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ENSO influence on Holocene Aboriginal populations in Queensland, Australia
Journal of Archaeological Science 33 (2006) 1744e1748 http://www.elsevier.com/locate/jas
ENSO influence on Holocene Aboriginal populations in Queensland, Australia Chris S.M. Turney*, Douglas Hobbs GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia Received 10 November 2005; received in revised form 6 March 2006; accepted 16 March 2006
Abstract In the Pacific region, the onset of modern El Nin˜o/Southern Oscillation (ENSO) activity at approximately 5000 years ago may have played a significant role in the development of cultures in the Pacific basin. Within Australia, similar trends in population and resource use have been identified but largely ascribed to cultural changes. To test human responses to changing ENSO activity through the Holocene we analysed a comprehensive suite of 710 radiocarbon ages from archaeological sites in ENSO-sensitive Queensland. We observe a dramatic and sustained increase in landscape activity at inland sites from 4860 15 years ago, statistically indistinguishable from the timing of the onset of modern ENSO activity. Subsequent changes in long-term activity directly impacted on human populations indicating that once established, ENSO maintained a continuous influence on disparate cultures throughout the Pacific basin. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Pacific Ocean El Nin˜o/Southern Oscillation; Mid-Holocene cultural and archaeological change; Resource use; Landscape management; Fire; Rainforest culture
1. Introduction The changing dynamics of the atmosphereeocean system driven by the El Nin˜o/Southern Oscillation (ENSO) has received considerable research interest in attempting to understand past climatic, environmental and archaeological changes [9,12,22,27]. Major climatic perturbations associated with the ENSO phenomenon are known to have taken place at a range of different timescales, including the last glaciale interglacial cycle [30,31], the mid-Holocene [10], and in the recent past [15,23]. In the Pacific region, the onset of modern ENSO activity appears to have commenced approximately 5000 years ago [18,20,25], thousands of years after human populations became established over much of the region [1,19,20,28,32].
* Corresponding author. Fax: þ61 2 42214250. E-mail address: [email protected] (C.S.M. Turney). 0305-4403/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2006.03.007
Forcing changes in human settlement and resource use, the onset of ‘modern’ ENSO activity may have played a significant role in the development of eastern Pacific cultures [27,29]. Within Australia, similar trends in population and resource use have been identified but largely ascribed to cultural changes, such as stone tool development, economic intensification, changes in settlement patterns and/or exploitation of seashore resources [16,21,27]. Although these all have merit in explaining different aspects of the Australian archaeological record, the potential role of environmental change in contributing to these developments has been often neglected or relegated to a minor role (for exceptions see [8,12,26]). During El Nin˜o episodes, a northward movement of the Inter-Tropical Convergence Zone and a northeastward migration of the South Pacific Convergence Zone results in a significant decrease in summer precipitation (typically 150e300 mm below seasonal average) over much of Queensland [5,11,18], making it extremely sensitive to changes in ENSO activity. Furthermore, Queensland has a rich archaeological record spanning over 35,000 years [6] that has been
C.S.M. Turney, D. Hobbs / Journal of Archaeological Science 33 (2006) 1744e1748
extensively radiocarbon dated since the 1960s, providing an excellent opportunity to test hypotheses regarding human responses to ENSO variability in the southwest Pacific region. 2. Methods A principal indicator of mid-Holocene change in Australian Aboriginal activity is the significant increase in the number of radiocarbon ages reported from archaeological contexts. Although this has often been interpreted as reflecting a major population increase [21], it is unlikely that a simple relationship exists between population and the number of radiocarbon ages. Although a precise interpretation is probably not possible, the increased number of ages from the mid-Holocene most probably reflects greater activity in the landscape [12,17]; something that does not preclude an increase in population. Individual sites and the generally limited number of associated radiocarbon ages, however, make it difficult to precisely date the onset of increased activity and test whether the timing was synchronous within and across Australia. Where compilations