Washington: El Nino years can have a big impact on phytoplanktons — the tiniest plants in the ocean — disrupting the marine food chain and affecting fisheries and the livelihoods of fishermen, NASA scientists said. In El Nino years, huge masses of warm water —equivalent to about half of the volume of the Mediterranean Sea —slosh east across the Pacific Ocean towards South America.
While this warm water changes storm systems in the atmosphere, it also has an impact below the ocean’s surface. El Nino’s mass of warm water puts a lid on the normal currents of cold, deep water that typically rise to the surface along the equator and off the coast of Chile and Peru, said Stephanie Uz, ocean scientist at NASA's Goddard Space Flight Centre in Maryland.
In a process called upwelling, those cold waters normally bring up the nutrients that feed the tiny organisms, which form the base of the food chain.
“An El Nino basically stops the normal upwelling. There's a lot of starvation that happens to the marine food web,” Uz said.
These tiny plants, called phytoplankton, are fish food - without them, fish populations drop, and the fishing industries that many coastal regions depend on can collapse. With NASA satellite data, and ocean colour software called SeaDAS, Uz has been mapping where these important phytoplankton appear.
The ocean colour maps, based on a month's worth of satellite data, can show that El Nino impact on phytoplankton. In December 2015, at the peak of the current El Nino event, there was more blue and less green chlorophyll in the Pacific Ocean off of Peru and Chile, compared to the previous year, researchers said. They are also watching as the El Nino weakens this spring, to see when and where the phytoplankton reappear as the upwelling cold water brings nutrients back to the region.
Researchers are noting reduced food available along the food chain around the Galapagos Islands, for example. There has also been a drop in phytoplankton off the coast of South America.
Scientists have more tools on hand to study this El Nino, and can study more elements of the event, Uz said. They're putting these tools to use to ask questions not just about ocean ecology, but about the carbon cycle as well.
“We know how important phytoplankton are for the marine food web, and we're trying to understand their role as a carbon pump,” Uz said. The carbon pump refers to one of the ways the Earth system removes carbon dioxide from the atmosphere. When phytoplankton die, their carbon-based bodies sink to the ocean floor, where they can remain for millions of years.
El Nino is a naturally occurring disruption to the typical ocean currents, so it is important to understand the phenomenon to better attribute what occurs naturally and what occurs due to human-caused disruptions, she said.
