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An ocean iodine cycling model is presented, which predicts upper ocean iodine speciation. The model comprises a three‐layer advective and diffusive ocean circulation model of the upper ocean and an iodine cycling model embedded within this circulation. The two primary reservoirs of iodine are represented, iodide and iodate. Iodate is reduced to iodide in the mixed layer in association with primary production, linked by an iodine to carbon (I:C) ratio. A satisfactory model fit with observations cannot be obtained with a globally constant I:C ratio, and the best fit is obtained when the I:C ratio is dependent on sea surface temperature, increasing at low temperatures. Comparisons with observed iodide distributions show that the best model fit is obtained when oxidation of iodide back to iodate is associated with mixed layer nitrification. Sensitivity tests, where model parameters and processes are perturbed, reveal that primary productivity, mixed layer depth, oxidation, advection, surface freshwater flux, and the I:C ratio all have a role in determining surface iodide concentrations, and the timescale of iodide in the mixed layer is sufficiently long for nonlocal processes to be important. Comparisons of the modeled iodide surface field with parameterizations by other authors show good agreement in regions where observations exist but significant differences in regions without observations. This raises the question of whether the existing parameterizations are capturing the full range of processes involved in determining surface iodide and shows the urgent need for observations in regions where there are currently none. Plain Language Summary: Iodine in the ocean is important because small emissions of iodine species to the atmosphere have a significant impact on ozone and air quality. Iodine is converted between two chemical forms by phytoplankton and bacteria, but only one chemical form (iodide) results in atmospheric emissions. We have developed a model that predicts the amount of each type of iodine in the global oceans. We find that this distribution has a more complex structure than that suggested by the limited number of observations, with the ocean circulation playing an important role. The model improves our understanding of both ocean iodine cycling and the resultant impacts on ozone distribution and air quality and also shows that biological and chemical changes to the oceans due to increased atmospheric greenhouse gas concentrations are likely to result in significant changes in ocean iodine, with implications for atmospheric air quality and global elemental cycles. Key Points: We develop a model for iodine speciation and cycling in the oceanThe predicted surface iodide distribution has a zonal structure not readily discernable by the limited observations to dateOcean circulation is found to have an important role in determining the spatial distribution of iodide [ABSTRACT FROM AUTHOR]

To mark the publication of the special collection in honor of Robert (Bob) A. Duce in the Journal of the Atmospheric Sciences, we have summarized his most important contributions to the subject of biogeochemical coupling between the atmosphere and ocean. Here we have divided these contributions into four themes--deposition from the atmosphere and its effects on the oceans, volatile elements emitted from the oceans, sea surface biology and aerosol formation, and marine aerosols and clouds. It is our intent that this summary along with the papers in this special collection provide an overview of the enormous contributions that Bob Duce has made to the subject during his distinguished scientific career. [ABSTRACT FROM AUTHOR]

Recent studies have highlighted the impact of sea surface iodide concentrations on the deposition of ozone to the sea surface and the sea to air flux of reactive iodine. The use of models to predict this flux demands accurate, spatially distributed sea surface iodide concentrations, but to date, the observational data required to support this is sparse and mostly arises from independent studies conducted on small geographical and temporal scales. We have compiled the available measurements of sea surface iodide to produce a data set spanning latitudes from 69°Sto 66°N, which reveals a coherent, large scale distribution pattern, with highest concentrations observed in tropical waters. Relationships between iodide concentration and more readily available parameters (chlorophyll, nitrate, sea surface temperature, salinity, mixed layer depth) are evaluated as tools to predict iodide concentration. Of the variables tested, sea surface temperature is the strongest predictor of iodide concentration. Nitrate was also strongly inversely associated with iodide concentration, but chlorophyll-a was not. [ABSTRACT FROM AUTHOR]