of radiocarbon ages have been investigated they have largely been undertaken on an uncalibrated timescale [12,17], precluding robust comparisons to independentlydated reconstructions of change outside Australia. To test human responses to changing ENSO activity through the Holocene [20] we analysed a comprehensive suite of radiocarbon ages obtained from Queensland archaeological contexts (Fig. 1) [33,34]. A total of 710 radiocarbon ages were calibrated to 2s using the IntCal04 and Marine04 datasets [24] with a Southern Hemisphere offset of 40 13 years and the probabilities of individual age distributions for the separate categories summed and normalised to unit area using CALIB5. Sites were independently categorised as inland and
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coastal (<1 km from present day coastline) [33,34], with the latter separated according to marine (e.g. marine shells) or terrestrial (e.g. charcoal) as a measure of resource use. No selection criteria were used for the available radiocarbon ages; the large number in this study precludes significant skewing of the dataset and provides an excellent opportunity to identify longterm trends. For marine samples, the ages were calibrated against Marine04 with a DR for the east central Australian coast of 12 6 years. All ages are given as calibrated years before AD 1950. 3. Holocene changes in landscape activity and ENSO variability Elevated probability values from 4860 15 years ago indicate a marked increase in landscape activity at inland sites (Fig. 2A), possibly as a result of a significant expansion in the Aboriginal population. Prior to this time, relatively little activity is recognised, which we interpret to reflect a low population density. Activity at coastal locations occurs significantly later in time, however. A small change in probability values at coastal locations characterised by a dominance of terrestrial resource use is broadly coincident with the time of inland expansion (Fig. 2B) but only significantly increases from 3210 10 years ago. In contrast, coastal locations characterised by a dominance of marine resource use (Fig. 2C) are not intensively utilised until much later, with the first significant sustained period of increase commencing around 2140 years ago and culminating 1400 years ago. From this time, there is an almost exponential expansion in activity in both inland and coastal locations (Fig. 2). Differences in the timing of expansion recognised here as a result of sampling bias can be discounted. Any continental shelf population
INDO–PACIFIC WARM POOL
N
INDO–PACIFIC WARM POOL
ITCZ ITCZ
EAC
EAC
0
1000 km
Fig. 1. Location of sites and atmospheric circulation during the austral summer with annual mean location of ocean masses [5,9,33]. Site locations are shown as solid circles. ‘ITCZ’ denotes Inter-Tropical Convergence Zone and ‘EAC’ denotes East Australian Current.
C.S.M. Turney, D. Hobbs / Journal of Archaeological Science 33 (2006) 1744e1748
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A
0.0007
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Onset of modern
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Queensland inland probabilities (n=382)
0.0006 0.0005 0.0004 0.0003 0.0002 0.0001
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0
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10
0 0.0008
0.0010 0.0006
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Probability (n=710)
Queensland marine (terrestrial) probability (n=126)
B
ENSO activity
30
0.0006
0.0004
0.0004
Greater activity in landscape?
0.0002
0.0002
0 0.00100
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Major expansion in population?
Queensland coastal (marine) probability (n=202)
0
1
2
3
4
5
6
7
8
9 10 11 12
Calibrated years BP 0.00075
Fig. 3. Changes in (A) the number of ENSO events per 100 years through the Holocene [20] and (B) summed probabilities of all Holocene calibrated Queensland archaeological radiocarbon ages. Modern ENSO activity shown as solid line in (A). Grey zonation denotes major periods of sustained modern ENSO activity and associated increases in human activity across Queensland.
0.00050
of the events appears to follow a millennial-scale periodicity from 5000 years ago with subsequent peaks centred on 3800, 2500 and a major sustained increase around 1000 years ago, all coincident with similar phases in ENSO activity [20].
0.00025
0 0
1
2
3
4
5
6
7
8
9 10 11 12
Calibrated years BP Fig. 2. Comparison between the summed probability plots of Queensland (A) inland, (B) coastal (terrestrial) and (C) coastal (marine) Holocene radiocarbon ages [33,34]. Grey zonation denotes inferred significant increases in Queensland populations within (I) inland, (II) coastal (terrestrial) and (III) coastal (marine) locations.
