While marine records of the Eocene-Oligocene transition indicate a generally coherent response to global cooling and the growth of continental ice on Antarctica, continental records indicate substantial spatial variability. Marine Eocene-Oligocene transition records are marked by an ∼+1.1‰ foraminiferal δ18O shift, but continental records rarely record the same geochemical signature, making both correlation and linking of causal mechanisms between marine and continental records challenging. Here, a new high-resolution continental δ18O record, derived from the freshwater gill-breathing gastropod Viviparus lentus, is presented from the Hampshire Basin, UK. The Solent Group records marine incursions and has an established magnetostratigraphy, making it possible to correlate the succession directly with marine records. The V. lentus δ18O record indicates a penecontemporaneous, higher-magnitude shift (>+1.4‰) than marine records, which reflects both cooling and a source moisture compositional shift consistent with the growth of Antarctic ice. When combined with “clumped” isotope measurements from the same succession, about half of the isotopic shift can be attributed to cooling and about half to source moisture change, proportions similar to marine foraminiferal records. Thus, the new record indicates strong hydrological cycle connections between marine and marginal continental environments during the Eocene-Oligocene transition not observed in continental interior records.