By Christiana Freitag
Medill News Service, Dec. 15, 2024
On an island of indigenous species, like the panther chameleon, the ring-tailed lemur and the cat-like fossa, found nowhere else on Earth, Madagascar caves also contain time capsules of the climate history of the western Indian Ocean.
Now, paleoclimatologists are investigating what Madagascar can tell us about the past and future of monsoons as climate change accelerates.
“The question was to understand the mechanism connecting the Atlantic and Indian Oceans in the past and whether that has any role in future climate change,” said Ben Tiger, a Ph.D. candidate in the Massachusetts Institute of Technology – Woods Hole Oceanographic Institution Joint Program.
Tiger had been entranced by Madagascar’s unique biome ever since his first visit there during a sustainable development trip with Washington University. It was serendipitous when he started his Ph.D. at MIT-WHOI and joined a research team focused on Madagascar’s cave systems to investigate ocean systems in the Indian Ocean.
The MIT-WHOI research first focused on Madagascar to understand the human impacts on species unique to Madagascar when humans arrived around 1,000 to 1,500 years ago, according to Tiger.
“There were huge shifts in the ecosystem during that time: the extinction of certain charismatic megafauna like giant lemurs and hippos that don’t exist on the island anymore,” Tiger said. “So the question was, is this a climate story or a human, environmental-change story? And with stalagmites, you can answer that question.”
MIT-WHOI P.h.D. candidate Ben Tiger discusses how Madagascar’s unique biome informs his work on climate systems in the Indian Ocean at the Comer Climate Conference in southwestern Wisconsin. Tiger presented his research on Madagascar speleothems at the conference in October 2024. (Christy Freitag/Medill)
Stalagmites, mound-like mineral deposits from cave floors, revealed that Madagascar’s climate hadn’t changed when these indigenous species went extinct – suggesting to Tiger and his team that Madagascar’s biome extinctions had more to do with human influence than climate shifts.
Thus began Tiger’s paleoclimate study on northern Madagascar stalagmites to understand not only what they tell scientists about the island’s biodiversity, but also clues to Indian Ocean activity during the last glacial period – an underreported ocean system compared to the North Atlantic, according to Tiger.
“Most [ocean climate research] is focused in the North Atlantic because of U.S. and European science efforts,” Tiger said. “More recently, there’s more coverage of the Indian Ocean. But that’s only a couple decades-worth of data, so it’s definitely lacking.”
Tiger’s study focused on extracting stalagmites from Anjohibe (the “Big Cave”) in northwestern Madagascar. Stalagmites form from mineral-laden drip water from the ceilings of caves that form calcium carbonate deposits that spire upward from the floor. They serve as precipitation time capsules that can reveal the extremity and frequency of monsoons as far back as 27,000 years ago. This study serves as the oldest record of monsoons in Madagascar.
Understanding how monsoons behaved in the past enables paleoclimatologists such as Tiger to predict how monsoons will behave in the future as ocean currents destabilize from climate change. Contrary to scientific understanding that rain belts warming makes climate wetter, Tiger’s research found that Madagascar’s climate experienced widespread drying during this sudden climate warming event with a huge discharge of meltwater around 27,000 years ago.
“That’s what led us to believe that maybe it was these east-west temperature differences in the Indian Ocean rather than these rain belt shifts north to south that were more important,” Tiger said.
Tiger presented this research to leading climate researchers at the 2024 Comer Climate Conference in southwestern Wisconsin this fall. One attendee, Yuxin Zhou, postdoctoral scholar at the University of California, Santa Barbara, said he was fascinated by Tiger’s findings as it relates to his own research on the Atlantic Meridional Overturning Circulation (“AMOC”).
AMOC is an “ocean conveyor belt” that circulates water within the Atlantic Ocean, carrying warm water north and cold water south. Put simply, when AMOC weakens, extreme weather events increase. Tiger’s work, which focused on the relationship between the Atlantic and Indian Oceans, revealed the dangers of AMOC slowing down on monsoon seasons in the Indian Ocean.
“Ben compared the worst-case scenario and best-case scenario of AMOC weakening and how that difference will affect east African precipitation and farmers that can be potentially impacted,” Zhou said.
Zhou reflected on the timeliness of Tiger’s research. In March 2024, the only American drilling ship dedicated to ocean research shut down, impacting the ability for researchers such as Zhou and Tiger to acquire new sentiments for further climate system explorations.
“[Tiger] made a conscious effort to project what he learned from the past to what we might experience in the future,” Zhou said. “I think this is doubly important in this era of paleoscience. [We’re] in a tough period of time right now because we’re losing a primary drilling ship that we’ve used to study the ocean.”
By analyzing the precipitation of Madagascar’s stalagmites, Tiger’s research reveals the implications of increasing monsoons on regional agriculture in East Africa, India and Indonesia that rely on rainfall. It also highlights the urgency of understanding a weakening AMOC in the tropics as extreme weather events increase.
“By understanding how climate can change in the past, we hope that people can better prepare for these longer-term changes coming up,” Tiger said.
With a greater need for this research, Tiger plans to return to Madagascar in spring 2025 to continue field research at the Anjohibe cave.
“I think we as a [paleoclimatology] community need to reposition and recommit our effort to link the past and the future to show that what we do has value,” Zhou said. “What Ben is doing is exactly what we need to show.”
Image at top: Stalagmites in Anjohibe caves (the “Big Cave” in Malagasy), northwestern Madagascar. (Photo Courtesy of Ben Tiger/MIT-WHOI, Credit: Nick Scroxton/Maynooth University)
