A multi-proxy paleolimnological reconstruction of Holocene climate conditions in the Great Basin, United States

A sediment core spanning  7000 cal yr BP recovered from Stella Lake, a small sub-alpine lake located in Great Basin National Park, Nevada, was analyzed for subfossil chironomids (non-biting midges), diatoms, and organic content (estimated by loss-on-ignition (LOI)). Subfossil chironomid analysis indicates that Stella Lake was characterized by a warm, middle Holocene, followed by a cool “Neoglacial” period, with the last two millennia characterized by a return to warmer conditions. Throughout the majority of the core the Stella Lake diatom-community composition is dominated by small, periphytic taxa which are suggestive of shallow, cool, alkaline, oligotrophic waters with extensive seasonal ice cover. A reconstruction of mean July air temperature (MJAT) was developed by applying a midge-based inference model for MJAT (two-component WA-PLS) consisting of 79 lakes and 54 midge taxa (r_jack² = 0.55, RMSEP = 0.9°C). Comparison of the chironomid-inferred temperature record to existing regional paleoclimate reconstructions suggests that the midge-inferred temperatures correspond well to regional patterns. This multi-proxy record provides valuable insight into regional Holocene climate and environmental conditions by providing a quantitative reconstruction of peak Holocene warmth and aquatic ecosystem response to these changes in the Great Basin, a region projected to experience increased aridity and higher temperatures.     

中世纪气候异常期和小冰期中国华北与北美西南部年代际干湿变化的关系

百年尺度冷、暖背景下不同区域年代际干湿变化的关系是历史气候变化领域的重大问题之一。本研究利用基于历史文献重建的中国华北干湿指数(Dry-wet index)和基于树轮年表重建的北美西南部帕默尔干旱指数(PDSI), 采用100年窗口的滑动相关分析, 计算了两地年代际干湿变化的相关关系, 对比了中世纪气候异常期(MCA)和小冰期(LIA)两地相关关系的差异, 并利用PMIP3和PMIP4共11个模式的过去千年气候变化模拟数据, 诊断了其成因。研究发现: 1)代用资料展示出MCA期间中国华北与北美西南部年代际干湿变化为正相关(r=0.32, p < 0.05), LIA期间则为负相关(r=-0.27, p < 0.05); 2)GISS-E2-R模式基本再现了代用资料揭示的工业革命前两地干湿变化相关关系的变化特征, 尤其是MCA和LIA的差异; 3)MCA期间, 中国华北与北美西南部年代际干湿变化正相关主要是因两地水汽条件同时匮乏所致, 这可能是源于负位相太平洋-北美(PNA)遥相关的影响; LIA期间, 中国华北与北美西南部年代际干湿变化负相关主要是因中国华北水汽匮乏, 而北美西南部水汽充沛所致, 这可能是源于负位相北太平洋涛动(NPO)遥相关的影响。上述结果为深入辨识百年尺度冷、暖背景下中国华北与北美西南部年代际干湿变化之间的关系提供了新证据, 为预估未来全球升温情景下中国或北美年代际干湿特征提供预警信号。

     

大兴安岭北部满归泥炭孢粉重建的过去2100年古气候

大兴安岭地处季风气候的尾闾区,是一个研究全球变化的关键区域。但由于该地区古气候代用指标（树轮、孢粉、石笋等）获取比较困难,历史文献也缺乏,使得古气候研究受到了限制。本研究通过大兴安岭北部的漠河县满归镇附近一个厚88 cm的泥炭剖面的孢粉记录,根据831个表土样品的花粉数据和附近90个气象台站30年的地面观测数据,运用现代类比法（Modern Analogue Technique,简称MAT）重建了该地区过去2100年的年均温（T_ann）、年降水量（P_ann）、1月均温（T_jan）和7月均温（T_july）,结果表明T_ann和T_jan的波动达到2.4℃,T_july的波动为1.7℃,P_ann波动为28.2 mm。该地区的气候变化分为3个阶段：阶段Ⅰ（150 BC~850 A.D.）温度和降水量相对较低,年均温比现代30年均值低约0.5℃;阶段Ⅱ（850~1300 A.D.）以温度升高-降低的波动为特征,升温在1070~1170 A.D.期间最明显,年均温比现代30年平均值高0.2℃,这一时期相当于欧洲中世纪气候异常期（the Medieval Climate Anomaly,简称MCA）;阶段Ⅲ（1300~2000 A.D.）早期（1300~1900 A.D.）以气温较低为特征,这一时期相当于小冰期（the Little Ice Age,简称LIA）,年均温比现代30年平均值低0.8℃,晚期（1900~2000 A.D.）呈现升温的趋势。

     

Decadal-scale autumn temperature reconstruction back to AD 1580 inferred from the varved sediments of Lake Silvaplana (southeastern Swiss Alps)

A quantitative high-resolution autumn (September-November) temperature reconstruction for the southeastern Swiss Alps back to AD 1580 is presented here. We used the annually resolved biogenic silica (diatoms) flux derived from the accurately dated and annually sampled sediments of Lake Silvaplana (46°27′N, 9°48′E, 1800 m a.s.l.). The biogenic silica flux smoothed by means of a 9-yr running mean was calibrated (r = 0.70, p < 0.01) against local instrumental temperature data (AD 1864-1949). The resulting reconstruction (± 2 standard errors = ± 0.7 °C) indicates that autumns during the late Little Ice Age were generally cooler than they were during the 20th century. During the cold anomaly around AD 1600 and during the Maunder Minimum, however, the reconstructed autumn temperatures did not experience strong negative departures from the 20th-century mean. The warmest autumns prior to 1900 occurred around AD 1770 and 1820 (0.75 °C above the 20th-century mean). Our data agree closely with two other autumn temperature reconstructions for the Alps and for Europe that are based on documentary evidence and are completely unrelated to our data, revealing a very consistent picture over the centuries.