This study reports on diversity and distribution of planktonic foraminifera (PF) in the Barents Sea Opening (BSO). Populations of PF living in late
summer (collected by means of stratified plankton tows) and recently deposited individuals (sampled by interface corer) were compared. High
abundances reaching up to 400
Polar areas are sensitive to global temperature changes, particularly in the Arctic where warming occurs faster than in the rest of the world and has
accelerated over the past 50 years (Shepherd, 2016). This Arctic amplification appears to be mainly caused by sea-ice loss under increasing
Taking the opportunity of a cruise dedicated to the exploration of the physical oceanography of the western Barents Sea (MOCOSED 2014 cruise), we
investigated the connections between the spatial variability of living PF, phytoplankton communities (Giraudeau et al., 2016) and the hydrological
system through a south-to-north transect, between northern Norway and Spitsbergen [68–76]
The studied area covers the western Barents Sea margin, i.e. Barents Sea Opening (BSO), where the surface and intermediate ocean circulation are characterized by the confrontation of the North Atlantic and the Arctic waters (Fig. 1). The seasonal and interannual dynamics of these two water masses, interacting with the complex topography of the western margin (Storfjordrenna and Bjørnøyrenna glacial troughs separated by shallow Spitsbergenbanken), determine the position of the Polar Front (Loeng, 1991). The Norwegian Atlantic Current (NwAC) carries Atlantic Water into the Barents Sea. Along the western Barents Sea margin, Atlantic Water is transported to the Fram Strait by the West Spitsbergen current (Skagseth et al., 2008; Oziel et al., 2017; Fig. 1).
Sampling map of the MOCOSED cruise in the western Barents Sea with schematic surface circulation (red arrows: Atlantic Water; blue arrows: Arctic Water; green arrow: Norwegian Coastal Current; adapted from Oziel et al., 2017). Little green dots display the 32 CTD–Niskin stations along the south-to-north transect; large blue circles show the location of the nine MultiNet stations; medium red circles underline the five multicore stations.
In the southern part of the transect a strong thermohalocline clearly underlined a surface mixed layer of about 30–35
The Chl
South–north, 0–100
In late summer 2014, from 8 August to 20 September, the SHOM (French Hydrographic Office) operated the oceanographic cruise MOCOSED 2014, on board the
R/V
Living PF were collected at 7 of the 32 conductivity–temperature–depth (CTD) south-to-north transect stations (3 to 9) and at two stations (1 and 2) located
west to east
Location (latitude and longitude), sampling date and water depth, of the nine MultiNet and five multitube stations, incremented from south to north (stations 1 and 2 being positioned beside the main transect midpoint 6). Stations where phytoplankton analyses were performed are also indicated.
For protein extraction and measurement, a few living individuals (
At five sites of the main CTD transect, an interface corer (multitube type, Oktopus GmbH, Institut National des Sciences de l'Univers division of Brest,
France) was used to simultaneously obtain eight short sediment cores (less than 1
Data from the seven stations of the south-to-north CTD transect with five depth values per station were compiled to display the repartition of PF absolute
abundances (for total assemblage and species specific) in the upper 100 m of the vertical section across the BSO. Abundances of living
specimens below 100
Distribution of planktonic foraminifera total abundances (
Total concentrations of living PF fauna varied between 0 and 400
Distribution of the four major species abundances (
In the surface waters of the south-to-north transect (0–20
The NMDS analysis of species abundances with regard to environmental parameters (latitude of the station, temperature, salinity, Chl
Standard non-metric multidimensional scaling (NMDS) ordination analysis of planktonic foraminifera species distribution (red dots) with
temperature, salinity, Chl
Individual protein content (BCA method) and associated test minimum diameter were measured for a total of 272 specimens of the four major species,
including 32 specimens of
Boxplot of the size-normalized protein biomass (SNP,
Minimum diameters of the 272 selected tests cover a large size range, from 65 to 315
Descriptive statistics (minimum, maximum, average, and median values in micrometres) of the minimum (i.e. the shortest) diameter of all the 272 BCA measured specimens, per species.
Concentrations of planktonic foraminifera with colourless empty tests varied from a maximum of 6200
Relative species occurrence (percent of the total fauna) of planktonic foraminifera found in the upper 0.5
Concentrations of planktonic foraminifera bearing a coloured cytoplasm (Fig. 7b) varied from 100 to 300
In the late summer of 2014 the hydrology at the BSO was characterized by a strong water stratification with a 30
The remarkable point of our results is the dominance of
A discrepancy between the species-specific distribution patterns was observed in late summer 2014 at the BSO. The low abundances of
Potential differences in diet preferences could explain the observed species distribution in late summer 2014 at the BSO. Both
Proteins are the main component of zooplankton biomass (
The PF species compositions recorded during the late summer 2014 in the water column and in surface sediments are similar while species relative
abundances are drastically different. Indeed, the living fauna (collected by plankton net) displays large relative and absolute abundances of the two
species
Furthermore, the analysis of sediment from the five core tops demonstrated important differences between the assemblages of fossil fauna and recently
settled tests (likely coming from surface spring–summer production), i.e. Rose Bengal-stained tests bearing not yet decomposed cytoplasm. For
example, at 71.3
The sampling and analytic approaches deployed during the MOCOSED14 cruise and combining the use of plankton net, core-top, molecular biology (protein measurement), environmental parameters and phytoplankton characterization provide us with a unique dataset to better constrain the distribution of planktonic foraminifera within the highly complex studied area of the western Barents Sea.
The observed abundances of PF in the studied area are high offshore and the lower densities were recorded close to the Norwegian and Spitsbergen coasts.
These observations highlight the fact that waters under continental influences (nutrient-enriched, more turbid) are rather inhospitable for PF
production. The PF species composition observed at the BSO is diverse, with more than 10 different species in the net samples including
Unlike their species-specific abundance pattern of distribution, size-normalized protein concentrations of all four major species decrease with
increasing latitude (and a decrease in temperature and Chl
Data will be made available on request to the main author until their online publication on
JM and HH designed the study. JM, VH, ID and JS generated the data and carried out the analyses. TG provided access to the MOCOSED 2014 cruise. All authors contributed to writing the manuscript.
The authors declare that they have no conflict of interest.
The authors are thankful to the crew and captain of R/V
The article processing charges for this open-access publication were covered by the University of Bremen.
This paper was edited by Carol Robinson and reviewed by three anonymous referees.