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1. Red maple tree root water uptake depths are influenced by neighboring tree species composition

   https://doi.org/10.1093/treephys/tpaf049  

   Sobota, Matthew; Li, Kevin; Knighton, James (May 2025, Tree Physiology)

   Meinzer, Frederick (Ed.)

   Abstract Understanding how mixed-species forests uptake subsurface water sources is critical to projecting future forest water use and stress. Variation in root water uptake (RWU) depths and volumes is common among trees but it is unclear how it is affected by species identity, local water availability or neighboring tree species compositions. We evaluated the hypothesis that RWU depths and the age of water (i.e., time since water entered soils as precipitation) taken up by red maples (Acer rubrum) varied significantly between two forested plots, both containing red maples, similar soils, topography and hydrologic conditions, but having different neighboring tree species. We measured soil moisture contents as well as stable isotopes (δ2H, δ18O) in plant xylem water and soil moisture across two years. These data were used to calibrate process-based stand-level ecohydrological models for each plot to estimate species-level RWU depths. Model calibration suggested significant differences in red maple tree RWU depths, transpiration rates and the ages of water taken up by maples across the two stands. Maple trees growing with ash and white spruce relied on significantly deeper and older water from the soil profile than maple trees growing with birch and oak. The drought risk profile experienced by maple trees differed between the plots as demonstrated by strong correlations between precipitation and model simulated transpiration on a weekly time scale for maples taking up shallow soil moisture and a monthly time scale for maples reliant on deeper soil moisture. These findings carry significant implications for our understanding of water competition in mixed-species forests and for the representation of forest rooting strategies in hydrologic and earth systems models. 

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2. Validating a novel capability of assessing pathways of animal water gain and loss

   https://doi.org/10.1098/rsos.241942  

   Steele, Zachary T; Caceres, Karen; David, Zachary A; Shollenberger, Lisa M; Gerson, Alexander R; Newsome, Seth D; Whiteman, John P (May 2025, Royal Society Open Science)

   Understanding variations in the routes by which wild animals gain and lose water is challenging, and common methods require longitudinal sampling, which can be prohibitive. However, a new approach usesΔ′¹⁷O_BW(Δ′¹⁷O of animal body water), calculated from measurements ofδ′¹⁷O andδ′¹⁸O in a single sample, as a natural tracer of water flux.Δ′¹⁷O_BWis promising, but its relationship to organismal variables such as metabolic rate and water intake have not been validated. Here, we continuously measured oxygen influxes and effluxes of captive deer mice (Peromyscus maniculatus), and manipulated their water intake and metabolic rate. We used these oxygen flux data to predictΔ′¹⁷O_BWfor the mice and compared these model predictions withΔ′¹⁷O_BWmeasured in blood plasma samples. As expected,Δ′¹⁷O_BWpositively correlated with drinking water intake and negatively correlated with metabolic rate. All predictedΔ′¹⁷O_BW(based on measured oxygen fluxes) values differed from measuredΔ′¹⁷O_BWvalues by <30 per meg (mean absolute difference: 11 ± 9 per meg), suggesting high accuracy for this modelling approach because studies currently report a range of 300 per meg forΔ′¹⁷O_BWamong mammals, birds and fish. 

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3. Large herbivore δ ¹⁸ O as a proxy for aridity in the South African winter and year-round rainfall zone

   https://doi.org/10.1017/qua.2024.21  

   Luyt, Julie; Faith, J Tyler; Sealy, Judith (November 2024, Quaternary Research)

   Abstract This study explores patterning in δ¹⁸O values of tooth enamel in contemporary African herbivores from mainly C₃-dominated ecosystems. Evapotranspiration causes plants to lose H₂¹⁶O to a greater extent than H₂¹⁸O, leaving leaves enriched in¹⁸O. In eastern Africa, ES species (evaporation-sensitive species: those obtaining water from food) tend to have more positive δ¹⁸O_enamelvalues than EI species (evaporation-insensitive species: those heavily dependent on drinking water); the magnitude of the difference increases with increasing aridity. We find the same pattern applies in the winter and year-round rainfall region of southern Africa, allowing us to use δ¹⁸O_enamelin fossil animals to examine paleo-aridity. We apply this approach to infer aridity at Quaternary fossil assemblages from present-day winter and year-round rainfall zones, including Elandsfontein (ca. 1–0.6 Ma), Hoedjiespunt (ca. 300–130 ka), and Nelson Bay Cave (23.5–3 ka). This analysis suggests that (1) at various times during the Pleistocene, Elandsfontein and Hoedjiespunt environments were wetter than last glacial maximum (LGM) to Holocene environments at Nelson Bay Cave (year-round rainfall zone); and (2) considered alongside other evidence from the year-round rainfall zone, wetter conditions across the Pleistocene–Holocene transition at Nelson Bay Cave suggests that climate changes at near-coastal sites may be out of phase with the adjacent interior. 

