2 minute read
Giant clams
OUR ENVIRONMENT Giant clams
Opening up climate secrets
ANSTO and the Chinese Academy of Sciences are uncovering centuries of climate history locked inside the shells of two giant clam shells confiscated by the Australian Fisheries Management Authority from fishing boats that had been illegally harvesting giant clams in Australian waters.
Weighing more than 100 kg each, the organisation’s researchers used the shells to learn more about the history of temperatures in the Arafura Sea over the past 150 years and gain a better understanding of the monsoon winds that strongly affect the climate in the North and East of Australia.
The shells played an important part in an existing collaboration between ANSTO and scientists at the Chinese Academy of Sciences in Xi’an, who have pioneered the use of giant clam shells to piece together the history of monsoons in the South China Sea. The collaboration aims to pool the expertise of ANSTO and the Academy to thoroughly understand the trends and patterns of the region’s monsoons. The work also involves analysing sediments in extinct volcano craters and stalagmites, in addition to the clam shells, to unravel tropical climate history.
Giant clams live for about 100 years. Each year, a new layer is added to their shells, like the rings on a tree. By measuring the ratio of the elements calcium and strontium in each layer, scientists can calculate the sea surface temperature at the time it was laid down.
Ocean temperatures are important for those who live on land too. By affecting winds and ocean currents, sea surface temperatures determine the levels of rainfall over the land, contributing to phenomena such as ‘the wet’, when monsoon winds bring rain to Australia’s north.
The Chinese scientists had already used both fossil and current clam shells to provide a picture of the climate in their region. One fossil shell they found was 2500 years old, providing temperature data from more than two millennia ago. ANSTO used a high-precision optical and X-ray Fluoresence Scanner to determine the number and position of the annually-added layers, formally called laminations. Then tiny samples were drilled out from within each layer and analysed, using a type of imaging known as inductively coupled plasma – atomic emission spectroscopy, to measure the calcium-to-strontium ratios.
The information that comes from examining the shells could potentially extend the sea temperature records for the Arafura Sea back to 150 years ago.
Pictured
Prof Henk Heijnis studying the giant clam shell from the Arafura Sea.
Contact
henk.heijnis@ansto.gov.au
COLLABORATORS
1
ANSTO
2
Chinese Academy of Sciences
RESEARCH FACILITY / TECHNIQUE
High-precision optical and X-ray scanner Inductively coupled plasma — atomic emission spectroscopy RESEARCHER TEAM
Prof Zhisheng AN Prof John DODSON Prof Henk HEIJNIS Prof Hong YAN
Arafura Sea
