Ocean variability at decadal time-scales remains poorly described partly because of the scarcity of high temporal resolution marine records. Here, we present a reconstruction of Sea Surface

Organic carbon concentration and isotopic composition were determined in samples of atmospheric particulate matter collected in 1979 at remote marine locations (Enewetak atoll, Sargasso Sea) during the SEAREX (Sea‐Air Exchange) program field experiments. Atmospheric Particulate Organic Carbon (POC) concentrations were found to be in the range of 0.3 to 1.2µg.m−3, in agreement with previous literature data. The major mass of POC was found on the smallest particles (r<0.5µm). The 13C/12C of the small particles is close to the one expected (δ13C = 26 ± 2‰) for atmospheric POC of continental origin. For all the samples analysed so far, it appears that more than 80% of atmospheric POC over remote marine areas is of continental origin. This can be explained either by long‐range transport of small sized continental organic aerosols or by the production of POC in the marine atmosphere from a vapor phase organic carbon pool of continental origin. The POC in the large size fraction of marine aerosols (<20% of the total concentration) is likely to have a direct marine origin since its carbon isotopic composition is close to the expected value (δ13C = −21 ± 2‰) for POC associated with sea‐salt droplets transported to the marine atmosphere.

[1] The C 37 -C 39 alkenones were quantified in suspended particulate matter obtained from the surface waters of the North Atlantic, including the Nordic seas, over a temperature range of 4°-20°C.

[1] A decadal resolution time series of sea surface temperature (SST) spanning the last two millennia is reconstructed by combining a proxy record from a new sediment sequence with previously published data from core MD99-2275, north of Iceland. The alkenone based SST reconstruction is validated with historic observational data and compared to a new similar temporal resolution reconstruction obtained from sediment core RAPiD21-3K, in the subpolar North Atlantic. The two SST paleorecords show consistent multidecadal scale coolings throughout the interval and similar expressions during the contrasted climatic periods 'colloquially known' as the Medieval Climatic Anomaly (MCA) and Little Ice Age (LIA). In order to further understand the temporal and spatial SST variations and investigate the influence of natural forcings on the observed SST changes during the last millennium, we compare our time series to simulations using the Institut Pierre-Simon Laplace IPSLCM4-v2 climate model. This comparison highlights the potential importance of volcanism as a natural forcing driving coherent abrupt cooling events captured in the subpolar North Atlantic records.

The mass-particle size distributions (MSDs) of Na, Al, Cd, and Pb were determined from 17, 1-5 day, high-volume cascade impactor samples collected throughout the Western Mediterranean atmosphere between 1980 and 1983. As expected, the mass median diameter (MMD) was the largest for Na, representative of sea-salt aerosol, with a median value of 5.9 pm. The median value for the MMD for Al, representative of mineral aerosol, was 2.8 pm.The smallest values of the MMD were found for pollution-derived elements, Cd and Pb: 0.7 pm. In most cases, the MSDs, for each of the elements, were log-normal. Total dry deposition velocities were calculated from the two-layer deposition model of Slinn and Slinn (1980) using three approaches: (i) by characterizing the distribution as a MMD, (ii) by considering the size distribution as directly given by the cascade impactor, (iii) by fitting the assumed log-normal distribution and dividing it into 100 successive intervals. The first approach appeared to give underestimates. The two other approaches yielded similar results for Cd and Pb, of the order of 0.05 cm S K I , For these elements, however, more than 20% of the total dry deposition flux was due to particles with diameters of 7.2 pm or greater (collected by impactor stage 1). For Na and Al, the third approach yielded values at least one order of magnitude higher than when using the two others. This clearly underlines the major role played by large particles in controlling the dry deposition of sea-salt and mineral aerosol particles. Direct measurements of Al dry deposition, made in 1985-1986 on the northwestern coast of Corsica, agree best with the values predicted by the third approach (mean calculated and measured values of 1.8 and 3.0 cm s-I respectively). Scanning electron microscopy examinations of samples confirm that mineral aerosol particles with diameters of 10 pm or greater dominate the dry deposition flux. Preliminary data indicate that for mineral aerosol particles, this flux is, on a yearly basis, about half of the wet deposition flux. However cascade impactor data are not adequate to retrieve true mass-particle size distribution in the size range which controls dry deposition ( D > 7 pm), and this is shown to be the source for one order of magnitude uncertainties in dry deposition calculations.

No abstract

No abstract

No abstract