Eastern Kara Sea Research Articles

Vertical distribution of primary production and chlorophyll a in the eastern Kara Sea: Relations with river plume effects in late summer and autumn

Quantification of the vertical distribution of chlorophyll a (Chl-a), as one of characteristics of primary production (PP), is critically important to estimate annual PP in the water column (IPP) using models and remote sensing data. IPP estimation in optically complex and highly variable waters such as the Kara Sea is not a trivial task. In the present study, based on the data obtained during three multidisciplinary cruises to the eastern regions of the Kara Sea in August–October, the differences in the vertical distribution of Chl-a and PP under and without the influence of the river plume (Case II and Case I water types, respectively) are established. In Case I waters in August 2014, under the low values of the diffuse attenuation coefficient (Kd) of downwelling photosynthetically available radiation (PAR) (the median value (Me) Kd = 0.158 m-1) and the deep euphotic layer (Zeu) (Me = 30 m), the deep chlorophyll maximum (DCM) was well-pronounced. At the end of September 2015 in Case II waters influenced by the river runoff, when Me Kd increased 1.7-fold and Zeu decreased 1.3-fold, the DCM was absent. Also, the DCM was not manifested at the end of the growing season, under conditions of extremely low underwater PAR (Me = 0.35 mol quanta m−2 d−1). In the sampling period, the PP maxima were observed at the surface and the DCM did not influence the vertical PP distribution. The depth of the nitracline was directly associated with the distribution of riverine waters and determined the depth and degree of DCM manifestation. The outcomes of the presented study suggest that a decrease in subsurface PAR influenced by the impact of riverine waters and the total decline of incident radiation from August to October determine the vertical distribution of PP and Chl-a.

Zooplankton of the Eastern Kara Sea: Response to a Short Ice-Free Period

—A characteristic feature of the eastern Kara Sea, which is separated from its central part by the shallow Central Kara Rise, is a later ice breakup, a shorter ice-free period, and lower water temperature. Zooplankton in this part of the sea is virtually unstudied. The first data on the composition, spatial distribution of zooplankton, age structure and feeding of the dominant species, and their grazing impact on phytoplankton were obtained in the cruise 125 of the R/V Professor Shtokman (September 2013) and cruise 63 of the R/V Akademik Mstislav Keldysh (September 2015) to the eastern Kara Sea. 2015 was a typical year in terms of the ice regime for this region, while in 2013, seasonal ice coverage lasted longer than usual. Zooplankton biomass (17–112 mg dry weight m–3), to which copepods Calanus glacialis contributed the main portion, were close to the values in the central Kara Sea in September. The seasonal development of the C. glacialis population began much later than in the central Kara Sea, but development of Metridia longa was not influenced by the specifics of the ice regime and hydrophysical conditions in the eastern Kara Sea. The interannual differences in the timing of ice retreat had almost no effect on the zooplankton abundance, seasonal development of the dominant copepod populations, feeding activity, and grazing impact on phytoplankton.

Ecosystems of Siberian Arctic Seas–2022: Ecosystem of the Eastern Kara Sea, Ecological Risks Accumulated in the Basin (Cruise 89 of the R/V Akademik Mstislav Keldysh)

Ecosystems of Siberian Arctic Seas–2022: Ecosystem of the Eastern Kara Sea, Ecological Risks Accumulated in the Basin (Cruise 89 of the R/V Akademik Mstislav Keldysh)

Ecosystems of Siberian Arctic Seas – 2022: Ecosystem of the Eastern Kara Sea, Ecological Risks Accumulated in the Basin (89 Cruise of Research Vessel “Akademik Mstislav Keldysh”)

89 cruise of R/V “Akademik Mstislav Keldysh” was organized by Shirshov Institute of Oceanology in a frame of the Program “Marine Ecosystems of Siberian Arctic” and was held form 19 September to 10 October 2022. 60 scientists from the institutes of Russian Academy of Sciences, Moscow State University, Moscow Institute of Physics and Technology, VNIRO and MES participated in the cruise. Coordinated hydrophysical, hydrochemical, biooceanological, geochemical research, valuation of greenhouse gases concentration in above-water atmosphere were carried out over the shelf and continental slope of the eastern poorly known part of the Kara Sea. Ecosystem of Blagopoluchiya Bay (Novaya Zemlia) and conditions of disposals of radioactive waste in the bay were in a focus of the research as well.

