Quaternary Palynological Records from Perched Lake Sediments, Fraser Island, Queensland, Australia: Rainforest, Forest History and Climatic Control

Abstract

Pollen, carbonised particle and chemical analysis of a 6 m core from the Old Lake Coomboo Depression, a perched lake basin situated in one of the oldest dune systems on Fraser Island, demonstrates vegetation and hydrological change through a series of glacial cycles. The pollen assemblage shifts from predominantly rainforest with Araucaria sp. (Juss.) surrounding a deep water lake at c. 600 ka, to a dryer rainforest with Podocarpus sp. (L’Herit) and an intermediate lake after c. 350 ka, to a more sclerophyllous forest until before the Last Glacial Maximum (LGM). During the Last Interglacial (c. 120 ka) and before (c. 22 ka) the LGM, Araucaria sp. pollen frequencies increase before falling dramatically, open forest appears to shift to the robust association of myrtaceous shrubs characteristic of the older dune systems to the west of the island, and lake levels fall probably below the lake floor. After the LGM, open forest returns, but Araucaria sp. pollen frequencies never recover and the lake becomes an ephemeral system with a fluctuating water-table in the Holocene. The record is interpreted as reflecting retrogressive vegetation succession driven primarily by an overall decrease in effective precipitation over, at least, the last 350 ka. The inferred long-term changes in climate have major implications for the survival of relict rainforest.