Abstract
Temporal and spatial dynamics of phytoplankton and zooplankton in the Barents Sea have been investigated during the last three decades using remote sensing and in situ observations. Satellite-derived sea surface temperatures increased in the period 1998–2017 by 1.0 °C as an average for the Barents Sea. We found significant positive relationships between ice-free conditions (open water area and duration) and satellite-based net primary production (NPP). The estimated annual NPP for the Barents Sea more than doubled over the 1998–2017 period, from around 40 to over 100 Tg C. The strong increase in NPP is the result of reduction of sea ice, extending both the area and period available for phytoplankton production. In areas where ice extent has decreased, satellite-derived chlorophyll a shows that the timing of the peak spring phytoplankton bloom has advanced by over a month. Our results reveal that phytoplankton dynamics in the ecosystem have been changing rapidly and that this change is driven mainly by bottom-up climatic processes. Autumn mesozooplankton biomass showed strong interannual variability in the 1990s, displaying an inverse relationship with capelin biomass, the most abundant planktivorous fish. In some regions, e.g. Central Bank, capelin biomass explained up to 50% of the mesozooplankton variability during 1989–2017. Though capelin biomass has varied considerably, mesozooplankton biomass has remained rather stable since the mid-2000s (6–8 g dry wt. m−2), resulting in a weakening of the negative relationship between capelin and mesozooplankton biomass in recent years. The stable zooplankton biomass indicates favorable conditions (prolonged/increased NPP) for mesozooplankton production, partly counteracting high predation levels. Overall, we observed trends in phytoplankton phenology that were strongly associated with changes in sea ice cover driven by fluctuations in temperature regime, a trend that may intensify should the ecosystem become even warmer due to climate change. Further reductions of sea ice and associated ice algae is expected to have adverse effects on sympagic fauna and ice dependent species in the Arctic food web. The ice-free conditions may promote further Atlantification (or borealization) of plankton and fish communities in the Barents Sea.
Highlights
High latitude seas are cold-water, high-productivity systems that can sustain large fish stocks important for fisheries (ICES/WGIBAR, 2018)
It should be noted that our results suggest that we are on course to a permanently ice-free Barents Sea: for the warmest, recent years we are approaching the total area of an ice-free Barents Sea as open water (Fig. 11A), and the full year as the open water duration (Fig. 11B)
Our results show that the increase in temperature and decrease in sea ice cover in the Barents Sea have led to larger open water areas, especially in the north and east, resulting in higher net primary production (NPP) by ~100% over the 20 years from 1998 to 2017
Summary
High latitude seas are cold-water, high-productivity systems that can sustain large fish stocks important for fisheries (ICES/WGIBAR, 2018). These polar seas are predicted to be affected (Kelly, 2016). Loss of sea ice, warming of ocean waters, and potential changes in the timing of productive seasons have been documented (ICES/WGIBAR, 2018) and are likely to continue in the years to come (Kelly, 2016). Climate change and variability may affect the whole pelagic food web from phytoplankton to zooplankton to higher trophic levels (Kelly, 2016; Reygondeau and Beaugrand, 2011; Richardson, 2008). Key copepod species Calanus finmarchicus and C. glacialis, as well as krill (euphausiids) Thysanoessa inermis and T. raschii, are regarded as predominantly herbivorous (Dalpadado et al, 2008; Dalsgaard et al, 2003), allowing an efficient trophic transfer of energy from phytoplankton to fish (e.g. Dalpadado et al, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
