Abstract
ABSTRACTCarbon 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 δ13Cdiatom from 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. δ13Cdiatom co‐varied with δ13Cbulk through the last glacial and Holocene. This suggests carbon supply was again dominant and exceeded authigenic demand. This first systematic evaluation of contemporary δ13Cdiatom controls demonstrates that diatoms have the potential to supply a record of carbon cycling through lake catchments from sediment records over millennial timescales.
Highlights
Stable isotope analyses of the siliceous cell walls of diatoms provide insights into a broad range of environmental processes tracked from the perspective of a single, ecologically well-constrained organism
Stable isotope analysis of diatom organic molecules, occluded in silica, constrains uncertainties associated with measurements of undifferentiated sedimentary carbon
The occluded organic matter provides a carbon archive largely protected from degradation, oxidation and diagenesis
Summary
Stable isotope analyses of the siliceous cell walls (frustules) of diatoms provide insights into a broad range of environmental processes tracked from the perspective of a single, ecologically well-constrained organism. Most diatom-based stable isotope studies have focused on the stable oxygen and silicon isotope composition (d18Odiatom and d30Sidiatom) of diatoms from lacustrine and marine sediments (Leng and Barker, 2006; Swann and Leng, 2009; Leng and Henderson, 2013). D30Sidiatom in freshwater is used to understand changes in climate, weathering and soil processes through the balance of silicon supply and demand (De La Rocha et al, 2000; Ding et al, 2004; Street-Perrott et al, 2008). Diatom frustules are a host for carbon isotopes measured on organic molecules occluded within diatom frustule walls (d13Cdiatom). This occluded organic matter comprises proteins and long-chain polyamines (Kro€ger and Poulsen, 2008) and represents a source of carbon potentially
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