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Last updated 06.06.2005
Marek Zajaczkowski* , Patrycja Jernas**
of Oceanology Polish Academy of Sciences.Sopot 81-712, Powstanców
Warszawy 55, Poland
** University of Gdansk, Faculty of Biology, Geography and Oceanology, student of Oceanography
Central part of Hornsund
Studies of Arctic benthic foraminifera permit
to our understanding of high latitude marine environment. Diagnosis of
relationship between recent
foraminifera distribution and environment condition also may provide modern
analogues for fossil assemblages of the Holocen, when climate and hydrological
condition of Northern hemisphere varied from warm Atlantic period to cold
a “Little Ice Age”. Climate warming from the beginning of XX
century has caused the retreat of many Svalbard glaciers (Lefauconnier and
Hagen 1990, Ziaja 2001, Hagen et al. 2003) and, in consequence, increase
of turbid meltwater supply to the fjords and bottom sediment accumulation
rate. This process is especially intensieve during the last ten years (Zajaczkowski
et al. 2004). Benthic foraminifera distribution in the Hornsund is known
briefly by Hald and Korsun (1997). The knowledge about foraminifera distribution
patterns in the particular layers of Hornsund sediment is very poor. It is
known that benthic foraminifera are not confined to the surface layers of
the sediment and in some cases the mojority of their standing stocks can
be encountered below sediment surface (Murray 1992, Hunt and Corliss 1993,
Moodley et al. 1998). This phenomena was initially interpreted as the result
of passive transport by storms, currents or bioturbation (Richter 1964, Collison
1980, Moodley 1990) however, in recent foraminiferal study, both: environmental
and in laboratory, many authors become convinced that foraminifera are capable
of active migrating through sediment in direct response to chemical and physical
gradients in the pore water (Alve 1995, Alve and Bernhard 1995, Moodley et
al. 1998). The aim of this study is to present new foraminifera data in dependency
of the distance from glacier fronts and rate of sediment accumulation in
different layers of the Hornsund sediment.
Fig.1 Main sea currents in the region of Southern Spitsbergen (upper). The cross section along A-B transect (below) based on APEX 2004. The red colored is Atlantic water of WSC (West Spitsbergen Current). In blue is the water flowing from the Barents Sea (SC – Sørkapp Current). The zone of the polar front is usually between 13º and 14º 30’ E but is characterized by strong inter-annual variations (Saloranta and Haugan 2004).
The southwestern coast of Spitsbergen is a climatically sensitive area. The main reason for this is the present oceanographic regime characterised by north-flowing warm Atlantic Water in the West Spitsbergen Current and cold Polar Water transported by Sørkapp Current (Fig.1). On the contact of the above mentioned currents develops the polar front which is characterised by strong gradients in temperature and salinity. The average difference of water masses properties on both sides of the front is: 5oC and 2 PSU (Kostianoy et al. 2004). Small geographical displacements in the ocean fronts in this area may impose large climatic changes affecting life habitats and earth processes in the area.
Hornsund is a 30km long and 12-15km wide fjord with a maximum depth of 251m and 50 – 100m high sill in the entrance. Sill causes that near bottom zone of central basin is not under Atlantic water influence, therefore winter cooled water is observed in the inner and central part of fjord, during the summer. Tidal glaciers form large part of the inner fjord basin coastline. Hornsund, the southernmost of Spitsbergen fjords is the only Arctic fjord. Other accessible fjords of the western coast are under strong Atlantic water influence, while the Hornsund fauna is of more Arctic in comparison to adjacent areas. It gives an unique opportunity to study the moving border between two contrasting zoogeographical provinces (Subarctic and Arctic) divided by the polar front. Habitat diversity within the fjord is high, and many sites have a complex array of habitat types in a small area. Wave exposure varies from extremely exposed to very sheltered, often within a short distance. All habitats within the region of Svalbard are present.
Hornsund is the only location in the European Sector of Arctic included in the frame of UE Programme BIOMARE to ATBI type (All Taxon Biodiversity Inventory) (Warwick et al. 2003). It is mainly due to its virgin state. Since the 1970 Hornsund fiord is in the borders of National Park of Southern Spitsbergen. In the previous time was not exploited by fishery and its bottom was not dredged. Moreover the fjord was not polluted and the only anthropogenic element is Polish Polar Station with 12 scientists working all the year. Wastes from the station are professionally treated and cleaned. Selection of this study site guarantees that the results (e.g. benthic foarminfera composition) are not influenced by human activity.
Sampling stations were located in the central deeps along the axe of Hornsund fiord (Fig.2, Tab.1)). Sediment cores were retrieved with a Nemisto gravity corer, 7 cm diameter during r/v OCEANIA cruise in July 2002. Cores were divided to 1cm slices after sampling and frozen in separated bags to – 20ºC. In the laboratory, samples were weighted and wet sieved with mesh openings of 125µm and 63µm. The content on the meshes was coloured with bengal-rose and alcohol mixture to examine number of live and dead individuals. All three fractions were dried and weighted. The sediment on the 63µm and 125µm mesh was analyzed with stereo-microscope and in case of large sample, content was divided using a dry micro-splitter. All specimens were collected in counting plate with 49 lining fields. Fraction < 63µm was used for radio-nuclides analyze of 210Pb and 137Cs to estimate accumulation rate of the bottom sediments.
|15º 26.939’||76º 57.339’|
|15º 51.197’||76º 58.439’|
|16º 12.132’||76º 58.810’|
|16º 29.205’||77º 0.731’|
Tab.1 List of coring stations in Hornsund
Fig.2 Coring stations in the Hornsund
Foraminifera are found in all marine environments. Due to their biodiversity and good preservation in the sediment (hard tests) they are good indicators of climatic and hydrological changes. They may be planktic (about 40 species) or benthic (more than 4000 species) in mode of live. The Order Foraminifera belongs to the Kingdom Protista, Subkingdom Protozoa, Phylum Sarcomastigophora, Subphylum Sarcodina, Superclass Rhizopoda, Class Granuloreticulosa.
Foraminifera (short: forams) are single-celled protist with test. Tests, because in some forms the protoplasm covers the exterior of the shell. The tests are commonly divided into chambers which are added during growth. The morphology of forams tests varies remarkably however in terms of their clasification two features are most important:
• Chamber arrangement
• Aperture style
Variations around Chamber arragment:
Planispiral to biserial
Trochospiral; dorsal, edge and ventral view
Variations around aperture style:
Open end of tube
With phialine lip
With bifid tooth
With umbilical teeth
With umbilical bulla
Redrown from Loeblich and Tappan (1964)