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

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.

Impact of Earth’s orbit and freshwater fluxes on Holocene climate mean seasonal cycle and ENSO characteristics

“…We present the results of the t test showing both the 5 and 10% confidence level (dotted lines). This figure shows that the reduced SST warming rate induced by insolation changes during the autumn preceding the peak warming are statistically significant from control for 9.5 Table 2 Syntheses of the different studies used to infer the changes in temperature, precipitation and variability during early to midHolocene (Stott et al 2004;Shulmeister and Lees 1995;Turney et al 2004;Riedinger et al 2002;Koutavas et al 2006;Partin et al 2007;Benway et al 2006;Kienast et al 2006;Pahnke et al 2007;Koutavas et al 2002;Tudhope et al 2001;Rodbell 1999;Moy et al 2002;Haug et al 2001;Lea et al 2000 …”

Successive phases of Holocene reef flat development: Evidence from the mid- to outer Great Barrier Reef

“…Whilst increased ENSO variability (~4-5 ka) in the Indo-Pacific remains controversial (Clement et al, 2000, Corrège et al, 2000, Cobb et al, 2013, McGregor et al, 2013, McGregor and Gagan, 2004, warmer and wetter conditions during the mid-Holocene have been identified both from fossil corals in the GBR (Gagan et al, 1998, Roche et al, 2014 and from terrestrial records from northeast Australia (Kershaw, 1976, Kershaw, 1983, Nott and Price, 1994, Shulmeister and Lees, 1995, Reeves et al, 2013. Wetter climatic conditions during the mid-Holocene would have resulted in stronger flood events and a greater annual range of salinities, particularly for the central GBR (Roche et al, 2014) located adjacent to the Burdekin River (the largest river in northeast Queensland).…”

Mid- to late-Holocene El Niño-Southern Oscillation dynamics reflected in the subtropical terrestrial realm

“…(ages in calendar years unless stated otherwise) (1,2), is thought to mark the onset of modern-day precipitation patterns in low-latitude regions. Proxy records of climate change indicate that the increased amplitude of ENSO variability had a clear impact on regional hydrological budgets of tropical parts of the Indo-Pacific region, South America, and Africa (3)(4)(5). Because the mode and intensity of ENSO varied with the orbital precession during the Holocene (6), the solar radiation budget is likely to have influenced global hydrological patterns.…”