Mesoscale eddies influencing the sub-Antarctic Prince Edward Islands Archipelago: Origin, pathways, and characteristics

Abstract

Mesoscale eddies are known to strongly influence oceanographic properties and biological responses. Since eddies can transport physical characteristics and biota, knowledge of their origin, pathways, and characteristics is important for understanding their potential impacts on ecosystems such as the Prince Edward Island (PEI) archipelago. Over a 26-year period (1993–2018), a total of 395 (724) cyclonic and 377 (515) anticyclonic eddies were identified and tracked using satellite altimetry in the PEI and Southwest Indian Ridge (SWIR) regions of the Southern Ocean, respectively. The majority of these eddies were formed locally, were relatively short-lived (<60 days), and did not propagate far (<150 km) from their origin. More than half of the eddies remained within each respective region throughout their lifespans. In both regions, most mean eddy diameters ranged between 60 and 100 km, with anticyclonic eddies reaching, on average, larger diameters than cyclonic eddies. Mean propagation speeds varied between 0.04 and 0.07 m s-1, but eddies that remained in each region tended to propagate slightly slower than those that travelled into and out of each respective region. Most eddies in the PEI region exhibited net eastward propagation and northward displacement, with only a few showing overall westward motion and southward displacement. Surprisingly, over the 26-year period, only 14 cyclonic eddies and 1 anticyclonic eddy entered the PEI region, after originating in the SWIR region. This indicated that the SWIR eddy hotspot region has much less of a direct influence on the PEI region than previously thought. Most eddies from the SWIR passed along the southern boundary of the PEI region, far south of the islands themselves. Preferential formation locations and propagation pathways were not only associated with changes in the underlying bathymetry and the strength and direction of the background flow, but also appeared to be related to the positions of various branches of the sub-Antarctic Front and the Antarctic Polar Front.