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Seasonal variability of δ18O and δ13C of planktic foraminiferain the Bering Sea and central subarctic Pacific during 1990-2000

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Title
Seasonal variability of δ18O and δ13C of planktic foraminiferain the Bering Sea and central subarctic Pacific during 1990-2000
Authors
Asahi, Hirofumi
Okazaki, Yusuke
Ikehara, Minoru
Khim, Boo-Keum
Nam, Seung-Il
Takahashi, Kozo
Subject
Geology; Oceanography; Paleontology
Keywords
Paleoceanography; Planktic foraminifera; Subarctic; Bering Sea; T/S Oshoro-Maru IV
Issue Date
2015
Citation
Asahi, Hirofumi, et al. 2015. "Seasonal variability of δ18O and δ13C of planktic foraminiferain the Bering Sea and central subarctic Pacific during 1990-2000". Paleoceanography, 30(10): 1328-1346.
Abstract
We evaluated a 10 year time series of δ18O and δ13C records from three planktic foraminifers (Neogloboquadrina pachyderma, Globigerina umbilicata, and Globigerinita glutinata) in the Bering Sea and central subarctic Pacific with a focus on their responses to environmental changes. Foraminiferal δ18O followed the equilibriumequation for inorganic calcite, with species-specific equilibriumoffsets ranging fromnearly zero ( 0.02‰for N. pachyderma and 0.01‰ for G.umbilicata) to 0.16‰(G. glutinata). Equilibrium offsets in our sediment trap sampleswere smaller than those fromplankton tow studies, implying that foraminiferal δ18Owas modified by encrustation during settling. Habitat/calcification depths varied from 35-55m (N. pachyderma and G.umbilicata) or 25-45m (G. glutinata) duringwarm, stratified seasons to around 100m during winter, when the mixed layer depth increases. Unlike δ18O, foraminiferal δ13C showed species-specific responses to environmental changes. We found a dependency of δ13C in G.umbilicata on CO3-2 concentrations in ambient seawater that agreed reasonably well with published laboratory results, suggesting that δ13C of G.umbilicata is subject to vital effects. In contrast, δ13C of N. pachyderma and G. glutinata are likely affected by other species-specific biological activities. Seasonal flux patterns reveal that fossil records of N. pachyderma and G. glutinata represent annual mean conditions, whereas that of G.umbilicata most likely indicates those of a specific season. Because none of these three taxawas abundant from December to February, their fossil records likely do not reflect isotope signals from cold seasons.
DOI
http://dx.doi.org/10.1002/2015PA002801
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