Sergei Korsun

BENTHIC FORAMINIFERAL ASSEMBLAGES FROM THE SOUTHERN KARA SEA, A RIVER-INFLUENCED ARCTIC MARINE ENVIRONMENT

Calcareous foraminifers and hydrographic parameters in 113 bottom samples from the southern Kara Sea were examined to improve the usage of foraminifers as paleoenvironmental proxies for river-dominated high-latitude continental shelves. Foraminiferal taxa form a succession from near-estuarine to distal open-sea locations, characterized by a gradual increase in salinities. Foraminiferal assemblages are discriminated into three groups: river-proximal, -intermediate, and -distal. This succession appears to be controlled by a combination of feeding conditions and bottom salinities, and are related to riverine fluxes of freshwater, organic matter, and sediments. Morphological and behavioral adaptations of foraminifers to specific environments are discussed.

SEASONAL DYNAMICS OF BENTHIC FORAMINIFERA IN A GLACIALLY FED FJORD OF SVALBARD, EUROPEAN ARCTIC

Seasonal variations in benthic foraminiferal populations from a sediment-laden fjord were analyzed in order to provide insights into arctic foraminiferal ecology and to improve the interpretation of the late-glacial record. The fjord is 25 km long and 100 m deep with a large tidewater glacier at the fjord head. A pilot transect of eight stations sampled in August 1995 revealed the typical off-glacier sequence of foraminiferal taxa. Unidentified allogromiids were abundant in the vicinity of the ice front. Further down the fjord Elphidium excavatum f. clavatum and Cassidulina reniforme co-dominated the glacier-proximal fauna. Nonionellina labradorica and Islandiella norcrossi characterized the glacier-distal setting. In 1996 three glacier-proximal stations were then sampled in March, May, July, August, September and November. Compared to the summer of 1995 the summer of 1996 was colder, resulting in weaker glacial meltwater discharge, and the foraminiferal fauna became less influenced by glaciers. This is portrayed by an increase in glacier-distal N. labradorica and a decrease in glacier-proximal C. reniforme and especially E. excavatum. Taxonomic diversity was higher in winter, possibly reflecting a more stable environment in the absence of the turbid meltwater plume, the source of ecological stress.

Spatial and temporal influence of glaciers and rivers on the sedimentary environment in Sassenfjorden and Tempelfjorden, Spitsbergen

Abstract Multiproxy analyses including hydrographical, geochemical, foraminferal, lithological and geophysical data reveal variable influences of the glaciers Tunabreen and von Postbreen as well as the river Sassenelva on the sedimentary environment in two Spitsbergen fjords during the Late Weichselian and the Holocene. Grounded ice covered the study area during the last glacial. The glacier fronts retreated stepwise during the latest Weichselian/earliest Holocene, and the glaciers were probably small during the early Holocene. A growth of Tunabreen occurred between 6 and 4 cal ka BP. Reduced input from Tunabreen from c. 3.7 cal ka BP was probably a result of suppressed iceberg rafting related to the enhanced formation of sea ice and/or reduced meltwater runoff. During the past two millennia, the glacier fronts advanced and retreated several times. The maximum Holocene glacier extent was reached at the end of a surge of von Postbreen in AD 1870. Characteristics of the modern glaciomarine environment include: (1) different colours and bulk-mineral assemblages of the turbid waters emanating from the main sediment sources; (2) variable locations of the turbid-water plumes as a consequence of wind forcing and the Coriolis effect; (3) stratified water masses during summers with interannual variations; (4) increasing productivity with increasing distance from the glacier fronts; (5) foraminifera-faunal assemblages typical for glacierproximal settings; and (6) periodical mass-transport activity.

