Arctic Deep Water Research Articles

Dense populations of Archaea associated with the demosponge Tentorium semisuberites Schmidt, 1870 from Arctic deep-waters

The associated microbial community in the mesohyl of the Arctic deep-water sponge Tentorium semisuberites Schmidt, 1870 (Hadromerida, Demospongiae) is dominated by Archaea. This is the result of an integral approach applying analyses of microbial lipid biomarkers as well as microscopic investigations using differential fluorescence in situ hybridisation with universal probes and counterstaining with 4′,6′-diamidino-2-phenylindole (DAPI) on sponge sections based on samples collected in the Greenland Sea in 2001, 2002 and 2005. The distribution of isoprenoidal C40 hydrocarbons of the biphytane series suggests that affiliates of both major archaeal kingdoms, the Crenarchaeota and the Euryarchaeota, are present in the choanosome of T. semisuberites. Positive signals using the oligonucleotide probe ARCH915 indicate high numbers of Archaea in the mesohyl of this sponge. Based on optical estimations 70–90% of all microbial DAPI signals accounted for archaeal cells. Archaea in these high proportions have never been described in an Arctic deep-sea hadromerid sponge, nor in any other demosponge species. Similar observations in specimens collected over a time scale of 4 years suggest permanent sponge-Archaea associations.

Mesozooplankton community structure, abundance and biomass in the central Arctic Ocean

During the "International Arctic Ocean Expedition 1991" (20 August–21 September 1991) mesozooplankton was sampled at six stations in the Nansen, Amundsen and Makarov Basins of the central Arctic Ocean from 1,500 m depth to the surface by multiple opening/closing net hauls. Total mesozooplankton abundance decreased from 268 ind. m–3 in the surface layer (0–50 m) to <25 ind. m–3 below 200 m depth. The small copepods Oithonasimilis and Microcalanuspygmaeus, as well as copepod nauplii, were most abundant close to the surface, while Oncaeaborealis and Spinocalanus spp. frequently occurred at greater depth. Mesozooplankton dry mass (DM) integrated over the upper 1,500 m of the water column was surprisingly stable throughout the investigation area and measured 2.0±0.3 g DM m–2. Dry mass in the upper 50 m measured 20.9 mg m–3 and was dominated by Calanushyperboreus (57.4%) and C. glacialis (21.1%). C. finmarchicus was very abundant only in the Nansen Basin. Below 200 m the calanoid copepods Metridialonga, Microcalanuspygmaeus and Pareuchaeta spp., the decapod Hymenodoraglacialis and chaetognaths of the genus Eukrohnia were the principal contributors to biomass values of <1 mg DM m–3. Hence, vertical changes in abundance, biomass and species composition were much more pronounced than regional differences between the basins. Three different mesozooplankton communities were differentiated according to their faunistic composition and are discussed in context with the major water masses: Polar Surface Water, Atlantic Layer and Arctic Deep Water.

The simultaneous use of tracers for ocean circulation studies

A method for the simultaneous use of tracers for oceanic circulation studies is developed. To permit the inclusion of tracers that are subject to biochemical transformation a simple model for photosynthesis, bacterial decomposition and chemical dissolution is formulated based on the use of Redfield ratios for the chemical compounds interaction. The finite difference analogue to the steady state tracer continuity equation, applied to the tracers chosen, leads to a set of simultaneous algebraic equations that in principle can be solved by matrix inversion methods. Two cases are considered: (1) The problem is indeterminate, which may be the case when too few tracers are available and/or some tracer equations are redundant. A solution is obtained by minimizing the transport vector; (2) The problem is incompatible, which may result from making use of many tracers. A solution is obtained by minimizing the errors in satisfying the tracer continuity equations. The method is applied to a 12-box model of the world oceans by considering the surface water, intermediate water, deep water and bottom water of the Arctic, Atlantic, Antarctic and Pacifichndian Oceans (with some simplification for the polar seas). Total dissolved inorganic carbon, alkalinity, phosphorus, oxygen and radiocarbon are used as tracers. A series of steady state solutions are presented and the uncertainties as dependant on box configuration and erroneous or nonrepresentative data are analysed. In the reference solution, circulation cells emerge where Antarctic surface water penetrates into intermediate levels of the two major oceans, from where it undergoes lifting and, at the surface, advection back towards the south. In the Atlantic, much of the penetrating water reaches as far north as to involve the Arctic deep water, which sinks and moves towards the deep Antarctic Ocean through the deep Atlantic. The total upwelling in the Antarctic Ocean is about 30 Sv. Turbulent exchange prevails between surface and intermediate waters in both major oceans with an average K, of about 1 cm 2 s -1 . Particular consideration is given to the transfer of carbon by computing the changes in total carbon and radiocarbon that are induced by fossil fuel combustion and nuclear bomb testing by using the steady state circulation and turbulent transfer deduced. It is concluded that better spatial resolution is required to determine the role of the ocean as a sink for injections of carbon and radiocarbon. DOI: 10.1111/j.1600-0889.1983.tb00025.x

Planktonic Foraminifera in Hemipelagic Sediments: Shell Preservation off Portugal and Morocco

The preservation of planktonic foraminiferal shell assemblages in sediments can be characterized by their degree of fragmentation. The amount of carbonate removed from the shells can easily be estimated and it is therefore possible to calculate their total loss of CaCO 3 . Arctic deep water today reaches the abyssal plains off Portugal, resulting in high carbonate solution rates and therefore intensive shell fragmentation, while shells from similar depths off Morocco are nearly unfragmented. Late Pleistocene sediments in both areas yield well-preserved planktonic Foraminifera. This is important for the reconstruction of Pleistocene North Atlantic deep-water hydrography. In both areas continental-slope assemblages are better preserved with decreasing water depth, with the exception of its uppermost part where the rate of carbonate solution increases.