Lake-level changes in the Late Weichselian Lake Tovelde, Mon, Denmark: induced by changes in climate and base level

The lacustrine Tovelde basin is a key locality for the study of Late Weichs elian sedimentological, geochemical and climatic development in Denmark. It is situated on the south coast of the island of Mon 2.5-7.5 ra above prese nt day sea-level. The sediment record covers a time span from about 14,700 to 9000 cal yr BP and starts with resedimented till. Onset of climate ameli oration and environmental stability is reflected by onset of lacustrine dep osition of increasingly more organic-rich deposits at 14,300 cal yr BP foll owing the deglaciation of the Young Baltic readvance. The lacustrine succession was deposited during overall lake-level rise inte rrupted by four short-lived falls. During Younger Dryas time, Greenland sta dial-1 (event zone GS-1) lake-level rise resulted in the merging of several smaller lakes into one large lake. The early part of the Younger Dryas was characterized by a cold and dry climate and low precipitation, that did no t favour the melting of stagnant or active ice. The marked Younger Dryas la ke-level rise was probably driven by a rise in base- and ground-water level in the Baltic Basin caused by damming of the Baltic Ice Lake. This was fol lowed by a significant water level rise in the southern Baltic basin during which the Faxe Bugt transgression occurred at around 10,600 C-14 yr BP. The expanded Younger Dryas Lake Tovelde came to an end around 10,000 C-14 y r BP at the transition into the early Preboreal when the Baltic Ice Lake un derwent a catastrophic tapping, event. A renewed lake level rise took place after 9600 C-14 yr BP in Preboreal time and continued into the Boreal when a drastic lowering of Lake Tovelde level took place. The resulting forced regression transformed the large lake into smaller lakes and a marker horiz on with macrophyte debris, gastropods, bivalves and small vertebrates was f ormed by redeposition of lake-margin sediments. The lacustrine deposits of Lake Tovelde contains abundant Late Glacial fres hwater and terrestrial microvertebrates and molluscs. The low water levels in the Lake Tovelde and in the Baltic Basin were contemporaneous resulting in the formation of land bridges between Sweden, Germany and Denmark, inclu ding the island of Bornholm. Such land bridges were established on three oc casions allowing immigration of terrestrial microvertebrates to Denmark fro m the east and partly from the south as reflected in species composition, d ensity and diversity in the Tovelde succession. Sedimentological, geochemic al and palaeoecological data show that Lake Tovelde underwent significant f luctuations. Some of which can be directly linked to climate changes. Some rises correlate, however, with damming of the Baltic Basin caused by isosta tic uplift of barriers. High-resolution stratigraphy may thus allow distinc tion between lake-level changes caused by climate fluctuations and base-lev el changes which are ultimately related to isostasy. (C) 2001 Elsevier Scie nce B.V. All rights reserved.