NOAA/WDS Paleoclimatology - Scoop Lake, South Greenland 3000 Year Chironomid d18O and Temperature

Recent work has documented glacier advances in West Greenland coincident with the Medieval Climate Anomaly (MCA) and warmth across much of northern Europe. The North Atlantic Oscillation (NAO) has been invoked to explain antiphasing of temperatures between these North Atlantic regions. Historical and model observations suggest negative correlation between the mode of NAO and both temperature and d18O values of precipitation over much of Greenland. We test for a hypothesized positive NAO mode and associated cool conditions during the MCA in South Greenland within the Norse Eastern Settlement by reconstructing d18O values of precipitation at subcentennial resolution over the past 3000 yr using aquatic insect subfossils preserved in lake sediments. More positive d18O values are found between 900 and 1400 CE, indicating a period of warmth in South Greenland superimposed on late Holocene insolation-forced Neoglacial cooling, and thus not supporting a positive NAO anomaly during the MCA. Highly variable d18O values record an unstable climate at the end of the MCA, preceding Norse abandonment of Greenland. The spatial pattern of paleoclimate in this region supports proposals that North Atlantic subpolar ocean currents modulated South Greenland's climate over the past 3000 yr, particularly during the MCA. Terrestrial climate in the Labrador Sea and Baffin Bay regions may be spatially heterogeneous on centennial time scales due in part to the influence of the subpolar gyre.

近期研究已证实，格陵兰岛西部的冰川推进与中世纪气候异常期（Medieval Climate Anomaly, MCA）及北欧大部分地区的暖期同步发生。北大西洋涛动（North Atlantic Oscillation, NAO）被用以解释这些北大西洋区域间的温度反相变化。历史观测与模式模拟结果显示，在格陵兰岛大部分区域，北大西洋涛动模态与气温及降水的δ¹⁸O值均呈负相关。本研究通过利用湖相沉积物中保存的水生昆虫亚化石，重建过去3000年以来的降水δ¹⁸O记录（分辨率达亚百年尺度），以此检验中世纪气候异常期格陵兰岛南部北欧人东定居点区域存在正相位北大西洋涛动模态及伴随冷态的假说。公元900至1400年间的δ¹⁸O值整体偏高，表明格陵兰岛南部存在一段叠加于晚全新世太阳辐射驱动的新冰期降温背景之上的暖期，因此不支持中世纪气候异常期存在正相位北大西洋涛动异常的结论。δ¹⁸O值的剧烈波动记录了中世纪气候异常期末期的气候不稳定状态，该时期早于北欧人放弃格陵兰岛的时间。该区域的古气候空间分布格局支持下述假说：过去3000年以来，北大西洋亚极洋流调控了格陵兰岛南部的气候，其中在中世纪气候异常期这一特征尤为显著。拉布拉多海与巴芬湾区域的陆地气候在百年尺度上可能存在空间异质性，这在一定程度上受亚极环流的影响。