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Current studies which use the oxygen isotope composition from diatom silica (δ¹⁸O_diatom) as a palaeoclimate proxy assume that the δ¹⁸O_diatom value reflects the isotopic composition of the water in which the diatom formed. However, diatoms dissolve post mortem, preferentially losing less silicified structures in the water column and during/after burial into sediments. The impact of dissolution on δ¹⁸O_diatom values and potential misinterpretation of the palaeoclimate record are evaluated.

Diatom frustules covering a range of ages (6 samples from the Miocene to the Holocene), environments and species were exposed to a weak alkaline solution for 48 days at two temperatures (20 °C and 4 °C), mimicking natural dissolution post mucilage removal. Following treatment, dissolution was assessed using scanning electron microscope images and a qualitative diatom dissolution index. The …