Climate Change and its Influence on Sulfur Enrichment in the Freshwater Lake Sediment
Date Issued
2014
Date
2014
Author(s)
TZENG, Jing-Yang
Abstract
Lake Baikal is one of the deepest fresh water and the oldest lake in the world. Situated at the polar region, this is subjecting the lake easily responding to smaller magnitude of climatic changes. According to Watanabe （2004）, records of millions of years of climate change were kept in this lake and that climatic change was the only factor controlling the amount of terrigenous materials entering this lake as recorded in carbon, nitrogen, sulfur contents and isotopic compositions. In addition, limited redox reaction could occurred in this fresh water land lock lake environment due to a limit source of sulfur could entering this fresh-water environment such that sulfate become to be a limiting factor in the sulfur cycle. Climatic change could play a major role in alternating supply of sulfate to this environment. During interglacial warm period, increase fluxes of river sulfate and organic carbon entering the lake and resulting in higher flux of pyrite formation by a higher degree of anoxic sulfate reduction. On the other hand, little pyrite could deposit during cold glaciation periods with a limited river supply sulfate. Lake Baikal, however, unlike most other freshwater lake, is subjecting to continental rifting. A number of hydrothermal vents and cold seeps have been found in the lake which could bring in different types and extra sulfur to the Lake. In order to investigate sources of sulfur and influence of climate change may have had in this freshwater lake, we employed a lake wide sampling strategy, including lake, river, spring water samples as well as lake sediment for pore water sulfate, sulfur isotope, sedimentary pyrite, organic carbon and biogenic silica contents, and organic carbon C14.
Similar to Watanabe''s results, this study also found large degree of variations in pyrite concentration in sediment. However, large degree of variations over sulfate concentration were found. Higher concentrations of sulfate existed, in particular, in hydrothermal vents and spring water as well as those in some limited areas of river water. Contrary to Watanabe’s finding, the results of this study indicate that river may not be the only source of sulfur entering this fresh water lake. Furthermore, pyrite enrichments in the sediment occurred not during climatic warm periods but during cold periods. Sediments rich in pyrite were also found in some cold seeps sediments. The result of this study showed that river is not the only source of sulfur entering this freshwater lake. The occurrences of higher degree of pyrite formation during climatic cold periods demonstrated that vents and seeps could be the major source（s） of sulfur in this freshwater lake.
Subjects
淡水湖泊
古氣候變化
硫酸鹽還原作用
甲烷厭氧氧化作用
SDGs
Type
thesis
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