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The ongoing rise in atmospheric CO concentration is causing rapid increases in seawater pCO levels. However, little is known about the potential impacts of elevated CO availability on the phytoplankton assemblages in the Southern Ocean's oceanic regions. Therefore, we conducted four incubation experiments using surface seawater collected from the subantarctic zone (SAZ) and the subpolar zone (SPZ) in the Australian sector of the Southern Ocean during the austral summer of 2011-2012. For incubations, FeCl solutions were added to reduce iron (Fe) limitation for phytoplankton growth. Ambient and high (~750 µatm) CO treatments were then prepared with and without addition of CO-saturated seawater, respectively. Non-Fe-added (control) treatments were also prepared to assess the effects of Fe enrichment (overall, control, Fe-added, and Fe-and-CO-added treatments). In the initial samples, the dominant phytoplankton taxa shifted with latitude from haptophytes to diatoms, likely reflecting silicate availability in the water. Under Fe-enriched conditions, increased CO level significantly reduced the accumulation of biomarker pigments in haptophytes in the SAZ and AZ, whereas a significant decrease in diatom markers was only detected in the SAZ. The CO-related changes in phytoplankton community composition were greater in the SAZ, most likely due to the decrease in coccolithophore biomass. Our results suggest that an increase in CO, if it coincides with Fe enrichment, could differentially affect the phytoplankton community composition in different geographical regions of the Southern Ocean, depending on the locally dominant taxa and environmental conditions. [ABSTRACT FROM AUTHOR]

Large amounts of pollutants reach polar regions, particularly the Arctic, impacting their communities. In this study we analyzed the toxic levels of Hg, Cd and Pb to natural phytoplankton communities of the Arctic and Southern Oceans, and compared their sensitivities with those observed on phytoplankton natural communities from temperate areas. Mercury was the most toxic metal for both Arctic and Antarctic communities, while both Cd and Pb were toxic only for the Antarctic phytoplankton. Total cell abundance of the populations forming the Arctic community increased under high Cd and Pb concentrations, probably due to a decrease of the grazing pressure or the increase of the most resistant species, although analysis of individual cells indicated that cell death was already induced at the highest levels. These results suggest that phytoplankton may have acquired adapting mechanisms to face high levels of Pb and Cd in the Arctic Ocean. [Copyright &y& Elsevier]

Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. Recent environmental changes such as a rise in sea surface temperature (SST) are likely to impact on net primary productivity (NPP) and phytoplankton community composition. However, their spatiotemporal relationships are still unclear in the Southern Ocean. Here we assessed the relationships between NPP, dominant phytoplankton groups, and SST in the Indian sector of the Southern Ocean over the past decade (1997--2007) using satellite remote sensing data. As a result, we found a statistically significant reduction in NPP in the polar frontal zone over the past decade during austral summer. Moreover, the decrease in NPP positively correlated with the dominance of diatoms (Kendall's rank correlation τ = 0.60) estimated by a phytoplankton community composition model, but not correlated with SST. In the seasonal ice zone, NPP correlated with not only the dominance of diatoms positively (τ = 0.56), but also the dominance of haptophytes (τ =--0.54) and SST (τ =--0.54) negatively. Our results suggested that summer NPP values were strongly affected by the phytoplankton community composition in the Indian sector of the Southern Ocean. [ABSTRACT FROM AUTHOR]

Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. Recent environmental changes such as a rise in sea surface temperature (SST) are likely to impact on net primary productivity (NPP) and phytoplankton community composition. However, their spatiotemporal 5 relationships are still unclear in the Southern Ocean. Here we assessed the relationships between NPP, dominant phytoplankton groups, and SST in the Indian sector of the Southern Ocean over the past decade (1997-2007) using satellite remote sensing data. As a result, we found a statistically significant reduction in NPP in the polar frontal zone over the past decade during austral summer. Moreover, the decrease in NPP positively correlated with the dominance of diatoms (Kendall's rank correlation τ = 0.60) estimated by a phytoplankton community composition model, but not correlated with SST. In the seasonal ice zone, NPP correlated with not only the dominance of diatoms positively (τ = 0.56), but also the dominance of haptophytes (τ = -0.54) and SST (τ = -0.54) negatively. Our results suggested that summer NPP values were strongly affected by the phytoplankton community composition in the Southern Ocean. [ABSTRACT FROM AUTHOR]

