The working standard was calibrated after the end of the experiment, in the laboratory, relative to a commercial multi-component gas standard supplied by Apel-Riemer Environmental Inc. The most abundant marine organic compound identified in the mesocosm enclosures was DMS at concentrations
ranging from 0.3 to 6 nM. Isoprene was the second most abundant tracer (0.02 to 0.42 nM), followed by (−) α-pinene (0.0041 to 0.063 nM) and (+) α-pinene (0.002 to 0.055 nM). In Fig. 6, we present our findings for DMS and isoprene over a period of 29 days. Each line shows the mean value of a pCO2 group (low, middle and high pCO2) and the error bars display the standard deviation Bortezomib research buy of each group. For DMS ( Fig. 6(A)), generally the same trend was observed for all three pCO2 groups over the course of the experiment. One small concentration increase appeared on day 3 followed by a bigger increase which started around day 15 and continued until the end of the experiment. From day 8 onward, a clear consistent concentration difference was observed between the three CO2 treatments. Significantly
higher DMS concentrations were observed in the low pCO2 mesocosms, while higher pCO2 concentrations led to smaller DMS production. This study suggests that a higher CO2 world would result in lower DMS emissions. Previous mesocosm studies in 2004 and 2006 (Avgoustidi et al., 2012 and Hopkins et al., 2010) have shown the same CO2 effect on DMS emissions. One exception to Sirolimus solubility dmso this apparent consensus was a mesocosm study in 2005 which reported no significant differences between treatments (Vogt et al., 2008a) or even small increase of DMS production (Wingenter et al., 2007). The different responses of DMS to elevated CO2 could have been a function
of different phytoplankton compositions and abundances as well as different physical and biological processes (Avgoustidi et al., 2012, Hopkins et al., 2010, Vogt et al., 2008a and Wingenter et al., 2007). For isoprene (Fig. 6(B)), the situation was different. Differences in the concentration levels were apparent between the three CO2 treatments although low CO2 levels and high isoprene emissions did not correspond as clearly as in the case of DMS. At the beginning and end ID-8 of the experiment, all CO2 treatments provided similar isoprene concentrations. Between days 1–4 and 8–15, the middle CO2 treatment showed higher isoprene emissions. A possible explanation could be the uneven distribution of phytoplankton families mainly responsible for isoprene production in these mesocosms. A more detailed investigation on the effect of elevated CO2 on DMS, isoprene, (+) α-pinene and (−) α-pinene based on correlations with the available biological datasets will be reported in a following publication.
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