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1. Extreme Zr stable isotope fractionation during magmatic fractional crystallization

   https://doi.org/10.1126/sciadv.aax8648  

   Ibañez-Mejia, Mauricio; Tissot, François L. (December 2019, Science Advances)

   Zirconium is a commonly used elemental tracer of silicate differentiation, yet its stable isotope systematics remain poorly known. Accessory phases rich in Zr 4+ such as zircon and baddeleyite may preserve a unique record of Zr isotope behavior in magmatic environments, acting both as potential drivers of isotopic fractionation and recorders of melt compositional evolution. To test this potential, we measured the stable Zr isotope composition of 70 single zircon and baddeleyite crystals from a well-characterized gabbroic igneous cumulate. We show that (i) closed-system magmatic crystallization can fractionate Zr stable isotopes at the >0.5% level, and (ii) zircon and baddeleyite are isotopically heavy relative to the melt from which they crystallize, thus driving chemically differentiated liquids toward isotopically light compositions. Because these effects are contrary to first-order expectations based on mineral-melt bonding environment differences, Zr stable isotope fractionation during zircon crystallization may not solely be a result of closed-system thermodynamic equilibrium. 

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2. Ancient Beringian paleodiets revealed through multiproxy stable isotope analyses

   https://doi.org/10.1126/sciadv.abc1968  

   Halffman, Carrin M.; Potter, Ben A.; McKinney, Holly J.; Tsutaya, Takumi; Finney, Bruce P.; Kemp, Brian M.; Bartelink, Eric J.; Wooller, Matthew J.; Buckley, Michael; Clark, Casey T.; et al (September 2020, Science Advances)

   null (Ed.)

   The earliest Native Americans have often been portrayed as either megafaunal specialists or generalist foragers, but this debate cannot be resolved by studying the faunal record alone. Stable isotope analysis directly reveals the foods consumed by individuals. We present multi-tissue isotope analyses of two Ancient Beringian infants from the Upward Sun River site (USR), Alaska (~11,500 years ago). Models of fetal bone turnover combined with seasonally-sensitive taxa show that the carbon and nitrogen isotope composition of USR infant bone collagen reflects maternal diets over the summer. Using comparative faunal isotope data, we demonstrate that although terrestrial sources dominated maternal diets, salmon was also important, supported by carbon isotope analysis of essential amino acids and bone bioapatite. Tooth enamel samples indicate increased salmon use between spring and summer. Our results do not support either strictly megafaunal specialists or generalized foragers but indicate that Ancient Beringian diets were complex and seasonally structured. 

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3. Finding the seasons in tree ring stable isotope ratios

   https://doi.org/10.1002/ajb2.1083  

   Monson, Russell K.; Szejner, Paul; Belmecheri, Soumaya; Morino, Kiyomi A.; Wright, William E. (May 2018, American Journal of Botany)
4. Forming Earth’s Continental Crust: A Nontraditional Stable Isotope Perspective

   https://doi.org/10.2138/gselements.17.6.413  

   Aarons, Sarah M.; Johnson, Aleisha C.; Rader, Shelby T. (December 2021, Elements)

   The formation of continental crust via plate tectonics strongly influences the physical and chemical characteristics of Earth’s surface and may be the key to Earth’s long-term habitability. However, continental crust formation is difficult to observe directly and is even more difficult to trace through time. Nontraditional stable isotopes have yielded significant insights into this process, leading to a new view both of Earth’s earliest continental crust and of what controls modern crustal generation. The stable isotope systems of titanium (Ti), zirconium (Zr), molybdenum (Mo), and thallium (Tl) have proven invaluable. Processes such as fractional crystallization, partial melting, geodynamic setting of magma generation, and magma cooling histories are examples of processes illuminated by these isotope systems. 

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5. Stable isotope tracing reveals compartmentalized nitrogen assimilation in scleractinian corals

   https://doi.org/10.3389/fmars.2022.1035523  

   Chiles, Eric N.; Huffmyer, Ariana S.; Drury, Crawford; Putnam, Hollie M.; Bhattacharya, Debashish; Su, Xiaoyang (November 2022, Frontiers in Marine Science)

   Corals form symbiotic relationships with dinoflagellate algae of the family Symbiodiniaceae, bacteria, and other microbes. Central to that relationship is the regulation of nutrition flux between the animal host and the photosynthetic Symbiodiniaceae that it is reliant on for the majority of metabolic needs. Nitrogen availability controls the growth and density of Symbiodiniaceae within coral tissues and has been proposed to play a role in host derived symbiosis regulation. Warming ocean temperatures and subsequent increases in dissolved organic carbon can potentially increase nitrogen fixation and lead to bleaching. We investigated the importance of nitrogen metabolism in vivo with LC-MS based stable isotope tracing using nubbins from three species of Hawaiian coral, the more heat tolerant Montipora capitata and Porites compressa and the more heat sensitive Pocillopora acuta , that were collected from reefs in Kāne’ohe Bay, O’ahu. In addition to 15 N incorporation into nucleotides, amino acids, and urea cycle metabolites, we also observed significant isotopic labeling in dipeptides, supporting their previous identification as major heat stress response metabolites. Surprisingly, the dipeptides are highly enriched in 15 N compared to free amino acids, which are the biosynthetic precursors for dipeptides. This suggests that there is a high turnover of dipeptide pools and distinct biosynthetic mechanisms that separately mediate amino acid and dipeptide production. These preliminary data show that nitrogen assimilation in the coral holobiont is likely compartmentalized, with rapid assimilation and quick dipeptide turnover occurring in one region of the holobiont and slow turnover of other nitrogen containing metabolites in other region(s). 

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