The production of volatile iodocarbons by biogenic marine aggregates

Hughes, Claire; Malin, Gillian; Turley, Carol; Keely, Brendan J.

doi:10.4319/lo.2008.53.2.0867

Cited by 55 publications

(36 citation statements)

References 23 publications

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“…The average C 2 H 5 I concentration (0.14 pmol l -1 ) was within the range of previously reported values (0.10-0.27 pmol l -1 ) in the Atlantic section of the Southern Ocean (50-60°S) during the austral summer (Abrahamsson et al, 2004). Hughes et al (2008) have reported that biogenic marine aggregates collected in the subarctic Atlantic water, including plankton concentrate, diatom mucilage, and phytodetritus, produce C 2 H 5 I at a high rate (0.31 pmol l -1 h -1 ). The high biological productivity in subpolar water containing high levels of biogenic aggregates would lead to a high rate of C 2 H 5 I production in seawater.…”

Section: Distributions Of C 2 H 5 I Concentration and Sea-to-air Fluxsupporting

confidence: 88%

Determination of Henry^|^rsquo;s law constant of halocarbons in seawater and analysis of sea-to-air flux of iodoethane (C2H5I) in the Indian and Southern oceans based on partial pressure measurements

Ooki

Yokouchi

2011

Geochem. J.

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The sea-to-air flux of a VOC can be calculated from the following equation:where V is the gas transfer velocity (cm s -1 ), which depends on wind speed; pVOC water and pVOC air are the partial pressures of the VOC in water and air, respectively; and K H is the Henry's law constant for the VOC. The gas transfer velocity can be calculated from the Wanninkhof (1992) formulation as followswhere u is the wind speed and Sc is the Schmidt number.The K H values for chlorofluorocarbons CFC-11 and CFC-12 (which are used as tracers to track the history of deep seawater previously exposed to the atmosphere) as functions of seawater temperature and salinity have been reported by several investigators (Hunter-Smith et al., 1983;Warner and Weiss, 1985;Wisegarver and Cline, 1985), and values for some halocarbons (e.g., CH 3 I, CH 2 Br 2 , and CH 2 ClI) in seawater have also been reported (HunterSmith et al., 1983;Elliott and Rowland, 1993;Gossett, 1987;Moore et al., 1995;Moore, 2000 The sea-to-air flux of C 2 H 5 I (iodoethane) in the Indian Ocean and the Southern Ocean was estimated from the Henry's law constant (K H ) and the measured partial pressures of C 2 H 5 I in surface seawater and air. The values of K H , defined as the ratio of molar concentration (mol l -1 ) to partial pressure (atm), for ten volatile organic compounds (VOCs) (CFCl 3 (CFC-11), C 5 H 8 (isoprene), C 2 H 2 F 4 (HFC-134a), CHF 2 Cl (HCFC-22), CH 3 I, CH 2 Br 2 , C 2 H 5 I, CH 2 Cl 2 , CH 2 ClI, and CHBr 3 ) were measured with an equilibrator and a purge-and-trap system in combination with gas chromatography-mass spectrometry. Ours is the first report of the K H values for C 2 H 5 I and C 5 H 8 as functions of temperature. The K H values for the other VOCs were in good agreement with previously reported values. We calculated the sea-to-air flux of C 2 H 5 I using the newly determined K H . Large sea-to-air fluxes (average, 0.04 nmol m -2 h -1 ) were widespread in the Southern Ocean. We suggest that high biological productivity led to a high rate of C 2 H 5 I production in the subpolar water, and that the strong winds that frequently blow over the Southern Ocean resulted in the large sea-to-air flux.

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Section: Distributions Of C 2 H 5 I Concentration and Sea-to-air Fluxsupporting

confidence: 88%

Determination of Henry^|^rsquo;s law constant of halocarbons in seawater and analysis of sea-to-air flux of iodoethane (C2H5I) in the Indian and Southern oceans based on partial pressure measurements

Ooki

Yokouchi

2011

Geochem. J.

