FACT SHEETS

Getting to the bottom of 200,000 years of history

24.10.18 by Zoë Taylor

ALMOST 20 metres of sediment from the bed of a Northern Territory lagoon with, the potential to unlock vital clues to our environment and human history, have been retrieved by CABAH researchers.

Girraween Lagoon, near Darwin, is a significant Aboriginal site and gained a place in modern Australian popular culture as a location for filming the iconic water bottle scene in Crocodile Dundee. Now, sediment from the 400m diameter lagoon could provide new insights to deep history of the region.

Time capsules

A team of researchers, led by Professor Michael Bird from James Cook University, used a custom-made raft to float a rig to the middle of the lagoon. Over five days, they harnessed the power of a hydraulic jack hammer, to drive a series of plastic tubes into the lagoon bed.

Preparing the raft and rig on Girraween Lagon
SEDIMENT CORES
It took five days to hammer almost 20 metres into the lagoon bed
CLIMATE CHANGE
The cores hold vital clues to past environments and climates

“It’s like a tape recorder looking back into the past."


By repeatedly hammering in one and two-metre tubes, to the depth of almost 20 meters, they retrieved a collection of sediment cores that contain environmental evidence over a vast period of time beyond the last Ice Age.

“It’s like a tape recorder looking back into the past – the further you go into the sediment, the further you go back in time,” explained Prof Bird, a geologist and leader of the CABAH Landscapes theme.

“We can see the interval when humans were first in the area. So, in due course, we will be able to learn more about the environment they were inhabiting.”

Core research

The cores, frozen and cut into half metre lengths, represent a “brilliant record” of the past and will be closely examined over the next two years, Prof Bird added.

In the laboratory, they can be sliced again and anaylsed to look for chemical evidence of environmental changes such as vegetation, fires and rainfall.

Dr Cassandra Rowe surveying vegetation around Girraween Lagoon

The field work took place following extensive discussions with the Traditional Owners, The Larrakia Nation. During a recent field trip, a group of young Larrakia Rangers spent time with the CABAH team, learning about the research.

Place of flowers

Girraween is an Aboriginal word, meaning ‘place of flowers. Palaeoecologist Dr Cassandra Rowe has been monitoring vegetation in and around the lagoon and is excited at the prospect of examining pollen grains from the sediment cores.

Working with slices of about two cubic centimeters, Dr Rowe, who is based at JCU, is able to isolate pollen grains and examine them under a microscope.

The field work took place following extensive discussions with the Traditional Owners, The Larrakia Nation. During a recent field trip, a group of young Larrakia Rangers spent time with the CABAH team, learning about the research.

Place of flowers

Girraween is an Aboriginal word, meaning ‘place of flowers. Palaeoecologist Dr Cassandra Rowe has been monitoring vegetation in and around the lagoon and is excited at the prospect of examining pollen grains from the sediment cores.

Working with slices of about two cubic centimeters, Dr Rowe, who is based at JCU, is able to isolate pollen grains and examine them under a microscope.

Under the microscope

The microscopic clues can will be used to piece together the answers to fundamental questions about the past, such as the impact of human arrival, megafauna extinction and whether the climate during the last interglacial period 130,000 years ago was similar to today.

“The pollen has preserved really nicely,” Dr Rowe said. “I have around 130 different pollen types, representing different plants. The detail that gives us is quite extraordinary.”

“Pollen needs a permanently moist position to preserve well. To have this site like Girraween that’s preserved everything in great detail, providing information on vegetation structure and composition, is really exciting,” she added.

The team, including Michael Brand, Costijn Zwart, Chris Wurster and Xennephone Hadeen, bring together diverse expertise and will also use the cores to learn about past use of fire and climate change signals.

Microscopic pollen grains
Clockwise from top left – Nymphoides (waterlily), Dendrophthoe (mistletoe), Melaleuca (paperbark) and Grevillea.

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