Search

9 pags., 3 figs., Polar stratospheric ozone has decreased since the 1970s due to anthropogenic emissions of chlorofluorocarbons and halons, resulting in the formation of an ozone hole over Antarctica. The effects of the ozone hole and the associated increase in incoming UV radiation on terrestrial and marine ecosystems are well established; however, the impact on geochemical cycles of ice photoactive elements, such as iodine, remains mostly unexplored. Here, we present the first iodine record from the inner Antarctic Plateau (Dome C) that covers approximately the last 212 years (1800-2012 CE). Our results show that the iodine concentration in ice remained constant during the pre-ozone hole period (1800-1974 CE) but has declined twofold since the onset of the ozone hole era (~1975 CE), closely tracking the total ozone evolution over Antarctica. Based on ice core observations, laboratory measurements and chemistry-climate model simulations, we propose that the iodine decrease since ~1975 is caused by enhanced iodine re-emission from snowpack due to the ozone hole-driven increase in UV radiation reaching the Antarctic Plateau. These findings suggest the potential for ice core iodine records from the inner Antarctic Plateau to be as an archive for past stratospheric ozone trends., This project received funding from the European Union’s Horizon 2020 Research and Innovation program under grant agreement no. 689443 via project iCUPE (Integrative and Comprehensive Understanding on Polar Environments), part of the European Commission (ERA-PLANET) and by the “Programma Nazionale per la Ricerca in Antartide” (PNRA, project number PNRA16_00295). This study also received funding from the European Research Council Executive Agency under the European Union’s Horizon 2020 Research and Innovation programme (Project ‘ERC-2016-COG 726349 CLIMAHAL’). NCAR is sponsored by the National Science Foundation under Grant Number 1852977. R.P.F. would like to express thanks for the financial support from CONICET-UNCuyo (SIIP-06/M111) and ANPCyT (PICT 2015-0714). This research was also supported by the Korea Polar Research Institute (KOPRI) project (PE20030) and by the Grant to Department of Science, Roma Tre University (MIUR-Italy Dipartimenti di Eccellenza)

17 pags., 4 figs., 2 tabs., Sea ice plays a pivotal role in Earth's climate and its past reconstruction is crucial to investigate the connections and feedbacks with the other components of the climate system. Among the available archives that store information of past sea ice are marine and ice cores. Recent studies on the IP biomarker extracted from marine sediments has shown great skill to infer past changes of Arctic sea ice. In ice matrixes, sodium, bromine and iodine have shown potential to store the fingerprint of sea ice presence. The development of an unambiguous sea ice proxy from ice cores, however, has proven to be a challenging task especially in the Arctic realm. In this work we analyze the sodium, bromine and iodine records in the RECAP ice core, coastal eastern Greenland, to investigate the sea ice variability in the northern North Atlantic Ocean through the last 11,000 years of the current interglacial, i.e. the Holocene. We compare the RECAP records with marine sea ice proxy records available from the northern North Atlantic. We suggest that RECAP sodium concentrations can be associated with variability of sea ice extent, while the bromine-to-sodium ratios and iodine are associated respectively with seasonal sea ice and bioproductivity from open ocean and fresh sea ice surfaces. According to our interpretation, we find that sea ice was at its lowest extent and seasonal in nature during the early Holocene in all regions of the North Atlantic. Increasing sea ice signals are seen from ca. 8–9 ka b2k, in line with long-term Holocene cooling. The increasing sea ice trend appears uninterrupted in the Fram Strait and North Iceland while reaching a maximum ca. 5 ka b2k in the East Greenland region. Sea ice modifications during the last 5000 years display great variability in East Greenland with intermediate conditions between the early and mid Holocene, possibly associated with local fjord dynamics. The last sea ice maximum was reached across all regions 1000 years b2k., The RECAP ice coring effort was financed by the Danish Research Council through a Sapere Aude grant, the NSF through the Division of Polar Programs, the Alfred Wegener Institute, and the European Research Council under the European Community's Seventh Framework Programme (FP7/2007e2013)/ERC grant agreement The RECAP ice coring effort was financed by the Danish Research Council through a Sapere Aude grant, the NSF through the Division of Polar Programs, the Alfred Wegener Institute, and the European Research Council under the European Community's Seventh Framework Programme (FP7/2007e2013)/ERC grant agreement 610055 through the Ice2Ice project. Additional funding support for the paper has been provided by the Centre for Climate Dynamics at the Bjerknes Centre. through the Ice2Ice project. Additional funding support for the paper has been provided by the Centre for Climate Dynamics at the Bjerknes Centre.

