evaporated. The variability in Δ′17O within environments classified by the same aridity may relate to the fact that pedogenic carbonates record soil conditions only during times of carbonate mineralization, which may deviate from annual conditions. Thus, Δ′17O may be useful in understanding the specific circumstances of pedogenic carbonate formation but may not provide incontrovertible evidence of the magnitude of environmental aridity. Evaporative modification of δ18O values of pedogenic carbonates can be detected with Δ′17O, thereby improving estimates of δ18O of unevaporated waters. Our data show that evaporation must be (re)considered for all paleoclimate inferences based on the δ18O of pedogenic carbonate. The addition of Δ′17O will re-energize paleoclimate studies that use (or have avoided using) δ18O of pedogenic carbonate.

The Busidima Formation in the Afar region, Ethiopia, spans the Quaternary and records the cultural evolution of the genus Homo. Yet, the Middle Pleistocene to Holocene fluvial environments in which early humans lived are undersampled in eastern Africa. This paper examines the stratigraphy, geochronology and paleoenvironments of the newly designated Odele Member of the uppermost Busidima Formation (<152 thousand years ago (ka)), which has received little attention despite representing a critical period in the evolution of early Homo sapiens and its migration out of Africa. The Odele Member is 40-50 m thick and is dated using tephrochronology, radiometric, luminescence, and electron spin resonance techniques. The member spans 151 to 7 ka, defined at the base by the widespread Waidedo Vitric Tuff (WAVT, 151 +/- 16 ka modeled age and 95.4% credible interval - C.I.). There are two prominent erosional unconformities in the Odele Member, a lower one after the WAVT deposition with a modeled 95.4% C.I. range of 124-97 ka; and an upper one involving widespread alluvial fan incision commencing between 21.7 and 12.9 ka. The uppermost Odele Member also contains black, organic-rich mats, redox features, reed casts, and freshwater gastropods marking wetter conditions during the terminal Pleistocene and Early Holocene. A black, fine-grained relict soil coeval with the Halalalee paleosol bounds the top of the Odele Member and has mollic and vertic properties, weathering since similar to 12 ka. These incision events and prominent paleosol development near/at the top of the Busidima Formation document Middle to Late Pleistocene Awash River incision to its present-day course. Paleo-rainfall estimates suggest that the Early Holocene-age Halalalee paleosol weathered under a climate with mean annual rainfall 10-15% higher than today. A compilation of radiocarbon ages from aquatic gastropods, carbonized wood and charcoal from the upper Odele Member shows wetter and possibly more vegetated conditions during late marine isotope stage (MIS) 3 and the African Humid Period (AHP) that are tightly coupled with precession-driven summer insolation maxima. These key findings suggest that periods of incision, aggregation, and landscape stability in the Odele Member have an orbital precession pacing. The Odele Member revises upward the age of the Busidima Formation to 7 ka, showing that it spans into the Holocene and now includes Middle and Later Stone Age archaeological traditions. (c) 2023 Elsevier Ltd. All rights reserved.

The 18O/16O ratios of biominerals have been widely used for reconstructing ecophysiology and climatic settings of modern and extinct animals. However, the 18O/16O ratios of body water, which largely determine the 18O/16O ratios of biominerals, are influenced by a host of competing factors. Regional climate and local hydrology are dominant controls on water isotopic composition before water is consumed by an animal. Behavioral and physiological factors, modified by local climate, also have a strong influence on body water compositions. The addition of a third isotope, 17O (expressed as Δ’17O) potentially allows for further resolution of these factors. Here we construct a generalized triple oxygen isotope mass balance model based on the 18O model of (Kohn 1996) (Geochim. Cosmochim. Acta 60, 4811–4829) and examine the influence on vertebrate animal body water Δ’17O of numerous climatic, ecological, and isotopic variables. We evaluate the model against new and previously published triple oxygen isotope data from modern and fossil animals. The model predicts that animals from arid environments will have wider ranges and lower minimum values of body water Δ’17O than animals living in humid environments. Leaf water consumers are more sensitive to variations in relative humidity and have lower Δ’17O than surface water consumers, which more closely track meteoric water compositions. In this model, factors such as body mass and relative proportions of evaporative versus nonevaporative effluxes from the animal have a lesser influence on animal Δ’17O. If δ18O of meteoric water is invariant, body water isotopic compositions will form approximately linear arrays in Δ’17O versus δ18O space with slopes of ∼0.52. Study of Δ’17O becomes most useful when δ18O of meteoric water is variable or unknown (as is generally the case for fossil animals); in this case Δ’17O of body water responds more strongly to changes in relative humidity, evaporated water inputs, and animal water use efficiency. These predictions are generally supported by observations of Δ’17O for modern animals. This agreement suggests that Δ’17O analysis of animal tissues has great potential as a paleo-aridity proxy in continental environments and as a proxy for learning about the ecology of modern and extinct animals.

