Application of stable carbon isotopes for reconstructing salt‐marsh floral zones and relative sea level, New Jersey, USA

Abstract

We investigated use of δ13C in bulk organic sediment to define the botanical origin of samples preserved in coastal sediment as a means to reconstruct relative sea level in New Jersey, USA. Modern transects at three sites demonstrated that low and high salt‐marsh floral zones dominated by C4 species (Spartina alterniflora and Spartina patens) were associated with sediment δ13C values between −18.9‰ and −15.8‰ and occurred from mean tide level (MTL) to mean higher high water (MHHW). Brackish transitional settings vegetated by Phragmites australis with Iva fructescens and Typha sp. (C3 species) and freshwater upland samples (C3 species) were characterized by bulk sediment δ13C values of −27.0‰ to −22.0‰ and existed above MHHW. Parallel transects at one site suggested that intra‐site variability was not discernible. The utility of δ13C values for reconstructing relative sea level in New Jersey is limited by an inability to differentiate between brackish sediments related to sea level and freshwater upland samples. To facilitate this distinction in a 4.4 m core, we used a multi‐proxy approach (δ13C values with presence or absence of agglutinated foraminifera) to recognize indicative meanings for four sample types. Sediment with δ13C values greater than −18.9‰ was derived from a vegetated salt‐marsh and formed between MTL and MHHW. Sediment with δ13C values less than −22.0‰ and containing agglutinated foraminifera formed in a brackish transitional zone between MHHW and highest astronomical tide (HAT). This is the narrowest elevational range of the four sample types and most precise sea‐level indicator. Sediment with δ13C values less than −22.0‰ and lacking foraminifera can only constrain the upper bound of former sea level. Samples with intermediate values (−22.0‰ to −18.9‰) formed between MTL and HAT. Using these indicative meanings and radiocarbon dates, we suggest that a transition from brackish to salt‐marsh δ13C values recorded in the core took approximately 350 years (from 1800 to 1450 cal. a BP). Copyright © 2011 John Wiley & Sons, Ltd.

Quantifying the Contribution of Sediment Compaction to late Holocene Salt-Marsh Sea-Level Reconstructions, North Carolina, USA

“…Such differences would also be observed in other measurements of organic content, such as Total Organic Content, given the relatively small sample size obtained using a Russian core (e.g. Kemp et al, 2012).…”

Sea-level change during the last 2500 years in New Jersey, USA

“…sediment, and buried sediment at the Leeds Point site concluded that no systematic, post-burial shift could 226 be discerned for bulk sediment derived from salt-marsh plants ( Kemp et al, 2012c To utilize all available palaeoenvironmental information, PME was estimated for core samples by 234 combining results from the foraminiferal transfer function and downcore measurements of δ 13 C. The 235 range of transfer function reconstructions was restricted to elevations in agreement with those estimated 236 from measured δ 13 C values. The restricted ranges were treated as having uniform probability 237 distributions in subsequent analysis.…”

“…* denote dates that are not reported following standard rounding of 675 radiocarbon age and error. Samples marked with ‡ were previously published in (Kemp et al, 2012c). Ds 676 = Distichlis spicata; Spt = Spartina patens; HW = fragment of wood lying horizontal in core, Pa = 677 Phragmites australis; Sa = Schoenoplectus americanus.…”

Testing the use of microfossils to reconstruct great earthquakes at Cascadia

“…Stable carbon isotopes and Rock-Eval Pyrolysis yield clues to the botanical and environmental origin of organic material preserved in coastal sediment (Kemp et al, 2012). Pyrolysis was performed on 60 mg of powdered sediment (dry/wt) using a RockEval 6 analyzer (Vinci Technologies) following the methods of Behar et al (2001).…”