鄱阳湖沉积物近8ka来有机质碳同位素记录及其古气候变化特征

Organic carbon isotope records of the Poyang Lake sediments and their implications for the paleoclimate during the last 8 ka

通过对鄱阳湖沉积物的高密度采样和有机质碳同位素分析,讨论了鄱阳湖近8ka来的古气候环境。鄱阳湖沉积物有机质δ13C值为-22.42‰～-32.42‰,属C3类植物来源。暖湿期δ13C值相对偏负;冷(凉)干期δ13C值相对偏正。这些记录表明,鄱阳湖近8ka来经历了4次暖湿和4次冷(凉)干的气候环境变化,7900～3660aB.P.、3440～2990aB.P.、2940～2170aB.P.、1820～650aB.P.属相对温暖湿润的气候环境;3660～3440aB.P.、2990～2940aB.P.、2170～1820aB.P.、650～200aB.P.为相对冷凉干旱的气候环境,自200aB.P.(1750A.D.)以来湖区气候开始转暖。暖湿期持续时间较长,冷(凉)干期持续时间较短,1000aB.C.左右为一次重要的气候变冷事件。我国全新世几个特征性气候在湖区均有不同的显示,并与孢粉、硅藻、历史记录所反映的古气候环境对应性较好,可以作为恢复古气候变化的灵敏指标。

The paleoclimate during the last 8 ka is presented through the high resolution organic carbon isotope records of the Poyang Lake sediments. The δ 13C values range from - 22.42‰ to - 32.42‰ , indicating C3 plant dominated source. Therefore, the variations of the δ 13C values of these sediments may largely arouse from the response of the C3 plants to the climate changes, other than the substitution of the C4 plants. Four warm and wet periods (7 900～ 3 660 a B.P., 3 440～ 2 990 a B.P., 2 940～ 2 170 a B.P. and 1 820～ 650 a B.P.), and four cold (cool) and dry periods (3 660～ 3 440 a B.P., 2 990～ 2 940 a B.P., 2 170～ 1 820 a B.P. and 650～ 200 a B.P.) are identified from the carbon isotope records, where declined δ 13C values indicate warm and wet climate, and elevated δ 13C values indicate cold/dry climate. Such paleoclimate interpretation agrees well with other records of these sediments, the palynology and diatom data for instance, and the documentary records of this area.