Oxygen isotope records of Holocene climate variability in the Pacific Northwest
Oxygen isotope records of Holocene climate variability in the Pacific Northwest
复制标题
DOI：
10.1016/j.quascirev.2016.04.012
复制
发表时间：
2016-06
影响因子：
4
通讯作者：
B. Steinman;David P. Pompeani;M. Abbott;J. Ortiz;N. Stansell;M. Finkenbinder;L. Mihindukulasooriya
中科院分区：
文献类型：
--
作者：
B. Steinman;David P. Pompeani;M. Abbott;J. Ortiz;N. Stansell;M. Finkenbinder;L. Mihindukulasooriya
克莱兰湖(不列颠哥伦比亚省东南部)、天堂湖(不列颠哥伦比亚省中部)和石灰湖(华盛顿州东部)的自生碳酸盐氧同位素(δ18O)测量提供了太平洋西北部全新世降水-蒸发平衡变化的∼9000a记录。克莱兰湖和天堂湖都是表面上封闭的小型盆地系统，没有活跃的流入或流出。莱姆湖表面上是开放的，有季节性的溢流。Cleland和Paradise小区沿局部蒸发线的水同位素值表明，降水-蒸发平衡对湖泊水文有很大的影响。相比之下，石灰湖水的同位素值位于当地的大气水线上，表明蒸发的影响很小。为了在高时间分辨率上推断过去的水文平衡变化，我们以1-60∼mm的间隔(平均每个样本3-33年)对克莱兰、天堂和石灰湖沉积岩心进行采样，并测量了每个样本中细粒(<；63μm)自生CaCO3的同位素组成。在距今7600年至2200年(Yr BP)之前，克莱兰湖沉积物中出现了δ18O负值，这表明闭合盆地湖泊的条件更潮湿；2200年BP之后，δ18O值出现更正值，表明湖泊条件更干燥。克莱兰湖记录中以δ2400yr BP为中心的高度负的∼18O值表明，由于气候显著变湿，此时湖泊水位很高(并且湖泊可能已经泛滥)。同样，天堂湖沉积物δ18O值在7600~4000yr BP之间相对较低，从∼4000年到3000yr BP和从∼2000yrBP到现在都是相对较低的，表明全新世中期至晚全新世气候变得更加干燥。石灰湖的δ18O记录主要反映了降水同位素组成的变化，比闭盆湖记录的变化小，并遵循从中全新世到现在的总体增加趋势。这些结果与湖泊水位、降水量和降水同位素组成变化的几个近端重建相一致，也可能反映了现代厄尔尼诺-南方涛动(ENSO)在全新世晚期的建立，这是从太平洋盆地天气学海洋-大气变化的替代证据推断的。作为古气候模拟对比项目第三阶段(PMIP3)的一部分，中全新世(6000年BP)气候模式模拟的结果表明，在北美西部的大部分地区，冷季(10-3月)比全新世晚期更潮湿，暖季(4-9月)比全新世晚期要干燥得多，导致北美西部总体气候干燥，水文气候季节性增强。这与克莱兰和天堂δ18O记录的推论是一致的，湖泊模拟实验表明，这是受冷季降水-蒸发平衡的强烈影响。这也解释了δ18O湖记录与来自大太平洋西北地区的其他水文气候变化指标之间的明显不一致，这些指标对冷季气候不太敏感，因此表明中全新世期间的条件相对干燥。克莱兰湖∼18O数据中δ2400yr BP处的突然负漂移，以及在此之后显著向更正值的转变，表明海洋-大气动力学的逐渐变化可以在北美西部内陆地区产生突然的、非线性的水文气候响应。
Oxygen isotope (δ18O) measurements of authigenic carbonate from Cleland Lake (southeastern British Columbia), Paradise Lake (central British Columbia), and Lime Lake (eastern Washington) provide a ∼9000 year Holocene record of precipitation-evaporation balance variations in the Pacific Northwest. Both Cleland Lake and Paradise Lake are small, surficially closed-basin systems with no active inflows or outflows. Lime Lake is surficially open with a seasonally active overflow. Water isotope values from Cleland and Paradise plot along the local evaporation line, indicating that precipitation-evaporation balance is a strong influence on lake hydrology. In contrast, Lime Lake water isotope values plot on the local meteoric water line, signifying minimal influence by evaporation. To infer past hydrologic balance variations at a high temporal resolution, we sampled the Cleland, Paradise, and Lime Lake sediment cores at 1–60 mm intervals (∼3–33 years per sample on average) and measured the isotopic composition of fine-grained (<63 μm) authigenic CaCO3in each sample. Negative δ18O values, which indicate wetter conditions in closed-basin lakes, occur in Cleland Lake sediment from 7600 to 2200 years before present (yr BP), and are followed by more positive δ18O values, which suggest drier conditions, after 2200 yr BP. Highly negative δ18O values in the Cleland Lake record centered on ∼2400 yr BP suggest that lake levels were high (and that the lake may have been overflowing) at this time as a result of a substantially wetter climate. Similarly, Paradise Lake sediment δ18O values are relatively low from 7600 to 4000 yr BP and increase from ∼4000 to 3000 yr BP and from ∼2000 yr BP to present, indicating that climate became drier from the middle through the late Holocene. The δ18O record from Lime Lake, which principally reflects changes in the isotopic composition of precipitation, exhibits less variability than the closed-basin lake records and follows a generally increasing trend from the mid-Holocene to present. These results are consistent with several proximal reconstructions of changes in lake-level, precipitation amount, and precipitation isotopic composition and may also reflect the establishment of modern El Niño Southern Oscillation (ENSO) variability in the late Holocene, as inferred from proxy evidence of synoptic ocean-atmosphere changes in the Pacific basin. Results from mid-Holocene (6000 yr BP) climate model simulations conducted as part of the Paleoclimate Modeling Intercomparison Project Phase 3 (PMIP3) indicate that in much of western North America, the cold season (October–March) was wetter and the warm season (April–September) was considerably drier relative to the late Holocene, leading to an overall drier climate in western North America with enhanced hydroclimatic seasonality. This is consistent with inferences from the Cleland and Paradise δ18O records, which lake modeling experiments indicate are strongly influenced by cold season precipitation-evaporation balance. This also explains apparent inconsistencies between the lake δ18O records and other proxies of hydroclimatic change from the greater Pacific Northwest region that are less sensitive to cold season climate and thus indicate relatively drier conditions during the mid-Holocene. The abrupt negative excursion at ∼2400 yr BP in the Cleland Lake δ18O data, as well as the marked shift to more positive values after this time, demonstrate that gradual changes in ocean-atmosphere dynamics can produce abrupt, non-linear hydroclimate responses in the interior regions of western North America.