increase prior to the mid-Holocene would have generated the opposite pattern to that observed following sea level stabilisation in the region 5800 years ago [14]. Summing the probabilities of the different site locations (Fig. 3), we find that the increase in Queensland values is statistically indistinguishable from the onset of modern ENSO conditions reported for the mid-Holocene [20]. The timing
4. Potential effects of ENSO activity on resource exploitation An increased frequency of ‘warm’ ENSO events from the mid-Holocene appears to have led to a considerable increase in activity in the landscape. A shift to more frequent ENSO activity would have led to drier conditions across Queensland [5], implying a reduction in the carrying capacity of the land. There are several mechanisms, however, by which subsistence strategies may have been adapted to effect greater resource exploitation. An increased frequency of ‘warm’ ENSO events in the mid-Holocene would have greatly increased the efficacy of using fire as a regime for managing the inland landscape of Queensland, improving hunting success rates and
C.S.M. Turney, D. Hobbs / Journal of Archaeological Science 33 (2006) 1744e1748
regenerating plant food [8]. In areas of rainforest, expansion of this vegetation type would have been limited from this time. The drier conditions in combination with increased burning in the landscape would have led to the fragmentation and opening up of rainforest [18] and increased the populations of certain marsupial species [13] potentially allowing greater exploitation of a resource not previously used significantly by indigenous peoples. Such a scenario is consistent with the mid-Holocene development of the first Australian rainforest culture populations at this time [3]. The implied role of ENSO activity suggests that Australian Aboriginal tropical rainforest culture developed independently of other Pacific areas as an adaptation to changing environmental conditions. With the onset of modern ENSO activity and the adaptation of subsistence strategies, a considerably greater expansion appears to have taken place, implying increasing movement of people across the landscape. Strategic lessons were probably learnt in resource exploitation to sustain a continued expansion that eventually translated into greater colonization and exploitation of coastal locations. The increased use of coastal areas occurred at broadly the same time as subsequent changes recorded at inland locations, suggesting an ENSO link. Resource-rich coastal locations, such as mangroves, had developed significantly earlier than the changes reported here [4] but the onset of modern ENSO activity would have resulted in reduced flooding [9] and muted changes in daily sea level [2,7]. These might have allowed longer periods for more sustained exploitation of the inter-tidal zone that were sufficient to support intensified activity in these areas. Although strategic lessons must have been learnt, periodic changes in ENSO after 5000 years ago appear to have been sufficient to have directly impacted on the activity in the landscape. During periods of reduced ENSO activity, there are substantial decreases in the probability distribution of calibrated radiocarbon ages (Fig. 3), implying less need to forage as widely across the landscape at these times. Aboriginal populations therefore appear to have successfully adapted to and exploited changing ENSO variability, utilising larger areas of land and resulting in greater activity in the landscape. Future work is now critical to refine the selection and calibration of radiocarbon datasets to determine whether such patterns are manifested across Australia, particularly during earlier periods of known changing ENSO activity [6,31]. 5. Conclusions The onset of modern El Nin˜o/Southern Oscillation (ENSO) activity at approximately 5000 years ago is believed to have played a significant role in the development of cultures in the eastern Pacific basin, but is largely discounted when interpreting change in the Australian archaeological record. By analysing Queensland radiocarbon dated archaeological sequences as a proxy of Aboriginal activity in the landscape, we show a dramatic and sustained increase coincided with the onset of modern ENSO activity. The increasingly variable climate appear to have forced populations to develop new and varied strategies for survival and unwittingly this may have