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“…Figure 6 shows halocarbon profiles through the full depth of the water column at the ice station. Profiles of C 2 H 5 I, and C 3 H 7 I show a strong peak at 10 m, just above the mixed layer depth at 12 m. Previous measurements [Hughes et al 2008] have shown these halocarbons can be produced in marine aggregates which are likely to collect here, as they sink from the upper photic zone due to gravity, but are prevented from sinking further due to the pycnocline barrier. CH 2 Br 2 is the only halocarbon which shows a similar profile to Chl a.…”

Section: Halocarbons In Seawatermentioning

confidence: 77%

“…A 9 cm diameter SIPRE corer (Mark II coring system from Kovacs Enterprises 4 nitrogen is difficult to organise (Hughes et al 2008, Hughes et al 2009). Trapping efficiencies were measured and applied to the data.…”

Section: Sample Collection -Sea Ice Brine From Coresmentioning

confidence: 99%

Halocarbons associated with Arctic sea ice

Atkinson¹,

Hughes²,

Shaw³

et al. 2014

Deep Sea Research Part I: Oceanographic Research Papers

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Halocarbons associated with Arctic sea ice, Deep-Sea Research I, http://dx.doi.org/10. 1016/j.dsr.2014.05.012 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Abstract Short-lived halocarbons were measured in Arctic sea-ice brine, seawater and air above the Greenland and Norwegian seas (∼81°N, 2 to 5°E) in mid-summer, from a melting ice floe at the edge of the ice pack. In the ice floe, concentrations of C 2 H 5 I, 2-C 3 H 7 I and CH 2 Br 2 showed significant enhancement in the sea ice brine, of average factors of 1.7, 1.4 and 2.5 times respectively, compared to the water underneath and after normalising to brine volume. Concentrations of mono-iodocarbons in air are the highest ever reported, and our calculations suggest increased fluxes of halocarbons to the atmosphere may result from their sea-ice enhancement. Some halocarbons were also measured in ice of the sub-Arctic in Hudson Bay (∼55°N, 77°W) in early spring, ice that was thicker, colder and less porous than the Arctic ice in summer, and in which the halocarbons were concentrated to values over 10 times larger than in the Arctic ice when normalised to brine volume. Concentrations in the Arctic ice were similar to those in Antarctic sea ice that was similarly warm and porous. As climate warms and Arctic sea ice becomes more like that of the Antarctic, our results lead us to expect the production of iodocarbons and so of reactive iodine gases to increase. IntroductionThere has been much speculation about sources of reactive halogens in the polar troposphere. The presence of high concentrations of both iodine and bromine monoxide (IO and BrO) over Antarctica and its sea ice [Saiz-Lopez et al. 2007, Schoenhardt et al. 2008 suggests an iodine-selective mechanism, as the sum of iodide plus iodate is 1000 times less abundant than bromide in seawater. Although IO has been measured above sub-Arctic sea ice at amounts of up to 4 pptv [Mahajan et al. 2010], this is less than a quarter the Antarctic concentrations.

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“…These results suggest that halocarbons, such as CH 3 Cl, CH 3 Br, CH 2 ClI, and CH 2 I 2 , were probably not produced by the diatom-dominated bloom at this site and production of these compounds could be affected by species of pico-sized phytoplankton and/or the composition of the assemblage of microorganisms. Hughes et al (2008) reported that volatile iodocarbons were produced from biogenic marine aggregates. Marine aggregates exhibit diversity in organic matter content and microbial composition between different geographic locations and depths in the water column, and this variability could affect the iodocarbon production rate (Hughes et al 2008).…”

Section: (3) Size-fractionated Chlorophyll-a and Methyl Halide Concenmentioning

confidence: 99%

“…Hughes et al (2008) reported that volatile iodocarbons were produced from biogenic marine aggregates. Marine aggregates exhibit diversity in organic matter content and microbial composition between different geographic locations and depths in the water column, and this variability could affect the iodocarbon production rate (Hughes et al 2008). This result also suggests that the composition of microorganisms leads to variations in halocarbon productions.…”

Section: (3) Size-fractionated Chlorophyll-a and Methyl Halide Concenmentioning

confidence: 99%