Paleoecological evidence of climate change and historical patterns of planktonic diatom diversity inferred from the Lake Baikal (Russia) sediment record.

Abstract

Two short sediment cores and a 100-m long sediment core from Lake Baikal, Russia, were analyzed for changes in siliceous microfossil composition and abundance that reflected the history of mid-Asian climate change during the last 500,000 years. Absolute abundance of microfossils varied from levels with no preserved remains to Holocene sediments with $>$300 $\times$ 10$\sp6$ microfossils per g dry sediment. A short-term climate shift (Little Ice Age, ca. 1630's-1830's A.D.) was evident in a core from Baikal's northern basin by increased relative abundance of endemic Cyclotella spp. that would be expected with longer ice cover. A core from Baikal's southern basin preserved signals of human-induced changes in Lake Baikal as increases in productivity following settlement in the Baikal basin and the proliferation of non-indigenous plankton species. Longer-term climate patterns of glacial and interglacial climate cycling were evident in patterns of low and high deposition of siliceous microfossils, respectively. Peaks in absolute microfossil abundance were inferred to represent greater plankton productivity during known interglacial and interstadial periods. Correspondence analysis of absolute abundance of dominant siliceous microfossils and core depths resolved four major microfossil-age zones in sediments covering the last 200,000 years. Microfossil zones were partially alignable with mid-Siberian highland glaciations, but better aligned with the $\sp{18}$O marine isotope record, an independent model of global paleoclimate change. Close correspondence of microfossils with the $\sp{18}$O marine isotope record suggests that microfossils are a useful paleoclimate indicator in Lake Baikal. Planktonic diatom diversity has remained low in Lake Baikal during the last 500,000 years. Most species have been endemic and persisted for two or more glacial/interglacial climate cycles. Species richness during interglacial and interstadial periods has varied between six and 21 species, suggesting that few planktonic niches exist in the pelagic zone of ancient lakes. One planktonic diatom has persisted in Lake Baikal for the last 500,000 years. Specimens from modern plankton collections were studied with light and scanning electron microscopy; morphological, ecological, and life history differences warranted the description of Aulacoseira skvortzowii as a new endemic species.