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provided the necessary platform to enable populations to more efficiently extract energy from the environment, potentially supporting a larger population. Subsequent changes mirror ENSO variability and indicate that once established, ENSO maintained a continuous influence on populations throughout the Pacific basin. Acknowledgements CSMT acknowledges the provision of a Queen Elizabeth II Fellowship from the Australian Research Council. Many thanks to numerous colleagues for informative discussions on the above issues. References [1] J.M. Bowler, H. Johnston, J.M. Olley, J.R. Prescott, R.G. Roberts, W. Shawcross, N.A. Spooner, New ages for human occupation and climatic change at Lake Mungo, Australia, Nature 421 (2003) 837e840. [2] J.A. Church, J. Hunter, K. McInnes, N.J. White, Sea-level rise and the frequency of extreme event around the Australian coastline, Proceedings of Coast to Coast 2004, Hobart, 2004. [3] R. Cosgrove, Origin and development of Australian Aboriginal tropical rainforest culture: a reconsideration, Antiquity 70 (1996) 900e912. [4] G.M. Crowley, M.K. Gagan, Holocene evolution of coastal wetlands in wet-tropical northeastern Australia, The Holocene 5 (1995) 385e399. [5] A. Dai, T.M.L. Wigley, Global patterns of ENSO-induced precipitation, Geophysical Research Letters 27 (2000) 1283e1286. [6] B. David, R. Roberts, C. Tuniz, R. Jones, J. Head, New optical and radiocarbon dates from Ngarrabullgan Cave, a Pleistocene archaeological site in Australia: implications for the comparability of time clocks and for the human colonisation of Australia, Antiquity 71 (1997) 183e188. [7] M. Feng, Y. Li, G. Meyers, Multidecadal variations of Fremantle sea level: footprint of climate variability in the tropical Pacific, Geophysical Research Letters 31 (2004). doi:10.1029/2004GL019947. [8] T. Flannery, The Future Eaters. Reed New Holland, Sydney, 1997. [9] M.K. Gagan, E.J. Hendy, S.G. Haberle, W.S. Hantoro, Post-glacial evolution of the Indo-Pacific Warm Pool and El Nin˜o-Southern Oscillation, Quaternary International 118e119 (2004) 127e143. [10] M.K. Gagan, L.K. Ayliffe, J.W. Beck, J.E. Cole, E.R.M. Druffel, R.B. Dunbar, D.P. Schrag, New views of tropical paleoclimates from corals, Quaternary Science Reviews 19 (2000) 45e64. [11] C.R. Godfred-Spenning, C.J.C. Reason, Interannual variability of lowertropospheric moisture transport during the Australian Monsoon, International Journal of Climatology 22 (2002) 509e532. [12] S.G. Haberle, B. David, Climates of change: human dimensions of Holocene environmental change in low latitudes of the PEPII transect, Quaternary International 118e119 (2004) 165e179. [13] J. Kanowski, M.S. Hopkins, H. Marsh, J.W. Winter, Ecological correlates of folivore abundance in north Queensland rainforests, Wildlife Research 28 (2001) 1e8. [14] K. Lambeck, J. Chappell, Sea level change through the last glacial cycle, Science 292 (2001) 679e686. [15] N.K. Larkin, D.E. Harris, ENSO warm (El Nino) and cold (La Nina) event life cycles: ocean surface anomaly patterns, their symmetries, asymmetries and implications, Journal of Climate 15 (2002) 1118e1141. [16] H. Lourandos, Continent of hunter-gatherers: new perspectives in Australian prehistory, Cambridge University Press, Cambridge, 1997. [17] H. Lourandos, B. David, Long-term archaeological and environmental trends: a comparison from late Pleistocene-Holocene Australia, in: P. Kershaw, B. David, N. Tapper, D. Penny, J. Brown (Eds.), Bridging Wallace’s Line: The Environmental and Cultural History and Dynamics of the SE-Asian-Australian Region, Advances in Geoecology 34, Catena Verlag, Reiskirchen, 2002, pp. 307e339.
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[18] M.S. McGlone, A.P. Kershaw, V. Markgraf, El Nin˜o/Southern Oscillation climatic variability in Australasian and South American palaeoenvironmental records, in: H.F. Diaz, V. Markgraf (Eds.), El Nin˜o: Historical and Paleoclimatic Aspects of the Southern Oscillation, Cambridge University Press, Cambridge, 1992, pp. 435e462. [19] D.J. Meltzer, Monte Verde and the Pleistocene peopling of the Americas, Science 276 (1997) 754e755. [20] C.M. Moy, G.O. Seltzer, D.T. Rodbell, D.M. Anderson, Variability of El Nin˜o/Southern Oscillation activity at millennial timescales during the Holocene epoch, Nature 420 (2002) 162e165. [21] J. Mulvaney, J. Kamminga, Prehistory of Australia, Allen & Unwin, Crows Nest, 1999. [22] C. Pelejero, E. Calvo, G.A. Logan, P. De Deckker, Marine isotopic stage 5e in the Southwest Pacific: similarities with Antarctica and ENSO inferences, Geophysical Research Letters 30 (2003). doi:10.1029/ 2003GL018191. [23] W.H. Quinn, V.T. Neal, S.E.A. de Mayolo, El Nin˜o occurrences over the past four and a half centuries, Journal of Geophysical Research 92 (1987) 14449e14461. [24] P.J. Reimer, M.G.L. Baillie, E. Bard, A. Bayliss, J.W. Beck, C.J.H. Bertrand, P.G. Blackwell, C.E. Buck, G.S. Burr, K.B. Cutler, P.E. Damon, R.L. Edwards, R.G. Fairbanks, M. Friedrich, T.P. Guilderson, A.H. Hogg, K.A. Hughen, B. Kromer, IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP, Radiocarbon 46 (2004) 1029e1058. [25] D.T. Rodbell, G.O. Seltzer, D.M. Anderson, M.B. Abbott, D.B. Enfield, J.H. Newman, An w15,000-year record of El Nin˜o-driven alluviation in southwestern Ecuador, Science 283 (1999) 516e520.
