Geomorphological evidence for late Holocene climatic change in northern Australia

Abstract

The hypothesis that the late Holocene climate of northern Australia has been characterised by periods of reduced rainfall has been examined by constructing a detailed chronostratigraphy of climatically sensitive geomorphological sites, in particular dunefields and lake deposits. There is clear evidence of aridity during the last glacial period (c. 18,000 BP), and disturbance of coastal deposits by rising sea level until 5500 BP. Following the flooding of the shallow Sunda and Sahul shelves, the climate of northern Australia appears to have become increasingly variable with an arid trend interrupted by periods of increased rainfall between 3500 and 2800 BP, again between 2100 and 1600 BP and possibly twice during the last 1000 years. It is proposed that the dry episodes are associated with persistent, large‐scale sinking, dry south‐easterly flows over the Australian tropics inhibiting the onset of the north Australian monsoon. These are similar to flows associated with present‐day ENSO events. The pattern suggests that ENSO may be associated with a larger process which may not have begun to operate until the flooding of the shallow Sunda and Sahul shelves and the opening of the Indonesian throughflow between the Pacific and Indian oceans.