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

Abstract

Ocean acidification and carbonation, driven by anthropogenic emissions of carbon dioxide (CO<sub>2</sub>), have been shown to affect a variety of marine organisms and are likely to change ecosystem functioning. High latitudes, especially the Arctic, will be the first to encounter profound changes in carbonate chemistry speciation at a large scale, namely the under-saturation of surface waters with respect to aragonite, a calcium carbonate polymorph produced by several organisms in this region. During a CO<sub>2</sub> perturbation study in Kongsfjorden on the west coast of Spitsbergen (Norway), in the framework of the EU-funded project EPOCA, the temporal dynamics of a plankton bloom was followed in nine mesocosms, manipulated for CO<sub>2</sub> levels ranging initially from about 185 to 1420 μatm. Dissolved inorganic nutrients were added halfway through the experiment. Autotrophic biomass, as identified by chlorophyll <i>a</i> standing stocks (Chl <i>a</i>), peaked three times in all mesocosms. However, while absolute Chl <i>a</i> concentrations were similar in all mesocosms during the first phase of the experiment, higher autotrophic biomass was measured as high in comparison to low CO<sub>2</sub> during the second phase, right after dissolved inorganic nutrient addition. This trend then reversed in the third phase. There were several statistically significant CO<sub>2</sub> effects on a variety of parameters measured in certain phases, such as nutrient utilization, standing stocks of particulate organic matter, and phytoplankton species composition. Interestingly, CO<sub>2</sub> effects developed slowly but steadily, becoming more and more statistically significant with time. The observed CO<sub>2</sub>-related shifts in nutrient flow into different phytoplankton groups (mainly dinoflagellates, prasinophytes and haptophytes) could have consequences for future organic matter flow to higher trophic levels and export production, with consequences for ecosystem productivity and atmospheric CO<sub>2</sub>

Marine CDOM accumulation during a coastal Arctic mesocosm experiment: No response to elevated pCO2 levels

“…A detailed description of the experimental setup and sampling procedures is given in Riebesell et al [2013b], Schulz et al [2013], and Czerny et al [2013a]. Briefly, the KOSMOS are enclosures (17 m long and 2 m wide) that are attached to hard floating frames and made of 0.5-1 mm thick thermoplastic polyurethane, which absorbs almost 100% of the incoming UV radiation, while it is transparent to PAR [Riebesell et al, 2013b;Schulz et al, 2013].…”

“…Salinity and temperature data were derived from a CTD60M probe (Sea and Sun Technology) (details in Schulz et al [2013]). Concentrations of chlorophyll a and pigment analyses were done by high-performance liquid chromatography (WATERS HPLC with a Varian Microsorb-MV 100-3 C8 column) according to Barlow et al [1997].…”

“…In the fjord, chl a was more variable without any distinct pattern of variability. For more details on phytoplankton biomass development, see Schulz et al [2013].…”

Ocean Acidification-Induced Restructuring of the Plankton Food Web Can Influence the Degradation of Sinking Particles

“…While these studies helped in developing a principal understanding of how OA affects the physiology of single species, we are still largely lacking the understanding of how OA effects may manifest on the community level (Riebesell and Gattuso, 2015). Existing "whole community" studies show that both direct effects of OA on single species and indirect effects through changes in plankton community structure (Hall-Spencer et al, 2008;Fabricius et al, 2011;Schulz et al, 2013;Paul et al, 2015;Bach et al, 2016;Gazeau et al, 2016) can significantly influence biogeochemical cycles in the ocean.…”

The Arctic picoeukaryote <i>Micromonas</i> pusilla benefits synergistically from warming and ocean acidification

“…Such positive response to OA could indicate that picoeukaryotes such as M. pusilla 337 are mainly dependent on diffusive CO 2 supply and thus directly benefit from higher CO 2 338 concentrations Schulz et al, 2013;Schulz et al, 2017). 339…”