Abstract
The role played by river networks in regional and global carbon cycle is receiving increasing attention. Despite the potential of radiocarbon measurements (14C) to elucidate sources and cycling of different riverine carbon pools, there remain large regions such as the climate-sensitive Tibetan Plateau for which no data are available. Here we provide new 14C data on dissolved organic carbon (DOC) from three large Asian rivers (the Yellow, Yangtze and Yarlung Tsangpo Rivers) running on the Tibetan Plateau and present the carbon transportation pattern in rivers of the plateau versus other river system in the world. Despite higher discharge rates during the high flow season, the DOC yield of Tibetan Plateau rivers (0.41 gC m-2 yr-1) was lower than most other rivers due to lower concentrations. Radiocarbon ages of the DOC were older/more depleted (511±294 years before present, yr BP) in the Tibetan rivers than those in Arctic and tropical rivers. A positive correlation between radiocarbon age and permafrost watershed coverage was observed, indicating that 14C-deplted/old carbon is exported from permafrost regions of the Tibetan Plateau during periods of high flow. This is in sharp contrast to permafrost regions of the Arctic which export 14C-enriched carbon during high discharge periods.
Highlights
Global river export of dissolved organic carbon (DOC) to the oceans is a key component of the global carbon cycle and is subject to climate forcing [1]
Compared with DOC concentrations measured with high-temperature oxidation method, which was performed on a Shimadzu TOC analyzer and UV oxidation method, we found the conversion efficiency of DOC after the UV exposure [21] can be as high as 102±3% in this study
Rivers running on an area with higher density of Soil organic carbon (SOC) usually have higher DOC concentrations
Summary
Global river export of dissolved organic carbon (DOC) to the oceans is a key component of the global carbon cycle and is subject to climate forcing [1]. With a huge carbon store of 12.3 Pg-C (1 Pg = 1015 g) on the Tibetan Plateau [13] and more than ten large rivers (e.g. Yellow River, Yangtze River, Yarlung Tsangpo, etc.) running on this region [14], old soil carbon might be released by the hydrological changing in this climatic-sensitive area.
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