Ecosystem regimes and responses in a coupled ancient lake system from MIS 5b to present: the diatom record of lakes Ohrid and Prespa

Abstract

Abstract. We reconstruct the aquatic ecosystem interactions since the last interglacial period in the oldest, most diverse, hydrologically connected European lake system, by using palaeolimnological diatom and selected geochemistry data from Lake Ohrid “DEEP site” core and equivalent data from Lake Prespa core, Co1215. Driven by climate forcing, the lakes experienced two adaptive cycles during the last 92 ka: "interglacial and interstadial" and "glacial" cycle. The short-term ecosystems reorganizations, e.g. regime shifts within these cycles substantially differ between the lakes, as evident from the inferred amplitudes of variation. The deeper Lake Ohrid shifted between ultra oligo- and oligotrophic regimes in contrast to the much shallower Lake Prespa, which shifted from a deeper, (oligo-) mesotrophic to a shallower, eutrophic lake and vice versa. Due to the high level of ecosystem stability (e.g. trophic state, lake level), Lake Ohrid appears relatively resistant to external forcing, such as climate and environmental change. Recovering in a relatively short time from major climate change, Lake Prespa is a resilient ecosystem. At the DEEP site, the decoupling between the lakes' response to climate change is marked in the prolonged and gradual changes during the MIS 5/4 and 2/1 transitions. These response differences and the lakes' different physical and chemical properties may limit the influence of Lake Prespa on Lake Ohrid. Regime shifts of Lake Ohrid due to potential hydrological change in Lake Prespa are not evident in the data presented here. Moreover, a complete collapse of the ecosystems functionality and loss of their diatom communities did not happen in either lake for the period presented in the study.

Site M0079

“…NA = not applicable/not known. Diatom preferences are according to the information available online at http://www.algaebase.org, http://www.marinespecies.org, and https://westerndiatoms.colorado.edu and from Krammer andLange-Bertalot (1991), Van Dam et al, (1994), Houk et al (2010), Reed et al (2010), and Cvetkoska et al (2012Cvetkoska et al ( , 2016…”

Site M0078

“…NA = not applicable/not known. Diatom preferences are according to the information available at and fromKrammer and Lange-Bertalot (1991),Van Dam et al (1994),Houk et al (2010),Reed et al (2010), andCvetkoska et al (2012Cvetkoska et al ( , 2016.…”

Reply letter

“…High-resolution studies of diatoms in both lake sediment records indicate little evidence for a response of the diatom community related to the H4 event, but they do show a clear and rapid change following tephra deposition . This strong change is likely due to fertilisation and the availability of nutrients, particularly silica, such as it was shown in laboratory studies and leaching experiments of tephra with Lake Ohrid water (D'Addabbo et al, 2015). After the initial response, diatom community compositions in lakes Ohrid and Prespa returned to their quasi pre-disturbance state.…”