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

In order to understand the panarchy and interactions since the last interglacial period in the oldest, most diverse and hydrologically connected European lake system, we assess changes in the diatom record and selected geochemistry data from Lake Ohrid's "DEEP site" core and compare it with the diatom and multi-proxy data from Lake Prespa core Co1215. Driven by climate forcing, tephra impact and/or human influence, the lakes experienced two adaptive cycles during the last 92 ka: "interglacial and interstadial-regime" and "glacial-regime". The patterns of regime shifts appear synchronous in both lakes, while differences occur in the inferred amplitudes of the variations. The deeper Lake Ohrid shifted between ultraoligo- and oligotrophic regimes in contrast to the more shallow Lake Prespa, which shifts from (oligo-) mesotrophic to eutrophic conditions. In response to external forcing, Lake Ohrid exhibits a high capacity to buffer disturbances, whereas Lake Prespa is much more resilient and "recovers" in relatively short time. This decoupling of the response is evident during the MIS 5/4 and 2/1 transitions, when Lake Ohrid displays prolonged and gradual changes.

The lakes' specific differences in the response and feedback mechanisms and their different physical and chemical properties, probably confine a direct influence of Lake Prespa's shallow/eutrophic regimes over the productivity regimes of Lake Ohrid. Regime shifts of Lake Ohrid due to the hydrological connectivity with Lake Prespa are not evident in the data presented here. Moreover, complete ecological collapse did not happened in both lakes for the period presented in the study.