Chinese researchers have studied the turbulent mixing of the equatorial Pacific Ocean and estimated that the halocline layer mixing happens more often in La Nina than in El Nino years.

The vertical structure of the subsurface layer in the western equatorial Pacific Ocean is unique because of heavy rainfall. The temperature mixed layer extends from the surface to a higher depth, typically between 50 to 80 meters. The surface-density mixed layer is usually lower, typically between 20 to 30 meters.

The 20-60-meter-thick layer is a halocline layer. The presence of the halocline layer can prevent entrainment of cold deeper water into the warmer surface layer, thus inhibiting cooling of the surface water and helping maintain shallow-surface mixed layers. Therefore, the halocline layer is called a barrier layer, facilitating El Nino development.

The researchers from the Institute of Oceanology under the Chinese Academy of Sciences found frequent turbulent mixing in the barrier layer by observing the equatorial Pacific Ocean.

The observed barrier layer mixing is as strong as in the mixed layer, yielding effective heat transfers across the isothermal layer base, noted their research article published in the journal Geophysical Research Letters.

The estimated barrier layer mixing is ubiquitous, ranging between 20 to 60 percent spatially and peaking at around zero degrees north latitude and 160 degrees west longitude. Moreover, it occurs more frequently in La Nina than in El Nino years.

The researchers admitted how the barrier layer mixing impacts the El Nino development deserves further exploration.

La Nina is the opposite of the El Nino ocean-atmosphere warming phenomenon.

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