The application of δ¹³C, TOC and C/N geochemistry to reconstruct Holocene relative sea levels and paleoenvironments in the Thames Estuary, UK

Abstract

We examined the use of δ13C, TOC and C/N geochemistry of sedimentary organic matter to reconstruct former sea levels and paleoenvironments in the absence of suitable microfossil data. The modern distribution of δ13C, TOC and C/N of 33 vegetation and 74 surface sediment samples collected from four coastal wetlands in the Thames Estuary and Norfolk, UK are described. The δ13C, TOC and C/N geochemistry of sediments varied in relation to the input of in situ vascular vegetation versus allochthonous particulate organic matter and algae, which was controlled primarily by tidal inundation. We reviewed published and unpublished studies to produce an English database of vegetation (n = 257) and sediment (n = 132) δ13C, TOC and C/N geochemistry. Four elevation‐dependent environments in the database had statistically distinct δ13C, TOC and C/N values: (1) tidal flat/low marsh (δ13C: −24.9 ± 1.2‰; TOC: 3.6 ± 1.7%; C/N: 9.9 ± 0.8); (2) middle marsh/high (δ13C: −26.2 ± 1.0‰; TOC: 9.8 ± 6.7%; C/N: 12.1 ± 1.8); (3) reed swamp (δ13C: −27.9 ± 0.7‰: TOC: 36.5 ± 11.5%; C/N: 13.9 ± 1.2); and (4) fen carr (δ13C: −29.0 ± 0.6‰; TOC: 41.6 ± 5.7%; C/N: 17.4 ± 3.1). The δ13C, TOC and C/N geochemistry database was applied to a Holocene sediment core collected from the Thames Estuary to produce three new sea‐level index points and one limiting date, illustrating the utility of δ13C, TOC and C/N values to reconstruct Holocene relative sea levels. Copyright © 2015 John Wiley & Sons, Ltd.

A 7000‐year high‐resolution lake sediment record from coastal central Chile (Lago Vichuquén, 34°S): implications for past sea level and environmental variability

“…and species of silicoflagellates indicate deposition in a marine environment. The TOC/TN mean values are around 8.5, common for coastal sediments (Hodgson et al ., ; Khan et al ., ).…”

“…Diatom content, however, is not very high (BioSi: ∼6%). Higher TOC/TN values suggest that a higher influx of terrestrial organic matter from littoral swamps and marshes (Meyers and Ishiwatari, ; Meyers and Teranes, ; Hodgson et al ., ; Khan et al ., ) could be partially responsible for this higher organic content. Subunit 2.B shows higher Fe/Mn values indicative of more anoxic conditions at the bottom of the lake, and a weaker mixing pattern in the basin compared to previous environments.…”

Source organic matter analysis of saltmarsh sediments using SIAR and its application in relative sea‐level studies in regions of C4 plant invasion

“…The systematic variation of C org sources with tidal elevation and the preservation of diagnostic d 13 C and C/ N signatures within saltmarsh sediments have resulted in a series of studies employing bulk sediment geochemistry to infer coastal and RSL change (Wilson et al 2005b;Lamb et al 2007;Da Cruz Miranda et al 2009;Castro et al 2010;Kemp et al 2010;Khan et al 2015). Whilst vertical trends in these data are typically robust, spatial and temporal variability in C org inputs and diagenetic fractionation, coupled with additional factors such as changing marsh morphology, complicate the use of specific values as precise indicators of tidal elevation (Wilson et al 2005b;Lamb et al 2006Lamb et al , 2007.…”

“…However, sequential data can reveal consistent trends of increasing or decreasing marine influence, whilst threshold values can assist in discriminating between broad elevation zones which, when used in combination with more precise indicators, refine RSL reconstruction (e.g. For example, in their RSL reconstruction from the Thames Estuary, UK, Khan et al (2015) excluded locations sites with invasive Spartina species from their modern analogue data set. As with all reconstruction approaches based on uniformitarian principles, accurate characterization of the modern analogues from which past conditions are inferred is a key determinant of reconstruction validity.…”

Carbon stable isotope (δ13C) and elemental (TOC, TN) geochemistry in saltmarsh surface sediments (Western Brittany, France): a useful tool for reconstructing Holocene relative sea‐level

“…As is true for microfossils, δ 13 C, TOC and TN values mainly follow altitudinal gradients across the marshes, which reflect (i) the spatial distribution of the different saltmarsh plant species as a function of ecological factors such as salinity, inundation frequency and hydrological stress (e.g. Chmura and Aharon, ; Wilson et al , , ; Lamb et al , , ; Engelhart et al , ; Khan et al , Milker et al , ); (ii) differences in the sources of the organic matter (OM) furnished to the saltmarsh sediments [ in situ plant litter decomposition, marine and freshwater dissolved and particulate organic carbon (DOC, POC)]; and (iii) differences in the decomposition processes of the organic compounds. This elevation‐dependent distribution of δ 13 C and bulk elemental geochemistry (TOC, TN and, as a result, C/N ratios) values of saltmarsh surface sediments promoted the latter as potential RSL proxies.…”