NOAA/WDS Paleoclimatology - Melvin - Yanworth - QUSP - ITRDB BRIT060

We present a millennial long dendroclimatic reconstruction of spring/summer precipitation for southern-central England. Previous research identified a significant moisture stress signal in ring-width data measured from oak trees growing in southern England. In this study, we build upon this earlier work, specifically targeting south-central England, to derive a well replicated oak ring-width composite chronology using both living and historical material. The data-set includes 352 living trees (AD 1629-2009) and 1540 individual historical series (AD 663-1925). The period expressed by at least 50 trees in any year is AD 980-2009. Calibration experiments identify the optimal seasonal predictand target as March-July precipitation (1901-2007: r2 = 0.33). However, comparison with the long Kew Gardens precipitation record indicates a weakening in tree-growth/climate response from ~1800 to 1920 which we speculate may be related to smoke and sulphur dioxide (SO2) emissions at that time which may have also contributed to a decrease in tree productivity. The time-series derived using the regional curve standardisation method to capture lower frequency information shows a mediaeval period with alternating multi-decade-long dry and wet periods, with AD 1153-1172 being the wettest reconstructed 20-year period in the whole record. Drier conditions are prevalent from ~1300 to the early sixteenth century followed by a period of increasing precipitation levels. The most recent four centuries of the record appear similar to the mediaeval period with multiple decade-long dry and wet periods. The late twentieth century is the second reconstructed wettest period. These centennial hydroclimatic trends are in broad agreement with independent regional scale hydroclimatic reconstructions from tree-ring (East Anglia), historical, speleothem and peat water level proxy archives in the United Kingdom and appear coupled with reconstructed sea surface temperature changes in the North Atlantic which in turn influence the Atlantic meridional overturning circulation and westerly airflow across the UK.

本研究构建了英格兰中南部地区春季/夏季降水的千年尺度树木气候重建（dendroclimatic reconstruction）序列。既往研究已从英格兰南部生长的栎树年轮宽度数据中，识别出显著的水分胁迫信号。本研究在此前工作基础上，以英格兰中南部为研究区域，利用活体栎树与历史标本两种材料，构建了复现性良好的栎树年轮宽度合成年表。本数据集包含352株活体栎树样本（公元1629年-2009年）以及1540条独立历史年轮序列（公元663年-1925年）。任意年份至少有50株树提供有效数据的时段为公元980年至2009年。校准实验表明，最优季节预报量为3月至7月降水量（1901年-2007年，决定系数r²=0.33）。然而，与长期英国皇家邱园降水记录对比发现，约1800年至1920年间树木生长与气候的响应关系出现弱化；我们推测这可能与当时的烟尘与二氧化硫（SO₂）排放有关，此类排放或同时导致树木生产力下降。本研究采用区域曲线标准化（regional curve standardisation）方法以捕捉低频气候信号，所得时间序列显示，中世纪时期存在交替出现的数十年尺度干湿周期，其中公元1153年-1172年为整条重建序列中最湿润的20年时段。约公元1300年至16世纪初期以偏干气候为主，随后降水量逐步回升。近四个世纪的记录特征与中世纪时期相似，同样存在多组数十年尺度的干湿周期。20世纪后期为序列重建结果中第二湿润的时段。这些百年尺度水文气候趋势，与英国东安格利亚地区的树木年轮、历史记录、石笋（speleothem）以及泥炭水位代用指标等独立区域尺度水文气候重建结果基本一致；同时该序列与北大西洋海表面温度重建变化存在耦合关系，而北大西洋海温变化又可通过影响大西洋经向翻转环流（Atlantic meridional overturning circulation）与横跨英国的西风气流（westerly airflow），进而调控区域气候。