Implications of single-step graphitization for reconstructing Late Holocene relative sea level using radiocarbon-dated organic coastal sediment

Juliet P. Sefton, Andrew C. Kemp, Kathryn L. Elder, Roberta L. Hansman, Mark L. Roberts

Research output: Contribution to journalArticleResearchpeer-review

1 Citation (Scopus)

Abstract

Late Holocene relative sea-level reconstructions are commonly generated using proxies preserved in salt-marsh and mangrove sediment. These depositional environments provide abundant material for radiocarbon dating in the form of identifiable macrofossils (salt marshes) and bulk organic sediment (mangroves). We explore if single-step graphitization of these samples in preparation for radiocarbon dating can increase the number and temporal resolution of relative sea-level reconstructions without a corresponding increase in cost. Dating of salt-marsh macrofossils from the northeastern United States and bulk mangrove sediment from the Federated States of Micronesia indicates that single-step graphitization generates radiocarbon ages that are indistinguishable from replicates prepared using traditional graphitization, but with a modest increase in error (mean/maximum of 6.25/15 additional 14C yr for salt-marsh macrofossils). Low 12C currents measured on bulk mangrove sediment following single-step graphitization likely render them unreliable despite their apparent accuracy. Simulated chronologies for six salt-marsh cores indicate that having twice as many radiocarbon dates (since single-step graphitization costs ∼50% of traditional graphitization) results in narrower confidence intervals for sample age estimated by age-depth models when the additional error from the single-step method is less than ∼50 14C yr (∼30 14C yr if the chronology also utilizes historical age markers). Since these thresholds are greater than our empirical estimates of the additional error, we conclude that adopting single-step graphitization for radiocarbon measurements on plant macrofossils is likely to increase precision of age-depth models by more than 20/10% (without/with historical age markers). This improvement can be implemented without additional cost.

Original languageEnglish
Pages (from-to)1139-1158
Number of pages20
JournalRadiocarbon
Volume64
Issue number5
DOIs
Publication statusPublished - 10 Oct 2022
Externally publishedYes

Keywords

  • age-depth model
  • mangrove
  • Massachusetts
  • Micronesia
  • salt marsh

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