The Biogeochemistry Of Sedimentary Organic Matter In Marginal Seas

A majority of organic carbon (OC) deposited in estuaries and shelves were transported into coastal zones by rivers, and this OC takes part in the global carbon cycle. Hence, it is important to study the behavior of OC in estuaries in order to better understand the land-ocean interaction and global carbon cycle. In this thesis, surface sediment samples from Changjiang Estuary and Hangzhou Bay, and along the northern Bering and Chukchi Seas were analyzed for bulk elemental composition (TOC, TN), stable carbon isotopic composition (δ13C) and lignin phenols in order to investigate the origin, transport and decay of sedimentary OC in these systems.Our results showed that terrestrial OC signal was strong along Changjiang Estuary, and decreasing seaward due to dilution by marine OC farther offshore. Compared with Changjiang River Estuary, Hangzhou Bay has the similar dispersal trend of terrestrial OC, but has higher values of TOC (%), C/N ratio and lignin concentration than Changjiang Estuary. This is because of the unique hydrogeology and tidal current of Hangzhou Bay which retained some terrestrial OC and this terrestrial OC underwent further decomposition whilst in the bay. The majority of sedimentary OC in Hangzhou Bay originated from Changjiang River, and these materials underwent further decomposition during transport.In the northern Bering Sea, the woody gymnosperm signal predominated near the coastal zone off the Yukon River, while non-woody debris predominated in the central and northern area. The (Ad/Al)v and (Ad/Al)s values in the northern Bering Sea increased gradually northward, and the higher values occurred in the Bering Strait than in the northern Bering Sea, indicating decomposition of terrestrial OC during transport northward. Chukchi Sea sediments were composed of a mixture of fresh and degraded lignin materials, as well as non-woody and woody angiosperm and gymnosperm tissues. In southern Chukchi Sea, the signal of more degraded non-woody tissues was stronger than that in the northern part. The fresh gymnosperm tissues in Chukchi Sea were mainly from eastern Siberia. The non-woody angiosperm tissues were most likely input by Mackenzie River. In the northern Chukchi Sea, fresher lignin materials and higher woody tissues were observed, which could have been transported to these locations via sediment ice rafting.