The climate history of Indonesia wields a substantial influence on the global climate as a whole, says a study published last week (24 March) in the Proceedings of the National Academy of Sciences.
The Indonesian archipelago sits in the Indo-Pacific Warm Pool, an expanse of ocean that supplies a sizable fraction of the water vapour in the Earth’s atmosphere and plays a role in the El Niño cycles of periodic warming in the Pacific Ocean.
The study finds that the normally wet tropical climate of Indonesia was interrupted by a severe dry period from around 33,000 years ago until about 16,000 years ago. The period coincided with the peak of the last ice age, when glaciers covered vast swathes of the Northern Hemisphere.
James Russell, lead researcher and associate professor of geological sciences at Brown University in the United States, says the prolonged dry spell in Indonesia during that ancient period could have likely created a feedback loop that amplified ice age cooling.
For climate scientists, the findings are a big advance. “They can anchor our understanding of global warming,” Russell says. “A very large fraction of the Earth’s water vapour comes from evaporation of the ocean around Indonesia.”
To arrive at their conclusion, Russell and his colleagues assembled a 60,000-year record of rainfall from sediment cores in Lake Towuti, an ancient lake on the island of Sulawesi in central Indonesia and the country’s largest tectonic lake.
It is estimated that the sediments of Lake Towuti preserve up to 800,000 years of climate data. “It is a very long and continuous climate record, likely the longest in South-East Asia, making it an extremely unique and scientifically important lake,” Russell tells SciDev.Net.
From the lake sediments, the research team looked at titanium, an element commonly used to gauge surface runoff. They found a marked dip in titanium levels in sediments dated between 33,000 and 16,000 years ago, a strong indicator that the surface runoff slowed during that time. That finding was buttressed by another proxy of rainfall — carbon isotopes from plant leaf wax.
The sediment cores show an increase in abundance of grass in the same sediments that showed a decrease in surface runoff. The results suggest a dry time strong enough to alter the region’s vegetation that was closely associated with the peak glaciation in the Northern Hemisphere.
The next step for the research team is to obtain a long drill core of the entire sediment sequence in Lake Towuti. Indonesian team member Satria Bijaksana, a geophysics professor of the Bandung Institute of Technology, tells SciDev.Net that scientists from nine countries are now preparing a larger coring/drilling expedition in Lake Towuti for 2015.
“We aim to take longer sediment cores so that we can get longer paleoclimatic records,” he says.