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1. What plant is that? Chemotaxonomy from n-alkane molecular distributions of East African plants with implications for paleoecology

   Shi, S. C.; Cerling, T. E.; Uno, K. T. (December 2018, American Geophysical Union, Fall Meeting 2018, abstract #PP31D-1701)

   Plant wax n-alkanes serve as reliable biomarkers given their abundance, stability, and distribution in the sedimentary record. As a result, their utility as isotopic indicators of vegetation and hydroclimate is well-established. A less well studied aspect of plant n-alkanes is the use of their molecular distributions, or differences in the relative abundances of homologues, for chemotaxonomy. Limited plant n-alkane datasets from southern and western Africa suggest molecular distributions can differentiate C4 grasses from C3 woody vegetation. Here we examine a suite of plants from East Africa, where almost no plant biomarkers data exists from modern plants. In this study, over 100 samples of 19 species of plants were collected monthly from the Samburu National Reserve in Kenya from October 2001 to March 2003, across multiple growing seasons; n-alkane distributions and concentrations from both individual species and designated plant functional types (PFTs) - based on both photosynthetic pathway and growth form - were investigated. Previously published n-alkane data from western and southern Africa, or the "All Africa" dataset, were examined to further understand potential spatial differences in biomarker distributions. n-alkane distributions in both datasets vary in both individual species and within PFTs. Principal Components Analysis (PCA) was used to analyze distributions of n-alkanes in individual species and in PFTs, to determine the primary sources of variability. Results indicate that n-alkane distributions can be used to separate some individual species - namely, C4 grasses - and can be used to separate PFTs. C4 grasses and C3 woody vegetation were successfully separated in both datasets. Additionally, we found that n-alkane concentrations vary by four orders of magnitude across homologues and PFTs. A compiled African plant data set shows that C31 concentration is the most representative of the plant community for C4 grasses, C3 shrubs, and C3 trees and thus, is most ideal for stable isotope vegetation reconstructions. These data suggest that an organic geochemical approach to plant taxonomy is crucial to future biomarker applications for reconstructing vegetation distribution and structure in past ecosystems. 

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2. Leveraging Groundwater Dynamics to Improve Predictions of Summer Low‐Flow Discharges

   https://doi.org/10.1029/2023WR035126  

   Johnson, Keira; Harpold, Adrian; Carroll, Rosemary W. H.; Barnard, Holly; Raleigh, Mark S.; Segura, Catalina; Li, Li; Williams, Kenneth H.; Dong, Wenming; Sullivan, Pamela L. (August 2023, Water Resources Research)

   Abstract Summer streamflow predictions are critical for managing water resources; however, warming‐induced shifts from snow to rain regimes impact low‐flow predictive models. Additionally, reductions in snowpack drive earlier peak flows and lower summer flows across the western United States increasing reliance on groundwater for maintaining summer streamflow. However, it remains poorly understood how groundwater contributions vary interannually. We quantify recession limb groundwater (RLGW), defined as the proportional groundwater contribution to the stream during the period between peak stream flow and low flow, to predict summer low flows across three diverse western US watersheds. We ask (a) how do snow and rain dynamics influence interannual variations of RLGW contributions and summer low flows?; (b) which watershed attributes impact the effectiveness of RLGW as a predictor of summer low flows? Linear models reveal that RLGW is a strong predictor of low flows across all sites and drastically improves low‐flow prediction compared to snow metrics at a rain‐dominated site. Results suggest that strength of RLGW control on summer low flows may be mediated by subsurface storage. Subsurface storage can be divided into dynamic (i.e., variability saturated) and deep (i.e., permanently saturated) components, and we hypothesize that interannual variability in dynamic storage contribution to streamflow drives RLGW variability. In systems with a higher proportion of dynamic storage, RLGW is a better predictor of summer low flow because the stream is more responsive to dynamic storage contributions compared to deep‐storage‐dominated systems. Overall, including RLGW improved low‐flow prediction across diverse watersheds. 

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3. The secret life of garnets: A comprehensive, standardized dataset of garnet geochemical analyses integrating localities and petrogenesis.

   https://doi.org/10.5194/essd-15-4235-2023  

   CHIAMA, K; GABOR, M; LUPINI, I; RUTLEDGE, R; NORD, J A; ZHANG, S; BOUJIBAR, A; BULLOCK, E S; WALTER, M J; LEHNERT, K; et al (September 2023, Earth system science data discussions)

