Ostracod species of the genus <em>Cytheropteron</em> from late Pleistocene-Holocene and recent sediments of the Laptev Sea (Arctic Siberia)

Sixteen species of the genus Cytheropteron from the Laptev Sea Late Pleistocene, Holocene deposits and Recent surface sediments have been described. Analysis of the literature on this subject and the collections of O.M.Lev from St. Petersburg, together with our own material from the Laptev Sea, allowed us to introduce certain changes in the taxonomy of this genus. One species Cytheropteron laptevensis Stepanova sp. nov. is described as new

Recent Ostracoda from the Laptev Sea (Arctic Siberia): Species assemblages and some environmental applications

Ostracod assemblages from coretop sediments collected at 26 localities at different depths of the Laptev Sea shelf and upper continental slope were investigated for assemblage studies. A total of 41 species belonging to 19 genera and 12 families have been identified. Three assemblages have been established that could be linked to environmental factors such as water depth, bottom salinities, water mass circulation and sea-ice transportation. The species-rich and abundant assemblages of the western and central Laptev Sea were related to the Atlantic waters occupying the upper continental slope. These include relatively deep-water forms that show clear affinities to North Atlantic and Arctic Ocean assemblages (Cytheropteron biconvexa, C. testudo, C. simplex, C. nodosoalatum, C. inflatum, C. porterae, Krithe glacialis, K. minima, Pseudocythere caudata, Polycope punctata, P. orbicularis). In the eastern middle shelf region, the assemblage is comprised of Acanthocythereis dunelmensis together with other normal marine species (Semicytherura complanata, Elofsonella concinna, Cluthia cluthae). This assemblage seems connected to the winter flaw polynya which is believed to be the main area of sediment entrainment into sea ice. The inner shelf assemblage of the southern Laptev Sea is dominated by shallow-water euryhaline species (Paracyprideis pseudopunctillata and Heterocyprideis sorbyana) with admixture of the brackish-water species Roundstonia macchesneyi. The unusual occurrence of a number of shallow-water ostracod species on the upper continental slope may be explained by ice-rafting which these ostracods are probably able to survive

Stable oxygen and carbon isotopes in modern benthic foraminifera from the Laptev Sea shelf: implications for reconstructing proglacial and profluvial environments in the Arctic

Measurements of δ18O and δ13C isotopes in three benthic foraminiferal species from surface sediments of the eastern Laptev Sea are compared to water δ18O values and δ13C values of dissolved inorganic carbon (DIC). Samples investigated originate from two environmentally contrasting core locations, which are influenced by riverine freshwater runoff to a varying degree. At the river-distal site, located within relatively stable marine conditions on the outer shelf, Elphidiella groenlandica, Haynesina orbiculare and Elphidium excavatum forma clavata show a positive specific offset of 1.4‰, 1.5‰ and 1‰, respectively, in their δ18O values relative to the expected value for inorganic calcite precipitated under equilibrium conditions. At the site close to the Lena River confluence, with enhanced seasonal hydrographic contrasts, calculated δ18O offsets in E. groenlandica and in H. orbiculare remain about the same whereas E. e. clavata displays a distinctly negative offset of −1.8‰. The δ18O variation in E. e. clavata is interpreted as a vital effect, a finding which limits the potential of this species for reconstructing freshwater-influenced shelf paleoenvironments on the basis of oxygen isotopes. This interpretation gains support when comparing foraminiferal δ13C with the δ13CDIC of the water. While some of the difference in the carbonate δ13C seems to be controlled by a riverine-related admixture of DIC, clearly defined δ13C ranges in each of the three foraminifera at the river-proximal site shows that also the carbon isotopic signature in E. e. clavata is particularly affected by environmental factors

Last postglacial environmental evolution of the Laptev Sea shelf as reflected in molluscan, ostracodal and foraminiferal faunas

Temporal and spatial variations in the species composition of modern and Holocene assemblages of molluscs, ostracods, and foraminifers from the Laptev Sea shelf (Arctic Siberia) have been investigated to reconstruct palaeoenvironmental changes during the last postglacial times and associated sea-level rise. Analysis of coretop sediment samples allowed to distinguish four modern assemblages. The specific habitat preferences of these species groups, such as water depth and salinity, were then used to interpret past environmental changes on the basis of two radiocarbon-dated sediment cores from the eastern middle shelf region, i.e., obtained from the Yana (51 m water depth) and Lena (45 m water depth) palaeovalleys. Despite the water depth difference of the two core sites, all downcore data document uniform fossil evidence for a gradual transformation of the Laptev Sea shelf from a terrestrial to a marine environment due to the southward transgressing sea. Three major phases have been recognized. These reflect: (1) a nearshore brackish-water environment of the initial stage of inundation (11.3–11.1 in the Yana and 11.2–10.8 cal. ka in the Lena palaeovalley); (2) a shallow inner-shelf, fluvially affected environment (11.1–10.3 and 10.8–8.2 cal. ka); (3) a modern-like marine environment which eventually became established since 10.8 and 8.2 cal. ka, depending on the specific water depth of each core site

