Holocene diatom flora and stratigraphy from sediment cores of two Antarctic lakes (King George Island)

The diatom stratigraphy of Holocene sediment cores from two Antarctic lakes (Mondsee, Tiefersee; 62° 10 S/58° 50 W) of King George Island was investigated. The diatom assemblages were dominated by cosmopolitan species. The flora was composed of three main components: 1) taxa of submersed bryophytic habitats, which also occur in the bryophilic diatom flora of southern South America; 2) species of various terrestrial habitats, including some specific subantarctic taxa; 3) species distributed in coastal inland waters influenced by sea-spray.Changes in sediment pattern and diatom species composition seemed to reflect climatic changes. At least three different core sections were distinguished in both lakes: Two sections rich in mosses occur between approx. 7000–4700 B.P. and from 3200 B.P. to present, in general resembling present day conditions. In between is a section of high allochthonous content with generally low diatom concentrations and rising percentages of aerophilic, halophilic and alkaliphilic diatoms. An increase of melt water discharge, possible sea-spray influence, and lake- level fluctuations are discussed.Three new taxa are described: Achnanthes metakryophila nov. spec., Achnanthes renei nov. spec., Navicula australomediocris nov. spec. The taxonomy of selected taxa is discussed.