Increased radiocarbon dating resolution of ombrotrophic peat profiles reveals periods of disturbance which were previously undetected

Abstract

Abstract We tested the robustness of three previously published age-depth models by supplementing them with five new 14C AMS dates. The age-models were calculated for profiles retrieved from ombrotrophic peatlands in northern Poland (Bagno Kusowo, Gązwa, and Mechacz Wielki bogs). For the Bagno Kusowo and Mechacz Wielki bogs, the addition of new dates did not significantly change the shape of the age-depth models. In the topmost sections of these peat profiles the new dates did not conform with previously published models. The updated age-depth model from the Gązwa bog profile revealed the presence of 14C date inversions, which led to multiple chronology scenarios. The section of the Gązwa profile with the outliers was characterised by (i) a higher amplitude of reconstructed water table fluctuations in comparison with the lower peat layers and (ii) a higher frequency of layers with macrocharcoal (indicating local fires). However, no relationship was found between the presence/absence of Arcella discoides, Eriophorum vaginatum (hydrological disturbances), and coprophilous fungi (presence of herbivores or omnivores) and peat layers under and above the section with 14C date inversions. Moreover, a section with outlying 14C dates did not differ in terms of disturbance indicator content compared with the profiles from Bagno Kusowo and Mechacz Wielki. Although our study does not give a clear explanation for the presence of the section rich in outlying dates in the Gązwa profile, it proves that with low-resolution dating it might be very difficult to detect sections of peat disturbance. In addition, obtaining the most accurate reconstruction of the vertical depth range of post-bomb dates in a peat core may improve age-depth models for the youngest peat layers.