Michael Meyerhöfer

Enhanced biological carbon consumption in a high CO2 ocean

The oceans have absorbed nearly half of the fossil-fuel carbon dioxide (CO2) emitted into the atmosphere since pre-industrial times, causing a measurable reduction in seawater pH and carbonate saturation. If CO2 emissions continue to rise at current rates, upper-ocean pH will decrease to levels lower than have existed for tens of millions of years and, critically, at a rate of change 100 times greater than at any time over this period. Recent studies have shown effects of ocean acidification on a variety of marine life forms, in particular calcifying organisms. Consequences at the community to ecosystem level, in contrast, are largely unknown. Here we show that dissolved inorganic carbon consumption of a natural plankton community maintained in mesocosm enclosures at initial CO2 partial pressures of 350, 700 and 1,050 μatm increases with rising CO2. The community consumed up to 39% more dissolved inorganic carbon at increased CO2 partial pressures compared to present levels, whereas nutrient uptake remained the same. The stoichiometry of carbon to nitrogen drawdown increased from 6.0 at low CO2 to 8.0 at high CO2, thus exceeding the Redfield carbon:nitrogen ratio of 6.6 in today’s ocean. This excess carbon consumption was associated with higher loss of organic carbon from the upper layer of the stratified mesocosms. If applicable to the natural environment, the observed responses have implications for a variety of marine biological and biogeochemical processes, and underscore the importance of biologically driven feedbacks in the ocean to global change.

Associations of cyanobacterial toxin, nodularin, with environmental factors and zooplankton in the Baltic Sea

Concentrations of a cyanobacterial toxin, nodularin, were measured in the Baltic Sea in 1998 and 1999. Statistical associations of nodularin concentrations with environmental factors were tested by multiple regression analysis. To reveal the toxin-producing organism, colonies of Aphanizomenon and filaments of Nodularia were picked and analyzed for peptide toxins. It was also investigated whether there was an association with zooplankton and Nodularia. All the measured seston samples contained nodularin, but other toxins were not detected by the HPLC analysis. In both years, the highest nodularin concentrations were found at the surface water layer. The nodularin concentrations were positively correlated with silicate concentrations in water. High concentrations of silica in surface water may indicate recent upwelling, which in turn renders surface water rich in nutrients. This upwelling is likely to intensify cyanobacterial growth and toxin production, which may explain this rather unexpected result. The picked Aphanizomenon colonies did not contain nodularin and the dissolved nodularin concentrations were below detection limit. Thus it was concluded that most of the nodularin was bound to Nodularia cells. The abundances of zooplankton (copepods, rotifers, and cladocerans) were unrelated to Nodularia, but were positively associated with Aphanizomenon.

Unexpected consequences of increasing CO2 and ocean acidity on marine production of DMS and CH2ClI: potential climate impacts

Increasing atmospheric mixing ratios of CO2 have already lowered surface ocean pH by 0.1 units compared to preindustrial values and pH is expected to decrease an additional 0.3 units by the end of this century. Pronounced physiological changes in some phytoplankton have been observed during previous CO2 perturbation experiments. Marine microorganisms are known to consume and produce climate-relevant organic gases. Concentrations of (CH3)2S (DMS) and CH2ClI were quantified during the Third Pelagic Ecosystem CO2 Enrichment Study. Positive feedbacks were observed between control mesocosms and those simulating future CO2. Dimethyl sulfide was 26% (±10%) greater than the controls in the 2x ambient CO2 treatments, and 18% (±10%) higher in the 3xCO2 mesocosms. For CH2ClI the 2xCO2 treatments were 46% (±4%) greater than the controls and the 3xCO2 mesocosms were 131% (±11%) higher. These processes may help contribute to the homeostasis of the planet.

Rhodolith beds (Corallinales, Rhodophyta) and their physical and biological environment at 80°31′N in Nordkappbukta (Nordaustlandet, Svalbard Archipelago, Norway)

Teichert S., Woelkerling W., Rüggeberg A., Wisshak M., Piepenburg D., Meyerhöfer M., Form A., Büdenbender J. and Freiwald A. 2012. Rhodolith beds (Corallinales, Rhodophyta) and their physical and biological environment at 80°31′N in Nordkappbukta (Nordaustlandet, Svalbard Archipelago, Norway). Phycologia 51: 371–390. DOI: 10.2216/11-76.1 Polar coralline red algae (Corallinales, Rhodophyta) that form rhodoliths have received little attention concerning their potential as ecosystem engineers and carbonate factories; although, recent findings revealed that they are much more widespread in polar waters than previously thought. The present study deals with the northernmost rhodolith communities currently known, discovered in 2006 at 80°31′N in Nordkappbukta (North Cape Bay) at Nordaustlandet, Svalbard. These perennial coralline algae must be adapted to extreme seasonality in terms of light regime (c. 4 months winter darkness), sea ice coverage, nutrient supply, turbidity of the water column, temperature and salinity. The rhodolith communities and their environment were investigated using multibeam swath bathymetry, CTD measurements, recordings of the photosynthetic active radiation (PAR) and determination of the water chemistry, seabed imaging and targeted sampling by means of the manned submersible JAGO as well as benthic collections with a dredge. The coralline flora was composed mainly of Lithothamnion glaciale, with a lesser amount of Phymatolithon tenue. Based on their distribution and development at different depth levels, a facies model was developed. Rhodoliths occurred between 30 and 51 m, while coralline algae attached to cobbles were present as deep as 78 m. Measurements of the PAR indicated their adaptation to extreme low light levels. Ambient waters were always saturated with reference to calcite and aragonite for the whole area. The rhodolith-associated macrobenthic fauna samples yielded 59 species, only one of which was typically Arctic, and the concomitant appearance of corallines and grazers kept the corallines free from epiphytes and coequally provided feeding grounds for the grazers. Overall, L. glaciale and P. tenue appeared to be well adapted to the extreme environment of the Arctic.

Phytoplankton blooms at increasing levels of atmospheric carbon dioxide: experimental evidence for negative effects on prymnesiophytes and positive on small picoeukaryotes

Anthropogenic emissions of carbon dioxide (CO2) and the ongoing accumulation in the surface ocean together with concomitantly decreasing pH and calcium carbonate saturation states have the potential to impact phytoplankton community composition and therefore biogeochemical element cycling on a global scale. Here we report on a recent mesocosm CO2 perturbation study (Raunefjorden, Norway), with a focus on organic matter and phytoplankton dynamics. Cell numbers of three phytoplankton groups were particularly affected by increasing levels of seawater CO2 throughout the entire experiment, with the cyanobacterium Synechococcus and picoeukaryotes (prasinophytes) profiting, and the coccolithophore Emiliania huxleyi (prymnesiophyte) being negatively impacted. Combining these results with other phytoplankton community CO2 experiments into a data-set of global coverage suggests that, whenever CO2 effects are found, prymnesiophyte (especially coccolithophore) abundances are negatively affected, while the opposite holds true for small picoeukaryotes belonging to the class of prasinophytes, or the division of chlorophytes in general. Future reductions in calcium carbonate-producing coccolithophores, providing ballast which accelerates the sinking of particulate organic matter, together with increases in picoeukaryotes, an important component of the microbial loop in the euphotic zone, have the potential to impact marine export production, with feedbacks to Earths climate system.