The paleoclimatology of Lake Baikal: A diatom synthesis and prospectus

Abstract The paleoclimatic archive held in Lake Baikal sediments is of significant importance, given the lake's position in one of the world's most continental regions where there are few continuous, high quality records spanning the Quaternary. Here I review diatom and associated biogenic silica records from Lake Baikal sediments and provide a paleoclimatic synthesis of changes at various timescales over the Quaternary. I initially highlight major climatic and hydrological aspects of Lake Baikal, as understanding the contemporary system (both regionally and within the lake) are fundamental to understanding past change interpreted from the sedimentary archive. In this respect, special attention is given to factors that can affect the integrity of the diatom record, most notably dissolution processes. These mechanisms are likely to have had a relatively greater impact on the preservation of diatom valves during glacial periods because of overall lower diatom productivity. Lower diatom numbers and relative increased dissolution during cold periods explains the lack of diatoms and low biogenic silica concentrations found in the lake sediments during glacial periods. The biogenic record highlights the nature of the 100 ka cycle especially during the last 800 ka, although there is also a strong precessional component. Further work is needed to reassess biological responses in Lake Baikal with respect to different orbital forcing mechanisms, together with their impacts on evolution and speciation of diatoms. The biological record from Lake Baikal confirms that the last interglacial in central Asia lasted approximately 10.5 ka. Productivity in the lake (as inferred from diatom biovolume accumulation rates) exhibits millennial-scale variability with the occurrence of centennial-scale reductions in diatom biomass throughout the last interglacial period. The most severe reduction in diatom biomass (at c. 120 ka BP) is concurrent with millennial-scale cooling in the North Atlantic region. Links to changes in North Atlantic ocean thermohaline circulation via teleconnections are also evident in the nature of the abrupt ecological changes in the lake throughout the last 60 ka, linked to ice-rafting into the North Atlantic, otherwise known as Heinrich events. New robust radiocarbon chronologies for sediments deposited during the late glacial and Holocene in Lake Baikal allow detailed, multi-decadal records to be constructed for the last 14,000 years. Cooling events associated with millennial-scale cycles are also apparent in the Lake Baikal record, and both the diatom record and oxygen isotope record of the diatom silica highlight that biological responses to these abrupt events are almost simultaneous. Comparisons made between Lake Baikal records with others worldwide highlights that many of the Holocene cooling events are associated with melt-water outburst from the Laurentide ice sheet, and changes in solar insolation. During the last 1000 years, snow cover on Lake Baikal has been inferred from past diatom assemblages, and is closely linked to weakening of the North Atlantic Oscillation, allowing increasing intensity of the Siberian High to develop and during the 17th and 18th centuries. In the last 150 years, diatom species have been shown to be sensitive indicators of recent warming. However, impacts from future global warming will be complex, and are likely to impact not only on the balance between endemic and cosmopolitan diatoms throughout the lake, but on the balance between siliceous and non-siliceous algae, and sources of primary productivity.