Surface-water freshening and high-latitude river discharge in the Eocene North Sea

A shark-tooth apatite [delta][sup.18]O record of the early Palaeogene North Sea reflects changes in regional hydrography by showing variable temperatures and salinities. A 2-4 Ma period in the early Eocene was particularly influenced by substantial surface-water freshening, indicated by a 3-4[per thousand] reduction of [delta][sup.18] O values. The magnitude of the [delta][sup.18]O decrease indicates a depletion in [sup.18]O of surface waters by 2-3[per thousand] relative to Eocene mean ocean water. This value is lower than that of coeval lakes reconstructed from freshwater gastropod [delta][sup.18]O values from the Paris Basin, suggesting that large rivers with high-latitude catchment areas drained into the North Sea. The period of surface-water freshening began close to the Palaeocene--Eocene thermal maximum, when relative sea-level fall, tectonic uplift and basaltic volcanism caused a temporary isolation of the North Sea. North Atlantic and North Sea surface waters became reconnected during a series of early Eocene transgressions.