Holocene carbon dynamics at the forest-steppe ecotone of southern Siberia

摘要

The forest–steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to\udpush the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a dee-\udper understanding of long-term forest–steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimno-\udlogical approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to\udunderstanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m\ud2\udyr\ud1\ud) and isotope com-\udposition of organic matter (d\ud13\udC\udTOC\ud). Forest–steppe dynamics were reconstructed using pollen, and diatom records\udprovided measures of primary production from near- and off-shore communities. We used a generalized additive\udmodel (GAM) to identify significant change points in temporal series, and by applying generalized linear least-\udsquares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon\uddynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to\udabrupt sub-Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR\udvalues range between 2.8 and 12.5 g C m\ud2\udyr\ud1\ud. Peak burial rates (and greatest variability) occurred during the early\udHolocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the\udneoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr\udBP provide compelling evidence for the sensi-\udtivity of the region to sub-Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake\udBaikal sediments during the Holocene, almost one-quarter of which was buried during the early Holocene alone.\udCombined, our results highlight the importance of understanding the close linkages between carbon cycling and\udhydrological processes, not just temperatures, in southern Siberian environments.