The biogeochemistry of iodine in temperate coastal ecosystems is largely mediated by macroalgae, which act as a major biological sink and source of iodine. Their capacity to accumulate, retain and release iodine has been associated with abiotic and biotic stressors, but quantitative information is limited. We evaluated the seasonal iodine retention capacity of eleven macroalgal species belonging to different systematic groups, collected from two sites in Ireland. Iodine accumulation and retention were then further quantified in Fucus vesiculosus and Laminaria digitata in relation to I- concentrations in seawater and temperature. In general, iodine contents were ~101 -102 μmol · (g dw)-1 for Laminariales, 100 -101 μmol · (g dw)-1 for Fucales, 10-1 -100 μmol · (g dw)-1 for Rhodophyta, and 10-1 μmol · (g dw)-1 for Chlorophyta. Typically, algal iodine contents were above average in winter and below average in summer. Iodine accumulation in F. vesiculosus and L. digitata depended on I- availability and followed the Michaelis-Menten kinetic. The ratio of maximum accumulation rate to half accumulation coefficient (ρmax : Kt ) was 2.4 times higher for F. vesiculosus than for L. digitata, suggesting that F. vesiculosus was more efficient in iodine accumulation. Both species exhibited a temperature-dependent net loss of iodine, and only an exposure to sufficient external I- concentrations compensated for this loss. This study revealed that both environmental (e.g., I- in seawater, temperature) and organismal (e.g., the status of the iodine storage pool) variables determine retention and variability in iodine in temperate seaweeds.

Based on the results of a pilot study in 2007, which found high mixing ratios of molecular iodine (I2) above the intertidal macroalgae (seaweed) beds at Mweenish Bay (Ireland), we extended the study to nine different locations in the vicinity of Mace Head Atmospheric Research Station on the west coast of Ireland during a field campaign in 2009. The mean values of I2 mixing ratio found above the macroalgae beds at nine different locations ranged from 104 to 393 ppt, implying a high source strength of I2. Such mixing ratios are sufficient to result in photochemically driven coastal new-particle formation events. Mixing ratios above the Ascophyllum nodosum and Fucus vesiculosus beds increased with exposure time: after 6 h exposure to ambient air the mixing ratios were one order of magnitude higher than those initially present. This contrasts with the emission characteristics of Laminaria digitata, where most I2 was emitted within the first half hour of exposure. Discrete in situ measurements (offline) of I2 emission from ambient air-exposed chamber experiments of L. digitata, A. nodosum and F. vesiculosus substantially supported the field observations. Further online and time-resolved measurements of the I2 emission from O3-exposed macroalgal experiments in a chamber confirmed the distinct I2 emission characteristics of A. nodosum and F. vesiculosus compared to those of L. digitata. The emission rates of A. nodosum and F. vesiculosus were comparable to or even higher than L. digitata after the initial exposure period of ~20–30 min. We suggest that A. nodosum and F. vesiculosus may provide an important source of photolabile iodine in the coastal boundary layer and that their impact on photochemistry and coastal new-particle formation should be reevaluated in light of their longer exposure at low tide and their widespread distribution.

