Search

The temporal variations in distribution pattern of Scots pines (Pinus sylvestris L.) have been used as an annual resolution record of past lake-level changes. Logs, preserved for thousands of years in bog and lakes (subfossil wood), were sampled from small lakes of the Scandinavian Mountains in west-central Sweden to construct a tree-ring chronology from an area where pines are sensitive to growth season (ie, summer) temperature. The chronology spans from AD 2006 to 4868 BC, with two minor gaps at 1600 BC and AD 900 and one larger gap at 2900 BC. The dendrochronological approach can provide a high quality long-term perspective on lake level fluctuations, which possibly can be coupled to changes in humidity. Submerged trunks were found in situ, embedded in sediments, and because trees from the earliest periods were not necessarily found at the deepest levels, this shows clearly that lake levels must have been lower than present at the time of tree-growth. The lake levels must have fluctuated, creating alternating conditions of pine regeneration and mortality. The fluctuating lake levels recorded are suggested to be a result of regional humidity increases and decreases, mainly governed by precipitation changes. Periods of lower lake levels were inferred at 4900-4800 BC, 3800-3600 BC, 3400-3250 BC, 2400-2200 BC, 2100-1800 BC, 1500-1100 BC, 900-800 BC, 400-100 BC, AD 50-300, AD 400-600, AD 900-1100, AD 1350-1500 and AD 1700-1800. Periods of higher lake levels are tentatively encountered at 3600-3400 BC, 3200-2900 BC, 2200-2100 BC, 1700-1500 BC, 1100-900 BC, 800-400 BC, 100 BC-AD 50, AD 300-400, AD 750-900, AD 1100-1250 and AD 1550-1700. [ABSTRACT FROM AUTHOR]

Maximum latewood density (MXD) chronologies have been widely used to reconstruct summer temperature variations. Precipitation signals inferred from MXD data are, however, rather scarce. In this study, we assess the potential of using MXD data derived from Scots pine (Pinus sylvestris L.) growing in the Stockholm archipelago (Sweden) to reconstruct past precipitation variability. In this area, slow-growing pine trees emerge on flat plateaus of bedrock outcrops with thin or absent soil layers and are, therefore, sensitive to moisture variability. A 268-year-long MXD chronology was produced, and climate–growth relationships show a significant and robust correlation with May–July precipitation (PMJJr = 0.64, p < 0.01). The MXD based May–July precipitation reconstruction covers the period 1750–2018 CE and explains 41% of the variance (r2) of the observed precipitation (1985–2018). The reconstruction suggests that the region has experienced more pluvial phases than drought conditions since the 1750s. The latter half of the 18th century was the wettest and the first half of the 19th century the driest. Climate analysis of "light rings" (LR), latewood layers of extreme low-density cells, finds their occurrence often coincides with significantly dry (<41 mm precipitation) and warmer (1–2 °C above average temperature), May–July conditions. Our analysis suggests that these extremes may be triggered by the summer North Atlantic Oscillation (SNAO). [ABSTRACT FROM AUTHOR]