Bulk sediment 14C dating in an estuarine environment: How accurate can it be?

Bryan C. Lougheed, Stephen P. Obrochta, Conny Lenz, Anette Mellström, Brett Metcalfe, Raimund Muscheler, Maja Reinholdsson, Ian Snowball, Lovisa Zillén

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Abstract

Due to a lack of marine macrofossils in many sediment cores from the estuarine Baltic Sea, researchers are often forced to carry out 14C determinations on bulk sediment samples. However, ambiguity surrounding the carbon source pathways that contribute to bulk sediment formation introduces a large uncertainty into 14C geochronologies based on such samples, and such uncertainty may not have been fully considered in previous Baltic Sea studies. We quantify this uncertainty by analyzing bulk sediment 14C determinations carried out on densely spaced intervals in independently dated late-Holocene sediment sequences from two central Baltic Sea cores. Our results show a difference of ~600 14C yr in median bulk sediment reservoir age, or R(t)bulk, between the two core locations (~1200 14C yr for one core, ~620 14C yr for the other), indicating large spatial variation. Furthermore, we also find large downcore (i.e., temporal) R(t)bulk variation of at least ~200 14C yr for both cores. We also find a difference of 585 14C yr between two samples taken from the same core depth. We propose that studies using bulk sediment 14C dating in large brackish water bodies should take such spatiotemporal variation in R(t)bulk into account when assessing uncertainties, thus leading to a larger, but more accurate, calibrated age range.

Original languageEnglish
Pages (from-to)123-131
Number of pages9
JournalPaleoceanography
Volume32
Issue number2
Early online date22 Jan 2017
DOIs
Publication statusPublished - Feb 2017

Keywords

  • Quaternary geochronology, Radioisotope geochronology, Marginal and semi-enclosed seas, radiocarbon, bulk sediment, reservoir age, Baltic Sea, estuary, 14C

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