Early Miocene subtropical water temperatures in the southeast Pacific

Cenozoic climate of western South America is strongly controlled by features like Andean uplift and the Humboldt Current. The first strontium isotope age data from central and southern Chile provide a latest Oligocene to late early Miocene age for classic warm-water mollusk faunas reaching as far south as 45°S. Comparison with the biogeography of congeneric living species indicates that sea surface temperatures off central and southern Chile during that time were at least 5 °C higher than today; i.e., minimum annual mean sea surface temperatures for Darwin's Navidad fauna at 34°S are estimated as 20 °C. As expected, the number of tropical taxa decreases towards the south but several are still present as far south as 45°S. The ages scatter relatively broadly between ~ 24 and ~ 16 Ma, partly even within individual localities. Shallow-water and deeper-water faunas are revealed to have similar ages. When considered in light of convincing micropaleontological evidence for late Miocene to early Pliocene depositional ages, the Sr isotope data support a hypothesis that the mollusk fauna is reworked.