Glacial/Interglacial Changes in the Carbon Cycle of Lake Baikal

Abstract

This chapter presents a conceptual framework for understanding the impact of glacial/ interglacial climate changes on the carbon cycle of Lake Baikal. To do so, we bring together evidence from mass-balance estimates, from the carbon and nitrogen compositions of plankton, particulate organic matter and the surface layer of bottom sediments, and watershed soils and riverine sediments, as well as from Lake Baikal organic sedimentary records of the last glacial/ interglacial transition and of the last climatic cycle to 130Ka BP. The goal of this synthesis is to offer new ways of examining organic carbon paleoproductivity records. Autochthonous primary production is the dominant source of organic matter (OM) in Lake Baikal sediments. The OM composition in pelagic sediments of Lake Baikal lies within the range of the primary produced particulate organic matter which sinks beyond the trophogenic layer. At the same time, the replenishment of the dissolved carbon pool of Lake Baikal is largely dependent on the input of terrigenous organic matter, which is assimilated and actively recycled in the lake. Therefore, allochthonous input does contribute to the observed present-day rate of carbon burial in Lake Baikal. However, by itself, terrigenous OM does not appear to constitute a major portion of OM in sediments, as suggested by mass-balance estimates and by a comparison of the C/N and δ13C ratios of various carbon sources with those of Lake Baikal bottom sediments. The sedimentary total organic carbon content and the δ13C and C/N ratios indicate that past glacial/interglacial changes in OM accumulation were basin-wide, and mostly reflect internal changes in the lake's carbon cycle driven by the regional climate. These changes included the varying efficiency of carbon export from the photic zone, and dramatic fluctuations in the carbon pool of the lake, as reflected in the carbon isotope records during the last deglaciation.