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 ice-free period. This process affects the entire pelagic ecosystem of the Barents Sea, where the main part of the annual primary production of phytoplankton is formed during the spring bloom. Chlorophyll a concentration reflects changes in phytoplankton biomass and can serve as an indicator of its production characteristics. In the spring of 2021, hydrological characteristics of water masses, as well as the distribution of concentrations of chlorophyll a and nutrients, were studied in the ice-free water area of the Barents Sea. The year of 2021 was characterized by negative ice cover anomalies. The location and length of the areas of increased (or decreased) chlorophyll a concentrations were consistent with the alternation of water masses. Separate spots of early spring bloom were identified – in coastal waters in the southeastern and southwestern Barents Sea. In late March and early April 2021, maximum chlorophyll a concentrations in coastal waters reached values of about 1 mg·m−3. At the same time, in the Barents Sea and Arctic waters, the maximum content did not exceed 0.20 mg·m−3. The distribution of nutrients corresponded to that for the winter period when the vertical gradients of these parameters were not formed yet. The values of water saturation with oxygen exceeding 100% (to varying degrees throughout the studied area) characterized the activation of the photosynthesis process in the phytoplankton community. Analysis of long-term data showed 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 the Barents Sea water masses of various types – in Arctic, Atlantic, and coastal waters (maximum chlorophyll a concentration reached the value of 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 content was of 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 its bloom (according to satellite data) occurred much later, in May. Atlantification of the Barents Sea contributes to the formation of several bloom spots and the distribution of spring bloom over a larger area, which might affect the annual production indicators of the entire pelagic zone.

Keywords

• chlorophyll a
• spring bloom
• water masses
• Atlantification
• Barents Sea