Abstract The isotopic composition of seawater provides valuable information on how the Earth system has evolved. Here we present stable tungsten (δ186/184W) recorded in three ferromanganese (Fe-Mn) crusts spanning past 80 million years Pacific. δ186/184W Fe-Mn displays a pronounced decrease ∼0.2‰ from 60 Ma to 40 followed by value ∼0‰ since ca. Ma. Multiple lines evidence indicate an invariable...