More Like this

1. Ancient helium and tungsten isotopic signatures preserved in mantle domains least modified by crustal recycling

   https://doi.org/10.1073/pnas.2009663117  

   Jackson, Matthew G.; Blichert-Toft, Janne; Halldórsson, Saemundur A.; Mundl-Petermeier, Andrea; Bizimis, Michael; Kurz, Mark D.; Price, Allison A.; Harðardóttir, Sunna; Willhite, Lori N.; Breddam, Kresten; et al (November 2020, Proceedings of the National Academy of Sciences)

   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 anomalous¹⁸²W—an isotopic signature inherited during the earliest history of Earth—supporting an ancient origin of high³He/⁴He. However, it is not understood why some OIB host anomalous¹⁸²W while others do not. We provide geochemical data for the highest-³He/⁴He lavas from Iceland (up to 42.9 times atmospheric) with anomalous¹⁸²W and examine how Sr-Nd-Hf-Pb isotopic variations—useful for tracing subducted, recycled crust—relate to high³He/⁴He and anomalous¹⁸²W. These data, together with data on global OIB, show that the highest-³He/⁴He and the largest-magnitude¹⁸²W anomalies are found only in geochemically depleted mantle domains—with high¹⁴³Nd/¹⁴⁴Nd and low²⁰⁶Pb/²⁰⁴Pb—lacking strong signatures of recycled materials. In contrast, OIB with the strongest signatures associated with recycled materials have low³He/⁴He and lack anomalous¹⁸²W. 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 anomalous¹⁸²W have low W and⁴He concentrations compared to recycled materials and are therefore highly susceptible to being overprinted with low³He/⁴He and normal (not anomalous)¹⁸²W characteristic of subducted crust. Thus, high³He/⁴He and anomalous¹⁸²W are preserved exclusively in mantle domains least modified by recycled crust. This model places the long-term preservation of ancient high³He/⁴He and anomalous¹⁸²W in the geodynamic context of crustal subduction and recycling and informs on survival of other early-formed heterogeneities in Earth’s interior. 

   more » « less
2. ²¹⁰ Po and ²¹⁰ Pb Distributions Along the GEOTRACES Pacific Meridional Transect (GP15): Tracers of Scavenging and Particulate Organic Carbon (POC) Export

   https://doi.org/10.1029/2024GB008243  

   Cochran, J_Kirk; Wei, Ziran; Horowitz, Evan; Fitzgerald, Patrick; Heilbrun, Christina; Stephens, Mark; Lam, Phoebe_J; Le_Roy, Emilie; Charette, Matthew (November 2024, Global Biogeochemical Cycles)

   Abstract Distributions of the natural radionuclide²¹⁰Po and its grandparent²¹⁰Pb along the GP15 Pacific Meridional Transect provide information on scavenging rates of reactive chemical species throughout the water column and fluxes of particulate organic carbon (POC) from the primary production zone (PPZ).²¹⁰Pb is in excess of its grandparent²²⁶Ra in the upper 400–700 m due to the atmospheric flux of²¹⁰Pb. Mid‐water²¹⁰Pb/²²⁶Ra activity ratios are close to radioactive equilibrium (1.0) north of ∼20°N, indicating slow scavenging, but deficiencies at stations near and south of the equator suggest more rapid scavenging associated with a “particle veil” located at the equator and hydrothermal processes at the East Pacific Rise. Scavenging of²¹⁰Pb and²¹⁰Po is evident in the bottom 500–1,000 m at most stations due to enhanced removal in the nepheloid layer. Deficits in the PPZ of²¹⁰Po (relative to²¹⁰Pb) and²¹⁰Pb (relative to²²⁶Ra decay and the²¹⁰Pb atmospheric flux), together with POC concentrations and particulate²¹⁰Po and²¹⁰Pb activities, are used to calculate export fluxes of POC from the PPZ.²¹⁰Po‐derived POC fluxes on large (>51 μm) particles range from 15.5 ± 1.3 mmol C/m²/d to 1.5 ± 0.2 mmol C/m²/d and are highest in the Subarctic North Pacific;²¹⁰Pb‐derived fluxes range from 6.7 ± 1.8 mmol C/m²/d to 0.2 ± 0.1 mmol C/m²/d. Both²¹⁰Po‐ and²¹⁰Pb‐derived POC fluxes are greater than those calculated using the²³⁴Th proxy, possibly due to different integration times of the radionuclides, considering their different radioactive mean‐lives and scavenging mean residence times. 