Postglacial shelf erosion, riverine input and lake drainage in the eastern Kara Sea, Russia

Marine sediment core PS2719-1 represents a key sedimentary record for the reconstruction of the postglacial shelf evolution of the eastern Kara Sea west of the entrance to the Vilkitsky Strait. Sedimentological, chronological, geochemical, mineral magnetic and micropaleontological data were used to investigate the sedimentary evolution of the area in unprecedented detail. Four phases of sedimentation were identified, which are closely related to sea-level rise and input from the Yenisei and Taymyr Rivers. Sedimentation likely commenced directly after regional deglaciation prior to 13.6 cal ka BP. Basal sediments are coarse grained and rich in terrestrial organic matter, which points to shelf erosion as the dominating sedimentation process. Around 13.6 cal ka BP Yenisei River water masses reached the area, causing a shift in heavy mineral assemblages and a distinct peak in magnetic susceptibility. This phase was followed by increased sedimentation rates during the early Holocene, which were related to high sediment supply from Lake Taymyr, possibly due to the opening of an ice dam in the Lower Taymyra River area. These sediments are characterized by high terrestrial organic matter accumulation, a fine-grained composition, and a heavy mineral assemblage reflecting the sediment source on the Taymyr Peninsula. High burial rates are reflected by high Mn contents. The transition to modern conditions commenced already around 8.5 cal ka BP and were fully established at ca. 5 cal ka BP, being documented in mineral magnetic evidence and foraminiferal assemblages and are characterized by more marine conditions and a strong influence of the Yenisei River.

Sea ice conditions and navigability through the Northeast Passage in the past 40 years based on remote-sensing data

ABSTRACT Sea ice conditions and navigability along four typical routes of the Northeast Passage (NEP) are analysed using remote-sensing data from 1979 to 2019. The influence of air temperature (T air) and surface wind on the sea ice concentration (SIC) and the navigability of routes is determined. It is found that the annually averaged SICs of the different routes have decreased over the past 41 years. The fastest rate of decrease occurred in the Kara Sea (∼−1% per year), while the slowest rates of decrease occurred in the Laptev/East Siberian Sea (∼−0.42% per year). The number of navigable days for the Kara Sea has become ∼1–2 months longer than the Laptev/East Siberian Sea route as a result. The effect of T air on SIC, quantified by ΔSIC/ΔT air in the routes through the eastern Kara Sea and Laptev/East Siberian Sea in 2010s was ∼−0.04/°C, two to three times that seen during the 1980s. Air temperature is becoming a significant driving force of melting ice in these routes. Surface winds are also a crucial factor for the navigability of the Vilkitsky Strait and Long Strait, as they drive ice drift, and affect the navigability of the Kara Strait by introducing warm air.

Assessment of phytoplankton photosynthetic efficiency based on measurement of fluorescence parameters and radiocarbon uptake in the Kara Sea