The diet of three Antarctic copepods, Calanus simillimus, Rhincalanus gigas and Pleuromamma robusta, was studied from samples collected during the European iron fertilization experiment (EIFEX) in austral fall 2004. The diet was investigated using microscopical gut content analysis. The food spectra of the three copepod species showed a clear overlap. The pennate diatom Fragilariopsis kerguelensis was commonly found in all guts. Large numbers of cells were fractured, but some were found complete when arranged as chains. The same was true for the genus Chaetoceros, a centric diatom, of which even their long and complete setae could be observed. In general the ingested food particles extended over a wide size range up to a few 100 μm. The copepod C. simillimus, for example, fed on large foraminifera and swallowed them whole. Compared to C. simillimus and R. gigas, P. robusta guts contained a higher percentage and larger diversity of hard-shelled protozoa including tintinnids, Radiolaria and Acantharia. [ABSTRACT FROM AUTHOR]

The effect of combined iron, silicate, and light co-limitation was investigated in the three diatom species Actinocyclus sp. Ehrenberg, Chaetoceros dichaeta Ehrenberg, and Chaetoceros debilis Cleve, isolated from the Southern Ocean (SO). Growth of all species was co-limited by iron and silicate, reflected in a significant increase in the number of cell divisions compared to the control. Lowest relative Si uptake and drastic frustule malformation was found under iron and silicate co-limitation in C. dichaeta, while Si limitation in general caused cell elongation in both Chaetoceros species. Higher light intensities similar to SO surface conditions showed a negative impact on growth of C. dichaeta and Actinocyclus sp . and no effect on C. debilis. This is in contrast to the assumed light limitation of SO diatoms due to deep wind driven mixing. Our results suggest that growth and species composition of Southern Ocean diatoms is influenced by a sensitive interaction of the abiotic factors, iron, silicate, and light. [ABSTRACT FROM AUTHOR]

Eulerian time-series were completed at three sites on the south eastern shelf of the Sub-Antarctic Prince Edward Islands (PEI), from 9 to 27 April 2000, to investigate the spatial and temporal variability of mesozooplankton communities in relation to on-shelf hydrodynamics. Surface temperature and phytoplankton biomass were recorded daily at all three sites, while two Bongo net tows and vertical temperature profiles were collected daily at two sites. Contrary to predictions of on-shelf water retention at low ambient current velocities, cross-correlation analysis identified a northward advection of ∼8.23 cm s−1 over the study area. Day to day changes in both physical and biological parameters were associated with cross-shelf advection. However, sea temperature had a narrow range of 6.2–7.4°C, while average between sample Bray–Curtis similarity in zooplankton communities was high, exceeding 75%. The relatively consistent average sample biomass amounted to ∼494 tonnes dry weight of mesozooplankton per day being advected onto the south eastern sector of the PEI shelf. We hypothesise that the observed stability of both physical and biological parameters was due to the Sub-Antarctic Front, with its high volume transport and steep physical gradients, being far to the north of the islands. Spatial and temporal variability of hydrodynamics on the PEI shelf, and particularly its relationship to shifting frontal positions, is highlighted as a future research area necessary to quantify the gross delivery of allochthonous biomass to the PEI ecosystem. [ABSTRACT FROM AUTHOR]

The main objective of the article is to give an overview of the history and evolution of phytoplankton research in the Southern Ocean during the past century and a half. It traces the evolution of phytoplankton investigations as it went through several phases commencing with intensive collecting and cataloging and leading to theDiscoveryinvestigations with its extensive and detailed studies of Southern Ocean phytoplankton. Following, in the footsteps of theDiscoverywas the USNSEltaninwith its specialized cruises that centered around the study of the ecology of the primary producers and the dynamics of the lower trophic levels of the food chain. Spurred by the findings of theEltanincruises and with the growing concern over the impending exploitation of the Antarctic marine living resources, in particular krill, the BIOMASS program was initiated. The program was the first international collaborative effort to study the dynamic functioning of the Antarctic marine ecosystem. The success of the program has rekindled great international interest in the Southern Ocean which resulted in an explosion of programs such as SO-JGOFS, SO-GLOBEC, EPOS, and several others. In recent years, there has been a major shift in phytoplankton research in the Southern Ocean. This was in response to worldwide concern over the effects of global warming and stratospheric ozone depletion on species diversity, primary production and ecosystem function. This has led to process-oriented programs to study phenomena and processes of global significance in which Antarctica and its surrounding seas play key roles. [ABSTRACT FROM AUTHOR]

