Spatial variability of thermohaline parameters and phytoplankton composition of West Antarctica in summer season

Abstract

Spatial variability of thermohaline characteristics (temperature, salinity, and dissolved oxygen) and phytoplankton structure (composition, abundance, and biomass) of the Southern Ocean during austral summer were investigated. New data were obtained for a little-studied area of Antarctica: on transects along the eastern border of the Ross Sea along W156° (T1, length of 35 km, 6 stations), near the Russkaya station (T2, 87 km, 13 stations), at the single station (Roosevelt Island area, Bay of Whales, Ross Sea), and in the Bransfield Strait (T3, 118 km, 11 stations). The relevance of the analysis of this area is due to its location on the border of the shelf and continental slope with different parameters of temperature and water structure. Low salinity and different temperature characteristics were revealed in surface waters of T1 and T2: lower values for T2 (−1.5 °C) and higher for T1 (0 °C). For the Bransfield Strait waters (T3), typical data on salinity and oxygen content were obtained against the backdrop of slightly increased temperature (up to +2 °C). For the single station, relatively fresh, cold, and oxygenated water of the upper 100-meter layer was recorded, and low temperature values of the bottom area, with high mineralization, were registered. In the phytoplankton composition of the study area, 48 taxa of microalgae from 5 divisions were identified (Bacillariophyta, 38; Dinophyta, Cyanoprokaryota, and Chrysophyta, 3 taxa each; and Haptophyta, 1) and 1 macrophyte taxon (Rhodophyta). The maximum similarity in the species composition of phytoplankton (on average, 43%) was typical for shelf stations in different areas. The total abundance of phytoplankton in the study area of the Southern Ocean ranged within 4.3–264.0 thousand cells·L−1, and biomass, 0.07–1.18 mg·L−1. The main contributors to quantitative characteristics of phytoplankton throughout the study water area were diatoms, mainly representatives of the genus Fragilariopsis Hustedt, confined to the shelf and coastal areas. At a distance and in the open sea of transects T1 and T2 deeper than 50 m and in surface waters of transect T3, Phaeocystis antarctica Karsten (Haptophyta) developed in mass. For T2, the dependence of phytoplankton abundance on water temperature and salinity was revealed.

Keywords

• west antarctica
• bransfield strait
• shelf
• spatial variability
• thermohaline parameters
• phytoplankton