What is El Niño and why is 2016 interesting?

Contributed by MBARI Scientist and CeNCOOS Principal Investigator Dr. Francisco Chavez
 

In the late 1800's fishermen from northern Peru named a warm southward current El Niño (Spanish, The Child) because it appeared every year around Christmas. Years when this current was unusally strong and warm resulted in extremely high rainfall in this normally desertic location. The unusual years were also associated with disappearance and mortality of the typical fish, mammals and seabirds of the region and an influx of tropical species. Thus was born the El Niño phenomena. However, it was not until the late 1960’s that the local warming of the coastal ocean off Peru was linked to global scale changes in the atmosphere that are now part of every day news.

What is El Niño

El Niño has been extensively studied but it remains unpredictable, in terms of timing of onset and intensity. Once started, the developmental sequence of events are relatively well understood.

  • Anomalous winds in the western Pacific near Indonesia initiate Kelvin waves that propagate eastward along the equator, raising sea level and deepening the thermocline.
  • When these waves reach the South American coast they propagate poleward towards Alaska and Chile. This alters the thermal structure of the ocean, increasing upper ocean temperatures and decreasing biological productivity (i.e. less small plants are growing in the ocean).
  • The trade-mark signature of El Niño is anomalously warm sea surface temperature (SST) along the equatorial Pacific from the dateline to the coast of Peru. At lower latitudes the influence of the ocean drives the anomalous conditions, but at higher latitudes, like California, local meteorological anomalies caused by atmospheric teleconnections also influence the abnormal ocean conditions.
  • The global meteorological impacts of El Niño are related to dramatic changes in the intensity and location of low and high pressure atmospheric systems. The largest and steadiest low pressure system on the globe, the Indonesian low, named because it sits over Indonesia, is sucked eastward thousands of kilometers by the warm SST in the central Pacific and feeds the pineapple express of moisture responsible for increased precipitation over California. At the same time, subtropical Pacific high pressure systems weaken and this creates a ripple effect as low and high pressure systems throughout the globe change their intensity and location.

Intensity and Frequency

El Niño events occur once every 3 to 8 years and with varying strength. Their duration is on the order of 12-18 months. Over the past 60 years, strong El Niño events have impacted the West Coast of North America in 1957-58, 1982-83 an 1997-98. The current 2015-16 event will eventually be included in this category.  The 1982-83 and 1997-98 events brought worldwide attention to what is now known as the dominant mode of climate variability over the past century.

Comparison plots of sea surface temperature anomalies from Dec 1997 (the year of the  last strong El Niño) and Dec 2015

2015 - 2016

Present day conditions in the northeast Pacific have been unusual since late 2013.

The Blob

The 2015-16 El Niño has come on the heels of the so-called “blob”, coined by Nick Bond, for a large area of anomalously warm SST in the northeast Pacific that developed in late 2013 and early 2014.  By mid 2014 the warming had spread over the entire west coast of North America. The “blob” warming was not El Niño-like because: 1) it lacked the characteristic equatorial Pacific warming; 2) warming was restricted to the upper 20-40 meters of the ocean, which is unlike El Niño where the warm water penetrates deeper. A wide variety of ecosystem perturbations have been linked to this unusual warming, including a wide-spread bloom of domoic acid-producing pennate diatoms (a marine algae) that eventually led to the closure of the California Dungeness crab season in the Fall of 2015. The “blob” warming retreated in the spring of 2015 with the onset of the upwelling season but anomalous warming returned in the summer associated with El Niño.

El Niño

The characteristic signature of El Niño developed in the equatorial Pacific during the late spring and summer of 2015 and further intensified in the Fall. On October 17, 2015, the warmest daily-average SST ever measured (65.73 ̊ F) by the M1 mooring during it's 26 year history was recorded (the mooring is in the middle of Monterey Bay). The central California region was invaded by tropical species, one of the most notable being the pelagic red crab of the genus Pleurocondes, which ashored occasionally covering the local beaches with a blanket of red (see photo). Well-known predators of this organism, normally found off Baja, among them bluefin tuna, followed them northward to central California. The combination of local, tropical and offshore biota led to a dramatic increase in biodiversity along the California central coast.

 

The 2015-16 event has been referred to as Godzilla, a name picked up readily by the news, because it has been predicted to be the strongest ever. The jury is still out, however, on the magnitude of this event. Following the large 1997-98 event, subsequent El Niño’s changed in character. Rather than having anomalous SST stretching from Peru to the dateline, the warmer waters were restricted to the central Pacific. The Japanese nicknamed these events El Niño “Modoki”, a word that means “like but not the same”. The 2015-16 event has some Modoki characteristics with large anomalies in the central Pacific but weaker anomalies in the eastern Pacific along north and south America when compared to 1982-83 and 1997-98. Indeed SST in central California retreated after the peak on October 17 and recently has been well below that observed in 1997. Peru SST is anomalously warm but well below levels measured in 1982 and 1997. The warm waters in the central Pacific kicked off the global teleconnections in the atmosphere, and the United States is experiencing typical El Niño weather conditions.

My forecast remains that we will see a strong El Niño, but one less intense than 1982 and 1997, particularly less intense in the ocean. The combined blob and El Niño have resulted in conditions of unprecedented multi-year anomalies in the northeast Pacific relative to the last 50 years. This has led some to speculate that the prolonged warming may have more dramatic impacts on local marine ecosystems than other shorter lived and more intense events. It has also fueled discussion regarding the influence of humans on climate and if the unusual conditions are a result. Another scenario is a new climate regime showing itself in our relatively short records. It is likely that that there is some truth in all of these speculations, but they all highlight the need for continuing high-quality observations of our coastal and open oceans. Measurements of water temperature, nitrate and chlorophyll and other parameters are monitored by MBARI and other CeNCOOS partners along the California coast. MBARI measurements are updated daily and can be found on the MBARI website.


Learn more about El Niño and regional ocean temperatures on the new CeNCOOS El Niño page
Tags: