New insights into environmental controls on the occurrence and abundance of Group I alkenones and their paleoclimate applications: Evidence from volcanic lakes of northeastern China

Group 2i Isochrysidales produce characteristic alkenones reflecting sea ice distribution

“…This further validates that physiological response to decreased salinity would not result in increased C 37:4 production. Published DNA sequences that fall into Group 2i in our phylogenetic analyses were also observed in water and sediment samples from lakes in China 29,32 , Canada 33 , the USA, 29 and Antarctica 34 , where C 37:4 was the predominant alkenone. High %C 37:4 alkenone production is thus likely a shared characteristic across Group 2i Isochrysidales.…”

Abrupt Freshening Since the Early Little Ice Age in Lake Sayram of Arid Central Asia Inferred From an Alkenone Isomer Proxy

“…Such transitions may be related to the different requirements of certain major ions and/or nutrients for Group I and II Isochrysidales. Group I preferentially thrives in the oligotrophic freshwater environments with reduced major ions (Y. Yao et al, 2019), whereas Group II appears to have more stringent requirements for common major ions, such as Ca 2+ , Mg 2+ , and Na + (Pearson et al, 2008). As salinity increases with increases of certain major ions, Group II might gradually outcompete Group I.…”

“…Group II LCA data are from culture experiments of three common Group II species, Isochrysis galbana , Ruttnera (Chrysotila) lamellosa , and Tisochrysis lutea (Zheng et al, 2019). However, so far, there have been no studies successfully isolating and culturing the Group I Isochrysidales, so the surface sediments of freshwater lakes with Group I‐type LCA distributions were used for Group I (Longo et al, 2016, 2018; K. J. Wang, O'Donnell, et al, 2019; Y. Yao et al, 2019). The three‐dimensional diagram showing our compiled RIK 37 , RIK 38E , and C 38 Me/C 38 Et values clearly differentiates the Group I LCA distributions from the Group II LCAs (Figure 2b).…”

“…Long‐chain alkenones (LCAs) are a class of C 35 ‐C 42 di‐, tri‐, and tetra‐unsaturated methyl (Me) and ethyl (Et) ketones, exclusively produced by certain Isochrysidales within haptophyte lineages. In lacustrine settings, there are obvious transitions of two alkenone‐producing Isochrysidales groups as salinity increases (Longo et al, 2016): Group I occurs in freshwater/oligohaline lakes (Longo et al, 2016, 2018; Y. Yao et al, 2019), whereas Group II occurs in oligohaline/saline lakes, and its relative abundances increase with increasing salinity (Longo et al, 2016; Theroux et al, 2010). The distinctive LCA distributions of Group I Isochrysidales are characterized by the presence of isomeric tri‐unsaturated C 37 alkenones with Δ 14,21,28 double bond positions (C 37:3b ), in addition to the common Δ 7,14,21 (C 37:3a ) in Group II.…”

Supplemental Material: Permafrost thaw induced abrupt changes in hydrology and carbon cycling in Lake Wudalianchi, northeastern China

“…To reconstruct past hydrological changes in Lake Wudalianchi, we use RIK 37 index based on the isomeric ratio of tri-unsaturated C 37 alkenones produced by Group I and/or II Isochrysidales (Longo et al, 2016). From freshwater to oligohaline lakes, salinity serves as the main control for the transition among different groups of alkenone-producing Isochrysidales (Yao et al, 2020): Group I occurs in freshwater/oligohaline lakes (Longo et al, 2016;Yao et al, 2019b), whereas Group II becomes progressively more competitive as salinity increases (Group I rarely occurs in waters with salinity higher than 5‰) (Kaiser et al, 2019;Yao et al, 2020). In the Baltic Sea, for example, as salinity increases from near fresh in Bothnian Bay to brackish waters, Group II Isochrysidales become increasingly more competitive against Group I Isochrysidales ( Kaiser et al, 2019).…”