Pollen and dinoflagellate cyst counts on sediment core M72/5_628-1 (MD72/5-25-GC1) from the Black Sea

High-resolution pollen and dinoflagellate cyst records from sediment core M72/5-25-GC1 were used to reconstruct vegetation dynamics in northern Anatolia and surface conditions of the Black Sea between 64 and 20 ka BP. During this period, the dominance of Artemisia in the pollen record indicates a steppe landscape and arid climate conditions. However, the concomitant presence of temperate arboreal pollen suggests the existence of glacial refugia in northern Anatolia. Long-term glacial vegetation dynamics reveal two major arid phases ~64-55 and 40-32 ka BP, and two major humid phases ~54-45 and 28-20 ka BP, correlating with higher and lower summer insolation, respectively. Dansgaard-Oeschger (D-O) cycles are clearly indicated by the 25-GC1 pollen record. Greenland interstadials are characterized by a marked increase in temperate tree pollen, indicating a spread of forests due to warm/wet conditions in northern Anatolia, whereas Greenland stadials reveal cold and arid conditions as indicated by spread of xerophytic biomes. There is evidence for a phase lag of ~500 to 1500 yr between initial warming and forest expansion, possibly due to successive changes in atmospheric circulation in the North Atlantic sector. The dominance of Pyxidinopsis psilata and Spiniferites cruciformis in the dinocyst record indicates brackish Black Sea conditions during the entire glacial period. The decrease of marine indicators (marine dinocysts, acritarchs) at ~54 ka BP and increase of freshwater algae (Pediastrum, Botryococcus) from 32 to 25 ka BP reveals freshening of the Black Sea surface water. This freshening is possibly related to humid phases in the region, to connection between Caspian Sea and Black Sea, to seasonal freshening by floating ice, and/or to closer position of river mouths due to low sea level. In the southern Black Sea, Greenland interstadials are clearly indicated by high dinocyst concentrations and calcium carbonate content, as a result of an increase in primary productivity. Heinrich events show a similar impact on the environment in the northern Anatolia/Black Sea region as Greenland stadials.

本研究利用取自M72/5-25-GC1沉积岩芯的高分辨率孢粉与沟鞭藻囊孢（dinoflagellate cyst）记录，重建了距今64至20千年（ka BP）期间安纳托利亚北部的植被动态与黑海表层环境状况。此期间，蒿属（Artemisia）孢粉在孢粉记录中占优，指示当时为草原景观与干旱气候环境。然而，温带乔木花粉的伴生存在则表明安纳托利亚北部存在冰期避难所（glacial refugia）。长期冰期植被动态揭示了两个主要干旱阶段（约64~55 ka BP与40~32 ka BP）以及两个主要湿润阶段（约54~45 ka BP与28~20 ka BP），二者分别与夏季太阳辐射量的升高与降低相关。Dansgaard-Oeschger（D-O）旋回在25-GC1的孢粉记录中得到清晰体现。格陵兰间冰阶（Greenland interstadials）以温带乔木花粉的显著增加为特征，表明安纳托利亚北部因暖湿环境迎来森林扩张；而格陵兰冰阶（Greenland stadials）则表现为寒冷干旱的环境，这一特征由旱生生物群系（xerophytic biomes）的扩张所指示。有证据表明，初始增温与森林扩张之间存在约500至1500年的相位滞后，该现象可能与北大西洋区域大气环流的持续性变化有关。沟鞭藻囊孢记录中，裸纹藻（Pyxidinopsis psilata）与十字形刺球藻（Spiniferites cruciformis）占优，表明整个冰期阶段黑海处于半咸水环境。约54 ka BP时，海洋指标（海洋沟鞭藻囊孢、疑源类（acritarchs））含量下降，而32~25 ka BP期间淡水藻类的盘星藻属（Pediastrum）与丛粒藻属（Botryococcus）含量上升，揭示黑海表层水体出现淡化现象。此次水体淡化可能与该区域的湿润阶段、里海（Caspian Sea）与黑海的连通、浮冰带来的季节性淡化，以及低海平面导致的河口位置更近有关。在黑海南部，格陵兰间冰阶可通过高沟鞭藻囊孢浓度与碳酸钙（calcium carbonate）含量得到清晰识别，该现象源于初级生产力的提升。海因里希事件（Heinrich events）对安纳托利亚北部/黑海区域的环境影响与格陵兰冰阶相似。