Non-pollen palynomorphs as indicators of palaeoenvironmental changes: a case study from Lake Chokrak (the Crimean Peninsula)

Abstract

The paper presents the first study of the non-pollen palynomorphs assemblages of the upper Holocene sediments of hypersaline Lake Chokrak. As has been previously shown, the Crimean saline lakes tend to have low variety and frequencies of non-pollen palynomorphs (Mudie et al., 2011). The upper samples from Lake Chokrak have yielded high pollen frequencies, as well as a relatively diverse assemblage of NPPs, including acritarchs, dinoflagellate cysts, microforaminiferal linings, fungal spores, eggs of Artemia salina, ostracod jaws and arthropod parts. Acritarchs are represented mostly by Sigmopollis sp., which are abundant in all the studied samples, and by occasional Micrhystridium sp. and Pseudoschizaea circula. Among the fungal spores, Podospora, Delitschia and Sporormiella have been identified, indicating a former settlement. Three species of dinoflagellate cysts have been identified, Lingulodinium machaerophorum, Impagidinium caspiense and Spiniferites cf. crusiformis. These species are found in brackish/marine environments and do not tolerate high water salinity. They could have been transported to the lake by overflowing marine waters over the sand barrier between the lake and the Sea of Azov. Therefore, their appearance in the lake sediments may indicate possible sea-level changes and/or increased wave activity. So far, within the analysed top 2 m of the core, we can distinguish five intervals where dinocysts and microforaminiferal linings are present, possibly indicating increased marine influence,separated by four intervals where few or no brackish species have been found. Impagidinium caspiense is a dominant species among the dinocysts in all the samples, except the surface sample, where L. machaerophorum is much more abundant. This could indicate the increased salinity and/or higher nutrient loading to the Sea of Azov during the XX century. The allochthonous nature of dinocysts and some other NPPs in the Lake Chokrak sediments can play an important role in reconstructing level changes of the Sea of Azov and depositional environment of the lake, as well as contribute to the interpretation of pollen data.