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Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

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Title: Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific
Authors: Yamamoto, Masanobu Browse this author →KAKEN DB
Shimamoto, Akifumi Browse this author
Fukuhara, Tatsuo Browse this author
Naraoka, Hiroshi Browse this author
Tanaka, Yuichiro Browse this author
Nishimura, Akira Browse this author
Keywords: Alkenones
Unsaturation index
Sediment trap
The North Pacific
Carbon isotopes
Issue Date: Sep-2007
Publisher: Elsevier Ltd.
Journal Title: Deep Sea Research Part I : Oceanographic Research Papers
Volume: 54
Issue: 9
Start Page: 1571
End Page: 1592
Publisher DOI: 10.1016/j.dsr.2007.05.012
Abstract: Seasonal and depth variations in alkenone flux and molecular and isotopic composition of sinking particles were examined using a 21-month time-series sediment trap experiment at a mooring station WCT-2 (39°N, 147°E) in the mid-latitude NW Pacific to assess the influences of seasonality, production depth, and degradation in the water column on the alkenone unsaturation index UK′37. Analysis of the underlying sediments was also conducted to evaluate the effects of alkenone degradation at the water–sediment interface on UK′37. Alkenone sinking flux and UK′37-based temperature showed strong seasonal variability. Alkenone fluxes were higher from spring to fall than they were from fall to spring. During periods of high alkenone flux, the UK′37-based temperatures were lower than the contemporary sea-surface temperatures (SSTs), suggesting alkenone production in a well-developed thermocline (shallower than 30 m). During low alkenone flux periods, the UK′37-based temperatures were nearly constant and were higher than the contemporary SSTs. The nearly constant carbon isotopic ratios of C37:2 and C38:2 alkenones suggest that alkenones produced in early fall were suspended in the surface water until sinking. The alkenone sinking flux decreased exponentially with increasing depth. The decreasing trend was enhanced during the periods of high alkenone flux, suggesting that fresh and labile particles sank from spring to fall, while old and stable particles sank from fall to spring. The UK′37-based temperature usually increased with increasing depth. The preservation efficiency of alkenones was 2.7–5.2% at the water–sediment interface. Despite the significant degradation of the alkenones, there was little difference in UK′37 levels between sinking particles and the surface sediment.
Type: article (author version)
Appears in Collections:環境科学院・地球環境科学研究院 (Graduate School of Environmental Science / Faculty of Environmental Earth Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 山本 正伸

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