6. Unique (non-analogue) paleoenvironmental conditions of Late Pleistocene and Holocene terrestrial ecosystems of the Laptev Sea surroundings (detailed reconstruction)
T. Kuznetsova, N. Noskova, A. Bryantseva
14. Postglacial environmental changes in the western Laptev Sea: evidence from fossil benthic assemblages, isotope composition of microfossils and geochemical data
E. Taldenkova, S. Dem'yankov, A. Strezh
E. Abramova , S. Kirillov , I. Akhmetshina
The main idea of our project was to evaluate the role of Copepoda species, as a main component of the biological filter, in the sedimentation processes on the southeastern Laptev Sea shelf using data obtained in earlier studies on distribution, life cycles and seasonal dynamics of zooplankton. The main results are:
•the biological filter occupies the near-shore area in the western and the eastern parts of the Laptev Sea shelf, where small Copepoda are the most numerous organisms in the pelagic fauna;
•for all studied species the rate of filtration increases with body mass from naupliar stage to adult copepodid stages. The daily volume of water filtrated by all organisms occurring in 1 m3 of surface water in August-September, when the highest abundance was observed, is comparable with that recorded in May due to the differences in the age structure of populations in these months;
•during the whole active period of life (about 8 months) the animals from 1 m3 of surface layer filtrate approximately 13 liters of water (not taking into consideration the daily feeding rhythm);
•the seasonal vertical migrations of zooplankton in the Laptev Sea shelf might be considered as the main reason for seasonal variations in the daily volume of water filtrated by copepods.
D. Bolshiyanov, M. Pavlov, A. Makarov
The main aim of our project is a complex investigation of arctic lake sediments in order to reconstruct the paleoenvironment during the last millennium. The obtained data are an important link for studying the climate of the past and makes forecasting future climatic changes possible.In the course of the project, sediments of such arctic lakes as Izmenchivoye (Severnaya Zemlya Archipelago), Astronomicheskoye, Levinson-Lessing, Schel', Taimyr (Taimyr Peninsula), Lama, Kapchuk, Talikit, Tonel' (Putorana Plateau), Nikolay-Kyuele and Mentikilir (Lena Delta area) were investigated. In addition to the lakes stated in the project, three further lakes were surveyed. These are two lakes in the Arkhangelsk area: Zabugornoye and Kamennoye; and the lake in the Lena Delta on Buor-Khaya-Sise Island. One of the important results of the project is the reconstruction of the Little Ice Age (LIA) phases. Almost all investigated sediments have thin annually deposited lamination (varves). The calculation of these layers in connections with the analysis of spore-pollen, geochemical and other data allowed establishing sufficiently precise time frameworks of climatic fluctuations. The events of the LIA started and ended asynchronously in different parts of the Russian Arctic. The cooling of the LIA took place in 2 phases.
M.N. Grigoriev, I. Shapovalova, G. Kraev
Within the scope of this study, the main parameters of sub-sea permafrost evolution and distribution within the shallow shelf zone of the Laptev Sea were evaluated. Newly obtained data as well as other published and unpublished information concerning shoreface composition, permafrost features, lithology, morphology and hydrodynamics were reviewed and analyzed. Based on the available data sub-sea permafrost evolution was described and its distribution in the near-shore zone was estimated. The main objects of the investigations are: sub-sea permafrost table position, shoreface morphology, coastal dynamics, temperature and salinity regimes, bottom deposits and seabed sediment structures.
E. Gusev, P. Rekant, K. Malinkin
The aim of this project was to study the Kara and Laptev shelves' paleogeographic conditions in the Late Pleistocene and to compare these conditions. The basic data for studying were seismoacoustic profiles and data from bottom mooring stations. We analyzed samples of the Kara Sea Quaternary deposits by means of the modern equipment of the Otto Schmidt Laboratory. While during the Holocene the conditions of the Kara and Laptev seas were comparable, it is possible to speak about different paleogeographical conditions in the Late Pleistocene. We investigated the paleogeographical conditions at two key sites in the central and northern parts of the Kara Sea and at one site in the central part of the Laptev Sea.
K. Kosobokova, D. Martynova, A. Prudkovsky
The project was aimed at improving our understanding of the interdependency of biological and geochemical processes in the Kara and White seas. The role of zooplankton in the transformation of particulate organic matter in the water column was investigated on the basis of zooplankton populations in the White Sea. Faecal pellets of the dominant plankton organisms were obtained during feeding experiments and examined morphologically. Dry weight, organic carbon and nitrogen content, and C/N ratio of pellets of different types were measured. Faecal-pellet production rates were assessed under natural conditions. The structure of the zooplankton communities was studied both in the Kara and White seas in order to use the abundance and distribution data for assessing the potential zooplankton faecal-pellet production. Based on these data, the contribution of the pellet material to the vertical carbon flux was assessed for the different regions of the White and Kara seas. The regional and seasonal variations of the pellet carbon input observed during this study in both seas were strongly related to the structure of the zooplankton communities and distribution of populations of the dominant "pellet producers".
