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Abstract: Dating of sediment cores from the Baltic Sea has proven to be difficult due to uncertainties surrounding the 14C 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 14C 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, 14C 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 μg 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 (ΔR) is calculated by comparing the foraminifera 14C determinations to a PSV & Pb age model. This ΔR 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. [Copyright &y& Elsevier]

Reconstructions of palaeomagnetic secular variation (PSV) in sediment cores can be compared to well-dated regional PSV master curves to infer deposition age. The existing PSV master curve for Fennoscandia, “Fennostack” (Snowball et al., 2007), is limited to the past 10 ka. In this study, we construct a deglacial (for the interval 14–11 ka) PSV master curve for Fennoscandia by including data from a number of existing studies in the region, updating geochronologies where necessary. We also produce new deglacial PSV data from Baltic Sea long-core sediments. By selecting three suitable sites, one in southern Sweden and two in northwest Russia, we produce, for the first time, a deglacial PSV master curve for Fennoscandia, which will provide a useful alternative dating tool for deglacial time intervals, especially considering that deglacial sediments are often unsuitable for 14 C dating. Additionally, we use the deglacial PSV master curve to assess current hypotheses regarding geomagnetic field changes. Time varying geomagnetic field models constrained by Holocene PSV data from around the globe have predicted the presence of latitudinal and longitudinal patterns in the position of the north geomagnetic pole (NGP). Specifically, a 1350 year cycle in NGP latitude has been noted, along with two preferred dominant mode longitudinal bands for NGP; in Europe and North America (Korte et al., 2011; Nilsson et al., 2011). Most PSV studies of sediment are, however, limited to the Holocene epoch. By combining our deglacial PSV master curve with ‘Fennostack’, we are able to assess general patterns in inclination for the past 14 ka, and compare these to a general prediction of regional inclination for the last 14 ka, based on an extrapolation of the latitudinal and longitudinal NGP periodicity noted by Nilsson et al. (2011). The model prediction suggests that the Fennoscandian PSV for the past 14 ka should reveal three recurring intervals of generally steeper inclination due to a dominant NGP longitudinal band in Europe. We find that the Fennoscandian PSV does indeed show these intervals of generally steeper inclination for the time periods expected, supporting the hypothesised periodic NGP variation, which may represent an inherent feature of the geodynamo. [ABSTRACT FROM AUTHOR]