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New tungsten isotope data for modern ocean island basalts (OIB) from Hawaii, Samoa, and Iceland reveal variable 182W/184W, ranging from that of the ambient upper mantle to ratios as much as 18 parts per million lower. The tungsten isotopic data negatively correlate with ³He/⁴He. These data indicate that each OIB system accesses domains within Earth that formed within the first 60 million years of solar system history. Combined isotopic and chemical characteristics projected for these ancient domains indicate that they contain metal and are repositories of noble gases. We suggest that the most likely source candidates are mega–ultralow-velocity zones, which lie beneath Hawaii, Samoa, and Iceland but not beneath hot spots whose OIB yield normal 182W and homogeneously low ³He/⁴He.

Rare high-³He/⁴He signatures in ocean island basalts (OIB) erupted at volcanic hotspots derive from deep-seated domains preserved in Earth’s interior. Only high-³He/⁴He OIB exhibit anomalous 182W—an isotopic signature inherited during the earliest history of Earth—supporting an ancient origin of high ³He/⁴He. However, it is not understood why some OIB host anomalous 182W while others do not. We provide geochemical data for the highest-³He/⁴He lavas from Iceland (up to 42.9 times atmospheric) with anomalous 182W and examine how Sr-Nd-Hf-Pb isotopic variations—useful for tracing subducted, recycled crust—relate to high ³He/⁴He and anomalous 182W. These data, together with data on global OIB, show that the highest-³He/⁴He and the largest-magnitude 182W anomalies are found only in geochemically depleted mantle domains—with high 143Nd/144Nd and low 206Pb/204Pb—lacking strong signatures of recycled materials. In contrast, OIB with the strongest signatures associated with recycled materials have low ³He/⁴He and lack anomalous 182W. These observations provide important clues regarding the survival of the ancient He and W signatures in Earth’s mantle. We show that high-³He/⁴He mantle domains with anomalous 182W have low W and ⁴He concentrations compared to recycled materials and are therefore highly susceptible to being overprinted with low ³He/⁴He and normal (not anomalous) 182W characteristic of subducted crust. Thus, high ³He/⁴He and anomalous 182Ware preserved exclusively in mantle domains least modified by recycled crust. This model places the long-term preservation of ancient high ³He/⁴He and anomalous 182W in the geodynamic context of crustal subduction and recycling and informs on survival of other early-formed heterogeneities in Earth’s interior.

We employed two compelling and distinct methods, Fourier Transform Infrared Spectroscopy (FTIR) and Ramped Pyrolysis Oxidation (Ramped PyrOx), to examine the quality of organic matter (OM) stored in four peatlands located along a latitudinal gradient (Tropical (4˚N), Subtropical (27˚N), Boreal (48˚N), and Polar (68˚N)). FTIR was used to quantify the relative abundance of carbohydrates, a relatively labile compound class, and aromatics, which are more recalcitrant, in a sample set of four peat cores. These samples were then prepared using Ramped PyrOx, a second, independent method of determining OM quality that mimics the natural diagenetic maturation of OM that would take place over long timescales. Previous large-scale studies using FTIR to evaluate OM quality have observed that it generally increases with increasing latitude (more carbohydrates, less aromatics). Here, we demonstrate that the Ramped PyrOx approach both validates and complements the FTIR approach. The data stemming from each Ramped PyrOx preparation was input to a model that generates an estimated probability density function of the activation energy ( E ) required to break the C bonds in the sample. We separated these functions into three fractions (“low E ,” “medium E ,” and “high E ”) to create Ramped PyrOx variables that could be quantitatively compared to the compound class abundance data from FTIR. In assessing the agreement between the two methods, we found three significant relationships between Ramped PyrOx and FTIR variables. Low E fractions and carbohydrate content were positively correlated (R 2 = 0.51) while low E fractions were negatively correlated with aromatic content (R 2 = 0.58). Medium E fractions were found to be positively correlated with aromatics (R 2 = 0.69).

