Grain-size characteristics in lake Fuxian sediments: Implication for dry-humid transformation of Indian summer monsoon over the past 150 years

Abstract

Polymodal distributions and end-member modeling of grain-size in lacustrine sediments can reveal the changes in sedimentary processes, transportation mechanisms, and climatic changes. The temporal and spatial variation characteristics of grain-size were investigated in six sediment cores of the plateau deep-lake Fuxian, in southwest China, where the climate was driven by Indian Summer Monsoon (ISM). Results indicated that the size of the dominant grain-size exponentially decreased with the declining hydrodynamic condition towards the deep-water zones, with an exception of the maximum grain-size near the outlet of the lake. Measured grain-size distributions were classified into four end-members (EMs) with a basic end-member model algorithm (BasEMMA), of which could be linked to a distinct transport mechanism and source: EM1 (long-term suspended load from atmospheric dust) with the modal size of 0.3–11.2 µm, EM2 (off-shore suspended load from fine riverine input) with 7.9–14.2 µm, EM3 ((near-shore suspended load from coarse riverine input) with 15.9–31.7 µm, and EM4 (near-shore riverbed load from extremely coarse riverine input) with 35.6–70.9 µm, respectively. Temporal variation of EM2 + EM3 components of grain-size in Core F5 are responses to the changes in instrumentally recorded precipitation in Chengjiang (1961–2008) and ISM (1860–2006), which indicates that changes in river flow in response to changes in precipitation is the primary driver of clastic sediment deposition especially in the narrow section of the lake. Our findings indicate grain-size distribution and sediment compositions are significant tools for improving the understanding of the spatiotemporal heterogeneity in dry-humid transformation of ISM over the past 150 years.