The ratio Mg/Ca in planktonic foraminifera is a widely used proxy for the sea surface temperature. However, the debate over the salinity effect on planktonic Mg/Ca has complicated the application of this proxy. This debate arises from the large discrepancy between salinity effects observed in laboratory versus field studies. In this talk, I will present new Mg/Ca data in a planktonic foraminiferal species, Globigerinoides ruber (white), from the Atlantic sediment core-tops, which was used to argue for a large salinity effect. Based on the high-quality data, I will explain how the post-depositional dissolution and the habitat preference of the foraminifera can influence the salinity effect derived from the core-top planktonic Mg/Ca data. I will show that the salinity effect on planktonic Mg/Ca is small when the seasonality and calcification depths of foraminifera are taken into account. These new core-top Mg/Ca data reconcile the salinity effects on planktonic Mg/Ca derived from culturing experiments and core-tops, and demonstrate that Mg-palaeothermometer is negligibly affected by salinity change on the glacial-interglacial timescale.