The diatom stratigraphy and palaeoecology of lake Ohrid, Yugoslavia

Abstract

An 8.85 m core (No. 9) was taken from Lake Ohrid, Yugoslavia, in August 1973 at a depth of 210 m, approximately 6 km offshore of Gorcia, Yugoslavia. The core was sampled at 10-cm intervals and analyzed for moisture, organic and CaCO 3 content, and diatoms. There is a slight but steady decrease of moisture with depth, probably due to sediment compaction. The organic content showed little variation throughout the core ( x ̄ = 2.73 ± 0.39% of total weight). The CaCO 3 content from 885−110 cm depth also showed little change ( x ̄ = 2.32 ± 0.55% of total weight) but increased in the top meter of the core (100−0 cm, x ̄ = 11.03 ± 8.86% of total weight). Throughout the core there is an inverse relationship between organic and CaCO 3 content, particularly in the top meter. Extrapolation to the bottom of the core using linear regression based on 14C-dating yields a date of ca. 30,000 years B.P. Results indicate that Lake Ohrid has remained an oligotrophic lake throughout the period represented by Core 9. Diatom analysis shows one persistent group of diatoms throughout the core. This group consists of Cyclotella fottii, C. hustedtii, and C. hustedtii var.1 and is referred to as the Cyclotella complex. Between 885−650 cm (ca. 30,000−20,000 yr B.P.) there is a sharp increase in numbers and a slight increase in diversity of species. This may correspond with the beginning of the warmer, more humid middle Pleniglacial. Between 650−100 cm (ca. 20,000−10,000 yr B.P.) the Cyclotella complex appears usually alone in small number. There are a few other scattered species in this section, mainly Opephora martyi and Fragilaria pinnata. This section of the core probably corresponds with the cold upper Pleniglacial of the Würm (Weichselian). Between 100−0 cm (ca. 10,000−0 yr B.P.) there is the largest increase in number and diversity of species, particularly above 60 cm. The Cyclotella complex, C. ocellata, Cyclotella sp.1, Stephanodiscus astraea var. intermedia fo.11 and Stephanodiscus sp.1 are dominant. This is the only section of the core in which Stephanodiscus species occur, and probably corresponds with the Holocene.