Mesoscale eddies influencing the sub-Antarctic Prince Edward Islands archipelago: Temporal variability and impact

Mesoscale eddies in the Prince Edward Island (PEI) region of the Southern Ocean were identified and tracked using satellite altimetry over a 26-year period between 1993 and 2018. We further substantiated previous findings that eddies originating from the eddy hotspot east of the Southwest Indian Ridge have little direct effect on the PEIs, by demonstrating that over the 26-year period, only 3 cyclonic eddies from this hotspot region propagated close enough to interact with the PEI shelf. The majority of cyclonic and anticyclonic eddies that impacted the PEIs originated from the southern branch of the sub-Antarctic Front (S-SAF) and the northern branch of the Antarctic Polar Front (N-APF), further highlighting the importance of these fronts to the island ecosystem. Despite the fact that fewer than 10 eddies per year directly impact the islands, these eddies remain in contact with the PEI shelf and can thus influence conditions for a considerable part of the year, with eddy stirring likely influencing the islands more frequently than eddy trapping. There was no clear seasonal variation in the number and characteristics of these eddies, and long-term trends were also weak and mostly non-significant, likely due to the small number of eddies observed and the large variability between months and years. Nevertheless, our study presents the first 26-year investigation of the temporal variability of mesoscale eddies influencing the PEIs, providing a good baseline against which future changes can be assessed.

Automated summary

Mesoscale eddies in the Prince Edward Island (PEI) region of the Southern Ocean were identified and tracked using satellite altimetry over a 26-year period between 1993 and 2018. Most eddies impacting the PEIs originated from the southern branch of the sub-Antarctic Front (S-SAF) and the northern branch of the Antarctic Polar Front (N-APF), rather than from the eddy hotspot east of the Southwest Indian Ridge. Despite the small number of eddies directly impacting the islands each year, they can influence conditions for a considerable part of the year through contact with the PEI shelf, with eddy stirring potentially playing a more frequent role than eddy trapping.