The data set includes stable oxygen isotope data measured on the non-labile (HCl-extractable) phosphorus fraction (δ18O-PO4), extracted from each 1 cm layer of sediment core. This sediment core (LG3A) was dated via correlation with a parallel core (LG3C) using 8 age-depth tie points, for which core chronology was established by analysing 210Pb activity at the British Geological Survey Inorganic Geochemistry Laboratories.