Tracing estuarine organic matter sources into the southern North Sea using C and N isotopic signatures

Laura Bristow, Timothy D. Jickells, Keith Weston, Alina Marca, Ruth Parker, Julian E. Andrews

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Sources and distribution of particulate organic matter in surface waters of the Humber and Thames estuaries and in the East Anglian plume in the southern North Sea were investigated in winter 2006/2007. Carbon (C) and nitrogen (N) stable isotopes provided evidence for the presence of three particulate organic matter sources; riverine plankton (δ13C −30 ‰ and δ15N 7.9 ‰) identified in the Thames estuary only, marine plankton (average δ13C −21.4 ‰ and δ15N 4.5 ‰) and a third source with an enriched 13C signature (>−16.7 ‰) and elevated C:N ratio (>12.7). Particulate organic matter with enriched 13C values were observed throughout the Humber estuary and at the marine end-member of the Thames estuary. While bacterial cycling of organic carbon undoubtedly takes place within these estuaries, these processes on their own are unlikely to account for the isotopic signatures seen. The 13C enriched organic matter source is suggested to be due to particulate organic matter input from marsh plants and seagrasses such as Spartina spp. and Zostera on the adjacent salt marshes and mudflats and/or macroalgae along the banks of the estuaries. This 13C enriched signal was also identified approximately 50 km offshore within the southern North Sea, in the East Anglian plume, which transports UK riverine water off-shore in a discrete plume. This plume therefore provides a mechanism to transport this estuarine derived organic matter pool offshore out of the estuaries. These results indicate that estuarine derived organic matter from marsh plants, seagrasses and/or macroalgae contributes to the southern North Sea organic matter pool and is therefore likely to contribute to winter-time shelf sea carbon and nitrogen cycles.
Original languageEnglish
Pages (from-to)9-22
Number of pages13
Issue number1-3
Publication statusPublished - May 2013

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