The Foulden Maar deposit, a finely laminated lacustrine diatomite from the South Island of New Zealand, is the first high-resolution Oligocene-Miocene terrestrial climate record from the midlatitudes of the Southern Hemisphere. We use the presence of orbital and solar cycles within the physical properties records from the deposit to infer that the laminations are annual varves and that the deposit spans ∼100 k.y. When combined with magnetostratigraphy and 40Ar/39Ar data, we can assign the diatomite to chron C6Cn.2n (23.033–22.931 Ma), coeval with the rapid deglaciation of Antarctica during the second half of the Mi-1 transient glaciation event. Both obliquity and precession cycles occur in the physical properties records from the site, indicating a strong ocean-atmosphere coupling in the Southern Hemisphere and influence from both low and high latitudes. The appearance of a strong obliquity component, in particular, may indicate a transient incursion of the Subtropical Front onto the Campbell Plateau during the Mi-1 deglaciation.