Laboratoire de Physico-Chimie des Processus de Combustion et de l’Atmosphère (PC2A), UMR CNRS 8522, Université Lille 1, Cité Scientifique - Bâtiment C11, 59655 Villeneuve d’Ascq, France

INTRODUCTION

The aerosols in the marine boundary layer (MBL) consist of sulphate and halogen-containing sea salt particles. The sulphates are produced from the anthropogenic SO₂ emissions while the sea-salts are generated by the wave action or bubble bursting of the seawater. Sea-salt particles are the principal constituent of aerosol particles in MBL. Although the dominant mass fraction of marine aerosol is inorganic sea salt, organic matter also contributes to the overall mass. It has been reported that marine aerosols contain an organic fraction being mainly made up of fatty acids. Resulting from biological activity, it is assumed that fatty acids found in the particles or on their surface are ejected into the atmosphere along with sea salt ⁽¹⁾.

Given the high oxidizing capacity of the atmosphere, heterogeneous reactions between sea-salt particles and gas-phase radicals should be also considered in order to get a fine description of the atmospheric chemical reactions and global oxidants budget⁽²⁾. Heterogeneous atmospheric reactions may lead not only to changes in particulate chemical composition, but also their physical properties thereby affecting their optical or hygroscopic properties. Although OH radicals are the main daytime oxidants, halogen atoms (Cl, Br and I) may significantly participate to the oxidation processes especially in the marine boundary layer.

Atomic chlorine may represent the major oxidant of the troposphere at dawn at low concentrations of OH radicals. The chlorine species are photolyzed at sunrise to generate chlorine atoms which can modify the acidity budget, oxidize volatile organic compounds or contribute to sulphur oxidation in the aqueous phase⁽³⁾. Chlorine atoms have been detected in high concentrations not only in the marine boundary layer, but also at long distances from the coast⁽⁴⁾ and their concentrations can be up to 10⁶ atom.cm^{-3 (3)}.

In order to better understand the heterogeneous reactivity between these aerosol particles and chlorine reactive species, kinetic studies has been developed in our laboratory.

EXPERIMENTAL

The aim of this work is to study the kinetics of gas interactions on model aerosols surface. These heterogeneous reactions on model substrates have been investigated in a laminar coated wall flow tube reactor. The heterogeneous reactions of chlorine atoms on different particles were investigated at low pressure (~1 mbar) and at various temperatures.

Salt samples were prepared as powder substrates deposited on the internal surface of the reactor and as spray deposited substrates, using a constant output atomizer. The chlorine atoms were generated via microwave discharge in a mixture of molecular chlorine diluted in helium and detected at the exit of the reactor by a quadrupole mass spectrometer.

The measurement of the first order rate constant, k, is achieved by changing the contact time between the surface and the gas, using a movable injector. From the rate constant, we determine the uptake coefficient, γ, which represents the ratio between the number of gas molecules removed by the condensed phase and the number of gas molecules striking the interface per unit time.

Investigations were first done with model particles of NaCl and synthetic sea salt (SSS). NaCl is employed extensively in laboratory studies as a proxy for the sea salt particles. However, sea salt is a mixture of inorganic compounds, including a variety of metals and hydrates such as MgCl₂^.6H₂O, which have the potential to influence the chemistry of these salts. Experiments have also been performed with ammonium sulfate and nitrate particles, the major components in the secondary particles formed by the condensation of gaseous species of anthropogenic origin.

RESULTS

The uptake of chlorine atoms on particles was found to be fast with an uptake coefficient of
γ ~ 2 × 10^-2 for sodium chloride or γ ~ 4 × 10^-3 for SSS. Comparing the values of the uptake coefficient of SSS with those determined for NaCl, it should be noted that the synthetic sea salts are less reactive and it is then convenient to be careful in the transposition of the laboratory results to atmospheric sea salts.

The uptake of chlorine atoms on ammonium sulphate was γ ~ 1 × 10^-3 and for ammonium nitrate,
γ ~ 2 × 10^-3.

The reactivity of ammonium sulphate particles with chlorine atoms leads to an absent phenomenon for the other studied systems, more precisely, a surface saturation effect. After successive kinetics on the same surface, we observed that the reactivity of the particles decreases due to possible aging process. This means probably, a reaction on the surface of these particles.