[26] M.J. Rowland, Holocene environmental variability: have its impacts been underestimated in Australian pre-History? The Artefact 22 (1999) 11e48. [27] D.H. Sandweiss, K.A. Maasch, D.G. Anderson, Transitions in the midHolocene, Science 283 (1999) 499e500. [28] D.H. Sandweiss, H. McInnis, R.L. Burger, A. Cano, B. Ojeda, R. Paredes, M. del Carmen Sandweiss, M.D. Glascock, Quebrada Jaguay: early South American maritime adaptions, Science 281 (1998) 1830e1832. [29] D.H. Sandweiss, K.A. Maasch, F. Chai, C.F.T. Andrus, E.J. Reitz, Geoarchaeological evidence for multidecadal natural climatic variability and ancient Peruvian fisheries, Quaternary Research 61 (2004) 330e334. [30] A.W. Tudhope, C.P. Chilcott, M.T. McCulloch, E.R. Cook, J. Chappell, R.M. Ellam, D.W. Lea, J.M. Lough, G.B. Shimmield, Variability in the El Nin˜o-Southern Oscillation through a glacial-interglacial cycle, Science 291 (2001) 1511e1517. [31] C.S.M. Turney, A.P. Kershaw, S.C. Clemens, N. Branch, P.T. Moss, L.K. Fifield, Millennial and orbital variations of El Nin˜o/Southern Oscillation and high-latitude climate in the last glacial period, Nature 428 (2004) 306e310. [32] C.S.M. Turney, M.I. Bird, L.K. Fifield, R.G. Roberts, M.A. Smith, C.E. Dortch, R. Gru¨n, E. Lawson, L.K. Ayliffe, G.H. Miller, J. Dortch, R.G. Cresswell, Early human occupation at Devil’s Lair, southwestern Australia 50,000 years age, Quaternary Research 55 (2001) 3e13. [33] S. Ulm, J. Reid, Index of dates from archaeological sites in Queensland, Queensland Archaeological Research 12 (2000) 1e129. [34] S. Ulm, J. Reid, Index of dates from archaeological sites in Queensland: Upgrade version 1.4. Retrieved from:, 2004.
ENSO influence on Holocene Aboriginal populations in Queensland, Australia Chris S.M. Turney*, Douglas Hobbs GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia Received 10 November 2005; received in revised form 6 March 2006; accepted 16 March 2006
Abstract In the Pacific region, the onset of modern El Nin˜o/Southern Oscillation (ENSO) activity at approximately 5000 years ago may have played a significant role in the development of cultures in the Pacific basin. Within Australia, similar trends in population and resource use have been identified but largely ascribed to cultural changes. To test human responses to changing ENSO activity through the Holocene we analysed a comprehensive suite of 710 radiocarbon ages from archaeological sites in ENSO-sensitive Queensland. We observe a dramatic and sustained increase in landscape activity at inland sites from 4860 15 years ago, statistically indistinguishable from the timing of the onset of modern ENSO activity. Subsequent changes in long-term activity directly impacted on human populations indicating that once established, ENSO maintained a continuous influence on disparate cultures throughout the Pacific basin. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Pacific Ocean El Nin˜o/Southern Oscillation; Mid-Holocene cultural and archaeological change; Resource use; Landscape management; Fire; Rainforest culture
1. Introduction The changing dynamics of the atmosphereeocean system driven by the El Nin˜o/Southern Oscillation (ENSO) has received considerable research interest in attempting to understand past climatic, environmental and archaeological changes [9,12,22,27]. Major climatic perturbations associated with the ENSO phenomenon are known to have taken place at a range of different timescales, including the last glaciale interglacial cycle [30,31], the mid-Holocene [10], and in the recent past [15,23]. In the Pacific region, the onset of modern ENSO activity appears to have commenced approximately 5000 years ago [18,20,25], thousands of years after human populations became established over much of the region [1,19,20,28,32].
