湖泊科学   2020, Vol. 32 Issue (1): 259-270.  DOI: 10.18307/2020.0124. 0

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[复制中文]
DING Zongyan, ZHANG Jiawu, YANG Panpan, ZHOU Shan, ZHANG Yuzhi. Comparison of sediment proxies of cores and their environmental significance at different locations of Lake Toson in Qaidam Basin. Journal of Lake Sciences, 2020, 32(1): 259-270. DOI: 10.18307/2020.0124.
[复制英文]

2019-06-15 收稿
2019-08-15 收修改稿

### 码上扫一扫

(兰州大学资源环境学院, 西部环境教育部重点实验室, 兰州 730000)

Comparison of sediment proxies of cores and their environmental significance at different locations of Lake Toson in Qaidam Basin
DING Zongyan , ZHANG Jiawu , YANG Panpan , ZHOU Shan , ZHANG Yuzhi
(Key Laboratory of Western China's Environmental Systems, Ministry of Education, College of Earth Environmental Sciences, Lanzhou University, Lanzhou 730000, P. R. China)
Abstract: The consistency of proxies at different locations in a lake is of great importance to the reliability of regional climate reconstruction. At present, a single core in the central/deep lake was usually used to reconstruct the regional climate and environment change without verification. Here we compare the same proxy among the different core sediments from different locations of Lake Toson (37°04'-37°13'N, 96°50'-97°03'E, 2808 m a.s.l), which is located in Delingha, NE Tibetan Plateau. Core TSL15S1, TSL15S3, TSL15S7 and TSLG17 were recovered at the water depth of 1, 16.5, 16.5 and 25 m in Lake Toson, respectively. Based on the dating of 210Pb and 137Cs analyses, the changes of grain size, carbonate content and other proxies were compared and analyzed. The results show that the mean grain size is consistent at similar locations, while the grain size are quite different at distant locations within the lake. The grain size of sediments in the shallow water vary greatly in a short time scale, while the sedimentary environment in deep water is relatively stable, and the change is not obvious in the centurial. The variations of organic matter and carbonate content are consistent with each other, which indicates that carbonate may be affected by lake productivity. The organic matter content can reflect the size of lake productivity. The variations of carbonate content are consistent with the carbonate oxygen isotope in TSLC and the pollen A/C ratio of TL06, which was regarded as the substitute index of regional effective humidity. Therefore, the grain size in Lake Toson is reflecting the local sedimentary environment, and its relationship with the regional climate is not clear. Geochemical indexes are more reliable and are recommended for environment reconstructions in a well-mixed lake.
Keywords: Average particle size    carbonate content    organic matter    environmental proxies    Lake Toson    Qaidam Basin

1 研究区概况

 图 1 研究区及采样点位置(a)、德令哈气象站(1960-2016年)(b)、托素湖自动气象站(2017-2018年)(c)月均气温、降水数据 Fig.1 Study area and the cores site (a), monthly temperature and precipitation from Delingha Station (b) and Toson Station (c) (data from Delingha meteorological station during 1960-2016 AD, and Lake Toson automatic meteorological station during 2017-2018 AD)
2 材料与方法

 ${\rm{CaC}}{{\rm{O}}_3}\left( \% \right) = \frac{{0.16 \times 0.75P \cdot V}}{{m\left( {273 + T} \right)}} \times 100$ (1)

 ${\rm{OM}}\left( \% \right) = \frac{{\left( {{M_2} - {M_3}} \right)}}{{\left( {{M_2} - {M_1}} \right)}} \times 100$ (2)

3 结果 3.1 年代序列的建立

 图 2 TSL15S1、TSL15S3、TSL15S7与TSLG17孔岩芯沉积物137Cs及210Pbex的垂直分布 Fig.2 Vertical distributions of excess 137Cs and 210Pbex of the TSL15S1, TSL15S3, TSL15S7 and TSLG17

 图 3 托素湖4个短钻岩芯年代深度模型(图中1963为137Cs时标) Fig.3 The age-depth model of the four short cores from Lake Toson (the 1963 represented a 137Cs marker)
3.2 托素湖不同位置沉积物近100年来代用指标变化特征

 图 4 托素湖不同位置岩芯沉积物平均粒径(图中1 m为采样点水深，下同) Fig.4 Mean grain-size of the cores from five sites in Lake Toson (the 1 m represents the water depth of cores, the same below)

 图 5 托素湖不同位置沉积岩芯沉积物粒度组分 Fig.5 Grain size composition of sediments of the cores from four sites in Lake Toson

 图 6 托素湖不同沉积岩芯碳酸盐和有机质含量 Fig.6 Contents of carbonate and organic matter of the cores from five sites in Lake Toson

4 讨论 4.1 不同位置沉积岩芯指标变化及其环境意义

4.2 区域过去几十年来湖泊沉积记录的解释

 图 7 代用指标与区域记录、器测资料对比：(a)TSLG17孔有机质含量；(b)TSLG17孔碳酸盐含量；(c)TSLC孔自生碳酸盐氧同位素[14]；(d)TL06-1孔孢粉A/C值[8]；(e)年均相对湿度；(f)树轮重建的降水[45]；(g)年平均降水；(h)年蒸发量；(i)彭曼公式计算的蒸发量；(j)年均气温(所有器测数据均来自德令哈市气象站(1960-2017年)) Fig.7 Comparison of proxies with other core records of Lake Toson and instrumental data: (a) organic matter content of TSLG17, (b) carbonate content of TSLG17, (c) carbonate δ18O from TSLC[14], (d) A/C ratio of TL06-1[8], (e) relatively humidity, (f) the reconstructed regional precipitation based on tree ring[45], (g) annual average precipitation, (h) annual evaporation, (i) evaporation calculated by Penman formula, (j) annual average temperature (all instrumental data were taken from Delingha meteorological station during 1960-2017 AD)

5 结论

1) 湖泊内相近的沉积岩芯沉积物粒度变化具有一致性，但相距较远的岩芯之间粒度变化差异较大.浅水区的沉积物粒度(粒径)在短时间尺度上可以变化很大；而深水区的沉积环境比较稳定，在百年尺度上的变化都不明显.因此，托素湖粒度指标仅指示取样点沉积环境，与气候变化关系不明显.

2) 湖泊沉积物中有机质和碳酸盐总体变化趋势一致，有较好的相关性，且浅水区相关性更好，表明碳酸盐可能受到湖泊生产力的影响.湖泊内碳酸盐和有机质含量变化趋势的一致性表明在这类湖泊中选择地球化学指标恢复区域气候环境更可靠.