The uptake coefficient values are in agreement with the only available data from Remorov et al, 2008⁽⁵⁾ for sodium chloride and Martin et al, 1980⁽⁶⁾ for ammonium sulphate particles. To our knowledge, this is the first study to investigate the reactivity of chlorine atoms with synthetic sea salts and ammonium nitrate particles.

We have also observed that the temperature of the surface is an important factor which influences the uptake coefficient value. Studies at different temperatures have shown that γ increases when the temperature decreases. These values are largely influenced also by the effect of water vapours adsorbed on the particles surface. Furthermore, the appearance of new chlorine species (i.e. HOCl) has been observed and has to be quantified. A secondary product, Cl₂, was observed, owing to the heterogeneous recombination of halogen atoms on the surface of the particles. From these observations we were able to determine the heat of adsorption of Cl atoms on sodium chloride surfaces
(Q_ads= 63 kJ.mol^-1).

Experimental studies with palmitic acid, one of the most abundant fatty acid of particulate organic matter in the marine boundary layer are in progress in our laboratory. The initial uptake coefficient was measured and the first results will be presented. We observed a rapid formation of hydrogen chloride which corresponds with the disappearance of chlorine atoms. These studies have shown that the production of HCl and Cl˙ consumption is accompanied sometime by consumption or formation of Cl₂. During the heterogeneous study between Cl˙ and palmitic acid, a surface saturation effect was also observed.

The solid surfaces were analyzed after reaction by advanced microscopy techniques (XPS, TOF SIMS) during this study.

Further experiments are planned, including identification and quantification of new products formed in the condensed phase by GC/MS.

REFERENCES

⁽¹⁾Mochida M. et al. (2002), Journal of Geophysical Research, 107

⁽²⁾George I. J. and Abbatt J. P. D. (2010), Nature Chem, 2, 713-722

⁽³⁾Spicer C. W. et al. (1998), Letters To Nature, 394 (6691), 353-356

⁽⁴⁾Thornton J.A. et al. (2010), Nature, 464, 271-274 ⁽⁵⁾Remorov R.G. et al. (2008), Russian Journal of Physical Chemistry B, 1, 46-52

⁽⁶⁾Martin L.R. et al. (1980), J. Geophys. Res., 85, 5511-5518

Aurélie Colomb (A.Colomb@opgc.univ-bpclermont.fr; OPGC)

Impact on OCEANIC Frontal ZONES on atmospheric TRACE GASES composition

A. Colomb*(1), R.Paris (2), K.Desboeufs (2), R.Losno (2), B. Bonsang   (3), V.Gros (3), J. Williams (4), N. Yassaa (5), S. Belviso (3),

(1) Laboratoire de Météorologie Physique, UMR 6016/CNRS, Université Blaise Pascal, 63177 Aubière, Cedex, France

(2) Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR

7583/CNRS, Université Paris 12, 61 av. Général de Gaulle, 94010 Créteil, France

(3) Laboratoire des Sciences du Climat et de l’Environnement, UMR 1572 CEA/CNRS/UVSQ, Orme des Merisiers, 91191 Gif-sur-Yvette, France

(4) Max Planck Institute for Chemistry, Atmospheric Department, J.J. Becher Weg 25, D-55122 Mainz, Germany

(5) Laboratoire d´Analyse Organique Fonctionnelle, Faculté de Chimie, Université des Sciences et de la Technologie Houari Boumediene, U.S.T.H.B., BP 32 El-Alia Bab-Ezzouar, 16111 Algiers, Algeria

Considering the size and potential importance of the air-ocean interface, it is surprisingly poorly characterized in terms of organic trace gases. These organic species are known to play important roles in the Earth’s atmosphere, impacting on ozone chemistry and aerosol formation, thereby influencing the Earth’s overall oxidation capacity and radiative budget. For instance, volatile organic compounds (VOCs) are known to play a key role in the chemistry of both the troposphere and the stratosphere. In the presence of NOx (NO and NO_2 ) and sunlight, the photooxidation of reactive VOCs (e.g. isoprene) produces tropospheric ozone, a radiatively active gas that is toxic to both humans and plants. In contrast, halogen-containing organic species (e.g. CH_3 Cl and CH_3 Br) are known to contribute significantly to ozone destruction in the stratosphere. Furthermore, some VOC emissions such as dimethyl sulphide (DMS) can be oxidized to form aerosols ultimately, and may therefore have a direct effect on the Earth´s radiation budget.

