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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]

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. Groundwater discharge is a mechanism that transports chemicals from inland systems to the ocean, but it has been considered of secondary influence compared to rivers. Here the authors assess the global significance of groundwater discharge, finding that it has a unique and important contribution to ocean chemistry and Earth-system models. [ABSTRACT FROM AUTHOR]