Rapid shifts in the Baltic Sea region climate, detected from the ancient coastal formations and number of other ecosystems – how likely it is to happen again and what are the consequences?

Estonia is located in the norther part of the Baltic Sea region characterized by land uplift and prograding coasts. On uplifting sedimentary coasts, a variety of coastal landforms can be found. Sometimes the partly buried or elevated coastal formations appear as extensive stripe-like patterns populating coastal plains up to 5–10 km inland. These ridge systems are mostly called beach ridge plains, strandplains and foredune plains. The ridge systems are offering a unique opportunity to examine the events over at least the last 7,000 years when the Baltic Sea mean water table has been consistently dropping and a steady shoreline advancement has been punctuated by rare extreme events. We have found that the signs of past storms are clearly reflected in the internal structure and size of the ancient ridges. It can be assumed that high ridge systems containing extensive seaward-dipping layers formed 3,500–3,000 years ago are reflecting period of extreme storms and high influence of maritime climate, while the following small, nearly unnoticeable ridges, formed 3,000-2,200 years ago are reflecting calm period, probably with more continental climate. The current study is focusing on this shift in climatic conditions and is trying to find shifts in different ecosystems during the same period.

In this study, GIS analyses based on LiDAR topography were carried out in the coastal ridge systems. Number of study areas with different exposure to the storms and different rates of land uplift were selected. Ridge system patterns from the age of 3500-2200 BP were analysed. The ages for this study were acquired from published luminescence and radiocarbon dating results. Additionally, land uplift rates were used to determine approximate age of the formations. These results were compared with other studies based on the literature analyses. These analyses included: ground penetrating radar studies; records of aeolian sand influx into the coastal peat bogs in Estonia and in Northern Europe; past climatic records of northern Europe; and number of studies related to other ecosystems.

We have found that during the period of increased storminess and more maritime climate, 3500-3000 years ago, an increased sand influx was reported into the coastal peatbogs. Moreover, number of ground penetrated radar studies along Estonian coast have detected several extensive erosional layers in the internal structure of coastal landforms. In contrast, during the following period, such markers are completely missing. Additionally, notable change has been found in wetland ecosystems where we can find rapid shift from fen phase to raised bog phase around 3000 years ago. All these results are indicating that, for some reason, the climate in our region changed rapidly from western cyclones dominated maritime climate to much calmer and dryer continental climate.

What where the reasons behind this climatic shift, how it might have influenced different ecosystems, how likely it might happen again as a result of global warming and how we need to take it into account in coastal management plans will be also discussed in this poster.