Posts Tagged 'Arctic Ocean'



Effect of elevated CO2 on the dynamics of particle-attached and free-living bacterioplankton communities in an Arctic fjord (update)

In the frame of the European Project on Ocean Acidification (EPOCA), the response of an Arctic pelagic community (<3 mm) to a gradient of seawater pCO2 was investigated. For this purpose 9 large-scale in situ mesocosms were deployed in Kongsfjorden, Svalbard (78°56.2´ N, 11°53.6´ E), in 2010. The present study investigates effects on the communities of particle-attached (PA; >3 μm) and free-living (FL; < 3 μm > 0.2 μm) bacteria by Automated Ribosomal Intergenic Spacer Analysis (ARISA) in 6 of the mesocosms, ranging from 185 to 1050 μatm initial pCO2, and the surrounding fjord. ARISA was able to resolve, on average, 27 bacterial band classes per sample and allowed for a detailed investigation of the explicit richness and diversity. Both, the PA and the FL bacterioplankton community exhibited a strong temporal development, which was driven mainly by temperature and phytoplankton development. In response to the breakdown of a picophytoplankton bloom, numbers of ARISA band classes in the PA community were reduced at low and medium CO2 (~ 185–685 μatm) by about 25%, while they were more or less stable at high CO2 (~ 820–1050 μatm). We hypothesise that enhanced viral lysis and enhanced availability of organic substrates at high CO2 resulted in a more diverse PA bacterial community in the post-bloom phase. Despite lower cell numbers and extracellular enzyme activities in the post-bloom phase, bacterial protein production was enhanced in high CO2 mesocosms, suggesting a positive effect of community richness on this function and on carbon cycling by bacteria.

Continue reading ‘Effect of elevated CO2 on the dynamics of particle-attached and free-living bacterioplankton communities in an Arctic fjord (update)’

Effect of elevated CO2 on the dynamics of particle attached and free living bacterioplankton communities in an Arctic fjord

The increase in atmospheric carbon dioxide (CO2) results in acidification of the oceans, expected to lead to the fastest drop in ocean pH in the last 300 million years, if anthropogenic emissions are continued at present rate. Due to higher solubility of gases in cold waters and increased exposure to the atmosphere by decreasing ice cover, the Arctic Ocean will be among the areas most strongly affected by ocean acidification. Yet, the response of the plankton community of high latitudes to ocean acidification has not been studied so far. This work is part of the Arctic campaign of the European Project on Ocean Acidification (EPOCA) in 2010, employing 9 in situ mesocosms of about 45 000 l each to simulate ocean acidification in Kongsfjorden, Svalbard (78°56.2′ N 11°53.6′ E). In the present study, we investigated effects of elevated CO2 on the composition and richness of particle attached (PA;> 3 μm) and free living (FL; <3 μm> 0.2 μm) bacterial communities by Automated Ribosomal Intergenic Spacer Analysis (ARISA) in 6 of the mesocosms and the surrounding fjord, ranging from 185 to 1050 initial μatm pCO2. ARISA was able to resolve about 20–30 bacterial band-classes per sample and allowed for a detailed investigation of the explicit richness. Both, the PA and the FL bacterioplankton community exhibited a strong temporal development, which was driven mainly by temperature and phytoplankton development. In response to the breakdown of a picophytoplankton bloom (phase 3 of the experiment), number of ARISA-band classes in the PA-community were reduced at low and medium CO2(∼180–600 μatm) by about 25%, while it was more or less stable at high CO2 (∼ 650–800 μatm). We hypothesise that enhanced viral lysis and enhanced availability of organic substrates at high CO2 resulted in a more diverse PA-bacterial community in the post-bloom phase. Despite lower cell numbers and extracellular enzyme activities in the post-bloom phase, bacterial protein production was enhanced in high CO2-treatments, suggesting a positive effect of community richness on this function and on carbon cycling by bacteria.

Continue reading ‘Effect of elevated CO2 on the dynamics of particle attached and free living bacterioplankton communities in an Arctic fjord’

Response of bacterioplankton community structure to an artificial gradient of pCO2 in the Arctic Ocean

The influences of ocean acidification on bacterial diversity were investigated using DNA fingerprinting and clone library analysis of bacterioplankton samples collected from the largest CO2 manipulation mesocosm study that had been performed thus far. Terminal restriction fragment length polymorphism analysis of the PCR amplicons of the 16S rRNA genes revealed that bacterial diversity, species richness and community structure varied with the time of incubation but not the degree of ocean acidification. The phylogenetic composition of the major bacterial assemblage after a 30-day incubation under various pCO2 concentrations did not show clear effects of pCO2 levels. However, the maximum apparent diversity and species richness which occurred during incubation differed in the high and low pCO2 treatments, in which different bacterial community structure harbored. In addition, total alkalinity was one of the contributing factors for the temporal variations in bacterial community structure observed during incubation. A negative relationship between the relative abundance of Bacteroidetes and pCO2 levels was observed for samples at the end of the experiment. Our study suggested that ocean acidification affected the development of bacterial assemblages and potentially impacts the ecological function of the bacterioplankton in the marine ecosystem.

