Beschreibung: A decade of particle flux measurements providse the basis for a comparison of the eastem and westem provinces ofthe Nordic Seas. Ice-related physical and biological seasonality as well as pelagic settings jointly control fluxes in the westem Polar Province which receives southward flowing water of Polar origin. Sediment trap data from this realm highlight a predominantly physical flux control which leads to exports of siliceous particles within the biological marginal ice zone as a prominent contributor. In the northward flowing waters of the eastem Atlantic Province, feeding Strategie . life histories and the succession of dominant mesozooplankters (copepods and pteropods) are central in controlling fluxes. Furthermore, more calcareous matter is exported here with a shift in flux seasonality towards surnrner/autumn. Dominant pelagic processes modeled numerically as to their impact on annual organic carbon exports for both provinces confirrn that interannual flux variability is related to changes in the respective control mechanisms. Annual organic carbon exports are strikingly similar in the Polar and Atlantic Provinces (2.4 and 2.9 g m-2 y-1 at 500 m depth). despite major differences in flux control. The Polar and Atlantic Provinces. however, can be distinguished according to annual fluxes of opal ( l.4 and 0.6 g m-2 y-1) and carbonate (6.8 and 10.4 g m-2 y-1). lnterannual variability may blur this in single years. Thus. it is vital to use multi-annual data sets when including particle exports in general biogeochemical province descriptions. Vertical flux profiles (collections from 500 m, l000 min both provinces and 300-600 m above the seafloor deviate from the general vertical decline of fluxes due to particle degradation during sinking. At depths 〉 1000 m secondary fluxes (laterally advected/re uspended particles) are often juxtaposed to primary (pelagic) fluxes, a pattem which is most prominent in the Atlantic Province. Spatial variability within theAtlantic Province remains poorly understood. and the same holds true for interannual variability. No proxies are at hand for this province to quantitatively relate fluxes to physical or biological pelagic properties. For the easonally ice-covered Polar Province a robust relationship exists between particle export and ambient ice-regime (Ramseier et al. this volume; Ramseier et al. 1999). Spatial flux pattems may be differentiated and interannual variability can be analyzed in this manner to improve our ability to couple pelagic export pattems with benthic and geochemical sedimentary processes in seasonally ice-covered seas.

Beschreibung: Findings from experiments showed that the web-feeding euthecosomatous pteropod, Limacina retroversa, can produce rapidly sinking, mucous aggregates. It is suggested that, by adhesion, these aggregates scavenged picoplankton-sized particles, which were thus effectively cleared from the medium. In contrast, Calanus finmarchicusw as not able to clear these particles in our experiments. Sedimentation velocities of 10 aggregates measured in vivo were up to 1000 m day1, with an average of —300 m day-1 (not including two aggegates with neutral buoyancy). Mean velocities measured for feces of C.finmarchicus, Calanus hyperboreus and Thysanoessa sp. were considerably lower. We suggest that the sedimentation of L.retroversa aggregates was the source of mucous floes collected in sediment traps (Bathmann et al., Deep-Sea Res., 38,1341-1360,1991) and at the sea floor at 1200 m depth in the southern Norwegian Sea. This process may be an important mediator of sedimentation to the deep sea, when these pteropods are present in surface waters in large abundance.

Beschreibung: SUMMARYPhyto- and Protozooplankton were sampled in the upper 10 m of the water column in austral summer during a cruise of RV 'Polarstern' from January 6 to February 20 1985 in the eastern Bransfield Strait vicinity and in the northern, southeastern (off Vestkapp, twice: I and II) and southern Weddell Sea (Vahsel Bay across the Filchner Depression to Gould Bay). The plankton assemblages are discussed in relation to physical, chemical and biological factors in the different geographical areas in summer. Phytoplankton biomass (Phytoplankton carbon, PPC) ranged from 4-194 µg carbon/l and consisted on average of 65 % diatoms and 35 % autotrophic flagellates. Whereas in the northwest phytoplankton assemblages were dominated by small nanoflagellates (78 % of PPC), higher biomass of diatoms (54 - 94 % of PPC) occurred at the other sampling sites. In general autotrophic flagellates and small pennate diatoms dominated at oceanic stations; in neritic areas large centric diatoms prevailed. Chlorophyll a concentrations ranged from 0.25 to 3.14 µg chl a/ l with a mean of 1.13 µg chlorophyll a/ l and an average phytoplankton carbon/ chlorophyll a ratio of 39. Protozooplankton biomass (Protozooplankton carbon, PZC) ranged from 0-67 µg carbon/l and consisted of 49 % ciliates, 49 % heterotrophic dinoflagellates and 2 % tintinnids. Heterotrophic dinoflagellates were more important in the northern investigation areas (58 - 84 % of PZC). Ciliates dominated the protozooplankton in the southeast and south (56 - 65 % of PZC); higher abundances of tintinnids were observed only in the south (11 % of PZC). The most remarkable feature of the surface waters was the high protozooplankton biomass: protozooplankton amounted to 25 % on an average of the combined biomass of PPC plus PZC for the entire investigation period. Protozoan biomass in the southeastern and southern Weddell Sea occasionally exceeded phytoplankton biomass. Temperature, salinity, and inorganic nutrients were generally lower in the southern regions; at most of these stations a meltwater layer occurred in the upper meters of the water column. We suggest that this physical regime allows a well developed summer system with a high proportion of heterotrophic microplankton. In the eastern Bransfield Strait, in the northern Weddell Sea and close to the coast off Vestkapp (I), however, early summer conditions occurred with less protozooplankton contribution.