French summer droughts since 1326 CE: a reconstruction based on tree ring cellulose δ18O
French summer droughts since 1326 CE: a reconstruction based on tree ring cellulose δ18O
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DOI：
10.5194/cp-12-1101-2016
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发表时间：
2016-01-01
影响因子：
4.3
通讯作者：
Masson-Delmotte, Valerie
中科院分区：
文献类型：
--
作者：
Labuhn, Inga;Daux, Valerie;Masson-Delmotte, Valerie
干旱的重建对于了解过去的干旱动态至关重要，并有助于在气候变化的情况下评估未来的干旱情景。本文根据每年确定的栎属树木年轮纤维素氧同位素比率（δ O-18）的绝对年代表，重建了法国夏季干旱。样本取自枫丹白露（北纬48度23分，东经2度40分，西元1326-2000年）和昂古莱姆（北纬45度44分，东经0度18分，西元1360-2004年）两个地点的活树和历史建筑的木材。这些地点的纤维素δ O-18被证明是夏季气候的一个很好的代表，因为树木对温度和水分有效性很敏感。然而，在将三个队列的平均δ O-18值加入最终年表之前，需要进行校正。利用校正后的δ O-18年表，建立了以标准化降水蒸散指数（SPEI）表示的线性回归模型来重建干旱。SPEI与纤维素δ O-18之间的显著相关性（r近似于-0.70）以及独立数据对模型的验证支持了这些重建的有效性。在这两个地点，最近几十年的特点是干旱加剧。枫丹白露在前几个世纪主要表现出湿润的条件，而目前的干旱强度在昂古莱姆记录中并非前所未有。两个研究地点的δ O-18年代学在19世纪和20世纪高度相关，但在1600 - 1800 CE之间相关系数显著降低，这表明树木年轮代用指标在这一时期的气候敏感性较弱，或者法国北部和南部的气候异质性更强。未来对树木年轮同位素网络的研究可能会揭示过去干旱的季节性和空间模式是否可以解释这种脱钩。基于这两个地点的区域干旱重建显示，与法国葡萄收获日期的历史记录非常吻合，这是夏季气候的另一个代表。
The reconstruction of droughts is essential for the understanding of past drought dynamics and can help evaluate future drought scenarios in a changing climate. This article presents a reconstruction of summer droughts in France based on annually resolved, absolutely dated chronologies of oxygen isotope ratios (delta O-18) in tree ring cellulose from Quercus spp. Samples were taken from living trees and timber wood from historic buildings at two sites: Fontainebleau (48 degrees 23'N, 2 degrees 40'E; 1326-2000 CE) and Angouleme (45 degrees 44'N, 0 degrees 18'E; 1360-2004 CE). Cellulose delta O-18 from these sites proved to be a good proxy of summer climate, as the trees were sensitive to temperature and moisture availability. However, offsets in average delta O-18 values between tree cohorts necessitated a correction before joining them to the final chronologies.Using the corrected delta O-18 chronologies, we developed models based on linear regression to reconstruct drought, expressed by the standardized precipitation evapotranspiration index (SPEI). The significant correlations between the SPEI and cellulose delta O-18 (r approximate to -0.70), as well as the verification of the models by independent data support the validity of these reconstructions. At both sites, recent decades are characterized by increasing drought. Fontainebleau displays dominantly wetter conditions during earlier centuries, whereas the current drought intensity is not unprecedented in the Angouleme record.While the delta O-18 chronologies at the two studied sites are highly correlated during the 19th and 20th centuries, there is a significant decrease in the correlation coefficient between 1600 and 1800 CE, which indicates either a weaker climate sensitivity of the tree ring proxies during this period, or a more heterogeneous climate in the north and the south of France. Future studies of tree ring isotope networks might reveal if the seasonality and spatial patterns of past droughts can explain this decoupling. A regional drought reconstruction based on a combination of the two sites shows good agreement with historical records of grape harvest dates in France, which provide another proxy of summer climate.