Salinity of the Eocene Arctic Ocean from oxygen isotope analysis of fish bone carbonate

Stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle Eocene samples (∼55 to ∼45 Ma) recently recovered from the Lomonosov Ridge by Integrated Ocean Drilling Program Expedition 302 (the Arctic Coring Expedition). Theδ18O values of the Eocene samples ranged from −6.84‰ to −2.96‰ Vienna Peedee belemnite, with a mean value of −4.89‰, compared to 2.77‰ for a Miocene sample in the overlying section. An average salinity of 21 to 25‰ was calculated for the Eocene Arctic, compared to 35‰ for the Miocene, with lower salinities during the Paleocene Eocene thermal maximum, theAzollaevent at ∼48.7 Ma, and a third previously unidentified event at ∼47.6 Ma. At theAzollaevent, where the organic carbon content of the sediment reaches a maximum, a positiveδ13C excursion was observed, indicating unusually high productivity in the surface waters.