Saltier seas in spring double the chance of extreme El Niño events, study finds
Stronger El Niño events are more likely when springtime surface waters in the western Pacific Ocean become unusually salty, a new study in Geophysical Research Letters suggests. Traditionally, scientists have focused on temperature and wind patterns to understand El Niño—periodic shifts in the tropical Pacific between warmer and cooler conditions that influence weather patterns across the globe. But researchers now show that subtle variations in ocean salinity north of the equator during boreal spring (March to May) can substantially amplify El Niño's strength and nearly double the odds of an extreme event.
El Niño events form part of the El Niño–Southern Oscillation (ENSO), a natural cycle driven by interactions between the ocean and the atmosphere. During El Niño, warm surface waters spread eastward across the Pacific, raising ocean temperatures in regions that are usually cooler and triggering changes in weather patterns around the world.
When these events intensify, their impacts can be far-reaching, bringing drought to some regions and heavy rainfall to others. While atmospheric winds and sea surface temperatures have long been central to ENSO theory, the latest research suggests that ocean salinity also plays an important role.
How salt shapes the ocean
To most people, salinity simply refers to how salty seawater is. In ocean science, however, it is a precise measure of the amount of dissolved salt in the water. Salinity matters because saltier water is denser than fresher water, affecting how ocean layers are arranged and how currents move. These density differences influence sea level and the transport of heat across the Pacific.