Abstract
BackgroundClosed basins occupy 21% of the world’s land area and can substantially affect global carbon budgets. Conventional understanding suggests that the terminal areas of closed basins collect water and carbon from throughout the entire basin, and changes in lake organic carbon sinks are indicative of basin-wide organic carbon storages. However, this hypothesis lacks regional and global validation. Here, we first validate the depositional process of organic carbon in a typical closed-basin region of northwest China using organic geochemical proxies of both soil and lake sediments. Then we estimate the organic carbon sinks and human impacts in extant closed-basin lakes since the Last Glacial Maximum (LGM).ResultsResults show that 80.56 Pg organic carbon is stored in extant closed-basin lakes mainly found in the northern mid-latitudes. Carbon accumulation rates vary from 17.54 g C m−2 yr−1 during modern times, 6.36 g C m−2 yr−1 during the mid-Holocene and 2.25 g C m−2 yr−1 during the LGM. Then, we evaluated the influence by human activities during the late Holocene (in the past three thousand years). The ratio of human impacts on lake organic carbon storage in above closed basins is estimated to be 22.79%, and human-induced soil organic carbon emissions in the past three thousand years amounted to 207 Pg.ConclusionsWhile the magnitude of carbon storage is not comparable to those in peatland, vegetation and soil, lake organic carbon sinks from closed basins are significant to long-term terrestrial carbon budget and contain information of climate change and human impact from the whole basins. These observations improve our understanding of carbon sinks in closed basins at various time scales, and provide a basis for the future mitigation policies to global climate change.
Highlights
We evaluate changes of lake organic carbon sinks from closed basins of the Qilian Mountains as a case study for research into the mechanisms of closed-basin carbon sink. 234 soil samples were collected in total for analysis of organic proxies in order to validate the transformation of soil organic carbon in closed basins of the Qilian Mountains
Based on the dating results in closed basins of the Qilian Mountains, especially the consistence between OSL and calibrated 14C ages in Zhuyeze Lake, we believe that the reservoir effect is relatively small in this region, which is acceptable for analyzing the millennial-scale carbon sink changes (Fig. 2b) [30]
Conventional understanding of closed basins suggests their terminal areas collect water and carbon from throughout their entire drainage basins [26, 53]. We validated this hypothesis in closed basins of the Qilian Mountains using organic geochemical proxies of both soils and lake sediments
Summary
Closed basins occupy 21% of the world’s land area and can substantially affect global carbon budgets. Conventional understanding suggests that the terminal areas of closed basins collect water and carbon from throughout the entire basin, and changes in lake organic carbon sinks are indicative of basin-wide organic carbon storages. This hypothesis lacks regional and global validation. We estimate the organic carbon sinks and human impacts in extant closed-basin lakes since the Last Glacial Maximum (LGM). Closed basins of the Qilian Mountains, located in the arid region of northwest China, are appropriate areas to explore carbon storage mechanism (Fig. 1b). We calculated the organic carbon storage in closed-basin lakes (mainly located in northern mid-latitudes) since the LGM and evaluated the human impacts both on organic carbon sinks and on soil organic carbon emissions
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