It should be noted that the net primary production (NPP) of the ocean is comparable in size to that of the terrestrial biosphere (ca. 45 Pg/yr-1), even though there is approximately 100 times less biomass in the ocean than on land. The oceanic biomass is often concentrated at frontal zones where upwelling brings nutrients to the surface, sustaining marine life and leading to strong uptake and emission of chemical species between the air and sea. The frontal zones of the ocean can therefore be considered as being fast cycling, efficient ecosystems, in urgent need of better chemical characterization. The relative paucity of ocean-based data compared to terrestrial sites is due partly to accessibility issues, and partly to the high spatial and temporal variation within the limited biomass. The role of the ocean in the budgets of organic species requires urgent investigation. In reality the ocean surface may be a highly variable source or sink for many compounds, depending on the latitude, temperature, wind speed and biological composition of the surface water. Some organic species have been reported to be emitted from the ocean (including sulphur-containing gases , organohalogens and alkyl nitrates, while many other species are taken up, (e.g. acetone , and methanol ).

Recently satellite technology has been proven capable of providing ocean maps of where certain phytoplankton species dominate. Therefore future global models could, potentially, significantly improve our knowledge of ocean emissions, provided we know which organic gases are emitted from which phytoplankton species. Furthermore, if the Earth warms up in the future, as it is predicted to do, then concomitant changes can be expected in the distribution and speciation of phytoplankton , and the modeling of such changes, together with an assessment of potential ocean-atmosphere chemical feedbacks, again depends on the knowledge of which gas species are emitted from which phytoplankton species. The first step in this characterization is provided by laboratory experiments, followed up by mesocosm experiments and ultimately by ship campaigns. Some results of recent ship campaigns (MANCHOT in Indian Austral Ocean in December 2004, OOMPH between Cape Town and Punta Arenas in January 2007 and DRAKE in Drake Passage in March 2009,...) will be presented.

Véronique Garçon (veronique.garcon@legos.obs-mip.fr; LEGOS)

Climatically-active gases in the Eastern Boundary Upwelling and Oxygen Minimum Zone (OMZ) systems

Véronique Garçon, Christoph Garbe, Joël Sudre, Boris Dewitte, Hussein Yahia, Aurélien Paulmier and Isabelle Dadou

LEGOS, Toulouse, France, University of Heidelberg, Karlsruhe Institute of Technology, Germany, INRIA, Bordeaux, France

The EBUS (Eastern Boundary Upwelling Systems) and OMZs (Oxygen Minimum Zone) contribute very significantly to the gas exchange between the ocean and the atmosphere, notably with respect to the greenhouse gases (hereafter GHG). Off Peru, very few in-situ data of ocean-atmosphere CO2 fluxes are available presently, which justifies alternative approaches for assessing these fluxes.

GHG air-sea fluxes determination can be inferred from inverse modeling applied to VCDs (vertical column densities), extracted from satellite spectrometers, using state of the art modeling, at low spatial resolution. For accurately linking sources of GHGs to EBUS and OMZs, the resolution of the source regions needs to be increased. This task develops on new non-linear and multiscale processing methods for complex signals to infer a higher spatial resolution mapping of the fluxes and the associated sinks and sources between the atmosphere and the ocean. Such an inference takes into account the cascading properties of physical variables across the scales in complex signals. The use of coupled satellite data (e.g. SST and/or ocean colour) that carry turbulence information associated to ocean dynamics is taken into account at unprecedented detail level to incorporate turbulence effects in the evaluation of the air-sea fluxes.

We will present a framework as described above for determining sources and sinks of GHG from satellite remote sensing. The approach includes resolution enhancements from a multiscale processing method. The applicability will be validated against ground truth observations and numerical model studies.

Cécile Guieu (guieu@obs-vlfr.fr; LOV)

Atmospheric deposition onto oligotrophic marine systems: new insights from mesocosm studies.

Guieu Cécile¹, Ridame Céline², Pulido-Villena Elvira³, Bressac Matthieu¹, Blain Stéphane⁴, Wagener Thibaut⁵, Dulac Francois⁶, Desboeufs Karine⁷, Leblond Nathalie¹, Jean-Baptiste Luce¹, Stemman Lars¹, Obernesterer Ingrid⁴, Doxaran David¹, Bourrin François⁸,

1 : LOV-UMR7093, Villefranche sur mer ; 2 : UPMC-LOCEAN-IPSL, 3 : COM LMGEM Marseille, 4 : LOMIC-UPMC Banyuls sur mer ; 5 : COM LOBP Marseille, 6 : CEA-LSCE Gif-sur-Yvette, 7 : LISA-Universités Paris Diderot et Paris Est ; 8 : UMR 5110 CNRS - UPVD - Université de Perpignan.

