Benthische Foraminiferen in der Northeastwater-Polynaya, Europäisches Nordmeer.

Ahrens, Michael J. (1994) Benthische Foraminiferen in der Northeastwater-Polynaya, Europäisches Nordmeer. (Diploma thesis), Christian-Albrechts-Universität, Kiel, Kiel, Germany, 120 pp.

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During cruise ARK IX/2+3 of R.V. "Polarstern" (15. May-4.Aug. 1993) to the waters of the Northeastwater (NEW) Polynya (80°N, 15°W), the colonization pattern of live (rose-bengal) stained benthic foraminifera (>63 μm) was investigated. The purpose of the investigation was to describe the hitherto little known biofacies in the region, and, furthermore, to observe, in which manner the assumed high production system of the polynya influences the foraminifera community on the sea floor. For the latter purpose, faunal data was compared with environmental parameters. On 19 stations (depths: 170-500 m), over 60 species were identified, of which on average 12 species contributed over 90 % of the total living numbers. The species assemblage was dominated by Elphidium excavatum, Cassidu/ina teretis, /slandiella islandica, Nonion Jabradoricum, Labrospira jeffreysii (orTrochammina nana), Labrospira crassimargo and Textularia spp. and showed general similarities to other arctic shelf regions. Calcareous foraminifera contributed approximately 60 % of the total living numbers, while the remainig 40 % were agglutinated (arenatious) forms. Foraminifera were counted in 3 size fractions (63-125 μm, 125-250 μm amd >250 μm). About 70 % of all individuals were found in the smallest size fraction (63-125 μm), about 25 % in the medium fraction (125-250 μm). Living individual numbers (>63 μm) in the uppermost sediment layer ranged from 67 to 507 ind/10 cm3, averaging about 200 ind/10 cm3, and decreased exponentially into deeper sediment strata. 5 cm into the sediment, living numbers were less than 1O % of surficial population densities. In addition, species composition changed and diversity decreased with sediment depth. lt was possible to distinguish between species with population maxima in the uppermost sediment layer ("epifaunal") and species with population maxima in deeper sediment layers ("infaunal"). Cores were analyzed to a maximum depth of 5 cm and it was assumed that deeper strata contained merely negligible numbers of living foraminifera. The biomass of the benthic foraminif era (>63 μm) was estimated to 0.1-0.5 g C org/m2 on the basis of test size and individual numbers. The distribution pattern was highly variable (patchy) and could be explained only in part by the simultaneouly measured environmental data (depth, salinity, temperature, sediment-coarseness, sediment-chlorophyll): Although positive correlations of population density with chlorophyll-content and sand grain fraction (63-125 μm) were observable, and negative correlation with water depth, these environmental parameters explained only parts of the variance. Additionally, biological factors may be of significant influence on the foraminifera community in the polynya. lndications for predation by epibenthic isopods was found. Observations on a time-series, for which the same position was sampled 7 times in the course of 2 months, gave no indication of a marked change in the community structure over the summer: An expected growth of the community was not observable: Population densities showed no marked increase, the contribution of the different size fractions remained constant, and there was no observable shift in chamber size of Cassidulina teretis, which was measured specifically for this purpose. Neither was it possible to observe a change in foraminiferal metabolic activity (measured as ATP and Energy Charge). Population densities, biomass and metabolic activity of benthic foraminifera were comparable to deep-sea, ice-free regions in the Norwegian Sea. Thus, the hypothesis of a generally increased production and dynamics in the NEW-polynya is not supported by the observations on benthic foraminifera. The benthic community in the polynya may be de-coupled from the pelagic environment and may have much slower response times than previouly assumed.

Document Type: Thesis (Diploma thesis)
Thesis Advisor: Graf, Gerhard
Research affiliation: OceanRep > Institute for Marine Science Kiel
Date Deposited: 03 Jun 2021 07:32
Last Modified: 03 Jun 2021 07:33

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