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Author |
Gomez, I.; Wiencke, C.; Thomas, D.N. |
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Title |
Variations in photosynthetic characteristics of the Antarctic marine brown alga Ascoseira mirabilis in relation to thallus age and size |
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Journal Article |
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Year |
1996 |
Publication |
European Journal of Phycology |
Abbreviated Journal |
Eur J Phycol |
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Volume  |
31 |
Issue |
2 |
Pages |
167-172 |
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Keywords |
photosynthesis: thallus: carbon fixation; growth curves; algae; age; Thalli; marine flora; Ascoseira mirabilis; Antarctica |
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Abstract |
Growth, photosynthesis, dark respiration, chlorophyll a (Chl a) content and dry weight were measured in 2- and 3-year-old plants of Ascoseira mirabilis (Ascoseirales), cultivated in the laboratory under changing daylengths which matched the seasonal variations in the Antarctic. Determinations were made in four thallus regions. Growth of A. mirabilis was seasonal, with higher rates in spring. Parameters such as net photosynthesis (P sub(max)), photosynthetic efficiency ( alpha ), both measured on a fresh weight (FW) basis, and dry weight content, showed significant age- and size-dependent variations. In contrast, no variations were observed in dark respiration, initial light-saturating point of photosynthesis (I sub(k)) and Chl a contents. P sub(max) had maximum values close to 16.5 mu mol O sub(2)/g super(1) FW/h in 2-year-old plants, whereas in 3-year-old plants maximum values of 8 mu mol O sub(2)/g FW/h were determined. The alpha -values reached maximum rates of 1.4 and 0.6 mu mol O sub(2)/g FW/h/( mu mol photons/m super(2)/s) in 2- and 3-year-old plants, respectively. Light compensation point (I sub(c)), dry weight ratios and Chl a contents varied significantly along the length of the blade. Maximum dry:fresh weight ratios were observed in the basal region, with values close to 18%. Distal regions of the 3-year-old plants had significantly higher dry weight content than 2-year-old plants (17.5% and 13%, respectively). Chl a concentrations increased towards the middle regions of the thallus to values close to 0.35 mg Chl a/g FW. The results indicate that some morpho-functional processes in A. mirabilis, especially net photosynthesis and photosynthetic efficiency, are governed by age of the plant, thereby reflecting differences in biomass allocation and size. Our data also confirm the previously demonstrated relationship between growth and seasonal physiological activity that allows A. mirabilis to survive under the low light conditions prevailing in the Antarctic. |
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ISSN |
0967-0262 |
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Notes |
growth curves; size; Thalli; marine flora; thallus |
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no |
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Call Number |
refbase @ admin @ Gomez++1996 |
Serial |
737 |
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Author |
Kaartokallio, H.; Kuosa, H.; Thomas, D.N.; Granskog, M.A.; Kivi, K. |
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Title |
Biomass, composition and activity of organism assemblages along a salinity gradient in sea ice subjected to river discharge in the Baltic Sea |
Type |
Journal Article |
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Year |
2006 |
Publication |
Polar Biology |
Abbreviated Journal |
Polar Biol |
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Volume |
30 |
Issue |
2 |
Pages |
183-197 |
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Abstract |
A study was undertaken to examine the activity and composition of the seasonal Baltic Sea land-fast sea-ice biota along a salinity gradient in March 2003 in a coastal location in the SW coast of Finland. Using a multi-variable data set, the less well-known algal and protozoan communities, and algal and bacterial production in relation to the physical and chemical environment were investigated. Also, the first coincident measurements of bacterial production and dissolved organic matter (DOM) in a sea-ice system are reported. Communities in sea ice were clearly autotrophy-dominated with algal biomass representing 79% of the total biomass. Protozoa and rotifers made up 18% of biomass in the ice and bacteria only 3%. Highest biomasses were found in mid-transect bottom ice. Water column assemblages were clearly more heterotrophic: 39% algae, 12% bacteria and 49% for rotifers and protozoa. Few significant correlations existed between DOM and bacterial variables, reflecting the complex origin of ice DOM. Dynamics of dissolved organic carbon, nitrogen and phosphorus (DOC, DON and DOP) were also uncoupled. A functional microbial loop is likely to be present in the studied ice. Existence of an under-ice freshwater plume affects the ecosystem functioning: Under-ice water communities are influenced directly by river-water mixing, whereas the ice system seems to be more independent–the interaction mainly taking place through the formation of active bottom communities. |
