Journal
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
Volume 119, Issue 3, Pages 1609-1620Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2013JC009328
Keywords
methyl iodide; seasonal variability; time series analysis; mass balance
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Funding
- Surface Ocean Processes in the Anthropocene (SOPRAN) project
- Canada Excellence Research Chair in Ocean Science and Technology at Dalhousie University
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From October 2008 to November 2010, CH3I concentrations were measured in the Kiel Fjord together with potentially related biogeochemical and physical parameters. A repeating seasonal cycle of CH3I was observed with highest concentrations in summer (ca. 8.3 pmol L-1; June and July) and lowest concentrations in winter (ca. 1.5 pmol L-1; December to February). A strong positive correlation at zero lag between [CH3I] and solar radiation (R-2=0.93) was observed, whereas correlations with other variables (SST, Chlorophyll a) were weaker, and they lagged CH3I by ca. 1 month. These results appear consistent with the hypothesis that SSR is the primary forcing of CH3I production in surface seawater, possibly through a photochemical pathway. A mass balance of the monthly averaged data was used to infer mean rates of daily net production (P-net) and losses for CH3I over the year. The sea-to-air flux of CH3I in the Kiel Fjord averaged 3.1 nmol m(-2) d(-1), the mean chemical loss rate was 0.047 pmol L-1 d(-1), and P-net varied systematically from winter to summer (from 0 to 0.6 pmol L-1 d(-1)). P-net was correlated at zero lag with SST, SSR, and Chla (R-2=0.55, 0.67, and 0.73, respectively, p << 0.01). The lagged cross-correlation analysis indicated that SSR led P-net by 1 month, whereas the strongest cross correlations with Chla were at lags of 0 to +1 month, and SST lagged P-net by 1 month. The broad seasonal peak of P-net makes it difficult to determine the key factor controlling CH3I net production using in situ concentration data alone.
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