Atlantic tropical mix rewrites climate model rules

Upheaval of the upper ocean layer in the Atlantic Ocean tropics plays a crucial role in shaping long-term climate patterns around the world, according to a new study.

Researchers have discovered that changes in the ocean’s mixed layer (the uppermost section where wind and waves mix warm surface waters with cooler depths) are the main force behind a climate phenomenon known as Atlantic multidecadal variability (AMV) in the tropics.

High winds have a significant impact on global climate. They influence weather patterns from North America to Europe and Africa, affecting everything from hurricane activity in the Caribbean to rainfall in the Sahel region.

Dr Balaji Senapati, lead author of the study from the University of Reading, said: “Until now, it was thought that changes in the exchange of heat between the ocean and the atmosphere determined the climate patterns that affect the weather in different parts of the world. Our new study challenges this view, by demonstrating that the depth of the ocean’s mixed layer is the key player in global climate variability.”

“This research helps us better understand climate variability in the Atlantic and sheds light on the complex relationship between the ocean and the atmosphere and how our planet’s climate is shaped. Knowledge of natural climate variability is becoming increasingly valuable for developing effective mitigation strategies to address the challenges of climate change.”

Forecast improvements

The study, published this month in Geophysical Research Lettersfound that when the extratropical North Atlantic is warmer than average, the trade winds weaken. This weakening causes the mixed layer of the ocean to become shallower, especially in summer. As a result, solar energy warms a thinner layer of water, leading to more intense warming of the tropical Atlantic.

This process creates a feedback loop: warmer waters in the northern Atlantic weaken the trade winds, leading to a shallower mixed layer and further warming in the tropics. When the AMV transitions to its colder phase, this process reverses, leading to cooler temperatures across the entire Atlantic.

These findings have important implications for climate modeling and long-term forecasting. Many current climate models do not accurately represent these upper-ocean processes, which can lead to poor predictions of ocean wave motion and its global impacts. By incorporating this new understanding of ocean mixing into climate models, scientists hope to improve their ability to predict long-term climate trends and their associated effects on weather patterns around the world.