Mikhail Flint

Plankton distribution associated with frontal zones in the vicinity of the Pribilof Islands

We studied the effect of four types of fronts - the coastal front, the middle front, the shelf partition front and the shelf break front on the quantitative distribution and the composition of plankton communities in the Pribilof area of the eastern Bering Sea shelf in late spring and summer of 1993 and 1994. The coastal fronts near St. Paul and St. George Islands and the coastal domains encircled by the fronts, featured specific taxonomic composition of planktonic algae, high abundance and production of phytoplankton, as well as large numbers of heterotrophic nanoplankton. The coastal fronts were also characterized by high values of total mesozooplankton biomass, high concentrations of Calanus marshallae, as well as relatively high abundances of Parasagitta setosa and Euphausiacea compared to surrounding shelf waters. We hypothesize that wind induced erosion of a weak thermocline in the inner part of the coastal front as well as transfrontal water exchange in subthermocline layers result in nutrient enrichment of the euphotic layer in the coastal fronts and coastal domains in summer time. This leads to prolonged high primary production and high phytoplankton biomass. In this paper a new type of front ‐ the shelf partition front located 45-55 km to the north-east off St. Paul Island is described which is assumed to be formed by the flux of oceanic domain waters onto the shelf. This front features a high abundance of phytoplankton and a high level of primary production compared to the adjacent middle shelf. Near the southwestern periphery of the front a mesozooplankton peak occurred, composed of C. marshallae, with biomass in the subthermocline layer, reaching values typical for the shelf break front and the highest for the area. High abundance of phyto- and zooplankton as well as heterotrophic nanoplankton and elevated primary production were most often observed in the area adjacent to the shelf break front at its oceanic side. The phyto- and mesozooplankton peaks here were formed by oceanic community species. The summer levels of phytoplankton numbers, biomass and primary production in the shelf break frontal area were similar to those reported for the outer and middle shelf during the spring bloom and the coastal domains and coastal fronts in summer. In the environment with a narrow shelf to the south of St. George Island, the mesozooplankton peak was

Mass development of the planktonic diatom Proboscia alata over the bering sea shelf in the summer season

During most of the vegetation season from late May to early September, the large-sized diatom alga Proboscia alata forms local patches with high abundances and biomasses in different oceanographic domains of the eastern Bering Sea shelf. The average abundance and biomass of the species in these patches amounts to 0.7 × 106 cells/l and 5 g WW/m3, respectively, for the layer of 0–25 m, while the corresponding estimates for the layer of the maximal species concentrations are 4.0 × 106 cells/l and 38 g WW/m3 (1.6 g C/m3). These levels of abundance and biomass are typical of the spring diatom bloom in the region. The outbursts of P. alata mass development are an important element of carbon cycling in the pelagic zone of the shelf area in the summer season. The paradox of the P. alata summertime blooms over the middle shelf lies in their occurrences against the background of the sharp seasonal pycnocline and the deficiency in nutrients in the upper mixed layer. The duration of the outbursts in the P. alata development is about two weeks and the size of the patches with high abundances can be as large as 200 km across. Degradation of the P. alata summertime outbursts may occur during 4–5 days. The rapid sinking of the cells through the seasonal pycnocline results in an intense transport of organic matter to the bottom sediments. One of the possible factors responsible for the rapid degradation of the blooms is the affect on the population by ectoparasitic flagellates. At the terminal stages of the P. alata blooms, the share of infected cells may reach 70–99%.

Authigenic Mg-calcite at a cold methane seep site in the Laptev Sea

Authigenic minerals were studied in Holocene shelf sediments of the Laptev Sea (cold methane seep site, water depth 71 m). The study presents the first finds of large hard carbonate concretions with Mg-calcite cement in recent sediments of the Arctic shelf seas. These concretions differ from previously reported glendonites and concretions from bottom sediments of the White Sea, Kara Sea, Sea of Okhotsk, etc. A study of the morphology, microstructure, and composition of these newly reported concretions revealed the multistage formation of carbonates (structural varieties of Mg-calcite and aragonite). It was shown that organic matter played an important role in the formation of authigenic carbonates, i.e., in the formation of sedimentary–diagenetic Mg-calcite. The role of methane as a possible source for authigenic carbonate formation was estimated. It was found that methane-derived Mg-calcite accounts for 17–35% of concretion materials. Mg-calcite had δ13С-Сcarb values between–24 and–23‰ and δ13С-Сorg values between–44.5 and–88.5‰.

