The dataset is raw diatom counts (minimum 250 count size) from a sediment core taken from within high saltmarsh at the mouth of Dronning Marie Dal in south east Greenland (63.470N, -41.925W). The data was collected on 19/07/2014 during a research cruise to the area as part of the X_Centuries research project funded by the Danish Council for Independent Research 30 (FNU) (grant no. DFF-0602-02526B). The core was taken using a spade to dig a shallow pit from which a sediment section was extracted, wrapped in plastic and transported to the laboratory. Diatom samples were taken from the sediment core in the laboratory at 0.25 and 0.5 cm intervals using a scalpel. Sediment samples were prepared for diatom analysis using standard methods (Palmer and Abbott 1986). Counts were taken under a light microscope at 400x magnification. Only unbroken valves were counted. The taxonomy follows Van der Werff and Huls (1958-74), Hartley (1996) and Patrick and Reimer (1966, 1975). The core top elevation was surveyed in the field using a Sokkisha level to mean tide level, established via a pressure transducer that logged tidal variations at 15-min intervals at Timmiarmiut, 100 km to the South, during fieldwork. These tidal levels were related to tidal predictions at Tasiilaq, 300 km to the NE. This data was collected to reconstruct recent (last ~300 years) of relative sea-level changes from this area, in conjunction with the modern diatom training set also collected from this location.