The air and water temperatures remained higher than average and typical of warm years, close to those in 2017. In autumn, the Atlantic waters (>3°С) covered relatively large area, but it decreased compared to 2017; the Arctic and cold bottom waters (<0°С) still covered rather small areas, the area of the former was close to that in 2017 but the area of the latter increased. Ice coverage was much lower than average and close to that in 2017. There was no ice in the sea from August to October; in December, the ice coverage was the lowest since 1951.

In August–September 2018, the area covered by warm water (above 4, 3 and 1°С at 50, 100 m and near the bottom respectively) was close to that in 2017 at 50 and 100 m, and 12% smaller at the bottom (Fig. 3.1.16). The area covered by cold water (below 0°С) was also close to that in 2017 at 50 m but 7 and 8% larger than in 2017 at 100 m and near the bottom respectively (Fig. 3.1.16). Since 2000, the area covered by cold bottom water was the largest in 2003 and rather small in 2007, 2008, 2012, 2016 and 2017; in 2016, it reached a record low value since 1965.

Sea surface temperature (SST) (http://iridl.ldeo.columbia.edu) averaged over the southwestern (71–74°N, 20–40°E) and southeastern (69–73°N, 42–55°E) Barents Sea showed that positive SST anomalies (relative to the base period of 1982–2010) prevailed in both areas during 2018 (Fig. 3.1.9). The largest positive anomalies (>2.0°C) were found in the southeast of the sea in July–September; the December SST anomaly in this area reached a record high value since 1982. The smallest positive anomalies (<0.5°C) were observed in the southwest of the sea in April, May and July, and in the southeast from March to June (Fig. 3.1.9).

The Fugløya–Bear Island Section covers the inflow of Atlantic and Coastal water masses from the Norwegian Sea to the Barents Sea, while the Kola Section covers the same waters in the southern Barents Sea. Note a difference in the calculation of the temperatures in these sections; in the Fugløya–Bear Island Section the temperature is averaged over the 50–200 m depth layer while in the Kola Section the temperature is averaged from 0 to 200 m depth.

The volume flux into the Barents Sea varies with periods of several years and was significantly lower during 1997–2002 than during 2003–2006 (Fig. 3.1.4). In 2006, the volume flux was at a maximum during winter and very low during fall. After 2006, the inflow has mostly been relatively low. Throughout 2015 and in winter 2016, the inflow was around 1 Sv larger than the long-term average (Fig. 3.1.4). The exception was March 2016, when the volume flux was temporarily smaller than average. The data series presently stops in May 2016, awaiting the processing of measurement data following new instrumentation in the mooring array, thus, no information about the subsequent period is available as of yet.

Ice conditions in the Barents Sea in 2018 developed as in low-ice years. In January and February, the ice coverage (expressed as a percentage of the sea area) was respectively 20 and 17% lower than average (1981–2010) and close to that in 2017 (Fig. 3.1.3). The seasonal maximum of ice extent was, as usual, in April; the ice coverage was 53% that was 4% lower than average but 9% higher than in 2017. Ice melting started intensively in May. In summer (June–August), the ice coverage was 7–19% lower than average and 3–7% lower than in 2017.

In 2018, the winter (December–March) NAO index was 0.30 that was much lower than in 2017 (1.47). Over the Barents Sea, southeasterly winds prevailed in January–March 2018 and westerly winds – during the rest of the year. The number of days with winds more than 15 m/s was higher than usual most of the year. It was lower than normal only in the western and central parts of the sea in January and February. In some months (May, June and September in the west of the sea, June and September – in the center as well as April, July and September – in the east), the storm activity was a record high since 1981.

During the 2018 Barents Sea Ecosystem Survey (BESS) 83 fish species from 28 families were recorded in pelagic and bottom trawl catches, some taxa were recorded at genus or family level only (Prokhorova et al 2019). All recorded species belonged to seven zoogeographic group (Widely Distributed, South Boreal, Boreal, Mainly Boreal, Arcto-Boreal, Mainly Arctic and Arctic) defined in Andriashev and Chernova (1994).  In the following only bottom trawl catches of non-commercial fishes were used. Both demersal (including bentho-pelagic) and pelagic (neritopelagic, epipelagic, bathypelagic) species were included (Andriashev and Chernova, 1994, Parin, 1968, 1988).

Most Barents Sea fish species are demersal (Dolgov et al., 2011); this fish community consists of about 70–90 regularly occurring species which have been classified into zoogeographic groups. Approximately 25% are either Arctic or mainly Arctic species. The commercial species are all boreal or mainly boreal species (Andriashev and Chernova, 1995), except for Greenland halibut (Reinhardtius hippoglossoides) that is classified as either Arcto-boreal (Mecklenburg et al., 2013) or mainly Arctic (Andriashev and Chernova, 1995).

Zero-group fish are important consumers of plankton and are prey for other predators, and, therefore, are important for transfer of energy between trophic levels in the ecosystem. Estimated total biomass of 0-group fish species (cod, haddock, herring, capelin, polar cod, and redfish) varied from a low of 165 thousand tonnes in 2001 to a peak of 3.4 million tonnes in 2004 with a long-term average of 1.7 million tonnes (1993-2017) (Figure 3.5.1). Biomass was dominated by cod and haddock, and mostly distributed in central and northern-central parts of the Barents Sea.

Benthos is an essential component of the marine ecosystems. It can be stable in time, characterizing the local situation, and is useful to explain ecosystem dynamics in retrospect. It is also dynamic and shows pulses of new species distribution, such as the snow crab and the king crab, and changes in migrating benthic species (predatory and scavenger species such as sea stars, amphipods and snails with or without sea anemones). The changes in community structure and composition reflect natural and anthropogenic factors.

Mesozooplankton biomass in the Norwegian part of the Barents Sea in 2018 was slightly above the long-term average for the last 20 years. The mesozooplankton biomass in “Atlantic” subareas of the Barents Sea in 2018 were at similar levels as in previous years, and has shown declining trends on the Central Bank and Great Bank subareas since the peak in 1995. Krill biomass has shown an increasing trend during the last decades. Jellyfish biomass in 2017 was at its third highest level since 1980 – but could not be estimated for 2018.

The phytoplankton development in the Barents Sea is typical for a high latitude region with a pronounced maximum in biomass and productivity during spring. During winter and early spring (January-March) both phytoplankton biomass and productivity are quite low. The spring bloom is initiated during mid-April to mid-May and may vary strongly from one year to another. The bloom duration is typically about 3-4 weeks and it is followed by a reduction of phytoplankton biomass mainly due to the exhaustion of nutrients and grazing by zooplankton.

The ongoing warming were associated with increased water and air temperature, larger area covered by Atlantic and Mixed warm water masses and decreased ice coverage. The warming was also associated with
increased macro zooplankton such as krill and jellyfish biomass, increased fish recruitment (age 0) which trigger positive development of fish stocks (cod, haddock, deep water redfish, capelin and herring). Increased production and adequate fishing pressure in relation to stock size led to cod and haddock stock size increasing to record high levels and the capelin stock withstanding the high predation level.

The Barents Sea has been divided into 15 subareas or polygons (Figure 2.1.1). The division is based on topography and oceanography and is a modification (with some subdivision) of the system used by Eriksen et al. (2017) in a summary analysis of pelagic biomass. The four western areas, South-West, Bear Island Trough, Hopen Deep and Tor Iversen Bank, are areas covered mainly with Atlantic water and constitute the inflow region of Atlantic water with the splitting of the current branches east through the Kola Section (south of the Central Bank) and north in the Hopen Deep (west of the Central Bank).