Seasonal variation in the oxygen isotopic composition of different-sized planktonic foraminifer Neogloboquadrina pachyderma (sin.) in the north western North Pacific, and implications for reconstruction of the paleo-environment
Seasonal variation in the oxygen isotopic composition of different-sized planktonic foraminifer Neogloboquadrina pachyderma (sin.) in the north western North Pacific, and implications for reconstruction of the paleo-environment
复制标题
北太平洋西北部不同大小浮游有孔虫 Neogloboquadrina pchyderma (sin.) 氧同位素组成的季节变化及其对古环境重建的意义
DOI：
10.1029/2011pa002153
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
H.Nishi
中科院分区：
文献类型：
--
作者：
A.Kuroyanagi;H.Kawahata;H.Nishi
浮游有孔虫壳的氧同位素值（δ18O）是重建古环境最常用的指标之一。Neogloboquadrina pachyderma(sinstral) （N. pachyderma(sin.)）是亚极地和极地地区的优势有孔虫，广泛用于高纬度古构造。本研究考察了北半球δ 18o的季节变化。在北太平洋西北部收集了3.5年以上的沉积物捕集器样本。临界偏移值约为- 1‰，与以往浮游生物群落研究结果一致。大壳个体（180 ~ 250μm）比小壳个体（125 ~ 180μm）在更浅、更温暖的环境中分泌壳，壳尺寸的δ 18o差异具有季节变化特征。虽然体型较大的个体钙化速度较慢，δ 18o略重，但体型类之间的差异主要反映了水体居住环境的不同，并与分层的季节变化有关。在夏季，大型个体主要在25-35 m深度钙化，而小型个体在约45 m的背斜附近钙化。在冬季，两个大小级在45-65米处或稍高于弱斜斜处钙化。因此，贝壳δ 18o可以记录背斜深度附近的海洋环境，而δ 18o的尺寸特异性差异反映了水柱分层。年通量加权δ 18o值与非通量加权平均δ 18o值相对应，这是由于两个通量峰的贡献相同，而且不同粒径之间的差异也与分层有关。这表明化石δ 18o数据可以代表斜斜周围的年平均环境和过去的分层。
The oxygen isotope value (δ18O) of planktonic foraminifer shells is one of the most commonly used proxies to reconstruct the paleoenvironment.Neogloboquadrina pachyderma(sinistral) (N. pachyderma(sin.)) is a dominant foraminifer in subpolar and polar region that is used extensively for high‐latitude paleoreconstruction. The present study examined seasonal variation inδ18O ofN. pachyderma(sin.) using sediment trap samples collected over 3.5 years in the northwestern North Pacific Ocean. The vital offset value was about −1‰, which agrees with previous plankton tow studies. Large shell individuals (180–250μm) secrete their shells in a shallower and warmer environment than small ones (125–180μm), and the difference inδ18O between shell size showed seasonal variation. Although large individuals calcify at a slower rate with slightly heavierδ18O than small individuals, differences between size classes mainly reflect different habitation in the water column and are related to seasonal changes in stratification. During summer, large individuals would calcify mainly at 25–35 m depth, while small individuals calcify near the pycnocline at ∼45 m. During winter, both size classes calcify at or slightly above the weak pycnocline at 45–65 m. Thus, the shellδ18O could record the oceanographic environment around pycnocline depth, and size‐specific differences inδ18O reflect water column stratification. The annual flux‐weightedδ18O corresponded to non‐flux‐weighted meanδ18O value due to the equal contribution of two flux peaks and differences between size classes also related to the stratification. It suggests that fossilδ18O data could represent the annual mean environment around pycnocline and past stratification.