Palaeohydrology of the Australian southern margin during Late Cretaceous cooling and the opening of the Australo-Antarctic Gulf

Abstract:

The Late Cretaceous was a greenhouse world, characterised by elevated temperatures and high atmospheric pCO₂. Even in the context of an extreme greenhouse climate, existing data from the southern high latitudes (palaeolatitude of ~60˚S) suggest anomalous warmth, with sea-surface temperatures >30°C for much of the Late Cretaceous. Warmth peaked in the Turonian, followed by slow, steady cooling through to the Maastrichtian. As temperatures decreased through the Late Cretaceous, the southern high latitudes played an increasingly important role in ocean circulation. Whilst there Is strong evidence for shrinking of the Hadley Cell during global cooling, changes in high-latitude atmospheric circulation are poorly constrained.

New TEX₈₆ data from IODP Expedition 369 shows fluctuating sea-surface temperatures in the Australo-Antarctic Gulf during separation of Australia and Antarctica, in direct contrast with slow, steady cooling seen at other sites across the world. These data suggest a varying ocean connection between the Gulf and the southern Tethys, though any influence this changing connection may have had on atmospheric circulation and precipitation is unknown.

Here we present the first Late Cretaceous leaf-wax δD record from the Australo-Antarctic Gulf (IODP Expedition 369 Site U1512). This site provides a new perspective on palaeohydrology in the southern high latitudes, during the extremes of the mid-Cretaceous and during the recovery from OAE 2. Further, this record offers an opportunity to determine a link between global change and regional precipitation patterns and investigate the relative influence of regional and global temperatures on palaeohydrology.