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894 results on '"Riebesell U"'

159. Climate change, seasonal plankton succession and mismatch in food chains

Author

Sommer, U., Aberle, Nicole, Breithaupt, P., Engel, Anja, Hoppe, H. G., Jürgens, K., Lengfellner, K., Riebesell, U., Walther, Konrad, Wohlers, J., Sommer, U., Aberle, Nicole, Breithaupt, P., Engel, Anja, Hoppe, H. G., Jürgens, K., Lengfellner, K., Riebesell, U., Walther, Konrad, and Wohlers, J.

Published
2007

161. Effect of CO2 concentration on suspended particle dynamics during a mesocosm bloom experiment (Peece II)

Author

Engel, Anja, Bellerby, R., Delille, B., Schulz, K., Riebesell, U., Schartau, Markus, Engel, Anja, Bellerby, R., Delille, B., Schulz, K., Riebesell, U., and Schartau, Markus

Abstract

The influence of seawater CO2 concentration on the abundance and size of suspended particles (2-40 µm) was investigated during a mesocosm experiment at the large scale facility (LFS) in Bergen. In nine outdoor enclosures the partial pressure of CO2 (pCO2) in the seawater was modified by an aeration system. The triplicate mesocosm treatments simulated low (~190 parts per million by volume (ppmV) CO2), present day (~370 ppmV CO2) and high (~700 ppmV CO2) CO2 conditions. The inorganic nutrients nitrate and phosphate were added initially to the mesocosms to induce phytoplankton blooms. Samples for suspended particles were collected daily over a period of 19 days and analysed with the Coulter Counter and by Flow Cytometry. First results indicate that the CO2 treatment significantly affected the size distribution of solid particles, and led to larger surface to volume ratios at lower pCO2. Size is important for diffusion-limited exchange processes at the cell surface as well as for gravitational settling of the solid particles. The observed changes in particle size distribution are therefore discussed with respect to organic matter production and potential sedimentation in the mesocosms during the bloom. An outlook on possible implications of our findings for the future carbon cycling and export in the ocean will be presented.

Published
2007

167. Marine ecosystem community carbon and nutrient uptake stoichiometry under varying ocean acidification during the PeECE III experiment

Author

Bellerby, R. G. J., Schulz, K. G., Riebesell, U., Neill, C., Nondal, G., Johannessen, T., Brown, K. R., Bellerby, R. G. J., Schulz, K. G., Riebesell, U., Neill, C., Nondal, G., Johannessen, T., and Brown, K. R.

Abstract

Inorganic carbon and nutrient biogeochemical responses were studied during the 2005 Pelagic Ecosystem CO2 Enrichment (PeECE III) study. Inverse analysis of the temporal inorganic carbon dioxide system and nutrient variations was used to determine the net community stoichiometric uptake characteristics of a natural pelagic ecosystem production perturbed over a range of pCO2 scenarios (350, 700 and 1050 ?atm). Nutrient uptake showed no sensitivity to CO2 treatment. There was enhanced carbon production relative to nutrient consumption in the higher CO2 treatments which was positively correlated with the initial CO2 concentration. There was no significant calcification response to changing CO2 in Emiliania huxleyi by the peak of the bloom and all treatments exhibited low particulate inorganic carbon production (~15 ?mol kg?1). With insignificant air-sea CO2 exchange across the treatments, the enhanced carbon uptake was due to increase organic carbon production. The inferred cumulative C:N:P stoichiometry of organic production increased with CO2 treatment from 1:6.3:121 to 1:7.1:144 to 1:8.25:168 at the height of the bloom. This study discusses how ocean acidification may incur modification to the stoichiometry of pelagic production and have consequences for ocean biogeochemical cycling.

Published
2007

168. Effect of ocean acidification and elevated fCO2 on trace gas production by a Baltic Sea summer phytoplankton community.

Author

Webb, A. L., Leedham-Elvidge, E., Hughes, C., Hopkins, F. E., Malin, G., Bach, L. T., Schulz, K., Crawfurd, K., Brussaard, C. P. D., Stuhr, A., Riebesell, U., and Liss, P. S.

