Recorded 3rd July 2021
By Cass Lynch
Looking west from the Darling Scarp, a blue river sits in a green landscape, winding its way to the ocean. The river is fed by streams that flow over the scarp, picking up speed as gravity drags water down the slopes, flowing quickly over the hard surfaces of the ancient granite hills. When the water reaches the coastal plain it slows right down, encountering chains of dune systems oriented north south along the coast. The Swan River winds its way through the low points of these dunes, finding a narrow channel through limestone cliffs to flow to the sea.
Not long ago, the bilya, the river, was 20 kilometres longer. It flowed further west across low Country that is today is underwater. What we know as the submerged continental shelf was in fact dry land only 10,000 years ago. The island of Wadjemup, or Rottnest, today surrounded by coral reef, was a hill in a broad plain that was thickly forested with trees. In our time Rottnest is an island, and the low plains where kangaroos, emus, snakes and echidnas used to roam is now the domain of sharks, dolphins, stingrays and whales.
The reason for this change in sea level is earth’s current glacial-interglacial climate cycle. We experience an ice age every 100,000 years. During an ice age, ice sheets and glaciers draw water up out of the ocean and onto land which drops sea levels dramatically. The recent ice age was 20,000 years ago, and Noongar people had been in the southwest for 30,000 years by this point, so we watched the sea levels drop and then shivered through the long freeze that followed.
It takes a long time for the climate to cool down, but once the heat returns the warming is rapid. After the ice age Noongar mob watched the seas rise 120 metres, flooding the channel between Perth and Rottnest Island, and submerging 20 kilometres of coastline. Our Dreaming stories are located in the Nyitting, meaning ‘cold place’, and research suggests that our stories of the ‘cold times’ and the angry sea that rose after it, are in fact eyewitness accounts of these dramatic climate changes that have been passed down generation to generation. Our culture tells us that we live in a drowned world compared to our ancestors.
Country is adaptive in these gentle cycles of change. In the warm times, seagrasses move up the sandy slopes to stay in shallow water, then in the cold times they retreat back down as sea levels drop. The tuart and jarrah trees pull back as the waves approach, and the wattle and saltbush move forward, not wanting to be caught in the shade of the shifting forest.
Not every species is as swift to adapt. There are coral skeletons at the base of the submerged continental shelf, a grey graveyard of those who couldn’t climb the cliffs to populate the Rottnest plain as sea levels rose. Their community was tied to the rocks, immobile in their interlinked masses, with no choice but to watch the sun retreat and the water darken around them.
The seas are rising, as they have in the past, but something is different. The warm times should be finished, we are due to be entering the cooling phase, that long road to the next freeze. But there is too much carbon in the air and seas. Humans have enjoyed the pleasant climates of the interglacial, but our actions are warming the Earth and pushing us and Country into unknown territory.
There are deeper climates cycles sleeping under the surface of Noongar Country. 100 million years ago Perth was under 100 metres of sea water. It was the hot, carbon-rich Cretaceous, where the dry land of today was a sea floor with marine dinosaurs swimming high above. The shadows of the deep past darken our future. The fossilised bones of plesiosaurs sit in greensand deposits all around us, memory of a higher tide. Their time could come again.
Future, past. Exposed, submerged. In the cycles of deep time, the Swan Coastal Plain is an inbetween place, a dampland drenched in dreams both dry and drowned. Blink and the birds above turn to sting rays. Breathe and the wind becomes the waves.