Pollen evidence from tropical Australia for the onset of an ENSO-dominated climate at c. 4000 BP

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Abstract
The Holocene climatic history of tropical northern Australia is re-examined using the recently published pollen record from Groote Eylandt to corroborate and refine previous climatic inter pretations. We identify a four-stage Holocene comprising: (1) a continuous increase in effective precipitation (EP) from the beginning of the Holocene to about 5000 BP; (2) a mid-Holocene EP maximum from about 5000 to about 4000 BP; (3) a marked decline in EP somewhere between 4000-3500 Bp; and (4) an EP recovery in the last <2000 years. The mid-Holocene EP maximum is 1000 years later than Holocene EP maxima from temperate Southern Australia and suggests that the records are decoupled at this time. We focus on pollen evidence of environmental change at c. 4000 BP, which marks a break between a continuously ameliorating (increasing EP) climate but with small mean variation in the earlier Holocene and a steady (no directional trend) but highly variable later Holocene. We believe that this break represents the first evidence from the monsoonal lowlands of northern Australia for the onset of 'modern' ENSO-dominated ocean-atmosphere interactions in the Holocene. A simple conceptual model of trans-Pacific teleconnections is presented to explain this onset and as an hypothesis for testing.