NOAA/WDS Paleoclimatology - Columbia Icefield 1,000 Year Decadal Tree-Ring Isotope, RH, and Temperature

Modelling of tree-ring d13C and d18O data from the Columbia Icefield area in the eastern Rocky Mountains of western Canada provides fuller understanding of climatic and hydrologic variability over the past 1000 yr in this region, based on reconstruction of changes in growth season atmospheric relative humidity (RHgrs), winter temperature (Twin) and the precipitation d18O-Twin relation. The Little Ice Age (~AD 1530s-1890s) is marked by low RHgrs and Twin and a d18O-Twin relation offset from that of the present, reflecting enhanced meridional circulation and persistent influence of Arctic air masses. Independent proxy hydrologic evidence suggests that snowmelt sustained relatively abundant streamflow at this time in rivers draining the eastern Rockies. In contrast, the early millennium was marked by higher RHgrs and Twin and a d18O-Twin relation like that of the 20th century, consistent with pervasive influence of Pacific air masses because of strong zonal circulation. Especially mild conditions prevailed during the "Medieval Climate Anomaly" ~AD 1100-1250, corresponding with evidence for reduced discharge in rivers draining the eastern Rockies and extensive hydrological drought in neighbouring western USA.

针对加拿大西部落基山脉东部哥伦比亚冰原区域的树轮δ¹³C与δ¹⁸O数据开展建模研究，并通过重建生长季大气相对湿度（growth season atmospheric relative humidity, RHgrs）、冬季气温（winter temperature, Twin）以及降水δ¹⁸O与冬季气温的相关关系的变化，可更为全面地解析该区域过去1000年以来的气候与水文变率。小冰期（Little Ice Age，约公元1530年—1890年）以偏低的生长季大气相对湿度、冬季气温，且降水δ¹⁸O与冬季气温的相关关系与现代存在偏移，反映出经向环流增强与北极气团的持续影响。独立代用水文证据表明，彼时落基山脉东部流域的河流中，融雪维持了相对充沛的径流量。与之形成鲜明对比的是，千年早期的特征为偏高的生长季大气相对湿度与冬季气温，且降水δ¹⁸O与冬季气温的相关关系与20世纪相似，这与纬向环流强劲时太平洋气团占据主导的情形一致。约公元1100年—1250年的“中世纪气候异常期（Medieval Climate Anomaly）”气候尤为温和湿润，这与落基山脉东部流域河流径流量减少、邻近美国西部出现大范围水文干旱的证据相吻合。