渤海地区全新世孢粉序列及古环境演化

通过对取自黄河口外泥质区的BH-264孔的沉积孢粉进行分析,对渤海地区全新世古植被和古环境演化历史进行了恢复。在早全新世(距今9.5~7.6 ka)渤海地区气候温暖湿润,在陆缘海滨地带出现大量沼泽湿地,上面生长着莎草和香蒲等植被,在周围的山地、丘陵和平原地区植被以松属和落叶栎属为主,并伴生着桦木属、榆科、桑科等树种;在中全新世(距今7.6~5.8 ka)温度的升高和海平面上升,使BH-264孔沉积孢粉中松属占主导地位,不利于远距离传播的草本植物花粉含量降为全新世最低值;在距今5.8 ka以后东亚夏季风减弱和降雨量减少导致渤海西部陆源海滨地带植被以旱生草本藜科、蒿属和菊属为主,黄河三角洲的形成缩短了研究区的离岸距离,使这些草本植物花粉易于传播到BH-264孔中沉积。

Holocene palynological sequences and palaeoenvironmental changes in the Bohai Sea area

Palynological analyses combined with AMS14C dating were carried out in a gravity core BH-264 retrieved from a mud depositional system in the Huanghe River underwater delta (the Bohai Sea) to investigate the paleoclimate changes during the Holocene. In the early Holocene (9.5—7.6 ka BP) the pollen and spore assemblages indicate a warm and humid climate. During this stage, the Bohai seashore area is mainly composed of marshes as the vegetations mainly consisted of Cyperaceae and Typhaceae, and the surrounding mountainous, hilly and flat areas were mainly covered by Pinus and Deciduous quercus accompanied with Betula,Ulmaceae and Moraceae. In the mid-Holocene (7.6—5.8 ka BP), due to the increase of temperature and sea-level, Pinus dominated in the pollen and spore assemblages. However the content of pollen genus such as herb, which is not favourable totransportation for long distances, decreases to the lowest level in the Holocene in this warm stage. The East Asian summer monsoon (EASM) has decreased since 5.8 ka BP and as a result the rainfall in the surrounding area of Bohai Sea reduces and an arid environment dominates. Such xeric genus as Chenopodiaceae,Dendranthema,Artemisia are dominant in the seashore environment. Moreover, the formation of the Huanghe (Yellow River) Delta shortened the distance between the pollen supplying area and the investigation area, which resulted in higher efficiency for the transportation of pollen and spore to the sediment core BH-264.