T. Kuznetsova, N. Noskova, A. Bryantseva
The main goal of the project is to elaborate and verify the reconstructed basic environmental features of the Laptev Sea shelf area and coastal lowlands during the Late Pleistocene and Holocene. The project is based on complex analyses of paleozoological and paleobotanical remains combined with geochronological and stable-isotope data. Special attention was given to the interpretation of isotope data on fossil mammal bones in comparison and correlation with the data obtained from the analysis of stable isotope ratios in forage plants. Modern analytic methods of stable isotope ratios for fossil mammal remains allow reconstructing the environmental conditions in detail. All the collected data and expected results of the project are new.
T. Matveeva, L. Mazurenko, E. Logvina
The study allowed revealing hydro-geochemical peculiarities of the hydrate formation process and revealed the origin and composition of water and gas involved in the accumulation of gas hydrates associated with venting structures in the Sea of Okhotsk. Hydrogeochemical data suggest that not only free gas expulsion but also discharge of relatively mineralized water takes place. The two types of water differ in isotopic composition from each other and seawater and play a role in the formation of carbonates and gas hydrates. The source of uprising fluids varies with time. Biogenic methane generated in situ in the upper sediment strata and methane uprising from hydrocarbon reservoirs (also biogenic in origin) are two main sources of gas hydrates. Precipitation of gas hydrates under decreasing methane solubility during gas-saturated water input and segregation of water by free gas are two main mechanisms in the developed model of gas hydrate formation.
S. Pivovarov, M. Nitishinsky, A. Novikhin
New data of nutrient distributions were obtained. Silicate, phosphate, nitrate and nitrite concentrations were measured in 758 water samples. The young scientists of the team became familiar with new methods of chemical analyses.For the first time we obtained such data which allowed us to assess nutrient fluxes into the arctic marine systems as a result of coastal erosion. The contribution of coastal erosion to the total nutrient budget is far smaller than that of river input.Our studies on nutrient budgets show that almost all systems in the Kara and Laptev seas are net autotrophic systems despite their hydrography and independent of whether they are large or small-scale systems. The only exeption is the northern part of the Ob Gulf; here we find a heterotrophic system. The bottom layer in many systems is heterotrophic, especially in winter, when the destruction of organic matter exceeds its production.The contribution of different sources to the nutrient budgets depends on system dimension, and hydrological and ice conditions. River run-off dominates in the bays, which are directly subject to discharge of the great Siberian rivers. Coastal erosion dominates in the 500 m coastal belt. For large-scale systems, the main fluxes come from the bottom layer and from the Arctic Basin.
Ye.I. Polyakova, T. Klyuvitkina, E. Golovnina
The main goal of our study was to reveal temporal and regional peculiarities of hydrological and sedimentation processes in the western Laptev Sea and the neighboring regions of the southeastern Kara Sea. These regions are influenced by extensive riverine discharge. The study was based on the investigation of fossil algae assemblages in sediment cores as well as on detailed radiocarbon age control. Using diatom and aquatic palynomorph assemblages as a proxy the following major results were achieved: (i) the extent of the influence the Atlantic waters had on the northwestern Laptev Sea and southeastern Kara Sea during the postglacial time was revealed; (ii) variations of the surface water paleosalinities in the southeastern Kara Sea during the Holocene were reconstructed; (iii) changes in riverine discharge to the northwestern Laptev Sea and southeastern Kara Sea and the overwhelming influence of the postglacial transgression on the evolution of the Siberian arctic shelf water masses were revealed.
Pollen analysis of the two cores PS-51-159-10 and PS-51-154-11 and borehole KI001 from the outer and inner Laptev Sea shelf showed that interpretation of pollen results, pollen distribution in the spectra and its concentration have several similarities in the analyzed spectra.According to the obtained pollen results we assume that the sediments started to form under severe environmental conditions coinciding with the Late Pleistocene/Early Holocene environmental conditions as the bottom spectra is extremely poor in terms of pollen and spores content or other microfossils. All the pollen data is supported with radiocarbon data. The pollen spectra trend shows a clear transition from periglacial conditions with the dominance of transported coniferous pollen in the spectra and surroundings, represented by shrubby vegetation with xerophytes and steppe sedge, to Holocene period. The percentage spectra register rather unchangeable conditions throughout the core according to the percentage pollen diagram. Nevertheless, according to the concentration variability, which is more representative in our case it is clear that pollen production for the Holocene period varied greatly. It is likely to be explained by the ecological and environmental changes that might have occurred throughout this time span.
N.N. Romanovskii, A. Eliseeva, A. Belan
Two main objectives were studied in the research project:
•to jointly study the evolution and present condition of the ice-bearing permafrost and gas hydrate stability zone (GHSZ) on the Laptev Sea shelf and the western part of the East-Siberian Sea shelf; dynamics of the ice-bearing permafrost and GHSZ in rift structures of the arctic shelf. The first problem was investigated by means of modeling using the well-known model by Tipenko, Romanovskii and Kholodov (1999) and the published paleogeographical scenario by Romanovskii and Hubberten (2001). The paleogeographical scenario covers approximately 400 ky. Maps of the thickness of the offshore relict permafrost and GHSZ for the recent time were drawn up on the basis of the received data.
