Analysis of stalagmites from a cave in Peru reveals that global monsoon systems generally operate on a seesaw pattern, strengthening in one hemisphere while weakening in the other. However, a new study published in Nature shows that simultaneous weakening events have interrupted this cycle over the past 450,000 years.
Monsoon rains supply essential water for drinking, crops, and hydropower for billions of people across South Asia, Africa, and parts of the Americas, according to Phys.org. A team of researchers sought a longer record of rainfall activity in South America.
Earlier research established a seesaw dynamic between Asian and South American monsoons.
Peruvian Stalagmites Track 450,000 Years of Monsoon Activity
Researchers utilized stalagmites from a cave in Peru, as reported by Phys.org. The data covers roughly 450,000 years of rainfall activity in the Amazon Basin. The study authors compared the reconstruction with Asian monsoon records.
Comparing the new data with Asian records confirmed that the two monsoons usually changed in opposite directions. This seesaw effect is driven by orbital forcing, which dictates the mean position of the Intertropical Convergence Zone (ITCZ) and the strength of incoming solar radiation in each hemisphere.
Simultaneous Weakening Events
Researchers identified 10 synchronous monsoon events. The shared weakening events occurred during several transitions out of ice ages and across certain warmer intervals. These synchronous events persisted for several thousand years before the records returned to their typical opposing behavior.
Factors such as greenhouse gases and global temperature changes can modify standard orbital influences. These changes cause the global monsoon system to reorganize itself during periods of rapid warming.
Among the 10 synchronous monsoon events of the past 450 ka, interhemispheric weak monsoon intervals (WMIs) during terminations occur regularly, with a periodicity of about 100 kyr. These interhemispheric WMIs occur within intervals of major increases in atmospheric CO₂ and global temperature, which were intervals of reduced meridional temperature gradient.
Study authors, Nature