Lewis Christian B.
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ArticleMarine organic carbon and radiocarbon – present and future challenges(Cambridge University Press, 2022-01-25) Druffel, Ellen R. M. ; Beaupre, Steven R. ; Grotheer, Hendrik ; Lewis, Christian B. ; McNichol, Ann P. ; Mollenhauer, Gesine ; Walker, Brett D.We discuss present and developing techniques for studying radiocarbon in marine organic carbon (C). Bulk DOC (dissolved organic C) Δ14C measurements reveal information about the cycling time and sources of DOC in the ocean, yet they are time consuming and need to be streamlined. To further elucidate the cycling of DOC, various fractions have been separated from bulk DOC, through solid phase extraction of DOC, and ultrafiltration of high and low molecular weight DOC. Research using 14C of DOC and particulate organic C separated into organic fractions revealed that the acid insoluble fraction is similar in 14C signature to that of the lipid fraction. Plans for utilizing this methodology are described. Studies using compound specific radiocarbon analyses to study the origin of biomarkers in the marine environment are reviewed and plans for the future are outlined. Development of ramped pyrolysis oxidation methods are discussed and scientific questions addressed. A modified elemental analysis (EA) combustion reactor is described that allows high particulate organic C sample throughput by direct coupling with the MIniCArbonDAtingSystem.
ArticleDissolved organic radiocarbon in the eastern Pacific and Southern Oceans(American Geophysical Union, 2021-05-24) Druffel, Ellen R. M. ; Griffin, Sheila ; Lewis, Christian B. ; Rudresh, Megha ; Garcia, Noreen G. ; Key, Robert M. ; McNichol, Ann P. ; Hauksson, Niels E. ; Walker, Brett D.We report marine dissolved organic carbon (DOC) concentrations, and DOC Δ14C and δ13C values in seawater collected from the Southern Ocean and eastern Pacific GOSHIP cruise P18 in 2016/2017. The aging of 14C in DOC in circumpolar deep water northward from 69°S to 20°N was similar to that measured in dissolved inorganic carbon in the same samples, indicating that the transport of deep waters northward is the primary control of 14C in DIC and DOC. Low DOC ∆14C and δ13C measurements between 1,200 and 3,400 m depth may be evidence of a source of DOC produced in nearby hydrothermal ridge systems (East Pacific Rise).