Triple oxygen isotope ratios (Delta'O-17) offer new opportunities to improve reconstructions of past climate by quantifying evaporation, relative humidity, and diagenesis in geologic archives. However, the utility of Delta'O-17 in paleoclimate applications is hampered by a limited understanding of how precipitation Delta'O-17 values vary across time and space. To improve applications of Delta'O-17, we present delta O-18, d-excess, and Delta'O-17 data from 26 precipitation sites in the western and central United States and three streams from the Willamette River Basin in western Oregon. In this data set, we find that precipitation Delta'O-17 tracks evaporation but appears insensitive to many controls that govern variation in delta O-18, including Rayleigh distillation, elevation, latitude, longitude, and local precipitation amount. Seasonality has a large effect on Delta'O-17 variation in the data set and we observe higher seasonally amount-weighted average precipitation Delta'O-17 values in the winter (40 +/- 15 per meg [+/- standard deviation]) than in the summer (18 +/- 18 per meg). This seasonal precipitation Delta'O-17 variability likely arises from a combination of sub-cloud evaporation, atmospheric mixing, moisture recycling, sublimation, and/or relative humidity, but the data set is not well suited to quantitatively assess isotopic variability associated with each of these processes. The seasonal Delta'O-17 pattern, which is absent in d-excess and opposite in sign from delta O-18, appears in other data sets globally; it showcases the influence of seasonality on Delta'O-17 values of precipitation and highlights the need for further systematic studies to understand variation in Delta'O-17 values of precipitation.

Hydrogen stable isotope values of hydrated volcanic glass as a proxy for the isotopic composition of past meteoric waters provide an opportunity for reconstructing past climates. Here we present new hydrogen stable isotope values from 63 individual tuffs from the Afar region in the lower Awash Valley of eastern Ethiopia. The hydrogen isotopic results from volcanic glass spanning the last 6.4 Ma show a wide distribution with values ranging be-tween-89 and -32 parts per thousand (VSMOW). The variability is consistent with the observed paleo-depositional setting (i.e., lower values for fluvial settings while higher values are recorded in lacustrine settings). The reconstructed hydrogen isotopic values of parent waters are considerably lower than those of modern meteoric waters, sug-gesting a bias toward lower values during the hydration of volcanic glass. Reconstructed hydrogen stable isotope values of water derived from volcanic glass differ from other proxies of regional climate in northeast Africa, pointing to the controls of local meteoric waters on the hydrogen isotopic composition of volcanic glass. There is agreement between the reconstructed isotopic composition of parent waters and the lowest hydrogen isotopic values of modern precipitation in the Awash catchment that correspond to periods of large rainfall. This correspondence probably indicates that volcanic glass is preferentially hydrated during the wettest seasons. To test this idea, we compared the isotopic results from volcanic glass with the reconstructed isotopic composition of surface waters from soil carbonates deposited during the Pliocene and Pleistocene in the lower Awash Valley. The comparison reveals a considerable difference between proxies, with volcanic glass recording lower isotopic values than soil carbonates. Evaporative isotopic enrichment of water in shallow (<1 m) soil profiles probably accounts for the elevated values in soil carbonates. In contrast, the presence of smectite-rich vertisols above volcanic deposits appears to retard infiltration of meteoric waters deep into the subsurface. During rainfall events, vertisols swell and prevent all but the largest rainfall events from penetrating deep (>1 m) into the profiles and promoting the hydration of volcanic glass that display systematically lower isotopic values of meteoric waters than the mean annual rainfall.

