New evidences of seasonal deep ocean current variability in the north-eastern tropical Pacific Ocean impacted by remote gap winds

There has been a steady increase of interest in mining of deep-sea mineral in the Clarion-Clipperton Zone in the eastern Pacific Ocean during the last decade. This region is known as one of the most eddy-rich regions, typically at the mesoscale, which are mainly generated by the intense wind burst channelled through gaps in the Sierra Madre mountains in Central America. Here we use a combination of satellite and in situ observations to evaluate the relationship between deep-sea current variability at the region of potential future mining and Eddy Kinetic Energy (EKE) at the vicinity of gap winds.

A geometry-based eddy detection algorithm has been applied to altimetry sea surface height data for a period of 24 years from 1993 to 2016 in order to study the main characteristic parameters and the spatio-temporal variability of mesoscale eddies in the north-eastern tropical Pacific Ocean. Significant differences between the characteristics of eddies with different polarity (cyclonic vs. anti-cyclonic) were found. For eddies with lifetimes longer than 7 days, the total number of cyclonic eddies exceeds that of anticyclonic eddies by about 16%. However, anticyclonic eddies are larger in size and greater in vorticity, and survive longer in the ocean than cyclonic eddies (often 90 days or more). Besides the polarity of eddies, the location of eddy formation should be taken into consideration for investigating the variability of current velocity at deep ocean region as we found eddies originated by Tehuantepec (TT) gap wind lasting longer in the ocean and travel farther distances in different direction compare to eddies emanated from Papagayo gap wind. Long-lived anticyclonic eddies generated at the vicinity of the TT gap wind are observed to travel long distances up to 4500 km far offshore west of 110° W.

EKE anomalies observed in the surface of the interior ocean at a distance of ca. 2500 km from the coast correlate with the seasonal variability of EKE in the region of the TT gap winds with a time lag of 5-6 months. This is consistent with the required time for an anticyclone eddy with the average translation speed of 12 cm/s to reach the ocean interior. Significant seasonal variability of deep ocean current velocity recorded by ocean-bottom moorings at depth of 4100 m likely reflecting the energy transfer of surface EKE generated by the gap winds to the deep ocean is also found. On an interannual scale, a significant relationship between cyclonic eddy characteristics and El-Niño Southern Oscillation was found, whereas no robust correlation was detected for anticyclonic eddies.