Aerosol number concentrations and size distributions from 3 nm to 20 µm diameter were measured at the Mace Head Atmospheric Research Station, Co. Galway, Ireland, a coastal site on the eastern seaboard of the north Atlantic Ocean. Both on and offline size resolved aerosol composition measurements were also made using an Aerodyne Aerosol Mass Spectrometer (AMS) and ion chromatographic analysis of daily samples collected using a Micro-Orifice Uniform Deposit Impactor (MOUDI). Particle number concentrations, size distributions and AMS measurements were determined at 7 and 22 m above ground level to investigate local effects on the aerosol size distribution induced by the tidal zone. During periods of new particle formation ultrafine particle number concentrations are large and variable, however, outside these periods no variability in particle number was observed at any size, nor was the particle composition variable. Analysis of particle size distributions show that within each air mass observed particle number concentrations were very consistent. During anticyclonic periods and conditions of continental outflow Aitken and accumulation mode were enhanced by a factor of 5 compared to the marine sector, whilst coarse mode particles were enhanced during westerly conditions. Baseline marine conditions were rarely met at Mace Head during NAMBLEX and high wind speeds were observed for brief periods only. Loss rates of gaseous species to aerosol surfaces were calculated for a range of uptake coefficients. Even when the accommodation coefficient is unity, lifetimes of less than 100 s were never observed and rarely were lifetimes less than 500 s. Diffusional limitation to mass transfer is important in most conditions as the coarse mode is always significant, we calculate a minimum overestimate of 50% in the loss rate if this is neglected and so it should always be considered when calculating loss rates of gaseous species to particle surfaces. HO2 and HOI have accommodation coefficients of around 0.03 and hence we calculate lifetimes due to loss to particle surfaces of 2000 s or greater. Aerosol composition measurements using the AMS show accumulation mass modes of acidified sulphate and organic material, both of which have the same shape and are centred at around 350 nm vacuum aerodynamic diameter, implying an internal mixture. The organic and sulphate are approximately equally important, though the mass ratio varies considerably between air masses. Mass spectral fingerprints of the organic fraction in polluted conditions are similar to those observed at other locations that are characterised by aged continental aerosol. Even in marine conditions a background concentration of between 0.5 and 1 µg m−3 of both organic and sulphate was observed. Key differences in the mass spectra were observed during the few clean periods but were insufficient to ascertain whether these changes reflect differences in the source fingerprint of the organic aerosol. However, in an accompanying paper (Dall'Osto et al., 2005) periods of organic dominated aerosol particles were also observed and could be separated from the aged continental aerosol. The coarse mode was composed of sea salt and showed significant displacement of chloride by nitrate and to a lesser extent sulphate in polluted conditions.

Accurately accounting for new particle formation (NPF) is crucial to our ability to predict aerosol number concentrations and thus cloud properties, which is in turn vital in simulating radiative transfer and climate. Here we present an analysis of NPF events observed in the Greenland Sea during the summertime as part of the Aerosol-Cloud Coupling And Climate Interactions in the Arctic (ACCACIA) project. While NPF events have been reported in the Arctic before, we were able, for the first time, to detect iodine in the growing particles using an Aerosol Mass Spectrometer (AMS) during a persistent event in the region of the coastal sea ice near Greenland. Given the potency of iodine as a nucleation precursor, the results imply that iodine was responsible for the initial NPF, a phenomenon that has been reported at lower latitudes and associated with molecular iodine emissions from coastal macroalgae. The initial source of iodine in this instance is not clear, but it was associated with air originating approximately 1 day previously over melting coastal sea ice. These results show that atmospheric models must consider iodine as a source of new particles in addition to established precursors such as sulphur compounds.

An international comparison of two I-2-stabilized frequency-doubled Nd:YAG lasers at lambda = 532 nm has been performed between the Istituto di Metrologia ``G. Colonnetti'' (IMGC)/Politecnico di Milano (PoliMI) and the Physikalisch-Technische Bundesanstalt (PTB). Both lasers used saturated absorption of the P(54) 32-0 iodine transition as a frequency reference. The signals for stabilizing the lasers were obtained using the frequency modulation spectroscopy technique with an external iodine cell. A minimum value for the relative Allan standard deviation of 7 x 10(-14) was reached after an integration time of 40 s. The hyperfine line separations were measured by the beat-frequency method and compared with the frequency values recently reported by Ye and co-workers. Three different iodine cells were investigated. The range of frequency differences for the iodine cells IMGC(QU) and PTB1/98 between the two lasers was from -9 kHz to 7.3 kHz with a mean of 1.2 kHz and a standard deviation of 3.5 kHz. Taking into account the measured frequency offsets of the different iodine cells, the evaluated frequency repeatability of the optical standards was within 2.5 kHz.

The electronic structure, spectroscopic, and bonding properties of the ground, excited, and ionized states of iodine are studied within a four-component relativistic framework using the MOLFDIR program package, The experimentally determined properties of the (1) Sigma(g)(+) ground state are well reproduced by our results calculated at the CCSD(T) level of theory, Relativistic effects and core-valence correlation need to be included in order to get reliable results, but the Gaunt interaction can be neglected. The photoelectron spectrum and the potential energy curves of the ionized and excited states are calculated using relativistic configuration interaction and coupled cluster methods. The calculated properties of the excited states are generally in good agreement with the experimental data, as well as with the earlier theoretical results of Teichteil and Pelissier, An alternative assignment of some recently measured, low lying, ionized states is proposed. (C) 1997 American Institute of Physics.

