Disentangling the Impact of Global and Regional Climate Changes During the Middle Eocene in the Hampshire Basin: New Insights From Carbonate Clumped Isotopes and Ostracod Assemblages

We present a novel multiproxy data set (bulk and clumped isotopes on gastropod shells and variations in ostracod assemblages) of the Hampshire Basin (Southern-England) that sheds light on the connection between the North Sea and the Atlantic Ocean through the English Channel during the deposition of the Barton clay formation (latest Lutetian—Bartonian, middle Eocene; ∼41–40 Ma). During this time period, the English Channel operated as a gateway between the warmer Atlantic Ocean and the colder North Sea waters. High-latitude water mixing combined with the regional hydrological cycle and sea-level variations, may have contributed to mitigate the water temperatures in the Hampshire Basin, with an average recorded of ca. 25°C. In the uppermost part of the section the connection between the two water masses was limited or absent as evidenced by warmer (up to ca. 35°C) Atlantic Ocean temperatures in the Hampshire Basin. The large differences in average oxygen isotope composition of seawater (δ¹⁸O_water) recorded (from δ¹⁸O_water −1.7‰ to δ¹⁸O_water of −0.7‰) evidenced large salinity differences between the Atlantic Ocean and the North Sea. Ostracods suggest that the temporary connection between those two water masses was caused by relative regional sea-level variations. This scenario could be partially linked to glacio-eustatic sea-level changes related to climate fluctuations probably associated with the MECO event.