Monothalamous foraminiferans and gromiids (Protista) from western Svalbard: a preliminary survey

Abstract Monothalamous foraminifera were abundant in sediment samples from fjords and offshore areas around western Svalbard (water depth range 26–2472 m). The >500 µm fractions of samples from the inner parts of fjords yielded numerous delicate “allogromiids” (organic-walled) “saccamminids” and “psammosphaerids” (agglutinated), including species assigned to Cylindrogullmia, Gloiogullmia, Nemogullmia and Toxisarcon. Larger, more robust, tubular agglutinated species were abundant in the outer reaches of Tempelfjord, Isfjord and Van Meijenfjord (Hyperammina subnodosa, Hippocrepinella crassa), on the current-influenced upper slope off Isfjord (Pelosina variabilis, Rhabdammina abyssorum), and the deeper part of the continental slope off Isfjord (e.g. Hyperammina crassatina). Oval and sausage-shaped organisms resembling gromiids (probably relatives of the foraminifera) were sometimes abundant in the fjords. Finer size fractions (63–500 µm) of fjord samples yielded a rich variety of monothalamous species. Among the allogromiids, Micrometula sp. was widely distributed, while Tinogullmia sp. and an undescribed species were restricted to single stations in Kongsfjord and Van Meijenfjord, respectively. Saccamminids common in the finer fractions included Conqueria spp., Psammophaga sp., and undescribed species with silvery, white and brownish tests. Many of the smaller allogromiids and saccamminids in our Svalbard samples resemble species found in the Gullmarfjord on the Swedish west coast.

The 8200 cal. yr BP event reflected in the Arctic fjord, Van Mijenfjorden, Svalbard

Detailed stratigraphic investigations of a high-resolution sediment core from the Arctic fjord, Van Mijenfjorden, Svalbard, reveal significant reductions in benthic foraminiferal δ18O of 0.4‰ and 0.2—0.3‰ dated to c. 8200 and 8450 cal. yr BP, respectively. These reductions, combined with changes in the benthic foraminiferal fauna and IRD, indicate substantial changes in the hydrography of the fjord, such as freshening of the bottom water, enhanced sea ice distribution and reduced biogenic production. The age and duration (~100 years) of the youngest event is directly in phase with the 8200 cal. yr anomaly in the δ18O record GISP2 and NGRIP of the Greenland Ice Sheet. The changes around 8450 cal. yr BP compare well to the timing of the initial freshwater drainage of the proglacial Lake Agassiz. Therefore the proxy record of Van Mijenfjorden lends support to the theory, explaining the 8200 cal. yr BP event as a cumulative response to a freshwater-forced reduction in the meridional overturning circulation in the North Atlantic. A reduction in the meridional overturning circulation (MOC) may have changed the oceanic inflow to the fjord towards reduced influence of Atlantic Water and increased the dominance of fresher Arctic Water.

Biomass of foraminifera in the St. Anna Trough, Russian arctic continental margin

Abstract The abundance of large agglutinated tests in brown oxidized mud has suggested that high biomasses of foraminifera occur in troughs on the western Arctic Eurasian shelf. To verify this, we measured foraminiferal biomass (protoplasmic volume) at seven stations close to 800N in the St. Anna Trough, a shelf depression open to the Arctic Basin. The abundance of arenaceous tests was high owing to good postmortem preservation within a thick (30 cm) surface oxidized layer of the sediment. Foraminiferal biomass was moderate (range = 0.06-1.7 glm2) compared with common shelf values and increased with increasing water depth. The foraminiferal contribution to the biomass of the benthic community was negligible on the slopes of the trough but below 500 m water depth, where the macrofauna is scarce, the foraminifera:macrofauna ratio reached 0.3. The bulk of the foraminiferal biomass consisted of specimens approximately 2 mm in diameter. The volume of cytoplasm in tests of the dominant foraminiferan Reophax pil...

The Helgoland Experiment – assessing the influence of methodologies on Recent benthic foraminiferal assemblage composition

