Sedimentation controls on the preservation and time resolution of climate-proxy records from shallow fluctuating lakes

Lithological stratigraphies of Pb-210-dated sediment cores from four hydrologically interconnected fluctuating lake basins in Kenya are used to investigate how differences in basin morphometry and physical limnology influence the preservation and time resolution of sedimentary climate-proxy records. The potential of lakes to accumulate an undisturbed sediment record is primarily determined by their relative depth, the ratio between maximum depth and effective wind fetch. Chemically stratified crater lakes accumulate high-quality climate-proxy records because they complement great relative depth with topographical wind shelter, resistance of density stratification to propagation of wind-induced turbulence, and absence of bioturbation in anoxic bottom waters. The changes in water-column circulation and bottom dynamics that accompany lake-level fluctuations affect the time resolution of accumulating climate-proxy signals and thus the apparent magnitude;Ind frequency of inferred climatic events. An episode of low lake level can be both over- or underrepresented in the climate-proxy record depending on the severity of the drawdown relative to the lake's critical depth of sediment accumulation. Decade-scale hiatuses due to non-deposition or erosion at low lake level may be difficult to recognize because mixing of unconsolidated muds deposited before and after the lowstand can obliterate evidence that the record has been truncated. Regional correlation of climate-proxy records must consider both hydrology-related differences in the climatic sensitivity of lakes and sedimentation-related differences in the integrity of their climate-history archive. (C) 1999 Elsevier Science Ltd. All rights reserved.