Evidence of eddy-related deep-ocean current variability in the northeast tropical Pacific Ocean induced by remote gap winds

Abstract

Abstract. There has been a steady increase in interest in mining of deep-sea minerals in the Clarion–Clipperton Zone (CCZ) in the eastern Pacific Ocean during the last decade. This region is known to be one of the most eddy-rich regions in the world ocean. Typically, mesoscale eddies are generated by intense wind bursts channeled 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 in the region of potential future mining and eddy kinetic energy (EKE) in 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 analyze the main characteristic parameters and the spatiotemporal variability of mesoscale eddies in the northeast tropical Pacific Ocean (NETP). Significant differences between the characteristics of eddies with different polarity (cyclonic vs. anticyclonic) were found. For eddies with lifetimes longer than 1 d, cyclonic polarity is more common than anticyclonic rotation. However, anticyclonic eddies are larger in size, show stronger vorticity, and survive longer in the ocean than cyclonic eddies (often 90 d or more). Besides the polarity of eddies, the location of eddy formation should be taken into consideration when investigating the impacted deep-ocean region as we found eddies originating from the Tehuantepec (TT) gap winds lasting longer in the ocean and traveling farther distances in a different direction compared to eddies produced by the Papagayo (PP) gap winds. Long-lived anticyclonic eddies generated by the TT gap winds are observed to travel distances up to 4500 km offshore, i.e., as far as west of 110∘ W. EKE anomalies observed in the surface of the central ocean at distances 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. A significant seasonal variability of deep-ocean current velocities at water depths of 4100 m was observed in multiple-year time series data, likely reflecting the energy transfer of the surface EKE generated by the gap winds to the deep ocean. Furthermore, the influence of mesoscale eddies on deep-ocean currents is examined by analyzing the deep-ocean current measurements when an anticyclonic eddy crosses the study region. Our findings suggest that despite the significant modulation of dominant current directions driven by the bottom-reaching eddy, the current magnitude intensification was not strong enough to trigger local sediment resuspension in this region. A better insight into the annual variability of ocean surface mesoscale activity in the CCZ and its effects on deep-ocean current variability can be of great help to mitigate the impact of future potential deep-sea mining activities on the benthic ecosystem. On an interannual scale, a significant relationship between cyclonic eddy characteristics and El Niño–Southern Oscillation (ENSO) was found, whereas a weaker correlation was detected for anticyclonic eddies.

Monitoring of Anthropogenic Sediment Plumes in the Clarion-Clipperton Zone, NE Equatorial Pacific Ocean

“…The centre of the eddy at the sea surface passed the area at the beginning of May (Purkiani et al, in review). According to Purkiani et al (2020), the effect of the eddy at the seafloor in ~4 km depth would be expected 2 to 4 weeks later, which in our case would mean a date when our sensors had already been recovered from the seafloor. Even so, a model simulation by Purkiani et al (in review), shows that the effect of this specific eddy most likely only reached down to 1500 m water depth.…”

“…However, during the passage of mesoscale eddies, which have their clearest expression at the ocean surface but of which the effect occasionally extends to the seafloor at >4 km depth, average current speeds increase to ~8 cm s -1 , with peak values of up to 24 cm s -1 (Aleynik et al, 2017). Whilst background bottom currents are probably not strong enough to resuspend surface sediment most of the time, resuspension might well occur under peak bottom currents associated with these mesoscale eddies (Purkiani et al, 2020). Direct observations of (Martıńez Arbizu and Haeckel, 2015;Peukert et al, 2018) and SO268 (Gazis, 2020;Haeckel and Linke, 2021).…”

Impact of a long-lived anticyclonic mesoscale eddy on seawater anomalies in the northeastern tropical Pacific Ocean: a composite analysis from hydrographic measurements, sea level altimetry data, and reanalysis model products

“…Among the identified long-lived eddies, the one which was anticipated to most likely pass through the location of the German exploration contract area (eastern CCZ) was selected. A previous study in this area (Purkiani et al, 2020) shows that most of the long-lived ACEs in the NETP converge to a meridional corridor between 10 and 12 • N. In that study, an automated EDA developed by Nencioli et al ( 2010) was applied and tested on the long-term sea level anomaly (SLA) data to identify and characterize the mesoscale eddies in this region. To forecast the eddy center positions, a simple prediction method based on the average eddy position within the 7 d prior to the desired day was performed as follows:…”

“…Due to recent advances in the development of eddy detection algorithms (EDAs) and the widespread availability of satellite altimeter data, our knowledge on eddies and their surface characteristics has improved significantly (e.g., Chelton et al, 1998Chelton et al, , 2000Chaigneau and Pizarro, 2005;Chaigneau et al, 2008;Liang et al, 2009). Applying an EDA to 24 years of altimeter data (Purkiani et al, 2020), it has been shown that between four and six long-lived (lifetime > 90 d) anticyclonic eddies (ACEs) are generated in the NETP annually, mostly initiated off the west coast of Mexico by the Tehuantepec (TT) and Papagayo (PP) gap winds, which can travel distances greater than 1000 km westwards into the open ocean. The analysis of these long-lived eddies shows that they spread in a narrow meridional corridor between 10 and 12 • N in the interior of the ocean, taking 5-6 months to reach the designated region for future deep-sea mining in the eastern CCZ.…”

Preliminary Economic Feasibility Study of Ferromanganese Nodule Mining by Mechanical Lifting and Small-Scale Collectors

“…The most in-depth information is related with prototype FN collector tests in German and Belgian contract areas in CCZ [82,84]. Some basic studies in and around the areas [85,86], and numerical simulation studies of sediment plume [87,88] were reported on the basis of some baseline cruises. The prototype collector test and large-scale impact experiment finished in 2021 [89].…”