* Corresponding author. Fax: þ61 2 42214250. E-mail address: [email protected] (C.S.M. Turney). 0305-4403/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2006.03.007
Forcing changes in human settlement and resource use, the onset of ‘modern’ ENSO activity may have played a significant role in the development of eastern Pacific cultures [27,29]. Within Australia, similar trends in population and resource use have been identified but largely ascribed to cultural changes, such as stone tool development, economic intensification, changes in settlement patterns and/or exploitation of seashore resources [16,21,27]. Although these all have merit in explaining different aspects of the Australian archaeological record, the potential role of environmental change in contributing to these developments has been often neglected or relegated to a minor role (for exceptions see [8,12,26]). During El Nin˜o episodes, a northward movement of the Inter-Tropical Convergence Zone and a northeastward migration of the South Pacific Convergence Zone results in a significant decrease in summer precipitation (typically 150e300 mm below seasonal average) over much of Queensland [5,11,18], making it extremely sensitive to changes in ENSO activity. Furthermore, Queensland has a rich archaeological record spanning over 35,000 years [6] that has been
C.S.M. Turney, D. Hobbs / Journal of Archaeological Science 33 (2006) 1744e1748
extensively radiocarbon dated since the 1960s, providing an excellent opportunity to test hypotheses regarding human responses to ENSO variability in the southwest Pacific region. 2. Methods A principal indicator of mid-Holocene change in Australian Aboriginal activity is the significant increase in the number of radiocarbon ages reported from archaeological contexts. Although this has often been interpreted as reflecting a major population increase [21], it is unlikely that a simple relationship exists between population and the number of radiocarbon ages. Although a precise interpretation is probably not possible, the increased number of ages from the mid-Holocene most probably reflects greater activity in the landscape [12,17]; something that does not preclude an increase in population. Individual sites and the generally limited number of associated radiocarbon ages, however, make it difficult to precisely date the onset of increased activity and test whether the timing was synchronous within and across Australia. Where compilations of radiocarbon ages have been investigated they have largely been undertaken on an uncalibrated timescale [12,17], precluding robust comparisons to independentlydated reconstructions of change outside Australia. To test human responses to changing ENSO activity through the Holocene [20] we analysed a comprehensive suite of radiocarbon ages obtained from Queensland archaeological contexts (Fig. 1) [33,34]. A total of 710 radiocarbon ages were calibrated to 2s using the IntCal04 and Marine04 datasets [24] with a Southern Hemisphere offset of 40 13 years and the probabilities of individual age distributions for the separate categories summed and normalised to unit area using CALIB5. Sites were independently categorised as inland and
1745
coastal (<1 km from present day coastline) [33,34], with the latter separated according to marine (e.g. marine shells) or terrestrial (e.g. charcoal) as a measure of resource use. No selection criteria were used for the available radiocarbon ages; the large number in this study precludes significant skewing of the dataset and provides an excellent opportunity to identify longterm trends. For marine samples, the ages were calibrated against Marine04 with a DR for the east central Australian coast of 12 6 years. All ages are given as calibrated years before AD 1950. 3. Holocene changes in landscape activity and ENSO variability Elevated probability values from 4860 15 years ago indicate a marked increase in landscape activity at inland sites (Fig. 2A), possibly as a result of a significant expansion in the Aboriginal population. Prior to this time, relatively little activity is recognised, which we interpret to reflect a low population density. Activity at coastal locations occurs significantly later in time, however. A small change in probability values at coastal locations characterised by a dominance of terrestrial resource use is broadly coincident with the time of inland expansion (Fig. 2B) but only significantly increases from 3210 10 years ago. In contrast, coastal locations characterised by a dominance of marine resource use (Fig. 2C) are not intensively utilised until much later, with the first significant sustained period of increase commencing around 2140 years ago and culminating 1400 years ago. From this time, there is an almost exponential expansion in activity in both inland and coastal locations (Fig. 2). Differences in the timing of expansion recognised here as a result of sampling bias can be discounted. Any continental shelf population
INDO–PACIFIC WARM POOL
N
INDO–PACIFIC WARM POOL
ITCZ ITCZ
EAC
EAC
0
1000 km
Fig. 1. Location of sites and atmospheric circulation during the austral summer with annual mean location of ocean masses [5,9,33]. Site locations are shown as solid circles. ‘ITCZ’ denotes Inter-Tropical Convergence Zone and ‘EAC’ denotes East Australian Current.
C.S.M. Turney, D. Hobbs / Journal of Archaeological Science 33 (2006) 1744e1748
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A
0.0007
III
II
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I
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Onset of modern
ENSO events per 100 years
Queensland inland probabilities (n=382)
0.0006 0.0005 0.0004 0.0003 0.0002 0.0001
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0
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0.0012
20
10
0 0.0008
0.0010 0.0006
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Queensland marine (terrestrial) probability (n=126)
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ENSO activity
30
0.0006
0.0004
0.0004
Greater activity in landscape?
