Diatom-based reconstructions of hydrological variations and the underlying mechanisms during the past ∼520 years in the central Tianshan Mountains

Abstract

In order to deepen our understanding of water environment-related issues in the central Tianshan Mountains (TCTMs), it is necessary to study the change processes of hydrological variables and the underlying mechanisms within a longer time window that goes beyond the instrumental period. This study focuses on a high-resolution lacustrine sediment core drilled from an alpine lake in TCTMs with a hope that palaeohydrological changes inferred from diatom assemblages may provide an insight on details of water environment evolutions. The diatom inferred temperature was broadly consistent with the temperature records in its adjacent areas, representing a temperature trough during ∼1490 to ∼1835 CE and a general rising trend since ∼1835 CE. The diatom inferred pH (DI-pH) was generally low during ∼1490 to ∼1835 CE, and was high with a declined trend during ∼1835 to ∼2013 CE, being negatively correlated with TN or TOC and positively correlated with carbonate in sediments significantly. The diatom inferred conductivity (DI-Cond) was characterized with a significantly high salinity interval during ∼1490 to ∼1835 CE than that during ∼1835 to ∼2013 CE. The salinity during the past ∼520 years was modulated by interplays among precipitation driven by the Atlantic Multidecadal Oscillations, temperature-dictated evaporation, and temperature-led glacier melting. The water environment changes (lakewater temperature, DI-pH, DI-Cond and diatom assemblages) were identified with a remarkable shift at ∼1835 CE when the temperature began to climb up in TCTMs, implying that climate warming not only exerted influences on water resources but also on water properties in TCTMs.