Response of halocarbons to ocean acidification in the Arctic

Abstract

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 <i>p</i>CO₂ treatments from ~ 185 μatm to ~ 1420 μatm. In general, the response of halocarbons to <i>p</i>CO₂ was subtle, or undetectable. A large number of significant correlations with a range of biological parameters (chlorophyll <i>a</i>, 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 <i>p</i>CO₂ effect on various components of the plankton community, and a strong association between CH₃I and biological parameters, no effect of <i>p</i>CO₂ 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 <i>p</i>CO₂. There was no clear effect of <i>p</i>CO₂ 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

Effect of ocean acidification and elevated &lt;i&gt;f&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; on trace gas production by a Baltic Sea summer phytoplankton community

“…Elevated f CO 2 did not affect the concentration of iodocarbons in the mesocosms significantly at any time during the experiment, which is in agreement with the findings of Hopkins et al (2013) in the Arctic but in contrast to Hopkins et al (2010) and Webb (2015), where iodocarbons were measured to be significantly lower under elevated f CO 2 (Table 4). Concentrations of all iodocarbons measured in the mesocosms and the Baltic Sea fall within the range of those measured previously in the region (Table 5).…”

“…No effect of elevated f CO 2 was identified for any of the three bromocarbons, which compared well with the findings from previous mesocosms where bromocarbons were studied www.biogeosciences.net/13/4595/2016/ Biogeosciences, 13, 4595-4613, 2016 (Hopkins et al, 2010(Hopkins et al, , 2013Webb, 2015; Table 4). Measured concentrations were comparable to those of Orlikowska and Schulz-Bull (2009) and Karlsson et al (2008) measured in the southern part of the Baltic Sea (Table 3).…”

“…This production can lead to significant annual flux to the marine boundary layer in the order of 10 Tg iodine-containing compounds ("iodocarbons";O'Dowd et al, 2002) and 1 Tg bromine-containing compounds ("bromocarbons"; Goodwin et al, 1997) into the atmosphere. The effect of acidification on halocarbon concentrations has received limited attention, but two acidification experiments measured lower concentrations of several iodocarbons, while bromocarbons were unaffected by f CO 2 up to 3000 µatm (Hopkins et al, 2010;Webb, 2015), whereas an additional mesocosm study did not elicit significant differences from any compound up to 1400 µatm f CO 2 (Hopkins et al, 2013).…”

Preface &quot;Arctic ocean acidification: pelagic ecosystem and biogeochemical responses during a mesocosm study&quot;

“…The response of halocarbons to pCO 2 was subtle or undetectable: despite strong significant correlations with biological parameters, iodomethane (CH 3 I) dynamics were unaffected by pCO 2 . In contrast, a significant positive response to pCO 2 was obtained for diiodomethane (CH 2 I 2 ) with respect to concentration, the rate of net production and the sea-to-air flux; there was no clear effect of pCO 2 on bromocarbon concentrations or dynamics (Hopkins et al, 2013).…”

Halocarbon emissions and sources in the equatorial Atlantic Cold Tongue

“…Although CH 2 I 2 is generally assumed to be of biogenic origin in the open ocean (Moore and Tokarczyk, 1993;Yamamoto et al, 2001;Orlikowska and Schulz-Bull, 2009;Hopkins et al, 2013), great uncertainties remain as to which species are involved in its production. During MSM18/3, indications were found for different source species than of the other three compounds (chlorophytes and Prochlorococcus HL).…”