The genesis of kimberlites is unclear despite the economic and scientific interest surrounding these diamond-bearing magmas. One critical question is whether they tap ancient, deep mantle domains or the shallow convecting mantle with partial melting triggered by plumes or plate tectonics. To address this question, we report the He-Ne-Ar isotopic compositions of magmatic fluids trapped in olivine from kimberlites worldwide. The kimberlites which have been least affected by addition of deeply subducted or metasomatic components have Ne isotopes less nucleogenic than the upper mantle, hence requiring a deep-mantle origin. This is corroborated by previous evidence of small negative W isotope anomalies and kimberlite location along age-progressive hot-spot tracks. The lack of strong primordial He isotope signatures indicates overprinting by lithospheric and crustal components, which suggests that Ne isotopes are more robust tracers of deep-mantle contributions in intraplate continental magmas. The most geochemically depleted kimberlites may preserve deep remnants of early-Earth heterogeneities. Some diamondiferous kimberlite lavas can originate from ancient domains located at Earth’s core-mantle boundary, according to analyses of noble gas geochemistry of magmatic fluids trapped inside kimberlite hosted olivines.

Nitrogen (N) dominates Earth's atmosphere (78% N2) but occurs in trace abundances in silicate minerals, making it a sensitive tracer of recycled surface materials into the mantle. The mechanisms controlling N transfer between terrestrial reservoirs remain uncertain because low N abundances in mineral‐hosted fluid inclusions (FIs) are difficult to measure. Using new techniques, we analyzed N and He isotope compositions and abundances in olivine‐ and pyroxene‐hosted FIs from arc volcanoes in Southern Chile, Cascadia, Central America, and the Southern Marianas. These measurements enable an estimate of the global flux of N outgassing from arcs (4.0 × 1010 mol/yr). This suggests that Earth is currently in a state of net N ingassing, with roughly half of subducted N returned to the mantle. Additionally, the N outgassing flux of individual arcs correlates with the thickness of subducting pelagic sediment, suggesting that N cycling in the modern solid Earth is largely controlled by sediment subduction. Plain Language Summary Nitrogen (N) largely behaves like an inert gas, and so it is substantially more concentrated at Earth's surface than in Earth's deep interior. Over geologic time, N can be transported between the solid Earth and the surface, and its concentration can change in both of these settings. Volcanic gases transport N from the interior to the surface, while some surface N returns into the solid Earth via plate subduction. Here, we present measurements of N and helium (He) gas trapped within crystals in volcanic rocks to determine how much N is transported to the surface through volcanism associated with plate subduction. We find that the amount of N returning to the surface through volcanism is less than estimates of how much N is transported into the solid Earth, suggesting that, overall, N is being returned to the planet's deep interior. Additionally, we observe that the amount of oceanic sediment that is subducted correlates with the amount of N that comes out of volcanoes, making it the primary carrier of N into the solid Earth. Key Points Arc lavas yield fluxes of 4.0 × 1010 mol N/yr, similar to estimates from volcanic arc gases, likely resulting in net mantle ingassing of N Nitrogen isotopes and N‐He mixing models highlight that small contributions of sediment dominate volcanic arc N budgets Subducted sediment thickness correlates with N2/3He ratios, and likely controls arc N fluxes rather than slab parameters or thermal state

This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ13C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring results in line with accepted values. The application of a best-fit mass-balance correction yielded a procedural blank of 22.0 ± 6.0 µg C with Fm of 0.30 ± 0.20 and δ13C of –32.0 ± 3.0‰ for this period, which was notably higher and more variable than previously reported. Changes to the procedure, specifically elimination of higher organic carbon reagents and improved sample and reactor handling, reduced the blank to 11.0 ± 2.75 µg C, with Fm of 0.14 ± 0.10 and δ13C of –31.0 ± 5.5‰. A thorough determination of the entire sample processing blank is required to ensure accurate isotopic compositions of seawater DOC using the UV oxidation method. Additional efforts are needed to further reduce the procedural blank so that smaller DOC samples can be analyzed, and to increase sample throughput.

