2 research outputs found

    Links Between Oceanic Ozone Uptake and Ocean Biology

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    Dry deposition is a major sink of tropospheric ozone. Organic matter at the sea surface, which is primarily produced by marine biota such as phytoplankton, likely plays a key role in oceanic ozone deposition. This study investigates the fatty acid component of organic matter in the sea surface microlayer (SML) and underlying seawater (ULW). A solid phase extraction (SPE) method was used to extract fatty acids from SML, ULW and phytoplankton culture extracts. Overall, 150 SML and ULW samples collected off the southwestern UK coast over 18 months, and during a trans-Atlantic cruise were analysed using this method. Median total, saturated and unsaturated SML concentrations were 29.56, 11.22 and 5.56 µg L-1 respectively for the coastal samples and 15.69, 12.76 and 0.73 µg L-1 respectively for the open ocean. The measured fatty acids contributed between 0.002% - 8% of the total dissolved organic carbon. The fatty acids observed were predominantly of even carbon numbers, suggesting a phytoplankton source, with their carbon number distributions being comparable to the Phaeodactylum tricornutum and Synechococcus culture extracts and to intracellular phytoplankton fatty acid distributions reported in the literature. These results highlight the link between marine biota and seawater fatty acids and provide a better understanding of the biological and chemical drivers of marine ozone dry deposition

    Iodide, iodate & dissolved organic iodine in the temperate coastal ocean

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    The surface ocean is the main source of iodine to the atmosphere, where it plays a crucial role including in the catalytic removal of tropospheric ozone. The availability of surface oceanic iodine is governed by its biogeochemical cycling, the controls of which are poorly constrained. Here we show a near two-year time series of the primary iodine species, iodide, iodate and dissolved organic iodine (DOI) in inner shelf marine surface waters of the Western English Channel (UK). The median ± standard deviation concentrations between November 2019 and September 2021 (n=76) were: iodide 88 ± 17 nM (range 61-149 nM), iodate 293 ± 28 nM (198-382 nM), DOI 16 ± 16 nM (<0.12-75 nM) and total dissolved iodine (dIT) 399 ± 30 nM (314-477 nM). Though lower than inorganic iodine ion concentrations, DOI was a persistent and non-negligible component of dIT, which is consistent with previous studies in coastal waters. Over the time series, dIT was not conserved and the missing pool of iodine accounted for ~6% of the observed concentration suggesting complex mechanisms governing dIT removal and renewal. The contribution of excess iodine (I*) sourced from the coastal margin towards dIT was generally low (3 ± 29 nM) but exceptional events influenced dIT concentrations by up to ±100 nM. The seasonal variability in iodine speciation was asynchronous with the observed phytoplankton primary productivity. Nevertheless, iodate reduction began as light levels and then biomass increased in spring and iodide attained its peak concentration in mid to late autumn during post-bloom conditions. Dissolved organic iodine was present, but variable, throughout the year. During winter, iodate concentrations increased due to the advection of North Atlantic surface waters. The timing of changes in iodine speciation and the magnitude of I* subsumed by seawater processes supports the paradigm that transformations between iodine species are biologically mediated, though not directly linked
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