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Springer-Verlag |
Place of Publication |
Heidelberg |
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0722-4060 |
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Notes |
Sampling: Nine stations along a 40km salinity gradient from inner Pojo Bay through the Archipelago to the edge of the open sea |
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no |
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Call Number |
refbase @ admin @ Kaartokallio++2006 |
Serial |
744 |
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Author |
Mock, T.; Dieckmann, G.S.; Haas, C.; Krell, A.; Tison, J.-L.; Belem, A.L.; Papadimitriou, S.; Thomas, D.N. |
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Title |
Micro-optodes in sea ice: a new approach to investigate oxygen dynamics during sea ice formation |
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Journal Article |
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Year |
2002 |
Publication |
Aquatic Microbial Ecology |
Abbreviated Journal |
Aquat Microb Ecol |
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Volume |
29 |
Issue |
3 |
Pages |
297-306 |
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Keywords |
Fragilariopsis cylindrus; Oxygen; Methods; Micro-optodes; Sea ice; Biogeochemistry; Diatoms; Algae; Chlorophyll; Photosynthesis; Salinity effects; Sea water; Marine ecosystems; Chlorophylls; Dissolved oxygen; Gases; Epontic environment; Electrodes; Sensors; Brines; Ice-water interface; Ice formation; Bacillariophyceae |
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Abstract |
Oxygen micro-optodes were used to measure oxygen dynamics directly within the microstructure of sea ice by freezing the sensors into the ice during its formation. The experiment was conducted in a 4 m³ mesocosm filled with artificial seawater and inoculated with a unialgal culture of the common Antarctic ice diatom Fragilariopsis cylindrus (Bacillariophyceae) to a final chlorophyll a (chl a) concentration of 11 µg 1?¹. Ice growth was initiated 7 d after inoculation by reducing the air temperature to -10 plus or minus 2 degree C and terminated 17 d later. The final ice thickness was 27 cm. One optode was frozen into grease ice and 2 others into the skeletal layer of the growing ice sheet. Increasing oxygen concentrations during ice crystal formation at the water surface and the ice-water interface revealed a strong inclusion of oxygen, which was either physically trapped and/or the result of photosynthesising diatoms. The major portion of oxygen was present as gas bubbles due to super-saturation as a result of increasing salinity and oxygen production by diatoms. An increase in salinity due to a concurrent decrease in ice temperatures during subsequent sea ice development reduced the maximum concentration of dissolved oxygen within brine. Thus, dissolved oxygen concentrations decreased over time, whereas gaseous oxygen was released to the atmosphere and seawater. The sensors are a significant advance on more conventional microelectrodes, because the recordings can be temperature and salinity compensated in order to obtain precise measurements of oxygen dynamics with regard to total (dissolved and gaseous) and dissolved oxygen in sea ice. Optodes do not consume oxygen during measuremnet over a long period under extreme conditions, which is another advantage for long-term deployment in the field. |
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Publisher |
Inter-Research |
Place of Publication |
Oldendorf/Luhe |
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ISSN |
0948-3055 |
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Notes |
Marine |
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no |
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Call Number |
refbase @ admin @ Mock++2002 |
Serial |
749 |
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Author |
Granskog, M.A.; Kaartokallio, H.; Kuosa, H.; Thomas, D.N.; Ehn, J.; Sonninen, E. |
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Title |
Scales of horizontal patchiness in chlorophyll a, chemical and physical properties of landfast sea ice in the Gulf of Finland (Baltic Sea) |
Type |
Journal Article |
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Year |
2005 |
Publication |
Polar Biology |
Abbreviated Journal |
Polar Biol |
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Volume |
28 |
Issue |
4 |
Pages |
276-283 |
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Keywords |
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Abstract |