0.0002
0.0002
0 0.00100
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Major expansion in population?
Queensland coastal (marine) probability (n=202)
0
1
2
3
4
5
6
7
8
9 10 11 12
Calibrated years BP 0.00075
Fig. 3. Changes in (A) the number of ENSO events per 100 years through the Holocene [20] and (B) summed probabilities of all Holocene calibrated Queensland archaeological radiocarbon ages. Modern ENSO activity shown as solid line in (A). Grey zonation denotes major periods of sustained modern ENSO activity and associated increases in human activity across Queensland.
0.00050
of the events appears to follow a millennial-scale periodicity from 5000 years ago with subsequent peaks centred on 3800, 2500 and a major sustained increase around 1000 years ago, all coincident with similar phases in ENSO activity [20].
0.00025
0 0
1
2
3
4
5
6
7
8
9 10 11 12
Calibrated years BP Fig. 2. Comparison between the summed probability plots of Queensland (A) inland, (B) coastal (terrestrial) and (C) coastal (marine) Holocene radiocarbon ages [33,34]. Grey zonation denotes inferred significant increases in Queensland populations within (I) inland, (II) coastal (terrestrial) and (III) coastal (marine) locations.
increase prior to the mid-Holocene would have generated the opposite pattern to that observed following sea level stabilisation in the region 5800 years ago [14]. Summing the probabilities of the different site locations (Fig. 3), we find that the increase in Queensland values is statistically indistinguishable from the onset of modern ENSO conditions reported for the mid-Holocene [20]. The timing
4. Potential effects of ENSO activity on resource exploitation An increased frequency of ‘warm’ ENSO events from the mid-Holocene appears to have led to a considerable increase in activity in the landscape. A shift to more frequent ENSO activity would have led to drier conditions across Queensland [5], implying a reduction in the carrying capacity of the land. There are several mechanisms, however, by which subsistence strategies may have been adapted to effect greater resource exploitation. An increased frequency of ‘warm’ ENSO events in the mid-Holocene would have greatly increased the efficacy of using fire as a regime for managing the inland landscape of Queensland, improving hunting success rates and
C.S.M. Turney, D. Hobbs / Journal of Archaeological Science 33 (2006) 1744e1748
regenerating plant food [8]. In areas of rainforest, expansion of this vegetation type would have been limited from this time. The drier conditions in combination with increased burning in the landscape would have led to the fragmentation and opening up of rainforest [18] and increased the populations of certain marsupial species [13] potentially allowing greater exploitation of a resource not previously used significantly by indigenous peoples. Such a scenario is consistent with the mid-Holocene development of the first Australian rainforest culture populations at this time [3]. The implied role of ENSO activity suggests that Australian Aboriginal tropical rainforest culture developed independently of other Pacific areas as an adaptation to changing environmental conditions. With the onset of modern ENSO activity and the adaptation of subsistence strategies, a considerably greater expansion appears to have taken place, implying increasing movement of people across the landscape. Strategic lessons were probably learnt in resource exploitation to sustain a continued expansion that eventually translated into greater colonization and exploitation of coastal locations. The increased use of coastal areas occurred at broadly the same time as subsequent changes recorded at inland locations, suggesting an ENSO link. Resource-rich coastal locations, such as mangroves, had developed significantly earlier than the changes reported here [4] but the onset of modern ENSO activity would have resulted in reduced flooding [9] and muted changes in daily sea level [2,7]. These might have allowed longer periods for more sustained exploitation of the inter-tidal zone that were sufficient to support intensified activity in these areas. Although strategic lessons must have been learnt, periodic changes in ENSO after 5000 years ago appear to have been sufficient to have directly impacted on the activity in the landscape. During periods of reduced ENSO activity, there are substantial decreases in the probability distribution of calibrated radiocarbon ages (Fig. 3), implying less need to forage as widely across the landscape at these times. Aboriginal populations therefore appear to have successfully adapted to and exploited changing ENSO variability, utilising larger areas of land and resulting in greater activity in the landscape. Future work is now critical to refine the selection and calibration of radiocarbon datasets to determine whether such patterns are manifested across Australia, particularly during earlier periods of known changing ENSO activity [6,31]. 