The ongoing El Niño of 2010 is reducing marine populations according to scientists at NOAA and Scripps Institution of Oceanography.

Researchers are reporting a stronger than normal northward movement of warm water up the Southern California coast, a high sea-level event in January and low abundances of plankton and pelagic fish – all conditions consistent El Niño.

Sea surface temperatures along the entire West Coast of America are 0.5 to 1 degree Celsius (0.9 to 1.8 degrees Fahrenheit) warmer than normal and at points off Southern California are as much as 1.6 degrees Celsius (2.9 degrees Fahrenheit) higher than normal. The most unusually high temperatures were mapped around Catalina and San Clemente islands.

The high coastal sea levels may be caused by strong winter storms, scientists are investigating whether this is the case or whether they are primarily a result of El Niño.

A combination of satellite remote sensing and field measurements is offering scientists a broader view of the evolution of this El Niño that was not available during previous El Niños, which were especially strong in 1982-83 and 1997-98.

The two research centres use data collected by satellites and buoy-mounted instruments to measure sea surface temperature. Researchers embark on quarterly cruises off the California coast to collect vertical temperature profiles in the upper reaches of the water column. They also count eggs of commercially important fishes such as sardines and anchovies as well as measure plankton volumes to estimate the amount of “production” available to marine organisms. NOAA’s Advanced Survey Technologies Group assesses fish populations through acoustic surveys. In contrast with the last major El Niño, Scripps now deploys Spray gliders, diving robots that now gather ocean temperature and other data.

The scientists have observed a drop in biological abundance, or productivity, that appears to be related to the northward movement of warm water from the equator. The flow arrives in pulsing Kelvin waves that are detected by sea level and altimeter monitors and coastal tidal gauges. The layer of warm water often stifles the upwelling of nutrients from lower ocean depths that sustain larger populations of fishes and invertebrates.

A Kelvin wave is a gentle yet massive swell of warm water travelling across the Pacific from West to East. A typical Kelvin wave is 5 or 10 cm high, hundreds of kilometers wide, and a few degrees warmer than surrounding waters.

If El Niño conditions continue, they are likely to be characterized by weaker than normal upwelling and lower biological production. El Niño conditions are forecast to persist into spring. If so, they may result in fewer fish and breeding failure of seabirds.

Further Reading
A Curious Pacific Wave, Science@NASA
Scripps Institution of Oceanography