不同环境下湖泊矿物和湖水性质对碳埋藏的制约——以西藏郭扎错为例

Carbon Burial Inferred from Minerals and Lake Water Properties:A Case Study of Guozha Co in Tibet

湖泊沉积物不仅记录了湖泊演化的过程,还蕴含了丰富的碳储量。本文以青藏高原西部郭扎错407 cm长的湖芯为例,探讨了8.7 ka BP以来该湖由淡水湖演变到咸水湖的过程中,有机碳和无机碳沉积通量与储量的变化及影响因素。郭扎错无机碳沉积通量范围为4.6~35.1 g·m^(-2)·a^(-1),平均值为17 g·m^(-2)·a^(-1),无机碳储量范围为2.5×10^(6)~19.1×10^(6) t/a,平均值为9.2×10^(6) t/a,无机碳总储量约为18.5×10^(9) t。有机碳沉积通量范围为1.6~7.3 g·m^(-2)·a^(-1),平均值为4.0 g·m^(-2)·a^(-1),有机碳储量范围为1.5×10^(6)~3.3×10^(6) t/a,平均值为2.2×10^(6) t/a,有机碳总储量约为1.63×10^(9) t。8.7 ka BP以来,三个不同环境演化阶段(8.7~4.0 ka BP,4.0~1.5 ka BP,以及1.5 ka BP至今)中,4.0~1.5 ka BP气候寒冷干旱,湖泊为淡水湖,但无机碳和有机碳的沉积通量和储量都表现为低值。根据碳沉积通量和储量的变化特征发现,无机碳的沉积与碳酸盐矿物成因有关,而有机碳沉积则与黏土矿物的成因有关,二者都与环境、湖水性质变化有关,其中温度对无机碳沉积通量和储量的影响大于盐度的影响,而温度对有机碳沉积通量和储量的影响小于盐度的影响。

Lacustrine sediments not only record the evolutionary processes of lakes but also contain rich carbon reserves.Taking the 407 cm-long lake sediments of Guozha Co in western Qinghai-Tibet Plateau as an example,this paper discusses the changes and factors influencing the organic carbon and inorganic carbon flux,as well as the amount of carbon buried since 8.7 ka BP,during which the lake has evolved from freshwater to saline.The results show that,since 8.7 ka BP,the flux of inorganic carbon in Guozha Co has ranged from 4.6 to 35.1 g·m^(-2)·a^(-1),with an average of 17 g·m^(-2)·a^(-1),while the buried amount ranged from 2.5×10^(6) to 19.1×10^(6) t/a,with an average of 9.2×10^(6) t/a.Approximately 18.5×10^(9) t of inorganic carbon has been buried.The flux of organic carbon ranged from 1.6 to 7.3 g·m^(-2)·a^(-1),with an average of 4.0 g·m^(-2)·a^(-1),while the amount of organic carbon buried ranged from 1.5×10^(6) to 3.3×10^(6) t/a,with an average of 2.2×10^(6) t/a.Approximately 1.63×10^(9) t of organic carbon has been buried.Guozha Co has evolved from a freshwater lake in a warm climate setting during 8.7-4.0 ka BP to a freshwater lake in cold climate setting during 4.0-1.5 ka BP,and finally to a saline lake from 1.5 ka BP to present.The deposition flux and reserves of both inorganic carbon and organic carbon were lower during the period of 4.0-1.5 ka BP than in the other two periods.According to the characteristics of carbon deposition flux and reserves,inorganic carbon burial is related to carbonate minerals,while organic carbon burial is related to clay minerals,with both types of burial related to the environment and properties of the lake.Temperature had the most significant effect on both the flux and burial of inorganic carbon;however,salinity had a greater effect on organic carbon burial.