Diatom response to Asian monsoon variability during the Holocene in a deep lake at the southeastern margin of the Tibetan Plateau

Abstract

Diatom analysis was applied to a 5.56‐m‐long sediment core, spanning the last 7.8 ka, from Lake Chenghai on the southeastern margin of the Tibetan Plateau. Diatom assemblages are dominated by Cyclotella rhomboideo‐elliptica, Cyclostephanos dubius and small fragilarioid and periphytic taxa. These diatom taxa are interpreted to be sensitive to changes in trophic status and/or turbulence of the water column that are probably related to variations in precipitation and temperature induced through the Asian monsoon. High abundances of C. dubius, Staurosirella pinnata and periphytic taxa suggest higher trophic status (mesotrophic) and stronger turbulence in the water column in the middle Holocene (7.8–4.5 ka BP). During the period of 4.5–2.3 ka BP, a decline in C. dubius, S. pinnata and periphytic taxa, and an increase in C. rhomboideo‐elliptica with the appearance of Cyclotella ocellata suggests a response to decreasing trophic level (more oligotrophic). After 2.3 ka BP, the persistent increases in C. rhomboideo‐elliptica and the loss of Cyclotella ocellata mirrored a further decrease in trophic level (oligotrophic). The main changes in the diatom assemblages in the Lake Chenghai sediment core reflect direct and indirect climate forcing and in particular, the strength of monsoonal precipitation, which in turn corresponds to orbitally induced variability in Northern Hemisphere summer solar insolation since 7.8 ka BP.

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

“…4). This is consistent with the peak percentages of C. dubius during 7200e6400 cal yr BP in Chenghai Lake located in the Southwest monsoon region, suggesting increased southwest monsoon precipitation (Li et al, 2015a). Climate-related factors influence catchment nutrient export and hence have major effects on the bioavailability of nutrients for algae in lakes (Anderson, 2000;Fritz and Anderson, 2013).…”

“…The peak percentage of C. ocellata (~10%) was observed at~3500 cal yr BP in Lugu Lake, which matches very well with a~10% peak of the same diatom in Lake Chenghai, southwest China (Li et al, 2015a). Li et al (2015a) thought that this development of C. ocellata in Lake Chenghai was related to low nitrogen input into the lake in association to low temperature and precipitation. In Lugu Lake, the peak of C. ocellata at~3500 cal yr BP corresponded with the expansion of herb percentages (Artemisia) and gradual decline of Alnus and Tsuga (a rapid decline after 3400 cal yr BP) ( Fig.…”

“…4 and 6), corresponding to the Medieval Warm Period (MWP). The increase in relative abundance of C. dubius observed at 1200 cal yr BP at Lugu Lake is similar to the short-lived peaks of the same species in the sequence from Lake Chenghai, and suggests a warm and moist climate (Li et al, 2015a). An interval of relatively high temperature that occurred from~1200 to 800 cal yr BP, was also observed in the sediment records from Xingyun Lake in Yunnan (Chen et al, 2014).…”

“…Cyclostephanos and Cyclotella species dominate Holocene assemblages in many deep, alpine lakes (e.g., Titicaca, Yellowstone; Tapia et al, 2003;Bracht et al, 2008). These taxa are still dominant in the Holocene diatom sequence from Chenghai Lake, which is located on the southeastern edge of the Tibetan Plateau (Li et al, 2015a). The ecology of Cyclotella is complicated and while there is a response to climate, an interaction between thermal conditions, mixing depth and nutrient availability has been implicated recently (Saros et al, 2012;Saros and Anderson, 2015).…”

The Link between ENSO-like Forcing and Hydroclimate Variability of Coastal East Asia during the Last Millennium

“…Zone 2 (1320–1920 CE) is characterized by the great abundance of Staurosirella pinnata after ~1400 CE. This taxa is commonly found in shallow eutrophic lakes 39 , 40 . In the earlier part, there was a minor increase in Navicula spp.…”