The objectives of the project DUNE (a DUst experiment in a low-Nutrient, low-chlorophyll (LNLC) Ecosystem) are (1) to evidence to what extent atmospheric deposition represents a forcing for biogeochemical cycles and ecosystem functioning in a LNLC marine area and (2) to quantify the impact of atmospheric deposition on carbon export in oligotrophic areas. We chose an original experimental approach consisting in simulating dust deposition onto large (52 m3), clean mesocosms (allowing chemical measurements of trace elements). The two field campaigns that were conducted in the frame of the project, have shown that significant changes in the cycling of chemical elements and strong responses of the ecosystem at different trophic levels were induced by the deposition of dust particles. Both autotrophs and heterotrophs (bacteria, zooplankton) were significantly impacted by the dust addition and although the system was shown to be net heterotrophic in the mesocosms with dust addition, the carbon export efficiency was also much higher in those mesocosms. By coupling optical and biogeochemical measurements, we show that in addition to have induced the production of “fresh” organic matter by fertilization effect, the added particles have favored the downward export of a large amount of organic matter present in the water column before the seeding. Such mesocosm approach have shown that dust inputs to oligotrophic systems cannot be seen as a ‘simple fertilisation effect’ and that the aggregation/ballasting effect after the introduction of mineral particles is a key process in carbon export.

Alexie Heimburger (alexie.heimburger@lisa.u-pec.fr; LISA)

Dust deposition over South Ocean measured at Crozet an Kerguelen Island

A.Heimburger¹, R. Losno¹, S. Triquet¹, E. Bon¹ and A. Perot²

¹LISA, University Paris7 Denis Diderot, Paris Est Créteil, UMR CNRS 7583

²IPEV

Atmospheric deposition is one of the major source of nutrients to remote marine biota. Total deposition and crustal aerosols were monitored at Crozet and Kerguelen islands, in the Southern Ocean, during one and two years. Measured iron atmospheric deposition fluxes for the both sites are respectively 540 and 480 nmol.m-2.d-1. That result shows that dust deposition simulated by current atmospheric transport models is slightly underestimate. It shows too that indirect measures, using aerosols concentrations at ground level and scavenging ratio in literature, are inadequate to estimate atmospheric deposition over the Southern Ocean.

Emilie Journet (emilie.journet@lisa.u-pec.fr; LISA)

A new mineralogical database for atmospheric dust to estimate soluble iron fluxes to surface ocean.

Journet E., Balkansky Y and Harrison S.

Desert dust affects global climate through various environmental processes.Among them, we know that deposited mineral dust changes the global carbon budget by providing soluble iron to surface water to phytoplankton limited by the availability of iron. So far, many uncertainties persist about iron bioavailability that depends primarily on its solubility. According recent studies, one of the ways that will reduce these uncertainties is to inform the mineralogical composition of desert dust. But up to now, very little information has been gathered to describe the complex mixture of various minerals aggregated into desert dust. To fill in the clear need for a new data set to provide information on dust mineralogy, we present here an update of the soils mineralogical database provided by Claquin et al. in 1999. To build upon such database, we collected first a Database of soil surface mineralogy for 12 major minerals. Based on this information, we assigned a mean mineralogical composition for most soil types given by the FAO in the Harmonized World Soil Database. The main features of this mineralogical database are discussed. We highlight the ranges and the global mean value for the relative abundances each of these mineral in dust. This paves the way to introduce the mineralogical composition in a General Circulation Model with a chemistry-aerosol module. We will discuss the changes in atmospheric soluble iron fluxes when information about the detailed mineralogy is accounted for compared to a simulation when the averaged mineralogy is used.

