Based on the article, ‘Late Holocene climate change and human behavioural variability in the coastal wet-dry tropics of northern Australia: Evidence from a pilot study of oxygen isotopes in marine bivalve shells from archaeological sites‘, in Australian Archaeology 76 by Sally Brockwell, Ben Marwick, Patricia Bourke, Patrick Faulkner and Richard Willan.
When changes in human culture are detected archaeologically it’s often been the case that archaeologists evoke environmental and climatic changes as the causal mechanisms. But in most cases no direct or explicit link between environmental and cultural changes can be made, opening up such research to accusations of false positives and environmental determinism. In this article, Sally Brockwell and her colleagues seek to remedy this situation in the context of changes in the construction of shell mounds during the late Holocene across tropical northern Australia. The authors set out to determine whether there are indeed direct links between climatic and environment changes, and human responses in this context.
Shell mounds are distinctive cultural features in the Australian landscape. These are places where Aboriginal people disposed of the remains of shellfish, which they piled up to create large mounds, ranging in size from quite small to enormous features (such as the examples at Weipa on Cape York Peninsula). Ethnographic sources tell us that shellfish were important for the diets of Aboriginal people living near the coast and the archaeological record attests to the antiquity of shellfish as an important food resource for Aboriginal people in the past (see Bird and Bliege Bird 1997, and Meehan 1982). While mounds are usually composed of a variety of shellfish species, during the late Holocene in northern Australia most mounds comprise only of Anadara granosa (whose common name is the roughback cockle).
By focusing on shell mounds this article is of particular interest given the broad range of archaeological theories on why people chose to create these visually striking features in the landscape, and why they then stopped doing so. The archaeological evidence from across northern Australia demonstrates that shell mounding began ~3000 cal. years BP and continued until about 500 years ago, when it appears to cease in most areas. At the same time that mounding ceased there is good evidence that environmental changes had led to a decline in sandy/mudflat shell beds—the environment that the roughback cockle lives in. This evidence has led to arguments that there is a correlation between cultural changes (i.e. people eating these species and making shell mounds) and climatic uncertainty. But this link had not been adequately demonstrated.
In their research investigating the issue, Sally Brockwell and her colleagues use sclerochronological approaches, i.e. sequential stable isotope analysis; this is a common technique for reconstructing past climate and environments around the world, and can be applied to all sorts of materials, including teeth, bones, ice cores, corals and stalagnites/stalagmites. Oxygen isotope ratios of shells reflect the isotope values of the water they were growing in and can thus be a measure of the relative amount of summer monsoonal rainfall in an area, since this affects the isotope values of the water. In this context archaeologists can use this technique to identify how the shell isotope ratios reflect localised variations in temperature and rainfall.
In this study shell samples were selected from three different regions of the Northern Territory: Hope Inlet (Darwin), the Blyth River (central Arnhem Land) and Blue Mud Bay (northeastern Arnhem Land). As these shells were sourced directly from archaeological sites their analysis provides a way to establish a direct link between climatic changes and changes in human behaviour. In all three case sites, the authors found that trends in shellfish exploitation correlated to an overall trend towards aridity.
As this research is a pilot study more work will be needed to further confirm and continue to expand this line of inquiry. Already this research and its methods have important implications for future archaeological research as they demonstrate the potential of using archaeological materials to establish highly localised environmental records at the same scale as the archaeological record. Future research that looks to examine explicit links between environmental and cultural changes will indeed benefit from studies such as this.
Bird, D.W. and R.L. Bliege Bird 1997 Contemporary shellfish gathering strategies among the Meriam of the Torres Strait Islands, Australia: Testing predictions of a Central Place Foraging model. Journal of Archaeological Science 24:39–63.
Meehan, B. 1982 Shell bed to shell midden. Canberra: Australian Institute of Aboriginal Studies.
For more information on this topic see:
Andrus, C.F.T. 2011 Shell midden sclerochronology. Quaternary Science Reviews 30: 2892–2905.
Faulkner, P. 2009 Focused, intense and long-term: Evidence for granular ark (Anadara granosa) exploitation from late Holocene shell mounds of Blue Mud Bay, northern Australia. Journal of Archaeological Science 36:821–834.
Haberle, S. and A. Chepstow Lusty 2000 Can climate influence cultural development? A view through time. Environment and History 6:349–369.
Morrison, M. 2011 The shell mounds of Albatross Bay, Cape York Peninsula. Blog post retrieved 24 October 2013 <http://mickmorrison.com/?p=621>.
Szabo, K. 2002 Prehistoric Shellfish Gathering. Website retrieved 29 October 2013 <http://www.manandmollusc.net/history_food.html>.