High 3 He/ 4 He ratios in some basalts have been interpreted as evidence for ancient reservoirs preserved in the Earth’s mantle; however, such rocks have never been observed to host the primitive lead-isotopic compositions required for an early formation age. These authors show that Baffin Island and West Greenland lavas exhibit primitive lead-isotope ratios consistent with a mantle source age of 4.55–4.45 billion years, and that their source may be the most ancient accessible reservoir in the mantle. Primordial volcanism today Oceanic island lavas with high 3 He/ 4 He ratios are thought by some to sample a primordial terrestrial reservoir preserved in the Earth since it accreted from the solar nebula about 4.5 billion years ago, but these lavas have never been found to exhibit the primitive lead-isotopic compositions associated with such an early formation age. Now Matthew Jackson and colleagues show that Baffin Island and West Greenland lavas, previously found to host the highest terrestrial mantle 3 He/ 4 He ratios, have primitive lead-isotope ratios that are consistent with an ancient mantle source age of 4.55 billion to 4.45 billion years. The combined helium, lead and neodymium isotopic compositions in these lavas suggests that their source is the most ancient accessible reservoir in Earth's mantle — and it may be parental to all mantle reservoirs that give rise to modern volcanism. Helium is a powerful tracer of primitive material in Earth’s mantle. Extremely high 3 He/ 4 He ratios in some ocean-island basalts suggest the presence of relatively undegassed and undifferentiated material preserved in Earth’s mantle. However, terrestrial lavas with high 3 He/ 4 He ratios have never been observed to host the primitive lead-isotopic compositions that are required for an early (roughly 4.5 Gyr ago) formation age 1 , 2 . Here we show that Cenozoic-era Baffin Island and West Greenland lavas, previously found to host the highest terrestrial-mantle 3 He/ 4 He ratios 3 , 4 , 5 , exhibit primitive lead-isotope ratios that are consistent with an ancient mantle source age of 4.55–4.45 Gyr. The Baffin Island and West Greenland lavas also exhibit 143 Nd/ 144 Nd ratios similar to values recently proposed for an early-formed (roughly 4.5 Gyr ago) terrestrial mantle reservoir 6 , 7 . The combined helium-, lead- and Nd-isotopic compositions in Baffin Island and West Greenland lavas therefore suggest that their source is the most ancient accessible reservoir in the Earth’s mantle, and it may be parental to all mantle reservoirs that give rise to modern volcanism.

This note describes improvements of UV oxidation method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). The procedural blank is reduced to 2.6 ± 0.6 μg C, with Fm of 0.42 ± 0.10 and δ13C of –28.43 ± 1.19‰. The throughput is improved from one sample per day to two samples per day.

We report new geochemical data for submarine lavas from the Samoan region that greatly enhance the geochemical data set for volcanoes from the hot spot. Additionally, two volcanoes dredged in the northern Lau Basin, Futuna Island and Manatu seamount, are young (<5 Ma), appear to be genetically related, and may have been generated by melting a component of Samoan mantle that has been advected into the region. We also find evidence for three seamounts and one atoll along the Samoan hot spot track that are not geochemically related to Samoa. We use a plate motion model to show that three non‐Samoan hot spots, currently active in the Cook‐Austral Islands, provided volcanism to the Pacific Plate now in the Samoan region approximately 10–40 Ma. The four interloping volcanoes in the Samoan region exhibit geochemical affinities with the three hot spots. All three hot spots would have left a depleted, viscous, refractory keel that is coupled to the base of the Pacific lithosphere that has been “rafted” to the Samoan region. Therefore, the new data also have implications for the origin of the Samoan hot spot as its origin has been suggested to be a result of either a deep‐seated mantle plume or a consequence of lithospheric cracking. Without major modification of the current “propagating lithospheric cracks” model, it is not clear how such cracks could yield melts from the refractory keel present under the Samoan lithosphere. Instead, a region of buoyantly upwelling mantle, or plume, is suggested to generate the shield stage volcanism in the Samoan region.

Whether cooling occurred in the Southern Hemisphere during the Younger Dryas (YD) is key to understanding mechanisms of millennial climate change. Although Southern Hemisphere records do not reveal a distinct climate reversal during the late glacial period, many mountain glaciers readvanced. We show that the Puerto Bandera moraine (50°S), which records a readvance of the Southern Patagonian Icefield (SPI), formed at, or shortly after, the end of the YD. The exposure age (10.8 ± 0.5 thousand years ago) is contemporaneous with the highest shoreline of Lago Cardiel (49°S), which records peak precipitation east of the Andes since 13 thousand years ago. Absent similar moraines west of the Andes, these data indicate an SPI response to increased amounts of easterly-sourced precipitation--reflecting changes in the Southern Westerly circulation--rather than regional cooling.