Abstract. Ancient lakes, like lakes Ohrid and Prespa on the Balkan Peninsula, have become model systems for studying the link between geological and biotic evolution. Recently the scientific deep drilling program "Scientific Collaboration on Past Speciation Conditions in Lake Ohrid" (SCOPSCO) has been launched to better understand the environmental, climatic and limnological evolution of the lake. It revealed that Lake Ohrid experienced a number of environmental disturbances during its ca. 2.0 million year long history. They comprise disturbances that lasted over longer periods of times ("press events") such as Heinrich events as well as sudden and short disturbances ("pulse events") like the deposition of volcanic ashes. The latter include one of the most severe volcanic episodes during the Late Pleistocene, the eruption of the Campanian Ignimbrite (known as Y-5 marine tephra layer) from the Campi Flegrei caldera, dated at 39.6 ± 0.1 ka ago. The event is recorded by the deposition of a ca. 15 cm thick Y-5 tephra layer in sediment cores of lakes Ohrid (DEEP-5045-1) and Prespa (Co1204). This pulse event is overlain by the Heinrich event 4 (H4), 40.0–38.0 ka ago. In the current paper, diatoms were used as proxies to compare the responses of these lakes to the Y-5 (pulse) and the H4 (press) disturbances. Based on stratigraphically constrained incremental sum of squares cluster (CONISS) and unconstrained Partitioning Around Medoids (PAM) analyses, we found only little evidence that the diatom community compositions in either lake responded to the H4 event. However, the Y-5 influx caused clear and rapid diatom community changes. After the initial response, community composition in Lake Ohrid and, to a lesser extent, in Lake Prespa slowly returned to their quasi pre-disturbance state. Moreover, there is no evidence for disturbance-related extinction events. The combined evidence from these findings suggests that lakes Ohrid and Prespa likely did not experience regime shifts. It is therefore concluded that both lakes show resilience to environmental disturbance. However, it seems that Lake Ohrid is more resilient than Lake Prespa as the recovery of diatom communities is more pronounced and as its estimated recovery time is only ca. 1400 years vs. ca. 3600 years in Lake Prespa. The reasons for the differential responses remain largely unknown, but differences in geology, lake age, limnology, and intrinsic parameters of the diatom proxies may play a role. Given the relative robust results obtained, this study provides important new insights into the response of lakes to (multiple) environmental disturbances. Moreover, it contributes to one of the major goals of the SCOPSCO project – to evaluate the influence of major geological events onto the evolution of endemic taxa in Lake Ohrid.
AMS Radiocarbon Dating of Holocene Tephra Layers on Ulleung Island, South Korea