Localization of phytoplankton early spring bloom spots in the pelagic zone of the Barents Sea

Abstract

«Atlantification» of the Barents Sea leads to a decrease in the area of ice cover and an increase in the period of open water. This process affects the entire pelagic ecosystem of the Barents Sea, where the main part of the annual primary production is formed during the spring bloom of phytoplankton. Chlorophyll-a concentration reflects changes in phytoplankton biomass and can serve as an indicator of production characteristics. In the spring of 2021, hydrological characteristics of water masses and features of the distribution of the chlorophyll-a concentration and nutrients were studied in the ice-free water area of the Barents Sea. 2021 was characterized by negative ice cover anomalies. The location and length of the zones of increased (or decreased) chlorophyll-a concentrations were consistent with the alternation of water masses. Separate spots of early spring blooming were identified — in coastal waters in the southeast, and, in the southwest of the Barents Sea. In late March – early April 2021, the maximum concentrations of chlorophyll-a in coastal waters reached values of about 1 mg·m⁻³. At the same time, in the Barents Sea and Arctic waters, the maximum concentration did not exceed 0.20 mg·m⁻³. The distribution of biogenic elements corresponded to the winter period when the vertical gradients of these parameters had not yet formed. The value of water dissolved oxygen saturation above 100% (to varying degrees throughout the studied area) characterized the activation of the photosynthesis process in the phytoplankton community. An analysis of long-term data shows that the subsequent active spring phytoplankton bloom in years with negative ice cover anomalies occurred already in the second or third decade of April in various types of water masses of the Barents Sea — in Arctic, Atlantic and coastal waters (maximum chlorophyll-a concentrations reached 5.69 mg·m⁻³ in Arctic waters). In May, this process covered various types of water masses throughout the Barents Sea (maximum chlorophyll-a concentrations 5.08–5.77 mg·m⁻³).  In abnormally cold years, the low position of the ice edge in March – April limited the possible area of phytoplankton development, and the active phase of phytoplankton bloom occurred (according to satellite data) much later (May). Atlantification of the Barents Sea contributes to the formation of several bloom spots and the spread of spring bloom over a larger area, which might affect the annual production indicators of the entire pelagic.

Keywords: chlorophyll-a, spring bloom, water masses, atlantification, Barents Sea