Exploring the MMCO: A high-resolution stable isotope study of ODP site 1264, 17-15.5 Ma.

The middle-Miocene Climatic Optimum (MMCO) represents the climax of Neogene warmth and the last large-scale aberration of the global δ18O record during the Cenozoic transition into the icehouse world. However, it has rarely been studied in high-resolution (<5kyrs). Here, I present new stable isotope data from ODP site 208-1264 (Walvis Ridge, SE Atlantic) placed on an astronomically tuned age model. I further extend the record first published by Liebrand et al (2011) and extended by Mischa Saes (unpublished data, 2013). The data was placed on an astronomically tuned age model covering the interval between 16.97 and 15.46 Ma. This completes a data set covering over 9 million years (~24-15.5Ma) with a high temporal resolution of <5kyrs. The new stable isotope datasets convey valuable information on the astronomical forcing of the climate throughout the middle Miocene. The first δ18O drop related to the onset of the MMCO occurs at 17.3 Ma, leading up to a pronounced δ18O minimum between 17.02 and 16.03 Ma, modulated by the 2.4myr eccentricity cycle. A second striking minimum occurs ~15.6 Ma, modulated by a strong eccentricity maximum. Close inspection of the δ18O record reveals that the eccentricity is the main pacemaker of climate change during the middle Miocene. The Monterey carbon-isotope excursion is also evident in our data, although we do not capture the entire event. 400kyr filtering reveals the timing of carbon-isotope maximum events (CM1, 2, 3a and 3b) in agreement with records from site 1146 (Holbourn et al, 2007)