A theoretical flux of diatoms to the sediment was calculated in core RAPiD-21-03K at the corresponding depths to the SiO2/diatom measurements by dividing the mass flux of silica (from doi:10.1594/PANGAEA.981143) by the SiO2/diatom (from doi:0.1594/PANGAEA.981140). In this dataset, 'depth' is the midpoint distance each sediment sample was taken from the top of the core in m, 'age' is the calibrated age in both years before present and in common era calendar years, 'diatom flux' is the number flux of diatom valves to the sediment per cm² area per year.