The role of iron and light in controlling photosynthate production and allocation in phytoplankton populations of the Atlantic sector of the Southern Ocean was investigated in April–May 1999. The 14C incorporation into five biochemical pools (glucan, amino acids, proteins, lipids and polysaccharides) was measured during iron/light perturbation experiments. The diurnal Chl a-specific rates of carbon incorporation into these pools did not change in response to iron addition, yet were decreased at 20 ?mol photons m?2 s?1, an irradiance comparable with the one at 20–45 m in situ depth. This suggests that the low phytoplankton biomass encountered (0.1–0.6 ?g Chl a L?1) was mainly caused by light limitation in the deep wind mixed layer (>40 m). Regional differences in Chl a-specific carbon incorporation rates were not found in spite of differences in phytoplankton species composition: at the Antarctic Polar Front, biomass was dominated by a diatom population of Fragilariopsis kerguelensis, whereas smaller cells, including chrysophytes, were relatively more abundant in the Antarctic Circumpolar Current beyond the influence of frontal systems. Because mixing was often in excess of 100 m in the latter region, diatom cells may have been unable to fulfil their characteristically high Fe demand at low average light conditions, and thus became co-limited by both resources. Using a model that describes the 14C incorporation, the consistency was shown between the dynamics in the glucan pool in the field experiments and in laboratory experiments with an Antarctic diatom, Chaetoceros brevis. The glucan respiration rate was almost twice as high during the dark phase as during the light phase, which is consistent with the role of glucan as a reserve supplying energy and carbon skeletons for continued protein synthesis during the night. [ABSTRACT FROM AUTHOR]

Examines the mesozooplankton abundance, community structure and copepod grazing on phytoplankton in the Pacific sector of the Antarctic Polar Front. Approaches used in the measurement of copepod grazing on phytoplankton; Life cycle strategies of Antarctic copepods; Importance of phytoplankton carbon to the dietary carbon for copepods during spring and summer.

Investigates factors controlling pigment distribution across the Antarctic Polar Frontal region. Distinct assemblages on either side of the front as revealed by a mesoscale survey across the Polar Front; Relation between the dominance of diatoms over prymnesiophytes and mixed-layer depths; Location of the strongest vertical gradient in silicic acid and iron concentration which coincides with the maximum abundance of diatoms.

Examines the impact of meanders in the Antarctic Polar Frontal Zones (APFZ) on the concentration of phytoplankton. Processes regulating primary productivity in high current, low chlorophyll region; Temporal and spacial scales of biological and physical processes in the APFZ; Effect of vertical motion associated with meanders on the accumulation of phytoplankton biomass; Importance of nutrient availability in regulating phytoplankton photosynthesis.

Part II. Presents the results of a study of global carbon cycles in the Southern Ocean conducted by the United States Joint Global Ocean Flux Study (US JGOFS). Historical development of the US JGOFS program; Factors regulating the growth of phytoplankton in the Southern Ocean; Relation of the seasonal evolution of ecosystem structure to the flow of carbon and nutrients through the food web and to the fate of biogenic materials.

During the ANTARES 3 cruise in the Indian sector of the Southern Ocean in October–November 1995, the surface waters of Kerguelen Islands plume, and the surface and deeper waters (30–60 m) along a transect on 62°E from 48°36′S to the ice edge (58°50′S), were sampled. The phytoplankton community was size-fractionated (2 μm) and cell numbers, chlorophyll biomass and carbon assimilation, through Rubisco and β-carboxylase activities, were characterized. The highest contribution of <2 μm cells to total biomass and total Rubisco activity was reported in the waters of the Permanent Open Ocean Zone (POOZ) located between 52°S and 55°S along 62°E. In this zone, the picophytoplankton contributed from 26 to 50% of the total chlorophyll (a + b + c) with an average of 0.09 ± 0.02 μg Chl l–1 for <2 μm cells. Picophytoplankton also contributed 36 to 64% of the total Rubisco activity, with an average of 0.80 ± 0.30 mg C mg Chl a–1 h–1 for <2 μm cells. The picophytoplankton cells had a higher β-carboxylase activity than larger cells >2 μm. The mixotrophic capacity of these small cells is proposed. From sampling stations of the Kerguelen plume, a relationship was observed between the Rubisco activity per picophytoplankton cell and apparent cell size, which varied with the sampled water masses. Moreover, a depth-dependent photoperiodicity of Rubisco activity per cell for <2 μm phytoplankton was observed during the day/night cycle in the POOZ. In the near ice zone, a physiological change in picophytoplankton cells favouring phosphoenolpyruvate carboxykinase (PEPCK) activity was reported. A species succession, or an adaptation to unfavourable environmental conditions such as low temperature and/or available irradiance levels, may have provoked this change. The high contribution of picophytoplankton to the total biomass, and its high CO2 fixation capacity via autotrophy and mixotrophy, emphasize the strong regeneration of organic materials in the euphotic layer in the Southern Ocean. [ABSTRACT FROM PUBLISHER]