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A variety of palaeoclimatic records show a shift towards cooler, wetter and windier conditions in Europe around 2800 cal a BP. The shift broadly coincides with an increase of the atmospheric 14 C concentration, suggesting a connection between solar activity variations and climate change. Here we investigate a peat record from Undarsmosse in southern Sweden. In a previous study, based on a low-resolution chronology, this record showed increased aeolian sand influx and Sphagnum spore content around 2800 cal a BP, indicating high storm activity and wetter conditions. We applied the 14 C wiggle-match dating technique on the same record to construct a robust chronology to evaluate the temporal relationship to solar forcing. In addition, we performed plant macrofossil analysis to determine local vegetation changes. Based on the new chronology, a shift to a Sphagnumdominated bog, representing wetter conditions, and the onset of a period with increased storminess occurred around 2700 cal a BP. These changes are, within age model uncertainties, synchronous with climatic changes inferred from other sites in Europe, suggesting a shift in the larger scale atmospheric circulation, possibly triggered by decreased solar activity.

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.

We used the radiocarbon wiggle-match dating technique to date the varved sediments of Lake Gyltigesjön in southern Sweden with the main aim to construct an accurate chronology covering the period between about 3000 and 2000 cal BP. Wiggle-match dating was applied to bulk sediments to evaluate the possibility of constructing accurate chronologies in the absence of terrestrial plant macrofossils and when the amount of old carbon in the sediments is unknown. Facilitated by a floating varve chronology and relatively stable 14C reservoir ages, the results show the possibility to assess the contribution of old carbon solely based on the 14C wiggle-matching of bulk sediments. We confirm the wiggle-matched chronology and the 14C reservoir age of approximately 260 yr by cross-checking the results with 14C dating of macrofossils. The obtained calibrated ages based on bulk sediments have an uncertainty range of about 60–65 yr (95.4% confidence interval). This study confirms that 14C wiggle-match dating of bulk sediments is a viable tool when constructing high-resolution chronologies. The method is especially useful in Sun-climate studies since the timing between solar activity variations (expressed as 14C variations) and climate changes can be accurately determined.