   Integrating mineralogy with data science is critical to modernizing Earth materials research and its applications to geosciences. Data were compiled on 95 650 garnet sample analyses from a variety of sources, ranging from large repositories (EarthChem, RRUFF, MetPetDB) to individual peer-reviewed literature. An important feature is the inclusion of mineralogical “dark data” from papers published prior to 1990. Garnets are commonly used as indicators of formation environments, which directly correlate with their geochemical properties; thus, they are an ideal subject for the creation of an extensive data resource that incorporates composition, locality information, paragenetic mode, age, temperature, pressure, and geochemistry. For the data extracted from existing databases and literature, we increased the resolution of several key aspects, including petrogenetic and paragenetic attributes, which we extended from generic material type (e.g., igneous, metamorphic) to more specific rock-type names (e.g., diorite, eclogite, skarn) and locality information, increasing specificity by examining the continent, country, area, geological context, longitude, and latitude. Likewise, we utilized end-member and quality index calculations to help assess the garnet sample analysis quality. This comprehensive dataset of garnet information is an open-access resource available in the Evolutionary System of Mineralogy Database (ESMD) for future mineralogical studies, paving the way for characterizing correlations between chemical composition and paragenesis through natural kind clustering (Chiama et al., 2022; https://doi.org/10.48484/camh-xy98). We encourage scientists to contribute their own unpublished and unarchived analyses to the growing data repositories of mineralogical information that are increasingly valuable for advancing scientific discovery. 

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4. Resiliency of Silica Export Signatures When Low Order Streams Are Subject to Storm Events

   https://doi.org/10.1029/2021JG006660  

   Fernandez, N. M.; Bouchez, J.; Derry, L. A.; Chorover, J.; Gaillardet, J.; Giesbrecht, I.; Fries, D.; Druhan, J. L. (May 2022, Journal of Geophysical Research: Biogeosciences)

   Abstract Silicon stable isotope ratios (³⁰Si) of over 150 stream water samples were measured during seven storm events in six small critical zone observatory (CZO) catchments spanning a wide range in climate (sub‐humid to wet, tropical) and lithology (granite, volcanic, and mixed sedimentary). Here we report a cross‐site analysis of this dataset to gain insight into stream³⁰Si variability across low‐order catchments and to identify potential climate (i.e., runoff), hydrologic, lithologic, and biogeochemical controls on observed stream Si chemical and isotopic signatures. Event‐based³⁰Si exhibit variability both within and across sites (−0.22‰ to +2.27‰) on the scale of what is observed globally in both small catchments and large rivers. Notably, each site shows distinct³⁰Si signatures that are preserved even after normalization for bedrock composition. Successful characterization of observed cross‐site behavior requires the merging of two distinct frameworks in a novel combined model describing both non‐uniform fluid transit time distributions and multiple fractionating pathways in application to low‐order catchments. The combined model reveals that site‐specific architecture (i.e., biogeochemical reaction pathways and hydrologic routing) regulates stream silicon export signatures even when subject to extreme precipitation events. 

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5. Evolution of the South Pacific's Iron Cycle Over the Cenozoic

   https://doi.org/10.1029/2025PA005149  

   Tegler, Logan A; Horner, Tristan J; Nielsen, Sune G; Heard, Andy W; Squires, Katherine R; Severmann, Silke; Peucker‐Ehrenbrink, Bernhard; Blusztajn, Jerzy; Dunlea, Ann G (July 2025, Paleoceanography and Paleoclimatology)

   Abstract Iron (Fe) availability impacts marine primary productivity, potentially influencing the efficiency of the biological carbon pump. Stable Fe isotope analysis has emerged as a tool to understand how Fe is sourced and cycled in the water column; however its application to sediment records is complicated by overlapping isotope signatures of different sources and uncertainties in establishing chronologies. To overcome these challenges, we integrate Fe and osmium isotope measurements with multi‐element geochemical analysis and statistical modeling. We apply this approach to reconstruct the history of Fe delivery to the South Pacific from three pelagic clay sequences spanning 93 million years. Our analysis reveals five principal Fe sources—dust, distal background, two distinct hydrothermal inputs, and a magnesium‐rich volcanic ash. Initially, hydrothermal inputs dominated Fe deposition, but as the sites migrated away from their respective mid‐ocean ridges, other sources became prominent. Notably, from 66 to 40 million years ago (Ma), distal background Fe was the primary source before a shift to increasing dust dominance around 30 Ma. This transition implies that Fe in South Pacific seawater has been dust‐dominated since ≈30 Ma, despite extremely low dust deposition rates today. We speculate that the shift to episodic and low Fe fluxes in the South Pacific and Southern Ocean over the Cenozoic helped shape an ecological niche that favored phytoplankton that adapted to these conditions, such as diatoms. Our analysis highlights how Fe delivery to the ocean is driven by large‐scale tectonic and climatic shifts, while also influencing climate through its integral role in marine phytoplankton and Earth's biogeochemical cycles. 

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