Nonlinear response of summer temperature to Holocene insolation forcing in Alaska
Nonlinear response of summer temperature to Holocene insolation forcing in Alaska
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DOI：
10.1073/pnas.1110913108
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发表时间：
2011-11-29
影响因子：
11.1
通讯作者：
Hu, Feng Sheng
中科院分区：
文献类型：
--
作者：
Clegg, Benjamin F.;Kelly, Ryan;Hu, Feng Sheng
由于地球系统各组成部分之间复杂的相互作用，区域气候对太阳辐射岁差变化和人为温室气体增加等大尺度强迫的响应可能是非线性的。这种非线性行为构成了气候“惊喜”的主要来源，具有重要的社会经济和生态影响。古记录是阐明辐射强迫的非线性响应模式和机制的关键，但它们的实用性已大大限制了定量温度重建的缺乏。在这里，我们提出了全新世7月温度重建的基础上，从阿拉斯加三个湖泊的沉积物岩芯的吸浆虫分析。结果表明，在10，000 - 5，500校准年（cal）B. P.的夏季温度普遍低于现代，夏季温度峰值在5，000左右，之后是一个下降的趋势。这些模式与岁差日射的趋势形成鲜明对比，岁差日射从1万年前到现在减少了10%。5，500大卡B. P.之前的凉爽夏季与北冰洋西部夏季大面积冰盖、北极涛动正相的持续性、主要是拉尼娜现象以及阿拉斯加树线位置的变化相一致。这些结果说明夏季气温的非线性响应全新世日射辐射强迫在阿拉斯加亚北极，可能是因为在北极涛动和厄尔尼诺南方涛动和相关的陆地-大气-海洋反馈的状态变化。
Regional climate responses to large-scale forcings, such as precessional changes in solar irradiation and increases in anthropogenic greenhouse gases, may be nonlinear as a result of complex interactions among earth system components. Such nonlinear behaviors constitute a major source of climate "surprises" with important socioeconomic and ecological implications. Paleorecords are key for elucidating patterns and mechanisms of nonlinear responses to radiative forcing, but their utility has been greatly limited by the paucity of quantitative temperature reconstructions. Here we present Holocene July temperature reconstructions on the basis of midge analysis of sediment cores from three Alaskan lakes. Results show that summer temperatures during 10,0005,500 calibrated years (cal) B.P. were generally lower than modern and that peak summer temperatures around 5,000 were followed by a decreasing trend toward the present. These patterns stand in stark contrast with the trend of precessional insolation, which decreased by similar to 10% from 10,000 y ago to the present. Cool summers before 5,500 cal B.P. coincided with extensive summer ice cover in the western Arctic Ocean, persistence of a positive phase of the Arctic Oscillation, predominantly La Nina-like conditions, and variation in the position of the Alaskan treeline. These results illustrate nonlinear responses of summer temperatures to Holocene insolation radiative forcing in the Alaskan sub-Arctic, possibly because of state changes in the Arctic Oscillation and El Nino-Southern Oscillation and associated land-atmosphere-ocean feedbacks.