Recent Reservoir Ages for Danish Fjords and Marine Waters

Abstract

AMS 14C dates were measured for 28 mollusk shells collected live in Danish waters over the period ad 1885 to 1945. Fourteen samples were from fjords and 14 were marine samples from the Danish Skagerrak-Kattegat coastal area and from the Belts. Reservoir ages were calculated for all samples on the basis of the tree-ring calibration curve. For the marine samples, which cover the period ad 1885–1916, we found a weighted-average reservoir age of 377 ± 16 yr. The marine ∆R values (the difference between the measured 14C age and the age deduced from marine, mixed-layer model calculation of Stuiver, Pearson and Braziunas (1986)) were found to be uniform within the experimental uncertainty with a weighted average of ∆R = 13 ± 16 yr. Based on the observed scatter, the standard deviation is 21 yr. This result shows that it is justified to use the marine calibration curve with standard parameters (∆R = 0) when 14C-dating marine samples from the Danish area. Our value is consistent with the result ∆R = −33 ± 27 yr previously found for the Norwegian and Swedish Skagerrak-Kattegat coasts. In contrast, reservoir ages for Danish fjords were found to vary from 400 to >900 yr, far beyond experimental uncertainty. We ascribe this to varying content of dissolved, old soil carbonate (hard-water effect). Therefore, dating of samples from such fjord environments is expected to be uncertain by several hundred years.

The freshwater reservoir effect in radiocarbon dating

“…The R values range from -140 to 300 14 C years ( Figure 5), which is within the same order of magnitude as the values measured on 19th and 20th century (pre-bomb) shells from the Limfjord [28].…”

“…In contrast, low reservoir ages ( R <0) can be caused by increased CO 2 exchange at the water-atmosphere boundary, or by surface-water runoff or mineralisation of contemporaneous terrestrial organic matter. Similar variations were found in other Danish fjords [29], with reservoir ages up to 900 years [28]. Other coastal environments show high reservoir ages as well: In a Swedish isostatically isolated basin, reservoir effects as high as R = 1,100 to 700 14 C years were measured on clay gyttja that was deposited during the most saline coastal Litorina phase [96].…”

“…Furthermore, the FRE influences radiocarbon dating in fjords and estuaries and can lead to site and time specific reservoir ages [28][29][30].…”

Northwest Pacific Marine Reservoir Correction Estimated from Annually Banded Coral from Ishigaki Island, Southern Japan

“…Our data shows a variation (150-200 14 C yr) in ∆R values between 1900 and 1950. Temporal variations of reservoir age and ∆R value in the same interval have been reported in several oceanic areas such as the costal waters of Denmark (Heier-Nielsen et al 1995) and California (compiled by Stuiver et al 1986;Ingram and Southon 1997). These temporal ∆R changes are considerably greater than the analytical error of the dated sample and must be considered for calibrating marine 14 C age.…”

Marine Radiocarbon Reservoir Ages in Scottish Coastal and Fjordic Waters

“…The 14 C/ 12 C ratios of freshwater systems in igneous areas (such as NW Scotland) should be similar to atmospheric ratios (Broecker and Walton 1959) and are unlikely to be influenced by "hard water effects" from the surrounding bedrock geology in contrast to studies from other settings (e.g. Heier-Nielsen et al 1995). Spiker (1980) reported a conservative 14 C:salinity relationship for estuarine waters, and the significant influence of fresh water in fjordic hydrography suggests that Scottish fjords are likely to exhibit reduced marine reservoir ages when compared to average UK coastal values.…”