Seasonal variations in primary production (PP) in the Kara Sea are underresearched. Previous studies only collected data during autumn or in late summer. However, the middle of summer is close to the ...beginning of the growing season, when PP can contribute significantly to annual water column integrated primary production (IPP). In addition, differences can be expected in the spatial and vertical distribution of phytoplankton communities in this period. This gap in midsummer data was addressed within the framework of a multidisciplinary research cruise by the R/V “Akademik Mstislav Keldysh” (from 15 July to 18 August 2016). High values of IPP (> 200 mgC m
−2
day
−1
) and surface chlorophyll
a
(Chl
a
) concentration (Chl
0
> 1 mg m
−3
) were associated with the Ob–Yenisey river plume, located in the central part of the Kara Sea. Beyond the influence of the plume, in the western and southwestern regions of the Kara Sea, well-pronounced subsurface chlorophyll maxima (SCM) were observed. In some cases, the Chl
a
concentration in SCM exceeded Chl
0
by two orders of magnitude. SCM were often accompanied by subsurface PP maxima (SPM). At stations where SCM was pronounced, IPP values reached 500–800 mgC m
−2
day
−1
, and > 30 % of IPP was accounted for by SPM-integrated PP. Thus, in the middle of summer in the Kara Sea, IPP was linked with the chlorophyll-specific phytoplankton biomass and depended on the strength of the SCM.
It is believed that the waters of rivers flowing into the Kara Sea (predominantly discharge of the Yenisei and Ob rivers) can propagate to the east, penetrating the Laptev Sea with the current along ...the coast. This can occur with the so-called eastern transfer of continental runoff. During a cruise of the R/V
Akademik Mstislav Keldysh
in 2018, traces of riverine waters were discovered in the Vilkitsky Strait. Hydrochemical data suggest with great confidence that these waters were transported from the Ob–Yenisei estuary region. This is because in 2018, pronounced eastern transfer of water from the Kara to the Laptev Sea was observed. A year earlier, continental runoff was not observed in the strait. The fact that transformed riverine waters were transported into the strait from the Kara Sea is also corroborated by the results of surface water sampling along the route of the vessel.
Studies in waterbodies with peculiar salinity face problems in determining water salinity (mineralization). The conventional methods of determining salinity from conductivity or, in the past, ...chlorinity can yield significant errors. This article compares two methods for determining water salinity: the solid residue method and the measurement of sound velocity in water. It has been shown that the measurement of sound velocity (and temperature) can be used for reliable in situ determination of water salinity that is almost unfeasible by other methods (applicable only under laboratory conditions or yielding insufficient accuracy). Results of water salinity determination in different regions of the Aral Sea in 2012–2015 are presented.
The research is based on the materials collected during cruise 66 of R/V
Akademik Mstislav Keldysh
in the Yenisei estuary and over the adjacent Kara Sea shelf in the latitudinal range from 71°50.5′ ...to 75°55.0′ N. The studies were performed from July 25 to 27, 2016, three weeks after the end of the flood period. Two hundred fifty species of plankton algae were recorded. Well-pronounced latitudinal zoning in phytoplankton communities structure associated with changes in the hydrophysical and hydochemical conditions of the pelagic environmental was determined. The maximum species diversity was formed by diatoms, green and blue-green algae in the southern desalinated part of the estuary (<1 PSU) and by diatoms and dinoflagellates in the offshore areas. The highest algae abundance and biomass, 2.7–2.9 × 10
6
cell/L and 1.1–1.5 g/m
3
, respectively, were recorded in the inner desalinated part of the estuary, where freshwater diatoms of the genus Aulacoseira dominated. The distribution of freshwater algae northwards was bounded by the 12–15 PSU surface isohaline (74°20′ N). The most pronounced decline in phytoplankton abundance and biomass was found in the outer part of the estuary north of ~73° N. In the middle shelf to the north of the Yenisei estuary, the maximum abundance (up to 740 × 10
3
cell/L) and biomass (up to 240 mg/m
3
) of phytoplankton were recorded at the depths of 30–40 m with low illumination and high nutrient concentration, which was also typical of the Ob region in spring–summer.
