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1. Shelf‐Basin Interactions and Water Mass Residence Times in the Western Arctic Ocean: Insights Provided by Radium Isotopes

   https://doi.org/10.1029/2019JC014988  

   Kipp, Lauren E.; Kadko, David C.; Pickart, Robert S.; Henderson, Paul B.; Moore, Willard S.; Charette, Matthew A. (May 2019, Journal of Geophysical Research: Oceans)

   Abstract Radium isotopes are produced through the decay of thorium in sediments and are soluble in seawater; thus, they are useful for tracing ocean boundary‐derived inputs to the ocean. Here we apply radium isotopes to study continental inputs and water residence times in the Arctic Ocean, where land‐ocean interactions are currently changing in response to rising air and sea temperatures. We present the distributions of radium isotopes measured on the 2015 U.S. GEOTRACES transect in the Western Arctic Ocean and combine this data set with historical radium observations in the Chukchi Sea and Canada Basin. The highest activities of radium‐228 were observed in the Transpolar Drift and the Chukchi shelfbreak jet, signaling that these currents are heavily influenced by interactions with shelf sediments. The ventilation of the halocline with respect to inputs from the Chukchi shelf occurs on time scales of ≤19–23 years. Intermediate water ventilation time scales for the Makarov and Canada Basins were determined to be ~20 and >30 years, respectively, while deep water residence times in these basins were on the order of centuries. The radium distributions and residence times described in this study serve as a baseline for future studies investigating the impacts of climate change on the Arctic Ocean. 

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2. Extreme mantle heterogeneity in mid-ocean ridge mantle revealed in lavas from the 8°20' N near-axis seamount chain

   https://doi.org/10.26022/IEDA/111616  

   Anderson, Molly Anderson; Wanless, V. Dorsey; Perfit, Michael; Conrad, Ethan; Gregg, Patricia; Fornari, Daniel; Ridley, William (January 2021, Interdisciplinary Earth Data Alliance (IEDA))

   This dataset presents major and trace element and radiogenic isotopes geochemistry of glasses in mid-ocean ridge basalts, sampled along a chain of near-axis seamounts and volcanic ridges perpendicular to the East Pacific Rise. 

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3. A Lagrangian View of Trace Elements and Isotopes in the North Pacific

   https://doi.org/10.1029/2019JC015862  

   Hayes, Christopher T.; Fitzsimmons, Jessica N.; Jensen, Laramie T.; Lanning, Nathan T.; Hatta, Mariko; McGee, David; Boyle, Edward A. (March 2020, Journal of Geophysical Research: Oceans)

   Abstract Ocean time‐series sites are influenced by both temporal variability, as in situ conditions change, as well as spatial variability, as water masses move across the fixed observation point. To remove the effect of spatial variability, this study made sub‐daily Lagrangian observations of trace elements and isotopes (Al, Sc, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb,²³²Th, and²³⁰Th) in surface water over a 12‐day period (July–August 2015) in the North Pacific near the Hawaii Ocean Time‐series Station ALOHA. Additionally, a vertical profile in the upper 250 m was analyzed. This dataset is intercalibrated with GEOTRACES standards and provides a consistent baseline for trace element studies in the oligotrophic North Pacific. No diel changes in trace elements could be resolved, although day‐to‐day variations were resolved for some elements (Fe, Cu, and Zn), which may be related to organic matter cycling or ligand availability. Pb concentrations remained relatively constant during 1997–2015, presenting a change from previous decreases. Nutrient to trace element stoichiometric ratios were compared to those observed in phytoplankton as an indication of the extent of biological trace element utilization in this ecosystem, providing a basis for future ecological trace element studies. 

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4. Abundances of Uranium and Thorium Elements in Earth Estimated by Geoneutrino Spectroscopy

   https://doi.org/10.1029/2022GL099566  

   Abe, S.; Asami, S.; Eizuka, M.; Futagi, S.; Gando, A.; Gando, Y.; Gima, T.; Goto, A.; Hachiya, T.; Hata, K.; et al (August 2022, Geophysical Research Letters)

   Abstract The decay of the primordial isotopes²³⁸U,²³⁵U,²³²Th, and⁴⁰K has contributed to the terrestrial heat budget throughout the Earth's history. Hence, the individual abundance of those isotopes are key parameters in reconstructing contemporary Earth models. The geoneutrinos produced by the radioactive decays of uranium and thorium have been observed with the Kamioka Liquid‐Scintillator Antineutrino Detector (KamLAND). Those measurements have been improved with more than 18‐year observation time, and improvement in detector background levels mainly with an 8‐year nearly reactor‐free period, which now permit spectroscopy with geoneutrinos. Our results yield the first constraint on both uranium and thorium heat contributions. The KamLAND result is consistent with geochemical estimations based on elemental abundances of chondritic meteorites and mantle peridotites. The High‐Q model is disfavored at 99.76% C.L. and a fully radiogenic model is excluded at 5.2σassuming a homogeneous heat producing element distribution in the mantle. 

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5. Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES‐Era Data

   https://doi.org/10.1029/2020GB006814  

   Horner, T. J.; Little, S. H.; Conway, T. M.; Farmer, J. R.; Hertzberg, J. E.; Janssen, D. J.; Lough, A. J. M.; McKay, J. L.; Tessin, A.; Galer, S. J. G.; et al (November 2021, Global Biogeochemical Cycles)

   Abstract Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES‐era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate history. 

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