Research Articles (Earth Sciences)

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Browsing Research Articles (Earth Sciences) by Subject "Carbon cycle (Biogeochemistry)"

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    Assessment of C, N, and Si Isotopes as tracers of past ocean nutrient and carbon cycling
    (John Wiley & Sons, Inc., 2021) Farmer, J. R.; Hertzberg, J. E.; Cardinal, D.; Fietz, S.; Hendry, K.; Jaccard, S. L.; Paytan, A.; Rafter, P. A.; Ren, H.; Somes, C. J.; Sutton, J. N.
    Biological productivity in the ocean directly influences the partitioning of carbon between the atmosphere and ocean interior. Through this carbon cycle feedback, changing ocean productivity has long been hypothesized as a key pathway for modulating past atmospheric carbon dioxide levels and hence global climate. Because phytoplankton preferentially assimilate the light isotopes of carbon and the major nutrients nitrate and silicic acid, stable isotopes of carbon (C), nitrogen (N), and silicon (Si) in seawater and marine sediments can inform on ocean carbon and nutrient cycling, and by extension the relationship with biological productivity and global climate. Here, we compile water column C, N, and Si stable isotopes from GEOTRACES-era data in four key ocean regions to review geochemical proxies of oceanic carbon and nutrient cycling based on the C, N, and Si isotopic composition of marine sediments. External sources and sinks as well as internal cycling (including assimilation, particulate matter export, and regeneration) are discussed as likely drivers of observed C, N, and Si isotope distributions in the ocean. The potential for C, N, and Si isotope measurements in sedimentary archives to record aspects of past ocean C and nutrient cycling is evaluated, along with key uncertainties and limitations associated with each proxy. Constraints on ocean C and nutrient cycling during late Quaternary glacial-interglacial cycles and over the Cenozoic are examined. This review highlights opportunities for future research using multielement stable isotope proxy applications and emphasizes the importance of such applications to reconstructing past changes in the oceans and climate system.
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    A metamorphic origin for Europa's ocean
    (John Wiley & Sons, Inc, 2021) Daswani, Mohit Melwani; Vance, Steven D.; Mayne, Matthew J.; Glein, Christopher R.
    Europa likely contains an iron-rich metal core. For it to have formed, temperatures within Europa reached urn:x-wiley:00948276:media:grl62926:grl62926-math-00011250 K. Going up to that temperature, accreted chondritic minerals — for example, carbonates and phyllosilicates — would partially devolatilize. Here, we compute the amounts and compositions of exsolved volatiles. We find that volatiles released from the interior would have carried solutes, redox-sensitive species, and could have generated a carbonic ocean in excess of Europa's present-day hydrosphere, and potentially an early urn:x-wiley:00948276:media:grl62926:grl62926-math-0002 atmosphere. No late delivery of cometary water was necessary. Contrasting with prior work, urn:x-wiley:00948276:media:grl62926:grl62926-math-0003 could be the most abundant solute in the ocean, followed by urn:x-wiley:00948276:media:grl62926:grl62926-math-0004, urn:x-wiley:00948276:media:grl62926:grl62926-math-0005, and urn:x-wiley:00948276:media:grl62926:grl62926-math-0006. However, gypsum precipitation going from the seafloor to the ice shell decreases the dissolved S/Cl ratio, such that Clurn:x-wiley:00948276:media:grl62926:grl62926-math-0007S at the shallowest depths, consistent with recently inferred endogenous chlorides at Europa's surface. Gypsum would form a 3–10 km thick sedimentary layer at the seafloor.