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Groundwater-derived solute fluxes to the ocean have long been assumed static and subordinate to riverine fluxes, if not neglected entirely, in marine isotope budgets. Here we present concentration and isotope data for Li, Mg, Ca, Sr, and Ba in coastal groundwaters to constrain the importance of groundwater discharge in mediating the magnitude and isotopic composition of terrestrially derived solute fluxes to the ocean. Data were extrapolated globally using three independent volumetric estimates of groundwater discharge to coastal waters, from which we estimate that groundwater-derived solute fluxes represent, at a minimum, 5% of riverine fluxes for Li, Mg, Ca, Sr, and Ba. The isotopic compositions of the groundwater-derived Mg, Ca, and Sr fluxes are distinct from global riverine averages, while Li and Ba fluxes are isotopically indistinguishable from rivers. These differences reflect a strong dependence on coastal lithology that should be considered a priority for parameterization in Earth-system models.

The isotopic composition of barium ^[sup 138]Ba) has emerged as a powerful tracer of deep-ocean circulation, water mass provenance, and the oceanic Ba cycle. Although the δ[sup 138]Ba of water masses is primarily controlled by the balance between pelagic barite precipitation and Ba resupply from ocean circulation, questions remain regarding the isotopic offset associated with pelagic barite formation and how the resultant Ba isotope compositions are transmitted through the water column to marine sediments. To address these questions, we conducted a time series study of dissolved, particulate, and sedimentary Ba chemistry in the Gulf of Aqaba (GOA), in the northern Red Sea, from January 2015 to April 2016. These data span significant seasonal changes in hydrography, primary productivity, and aerosol deposition, revealing three principal findings. First, the dissolved Ba chemistry of the GOA is vertically uniform across the time series, largely reflecting water mass advection from the Red Sea, with mean dissolved Ba concentrations of 47.9 ± 4.7 nmol kg[sup -1] and mean δ[sup 13ί]^ = +0.55%" ± 0.07%" (±2 SD, n = 18). Second, despite significant variations in particulate matter composition and flux, the δ[sup 138]Ba of sinking particulate Ba maintained a consistent isotope composition across different depths and over time at +0.09% ± 0.06% (n = 26). Consequently, these data imply a consistent Ba isotope offset of -0.46% ± 0.10% (±2 SD) between sinking particulates and seawater. This offset is similar to those determined in previous studies and indicates that it applies to particulates formed across diverse environmental conditions. Third, barite-containing sediment samples deposited in the GOA exhibit δ[sup 13ί]^ = +0.34% ± 0.03%, which is offset by approximately +0.2% relative to sinking particles. While the specific mechanism driving this offset remains unresolved, our results highlight the importance of performing site-specific proxy validations and exercising careful site selection when applying novel paleoceanographic proxies. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: Trees are an important part of many ecosystems. The Global Tree Assessment data can be used to focus conservation and restoration efforts for the circa 30% of tree species that are threatened worldwide. The conservation status for the tree flora of Limahuli Valley on Kaua'i Island and a restoration plan for 11 endangered tree species is evaluated in the Global Tree Assessment framework. Lessons learned from Limahuli Valley, one of the most biodiverse valleys in the Hawaiian Islands, provide recommendations for developing long‐term sustainable restoration projects. Summary: Based on conservation status assessments of the world's circa 60,000 trees, the Global Tree Assessment (GTA) report revealed that 30% (17,500) of known tree species are currently at risk of extinction.This study aims to evaluate the conservation status for the tree flora of Limahuli Valley and a restoration plan for 11 endangered tree species, in the Global Tree Assessment framework.Of the 117 tree taxa found in Limahuli Valley, 83 (71%) have been assessed for the International Union for the Conservation of Nature (IUCN) Red List and 90% of the assessed tree taxa are threatened. However, only 19 (21%) of these are federally listed and nine tree taxa were not found under their current name or at all in the GlobalTree Portal, suggesting a need for additional curation as well as a conservation status assessment gap.Progress has been made in Limahuli Valley on most restoration goals suggested by the GTA framework, but challenges remain related to both access to material for restoration, mitigation of threats, and understanding correlates of survivorship. Furthermore, trees only constitute about 40% of the flora in Limahuli Valley, and it is important to also consider nontrees including ferns and allies to strive for restoration of an ecosystem as well as the targeted species. [ABSTRACT FROM AUTHOR]

• Extensive new Ba isotopic survey of modern barites. • First Proterozoic Ba isotopic results. • Provides genetic model for enigmatic post-Marinoan barite formation. • Provides evidence for stratified post-Marinoan ocean. • Provides arguments for why barite horizons are confined to Marinoan and not Sturtian or Paleoproterozoic strata. Measurements of triple oxygen isotope ratios in barite horizons within post-Marinoan cap carbonates have provided some of the most compelling evidence that the Marinoan glaciation was a Snowball Earth event. However, the origin of these barite horizons remains unresolved. To constrain the Ba sources, and thus formation mechanisms of these horizons, we analyzed the Ba isotope composition of post-Marinoan barite deposits from Northwest Canada, Northern Norway, Brazil and South China. We augment these analyses with a Ba isotope survey of almost 100 modern and ancient additional barite measurements, including samples from pelagic (or 'marine'), hydrothermal, terrestrial, Proterozoic stratiform and cold seep environments. Unlike modern cold seep or terrestrial barites, we find that globally-distributed post-Marinoan barites exhibit a relatively narrow isotopic range, suggesting a well-mixed, effectively limitless Ba source. Moreover, post-Marinoan deposits exhibit a similar mean Ba isotope composition to modern marine barites, which we interpret as evidence of a marine Ba source. Considered alongside existing geochemical, geological, and new Ba isotope survey data, we conclude that Ba in barite horizons was sourced from a well-mixed, Ba-replete but SO 4 -poor reservoir that accumulated during the Marinoan Snowball Earth interval. This deep Ba reservoir was then transported upward—either by ocean circulation or dolomitization of underlying cap carbonates—and was brought into contact with continental weathering-derived sulfate in a post-glacial meltwater surface layer. Thus, in addition to providing a plausible mechanism for generating globally-synchronous deposition of post-Marinoan barite horizons that reconciles all existing geochemical and geological data, our results demonstrate the utility of Ba isotopes to interrogate the origin of enigmatic barite deposits throughout the sedimentary record. [ABSTRACT FROM AUTHOR]