Physical and Biological Features of the Waters in the Outer Patagonian Shelf and the Malvinas Current

Abstract

The aim of this study is to trace how the fine-thermohaline and kinematic structure, formed over a section along 45.8° S in the interaction zone of the outer Patagonian Shelf (PS) and Malvinas (Falkland) Current (MC) System waters, affect the spatial distribution of bio-optical characteristics, phyto/zooplankton, birds, and marine mammals. For the first time, simultaneous multidisciplinary observations at high spatial resolution (~2.5 km) were performed in this region during the cruise of the R/V “Akademic Mstislav Keldysh” in February 2022. A fine structure of alternating upwelling and downwelling zones over the PS and slope was identified, which resulted from the interaction between the MC inshore branch (MCi), bottom topography, and wind. This interaction significantly affects all the physical, and optical characteristics analyzed in the work, as well as the biota of the region. It was found that the euphotic zone is larger in the downwelling zones than in the upwelling zones, and all spatially local maxima of phytoplankton photosynthetic efficiency are observed in the zones between upwelling and downwelling. Phytoplankton along the section were represented by 43 species. A total of 30 zooplankton species/taxa were identified. Three species of marine mammals and 11 species of birds were recorded in the study site. Most of the phytoplankton species list were formed by dinoflagellates, and picoplankton Prasinoderma colonial quantitatively dominated everywhere. Two floristic and three assemblage groups were distinguished among the analyzed phytoplankton communities. High phytoplankton biodiversity was observed above the PS and low above the PS edge and in the MCi core. Copepods mostly dominated in zooplankton. Subantarctic species/taxa of zooplankton concentrated in the nearshore waters of the PS, while Antarctic species/taxa were most abundant in the zone between the MCi and the MC offshore branch (MCo). The relative abundance of birds in the PS was several times higher than in the MCo. The minimum abundance of birds was in the MCi in the zone of the strongest upwelling identified above the PS edge.