•to determine the dynamics of the ice-bearing permafrost and GHSZ in rift structures of different sizes and the location on different parts of the East Siberian arctic shelf of the during the mentioned period. The results were the first estimation for the East Siberian arctic shelf because of a continuity of coexistence of the ice-bearing permafrost and GHSZ and also because of the possibility and occurrence conditions of the open taliks and "faults" in GHSZ through which emission of greenhouse gases can occur in sub-permafrost layers.
V. Shevchenko, A. Novigatsky, A. Klyuvitkin
Within the framework of our project we studied the role of atmospherically derived elements and compounds, suspended matter, ice-rafted sediments, and vertical particle fluxes in the processes taking place in the shelf seas of the western Russian Arctic (the Laptev, Kara, Barents, Pechora and White seas) on the basis of concepts and principles of the Russian-German Program "Laptev Sea System". In 2004 the participants of this project were responsible for studying aerosols, suspended matter and particle flux in the White Sea within the scope of the "White Sea System" Program under the leadership of Academician A.P. Lisitzin. This grant, therefore, studied the composition of aerosols, suspended particulate matter (SPM), sedimentary matter from sediment traps and bottom sediments collected during the expeditions to the White Sea. A strong seasonality of aerosol and suspended matter distribution and composition in the White Sea was revealed. We could show that the composition of White Sea aerosols is similar to the composition of aerosols of the arctic seas. Wit hrespect to some chemical elements (Pb, V, Cd) aeolian input into the White Sea is of great importance. The highest concentrations of SPM are registered during the spring flood; terrigenous material dominates in the composition of SPM at this time. In summer a less prominent peak in SPM concentration is observed, This is the result of phytoplankton bloom. The lowest concentrations of both terrigenous and biogenic SPM are registered in winter. The seasonality of SPM concentrations is reflected in the seasonality of vertical particle fluxes. The character of geochemical processes in the Northern Dvina, Onega and Kem' estuaries is similar to that in the large arctic estuaries.
In 2004 the author completed her PhD thesis entitled "Pleistocene-Holocene and recent Ostracoda of the Laptev Sea and their importance for paleoenvironmental reconstructions." This work is the first detailed investigation of the Late Pleistocene-Holocene and recent ostracods of the studied area. In total 45 species belonging to 22 genera and 13 families were identified; one species was described as new. For the first time three ecologically different assemblages linked to three areas of the sea (western-central, eastern and southern) were distinguished among recent Ostracoda. Fossil Ostracoda from AMS14C-dated sediment cores from the eastern shelf area (with lower datings 11.3-11.1 kyr) and the western continental slope (with lower dating 15.8 kyr) were also studied for the first time. The analysis of fossil ostracod assemblages allowed the author to supplement previously obtained data on the chronology of the postglacial transgression.
E. Taldenkova, S. Dem'yankov, A. Strezh
The project is aimed at reconstructing the postglacial paleoenvironmental history of the western Laptev Sea outer shelf and continental slope on the basis of a multiproxy approach (high-resolution benthic assemblage studies, oxygen isotope composition of microfossils, bulk geochemical parameters). The succession of benthic assemblages in core PS51/154-11 from the upper continental slope reveals the major features of the last postglacial environmental evolution in the area. Prior to 15.8 cal.ka the absence of calcareous biogenic remains probably results from oxygen deficiency in the bottom water layer due to perennial sea-ice cover. During the period from 15.8 to 13.8 the proximity of the paleocoast to the shelf break resulted in no or little fast-ice formation and in the existence of a nearshore polynya. The latter fact is shown by the high percentage of planktic foraminifers and ostracod assemblages from the debris flow deposits containing freshwater and brackish-water species. The presence of Cassidulina teretis indicates the first Atlantic-derived water inflow to the site already at 15.8 cal.ka, which is about 0.8 kyr earlier than in the Barents and Kara seas. Between 13.8 and 11.6 cal.ka species composition and the highest total abundance of benthic microfossils indicate a seasonally changeable environment and an increasing organic matter supply due to maximum freshwater outflow (with its peak at about 13.0 cal.ka) and shelf flooding (starting at 12.7 cal.ka). The sharp reduction in sedimentation rates after 11.1 cal.ka resulted in poor preservation of calcareous remains and low total abundances of microfossils although their taxonomic composition gives evidence for the maximum influence of Atlantic water inflow on the western Laptev Sea continental slope between 11.6 and 6.5 cal.ka. Modern-like environments were established since 6.5 cal.ka, which was generally correlative with sea-level stabilization. After 2.5 cal.ka high IRD content indicates active iceberg-rafting, which was not recorded previously.