5. Conclusions The onset of modern El Nin˜o/Southern Oscillation (ENSO) activity at approximately 5000 years ago is believed to have played a significant role in the development of cultures in the eastern Pacific basin, but is largely discounted when interpreting change in the Australian archaeological record. By analysing Queensland radiocarbon dated archaeological sequences as a proxy of Aboriginal activity in the landscape, we show a dramatic and sustained increase coincided with the onset of modern ENSO activity. The increasingly variable climate appear to have forced populations to develop new and varied strategies for survival and unwittingly this may have
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provided the necessary platform to enable populations to more efficiently extract energy from the environment, potentially supporting a larger population. Subsequent changes mirror ENSO variability and indicate that once established, ENSO maintained a continuous influence on populations throughout the Pacific basin. Acknowledgements CSMT acknowledges the provision of a Queen Elizabeth II Fellowship from the Australian Research Council. Many thanks to numerous colleagues for informative discussions on the above issues. References [1] J.M. Bowler, H. Johnston, J.M. Olley, J.R. Prescott, R.G. Roberts, W. Shawcross, N.A. Spooner, New ages for human occupation and climatic change at Lake Mungo, Australia, Nature 421 (2003) 837e840. [2] J.A. Church, J. Hunter, K. McInnes, N.J. White, Sea-level rise and the frequency of extreme event around the Australian coastline, Proceedings of Coast to Coast 2004, Hobart, 2004. [3] R. Cosgrove, Origin and development of Australian Aboriginal tropical rainforest culture: a reconsideration, Antiquity 70 (1996) 900e912. [4] G.M. Crowley, M.K. Gagan, Holocene evolution of coastal wetlands in wet-tropical northeastern Australia, The Holocene 5 (1995) 385e399. [5] A. Dai, T.M.L. Wigley, Global patterns of ENSO-induced precipitation, Geophysical Research Letters 27 (2000) 1283e1286. [6] B. David, R. Roberts, C. Tuniz, R. Jones, J. Head, New optical and radiocarbon dates from Ngarrabullgan Cave, a Pleistocene archaeological site in Australia: implications for the comparability of time clocks and for the human colonisation of Australia, Antiquity 71 (1997) 183e188. [7] M. Feng, Y. Li, G. Meyers, Multidecadal variations of Fremantle sea level: footprint of climate variability in the tropical Pacific, Geophysical Research Letters 31 (2004). doi:10.1029/2004GL019947. [8] T. Flannery, The Future Eaters. Reed New Holland, Sydney, 1997. [9] M.K. Gagan, E.J. Hendy, S.G. Haberle, W.S. Hantoro, Post-glacial evolution of the Indo-Pacific Warm Pool and El Nin˜o-Southern Oscillation, Quaternary International 118e119 (2004) 127e143. [10] M.K. Gagan, L.K. Ayliffe, J.W. Beck, J.E. Cole, E.R.M. Druffel, R.B. Dunbar, D.P. Schrag, New views of tropical paleoclimates from corals, Quaternary Science Reviews 19 (2000) 45e64. [11] C.R. Godfred-Spenning, C.J.C. Reason, Interannual variability of lowertropospheric moisture transport during the Australian Monsoon, International Journal of Climatology 22 (2002) 509e532. [12] S.G. Haberle, B. David, Climates of change: human dimensions of Holocene environmental change in low latitudes of the PEPII transect, Quaternary International 118e119 (2004) 165e179. [13] J. Kanowski, M.S. Hopkins, H. Marsh, J.W. Winter, Ecological correlates of folivore abundance in north Queensland rainforests, Wildlife Research 28 (2001) 1e8. [14] K. Lambeck, J. Chappell, Sea level change through the last glacial cycle, Science 292 (2001) 679e686. [15] N.K. Larkin, D.E. Harris, ENSO warm (El Nino) and cold (La Nina) event life cycles: ocean surface anomaly patterns, their symmetries, asymmetries and implications, Journal of Climate 15 (2002) 1118e1141. [16] H. Lourandos, Continent of hunter-gatherers: new perspectives in Australian prehistory, Cambridge University Press, Cambridge, 1997. [17] H. Lourandos, B. David, Long-term archaeological and environmental trends: a comparison from late Pleistocene-Holocene Australia, in: P. Kershaw, B. David, N. Tapper, D. Penny, J. Brown (Eds.), Bridging Wallace’s Line: The Environmental and Cultural History and Dynamics of the SE-Asian-Australian Region, Advances in Geoecology 34, Catena Verlag, Reiskirchen, 2002, pp. 307e339.
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