Sea Levels and Climatic Changes
More recently, the formation of the Great Barrier Reef was driven by Sea Level and Climatic changes. Over the last 500,000 years the reef has developed as sea level has risen and fallen over multiple glacial (ice ages) and interglacial cycles (warmer periods).
In a glacial period as ice forms at polar caps and in glaciers, sea level falls, while in interglacial periods ice melts causing sea level to rise once more. During these cycles sea level could change at a rate up to 5m per thousand years. The difference in sea level between interglacial periods was up to 120m. These differences caused drastic differences in marine habitats. For example, during the ice age around 18,000 years ago, people living in the region where Cairns city is now would have had to travel 60km to reach the coastline. This also meant that Fitzroy Island was part of the mainland.
During periods of high sea level, when the continental shelf was inundated, corals were able to grow in the warm shallow waters and create reefs. During these periods, reefs accumulated at rates more than 10m per thousand years. The formation of the Great Barrier Reef has occurred throughout many such periods of reef growth. It is important to understand that reef growth only occurred during periods where conditions were conducive to coral growth and reef formation. It is estimated that coral’s have only been exposed to conditions suitable for reef formation for ~10% of the ecological time between the last two interglacial periods. The short period in which the Great Barrier Reef formed makes the huge biodiversity even more remarkable.
Image: Moore Reef
Image: Green Island
Great Barrier Reef as we know it
The great barrier reef as we know it developed during the last period of sea level rise which began around 9,500 years ago. It is estimated that the primary reef growth began around 9,000 years ago and continued until approximately 4,000 – 5,000 years ago. For the most part, the sea level on the Great Barrier Reef has been relatively stable for the last 6000 years, allowing the Great Barrier Reef to continue developing to what is present today. The geological processes that have isolated populations for thousands of years are probably still in progress today. These factors have driven evolution along with the GBR connection to coral triangle via Torres Straits and are possible explanations why the GBR is one of the most diverse coral reefs in the world.
Image: A 6000 year old shell midden on Jiigurru (Lizard Island) (Credit: Walmbaar Aboriginal Corporation).
Image: Queensland Museum. Dugout canoe with one outrigger that can hold up to 5-6 people. Taken at the mouth of Russel Heads, Yidinji Country.
Image: Traditional Owners working on traditional shields.
During the last Ice age ~ 18,000 years ago, the Traditional Owners remained connected to the land and the sea. As sea level rose Aboriginal People began a westward retreat to what is now the east coast of Australia. These major environmental changes were recorded in Dreaming stories or Dreamtime which provides insight into a vastly different landscape, for example, Fitzroy Island and Double Island were part of the mainland.
There is a long history of Traditional Owners travelling to the islands and coral reefs of the Great Barrier Reef. They built sheet bark and dugout canoes to move around their sea country. There is evidence of use of most of the islands in the GBR at varying times over the last 10,000 years. Islands were used for social, ceremonial, and political reasons as well as for hunting fish, turtles, dugongs, and gathering shell meat and crustaceans.
There are more than 70 individual Aboriginal and Torres Strait Islander Traditional Owner groups with links to the Great Barrier Reef. There is evidence of permanent occupation of islands by these groups such as extensive fish traps and shell middens. Stone artifacts such as weapons, spears and tools provide the best evidence of interactions between island and coastal groups. Stones from South Molle Island were distributed more than 170km along the Queensland coastline. More recent evidence also shows that Great Barrier Reef Traditional Owner groups had extensive seafaring knowledge and established trade routes reaching the South Pacific Islands.
During the 1800’s interactions occurred between the Traditional Owners of the GBR and the early explorers and settlers that travelled North to setup industries. These first industries included Beche-De-Mer, Red Cedar and Gold. With these interactions began the dispossession of land, disruption of culture and exploitation of Indigenous people. No doubt this was a terrible time for Indigenous communities with countless lives being lost and their connection to country and culture was being seriously fragmented and potentially lost forever. During this time some individuals (explorers, early settlers and missionaries) had compassion and admiration for the nomadic North Queensland Traditional Owners culture and documented their findings. From their works there was a real appreciation of the local Indigenous culture in the Cairns Region for several aspects including:
- Seafaring (travel for 100’s of km’s in outrigger canoes)
- Geological History
- Artistic works
- Shelter construction
- Tools and weapons
- Ceremony and spirituality
- Funeral rites and proceedings
- A thousand Miles Away, A history of North Queensland to 1920 by GC Bolton (1991) Expedition to the Great Barrier Reef 1928-1929 – Part 1 – JCU Library
- History of Cairns from the 1870s. Cairns Regional Council
- Indigenous Cultures and Contact History: Timeline, Australian Museum.
- Narrative and reports of the Queensland North-East coast expedition, 1873 by GE Dalyrmple (1874)
- The Great Barrier Reef: A Queensland Museum Discovery Guide (2013)
- The Great Barrier Reef in Time and Space: Geology and Palaeobiology The Great Barrier Reef: Biology, Environment and Management(2018)
- The Great Barrier Reef of Australia: Its products and potentialities by William Saville Kent (1982)
- The History of Green Island by Dorothy Jones (1976).
- The town that was drowned: some North Queensland memories and anecdotes. Journal of the Royal Historical Society of Queensland by Clem Llewellyn Lack (1971).
- 20 000 Years Ago, Australian Institute of Marine Science.