| |
| |
|
|
|
|
| |
 |
Biogeochemistry of organic matter and associated elements along the river-estuary-ocean continuum
|
| |
|
|
Radiocarbon ages of organic matter transported by major Chinese rivers - What we have learned? (Invited)
Wednesday 9th @ 0930-0950, Conference Hall
Xuchen Wang* , Ocean University of China
Presenter Email: xuchenwang@ouc.edu.cn |
| Radiocarbon ages of organic matter transported by major Chinese rivers - What we have learned
Xuchen Wang1,2
1 Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education,
Ocean University of China, Qingdao, China
2 Center for Isotope Geochemistry and Geochronology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.
Rivers are the major conduits for the transport of land materials to the ocean. Each year, the world rivers deliver about 900 Tg (Tg = 1 x 1012g) of terrestrial carbon to the ocean and half of this riverine carbon is organic carbon. It is essential important to understand the fate and sources of the riverine organic carbon in order to better understand the carbon cycle in the coastal oceans. Here, we report our recent isotopic studies of organic carbon transported in several major Chinese rivers including: the Changjiang, Zhujiang, Huanghe, Heilongjiang and two mountainous rivers in Taiwan. We measured both radiocarbon (14C) and stable carbon isotope (13C) compositions for dissolved organic carbon (DOC), particulate organic carbon (POC) and solid phase extracted (SPE) DOC fractions. We also isolated and measured the isotopic values for particulate black carbon (PBC) and dissolved black carbon (DBC) in the rivers, and compared the values with these in the coastal waters.
Our results show that the radiocarbon values and ages of both DOC and POC varied significantly among the different rivers. The Changjiang, Zhujiang and Huanghe that are the largest three rivers together drain 30% of the China continent, carry old terrestrial OC. POC were older than DOC. The ages of POC in the Huanghe were the oldest reaching 4960 +/- 1690 yr BP. The 14C ages of DOC in the three rivers were around 1000 yr. In comparison, both POC and DOC carried by the Heilongjiang had modern ages that are significantly different than the three largest rivers. We also found that SPE-DOC had much younger 14C ages than bulk DOC, suggesting that riverine DOC is not homogeneous in terms of isotopic signatures. The 14C ages of DBC were much younger than the ages of the PBC in the rivers. Isotopic mass balance calculation indicates that the DBC contained a large fraction BC derived from biomass burning while the PBC comprised mainly fossil fuel combusted BC. The great age differences of the riverine OC indicate the different mobilization and transport time scales in rivers, and are controlled not only by the input of different sources and degradation status of terrestrial OC, but also different environmental settings of the drainage bases of the rivers.
|
|
|
|
|
|
|
|
|