Diatom-based inference of variations in the strength of East Asian spring wind speeds since mid-Holocene

Lake Jingpo is located in Ning'an County, Southeast Heilongjiang Province, northeast China and is strongly influenced by the East Asian monsoon system. Diatom analysis of the last 5000 cal. yr BP according to the results of AMS 14C dating provides a detailed history of paleoenvironment changes. The relative abundance of diatom species, Asterionella formosa, Aulacoseira, Cyclostephanos, Stephanodiscus and Discostella species can be used as a proxy of spring wind speed, which is supported by the results of seasonal diatom and reviews of literature on the autoecologies of these species. In the sediment, high relative abundance of A. formosa, Aulacoseira species indicates high wind-driven turbulence of the water column. The diatom record of the past 5000 years shows that the spring wind speed shifted from weak to strong to weak. In our result, the relative abundance of Aulacoseira species decreased sharply, while that of small-cell Cyclotella sensu lato (including Stephanodiscus, Cyclostephanos and Discostella) increased since 2000 cal. yr BP. The broad alternations between these species are probably keyed to mean temperature and wind variations that control lake circulation and stratification. Our results support the hypotheses that abiotic drivers affect the size structure of planktonic communities and that a warmer climate favors small-sized diatom cells. The change in the ratio of A. formosa and Aulacoseira species to Cyclostephanos, Stephanodiscus and Discostella species (AA/SC) basically correspond to change of the spring insolation (May) at 45°N. Abundance of diatoms in Lake Jingpo roughly corresponds to changes in the Mid- to Low-Latitude Circulation Index of the northern hemisphere as indicated by NH4+ concentration from the GISP2 ice-core, the strength of the Asian summer monsoon as recorded from Hani Peat in Northeastern China, and from a stalagmite found in the Dongge cave in southern China. The results are important in demonstrating the sensitivity of diatoms to climate change, and providing proxy evidence for spring wind speed marked by shifts of diatom type.