Data from: Using legacy data to reconstruct the past? Rescue, rigor and reuse in peatland geochronology

There is a growing interest for rescue and reuse of data from past studies (so-called legacy data). Data loss is alarming, especially where natural archives are under threat, such as peat deposits. Here we develop a workflow for reuse of legacy radiocarbon dates in peatland studies, including a rigorous quality assessment that can be tailored to specific research questions and study regions. A penalty score is assigned to each date based on criteria that consider taphonomic quality (i.e. sample provenance) and dating quality (i.e. sample material and method used). The weights of quality criteria may be adjusted based on the research focus, and resulting confidence levels may be used in further analyses to ensure robustness of conclusions. We apply the proposed approach to a case study of a (former) peat landscape in the northern Netherlands, aiming to reconstruct the timing of peat initiation spatially. Our search yielded 313 radiocarbon dates from the 1950s to 2019. Based on the quality assessment the dates—of highly diverse quality—were assigned to four confidence levels. Results indicate that peat initiation for the study area first peaked in the Late Glacial, dropped during the Boreal (10640 – 9220 cal y BP) and showed a second peak in the Subboreal (5660 – 2400 cal y BP). Further spatial analysis shows that for local valleys peat initiation occurred throughout the Holocene, with age-elevation plots indicating a prominent control by Holocene sea level rise. On plains and ridges peat initiation only occurred during the Subboreal, likely controlled by groundwater rise related to sea level rise. Our study highlights the potential of legacy data for palaeogeographic reconstructions, as it is cost-efficient and provides access to information no longer available in the field. However, data retrieval may be challenging and reuse of data requires that basic information on location, elevation, stratigraphy, sample and analysis details are documented irrespective of the original research aims