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

Boreal (Eemian) Transgression in the Northeastern White Sea Region: Multiproxy Evidence from Bychye-2 Section

Reconstructing interglacial marine environments helps us understand the climate change mechanisms of the past. To contribute to this body of knowledge, we studied a high-resolution 455 cm-thick sediment sequence of the Boreal (Eemian) marine beds directly overlying Moscovian (Saalian) moraine in the Bychye-2 section on the Pyoza River. We analyzed lithological and microfossil (foraminifers, ostracods, pollen, aquatic palynomorphs) variations at the studied site. Stratigraphical zonation is based on the local and well-established regional pollen zones, correlated with the western European pollen zones. The studied marine beds accumulated from the end of the Moscovian glacial (&gt;131 ka) until ca. 119.5 ka. We distinguished three successive phases: a seasonally sea-ice-covered, relatively deep, freshened basin in the initial rapid flooding stage (&gt;131–130.5 ka); a deep basin in the maximum flooding phase with less extensive sea ice cover (130.5–130.25 ka); and a shallow basin with reduced sea ice cover (130.25–119.5 ka). According to a pollen zone comparison with other sites, the regional glacioisostatic rebound started ca. 130 ka. The diverse warm-water assemblages of benthic foraminifers and ostracods containing typical Baltic Sea species occurred during the regression, mainly 128–124 ka, thus giving evidence for a relatively long-lasting connection between the White and Baltic Seas.</jats:p

High-resolution record of the Late Saalian–Eemian environmental changes in the northeastern White Sea Region (Bychye section) inferred from benthic foraminifers

Paleoenvironmental history of the White Sea region during the late Saalian–Eemian transition is reconstructed on the basis of the high-resolution record of benthic foraminifers from a 4.5 m thick marine sediment sequence directly overlying Saalian till in the Bychye section on the Pyoza River, NE White Sea Region. Besides benthic foraminifers which are the most abundant microfossil group in the studied section, also ostracods, pollen, aquatic palynomorphs as well as lithology and benthic foraminiferal stable isotope composition (δ18O, δ13C) were investigated. Palynological correlation with the previously studied sections confirms the age estimation from c. 133 to 120 ka (Devyatova, 1982; Grøsfjeld et al., 2006). Paleoecological analysis of foraminiferal assemblages is based on ecological preferences of different benthic species distinguished in modern Barents and Kara seas (Polyak et al., 2002, Korsun et al., 1994) supported by factor analysis. Five Ecozones were established which reflect rapid postglacial flooding of the territory after the disappearance of the Saalian ice sheet and consequent shallowing of the sea basin likely due to glacial rebound. Ecozone 1 corresponds to the earliest stage of inundation. Composition of microfossils suggests with the predominance of the arctic opportunistic species Elphidium clavatum among foraminifers suggests it was a cold Arctic coastal environment probably with turbid waters, high sedimentation rates and heavy seasonal sea-ice cover. Relative deepening of the shelf basin continued in Ecozone 2 as suggested by the high percentage of river-distal foraminifers indicating bottom water salinities above 30 and less heavy seasonal sea-ice cover. Foraminiferal assemblages are very similar to those occurring in the mid-shelf regions of the Laptev and Kara seas. The maximum flooding and deepening of the basin registered in Ecozone 3 as indicated by the highest percentage of the relatively deep-water species Melonis barleeanus. According to palynological composition, Ecozone 3 correlates with the early Eemian times (c. 128-130 ka). Maximum relative abundances of foraminiferal species Nonion labradoricum and Cassidulina reniforme indicate the warmest surface water conditions and high seasonal productivity. Marine environments resemble the Arctic outer shelf conditions with normal marine bottom water salinity and restricted sea ice cover. However these alternations are hardly a result of Atlantic water penetration since planktic foraminifers are absent and no indicative species are recorded among benthic foraminifers. Ecozone 4 represents the onset of regressive stage likely caused by isostatic crustal rebound as is witnessed by accumulation of sands, gradually decreasing taxonomic diversity and abundance of all microfossils, and introduction of subarctic ostracods and bivalves. Climatic conditions characterized as the most humid and warm gradually deteriorate towards the end of the record. Shallow-water nearshore environment in Ecozone 5 is supported by the abundance of river-proximal species and epifaunal foraminifers indicative of hydrodynamically active bottom waters. References Devyatova, E.I., 1982. Late Pleistocene environments as related to human migrations in the Dvina River basin and in Karelia. Petrozavodsk, 156 pp. (in Russian). Grøsfjeld, K., Funder S., Seidenkrantz M.-S., Glaister C., 2006. Last Interglacial marine environments in the White Sea region, northwestern Russia. Boreas, 35, 493-520. Korsun,S.A., Pogodina I.A., Tarasov G.A., Matishov G.G., 1994. Foraminifers from the Barents Sea (gidrobiology and quaternary paleoecology). Apatity, 136 pp. (in Russian). Polyak, L., Korsun, S., Febo, L., Stanovoy, V., Khusid, T., Hald, M., Paulsen, B.E., Lubinski, D.A., 2002. Benthic foraminiferal assemblages from the southern Kara Sea, a river-influenced arctic marine environment. J. of Foraminiferal Research, 32, 3, 252-273

Consequences of northern ice sheet size and melting history for the last interglacial climate

On a global scale, the last interglacial period is generally regarded a time of extreme climate warmth, high sea-level and largely reduced ice sheet size, for instance, on Greenland. In order to properly interpret the climate of the last interglacial in this region, it is critical to understand its development from the Saalian glacial maximum through the ensuing deglaciation (Termination 2). For this purpose we have compared deep-sea marine records from the Nordic seas with a high-resolution sequence of Eemian marine beds directly overlying Saalian till in northern Russia. The latter record allows for a fresh, detailed evaluation of a sequence of events on the basis of changes in lithology, microfossils (foraminifers, ostracods, pollen, aquatic palynomorphs) and benthic foraminiferal stable isotope data. The record is marked by the collapse of the huge Saalian shelf-based ice sheet which left a glaciostatically overdeepened Barents-Kara Sea shelf region, giving way to a rapid marine inundation. Although the early accumulation of marine sediments features a period of harsh, fluvially-affected environmental conditions with cold turbid waters and heavy seasonal sea-ice cover, the later occurrence of a typical Arctic shelf and deep-sea microfossil assemblage together with broad-leaved species in pollen spectra is representative of a climatic amelioration that ocurred in various steps. The recognition of a stepwise nature of the environmental development in northern Russia is recorded also in the deep-sea. There we note already during early Termination II a clear signal for intrusions of Atlantic water masses on the one hand, and high discharge rates of icebergs on the other. If these icebergs derived from a rapid collapse of the Barents-Kara seas ice sheet – this was much thicker and larger than in the Weichselian – then it seems very probable that the Atlantic water masses were able to protrude far eastward along the northern Eurasian periphery as a direct consequence of former ice sheet size and shelf overdeepening