OTOLITH CHEMISTRY REFLECTS FRONTAL SYSTEMS IN THE ANTARCTIC CIRCUMPOLAR CURRENT

Pronounced environmental trends across fronts suggest that the otolith chemistry of oceanic fish can resolve zones on either side, promoting application to population questions at similar spatial scales. Trace and minor elements laid down immediately prior to capture – along the edges of otoliths from Patagonian toothfish Dissostichus eleginoides – discriminated frontal zones in the Antarctic Circumpolar Current in the Southwestern Atlantic Ocean. Mean values differentiated sampling areas by up to 2.6 standard deviations, suggesting: 1) otolith Mg/Ca enrichment related to fish activity around the Burdwood Bank; 2) Mn/Ca enrichment associated with South America; 3) Sr/Ca linked to the presence of Circumpolar Deep Water; and 4) Ba/Ca to nutrient production and mixing. In the Polar Frontal Zone, meanders or eddies may account for affinities with neighbouring sampling areas, bringing water from the Subantarctic and Antarctic Zones onto the North Scotia Ridge. Moreover, fish age showed a significant relationship with depth and improved cross-validation by 14%, giving 85% classification rates to South American and Antarctic regions, and 57 to 83% to areas along the Patagonian Shelf. These results indicate that otolith chemistry reflects hydrography, detecting oceanic gradients across the slope of continental shelves and between zones separated by strong trends like fronts.