Contrasting responses of DMS and DMSP to ocean acidification in Arctic waters

Abstract

Abstract. Increasing atmospheric CO2 is decreasing ocean pH most rapidly in colder regions such as the Arctic. As a component of the EPOCA (European Project on Ocean Acidification) pelagic mesocosm experiment off Spitzbergen in 2010, we examined the consequences of decreased pH and increased pCO2 on the concentrations of dimethylsulphide (DMS). DMS is an important reactant and contributor to aerosol formation and growth in the Arctic troposphere. In the nine mesocosms with initial pHT 8.3 to 7.5, equivalent to pCO2 of 180 to 1420 μatm, highly significant but inverse responses to acidity (hydrogen ion concentration [H+]) occurred following nutrient addition. Compared to ambient [H+], average concentrations of DMS during the mid-phase of the 30 d experiment, when the influence of altered acidity was unambiguous, were reduced by approximately 60% at the highest [H+] and by 35% at [H+] equivalent to 750 μatm pCO2, as projected for 2100. In contrast, concentrations of dimethylsulphoniopropionate (DMSP), the precursor of DMS, were elevated by approximately 50% at the highest [H+] and by 30% at [H+] corresponding to 750 μatm pCO2. Measurements of the specific rate of synthesis of DMSP by phytoplankton indicate increased production at high [H+], in parallel to rates of inorganic carbon fixation. The elevated DMSP production at high [H+] was largely a consequence of increased dinoflagellate biomass and in particular, the increased abundance of the species Heterocapsa rotundata. We discuss both phytoplankton and bacterial processes that may explain the reduced ratios of DMS:DMSPt (total dimethylsulphoniopropionate) at higher [H+]. The experimental design of eight treatment levels provides comparatively robust empirical relationships of DMS and DMSP concentration, DMSP production and dinoflagellate biomass versus [H+] in Arctic waters.

Amplification of global warming through pH dependence of DMS production simulated with a fully coupled Earth system model

“…In these mesocosm experiments, the temporal evolution of DMS concentration within a confined natural water volume is investigated under different levels of CO 2 partial pressure with corresponding seawater pH (further information on the method is given in Archer et al, 2013). As in Six et al (2013) we assume a linear decrease in DMS production (P DMS ) with decreasing pH ( Fig.…”

“…Archer et al, 2013; see also the discussion in the Supplement of Six et al, 2013, and references therein). These findings were confirmed by follow-up mesocosm studies in warmer ocean regions such as the coastal waters of Korea or in the sub-tropics off the Canaries (Park et al, 2014;S.D.…”

Impact of ocean acidification on Arctic phytoplankton blooms and dimethyl sulfide concentration under simulated ice-free and under-ice conditions

“…The majority of these experimental studies revealed a negative impact of decreasing pH on DMS production (Hopkins et al, 2010;Avgoustidi et al, 2012;Archer et al, 2013;Webb et al, 2016), but some have reported either no effect or a positive effect (Vogt et al, 2008;Hopkins and Archer, 2014). Several hypotheses have been proposed to explain these contrasting results.…”

“…Some authors attribute the pH-induced variation in DMS production to an alteration of the physiological properties of the phytoplankton cells or of the bacterial DMSP metabolism (Vogt et al, 2008;Hopkins et al, 2010, Avgoustidi et al, 2012Archer et al, 2013;Hopkins and Archer, 2014;Webb et al, 2015Webb et al, , 2016, whereas others evoke an interaction between the DMSP producers and their grazers (Kim et al, 2010;Park et al, 2014). So far, only one study has looked at the impact of OA on DMS dynamics in the Arctic (Archer et al, 2013). The results of this mesocosm study, conducted near Svalbard, show a decrease in DMS concentrations at low pH, suggesting that OA may significantly reduce DMS emissions to the atmosphere in the Arctic.…”

Primary marine aerosol emissions from the Mediterranean Sea during pre-bloom and oligotrophic conditions: correlations to seawater chlorophyll <i>a</i> from a mesocosm study

“…In the context of ocean acidification, mesocosms have been used on several occasions for experimental time periods spanning from a few days to a few weeks, and were found to be efficient in studying the effects of this driver over such short time scales (Riebesell et al, 2008. Archer et al (2013) recently showed, during a mesocosm experiment in the Arctic, that with seawater acidification and increased CO 2 concentrations, average concentrations of DMS decreased by up to 60 % at the lowest pH. Inversely, concentrations of dimethylsulfoniopropionate (DMSP), the precursor to DMS, increased by up to 50 %.…”