Spatial distribution of relative electron transport rate (rETR) values, the maximum quantum efficiency of PSII (Fv/Fm), and biomass-specific primary production (PB, mg C (mg Chl a)−1 h−1) were described for the eastern part of the Kara Sea in the autumn (September). A characteristic feature of this period was a noticeable decrease in the length of the day and the elevation angle of the sun, leading to a significant decrease in surface photosynthetically active radiation (PAR). Despite low light in the euphotic zone, the phytoplankton maximum quantum efficiency of PSII (Fv/Fm) was high (0.5–0.7) in the upper 30-m layer of the water column, which indicates a potentially active state of phytoplankton. At the same time, the main productive activity of phytoplankton was linked to the surface 0–3 m and was closely related to the daily incident PAR and the share of diatoms in the total phytoplankton biomass. Despite a decrease in light level and following a reduction in the values for productive characteristics of the phytoplankton community, diatoms continued to play a major role in primary productivity in the eastern Kara Sea at the end of the vegetative season. Comparative analysis of data obtained by two different techniques – fluorescence measurements and experimental carbon fixation estimations – demonstrated a close relationship between rETR and PB. However, surface values of PB changed more strongly than rETR, which may, apparently, reflect different efficiency in the use of absorbed light energy in the synthesis processes. Photosynthetic efficiency, reflecting the extent of use of the light energy caught in processes of organic matter synthesis, can be expressed through the ratio between PB and rETR values. The PB/rETR ratio increased in areas characterized by drastic gradients of hydrophysical conditions: over the external coastal shelf, central shelf and lower continental slope of the St Anna Trough.

Abundance and activity of microorganisms at the water-sediment interface and their effect on the carbon isotopic composition of suspended organic matter and sediments of the Kara Sea

At ten stations of the meridian profile in the eastern Kara Sea from the Yenisei estuary through the shallow shelf and further through the St. Anna trough, total microbial numbers (TMN) determined by direct counting, total activity of the microbial community determined by dark CO2 assimilation (DCA), and the carbon isotopic composition of organic matter in suspension and upper sediment horizons (δ13C, per thousand) were investigated. Three horizons were studied in detail: (1) the near-bottom water layer (20-30 cm above the sediment); (2) the uppermost, strongly hydrated sediment horizon, further termed warp (5-10 mm); and (3) the upper sediment horizon (1-5 cm). Due to decrease in the amount of isotopically light carbon of terrigenous origin with increasing distance from the Yenisei estuary, the TMN and DCA values decreased, and the δ13C changed gradually from -29.7 to -23.9 per thousand. At most stations, a noticeable decrease in TMN and DCA values with depth was observed in the water column, while the carbon isotopic composition of suspended organic matter did not change significantly. Considerable changes of all parameters were detected in the interface zone: TMN and DCA increased in the sediments compared to their values in near-bottom water, while the 13C content increased significantly, with δ13C of organic matter in the sediments being at some stations 3.5- 4.0 per thousand higher than in the near-bottom water. Due to insufficient illumination in the near-bottom zone, newly formed isotopically heavy organic matter (δ13C(-) -20 per thousand) could not be formed by photosynthesis, active growth of chemoautotrophic microorganisms in this zone is suggested, which may use reduced sulfur, nitrogen, and carbon compounds diffusing from anaerobic sediments. High DCA values for the interface zone samples confirm this hypothesis. Moreover, neutrophilic sulfur-oxidizing bacteria were retrieved from the samples of this zone.

Peculiarities of the rare-earth element distribution in the modern bottom sediments of the White Sea and the lower reaches of the Severnaya Dvina River

The study of the rare-earth element (REE) systematics in the modern bottom sediments of the White Sea and the lower reaches of the Severnaya Dvina River showed that they were derived by the simple mixing of the detrital material from two geochemically contrasting provenances: the Kola-Karelian geoblock almost completely consisting of Archean rocks and the northwestern Mezen syneclise made up of the Upper Vendian, Paleozoic, and Mesozoic rocks. This is best manifested by the changes in ɛNd(0). In terms of the GdN/YbN and Eu/Eu*, most of the studied samples are comparable with the Post-Archean craton complexes, some of which resemble the average composition of the Archean mudstone. Based on the ΣREE and LaN/YbN, the modern bottom sediments are subdivided into two groups: (1) those close to basalts and granites and (2) those approximating common sedimentary rocks. From the lower reaches of the Pinega River to the Tersky coast, the maximal average (La/Yb)RPSC, (Gd/Yb)RPSC, LaN/YbN, and GdN/YbN ratios were determined in the samples taken at the boundary of Dvina Bay with the Basin, i.e., in the sediments with the highest content of the pelitic component. In general, the geochemical composition of the modern bottom sediments of almost the entire White Sea area was defined by input of the eroded products of the mature continental crust with the Severnaya Dvina River, the main river of the region. Such a setting, when the formation of the sediments in a peri- or intracontinental marine basin is controlled by one large river system, presumably may be propagated to the sedimentation in the Laptev Sea, the eastern Kara Sea, the Bay of Bengal, and other basins.