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

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

First discovers of Pleistocene authigenous carbonate crusts (ACC) at the Mendeleev Rise, Arctic Ocean

The Mendeleev Rise (or Mendeleev Ridge) is a part of Central Arctic Uplifts domain that extends from the Eastern Siberian Shelfto the central areas of the ocean, where it is adjacent to the Alpha Ridge bisecting the Amerasian Basin. The crust of Mendeleev Rise belongs to the continental type (Poselov et al. 2007). New geological, geophysical and tectonic data were obtained within Alpha-Mendeleev Rise after few expeditions to Arctic Ocean in year 2000, 2005 and 2012. Thousands of rock fragments were dredged: 50–65% – carbonate rocks (mainly dolomite and limestone); 20–25% – sandstones, siltstones, mudstones; 5–20% – igneous rocks (mainly granites, gabbro-dolerite and few types of basalt); ~ 10% – metamorphic rocks (mainly greenschist facies). Light dolomites with little flora and fauna represent about two-thirds of the total amount of carbonate rocks, the rest are limestones, often containing well-preserved faunal remains. Paleontological study of limestones show abundance of D-P 1 fauna remnants that give us an evidence of structural connection of Mendeleev Rise and Wrangel Island (Morozov et al. 2013). Carbonate crusts were dredged from steep slopes (25–29°) with neotectonic faults on two sites at water depth more than 2 km during expedition “Arktika-2012”. Primary study showed that crusts compose of strong matrix with rounded and angular debris of local (edaphogenic) material: dolomites, dolerites, granites, metasomatic and terrigenous rocks of different size (0.5 mm to 5 cm) (Morozov et al. 2013, Kremenetskii et al. 2015). Three samples of matrix and two of soft clay-carbonate crust’s cover were selected for detailed analysis. Petrographic features were studied using optical microscope, microprobe and X-ray analysis. Chemical elements analysis was performed with XRF and ICP-MS. All analyses were carried out in A.P. Karpinsky Russian Geological Research Institute (VSEGEI) in Saint-Petersburg. AAC’s Matrix studied with microprobe in details and consists offine-grained calcite with angular quartz grains from 1 μm to 300 μm. X-ray analysis shows calcite predominance in the matrix (>70%), rest content is presented with clasts of quartz, illite and albite – about 10%, dolomite, chlorite, montmorillonite, chamosite – 1–2%. Clasts of local debris are presented by two association: 1) large, mainly angular clasts with size from 0.5 mm to 5 cm; 2) small, mainly rounded clasts with size from 200 μm to 0.5 mm. Surface of matrix and debris is covered with soft rose clay-carbonate mass. Mineral content of clay-carbonate mass is: quartz and illite – 25–30%, calcite and albite 15–20%, chlorite, orthoclase, halite, dolomite, montmorillonite – 1–5%. Chemical composition (in percents) of matrix is close to clay-carbonate terrigenous rocks: SiO 2 – 18, Al 2 O 3 – 3.62, TiO 2 – 0.2, Fe 2 O 3 t – 1.4, MnO – 0.05 MgO – 2.35, CaO – 39.2, Na 2 O – 0.18, K 2 O – 0.47, P 2 O 5 – 0.12, L.O.I. – 34.3. Rose mass differs from matrix with silica – 46, CaO – 19, higher alkalis (Na and K) – 1.15 and 1.3. Difference in content of silica (18% vs 46%), CaO (39.2% vs 19%) says that AAC matrix and rose mass have various sources. In contrast to Paleozoic remnants in carbonates, the AAC contain planktonic and benthic foraminifera of Pleistocene age. In Arctic seas, these species are distributed in modern conditions mainly in places where the Gulf Stream arrives (Herman 1974). These data indicates local origin of ACC, main evidences includes distribution, good preservation of samples, local debris in matrix, paleontological age. However, carbonates are very limited in the Arctic Ocean (Emelyanov 2005, Chierici & Fransson 2009). In view of these parameters, AAC can’t form by itself so it may be due only to external factors. Bottom water doesn’t provide such factors. Neither necessary conditions nor material occur in these waters. So in our opinion AAC were formed with help of neotectonic fault which are supposed to be a possible path for hot fluids, which created the conditions for crusts forming and Paleozoic carbonate rocks was a source of CaCO 3