Findings indicate changes in equatorial undercurrent
October 2015 saw one of the strongest measured El Niño occurrences in the eastern Pacific. Scientists from Kiel travelled on board the research vessel Sonne to the low-oxygen regions east of the Galapagos Island and along the coast of Peru to gather new hydrographical data that gave rise to new insights into the impact of El Niño on the oceans.
In just a span of several years, El Niño has caused the largest natural temperature fluctuation in the tropical Pacific; the impact of this has been felt globally, leading to abnormal temperature increases in the central and eastern equatorial Pacific. It is accompanied by droughts and floods in various parts of the world; in 2015, the intensity of such occurrences was particularly strong, but it has since reduced in intensity. At the end of 2016, La Niña is expected to follow. This is El Niño’s counterpart and will lead to colder extremes of climate in the affected regions.
Last autumn, at the peak of El Niño, scientists from GEOMAR Helmholtz Centre for Ocean Research Kiel went on an expedition to the eastern equatorial Pacific to investigate the influence of El Niño on ocean currents and the buoyancy of the deep water off Peru.
The results of their research, published in the Ocean Science journal, shows that the equatorial current system has changed greatly. Author of the study Dr Lothar Stramma from GEOMAR said that in 2012, the team discovered that the speed of the equatorial undercurrent was almost 11 million cubic metres per second in the eastern Pacific. Three years later, it had decreased to 0.02 million cubic metres per second.
“The nutrient measurement off the Peruvian shelf shows nutrient-rich water of lower bouyancy from the deeper water layers, with this effect spreading southward. A reduced lift [less bouyancy] leads to less biological productivity and this has massive consequences for the otherwise productive fisheries in the region,” added Prof Dr Hermann Bange. In contrast, higher oxygen content was detected in the usually oxygen-poor regions of the eastern Pacific. This is caused by the new flow and water mass distributions during the El Niño. There is no sign of any weakening of the observed long-term decrease in the oxygen content of the tropical oceans.
The results, together with computer models, are now being used to improve predictions about El Niño.
Further information: www.geomar.de