Volcanic eruptions and warming climate disrupt long-standing link between Indian and Pacific oceans

A new study combining paleoclimate data and climate models suggests that large volcanic eruptions can disrupt the relationship between atmospheric circulation patterns over the tropical Indian and Pacific oceans. In addition, human-caused greenhouse gas emissions are now driving an unprecedented breakdown in interbasin coupling, according to researchers at the Woods Hole Oceanographic Institution (WHOI). Об этом сообщает издание Phys.org.

Volcanism can temporarily weaken connections between ocean basins, but anthropogenic forcing in recent decades has caused an "exceptional" shift in the relationship between Indian and Pacific Ocean climate variability, according to a Nature Communications study titled "Coupling of Pacific and Indian Ocean variability disrupted by 19th century volcanism."

Climate conditions in the Indian Ocean typically follow the behavior of the Pacific Ocean. However, since the 1980s, scientists have observed a breakdown of this covariability linked to climate change. With less than 100 years of quality instrumental data, it is difficult to assess how unusual these recent changes really are.

To provide long-term context, WHOI scientists used tropical paleoclimate archives—corals, tree rings and stalagmites—to extend the record of Indian and Pacific Ocean climate back to the early 1600s.

Volcanic eruptions broke the pattern

Consistent with modern observations, the paleo-records show that the two ocean basins were largely coupled for most of the past 400 years. But a key finding from this study is that the Indian–Pacific relationship appeared notably different during the early 19th century (1810–1850).

The researchers link this unusual period to a series of large tropical volcanic eruptions that disrupted the usual connections between the two ocean basins, with computer simulations covering the past millennium supporting this explanation.

The extent to which volcanic eruptions weakened Pacific influences on the Indian Ocean climate depended on the strength of the eruptions and the climate conditions at the time.

"This is one of the first studies to examine the breakdown in the connection between the Pacific and Indian oceans using evidence from past climates, modern observations, and climate models," said co-author Caroline Ummenhofer, a senior scientist at WHOI.

Recent changes stand apart

Showing how volcanic eruptions can weaken the Indian–Pacific relationship is only one outcome; this study helps frame how unprecedented and exceptional the recent breakdown is.

"The modern data we have is limited and doesn't go back far enough. With climate models and paleo-records, we are now able to say with more confidence that the recent changes we are seeing are really quite exceptional," said lead author Shawn Wang. Wang is a former WHOI graduate student and postdoctoral researcher, and he is currently a postdoctoral researcher at the University of Colorado Boulder.

Understanding this breakdown is important because connections between ocean basins help scientists predict future changes in rainfall and other aspects of the climate. While previous studies have often focused on individual ocean basins, this study looks at how the oceans influence one another.

"A key finding is that global warming and human emissions are now overwhelming the Pacific's natural influence on the Indian Ocean," Ummenhofer said.

"The Indian Ocean is a huge heat reservoir, and it can decouple from what the Pacific Ocean is doing. The results of this study underscore the independent behavior of the Indian Ocean," said co-author Delia Oppo, an emeritus research scholar at WHOI.