Ecosystem shifts at two mid-Holocene tipping points in the alpine Lake Son Kol (Kyrgyzstan, Central Asia)

Abstract

Tipping points can be defined as critical ecosystem thresholds that start self-enforced dynamics pushing systems into new stable states. Many lake ecosystems of arid Central Asia are sensitive to hydrological changes as they are located at the intersection of the influence of the dry Siberian Anticyclone and the relatively humid mid-latitude Westerlies, and their sediment records can be used to study past tipping points. We studied subfossil chironomid remains preserved in a ca. 6000-year-long sediment record from the Central Asian lake Son Kol (Central Kyrgyzstan) to reconstruct past ecosystem dynamics. Our results show abrupt transitions from a chironomid fauna dominated by macrophyte-associated, salinity-indicating taxa, to a vegetation-independent fauna, and subsequently to a macrophyte-associated, freshwater-indicating fauna. A comparison of the chironomid-based environmental reconstruction to other proxy indicators from the same record suggests a phase of increased Westerly strength starting about 4900 cal. yr BP. This increase led to enhanced precipitation and sediment fluxes into the lake, which in turn led to high turbidity levels and consequently to a macrophyte collapse causing abrupt changes in the chironomid fauna. At 4300 cal. yr BP, a weakening of the Westerlies in combination with higher lake levels led to lower turbidity and ultimately to the recovery of the macrophyte population and associated changes in the chironomid assemblage. These two sequences of events show how the occurrence of a gradual change in an external trigger (Westerlies) can trigger a cascade of within-lake processes (turbidity, macrophyte density) and may ultimately lead to an abrupt reorganization of the ecosystem (chironomid fauna), providing models for tipping points.

Is there a common threshold to subfossil chironomid assemblages at 16 m water depth? Evidence from the Tibetan Plateau

“…Salinity, often measured through electrical conductivity (Schwarz et al, 2017), is often related to water depth in closed lake systems, where the amount of ions is relatively constant, but salinity changes as water volume changes (Kasper et al, 2013. Therefore, water depth reconstructions for this region are often based on salinity-reconstructions as the signaling variable (Doberschütz et al, 2014;Haberzettl et al, 2005, Laug et al, 2020. Water depth reconstructions using salinity as an indirect indicator are only qualitative, though (Ohlendorf et al 2013(Ohlendorf et al , 2014, whereas reconstructions based on chironomid-water depth transfer functions can result in quantitative results (Kurek and Cwynar, 2009a;Cwynar et al, 2012).…”

The influence of Holocene forest dynamics on the chironomid fauna of a boreal lake (Flocktjärn, northeast Sweden)

“…Nevalainen & Luoto 2017; Robroek et al 2017; Engels et al 2020), on tracing past changes in the food web (van Hardenbroek et al 2010), and on the interactions between different parts of the ecosystem through studies of past tipping points (e.g. Laug et al 2020). However, there are still many unanswered questions related to the connectivity of different parts of the ecosystem.…”

Reviewing the Palaeoenvironmental Record to Better Understand Long-Term Human-Environment Interaction in Inner Asia During the Late Holocene

“…Several studies reconstructed a phase of increased or increasing moisture between ca. 5,000 and 4,000 BP including pollen spectra from Lake Karakul, north-eastern Tajikistan (Heinecke et al, 2018), lithological properties, pollen and chironomid records from Lake Kichikol, south-western Kyrgyzstan (Beer et al, 2007), pollen spectra from Lake Issyk Kol, north-eastern Kyrgyzstan (Leroy and Giralt, 2021), and chironomid spectra from Lake Son Kol, central Kyrgyzstan (Laug et al, 2020). However, other records obtained from the same lakes or studies conducted at other sites in the region suggest contradicting moisture trends.…”