Paleoenvironmental Interpretation of Events Leading to Declines in Planktonic Diatoms in the Late Pliocene and Pleistocene Record from Lake El’gygytgyn, Far East Russian Arctic

Abstract:

The Lake El’gygytgyn sediment core (ICDP 5011-1) contains a near-continuous record of diatoms extending to approximately 3.46 Ma, providing a means to evaluate past climate-related lake system changes in this unique terrestrial Arctic paleoclimate archive. Systematic down-core diatom counts at an average 4-kyr resolution and SEM observations of dominant planktonic taxa from selected intervals are presented here for the first time. During the Pleistocene, the record is characterized by repeated declines in plankton abundance coinciding with a shift in dominant planktonic genus or species. These events correspond to cold intervals inferred from other proxies, implying a mechanism such as severe ice and snow conditions on the lake leading to an extended decline in the plankton. In contrast, during the Pliocene portion of the record, although similar or longer declines in the plankton abundance occur, the plankton has a more stable character, dominated by previously undescribed species of the genus Pliocaenicus. The most significant change occurs after a plankton decline with sustained periphytic diatoms from approximately 2.93-2.80 Ma, when a species with a rimoportula and distinct alveolae is replaced by a species with relatively flat valves with such structures absent or too insignificant to observe in SEM. This zone does not correspond to a particular cold event, as identified by other proxy records, but corresponds to a consistent warm interval with low insolation variability. Thus, diatoms and diatom-related proxies may be recording different lake-system responses to climate during different portions of the lake’s history. Higher resolution analyses of these events will help to characterize the lake system changes occurring during climate events unfavorable for planktonic diatoms.