Subjects
OCEAN acidification, TRACE gases, BRACKISH waters, PHYTOPLANKTON, DIMETHYL sulfide, METHYL iodide
Abstract

The Baltic Sea is a unique environment as the largest body of brackish water in the world. Acidification of the surface oceans due to absorption of anthropogenic CO2 emissions is an additional stressor facing the pelagic community of the already challenging Baltic Sea. To investigate its impact on trace gas biogeochemistry, a large-scale mesocosm experiment was performed off Tvärminne Research Station, Finland in summer 2012. During the second half of the experiment, dimethylsulphide (DMS) concentrations in the highest fCO2 mesocosms (1075-1333 Î?atm) were 34% lower than at ambient CO2 (350 Î?atm). However the net production (as measured by concentration change) of seven halocarbons analysed was not significantly affected by even the highest CO2 levels after 5 weeks exposure. Methyl iodide (CH3I) and diiodomethane (CH2I2) showed 15% and 57% increases in mean mesocosm concentration (3.8 ± 0.6 pmol L-1 increasing to 4.3 ± 0.4 pmol L-1 and 87.4 ± 14.9 pmol L-1 increasing to 134.4 ± 24.1 pmol L-1 respectively) during Phase II of the experiment, which were unrelated to CO2 and corresponded to 30% lower Chl-É' concentrations compared to Phase I. No other iodocarbons increased or showed a peak, with mean chloroiodomethane (CH2ClI) concentrations measured at 5.3 (± 0.9) pmol L-1 and iodoethane (C2H5I) at 0.5 (± 0.1) pmol L-1. Of the concentrations of bromoform (CHBr3; mean 88.1 ± 13.2 pmol L-1), dibromomethane (CH2Br2; mean 5.3 ± 0.8 pmol L-1) and dibromochloromethane (CHBr2Cl, mean 3.0 ± 0.5 pmol L-1), only CH2Br2 showed a decrease of 17% between Phases I and II, with CHBr3 and CHBr2Cl showing similar mean concentrations in both Phases. Outside the mesocosms, an upwelling event was responsible for bringing colder, high CO2, low pH water to the surface starting on day t16 of the experiment; this variable CO2 system with frequent upwelling events implies the community of the Baltic Sea is acclimated to regular significant declines in pH caused by up to 800 Î?atm fCO2. After this upwelling, DMS concentrations declined, but halocarbon concentrations remained similar or increased compared to measurements prior to the change in conditions. Based on our findings, with future acidification of Baltic Sea waters, biogenic halocarbon emissions are likely to remain at similar values to today, however emissions of biogenic sulphur could significantly decrease from this region. [ABSTRACT FROM AUTHOR]

Published
2016
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183. Ocean acidification shows negligible impacts on high-latitude bacterial community structure in coastal pelagic mesocosms

Author

Roy, A.-S., primary, Gibbons, S. M., additional, Schunck, H., additional, Owens, S., additional, Caporaso, J. G., additional, Sperling, M., additional, Nissimov, J. I., additional, Romac, S., additional, Bittner, L., additional, Mühling, M., additional, Riebesell, U., additional, LaRoche, J., additional, and Gilbert, J. A., additional

Published
2013
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186. Temporal biomass dynamics of an Arctic plankton bloom in response to increasing levels of atmospheric carbon dioxide

Author

Schulz, K. G., primary, Bellerby, R. G. J., additional, Brussaard, C. P. D., additional, Büdenbender, J., additional, Czerny, J., additional, Engel, A., additional, Fischer, M., additional, Koch-Klavsen, S., additional, Krug, S. A., additional, Lischka, S., additional, Ludwig, A., additional, Meyerhöfer, M., additional, Nondal, G., additional, Silyakova, A., additional, Stuhr, A., additional, and Riebesell, U., additional

Published
2013
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187. Effect of elevated CO<sub>2</sub> on the dynamics of particle-attached and free-living bacterioplankton communities in an Arctic fjord

Author

Sperling, M., primary, Piontek, J., additional, Gerdts, G., additional, Wichels, A., additional, Schunck, H., additional, Roy, A.-S., additional, La Roche, J., additional, Gilbert, J., additional, Nissimov, J. I., additional, Bittner, L., additional, Romac, S., additional, Riebesell, U., additional, and Engel, A., additional

