Conflicting isotopic and biotic evidence for tropical sea-surface temperatures during the Tertiary

The biotic evidence from a varied group of shallow-water organisms including mangroves, zooxanthellate corals (mainly reefal), and larger foraminifera suggests that sea surface temperatures at low latitudes during the Tertiary (from at least the Early Eocene to the Middle Miocene) were subtropical to tropical in nature, and similar to temperatures prevailing at low latitudes at the present day (20–28°C). In a recent paper (Shackleton, 1984), the suggestion is made (on the basis of oxygen isotope studies of foraminiferal shells) that low latitude sea-surface temperatures during the Palaeogene and much of the Neogene were invariably lower than those in similar regions today, with a stable temperature of around 18°C. This paper discusses the conflicting evidence for sea surface temperatures obtained from palaeontological and isotopic sources, and suggests that palaeotemperatures derived from some isotopic studies are too low to account for the distribution and diversity of many Tertiary tropical and subtropical biotas.