The eastern extent of the Barents–Kara ice sheet during the Last Glacial Maximum based on seismic-reflection data from the eastern Kara Sea

We present sub-bottom profiling (sparker and Parasound) results from the eastern Kara Sea, on the Eurasian Arctic margin, which enable the identification of the Last Glacial Maximum (LGM) ice extent. The analysed profiles show that glacigenic diamicton is ubiquitous at the seafloor, east of about 95°E and 78°N. The eastern margin of this diamicton is expressed in a conspicuous morainic ridge at the entrance to the Vilkitsky Strait, and to the south the diamicton projection aligns with the LGM limit mapped at the north-western Taymyr. The bottom of the Voronin Trough further north is also covered with diamicton and has numerous erosional bedforms, indicating a streamlined flow of grounded ice along the trough. Accurate dating of the diamicton is not attainable, but the correlation of pre-diamict sediments to well-dated sections in the Laptev Sea, and available 14C ages from sediments on top of the diamicton, indicate its LGM age. These results support the palaeogeographic reconstruction that assumes the extension of the LGM Barents–Kara ice sheet as far east as Taymyr. This configuration implies that LGM ice blocked the drainage of the Ob and Yenisey rivers on the Kara shelf. This inference is consistent with the presence of large (>100 km wide) lenses of basin infill adjacent to the southern margin of the diamicton. However, the limited distribution of the eastern Kara ice lobe, not extending on Severnaya Zemlya, suggests that the ice was fairly thin and short-lived: insufficient for the accumulation of the gigantic proglacial lakes that occurred during earlier glaciations.

Polynya Area in the Kara Sea, Arctic, Obtained With Microwave Radiometry for 1979–2003

The polynya signature simulation method is applied to satellite microwave radiometry data to get the mean (January-April) polynya distribution in the Kara Sea for 1995-2004. Temporal variability of polynya location and extent is confirmed with the variability of ERA40 surface wind speeds. The mean (January-April) fraction of ice area of 65%-85% ice concentration relative to the mean daily total Kara Sea ice area agrees well (correlation coefficient: 0.79) with the mean daily total Kara Sea polynya area for 1996-2003. The resulting linear fit is used to extend the polynya area time series until 1979. During 1979-2003, the polynya area increased by 2400 km2/dec. This is accompanied with slightly increasing southerly winds. Polynyas in the eastern Kara Sea seem to play a nonnegligible role for the winter-time Kara Sea ice export.

Sediment dynamics in the Eurasian Arctic Ocean during the last deglaciation — The clay mineral group smectite perspective

This study focuses on sedimentological investigations of sediment cores recovered during the international Arctic′91, expeditions with the German research ice breaker RV “ Polarstern” to the European sector of the Arctic Ocean. Here, we deduce the last glacial/interglacial changes in transport mechanism and sedimentation from the clay mineral group smectite. We choose the smectites as an example of how sediment mineralogy can be linked with particular source regions (the Kara and Laptev seas), distinct transport mechanism (sea ice and surface currents) and sedimentation processes. Smectite contents in Arctic sediments discussed for two time slices, including the Last Glacial Maximum (LGM), and the last deglaciation (Termination I), reveal the highest variability subsequent to the retreat of the Eurasian ice sheets. Our results show that smectite anomalies in the Eurasian Basin are associated with distinct meltwater pulses and occurred around 13.5–13.0 14C ka B.P. Compelling evidence is provided that these anomalies are deduced from sea-ice entrained sediments from the eastern Kara Sea that entered the Arctic Ocean after ice-sheet break-up and eventually flooding of the Kara Sea. We propose that smectite anomalies in sediments of the eastern Arctic Ocean can be utilized to identify deglacial events and to help decipher configurations of the Eurasian ice sheets. The identification of smectite maxima along the modern sea-ice edge in the Eurasian Basin further indicates biologically enhanced sedimentation from melting sea ice allowing the reconstruction of seasonally open water in the region. Hence, considering the poor preservation conditions of primary paleoceanographic proxies in the Arctic Ocean, the clay mineral contents, particularly the smectite group, may be one alternative tool for paleoclimatic reconstruction in the Eurasian Basin.