Theoretical studies have predicted that concentrations of gaseous I-2 and IO of the order of 80-100 ppt and 4050 ppt, respectively, are required in coastal air to account for photochemically-driven coastal new-particle formation events to occur. However, measurements reported to date (i.e., similar to 20 ppt I-2

Aerosol dynamical box model simulations of coastal new particle formation were performed in order to investigate the nucleation and growth mechanisms in this environment. In the simulations the nucleating vapor was assumed to be iodine dioxide (OIO). Both Eulerian and Lagrangian type simulations were made and compared with observations. We tested three nucleation mechanisms: kinetic nucleation of OIO (K x [OIO](2)), activation of clusters by OIO (A x [OIO]) and sulphuric acid-induced activation of clusters containing OIO (B x [OIO] x [H2SO4]). All the nucleation mechanisms provided reasonable results, although the growth of particles due to condensation is inadequate in kinetic nucleation cases as compared with experimental measurements. Growth of newly formed particles could be assisted by any low-volatility vapors should their concentration exceed 10(9) cm(-3). Using the obtained values of coefficients K, A, and B we found that nucleation driven by iodine compounds in remote marine areas is possible, but by OIO and H2SO4 alone, only a minor fraction of newly formed particles is likely to reach detectable sizes. Owing to the scavenging by coagulation with background aerosol particles, few of them will likely reach climatically relevant sizes by acting as seed particles for other low-volatility vapors. In order to elucidate the significance of our results, more detailed measurements of OIO source and photolysis rates, dimensions of precursor areas, and particle chemical composition are needed.

Structured emission in the gas phase to two weakly bound valence states that correlate with the third dissociation limit, I-*(P-2(1/2))+I-*(P-2(1/2)), designated as (bb), from two third tier ion-pair states of I-2 correlating with I-(S-1(0))+I+(D-1(2)), the 1(g)(D-1(2)), and F(')0(u) (+)(D-1(2)) states, has been observed for the first time. The 1(u)(bb) state is shown to be bound by 377 +/- 2 cm(-1) and molecular constants have been determined. Vibrational structure in the 0(g)(+)(bb) state could not be resolved but the spectrum is consistent with the state being bound by 435 cm(-1). The relative integrated intensities of the emissions from both ion-pair states to various valence states have also been measured, and some aspects are rationalized in terms of the electronic configurations of the upper and lower states. Bound levels of a previously uncharacterized 1(g)(ab) valence state have also been observed in emission from the gamma 1(u)(P-3(2)) ion-pair state. The lower state is shown to be bound by 270 +/- 2 cm(-1) and molecular constants have been determined. (C) 2007 American Institute of Physics [DOI:10.1063/1.2795722]

We present investigations of the reactive iodine species (RIS) IO, OIO and I2 in a coastal region from a field campaign simultaneously employing active long path differential optical absorption spectroscopy (LP-DOAS) as well as passive multi-axis differential optical absorption spectroscopy (MAX-DOAS). The campaign took place at the Martin Ryan Institute (MRI) in Carna, County Galway at the Irish West Coast about 6 km south-east of the atmospheric research station Mace Head in summer 2007. In order to study the horizontal distribution of the trace gases of interest, we established two almost parallel active LP-DOAS light paths, the shorter of 1034 m length just crossing the intertidal area, whereas the longer one of 3946 m length also crossed open water during periods of low tide. In addition we operated two passive Mini-MAX-DOAS instruments with the same viewing direction. While neither OIO nor I2 could be unambiguously identified with any of the instruments, IO could be detected with active as well as passive DOAS. The IO column densities seen at both active LP-DOAS light paths are almost the same. Thus it can be concluded that coastal IO is almost exclusively located in the intertidal area, where we detected mixing ratios of up to 29±8.8 ppt (equivalent to pmol/mol). Nucleation events with particle concentrations of 106 cm−3 particles were observed each day correlating with high IO mixing ratios. Therefore we feel that our detected IO concentrations confirm the results of model studies, which state that in order to explain such particle bursts, IO mixing ratios of 50 to 100 ppt in so called "hot-spots" are required.