Carbon cycling within an East African lake revealed by the carbon isotope composition of diatom silica: a 25-ka record from Lake Challa, Mt. Kilimanjaro
Carbon cycling within an East African lake revealed by the carbon isotope composition of diatom silica: a 25-ka record from Lake Challa, Mt. Kilimanjaro
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DOI：
10.1016/j.quascirev.2012.07.016
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发表时间：
2013-04
影响因子：
4
通讯作者：
P. Barker;Elizabeth R. Hurrell;M. Leng;B. Plessen;C. Wolff;D. Conley;E. Keppens;I. Milne;B. Cumming;K. Laird;C. P. Kendrick;P. Wynn;D. Verschuren
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文献类型：
--
作者：
P. Barker;Elizabeth R. Hurrell;M. Leng;B. Plessen;C. Wolff;D. Conley;E. Keppens;I. Milne;B. Cumming;K. Laird;C. P. Kendrick;P. Wynn;D. Verschuren
湖泊的碳循环是大气和流域的供应与初级生产者产生的净需求之间的平衡，减去返回大气和沉积物储存的损失。评估这些过程的总和并根据湖泊历史的沉积物记录重建它们需要一系列方法和多代理方法。一项有前途的技术是探索硅藻硅藻壳中有机物的碳同位素组成（δ13C硅原子）。在这里，我们展示了乞力马扎罗山东侧查拉湖火山口沉积物中 25,000 年的 δ13C 硅藻记录，并结合其他代理数据，我们对湖泊碳循环历史的三个主要阶段进行了推断。从25ka到15.8ka年BP，δ13C硅藻与大量沉积物有机质（δ13Cbulk）的δ13C呈正相关，表明此时由高％生物成因二氧化硅记录的高硅藻生产力优先去除12C并富集湖水溶解的无机碳的δ13C。从 15.8 到 5.5 ka，δ13C 硅藻和 δ13C 体积之间的相关性被打破，表明湖泊的碳供应满足或超过了生产力的需求。从 5.5 ka BP 起，正相关性恢复，表明相对于外部供应，内部碳需求增加。硅藻壳结合的碳同位素提供了一种原始工具，用于检查湖泊碳预算的长期波动以及供需平衡随时间的变化。
The carbon cycle of a lake is a balance between supply from the atmosphere and catchment, and the net demand exerted by primary producers, minus losses back to the atmosphere and to sediment storage. Evaluating the sum of these processes and reconstructing them from sediment records of lake history requires a range of methods and a multi-proxy approach. One promising technique is to explore the carbon-isotope composition (δ13Cdiatom) of organic matter incorporated within the silica frustules of diatom algae. Here we present a 25,000-year record of δ13Cdiatomfrom the sediments of crater Lake Challa on the eastern flank of Mt. Kilimanjaro, and along with other proxy data we make inferences about the three major phases in the history of the lake's carbon cycle. From 25 ka to 15.8 ka years BP, δ13Cdiatomis positively correlated with the δ13C of bulk sediment organic matter (δ13Cbulk), indicating that high diatom productivity, as recorded by high % biogenic silica at this time, was preferentially removing12C and enriching the δ13C of lake-water dissolved inorganic carbon. From 15.8 to 5.5 ka the correlation between δ13Cdiatomand δ13Cbulkbreaks down, suggesting carbon supply to the lake satisfied or exceeded the demand from productivity. From 5.5 ka BP the positive correlation resumes, indicating an increase in the internal demand for carbon relative to external supply. Diatom frustule-bound carbon isotopes offer an original tool in examining long-term fluctuations in a lake's carbon budget and how the balance between supply and demand has changed through time.