Seasonal changes in light and physicochemical conditions have strong impacts on cyanobacteria, but how they affect community structure, metabolism, and biogeochemistry of cyanobacterial mats remains unclear. Light may be particularly influential for cyanobacterial mats exposed to sulphide by altering the balance of oxygenic photosynthesis and sulphide-driven anoxygenic photosynthesis. We studied temporal shifts in irradiance, water chemistry, and community structure and function of microbial mats in the Middle Island Sinkhole (MIS), where anoxic and sulphate-rich groundwater provides habitat for cyanobacteria that conduct both oxygenic and anoxygenic photosynthesis. Seasonal changes in light and groundwater chemistry were accompanied by shifts in bacterial community composition, with a succession of dominant cyanobacteria from Phormidium to Planktothrix, and an increase in diatoms, sulphur-oxidizing bacteria, and sulphate-reducing bacteria from summer to autumn. Differential abundance of cyanobacterial light-harvesting proteins likely reflects a physiological response of cyanobacteria to light level. Beggiatoa sulphur oxidation proteins were more abundant in autumn. Correlated abundances of taxa through time suggest interactions between sulphur oxidizers and sulphate reducers, sulphate reducers and heterotrophs, and cyanobacteria and heterotrophs. These results support the conclusion that seasonal change, including light availability, has a strong influence on community composition and biogeochemical cycling of sulphur and O2 in cyanobacterial mats.

Oxygen isotope distributions from lacustrine carbonates provide insights into climate and hydrological change, but it is difficult to isolate the influences of catchment precipitation δ18O, water temperature, and evaporation on lacustrine carbonate δ18O values. Recent work shows the potential for using a combination of clumped (Δ47) and triple oxygen isotope (Δ′17O) measurements to identify the roles of temperature and evaporation on carbonate δ18O values in lakes, allowing precipitation δ18O values to be inferred and facilitating paleoclimate reconstructions. However, modern calibration of this approach has been mostly limited to arid regions with a high ratio of evaporative losses over inputs (XE) and low relative humidity (h<0.7). Developing this tool for paleoclimate and paleoelevation reconstructions requires expanding the modern calibrations to a greater range of climatic and hydrologic conditions. We sampled four lakes in different hydrologic states under a single, high humidity climate regime (h=0.7–0.9) in the Lake Junín region of central Peru. Clumped isotope temperatures from lake carbonates reflect water temperatures during carbonate formation. Lake hydrology is the main control on the Δ′17O values of carbonates and waters: Δ′17O values are lowest in the larger lakes with higher XE when compared to smaller, headwater lakes where evaporation is minimal and Δ′17O is indistinguishable from that of precipitation. Reconstructed unevaporated catchment precipitation δ′18O (δ′18Orucp) values from lake waters rely on accurate characterization of λlake, the triple oxygen isotope evaporation slope. We explore the influence of humidity on λlake using both new observations and modeled data. Accounting for local humidity improves λlake estimates, which allows for more accurate reconstructions of δ′18Orucp. We generate a δ′18Orucp value of −15.2±2.1‰ from modern carbonates and waters (n=15) in the Lake Junín region, which is similar to amount weighted mean annual precipitation −14.1 (±2.2‰). This study illustrates that (1) Δ′17O can be used to differentiate between lakes with differing XE in humid climates, (2) lake carbonate Δ′17O and δ18O values can be used to evaluate the influence of evaporation on lake water δ18O values in a range of climates, and (3) modeling λlake under appropriate humidity conditions improves δ′18Orucp estimates from lake carbonate Δ′17O.

