Direct versus indirect climate controls on Holocene diatom assemblages in a sub-tropical deep, alpine lake (Lugu Hu, Yunnan, SW China)

Abstract

The reconstruction of Holocene environmental changes in lakes on the plateau region of southwest China provides an understanding of how these ecosystems may respond to climate change. Fossil diatom assemblages were investigated from an 11,000-year lake sediment core from a deep, alpine lake (Lugu Hu) in southwest China, an area strongly influenced by the southwest (or the Indian) summer monsoon. Changes in diatom assemblage composition, notably the abundance of the two dominant planktonic species, Cyclotella rhomboideo-elliptica and Cyclostephanos dubius, reflect the effects of climate variability on nutrient dynamics, mediated via thermal stratification (internal nutrient cycling) and catchment-vegetation processes. Statistical analyses of the climateediatom interactions highlight the strong effect of changing orbitally-induced solar radiation during the Holocene, presumably via its effect on the lake’s thermal budget. In a partial redundancy analysis, climate (solar insolation) and proxies reflecting catchment process (pollen percentages, C/N ratio) were the most important drivers of diatom ecological change, showing the strong effects of climateecatchmentevegetation interactions on lake functioning. This diatom record reflects long-term ontogeny of the lake-catchment ecosystem and suggests that climatic changes (both temperature and precipitation) impact lake ecology indirectly through shifts in thermal stratification and catchment nutrient exports.

Variations of the Indian summer monsoon over the last 30 000 years inferred from a pyrogenic carbon record from south‐west China

“…During the warm and wet Holocene, C 3 plants came to dominate this region. The variation in relative abundance of C 3 /C 4 plants unsurprisingly shows a general correlation with the higher plant pollen data obtained from the same core (Wang et al ., , ; Figure b,c). During MIS 2, low pollen concentrations and total arboreal pollen percentages suggest sparse vegetation cover and a relatively dry climate in the study region.…”

“…Comparison of the pyrogenic carbon record from Lake Lugu (a) with other records from adjacent regions. (b) Arboreal and herbaceous pollen concentration from Lake Lugu (Wang et al ., , Wang et al ., ); (c) tree pollen percentage record from Lake Lugu (Wang et al ., , Wang et al ., ); (d) stable carbon isotopic composition of n ‐alkane data from Core MD05‐2905 in the northern South China Sea (Zhou et al ., ); (e) δ 13 C PyC values from Lake Tengchongqinghai in south‐west China (Zhang et al ., ); (f) stable carbon isotopic composition of n ‐alkane data from Core SO188‐342KL in the Bay of Bengal (Contreras‐Rosales et al ., ); (g) CO 2 record from the EPICA Dome C ice core, Antarctica (Monnin, 2001; Monnin et al ., ).…”

The indirect response of an aquatic ecosystem to long‐term climate‐driven terrestrial vegetation in a subalpine temperate lake

“…Aquatic ecosystems are known to respond both “directly” and “indirectly” to climatic change (Ball et al., ; Battarbee, ). “Direct” aquatic ecosystem responses to climate change are principally influenced by changes in temperature and lake level on aquatic environments (Gell, Tibby, Fluin, Leahy, & Reid, ; Schindler, ; Smol & Cumming, ), while “indirect” responses include those that are mediated through the surrounding terrestrial environment via, for example, vegetation change that alters nutrient inputs and pH of watersheds (Augustinus, Bleakley, Deng, Shane, & Cochran, ; Huvane & Whitehead, ; Korsman & Segerstrom, ; Lancashire, Flenley, & Harper, ; Wang, Yang, Anderson, & Dong, ). Despite the importance of climate in driving terrestrial ecosystem dynamics, and the clear relationship between terrestrial and aquatic ecosystems (Augustinus et al., ; Engstrom, Fritz, Almendinger, & Juggins, ; Huvane & Whitehead, ; Korsman & Segerstrom, ), most research into long‐term aquatic ecosystem change focuses on the “direct” role of climate in driving aquatic ecosystem dynamics.…”

Sedimentary grain-size record of Holocene runoff fluctuations in the Lake Lugu watershed, SE Tibetan Plateau

“…is an alpine lake in Yunnan Province, in the SE margin of the Tibetan Plateau (Figure 1a). The lake is a deep, oligotrophic, freshwater lake, with strong seasonal stratification (Wang et al, 2016). The elevation of the lake surface is 2692.2 m a.s.l., the maximum water depth is 105.3 m, the average depth is 38.4 m, the lake surface area is 57.7 km 2 , and the watershed area is 216 km 2 (Zheng et al, 2014).…”

“…The lake is strongly stratified during summer and early autumn, and mixes completely during winter and spring (Wang et al, 2015). The estimated turnover time for the entire lake water is ~18 years, but the southern basin flushes more rapidly than the northern basin (Wang et al, 2016). The modern regional climate is subtropical monsoonal with distinct wet and dry seasons.…”