Late quaternary changes in carbon cycling on Mt. Kenya, East Africa:: an overview of the δ13C record in lacustrine organic matter

The delta(13)C signature of sedimentary organic matter acts as a tracer for past changes in the terrestrial and aquatic carbon cycles. Compound-specific delta(13)C analysis enables these two signals to be disentangled. We compare the molecular-isotopic records from a transect of five lakes between 1820 and 4595 in a.s.l. on Mt. Kenya, East Africa, spanning the last similar to 100,000 years, with multiproxy palaeoenvironmental data, in order to determine the mechanisms underlying Late Quaternary variations in carbon cycling at different altitudes. The amplitude of down-core variations in the delta(13)C values of total organic carbon varied from 4.8%. to 17.4%o. The delta(13)C signals in compounds of terrestrial, aquatic-macrophyte and algal origin were tightly coupled, reflecting strong atmospheric control. During the early glacial and the last glacial maximum, the effects of sub-ambient CO, and enhanced moisture stress reinforced each other, resulting in carbon starvation and very high delta(13)C values. In contrast, smaller, millennial-scale shifts in delta(13)C during the late-glacial and Holocene were driven primarily by fluctuations in monsoon precipitation. However, the impact of Late Quaternary atmospheric changes were complex, involving variations in biomass burning, vegetation cover, soil erosion, lake levels and water chemistry in addition to direct physiological responses by higher plants and algae. (C) 2004 Elsevier Ltd. All rights reserved.