Continue reading ‘Response of bacterioplankton community structure to an artificial gradient of pCO2 in the Arctic Ocean’

Response of bacterioplankton activity in an Arctic fjord system to elevated pCO2: results from a mesocosm perturbation study

The effect of elevated seawater carbon dioxide (CO2) on the activity of a natural bacterioplankton community in an Arctic fjord system was investigated by a mesocosm perturbation study in the frame of the European Project on Ocean Acidification (EPOCA). A pCO2 range of 175–1085 μatm was set up in nine mesocosms deployed in the Kongsfjorden (Svalbard). The bacterioplankton communities responded to rising chlorophyll a concentrations after a lag phase of only a few days with increasing protein production and extracellular enzyme activity and revealed a close coupling of heterotrophic bacterial activity to phytoplankton productivity in this experiment. The natural extracellular enzyme assemblages showed increased activity in response to moderate acidification. A decrease in seawater pH of 0.5 units roughly doubled rates of β-glucosidase and leucine-aminopeptidase. Activities of extracellular enzymes in the mesocosms were directly related to both seawater pH and primary production. Also primary production and bacterial protein production in the mesocosms at different pCO2 were positively correlated. Therefore, it can be suggested that the efficient heterotrophic carbon utilization in this Arctic microbial food web had the potential to counteract increased phytoplankton production that was achieved under elevated pCO2 in this study. However, our results also show that the transfer of beneficial pCO2-related effects on the cellular bacterial metabolism to the scale of community activity and organic matter degradation can be mitigated by the top-down control of bacterial abundances in natural microbial communities.

Continue reading ‘Response of bacterioplankton activity in an Arctic fjord system to elevated pCO2: results from a mesocosm perturbation study’

CO2 increases 14C-primary production in an Arctic plankton community

Responses to ocean acidification in plankton communities were studied during a CO2-enrichment experiment in the Arctic Ocean, accomplished from June to July 2010 in Kongsfjorden, Svalbard (78°56, 2′ N, 11°53, 6′ E). Enclosed in 9 mesocosms (volume: 43.9–47.6 m3), plankton was exposed to CO2 concentrations, ranging from glacial to projected mid-next-century levels. Fertilization with inorganic nutrients at day 13 of the experiment supported the accumulation of phytoplankton biomass, as indicated by two periods of high Chl a concentration.

This study tested for CO2 sensitivities in primary production (PP) of particulate organic carbon (PPPOC) and of dissolved organic carbon (PPDOC). Therefore, 14C-bottle incubations (24 h) of mesocosm samples were performed at 1 m depth receiving about 60% of incoming radiation. PP for all mesocosms averaged 8.06 ± 3.64 μmol C l−1 d−1and was slightly higher than in the outside fjord system. Comparison between mesocosms revealed significantly higher PPPOC at elevated compared to low pCO2 after nutrient addition. PPDOC was significantly higher in CO2 enriched mesocosms before as well as after nutrient addition, suggesting that CO2 had a direct influence on DOC production. DOC concentrations inside the mesocosms increased before nutrient addition and more in high CO2 mesocosms. After addition of nutrients, however, further DOC accumulation was negligible and not significantly different between treatments, indicating rapid utilization of freshly produced DOC. Bacterial biomass production (BP) was coupled to PP in all treatments, indicating that 3.5 ± 1.9% of PP, or 21.6 ± 12.5% of PPDOC provided sufficient carbon for synthesis of bacterial biomass. The response of 14C-based PP rates to CO2 enrichment was at odds with O2-based net community production (NCP) rates that were also determined during this study, albeit at lower light level. We conclude that the enhanced release of labile DOC during autotrophic production at high CO2 exceedingly stimulated activities of heterotrophic microorganisms. As a consequence, increased PP induced less NCP, as suggested earlier for carbon limited microbial systems in the Arctic.