   more » « less
3. Measurement of the CKM angle γ in B± → DK*(892)± decays

   https://doi.org/10.1007/JHEP02(2025)113  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (February 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> Measurements ofCPobservables and the CKM angleγare performed inB^±→DK^*(892)^±decays, whereDrepresents a superposition ofD⁰and$$ {\overline{D}}^0 $$ ${\overline{D}}^0$states, using the LHCb dataset collected during Run 1 (2011–2012) and Run 2 (2015–2018). A study of this channel is presented with theDmeson reconstructed in two-body final statesK^±π^∓,K⁺K⁻andπ⁺π⁻; four-body final statesK^±π^∓π^±π^∓andπ⁺π⁻π⁺π⁻; and three-body final states$$ {K}_{\textrm{S}}^0{\pi}^{+}{\pi}^{-} $$ $K_S^0{\pi }^{+}{\pi }^{-}$and$$ {K}_{\textrm{S}}^0{K}^{+}{K}^{-} $$ $K_S^0{K}^{+}{K}^{-}$. This analysis includes the first observation of the suppressedB^±→[π^±K^∓]_DK^*±andB^±→[π^±K^∓π^±π^∓]_DK^*±decays. The combined result givesγ= (63±13)°. 

   more » « less
4. The Mercury Isotopic Composition of Earth's Mantle and the Use of Mass Independently Fractionated Hg to Test for Recycled Crust

   https://doi.org/10.1029/2021GL094301  

   Moynier, Frédéric; Jackson, Matthew G.; Zhang, Ke; Cai, Hongming; Halldórsson, Sæmundur Ari; Pik, Raphael; Day, James M. D.; Chen, Jiubin (September 2021, Geophysical Research Letters)

   Abstract The element mercury (Hg) can develop large mass‐independent fractionation (MIF) (Δ¹⁹⁹Hg) due to photo‐chemical reactions at Earth's surface. This results in globally negative Δ¹⁹⁹Hg for terrestrial sub‐aerially‐derived materials and positive Δ¹⁹⁹Hg for sub‐aqueously‐derived marine sediments. The mantle composition least affected by crustal recycling is estimated from high‐³He/⁴He lavas from Samoa and Iceland, providing an average of Δ¹⁹⁹Hg = 0.00 ± 0.10, Δ²⁰¹Hg = −0.02 ± 0.0.09,δ²⁰²Hg = −1.7 ± 1.2; 2SD,N = 11. By comparison, a HIMU‐type lava from Tubuai exhibits positive Δ¹⁹⁹Hg, consistent with altered oceanic crust in its mantle source. A Samoan (EM2) lava has negative Δ¹⁹⁹Hg reflecting incorporation of continental crust materials into its source. Three Pitcairn lavas exhibit positive Δ¹⁹⁹Hg which correlate with⁸⁷Sr/⁸⁶Sr, consistent with variable proportions of continental (low Δ¹⁹⁹Hg and high⁸⁷Sr/⁸⁶Sr) and oceanic (high Δ¹⁹⁹Hg and low⁸⁷Sr/⁸⁶Sr) crustal material in their mantle sources. These observations indicate that MIF signatures offer a powerful tool for examining atmosphere‐deep Earth interactions. 

   more » « less
5. Redox‐Neutral S ‐nitrosation Mediated by a Dicopper Center

   https://doi.org/10.1002/anie.202102589  

   Tao, Wenjie; Moore, Curtis E.; Zhang, Shiyu (June 2021, Angewandte Chemie International Edition)

   Abstract A redox‐neutralS‐nitrosation of thiol has been achieved at a dicopper(I,I) center. Treatment of dicopper (I,I) complex with excess NO^.and thiol generates a dicopper (I,I) di‐S‐nitrosothiol complex [Cu^ICu^I(RSNO)₂]²⁺or dicopper (I,I) mono‐S‐nitrosothiol complex [Cu^ICu^I(RSNO)]²⁺, which readily release RSNO in 88–94 % yield. TheS‐nitrosation proceeds by a mixed‐valence [Cu^IICu^III(μ‐O)(μ‐NO)]²⁺species, which deprotonates RS‐H at the basic μ‐O site and nitrosates RS⁻at the μ‐NO site. The [Cu^IICu^III(μ‐O)(μ‐NO)]²⁺complex is also competent forO‐nitrosation of MeOH. A rare [Cu^IICu^II(μ‐NO)(OMe)]²⁺intermediate was isolated and fully characterized, suggesting theS‐nitrosation may proceed through the intermediary of analogous [Cu^IICu^II(μ‐NO)(SR)]²⁺species. This redox‐ and proton‐neutralS‐nitrosation process is the first functional model of ceruloplasmin in mediatingS‐nitrosation of external thiols, with implications for biological copper sites in the interconversion of NO^./RSNO. 

   more » « less