Late Holocene storm-trajectory changes inferred from the oxygen isotope composition of lake diatoms, south Alaska
Late Holocene storm-trajectory changes inferred from the oxygen isotope composition of lake diatoms, south Alaska
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DOI：
10.1007/s10933-008-9261-z
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发表时间：
2009
影响因子：
2.1
通讯作者：
C. Schiff;D. Kaufman;A. P. Wolfe;J. Dodd;Z. Sharp
中科院分区：
文献类型：
--
作者：
C. Schiff;D. Kaufman;A. P. Wolfe;J. Dodd;Z. Sharp
硅藻的氧同位素比值（δ 18 Odiatom）和南阿拉斯加湖泊湖水的氧和氢同位素比值（δW）提供了对过去大气环流变化的深入了解。湖水收集从31个湖泊沿着海拔样带和硅藻分离从湖泊沉积物从一个湖（云母湖）在阿拉斯加南部。一般来说，来自沿海湖泊的δW值与全球大气降水线（GMWL）重叠。内陆湖泊的δW值不落在GMWL上;它们落在局部蒸发线轨迹上，表明相对于海洋湖泊，源同位素被耗尽。从云母湖（60.96° N，148.15° W;海拔100米）58米深处采集了沉积物岩心，该湖是威廉王子湾西部的一个对蒸发不敏感的湖。利用13个陆地宏体化石样品的~（14）C年龄建立了MC-2岩心的年龄-深度模型，其跨度为9910 cal年。从46个0.5厘米厚的样品中分离出硅藻，并分析了它们的氧同位素比。分析采用了一种新设计的分步重复性技术，该技术使用CO2激光烧蚀系统，与质谱仪耦合，外部重现性为±0.2‰。云母湖沉积物的δ 18 O δ值介于25.2 ~ 29.8‰之间。δ 18 O2值在9.6 ~ 2.6ka之间相对一致，但自2.6ka以来，其变异性增加了4倍。高分辨率采样和分析我们的湖泊核心顶部100厘米表明，在过去2000年的大气候变化。世纪δ 18 O2值增加了+4.0‰。δ 18 O2值的变化可能与硅藻类群的变化或溶解效应无关。晚全新世偏移到较低的δ 18 O2值表明，由南向北的风暴轨迹减少，这可能对应于阿留申低压系统减弱的时间间隔延长。与该地区降水（δP）同位素记录的比较支持风暴轨迹假说，并增加了全新世期间北太平洋大气环流变化的证据。
The oxygen isotope ratios of diatoms (δ18Odiatom), and the oxygen and hydrogen isotope ratios of lake water (δW) of lakes in south Alaska provide insight into past changes in atmospheric circulation. Lake water was collected from 31 lakes along an elevation transect and diatoms were isolated from lake sediment from one lake (Mica Lake) in south Alaska. In general, δW values from coastal lakes overlap the global meteoric water line (GMWL). δW values from interior lakes do not lie on the GMWL; they fall on a local evaporation line trajectory suggesting source isotopes are depleted with respect to maritime lakes. Sediment cores were recovered from 58 m depth in Mica Lake (60.96° N, 148.15° W; 100 m asl), an evaporation-insensitive lake in the western Prince William Sound. Thirteen calibrated14C ages on terrestrial macrofossil samples were used to construct an age-depth model for core MC-2, which spans 9910 cal years. Diatoms from 46, 0.5-cm-thick samples were isolated and analyzed for their oxygen isotope ratios. The analyses employed a newly designed, stepwise fluorination technique, which uses a CO2laser-ablation system, coupled to a mass spectrometer, and has an external reproducibility of ±0.2‰. δ18Odiatomvalues from Mica Lake sediment range between 25.2 and 29.8‰. δ18Odiatomvalues are relatively uniform between 9.6 and 2.6 ka, but exhibit a four-fold increase in variability since 2.6 ka. High-resolution sampling and analyses of the top 100 cm of our lake cores suggest large climate variability during the last 2000 years. The 20th century shows a +4.0‰ increase of δ18Odiatomvalues. Shifts of δ18Odiatomvalues are likely not related to changes in diatom taxa or dissolution effects. Late Holocene excursions to lower δ18Odiatomvalues suggest a reduction of south-to-north storm trajectories delivered by meridional flow, which likely corresponds to prolonged intervals when the Aleutian Low pressure system weakened. Comparisons with isotope records of precipitation (δP) from the region support the storm-track hypothesis, and add to evidence for variability in North Pacific atmospheric circulation during the Holocene.