Nathalie Lefevre (nathalie.lefevre@locean-ipsl.upmc.fr; LOCEAN)

The role of the salinity on the CO2 variability in the western tropical Atlantic

Nathalie Lefèvre¹, Domingos Urbano², F. Gallois³, Denis Diverrès⁴

1 LOCEAN, UPMC, 4 place Jussieu, 75252 Paris Cedex 05, France

2 INPE, Cachoeira Paulista, São Paulo, Brazil

3 US 191 Centre IRD de Nouméa, Nouméa, New Caledonia

4 US 191, Centre IRD de Bretagne, 29280 Plouzané, France

A CO₂ sensor and an oxygen optode have been installed on the PIRATA moorings at 6^oS, 10^oW and 8^oN, 38^oW to monitor the hourly fugacity of CO₂ (fCO₂) and dissolved oxygen concentration in surface waters. In addition, two merchant ships (sailing along the routes France-Brazil and France-French Guiana) have been equipped with an autonomous CO₂ system to routinely measure atmospheric and oceanic fCO₂ during the voyages. This observational CO₂ network has been complemented by underway CO₂ measurements during two PIRATA Brazilian cruises in 2009 and 2010.

The fugacity of CO₂ and the dissolved oxygen concentration are affected by temperature and salinity changes, biological activity, air-sea exchange, and ocean circulation. The western tropical Atlantic is mainly a source of CO₂ for the atmosphere. However, strong CO₂ undersaturations are observed close to the American shelf, off the French Guiana, and are associated with very low salinity due the Amazon outflow. Further offshore, the seasonal migration of the inter-tropical convergence zone is also associated with lower CO₂.

Marina Levy (marina.levy@upmc.fr; LOCEAN)

Huricanne Impacts on Air-Sea CO₂ Fluxes

M. Lévy, M. Lengaigne, L. Bopp, E. Vincent, G. Madec, C. Ethé, D. Kumar, V. Sarma

A few case studies have illustrated the strong influence of tropical cyclones (TCs) on ocean-atmosphere CO2 fluxes (FCO2) by modifying the gas exchange coefficient and the oceanic pCO2. Based on a few observations, it has been suggested that TCs significantly increase the CO2 efflux from the ocean to the atmosphere.

However, limited availability of pCO2 observations under TCs harsh conditions has so far restricted global quantification of the TC-induced FCO2 to hazardous extrapolations. We use a state-of-the-art global ocean biogeochemical model driven by TC wind forcing derived from a 30-year historical TC database, sampling the ocean response to more than 3,000 TCs. The resulting modeled TC coolings compare very well with satellite estimates. The model also accurately reproduces the sharp pCO2 drawdown recorded after the passage of Hurricane Felix in the NW Atlantic. We found that TCs can generate CO2 fluxes directed from the ocean to the atmosphere or vise-versa, depending on the oceanic condition.

We identify two competing effects of TCs on FCO2 that are not synchronous.During the storm and depending on the sign of the difference of pCO2 between the ocean and atmosphere, TCs are responsible for large efflux or influx anomalies due to the strong winds. During several weeks after the storm, oceanic pCO2 is reduced in response to vertical mixing, which systematically causes an influx anomaly. Generally, the storm wind-effect and post-storm mixing effect have the same order of magnitude.

This implies that, contrary to previous estimates, TCs weakly impacts the CO2 efflux because the two effects oppose with each other when they blow over supersaturated areas (typically in the North Atlantic, North-East Pacific, Arabian Sea). In contrast, TCs increase the CO$_2$ influx because the two effects add up under undersaturated conditions (e.g. in the Westernmost North Pacific, Bay of Bengal, South Indian and Pacific Ocean). In total, we find that TCs account for 2% of the FCO2 during the cyclonic season over the tropical ocean (40N-40S), and explain less than 5% of the year-to-year variations of the FCO2, which is an order of magnitude less than the lowest previous estimates.

Rémi Losno (remi.losno@lisa.u-pec.fr; LISA)

Mercury total deposition at Kerguelen Island

R. Losno, S. Triquet, E. Bon, A.S. Chevallier, and A. Heimburger

LISA, Université Paris7 Denis Diderot Paris Est Créteil et UMR CNRS 7583

Mecury total deposition was measured during 4 field campaign at Kerguelen Island: February 2005, November 2008, December 2009 and December 2010. A strong relationship exists between the averaged monthly mercury deposition flux and the averaged monthly rainfall because the dissolved mercury concentration in rainwater does not vary a lot. Average dissolved mercury concentration is 2.60 ng/L but vary from 1.35 to 3.5 ng/L averaged on a few day period for all the collected samples. Two outlier's points as far as 9.5 ng/L were observed en 2009. The flux averaged each year over the sampling duration (1 month) was between 17 and 22 ng/m²/d except in 2008 where the month was particularly dry with a rainfall half and also a flux half. The amount of mercury found at Kerguelen are far below those observed in North Hemisphere (5 to 10 times) in remote areas but higher that found in antarctic snow (1 ng/kg, Sheppard et al., 1991)

