Giant clam shell revealed Great Barrier Reef's climate 200 years ago
Scientists decoded a clam shell to show summers at the reef were 0.6-1.2°C cooler in the 1800s than today.
When a giant clam grows, it records its life story in its shell, like tree rings. Researchers studied a 58-centimetre clam that lived from 1785 to 1827 at Jiigurru (Lizard Island Group) in the northern Great Barrier Reef.
Researchers counted almost 10,900 daily growth lines and drilled 784 tiny holes to analyse the chemistry. The oxygen in each layer revealed past sea temperatures; the carbon told them about rainfall.
Together, the chemical records gave a month-by-month picture of reef conditions before industrial warming began. Compared with data from 1995 to 2015, pre-industrial summers were much cooler, but winters were almost the same.
The clam also showed swings in wet and dry years, and shifts between warm El Niño-like and cool La Niña-like patterns. This kind of tropical ocean record has been rare, making the clam's diary a rare window into Southern Hemisphere climate.
- 1785 to 1827
- Clam lifespan studied
- 10,900 daily lines
- Growth lines counted
- 784 tiny holes
- Analysis holes drilled
Why it mattersThe record shows how much the reef has warmed and helps scientists understand natural climate shifts before human industry began.
AustraliaAustralia's most iconic reef has direct climate records spanning 40 years of modern measurement. A clam shell now extends that understanding back two centuries, revealing how much warmer the reef is today.
✓ Claims checked against the source and corrected before publish. checked 3 h ago
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