Methane as an Organic Matter Source and the Trophic Basis of a Laptev Sea Cold Seep Microbial Community

ABSTRACT An area of cold methane seeps at the bottom of the Laptev Sea was investigated. High rates of methane oxidation were revealed in the sediments and in the water column. Anaerobic methane oxidation carried out by the ANME-2 a/b consortium was coupled to sulfate reduction. Bacteria of the genera Sulfurovum and Arcobacter were the agents of the sulfur cycle. Methane unconsumed in the sediments diffused into the near-bottom water, where it was oxidized by methanotrophic bacteria. Methanotrophic activity was essential for development of symbiotrophic tubeworms of the upper sediment layers, which were responsible for the process of bioturbation.

Ecosystems of the Russian Arctic-2015 (63rd Cruise of the research vessel Akademik Mstislav Keldysh)

The ecosystems of the maritime Arctic have undergone pronounced restructuring over the past several decades, which is largely caused by global and regional climate changes, as well as by various anthropogenic impact. Many Arctic regions have accumulated high ecological risks. Geopolitical, economic, and ecological considerations determine the need to know which changes in the Arctic natural complexes should be expected in the near future. All of the above generates strong interest in studying Arctic ecosystems. The current state of both climatic and anthropogenic changes in the Arctic Basin largely depend on the processes that take place on the shelves of epicontinental Arctic seas. The shelves are zones of interaction between the Arctic Basin and continents, regions from where huge volumes (2300–2500 km3 per year) of continental runoff f low into the Arctic and where the runoff undergoes transformation. Over the Arctic Shelf waters form which lately enter the Central Arctic Basin. The process determines the transfer of nutrients, suspended and dissolved matter, and allochthonous materials, including pollutants brought to the shelf by river runoff. Russia, the largest Arctic state, whose jurisdiction embraces more than 70% of the Arctic Shelf, is destined to play a significant role in Arctic studies. Moreover, this has been established by the Strategy for Developing the Arctic Zone of the Russian Federation and Ensuring National Security until 2020, signed by the President of the Russian Federation on February 20, 2013.

Distribution and Feeding of Herbivorous Zooplankton in the Laptev Sea

Sampling was conducted along the quasi meridional transect at 130° E from the Lena River estuary to northern deep-sea regions of the Laptev Sea in September 2015. The latitudinal zonality and the impact of river runoff are manifested in the temperature and salinity distribution, concentration of particulate organic matter, and the structure of plankton communities. The differences in the chl a concentration and primary production along the transect are insignificant. The feeding rate of mesozooplankton herbivores was assessed by a fluorescence technique. The total consumption of phytoplankton biomass and primary production are estimated based on the feeding rate, abundance of zooplankton species, and their diel migrations. The daily grazing impact of zooplankton on phytoplankton biomass increases from 2% on the inner shelf to 3% on the mid-shelf, 5% on the outer shelf, and 10% in the deep-sea part of the basin. The consumption of primary production also increases: 1, 4.5, 5.7, and 13.9%, respectively. In the fall, the consumption of phytoplankton does not compensate the energy demands for respiration. The latitudinal zonality of the Laptev Sea appears not only in the hydrophysical water parameters and the structure of plankton communities, but also in their functional characteristics.

Plankton Communities in the Eastern Mediterranean Coastal Waters

Plankton in the Eastern Mediterranean Sea has got a relatively poor study compared to that in the other regions of the basin. The available data mostly cover the central and the northern parts of the Levantine basin [5, 10, 13]. The data on the plankton in the Eastern Mediterranean coastal waters and closely adjacent areas are very few. Most of them were presented by Abi-Saab and Lakkis [1, 2, 6, 7, 8, 9]. The studies by Abi-Saab and Lakkis ere done in the Lebanese coastal waters and focused on taxonomic composition and temporal/spatial variability of the plankton community in the surface layer only.