Climate and tectonic effects on Holocene development of an alpine lake (Muge Co, SE margin of Tibet)

Abstract

South-west China is an important area for determining variability of the SW Asian Monsoon; it is, however, also tectonically very active. Palaeolimnological studies in this region generally focus on climate as a direct driver of ecological change, rarely considering the effects of tectonic activity and catchment ontogeny. We present diatom and organic matter data from a Holocene sediment record from Muge Co, an alpine lake located on an active fault zone in the southeast margin of Tibet, and explore the possible drivers of ecological change. A major change occurred at 9000 cal. BP, when the diatom assemblage switched from benthic to predominantly planktonic forms, and organic matter content decreased rapidly. Comparison of the Holocene diatom record with a regional data set of lake surface sediments using detrended canonical correspondence analysis (DCCA) suggests that this change in diatom development was mainly associated with changing water depth, most likely linked to a seismically triggered landslide (which deepened the lake) rather than climate-driven hydrological change. However, diatom changes associated with principal components analysis (PCA) axis 2 agree well with inferred Holocene temperature changes. From the mid-Holocene, shifts in planktonic diatom species were probably related to indirect climate forcing, notably water column mixing depth and catchment vegetation–driven changes in dissolved organic carbon (DOC) and nutrient export. The diatom stratigraphy at Muge Co reflects a complex range of indirect climate- and catchment-controlled processes that were superimposed over a change in lake morphology resulting from tectonic activity.