Phytoplankton production and growth regulation in the Subarctic North Atlantic: A comparative study of the Labrador Sea-Labrador/Newfoundland shelves and Barents/Norwegian/Greenland seas and shelves

Abstract

A study was made of phytoplankton (distribution, phenology, physiology, productivity and community composition) and environment properties that influence their growth (light and nutrients) comparing the western Subarctic Atlantic (Labrador Sea, Labrador/Newfoundland shelves) with the eastern Subarctic (Barents, Norwegian and Greenland Seas and shelves) and drawing on ship-based observations, satellite ocean colour data (SeaWiFS) and output from a 3D coupled ecosystem-ocean circulation model, covering the last 15–25yrs. Similarities between regions were seen in geographic variability (e.g. latitudinal gradients), seasonal cycles and magnitude of phytoplankton biomass and productivity, and community composition. Regional differences were related to geographic location, presence/absence of ice, seasonal mixing, source waters (Arctic versus Atlantic) and nutrient supply, and response to atmospheric forcing. With regard to the latter, most of the observations considered in this study cover the recent period of rapid warming and the historical out-of-phase response (e.g. ice conditions, air and ocean temperatures, hydrography) of the western and eastern Subarctic Atlantic to atmospheric forcing is no longer apparent. Observations and modelling looking back over the last two decades suggest that the timing of the spring bloom and peak seasonal productivity are occurring progressively earlier in the year, particularly at high latitudes in both the western and eastern Subarctic. Climate change (ocean warming) is projected to increase overall phytoplankton productivity in the Subarctic Atlantic and will be manifest particularly in ice-influenced regions Labrador/Newfoundland Shelves, Barents/Greenland Seas and shelves and regions where Arctic outflow and Atlantic inflow influence phytoplankton dynamics. Northward movement of Atlantic waters as a result of climate change, manifest earliest in the eastern Subarctic (Norwegian/Barents Seas) will displace cold-water phytoplankton species with warm-water species and shift community transitions zones farther north in the coming decades.