Advanced

Using an independent geochronology based on palaeomagnetic secular variation (PSV) and atmospheric Pb deposition to date Baltic Sea sediments and infer 14C reservoir age

Lougheed, Bryan C.; Snowball, Ian LU ; Moros, Matthias; Kabel, Karoline; Muscheler, Raimund LU ; Virtasalo, Joonas J. and Wacker, Lukas (2012) In Quaternary Science Reviews 42. p.43-58
Abstract
Dating of sediment cores from the Baltic Sea has proven to be difficult due to uncertainties surrounding the C-14 reservoir age and a scarcity of macrofossils suitable for dating. Here we present the results of multiple dating methods carried out on cores in the Gotland Deep area of the Baltic Sea. Particular emphasis is placed on the Littorina stage (8 ka ago to the present) of the Baltic Sea and possible changes in the C-14 reservoir age of our dated samples. Three geochronological methods are used. Firstly, palaeomagnetic secular variations (PSV) are reconstructed, whereby ages are transferred to PSV features through comparison with varved lake sediment based PSV records. Secondly, lead (Pb) content and stable isotope analysis are used... (More)
Dating of sediment cores from the Baltic Sea has proven to be difficult due to uncertainties surrounding the C-14 reservoir age and a scarcity of macrofossils suitable for dating. Here we present the results of multiple dating methods carried out on cores in the Gotland Deep area of the Baltic Sea. Particular emphasis is placed on the Littorina stage (8 ka ago to the present) of the Baltic Sea and possible changes in the C-14 reservoir age of our dated samples. Three geochronological methods are used. Firstly, palaeomagnetic secular variations (PSV) are reconstructed, whereby ages are transferred to PSV features through comparison with varved lake sediment based PSV records. Secondly, lead (Pb) content and stable isotope analysis are used to identify past peaks in anthropogenic atmospheric Pb pollution. Lastly, C-14 determinations were carried out on benthic foraminifera (Elphidium spec.) samples from the brackish Littorina stage of the Baltic Sea. Determinations carried out on smaller samples (as low as 4 mu g C) employed an experimental, state-of-the-art method involving the direct measurement of CO2 from samples by a gas ion source without the need for a graphitisation step - the first time this method has been performed on foraminifera in an applied study. The PSV chronology, based on the uppermost Littorina stage sediments, produced ten age constraints between 6.29 and 1.29 cal ka BP, and the Pb depositional analysis produced two age constraints associated with the Medieval pollution peak. Analysis of PSV data shows that adequate directional data can be derived from both the present Littorina saline phase muds and Baltic Ice Lake stage varved glacial sediments. Ferrimagnetic iron sulphides, most likely authigenic greigite (Fe3S4), present in the intermediate Ancylus Lake freshwater stage sediments acquire a gyroremanent magnetisation during static alternating field (AF) demagnetisation, preventing the identification of a primary natural remanent magnetisation for these sediments. An inferred marine reservoir age offset (Delta R) is calculated by comparing the foraminifera C-14 determinations to a PSV & Pb age model. This Delta R is found to trend towards younger values upwards in the core, possibly due to a gradual change in hydrographic conditions brought about by a reduction in marine water exchange from the open sea due to continued isostatic rebound. (C) 2012 Elsevier Ltd. All rights reserved. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Age model, Baltic Sea, Foraminifera, Gaseous radiocarbon measurements, Geochronology, Gotland Deep, Palaeomagnetism, PSV, Pb deposition, Pb, pollution, Radiocarbon, Reservoir age, Delta R
in
Quaternary Science Reviews
volume
42
pages
43 - 58
publisher
Elsevier
external identifiers
  • wos:000304851100004
  • scopus:84860215385
ISSN
0277-3791
DOI
10.1016/j.quascirev.2012.03.013
project
MERGE
BECC
language
English
LU publication?
yes
id
cc0ac840-7d69-4e72-ae08-325ed7af3780 (old id 2903198)
date added to LUP
2012-07-24 10:03:26
date last changed
2017-04-09 03:06:42
@article{cc0ac840-7d69-4e72-ae08-325ed7af3780,
  abstract     = {Dating of sediment cores from the Baltic Sea has proven to be difficult due to uncertainties surrounding the C-14 reservoir age and a scarcity of macrofossils suitable for dating. Here we present the results of multiple dating methods carried out on cores in the Gotland Deep area of the Baltic Sea. Particular emphasis is placed on the Littorina stage (8 ka ago to the present) of the Baltic Sea and possible changes in the C-14 reservoir age of our dated samples. Three geochronological methods are used. Firstly, palaeomagnetic secular variations (PSV) are reconstructed, whereby ages are transferred to PSV features through comparison with varved lake sediment based PSV records. Secondly, lead (Pb) content and stable isotope analysis are used to identify past peaks in anthropogenic atmospheric Pb pollution. Lastly, C-14 determinations were carried out on benthic foraminifera (Elphidium spec.) samples from the brackish Littorina stage of the Baltic Sea. Determinations carried out on smaller samples (as low as 4 mu g C) employed an experimental, state-of-the-art method involving the direct measurement of CO2 from samples by a gas ion source without the need for a graphitisation step - the first time this method has been performed on foraminifera in an applied study. The PSV chronology, based on the uppermost Littorina stage sediments, produced ten age constraints between 6.29 and 1.29 cal ka BP, and the Pb depositional analysis produced two age constraints associated with the Medieval pollution peak. Analysis of PSV data shows that adequate directional data can be derived from both the present Littorina saline phase muds and Baltic Ice Lake stage varved glacial sediments. Ferrimagnetic iron sulphides, most likely authigenic greigite (Fe3S4), present in the intermediate Ancylus Lake freshwater stage sediments acquire a gyroremanent magnetisation during static alternating field (AF) demagnetisation, preventing the identification of a primary natural remanent magnetisation for these sediments. An inferred marine reservoir age offset (Delta R) is calculated by comparing the foraminifera C-14 determinations to a PSV & Pb age model. This Delta R is found to trend towards younger values upwards in the core, possibly due to a gradual change in hydrographic conditions brought about by a reduction in marine water exchange from the open sea due to continued isostatic rebound. (C) 2012 Elsevier Ltd. All rights reserved.},
  author       = {Lougheed, Bryan C. and Snowball, Ian and Moros, Matthias and Kabel, Karoline and Muscheler, Raimund and Virtasalo, Joonas J. and Wacker, Lukas},
  issn         = {0277-3791},
  keyword      = {Age model,Baltic Sea,Foraminifera,Gaseous radiocarbon measurements,Geochronology,Gotland Deep,Palaeomagnetism,PSV,Pb deposition,Pb,pollution,Radiocarbon,Reservoir age,Delta R},
  language     = {eng},
  pages        = {43--58},
  publisher    = {Elsevier},
  series       = {Quaternary Science Reviews},
  title        = {Using an independent geochronology based on palaeomagnetic secular variation (PSV) and atmospheric Pb deposition to date Baltic Sea sediments and infer 14C reservoir age},
  url          = {http://dx.doi.org/10.1016/j.quascirev.2012.03.013},
  volume       = {42},
  year         = {2012},
}