title: Interpretation and application of carbon isotope ratios in freshwater diatom silica.
abstract: Carbon incorporated into diatom frustule walls is protected from degradation enabling analysis for carbon isotope composition (δ13Cdiatom). This presents potential for tracing carbon cycles via a single photosynthetic host with well-constrained ecophysiology. Improved understanding of environmental processes controlling carbon delivery and assimilation is essential to interpret changes in freshwater δ13Cdiatom. Here relationships between water chemistry and δ13Cdiatomfrom contemporary regional data sets are investigated. Modern diatom and water samples were collected from river catchments within England and lake sediments from across Europe. The data suggest dissolved, biogenically produced carbon supplied proportionately to catchment productivity was critical in the rivers and soft water lakes. However, dissolved carbon from calcareous geology overwhelmed the carbon signature in hard water catchments. Both results demonstrate carbon source characteristics were the most important control on δ13Cdiatom, with a greater impact than productivity. Application of these principles was made to a sediment record from Lake Tanganyika. δ13Cdiatomco-varied with δ13Cbulkthrough the last glacial and Holocene. This suggests carbon supply was again dominant and exceeded authigenic demand. This first systematic evaluation of contemporary δ13Cdiatomcontrols demonstrates that diatoms have the potential to supply a record of carbon cycling through lake catchments from sediment records over millennial timescales.
authors.affiliation: Lancaster Environment Centre University of Lancaster Lancaster UK.
authors.forename: Megan
authors.initials: M
authors.lastname: Webb
authors.affiliation: Lancaster Environment Centre University of Lancaster Lancaster UK.
authors.forename: Philip A
authors.initials: PA
authors.lastname: Barker
authors.affiliation: Lancaster Environment Centre University of Lancaster Lancaster UK.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Wynn
authors.affiliation: Institute of Plant Sciences and Oeschger Centre for Climate Change Research University of Bern Bern Switzerland.
authors.forename: Oliver
authors.initials: O
authors.lastname: Heiri
authors.affiliation: Institute of Plant Sciences and Oeschger Centre for Climate Change Research University of Bern Bern Switzerland; Geography and Environment University of Southampton Southampton UK.
authors.forename: Maarten
authors.initials: M
authors.lastname: van Hardenbroek
authors.affiliation: Lancaster Environment Centre University of Lancaster Lancaster UK; STREAM Industrial Doctorate Centre University of Sheffield Sheffield UK.
authors.forename: Frances
authors.initials: F
authors.lastname: Pick
authors.affiliation: Department of Earth, Environmental and Planetary Sciences Brown University Providence RI USA.
authors.forename: James M
authors.initials: JM
authors.lastname: Russell
authors.affiliation: Stable Isotope Facility NERC Centre for Ecology & Hydrology, Lancaster Environment Centre Lancaster UK.
authors.forename: Andy W
authors.initials: AW
authors.lastname: Stott
authors.affiliation: NERC Isotope Geosciences Facilities British Geological Survey Nottingham UK; Centre for Environmental Geochemistry School of Geography University of Nottingham Nottingham UK.
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Leng
keywords: Lake Tanganyika; carbon cycling; diatom frustule carbon; palaeoclimate; stable carbon isotopes