Ocean acidification and marine trace gas emissions

Abstract

The oceanic uptake of man-made CO 2 emissions is resulting in a measureable decrease in the pH of the surface oceans, a process which is predicted to have severe consequences for marine biological and biogeochemical processes [Caldeira K, Wickett ME (2003) Nature 425:365; The Royal Society (2005) Policy Document 12 /05 (Royal Society, London)]. Here, we describe results showing how a doubling of current atmospheric CO 2 affects the production of a suite of atmospherically important marine trace gases. Two CO 2 treatments were used during a mesocosm CO 2 perturbation experiment in a Norwegian fjord (present day: ∼380 ppmv and year 2100: ∼750 ppmv), and phytoplankton blooms were stimulated by the addition of nutrients. Seawater trace gas concentrations were monitored over the growth and decline of the blooms, revealing that concentrations of methyl iodide and dimethylsulfide were significantly reduced under high CO 2. Additionally, large reductions in concentrations of other iodocarbons were observed. The response of bromocarbons to high CO 2 was less clear cut. Further research is now required to understand how ocean acidification might impact on global marine trace gas fluxes and how these impacts might feed through to changes in the earth's future climate and atmospheric chemistry.dimethylsulfide | halocarbons | atmospheric chemistry | climate

Rapid shifts in picoeukaryote community structure in response to ocean acidification

“…The phytoplankton populations in both treatments were dominated numerically by picoeukaryotes, whereas cryptophytes, prymnesiophytes (including coccolithophores) and other flagellates of uncertain taxonomic affiliations made the greatest contributions to phytoplankton biomass (Hopkins et al, 2010). Although not identified taxonomically, two size classes of picoeukaryotes ('small' and 'large') were present.…”

“…Biological sampling was initiated the next day (day 0), following the addition of nutrients to stimulate phytoplankton growth to final concentrations of 17 mmol l À1 NO 3 À and 1.0 mmol l À1 PO 4 2À (Hopkins et al, 2010). Throughout the experiment, the enclosure covers were only removed for sampling and the headspaces were flushed with air (ambient conditions) or CO 2 -enriched air (750 ppmV, acidified treatment) to help maintain pH.…”

“…Full details of the setup and management of the mesocosms during this experiment are provided by Hopkins et al (2010). Briefly, six clear polyethylene enclosures (2 m diameter, 3.5 m deep) located 200 m offshore were filled with unfiltered seawater (B11 m 3 ; 31.4 psu), pumped from a depth of 1 m below the pontoon supporting the enclosures.…”

“…The mesocosms were covered with high UV-transmitting horticultural polyethylene (photosynthetically active radiation transmission 92%) and three of the enclosures (1-3) were bubbled gently with air enriched to 750 ppmV CO 2(g) for two days, until the pH of the seawater within the enclosures had declined to B7.8 (range 7.81-7.82). The remaining three mesocosms (4-6) were bubbled with air for the same period (to control for any effects of bubbling) and pH values at the beginning of biological sampling were within the range 8.14-8.15 (Hopkins et al, 2010).…”

Will ocean acidification affect marine microbes?

“…Hopkins et al (2010) found decreased production of dimethylsulphide and volatile iodocarbon compounds under high pCO 2 conditions.…”