D.S. Sheppard, J.E. Patterson and M.K. McAdam, Mercury content of Antarctic ice and snow: Further results, Atmospheric Environment. Part A. General Topics, Volume 25, Issue 8, 1991, Pages 1657-1660

Anna Lourantou (alolod@locean-ipsl.upmc.fr; LOCEAN)

Variability of CO₂ fluxes in the NE part of the Kerguelen Plateau (Indian sector of the Southern Ocean) at a seasonal to decadal scale

Anna Lourantou & Nicolas Metzl

The rise of atmospheric CO₂ since the industrial revolution due to fossil emissions, deforestation and automobile use, is evident (1). One of the major research interests nowadays deals with the role of the global ocean towards this ongoing atmospheric CO₂ rise. The Southern ocean is known for its considerable atmospheric CO₂ storage capacity, which seems to decline throughout time (2). Nonetheless, Southern Ocean covers different zones with various characteristics (3); more attention should be therefore given on the examination of these zones separately (latitudinal distribution).

In this study, we examine the fCO₂ evolution (seasonal to decadal) between the sub-tropical and the sub-antarctic zone of the Indian sector of the Southern ocean. We treat hydrological (SST, SSS) and fCO₂ data from surface waters in the track between Kerguelen (49°21’S; 70°13’E) and Amsterdam (37°49’S; 77°33’E) islands. This transect has been frequently visited by the French Research Vessel Marion Dufresne. This permitted us to work on totally 17 cruises, which took place from 1991 until 2011, covering the 4 seasons (4). All data have been found in the SOCAT (Surface Ocean CO₂ ATlas) database, soon available to the public (5).

More specific attention will be given in the plateau of Kerguelen island, situated in the subantarctic zone, south of the Polar Front (6). In this area, a considerable phytoplankton bloom manifests every austral summer, which is accompanied by large biomass (expressed as chlorophyll-a) concentrations, due to Fe fertilization from the bottom (7). This study provides for the first time the response of biogeochemistry (fCO₂ further transformed to air-sea CO₂ fluxes) towards such biological phenomena in this region, just before the oceanographic cruise KEOPS2. The “island mass effect” has been previously examined for the Crozet archipelago and will be compared to this study (8). Implications of the role of the polar front position, as well as the topography, will be equally discussed. Comparisons with satellite-derived chla data will be also provided.

.

References

(1) IPCC report, 2007; (2) Le Quéré et al., Science 2007 ; (3) Metzl et al., TellusB 1999 ; (4) http://caraus.ipsl.jussieu.fr/oiso-accueil.html; (5) www.socat.info; (6) Park et al., DSRII 2009 ; (7) Blain et al., DSRI 2001 ; (8) Bakker et al., DSRII 2007

Marc Mallet (Marc.Mallet@aero.obs-mip.fr)

Impact of sea-surface aerosol radiative forcing on the oceanic primary production.

M. Mallet, M. Chami, B. Gentili, R. Sempere and P. Dubuisson

Celine Mari (celine.mari@aero.obs-mip.fr)

IGAC activities and their links with the SOLAS program

Lilliane Merlivat (merlivat@locean-ipsl.upmc.fr; LOCEAN)

Biological net community production (NCP)of carbon and oxygen based on high frequency measurements of fCO₂ and O₂ on a Pirata mooring in the tropical Atlantic

Nathalie Lefèvre and Liliane Merlivat

LOCEAN, Université Pierre et Marie Curie, UMR7159 UPMC/CNRS/IRD/MNHN, 4 Place Jussieu, case 100, Tour 45-46, 5ème étage, 75252 PARIS cedex 05, FRANCE