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4. Timing of Pedogenic Carbonate Formation in Fine‐Grained Soils: Decoupled T(Δ ₄₇ ) and δ ¹⁸ O _w Seasonal Bias

   https://doi.org/10.1029/2024PA005071  

   Havranek, Rachel; Snell, Kathryn; Brookins, Sarah; Davidheiser‐Kroll, Brett (February 2025, Paleoceanography and Paleoclimatology)

   Abstract Historically, clumped isotope thermometry (T(∆₄₇)) of soil carbonates has been interpreted to represent a warm‐season soil temperature based dominantly on coarse‐grained soils. Additionally, T(∆₄₇) allows the calculation of the oxygen isotope composition of soil water (δ¹⁸O_w) in the past using the temperature‐dependent fractionation factor between soil water and pedogenic carbonate, but previous work has not measured δ¹⁸O_wvalues with which to compare to these archives. Here, we present clumped isotope thermometry of modern soil carbonates from three soils in Colorado and Nebraska, USA, that have a fine‐to‐medium grain size, contain clay, and are representative of many carbonate‐bearing paleosols preserved in the rock record. At two of the three sites, Briggsdale, CO and Seibert, CO, T(∆₄₇) overlaps with mean annual soil temperature (MAST), and the calculated δ¹⁸O_woverlaps within uncertainty with measured δ¹⁸O_wat carbonate bearing depths. At the third site, in Oglala National Grassland, NE, mean T(∆₄₇) is 8–11°C warmer than MAST, and the calculated δ¹⁸O_whas a significantly higher isotope value than any observations of δ¹⁸O_w. At all three sites, even in the fall season, δ¹⁸O_wvalues at carbonate bearing depths overlap with spring rainfall δ¹⁸O_w, and there is little to no evaporative enrichment of δ²H_wand δ¹⁸O_wvalues. These data challenge long‐held assumptions that all pedogenic carbonate records a warm‐season bias, and that δ¹⁸O_wat carbonate‐bearing depths is affected by evaporative enrichment. 

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5. Seasonal SIMS δ18O record in Astarte borealis from the Baltic Sea tracks a modern regime shift in the NAO

   https://doi.org/10.3389/fmars.2023.1293823  

   Hughes, Hunter P; Surge, Donna; Orland, Ian J; Zettler, Michael L; Moss, David K (December 2023, Frontiers in Marine Science)

   IntroductionAstarte borealisholds great potential as an archive of seasonal paleoclimate, especially due to its long lifespan (several decades to more than a century) and ubiquitous distribution across high northern latitudes. Furthermore, recent work demonstrates that the isotope geochemistry of the aragonite shell is a faithful proxy of environmental conditions. However, the exceedingly slow growth rates ofA. borealisin some locations (<0.2mm/year) make it difficult to achieve seasonal resolution using standard micromilling techniques for conventional stable isotope analysis. Moreover, oxygen isotope (δ¹⁸O) records from species inhabiting brackish environments are notoriously difficult to use as paleoclimate archives because of the simultaneous variation in temperature and δ¹⁸O_watervalues. MethodsHere we use secondary ion mass spectrometry (SIMS) to microsample anA. borealisspecimen from the southern Baltic Sea, yielding 451 SIMS δ¹⁸O_shellvalues at sub-monthly resolution. ResultsSIMS δ¹⁸O_shellvalues exhibit a quasi-sinusoidal pattern with 24 local maxima and minima coinciding with 24 annual growth increments between March 1977 and the month before specimen collection in May 2001. DiscussionAge-modeled SIMS δ¹⁸O_shellvalues correlate significantly with bothin situtemperature measured from shipborne CTD casts (r² = 0.52, p<0.001) and sea surface temperature from the ORAS5-SST global reanalysis product for the Baltic Sea region (r² = 0.42, p<0.001). We observe the strongest correlation between SIMS δ¹⁸O_shellvalues and salinity when both datasets are run through a 36-month LOWESS function (r² = 0.71, p < 0.001). Similarly, we find that LOWESS-smoothed SIMS δ¹⁸O_shellvalues exhibit a moderate correlation with the LOWESS-smoothed North Atlantic Oscillation (NAO) Index (r² = 0.46, p<0.001). Change point analysis supports that SIMS δ¹⁸O_shellvalues capture a well-documented regime shift in the NAO circa 1989. We hypothesize that the correlation between the SIMS δ¹⁸O_shelltime series and the NAO is enhanced by the latter’s influence on the regional covariance of water temperature and δ¹⁸O_watervalues on interannual and longer timescales in the Baltic Sea. These results showcase the potential for SIMS δ¹⁸O_shellvalues inA. borealisshells to provide robust paleoclimate information regarding hydroclimate variability from seasonal to decadal timescales. 

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