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

Anson William Mackay; Alistair W R Seddon; Melanie J Leng; Georg Heumann; David W Morley; Natalia Piotrowska; Patrick Rioual; Sarah Roberts; George E A Swann

doi:10.1111/gcb.13583

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

Glob Chang Biol. 2017 May;23(5):1942-1960. doi: 10.1111/gcb.13583. Epub 2016 Dec 28.

Authors

Anson William Mackay¹, Alistair W R Seddon², Melanie J Leng^{3

4}, Georg Heumann⁵, David W Morley¹, Natalia Piotrowska⁶, Patrick Rioual⁷, Sarah Roberts⁸, George E A Swann⁸

Affiliations

¹ Environmental Change Research Centre, Department of Geography, UCL, London, WC1E 6BT, UK.
² Department of Biology and Bjerknes Centre for Climate Research, University of Bergen, PO Box 7803, Bergen, N-5020, Norway.
³ NERC Isotope Geosciences Facilities, British Geological Survey, Nottingham, NG12 5GG, UK.
⁴ Centre for Environmental Geochemistry, University of Nottingham, Nottingham, NG7 2RD, UK.
⁵ Steinmann Institute of Geology, Mineralogy and Paleontology, University of Bonn, Nussallee 8, 53115, Bonn, Germany.
⁶ Department of Radioisotopes, Institute of Physics - CSE, Silesian University of Technology, Konarskiego 22B, 44-100, Gliwice, Poland.
⁷ Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, PO Box 9825, Beijing, 100029, China.
⁸ School of Geography, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.

Abstract

The forest-steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to push the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a deeper understanding of long-term forest-steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to understanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m^-2 yr^-1 ) and isotope composition of organic matter (δ¹³ C_TOC ). Forest-steppe dynamics were reconstructed using pollen, and diatom records provided measures of primary production from near- and off-shore communities. We used a generalized additive model (GAM) to identify significant change points in temporal series, and by applying generalized linear least-squares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon dynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to abrupt sub-Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR values range between 2.8 and 12.5 g C m^-2 yr^-1 . Peak burial rates (and greatest variability) occurred during the early Holocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the neoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr bp provide compelling evidence for the sensitivity of the region to sub-Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake Baikal sediments during the Holocene, almost one-quarter of which was buried during the early Holocene alone. Combined, our results highlight the importance of understanding the close linkages between carbon cycling and hydrological processes, not just temperatures, in southern Siberian environments.

Keywords: Holocene; Lake Baikal; abrupt climate change; carbon; forest-steppe ecotone; palaeolimnology; permafrost.

MeSH terms

Carbon
Carbon Cycle*
Climate
Climate Change*
Forests
Geologic Sediments
Siberia

Substances

Carbon