This paper considers different types of the continental runoff distribution over the Kara Sea depending on hydrological and meteorological processes based on 1993–2014 expedition data of the Shirshov ...Institute of Oceanology. The results of calculating the relative contribution of fresh water from several sources (the Ob and Yenisei rivers and melted ice) using hydrochemical parameters are also given.
—
Research on the structure of phytoplankton communities of the East Siberian Sea has been carried out during the 69th cruise of the research vessel
Akademik Mstislav Keldysh
within the framework of ...the Program “Ecosystems of the Siberian Arctic Seas”. The materials were obtained from 5th to 9th September at two quasi-meridional transects from inner shelf areas adjacent to the Indigirka and Kolyma mouths towards the outer shelf. The list of dominant algae groups and species, estimates of abundance, biomass and features of the vertical distribution of phytoplankton are given for pelagic biotopes with different environmental conditions. The significant quantitative deficiency of phytoplankton in the East Siberian Sea in the summer season in comparison with the Laptev Sea is determined, which is especially pronounced in the eastern area of the basin. The algae abundance along the Indigirka transect varies in the range of 11.9 to 66.3 × 10
3
cell/L, and the biomass from 16.4 to 339.1 mg/m
3
. The corresponding values for the Kolyma transect are 7.7–90.3 × 10
3
cell/L and 9.4–42.1 mg/m
3
. The maximum values along both transects are recorded in the area of the outer border of the river plume with increasing surface salinity up to 21–25 PSU. The material obtained makes it possible to reveal significant differences in the structure of phytoplankton communities of western versus eastern areas of the East Siberian Sea, which confirms the well pronounced zonal heterogeneity of the basin.
The spatial distribution pattern of phytoplankton primary production (PP) and chlorophyll was studied by the data of three cruises in August–September 2015, 2017, and 2018. The integral primary ...production (IPP) in water columns along the transect from the Lena River mouth to the continental slope was 2.8 times higher than that along the transect from the Khatanga River mouth, which was explained by the illumination and mineral nutrition. The rise in the chlorophyll content in the layer of photosynthesis (Chl
pl
) along the transects across the continental slope was related to the formation of deep-water maxima. The increase in IPP and Chl
pl
was allocated to the continental slope. The mean IPP < 100 mg C/m
2
per day in August–September is the evidence of oligotrophy of the Laptev Sea late in summer and early in autumn.
Hydrochemical study in the Kara Sea was part of the program of the integrated expedition of the 59th cruise of the RV
Akademik Mstislav Keldysh
. Primary hydrochemical surveys were performed on the ...sections in the Yenisei Gulf, along the eastern and western branches of the St. Anna Trough, and across the Novozemel’skii Trough. Moreover, a flow-through system throughout, in which pH values of the surface waters were measured and samples for hydrochemical analyses were collected, was operated during vessel movement. A wide set of hydrochemical analyses was carried out, including tests for key nutrients (silicon and different forms of nitrogen and phosphorus), dissolved oxygen, and values of pH and total alkalinity. The report describes the hydrochemical conditions in the southwestern part of the Kara Sea. The basic results are presented and compared to those of the preceding integrated expeditions (49th cruise of the RV
Dmitrii Mendeleev
in 1993 and 54th cruise of the RV
Akademik Mstislav Keldysh
in 2007).
—
The studies were conducted along the transect (11 stations) from the inner part of Khatanga Bay in the south to the Laptev Sea continental slope in the north in September 17—20, 2017. Four biotopes ...with different parameters of the pelagic environment, composition, quantitative characteristics and vertical distribution of phytoplankton have been distinguished: the inner part of the Khatanga Bay, estuarine frontal zone, western shelf of the Laptev Sea and continental slope area. The inner part of Khatanga Bay and the continental slope are characterized by the highest values of phytoplankton abundance and biomass, which reach 1 × 10
6
cell/L and 160 mg/m
3
, respectively. The formation of the maximum at a depth of 45 m is typical for the phytoplankton vertical distribution in the continental slope area. Algal biomass in the maximum reaches 400 mg/m
3
which is the highest value for the transect. Well-pronounced latitudinal zoning in the structure of phytoplankton communities has been determined in the western part of the Laptev Sea similar to that in other regions of the Arctic seas under a strong impact of Siberian rivers discharge.
PDF