MIS 3 diatom assemblage and bulk organic carbon isotope data from Lake Baikal sediment core CON01-603-5@en

A Marine Isotope Stage (MIS) 3/early MIS 2 section from a structural high along the east coast of the North Basin of Lake Baikal was analysed for diatoms, C/N ratios, and organic carbon isotope ratios. Diatoms were present throughout MIS 3 and early MIS 2, with high concentrations of the planktonic taxa Cyclotella sp. c.f. gracilis between 54 and 51.5 kyr BP indicating relatively warm, interstadial, conditions. Following a %TOC inferred climatic cooling between 43.2 and 39.1 kyr BP, evidence of a more muted d13C(organic) and %TOC inferred climatic warming from c. 39.1-34.7 kyr BP coincides with a period of very high diatom concentrations, indicating high aquatic productivity, at the Buguldeika Saddle in the South Basin of Lake Baikal. No evidence exists for a 'Kuzmin' catchment erosional event in the North Basin during MIS 3. This, however, may reflect the location of the coring site away from major riverine inputs. Abrupt climatic cooling at the culmination of both warm phases in the North Basin are associated, on the basis of the palaeomagnetic age-model and correlations to existing sites in Lake Baikal, with the initiation of Heinrich events 5 (c. 50 kyr BP) and 4 (c. 35 kyr BP), respectively, in the North Atlantic. The amount of organic material declines across the MIS 3/MIS 2 transition while constant C/N ratios suggest organic material to be predominantly derived from phytoplankton. An increase in d13C(organic) at the MIS 3/MIS 2 transition may therefore indicate changes in aquatic productivity, pCO2 or the inorganic carbon pool.对贝加尔湖北盆地东缘构造隆起处的海洋同位素阶段（Marine Isotope Stage, MIS）3/早期MIS 2沉积剖面开展了硅藻、碳氮比及有机碳同位素比值分析。硅藻在MIS 3与早期MIS 2层位中均有分布，其中54~51.5千年BP（kyr BP）时段浮游类群纤细小环藻（Cyclotella sp. c.f. gracilis）含量极高，指示当时气候相对温暖，处于间冰阶环境。在43.2~39.1千年BP时段总有机碳百分含量（%TOC）反映气候变冷后，约39.1~34.7千年BP时段由有机碳δ¹³C与%TOC推断的气候回暖信号有所减弱，这与贝加尔湖南盆地布格德伊卡鞍部极高的硅藻浓度时段相吻合，指示当时水生生产力极高。MIS 3时期北盆地未发现“库兹明”流域侵蚀事件的相关证据，这或可归因于取芯位点远离主要河流输入区。基于古地磁年代模型以及与贝加尔湖其他已有研究位点的对比，北盆地两次暖期峰值阶段的突发性气候变冷，分别对应北大西洋地区海因里希事件（Heinrich events）5（约50千年BP）与海因里希事件4（约35千年BP）的启动时期。MIS 3/MIS 2转换界面处有机物质总量有所下降，而恒定的碳氮比则表明有机质主要来源于浮游植物。因此，MIS 3/MIS 2转换界面处有机碳δ¹³C的升高，可能指示水生生产力、大气二氧化碳分压（pCO₂）或无机碳库发生了变化。