Griffin Sheila

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Griffin
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Sheila
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  • Article
    Dissolved organic radiocarbon in the central Pacific Ocean
    (American Geophysical Union, 2019-05-02) Druffel, Ellen R. M. ; Griffin, Sheila ; Wang, Ning ; Garcia, Noreen G. ; McNichol, Ann P. ; Key, Robert M. ; Walker, Brett D.
    We report marine dissolved organic carbon (DOC) concentrations, and DOC ∆14C and δ13C values in seawater collected from the central Pacific. Surface ∆14C values are low in equatorial and polar regions where upwelling occurs and high in subtropical regions dominated by downwelling. A core feature of these data is that 14C aging of DOC (682 ± 86 14C years) and dissolved inorganic carbon (643 ± 40 14C years) in Antarctic Bottom Water between 54.0°S and 53.5°N are similar. These estimates of aging are minimum values due to mixing with deep waters. We also observe minimum ∆14C values (−550‰ to −570‰) between the depths of 2,000 and 3,500 m in the North Pacific, though the source of the low values cannot be determined at this time.
  • Article
    East Asian Monsoon variability since the sixteenth century
    (American Geophysical Union, 2019-04-16) Goodkin, Nathalie F. ; Bolton, Annette ; Hughen, Konrad A. ; Karnauskas, Kristopher B. ; Griffin, Sheila ; Phan, Kim Hoang ; Vo, Si Tuan ; Ong, Maria Rosabelle ; Druffel, Ellen R. M.
    The East Asian Monsoon (EAM) impacts storms, freshwater availability, wind energy production, coal consumption, and subsequent air quality for billions of people across Asia. Despite its importance, the EAM's long‐term behavior is poorly understood. Here we present an annually resolved record of EAM variance from 1584 to 1950 based on radiocarbon content in a coral from the coast of Vietnam. The coral record reveals previously undocumented centennial scale changes in EAM variance during both the summer and winter seasons, with an overall decline from 1600 to the present. Such long‐term variations in monsoon variance appear to reflect independent seasonal mechanisms that are a combination of changes in continental temperature, the strength of the Siberian High, and El Niño–Southern Oscillation behavior. We conclude that the EAM is an important conduit for propagating climate signals from the tropics to higher latitudes.
  • Article
    Dissolved 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).
  • Article
    Low reservoir ages for the surface ocean from mid-Holocene Florida corals
    (American Geophysical Union, 2008-05-13) Druffel, Ellen R. M. ; Robinson, Laura F. ; Griffin, Sheila ; Halley, Robert B. ; Southon, John R. ; Adkins, Jess F.
    The 14C reservoir age of the surface ocean was determined for two Holocene periods (4908–4955 and 3008–3066 calendar (cal) B.P.) using U/Th-dated corals from Biscayne National Park, Florida, United States. We found that the average reservoir ages for these two time periods (294 ± 33 and 291 ± 27 years, respectively) were lower than the average value between A.D. 1600 and 1900 (390 ± 60 years) from corals. It appears that the surface ocean was closer to isotopic equilibrium with CO2 in the atmosphere during these two time periods than it was during recent times. Seasonal δ 18O measurements from the younger coral are similar to modern values, suggesting that mixing with open ocean waters was indeed occurring during this coral's lifetime. Likely explanations for the lower reservoir age include increased stratification of the surface ocean or increased Δ14C values of subsurface waters that mix into the surface. Our results imply that a more correct reservoir age correction for radiocarbon measurements of marine samples in this location from the time periods ∼3040 and ∼4930 cal years B.P. is ∼292 ± 30 years, less than the canonical value of 404 ± 20 years.
  • Article
    Dissolved Organic Radiocarbon in the West Indian Ocean
    (American Geophysical Union, 2023-10-02) Druffel, Ellen R. M. ; Lewis, Christian B. ; Griffin, Sheila ; Flaherty, Alessandra ; Rudresh, Megha ; Hauksson, Niels E. ; Key, Robert M. ; McNichol, Ann P. ; Hwang, Jeomshik ; Walker, Brett D.
    We report marine dissolved organic carbon (DOC) concentrations, and DOC Δ14C and δ13C in seawater collected from the West Indian Ocean during the GO-SHIP I07N cruise in 2018. We find bomb 14C in DOC from the upper 1,000 m of the water column. There is no significant change in ∆14C of DOC in deep water northward, unlike that of dissolved inorganic carbon (DIC), suggesting that transport of deep water northward is not controlling the 14C age of DOC. Variability of DOC ∆14C, including high values in the deep waters, is more pronounced than in other oceans, suggesting that dissolution of surface derived particulate organic carbon is a source of modern carbon to deep DOC in the West Indian Ocean. Low δ13C are present at two of the five stations studied, suggesting a source of low δ13C DOC, or additional microbial utilization of deep DOC.