The aim of the present study was to compare preservation, staining and preparation techniques to assess the influence of different sample treatments and analyses on the accuracy of benthic foraminiferal assemblage data from NE Atlantic shelf seas. Replicate surface samples from the SE North Sea were preserved with ethanol–rose Bengal or formalin, some were stained after processing, or foraminifera were concentrated by flotation. Coloration of living specimens was different between samples treated with an ethanol–rose Bengal solution and those stained after washing. In the latter case, only the last two or three chambers were stained. The aliquot sample preserved with formalin showed dissolution features in agglutinated and porcellaneous species. Population density varied between different preservation, picking modes and investigators. The accuracy of picking was in the range of ±2 % (1σ), while external reproducibility ranged from −34 to +16 %. There was no significant difference between wet and dry picking. Samples that were concentrated by flotation generally yielded a lower number of specimens. Agglutinated species were under-represented in samples that were stained after washing and in the flotation concentrate. Size fractions showed a reduction of population density and Fisher alpha diversity index with increasing mesh size. Only half of the specimens and less than two-thirds of the species are captured if the >125 µm rather than >63 µm fraction is analysed. In oxygen minimum zones, where small-sized species dominate the assemblage, the recovery in larger size fractions could be lower.

ALLOGROMIIDS IN FORAMINIFERAL ASSEMBLAGES ON THE WESTERN EURASIAN ARCTIC SHELF

Allogromiids sensu lato , including the orders Allogromiida and Astrorhizida, are a commonly ignored group of marine benthos. Allogromiid standing crop was examined in 121 sediment samples from the Barents and Kara seas. In 44 of these samples, foraminiferal biomass was determined by calculation of cytoplasmic volume. Foraminiferal standing crop is dominated by small allogromiids in two types of stressed marginal environments—river-influenced shallows and glacially fed fjords. Allogromiid frequency also increases in oligotrophic depressions of the open shelf. Large astrorhizids such as Rhabdammina abyssorum, Pelosina variabilis and Hyperammina subnodosa , being common on fine-grained sediments which dominate the shelf, constitute biomasses of ca 3 mg/10cm 3 , exceeding by an order of magnitude the biomass of all other foraminifera combined. Foraminiferal biomass values are comparable to those of macrofauna in shelf depressions distant from land, thus suggesting that, at least in food-deficient areas, the allogromiid foraminifera are a key group in benthic energy flux.

Intertidal foraminiferal fauna and the distribution of Elphidiidae at Chupa Inlet, western White Sea

Abstract The bright colouration of the cytoplasm in intertidal rotaliid foraminifera and their particle-gathering activity reliably reveals live specimens in fresh samples, without any fixatives or dyes applied. Using this approach, we demonstrate that live representatives of three rotaliid species, all belonging to the genus Elphidium, were common on intertidal mud and sand beaches. Two species, E. excavatum clavatum and E. albiumbilicatum, lived close to freshwater outflows, whereas E. williamsoni occupied beaches bathed by waters with normal salinity (surface 26–27‰ in the western White Sea). A least 13 species were found alive in the intertidal zone. Among non-calcareous foraminifera, Miliammina fusca, Ammotium cassis and Ovammina opaca were the most numerous.

Composition of Harpacticoida (Crustacea, Copepoda) of the Laptev Sea in comparison with faunas of adjacent Arctic seas

The invertebrate fauna of the Laptev Sea is one of the least investigated in the Arctic. In particular, little is known about the Harpacticoida (Copepoda, Crustacea)—one of the main components of marine meiofauna. Major objectives of our study were (1) to describe harpacticoid composition obtained from three sublittoral stations, (2) to compile the check-list of the Laptev Sea harpacticoids, and (3) to perform a comparative analysis of the Laptev Sea harpacticoid fauna with faunas of other Arctic seas. Of 38 species found in our material, 25 are new for the sea, and four species are likely new to science. A total list for the Laptev Sea includes 76 species from 18 families. Interstitial and phytal forms are poorly represented, due to the rarity of suitable biotopes and/or undersampling. The majority of the provisional endemics were found in the bathyal and abyssal zones of the sea, while widely distributed species, except for the plankton, belong to the fauna of the soft sediments of the littoral zone. Comparative analysis of harpacticoids from the Arctic region (the Laptev, White, Barents, Kara, East Siberian and Beaufort Seas and the Greenland area) shows the considerable distinction between the Eastern (Siberian) and Western sub-regions. Further investigations are necessary to reveal a more detailed pattern in Harpacticoida distribution and to evaluate possible vectors of dispersal and biogeographic relationships in the high Arctic.