The eastern extent of the Barents–Kara ice sheet during the Last Glacial Maximum based on seismic-reflection data from the eastern Kara Sea

We present sub-bottom profiling (sparker and Parasound) results from the eastern Kara Sea, on the Eurasian Arctic margin, which enable the identification of the Last Glacial Maximum (LGM) ice extent. The analysed profiles show that glacigenic diamicton is ubiquitous at the seafloor, east of about 95°E and 78°N. The eastern margin of this diamicton is expressed in a conspicuous morainic ridge at the entrance to the Vilkitsky Strait, and to the south the diamicton projection aligns with the LGM limit mapped at the north-western Taymyr. The bottom of the Voronin Trough further north is also covered with diamicton and has numerous erosional bedforms, indicating a streamlined flow of grounded ice along the trough. Accurate dating of the diamicton is not attainable, but the correlation of pre-diamict sediments to well-dated sections in the Laptev Sea, and available 14 C ages from sediments on top of the diamicton, indicate its LGM age. These results support the palaeogeographic reconstruction that assumes the extension of the LGM Barents‐Kara ice sheet as far east as Taymyr. This configuration implies that LGM ice blocked the drainage of the Ob and Yenisey rivers on the Kara shelf. This inference is consistent with the presence of large (>100 km wide) lenses of basin infill adjacent to the southern margin of the diamicton. However, the limited distribution of the eastern Kara ice lobe, not extending on Severnaya Zemlya, suggests that the ice was fairly thin and short-lived: insufficient for the accumulation of the gigantic proglacial lakes that occurred during earlier glaciations.

Comparison study of the modern ostracod associations in the Kara and Laptev seas: Ecological aspects

Recent ostracod assemblages were investigated from coretop sediment samples collected in the eastern Kara Sea from water depths down to 300 m. A total of 45 species were identified, 27 of them were reported for the Kara Sea for the first time. The Kara Sea data were compared with our results on the distribution of ostracods in the eastern Laptev Sea. The spatial distribution of recent taxa and the ecological groupings demonstrate a clear relation to dominant environmental factors which range from estuarine to full-marine conditions. Four assemblages related to average summer bottom water salinities were established: (1) a freshwater assemblage from the inner estuaries of the Ob' and Yenisei rivers with salinities less than 2 and from thermokarst lagoons of the southern Laptev Sea coast with strong salinization in winter; (2) a brackishwater assemblage of the outer estuaries of the Ob' and Yenisei rivers with salinities up to 26; (3) a mixed euryhaline–marine assemblage dominated by euryhaline species Paracyprideis pseudopunctillata and Heterocyprideis sorbyana from the inner shelf river-affected zone of the Kara and Laptev seas, where salinities range between 26 and 32; (4) a taxonomically diverse marine assemblage dominated by shallow-water marine taxa from the northern parts of the Kara and Laptev shelves and upper continental slope with stable bottom environments and a salinity higher than 32. Abundant euryhaline species found at greater water depths are identified as part of an ice-rafted assemblage. They are possibly entrained into the newly formed fast ice during autumn storms and freeze-up period and then transported to the distal open-sea areas during summer.