Published
2013
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192. Synthesis of iron fertilization experiments: From the Iron Age in the Age of Enlightenment

Author

Baar, H. J. W. de, Boyd, P. W., Coale, K. H., Landry, M. R., Tsuda, A., Assmy, Philipp, Bakker, D. C. E., Bozec, Y., Barber, R. T., Brzezinski, M. A., Buesseler, K. O., Boye, M., Croot, P. L., Gervais, F., Gorbunov, M. Y., Harrison, P. J., Hiscock, W. T., Laan, P., Lancelot, C., Law, C. S., Levasseur, M., Marchetti, A., Millero, F. J., Nishioka, J., Nojiri, Y., Oijen, T., Riebesell, U., Rijkenberg, M. J. A., Saito, H., Takeda, S., Timmermans, K. R., Veldhuis, M. J. W., Waite, A. M., Wong, C. S., Baar, H. J. W. de, Boyd, P. W., Coale, K. H., Landry, M. R., Tsuda, A., Assmy, Philipp, Bakker, D. C. E., Bozec, Y., Barber, R. T., Brzezinski, M. A., Buesseler, K. O., Boye, M., Croot, P. L., Gervais, F., Gorbunov, M. Y., Harrison, P. J., Hiscock, W. T., Laan, P., Lancelot, C., Law, C. S., Levasseur, M., Marchetti, A., Millero, F. J., Nishioka, J., Nojiri, Y., Oijen, T., Riebesell, U., Rijkenberg, M. J. A., Saito, H., Takeda, S., Timmermans, K. R., Veldhuis, M. J. W., Waite, A. M., and Wong, C. S.

Published
2005

193. Testing the direct effect of CO2 concentration on a bloom of the coccolithophorid Emiliania huxleyi in mesocosm experiments

Author

Engel, Anja, Zondervan, Ingrid, Aerts, K., Beaufort, L., Benthien, Albert, Chou, L., Delille, B., Gattuso, J. P., Harlay, J., Heemann, C., Hoffmann, L., Jacquet, S., Nejstgaard, J., Pizay, M. D., Rochelle-Newall, E., Schneider, U., Terbrüggen, Anja, Riebesell, U., Engel, Anja, Zondervan, Ingrid, Aerts, K., Beaufort, L., Benthien, Albert, Chou, L., Delille, B., Gattuso, J. P., Harlay, J., Heemann, C., Hoffmann, L., Jacquet, S., Nejstgaard, J., Pizay, M. D., Rochelle-Newall, E., Schneider, U., Terbrüggen, Anja, and Riebesell, U.

Abstract

We studied the direct effects of CO2 and related changes in seawater carbonate chemistry on marine planktonic organisms in a mesocosm experiment. In nine outdoor enclosures (~11 m3 each), the partial pressure of CO2 (pCO2) in the seawater was modified by an aeration system. The triplicate mesocosm treatments represented low (~190 parts per million by volume (ppmV) CO2), present (~410 ppmV CO2), and high (~710 ppmV CO2) pCO2 conditions. After initial fertilization with nitrate and phosphate a bloom dominated by the coccolithophorid Emiliania huxleyi occurred simultaneously in all of the nine mesocosms; it was monitored over a 19-day period. The three CO2 treatments assimilated nitrate and phosphate similarly. The concentration of particulate constituents was highly variable among the replicate mesocosms, disguising direct CO2-related effects. Normalization of production rates within each treatment, however, indicated that the net specific growth rate of E. huxleyi, the rate of calcification per cell, and the elemental stoichiometry of uptake and production processes were sensitive to changes in pCO2. This broad influence of CO2 on the E. huxleyi bloom suggests that changes in CO2 concentration directly affect cell physiology with likely effects on the marine biogeochemistry.

Published
2005

198. Supplementary material to "Ocean acidification shows negligible impacts on high-latitude bacterial community structure in coastal pelagic mesocosms"

Author

Roy, A.-S., primary, Gibbons, S. M., additional, Schunck, H., additional, Owens, S., additional, Caporaso, J. G., additional, Sperling, M., additional, Nissimov, J. I., additional, Romac, S., additional, Bittner, L., additional, Riebesell, U., additional, LaRoche, J., additional, and Gilbert, J. A., additional

Published
2012
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