A mooring at 6^oS, 10^oW has been equipped with an oxygen optode and a Carioca sensor for monitoring hourly oxygen (O₂) and the fugacity of CO₂ (fCO₂) at 1.5 m depth since June 2006. Due to biofouling, the oxygen time-series lasted between 72 days in 2008 to 159 days in 2009. Using an alkalinity-salinity relationship determined for the area, dissolved inorganic carbon (DIC) is calculated. Short term and long term net community productions (NCP) are calculated using a mass balance approach for DIC and O₂ under the assumption of no mixing conditions. The mooring site is always supersaturated in oxygen except in 2007 when depleted oxygen waters are observed from June to September, during the upwelling season. Averaging all the short time events, NCP calculated from the rates of changes of O₂ and DIC leads to a NCP of 16.6  6.1 mmol C m^-2d^-1, ranging from 14.7 mmol C m^-2d^-1 in 2008 to 17.4 mmol C m^-2d^-1 in 2006. The mean daily oxygen biological production rate determined over the whole time series shows a significant year to year variability with 7.5 mmol C m^-2d^-1 in 2008 to 15.6 mmol C m^-2d^-1 in 2009. A photosynthetic quotient ranging between 1.0 to 1.3 has been determined when both carbon and oxygen NCP values are available.

Barbara Nozière (barbara.noziere@ircelyon.univ-lyon1.fr; IRCELYON)

Biosurfactants on aerosols: a link between biogenic activity and cloud formation?

Barbara Noziere, Christine Baduel, Sanna Ekström

Elvira Pulido (elvira.pulido@univmed.fr; LMGEM)

Dust pulses enhance bacterial mineralization of dissolved organic matter in P-depleted waters : results from mesocosm experiments in the Mediterranean Sea (DUNE project)

Elvira Pulido-Villena and the DUNE team

The impact of dust deposition on low-nutrient low-chlorophyll (LNLC) oceanic regions receives a growing interest given its potential to generate new production and to increase particulate carbon export. However, up to 50% of the carbon export in LNLC regions occurs in dissolved rather than in particulate form. By relieving the nutrient limitation of bacterial activity, dust pulses may modulate the cycling and fate of dissolved organic matter thus affecting carbon export. Recent experimental dust additions performed into large mesocosms in the frame of the DUNE project led to rapid and noticeable increases in surface phosphate concentration. Likely through the relieving of P-limitation, these dust additions significantly increased bacterial respiration rates. This observed stimulation of the bacterial mineralization of dissolved organic matter may change our view of how dust pulses affect carbon cycling in the LNLC regions of the ocean.

Virginie Racapé (virginie.racape@locean-ipsl.upmc.fr; LOCEAN)

Anthropogenic carbon changes in the North Atlantic Subpolar Gyre: what do we learn from δ13C ?

Racape V., Metzl N., Pierre C.

LOCEAN-IPSL, Université Pierre et Marie Curie, Paris-France

The North Atlantic Ocean, north of 50°N, is considered as one of the stronger anthropogenic CO₂ sinks, a consequence of the large heat loss and deep convection process during winter, as well as strong biological activity in summer and fall. However, anterior ocean CO₂ observations conducted in this region since 1981 suggest that the accumulation of anthropogenic carbon (Cant) is not steady and that Cant storage rates have been reduced since the mid-nineties [Perez et al., 2010]. This is likely associated to a large-scale climatic forcing, e.g. a shift in the North Atlantic Oscillation (NAO) in 1995-96. This is also coherent with a decreasing rate of air-sea CO₂ fluxes observed in the same region [e.g. Corbiere et al., 2007; Metzl et al, 2010]. In response to the increase in anthropogenic CO₂ emissions that are ¹³C-depleted, the carbon isotopic composition (δ¹³C) of atmospheric CO₂ decreases by 0.02 ‰ yr^-1; consequently, the δ¹³C values of dissolved inorganic carbon (δ¹³C_DIC) in sea water also decreases (so-called Suess Effect). Therefore, estimate of δ¹³C_DIC changes in the ocean offers a companion information for understanding the anthropogenic CO₂ storage [e.g. Quay et al., 1992]. In this context we will first describe new δ¹³C_DIC observations obtained in the North Atlantic Subpolar Gyre (OVIDE 2004, 2006) and compare the recent δ¹³C_DIC distributions with historical data (TTO, WOCE). We will also explore the evolutions of the relationships between δ¹³C_DIC , DIC and Cant concentrations that could help in our understanding of where and why the Cant storage rate is decreasing since more than a decade.

References

Corbière, A., et al., 2007. Interannual and decadal variability of the oceanic carbon sink in the North Atlantic subpolar gyre. Tellus, Ser. B, 59, 168–178.

