Co-evolution of terrestrial and aquatic ecosystem structure with hydrological change in the Holocene Baltic Sea

Abstract. The Baltic Sea experienced a number of marine transgressions and regressions throughout the Holocene. These fluctuations in sea level coupled with substantial regional ice melt led to isostatic adjustment and periodic isolation from the North Sea. Here, we determine the distributions and isotopic signatures of organic compounds preserved in a sediment record spanning the last ~ 11 ka in order to reconstruct environmental change under these dynamic conditions. Carbon and hydrogen isotope ratios of short-, mid-, and long-chain n-alkanes along with long-chain diol and glycerol dialkyl glycerol tetraether abundances were analyzed from Arkona Basin sediments sampled from the western Baltic Sea. In the earliest part of the record (10–8.2 ka), hydrogen isotope values of higher plant-derived n-alkanes revealed a change in dominant water source from an ice melt-derived to a precipitation-dominated hydrological regime. Following this shift in water source, carbon isotope values of n-alkanes suggest diversification of vegetation. Shifts in hydrology and vegetation did not coincide with established phase boundaries, but instead occurred mid-phase or spanned phase transitions, highlighting the fact that proxies may record changes on different time scales and suggesting that climate in the region was dynamic throughout the Holocene.