Horizontal variation of first-year landfast sea ice properties was studied in the Gulf of Finland, the Baltic Sea. Several scales of variation were considered; a number of arrays with core spacings of 0.2, 2 and 20 m were sampled at different stages of the ice season for small-scale patchiness. Spacing between these arrays was from hundreds of meters to kilometers to study mesoscale variability, and once an onshore–offshore 40-km transect was sampled to study regional scale variability. Measured variables included salinity, stable oxygen isotopes (δ18O), chlorophyll a (chl-a), nutrients and dissolved organic carbon. On a large scale, a combination of variations in the under-ice water salinity (ice porosity), nutrient supply and the stage of ice development control the build-up of ice algal biomass. At scales of hundreds of meters to kilometers, there was significant variability in several parameters (salinity, chl-a, snow depth and ice thickness). Analyses of the data from the arrays did not show evidence of significant patchiness at scales <20 m for algal biomass. The results imply that the sampling effort in Baltic Sea ice studies should be concentrated on scales of hundreds of meters to kilometers. Using the variations observed in the study area, the estimate for depth-integrated algal biomass in landfast sea ice in the Gulf of Finland (March 2003) is 5.5±4.4 mg chl-a m-2. |
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Address |
Granskog: Arctic Centre, University of Lapland, P.O. Box 122, 96101 Rovaniemi, Finland |
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Springer-Verlag |
Place of Publication |
Heidelberg |
Editor |
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English |
Summary Language |
English |
Original Title |
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ISSN |
0722-4060 |
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Baltic Sea; Gulf of Finland |
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no |
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Call Number |
refbase @ admin @ Granskog++2005 |
Serial |
739 |
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Author |
Krell, A.; Schnack-Schiel, S.B.; Thomas, D.N.; Kattner, G.; Zipan, W.; Dieckmann, G.S. |
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Title |
Phytoplankton dynamics in relation to hydrography, nutrients and zooplankton at the onset of sea ice formation in the eastern Weddell Sea (Antarctica) |
Type |
Journal Article |
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Year |
2005 |
Publication |
Polar Biology |
Abbreviated Journal |
Polar Biol |
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Volume |
28 |
Issue |
9 |
Pages |
700-713 |
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Keywords |
Weddell Sea; Asf; Hydrography; Phytoplankton; Seasonal change; Community composition; Primary production; Zooplankton |
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Abstract |
The quantitative and qualitative distribution of phytoplankton was investigated along five North–South transects in the eastern Weddell Sea during the transition from late autumn to winter. Relationships with the regional hydrography, progressing sea ice coverage, nutrient distribution and zooplankton are discussed and compared with data from other seasons. To the north of the Antarctic Slope Front (ASF) a remnant temperature minimum layer was found above the primary pycnocline throughout summer. Surface waters had not entirely acquired typical winter characteristics. While temperature was already in the winter range, this was not the case for salinity. Highest biomass of phytoplankton, with the exception of the first transect, was found in the region adjoining the ASF to the north. Absolute chlorophyll a (Chl a) concentrations dropped from 0.35 to 0.19 µg/1. Nutrient pools exhibited a replenishing tendency. Ammonium concentrations were high (0.75–2 µmol/1), indicating extensive heterotrophic activity. The phytoplankton in the ASF region was dominated by nanoflagellates, particularly Phaeocystis spp.. North of the ASF the abundance of diatoms increased, with Fragilariopsis spp., F. cylindrus and Thalassiosira spp. dominating. Community structure varied both due to hydrographical conditions and the advancing ice edge. The phytoplankton assemblage formed during late autumn were very similar to the ones found in early spring. A POC/PON ratio close to Redfield, decreasing POC concentration and a high phaeophytin/ Chl a ratio, as well as a high abundance of mesozooplankton indicated that a strong grazing pressure was exerted on the phytoplankton community. A comparison between primary production (PP) in the water column and the sea ice showed a shift of the major portion of PP into the ice during the period of investigation. |
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Springer-Verlag |
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Heidelberg |
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0722-4060 |
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Notes |
Isi:000231421200006 |
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no |
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Call Number |
refbase @ admin @ Krell++2005 |
Serial |
747 |
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