TY - JOUR
T1 - Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific
AU - Yamamoto, Masanobu
AU - Shimamoto, Akifumi
AU - Fukuhara, Tatsuo
AU - Naraoka, Hiroshi
AU - Tanaka, Yuichiro
AU - Nishimura, Akira
N1 - Funding Information:
We thank Kazuko Hino and Etsuko Kamata (Geological Survey of Japan) and Noriko Edasawa (Hokkaido University) for analytical assistance in the laboratory. Special thanks are due to the members of New Energy and Industrial Technology Development Organization (NEDO) WEST-COSMIC, and the staff of the General Environmental Technos Co., LTD. for sampling and their helpful discussions, to Tomohisa Irino, Ken Sawada, and Youichi Tanimoto (HU) for their valuable suggestions, and to Masatoshi Komiya (GSJ) for his help in analysis. We also acknowledge three anonymous reviewers for improving the paper. This study was financially supported by NEDO and the Agency of Industrial Science and Technology.
Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2007/9
Y1 - 2007/9
N2 - 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.
AB - 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.
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U2 - 10.1016/j.dsr.2007.05.012
DO - 10.1016/j.dsr.2007.05.012
M3 - Article
AN - SCOPUS:34547954507
VL - 54
SP - 1571
EP - 1592
JO - Deep-Sea Research Part I: Oceanographic Research Papers
JF - Deep-Sea Research Part I: Oceanographic Research Papers
SN - 0967-0637
IS - 9
ER -