Publication year: 1991
Source: Marine Chemistry, Volume 36, Issues 1-4, December 1991, Pages ix-x
Marko, Branica , Goran, [...]
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Publication year: 1991 Publication year: 1991 Experience during the EPOS-2 cruise on board the R/V “Polarstern” in 1988–1989 has led to the construction of a model which may contribute to the understanding of the problem of limiting factors for the primary production in the Antarctic Ocean. As in Mixed Layer (ML) theories, it is anticipated in the present model that the physical factors of mixing and self-shading are limiting when the major nutrients are abundant. However, whereas ML models presuppose considerable mixing in the ML and very low mixing below the ML, it is assumed here that there is a moderate amount of mixing from [...] Publication year: 1991 Qualitative and quantitative analyses of the tintinnids retrieved in surface and vertical (down to 1150 m ) samples in the Scotia, Weddell, Bransfield and Bellingshausen areas allow us to define three distinct zones: (A) the Scotia Sea, Bransfield Strait and oceanic waters of the northern-central Weddell Sea, dominated by Codonelopsis gaussi and Cymatocylis affinis/conmllaria; (B) shelf and mostly ice-covered areas of the southernmost Weddell Sea and the Bellingshausen Sea, characterized by Laackmanniella prolongata and Cymatocylis drygalskii; (C) Bransfield-Weddell waters around the tip of the Antarctic Peninsula, where Codonellopsis balechi accounts for 80% of the tintinnids. These areas have (often [...] Publication year: 1991 The surface layer properties of the Weddell Gyre were measured during a cruise of the R/V “Polarstern” in September and October 1989 on a transect between the tip of the Antarctic Peninsula (northwestern Weddell Sea) and Cape Norvegia (southeastern Weddell Sea). Sea ice cover, hydrography, and the distribution of inorganic nutrients and dissolved oxygen represented late winter conditions: a quasi-homogeneous Winter Water layer with near-freezing temperatures, high salinities and high levels of nitrate, and undersaturated with dissolved oxygen.The area investigated could be divided into three regions based on the physical, chemical and biological patterns: the western and eastern flanks [...] Publication year: 1991 An ecological model to calculate phytoplankton development and microbial loop dynamics in the marginal ice zone of the antarctic ecosystem has been established on the basis of physical and biological (phyto- and bacterioplankton biomass and activity and counting of two classes of heterotrophic nanoplankton) measurements carried out in the marginal ice zone of the Scotia-Weddell Sea sector of the Southern Ocean during sea ice retreat 1988 (EPOS 1 and 2 expeditions). Application of this model at latitudes where sea ice retreat occurs and in adjacent open sea and permanently ice-covered areas demonstrated that the marginal ice zone is a [...] Publication year: 1991 Nitrogen assimilation was measured in two austral summers in the Scotia Sea around the island of South Georgia as well as the Bransfield Strait. Nitrate and ammonium assimilation was measured using 15N techniques and the population was divided into two size classes, less than and greater than 20 μm. Water column integrated nitrogen assimilation rates varied between 2.43 and 26.50 mmol N m−2 day−1, the distribution being highly heterogeneous. The highest assimilation rate was found at a station near South Georgia, where the chlorophyll standing stock was elevated. A high assimilation rate was observed at a station in the [...] Publication year: 1991 The concepts developed for nutrient-limited areas are not readily applicable to the Southern Ocean, which is, paradoxically, an ‘oligotrophic’ but not nutrient-limited ecosystem. A synthesis of direct and indirect measurements clearly shows the uniqueness of the Southern Ocean:(1) The presence of a pycnocline allows the calculation of new production by measurement of the depletion of nitrate that results from winter mixing or from permanent nutrient supply. In the open ocean, the new production during the summer period averages 30 g C m−2. The complete depletion of nitrate (e.g. following fertilization with iron) would allow a new production during the [...] |
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