Dissolved iron (dFe) distributions and atmospheric and vertical subduction fluxes of dFe were determined in the upper water column for two meridional transects of the Atlantic Ocean. The data demonstrate the disparity between the iron biogeochemistry of the North and South Atlantic Ocean and show well-defined gradients of size fractionated iron species in surface waters between geographic provinces. The highest dFe and lowest mixed layer residence times (0.4-2.5 years) were found in the northern tropical and subtropical regions. In contrast, the South Atlantic Gyre had lower dFe concentrations (<0.4 n M) and much longer residence times (>5 years), presumably due to lower atmospheric inputs and more efficient biological recycling of iron in this region. Vertical input fluxes of dFe to surface waters ranged from 20 to 170 nmol m-2 d-1 in the North Atlantic and tropical provinces, whereas average fluxes of 6-13 nmol m-2 d-1 were estimated for the South Atlantic. Our estimates showed that the variable dFe distribution over the surface Atlantic (<0.1-2.0 n M) predominantly reflected atmospheric Fe deposition fluxes (>50% of total vertical Fe flux to surface waters) rather than upwelling or vertical mixing. This demonstrates the strength of the connection between land-derived atmospheric Fe fluxes and the biological cycling of carbon and nitrogen in the Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric concentrations of trace metals over the oceans are investigated through analysis of aerosol samples collected during cruises from the UK to the Falkland Islands and from South Africa to Australia. The readily soluble concentrations of Cu (4–256pmolm−3), Ni (0.1–54pmolm−3), Ba (0.2–60pmolm−3), Zn (6–316pmolm−3), Cd (0.01–0.29pmolm−3) and Pb (0.4–22pmolm−3) were measured in the aerosols, along with total concentrations of crustal elements (Fe, Al and Mn) to evaluate the crustal contributions. Air mass back trajectories suggested most of the aerosol samples had spent several days over the ocean prior to collection. The highest metal concentrations were observed in aerosols close to South Africa, Australia and major cities in South America, although these concentrations were lower than had been reported previously in the literature. Apart from Ba, which had a major crustal source, the trace metals were enriched relative to crustal sources in most samples, including some collected thousands of kilometers from emission sources. The mean trace metal concentrations in the remote Indian Ocean were lower than those measured in the Atlantic Ocean. Even lower concentrations are reported in the literature for the remote Pacific Ocean. In contrast to previous studies, no clear north–south gradient is observed in the concentrations of the trace metals in the aerosols. Lead isotope measurements were also carried out on aerosol samples using a multicollector inductively coupled plasma mass spectrometer to assist in source apportionment. Clear differences were noted in the isotope ratios collected on either side of the Indian Ocean with Australian lead ore dominating over much of the eastern and mid-southern Indian Ocean. Samples collected over the western Indian Ocean and Atlantic Ocean under South African influence had lead isotopes quite different from those seen in South African cities in the past, and are closer in ratio to the coal signature of the region. [Copyright &y& Elsevier]

Abstract: The aims of the Atlantic Meridional Transect (AMT) programme [www.amt-uk.org] are to quantify the nature and causes of ecological and biogeochemical variability in the planktonic ecosystems of the Atlantic Ocean, and to assess the effects of this variability on biological carbon cycling and air–sea exchange of radiatively active gases and aerosols. Marine and atmospheric data have been collected twice a year along a 13,500km transect in the Atlantic Ocean between 50°N and 52°S since 1995. The cruise track enables biogeochemical measurements to be made within the poorly studied North and South Atlantic oligotrophic gyres as well as within equatorial and coastal upwelling regions. The range of ecosystems sampled during AMT has facilitated the calibration and validation of newly developed optical, microbiological, molecular and analytical techniques and provided a testbed for comparative ecology and the development of atmospheric and oceanographic models. This paper describes the rationale and methodology of the programme. Upper-ocean measurements of density, nitrate and chlorophyll a (Chl a) are presented to illustrate seasonal, inter-annual and decadal variability in hydrography. Seasonal distributions of dissolved nitrous oxide (N2O) and methane (CH4) are used to derive estimates of the sea–air flux of these gases in the South Atlantic Gyre. Observations made during AMT and published since 2000 are reviewed, and the key findings are highlighted. The extent to which the programme aims have been achieved is discussed and improvements for the future suggested. [Copyright &y& Elsevier]