The 2015–2016 El Niño officially ended in early June. With its record-breaking sea surface temperatures, this El Niño rivaled the severe El Niño events of 1997–1998 and 1982–1983. However, in a new study, Jacox et al. suggest that despite its magnitude, the latest El Niño event had relatively weak effects on the marine ecosystem within the eastern Pacific Ocean’s California Current. Instead, preexisting warming anomalies continue to dominate.

The mighty California Current flows steadily southward off the west coasts of the United States and northern Mexico. Normally, summertime upwelling delivers cold, nutrient-rich water to the region that sustains the marine ecosystems found there. In El Niño years, warmer ocean waters dampen the supply of upwelled nutrients and limit biological productivity. These effects were particularly notable during the 1997–1998 El Niño.

To analyze the effects of the 2015–2016 El Niño, the researchers considered a variety of data, including sea surface temperature, chlorophyll levels, and wind speed. A network of underwater gliders deployed off the coast of California measured ocean temperature and density at various depths. The team also used a regional ocean model to compare this El Niño with the events of 1997–1998 and 1982–1983.

The data revealed that temperature and density anomalies in the California Current were much weaker than would be expected on the basis of observed tropical sea surface temperatures and past El Niños. This means that compared with the 1997–1998 and 1982–1983 events, the 2015–2016 El Niño likely had weaker effects on upwelling and ocean temperatures and therefore on biological productivity in the California Current.

However, biological productivity in the California Current is still lower than normal, thanks mostly to the “blob.” This large, unusually warm patch of water has lurked off the coast of the Pacific Northwest since 2013, affecting plankton levels and West Coast weather. When it comes to the California Current, the blob appears to eclipse many of the effects of the 2015–2016 El Niño. (Geophysical Research Letters, doi:10.1002/2016GL069716, 2016)

—Sarah Stanley, Freelance Writer