Metzl, N. et al., 2010. Recent acceleration of the sea surface fCO2 growth rate in the North Atlantic subpolar gyre (1993–2008) revealed by winter observations. Global biogeoch. cyc, 24.

Perez, F. F. et al., 2008. Temporal variability of the anthropogenic CO2 storage in the Irminger Sea. Biogeosciences, 5, 1669-1679

Quay, P., Tilbrook, B. and Wong, C. 1992. Oceanic uptake of fossil fuel CO₂: Carbon-13 evidence. Science 256, 74-79.

Karine Sellegri (K.Sellegri@opgc.univ-bpclermont.fr; LaMP)

Sources of marine aerosol from the Mediterranean sea as a function of the sea water biochemical composition and photochemical conditions : the SAM project

K. Sellegri, B. D'Anna, N. Marchand and R. Sempere

Sophie Tran (sophie.tran@lsce.ipsl.fr; LSCE)

Influences of biology and water masses on the variability of the marine source of CO and NMHC in the Arctic Ocean in summer 2010.

Tran S., Bonsang B., Gros V., Peeken I., Sarda-Esteve R.

Oceanic emissions of carbon monoxide (CO) and light non methane hydrocarbons (NMHC) are important for both their impact on marine atmospheric chemistry and their contribution to global CO and NMHC budgets. Owing to the large area of the oceans, even small fluxes of those compounds per unit area could result in large global oceanic emissions. This is particularly important in the Arctic Ocean which is sensitive to environmental changes linked to global warming. To explore processes leading to the formation of CO and NMHC at the sea surface and their transfer to the atmosphere, their concentration in surface seawater as well as in the water column down to 100m depth were measured during a cruise of RV Polarstern in June-July 2010 through the Norwegian Sea to the Arctic Ocean. These results combine the first simultaneous set of measurements for CO, NMHC, and biological data in surface water and vertical profiles for the Arctic Ocean.

The results presented here show the variability of dissolved CO and NMHC all along the transects including data on surface waters covered by the ice pack. Variability of alkenes seems to be well correlated to CO which originates from the photo degradation of chromophoric dissolved organic matter (CDOM) under UV radiation. Concerning the vertical profiles, we have observed a maximum of concentration of CO close to the surface (0-15m) in relation to the UV penetration maximum followed by a sharp decrease until -100m while the maximum of isoprene is correlated to the maximum of chlorophyll-a.

Such distributions seem to be related to the water masses properties with high concentration of CO in Polar water and high values of isoprene in Atlantic water. Some profiles of CO also show a secondary maximum at the maximum of fluorescence and oxygen. This secondary maximum is then attributed to a biological production acting as a secondary source. Alkenes profiles (mainly ethene, propene and butenes) and surprisingly some alkane profiles show the same pattern as CO, and suggest the same photo-production processes. Isoprene vertical distribution displays a clear maximum in depth (20-30 m) and appears to be well correlated with the fluorescence profile, in agreement with a pure biological origin.

These variations are interpreted with the help of biological data and enable to estimate the contribution of arctic surface waters in the CO and NMHC budgets.

Thibault Wagener (thibaut.wagener@univmed.fr; LOPB)

Temporal Changes in trace metal concentrations during an artificial dust deposition to Large Mesocosms (DUNE-2 Experiment)

Thibaut Wagener, Kathrin Wuttig, Anna Dammshäuser, Matthieu Bressac, Peter Streu, Cecile Guieu, Peter L. Croot

The deposition of atmospheric dust is one of the main external source to the ocean for elements abundant in crustal rocks. Once deposited the residence time of these elements in surface waters differs according to their chemical speciation and biological ultilization. In the present work we examined the temporal changes in the concentrations of Iron, Maganese and Aluminium within large mesocosms after the seeding with simulated aeolian dust of surface waters of the northwestern Mediterranean. Two artificial deposition events were performed during the course of this experiment: for each artificial Saharan dust fertilization to the mesocoms the changes in Mn, Fe and Al chemistry were followed over the following week. In this presentation, we will present results from this mesocosm experiment focusing on the similarities and differences between these 3 elements. This trace metal dataset makes a significant contribution to enhance our knowledge about the release of trace metals from Saharan dust in a low nutrient low chlorophyll area and the subsequent processes of biouptake and scavenging.