Late Cenozoic sedimentary environments in the Amundsen Basin, Arctic Ocean

Analyses of sediment cores recovered on the Arctic ’91 cruise with RV Polarstern to the Amundsen Basin and Lomonosov Ridge identify four main sedimentary facies and associated depositional sedimentary processes. These include: (1) homogenous mud facies interpreted as hemipelagic deposits, most abundant in the central parts of the Amundsen Basin; (2) fining upward cycle facies interpreted as fine-grained distal turbidite deposits, present in all Amundsen Basin cores, but most abundant laterally in the basin; (3) massive diamicton facies, found in the North Pole core; and (4) laminated diamicton facies, abundant in the upper parts of Lomonosov Ridge cores. Both diamictons are heavily influenced by ice-rafted debris, and the massive diamicton may result from redeposition of laminated diamicton downslope from the Lomonosov Ridge. The Lomonosov Ridge core exhibits a sedimentation rate of 29 mm/ka, while the sedimentation rates of turbidite rich sediments of the Amundsen Basin may be up to 10 times as high. Clay minerals show that the eastern Kara Sea and the Laptev Sea is the source area for most of the sediments, while some clay mineral zones may have their source in northern Greenland or the Barents Sea shelf.

Sea-ice transport of riverine particles from the Laptev Sea to Fram Strait based on clay mineral studies

The aim of this study was to identify pathways and processes of modern sediment transport from the Siberian hinterland to the Laptev Sea and further to the Arctic Ocean. Clay mineral analyses were performed on riverine suspended particulate material (SPM), surface sediments of the Laptev Sea shelf, and sea-ice sediments (SIS). Material collected during seven expeditions was included in this study. Clay mineral assemblages are used to decipher the distribution of riverine sediments on the shallow Laptev Sea shelf, the entrainment of fine particles into newly forming ice, and the transport of SIS from the Laptev Sea towards the ablation areas. A cluster analysis of our data set shows that the clay mineral assemblages of Laptev Sea shelf sediments and SIS are controlled mainly by the input of riverine SPM supplied by the Khatanga, Lena, and Yana Rivers. Whereas the western shelf clay-mineral province is characterized by enhanced smectite concentrations supplied by the Khatanga River, the eastern Laptev Sea is dominated by illite discharged through the Lena and Yana Rivers. The SIS smectite concentration serves as an indicator for sediment source areas on the circum-Arctic shelves. Subsequently, the Transpolar Drift can be distinguished into a Siberian Branch fed from the eastern Kara Sea and the western Laptev Sea, and a Polar Branch originating from the eastern Laptev Sea.

Influence of Sea Ice on Under-ice Mixing Under Stratified Conditions: Potential Impacts on Particle Distribution

The influence of ice drift upon the thermohaline structure of the upper sea-layer was studied based on CTD-probing near the edge of the eastern Kara Sea ice cover. This study was aimed at investigating the dynamics and spatial – temporal variability of thermohaline frontal boundaries connected with the moving ice edges of different concentration. Investigations revealed that locally mixed thin layers are formed in the subsurface layer under the influence of ice drift. Under conditions of uninterrupted stratification, redistribution and capture of suspended matter within these thin layers may occur. Furthermore, under conditions of freezing and demolition of density stratification in the surface layer, this matter can be redistributed and incorporated into sea ice.

Modelling the dispersion of 137Cs and 239Pu released from dumped waste in the Kara Sea

Three-dimensional, baroclinic, circulation models are applied to study the dispersal of radioactivity in the Barents Sea and Kara Sea. The release is supposed to occur at underwater dump sites for radioactive waste in the Kara Sea, used by the former Soviet Union. Two different spatial scales of dispersion are considered: the regional scale (the far field), which covers the shelves of the Barents and Kara Seas and the local scale (the near field) which is focused mainly on Abrasimov Bay where the dumping partly took place. The regional-scale model results suggest that, even for a worst case scenario, the radioactive contamination of Siberian coastal waters would be relatively small compared to observations in other marine systems (e.g the Baltic Sea and the Irish Sea). Realistic gradual release scenarios show very low concentrations in the central and eastern Kara Sea. A significant contamination of surrounding seas like the Laptev Sea, the Arctic Ocean or the Barents Sea by radioactive waste dispersion from the Kara Sea seems to be unlikely.