High Resolution Middle Eocene Marine Stable Isotope - Southern Ocean Sites

A prominent middle Eocene warming event is identified in Southern Ocean
deep-sea cores, indicating that long-term cooling through the middle and late
Eocene was not monotonic. At sites on Maud Rise and the Kerguelen Plateau, a
distinct negative shift in d18O values (~1.0‰) is observed ca. 41.5 Ma. This
excursion is interpreted as primarily a temperature signal, with a transient
warming of 4C over 600 k.y. affecting both surface and middle-bathyal deep
waters in the Indian- Atlantic region of the Southern Ocean. This isotopic
event is designated as the middle Eocene climatic optimum, and is interpreted
to represent a significant climatic reversal in the midst of middle to late
Eocene deep-sea cooling. The lack of a significant negative carbon isotope
excursion, as observed during the Paleocene–Eocene thermal maximum, and the
gradual rate of high-latitude warming suggest that this event was not
triggered by methane hydrate dissociation. Rather, a transient rise in pCO2
levels is suspected, possibly as a result of metamorphic decarbonation in the
Himalayan orogen or increased ridge/arc volcanism during the late middle
Eocene.