Continue reading ‘CO2 increases 14C-primary production in an Arctic plankton community’

Effect of ocean acidification on the fatty acid composition of a natural plankton community

The effect of ocean acidification on the fatty acid composition of a natural plankton community in the Arctic was studied in a large-scale mesocosm experiment, carried out in Kongsfjorden (Svalbard, Norway) at 79° N. Nine mesocosms of ~50 cbm each were exposed to different pCO2 levels (from natural background conditions to ~1420 μatm), yielding pH values (on the total scale) from ~8.3 to 7.5. Inorganic nutrients were added on day 13. The phytoplankton development during this 30 days experiment passed three distinct phases: (1) prior to the addition of inorganic nutrients, (2) first bloom after nutrient addition, and (3) second bloom after nutrient addition. The fatty acid composition of the natural plankton community was analysed and showed, in general, high percentages of polyunsaturated fatty acids (PUFAs): 44–60% of total fatty acids. Positive correlations with pCO2 were found for most PUFAs during phases 2 and/or 3, with the exception of 20:5n3 (eicosapentaenoic acid, EPA), an important diatom marker. There are strong indications for these correlations being mediated indirectly through taxonomic changes and the natural development of the communities in the mesocosms exposed to different pCO2 levels. While diatoms increased during phase 3 mainly in the low and intermediate pCO2 treatments, dinoflagellates were favoured by high CO2 concentrations during the same time period. This is reflected in the development of group-specific fatty acid trophic markers. No indications were found for a generally detrimental effect of ocean acidification on the planktonic food quality in terms of essential fatty acids. The significant positive correlations between most PUFAs and pCO2 reflected treatment-dependent differences in the community composition between the mesocosms rather than a direct positive effect of pCO2 on specific fatty acids.

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Response of halocarbons to ocean acidification in the Arctic

The potential effect of ocean acidification (OA) on seawater halocarbons in the Arctic was investigated during a~mesocosm experiment in Spitsbergen in June–July 2010. Over a period of 5 weeks, natural phytoplankton communities in nine ~50 m3 mesocosms were studied under a range of pCO2 treatments from ~185 μatm to ~1420 μatm. In general, the response of halocarbons to pCO2 was subtle, or undetectable. A large number of significant correlations with a range of biological parameters (chlorophyll a, microbial plankton community, phytoplankton pigments) were identified, indicating a biological control on the concentrations of halocarbons within the mesocosms. The temporal dynamics of iodomethane (CH3I) alluded to active turnover of this halocarbon in the mesocosms and strong significant correlations with biological parameters suggested a biological source. However, despite a pCO2 effect on various components of the plankton community, and a strong association between CH3I and biological parameters, no effect of pCO2 was seen in CH3I. Diiodomethane (CH2I2) displayed a number of strong relationships with biological parameters. Furthermore, the concentrations, the rate of net production and the sea-to-air flux of CH2I2 showed a significant positive response to pCO2. There was no clear effect of pCO2 on bromocarbon concentrations or dynamics. However, periods of significant net loss of bromoform (CHBr3) were found to be concentration-dependent, and closely correlated with total bacteria, suggesting a degree of biological consumption of this halocarbon in Arctic waters. Although the effects of OA on halocarbon concentrations were marginal, this study provides invaluable information on the production and cycling of halocarbons in a region of the world’s oceans likely to experience rapid environmental change in the coming decades.

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The influence of increased temperature and carbon dioxide levels on the benthic/sea ice diatom Navicula directa

Polar oceans are very susceptible to increased levels of atmospheric CO2 and may act as the world’s largest sink for anthropogenic CO2. Simultaneously, as atmospheric CO2 increases, sea surface temperature rises due to global warming. These two factors are important in regulating microalgal ecophysiology, and it has been suggested that future global changes may significantly alter phytoplankton species composition. This study aims to investigate potential consequences of global change in terms of increased temperature and CO2 enrichment on the benthic/sea ice diatom Navicula directa. In a laboratory experiment, the physiological response to elevated temperature and partial pressure of CO2 (pCO2) was investigated in terms of growth, photosynthetic activity and photosynthetic pigment composition. The experiment was performed under manipulated levels of pCO2 (380 and 960 ppm) and temperature (0.5 and 4.5°C) to simulate a change from present levels to predicted levels during a worst-case scenario by the year 2100. After 7 days of treatment, no synergetic effects between temperature and pCO2 were detected. However, elevated temperature promoted effective quantum yield of photosynthesis (∆F/Fm) and increased growth rates by approximately 43%. Increased temperature also resulted in an altered pigment composition. In addition, enrichment of CO2 appeared to reduce specific growth rates of N. directa. Even though growth rates were only reduced by approximately 5%, we hereby report that increased pCO2 levels might also have potential negative effects on certain diatom strains.

Continue reading ‘The influence of increased temperature and carbon dioxide levels on the benthic/sea ice diatom Navicula directa’


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