Holocene climate dynamics in Latvia, eastern Baltic region: a pollen-based summer temperature reconstruction and regional comparison

A pollen-based summer temperature (T-summer) reconstruction reveals the Holocene climate history in southeastern Latvia and contributes to the limited understanding of past climate behaviour in the eastern sector of northern Europe. Notably, steady climate warming of the early Holocene was interrupted c. 8350-8150 cal. yr BP by the well-known 8.2 ka cold event, recorded as a decrease of 0.9 to 1.8 degrees C in T-summer. During the Holocene Thermal Maximum, c. 8000-4000 cal. yr BP, the reconstructed summer temperature was similar to 2.5-3.5 degrees C higher than the modern reconstructed value, and subsequently declined towards present-day values. Comparison of the current reconstruction with other pollen-based reconstructions in northern Europe shows that the 8.2 ka event is particularly clearly reflected in the Baltic region, possibly as a result of distinct climatic and ecological gradients and the sensitivity of the vegetation growth pattern to seasonal temperature change. The new reconstruction also reveals that the Holocene Thermal Maximum was warmer in Latvia than in central Europe and Fennoscandia. In fact, a gradient of increasing positive temperature anomalies is detected from northernmost Fennoscandia towards the south and from the Atlantic coast in Norway towards the continental East European Plain. The dynamics of the temperate broadleaved tree species Tilia and Quercus in Latvia and adjacent northern Europe during the mid-Holocene give complementary information on the multifaceted climatic and environmental changes in the region.