Abstract: Sub-Antarctic islands are ideally placed to reconstruct past changes in Southern Hemisphere westerly wind behaviour. They lie within their core belt (50–60°S) and the strong winds deliver sea salt ions to the islands resulting in a west to east conductivity gradient in their water bodies. This means that the stronger (or weaker) the winds, the higher (or lower) the conductivity values measured in the water bodies. A survey of the water chemistry and diatom assemblages of lakes and ponds on sub-Antarctic Campbell Island (52°32′S, 169°8′E) revealed that, similar to other sub-Antarctic islands, conductivity was the most important, statistically significant ecological variable explaining turnover in diatom community structure. Based on this, a diatom–conductivity transfer function was developed (simple weighted averaging with inverse deshrinking: R2 = 0.86, R2jack = 0.66, RMSEP = 0.25 log10 μS cm−1). This transfer function will be applied to lake sediment cores from the western edge of the Campbell Island plateau to reconstruct past conductivity/sea spray and therefore directly reconstruct changes in Southern Hemisphere westerly wind strength within their core belt.