Speleothem oxygen isotope (delta O-18) records provide key insight into the rate and timing of terrestrial paleoclimate changes during the late Quaternary. However, it can be difficult to deconvolve the delta O-18 signal into individual components, which include processes related to moisture source, moisture transport, temperature, precipitation amount, infiltration, and the cave environment. We developed a framework that uses triple oxygen isotope distributions in speleothems to refine interpretations of delta O-18 speleothem records. This framework identifies the influence of dominant processes on delta O-18 values through time by their characteristic (although not necessarily unique) trends in Delta'O-17 vs. delta'O-18 space, where Delta'O-17 = delta('17O) - 0.528 delta O-'18 and delta('x) O = ln(delta(x) O + 1). Following Guo and Zhou (2019a), we expect that 'cave kinetic' processes (e.g., fast degassing at the drip site, prior calcite precipitation) will drive positive trends between delta'O-18 and Delta'O-17. In contrast, we can identify hydrologic processes from near-horizontal trends that reflect Rayleigh-type meteoric water processes and negative trends driven by changes in evaporation processes at the moisture source region or at the cave site, mineralization temperature, and seasonality in precipitation/infiltration amount. We applied this framework to four western USA speleothems from Cave of the Bells (Arizona), Leviathan Cave (Nevada), and Lehman Caves (Nevada). The Cave of the Bells and Leviathan data have nearhorizontal to negative trends indicating delta O-18 variability was driven largely by changes in Rayleigh distillation of atmospheric moisture and moisture source conditions, supporting prior interpretations. We analyzed two Lehman Caves records because they were likely influenced by non-equilibrium processes and the data show weak to moderate negative trends. For sample LMC-12b, chosen for its extreme 7.5% delta O-18 range, the trend is statistically distinct from the near-horizontal Rayleighprocess trend and most consistent with changes in local evaporation intensity and infiltration seasonality as primary drivers. None of these records displays a positive covariation slope between delta'O-18 O and Delta'O-17, suggesting limited variability in cave kinetic processes through time or unknown limitations to the kinetic model of Guo and Zhou (2019a). Additionally, reconstructed formation waters for all sites fall near the Delta'O-17 vs. delta'O-18 Local Meteoric Water Line, a correlation we suggest as a novel test of the absolute magnitude of isotopic offset due to cave kinetic processes. More broadly, our framework adds context to the only other study of carbonate speleothem triple oxygen isotope composition (Sha et al., 2020). We find that positive to negative Delta'O-17 vs. delta'O-18 trends likely exist in speleothem data that may reasonably be expected from regional climate processes and that, combined with other proxy data, triple oxygen isotope data will be useful in constraining interpretations of delta O-18(speleothem) records. (C) 2021 Elsevier Ltd. All rights reserved.

Reconstructing water availability in terrestrial ecosystems is key to understanding past climate and landscapes, but there are few proxies for aridity that are available for use at terrestrial site...

Surface soil glycerol dialkyl glycerol tetraether (GDGT) distributions are influenced by mean annual air temperature as well as soil pH. However, the controls on GDGT distributions with depth in soil profiles are less well-known. We report a study of soil profiles in warm, carbonate-precipitating, alkali soils in the Serengeti ecosystem, Tanzania. Measurements of temperature, pH, salinity, and complementary data available from carbonates and organics from the same soil pits provide an interpretive framework for the observed patterns in branched (br-) and isoprenoidal (iso-) GDGTs in soil profiles. While brGDGT distributions at the soil surface primarily reflect mean annual temperature, a warm bias at depth indicates additional sub-surface controls on brGDGT distributions. We consider whether degradation or in situ production in response to alkaline pH and salinity also modulate brGDGTs. We find that the Archaeol Caldarchaeol Ecometric (ACE) index correlates with soil salinity, which both increase with depth. These results support in situ microbial production in deeper soil settings, with pH and salinity controlling the microbial community composition. We also compared brGDGT-predicted mean annual air temperatures (MAAT) to published clumped isotope thermometry on carbonates in the same soils and found that the median temperatures of both proxies were the same at 23 degrees C. We suggest further comparison of proxy performance in carbonate-bearing soils and geological archives. Differences in the nature of the proxy recorders may broaden sample availability for paleothermometry and help to identify confounding factors in each proxy system.