Elena Jurado

Analysis of a potential “solar radiation dose–dimethylsulfide–cloud condensation nuclei” link from globally mapped seasonal correlations

[1] The CLAW postulate states that an increase in solar irradiance or in the heat flux to the ocean can trigger a biogeochemical response to counteract the associated increase in temperature and available sunlight. This natural (negative) feedback mechanism would be based on a multistep response: first, an increase in seawater dimethylsulfide concentrations (DMSw) and therefore its fluxes to the atmosphere (DMSflux); second, an increase in the atmospheric cloud condensation nuclei (CCN) burden as a consequence of DMS oxidation to form biogenic CCN (CCNbio); and third, an increase in cloud albedo due to higher CCN numbers. Monthly global climatological fields of the solar radiation dose in the upper mixed layer (SRD), surface oceanic DMSw, model outputs of hydroxyl radical concentrations (OH), and satellite-derived CCN numbers (CCNs )a re analyzed in order to evaluate the proposed ‘‘solar radiation dose-DMS-CCN’’ link from a global point of view. OH is included as the main atmospheric oxidant of the estimated DMSflux to produce CCNbio. Global maps of seasonal correlations between the variables show that the solar radiation dose is highly (positively) correlated with seawater dimethylsulfide over most of the global ocean and that atmospheric DMS oxidation is highly (positively) correlated with CCNs over large regions. These couplings are stronger at high latitudes, whereas the regions with negative or no correlation are located at low latitudes around the equator. However, CCNbio estimates for 15 regions of the global ocean show that DMS oxidation can be an important contributor to the CCNs burden only over pollution-free regions, while it would have a minor contribution over regions with high loads of continental aerosols. Globally, the mean annual contribution of CCNbio to total CCNs is estimated to be � 30%. Our results support that an oceanic biogenic mechanism that modulates cloud formation and albedo can indeed occur, although its impact seems rather weak over regions under a strong influence of continental aerosols. Nevertheless, our approach does not fully rule out that the observed correlations are due to an independent seasonal variation of the studied variables; seasonal couplings are necessary but not sufficient conditions to prove the CLAW hypothesis.

Integrated modelling of Polycyclic Aromatic Hydrocarbons in the marine environment: Coupling of hydrodynamic, fate and transport, bioaccumulation and planktonic food-web models

Spatio-temporal variability of pollutants in the environment is a complex phenomenon that requires a combined approach for its analysis. Whereas data on measured levels of contaminants in various environmental compartments is essential, it is not always possible to monitor at the necessary frequency and with the adequate spatial sampling distribution to capture this variability. Therefore a modelling approach able to complement experimental data and close the gaps in the monitoring programs is useful for assessing the contaminant dynamics occurring at different time scales. In this work a 1D water column fate model has been developed and tested for Polycyclic Aromatic Hydrocarbons (PAHs). The model has been coupled with a simple ecological model that includes a bioaccumulation module. Afterwards, the model has been used to study the temporal variability of contaminant concentrations as well as the fluxes between compartments. The results evidence the complex coupling between spatio-temporal scales and its influence on environmental concentration levels.

Quantifying the importance of the atmospheric sink for polychlorinated dioxins and furans relative to other global loss processes

Previous attempts to establish global mass balances for polychlorinated dioxins and furans (PCDD/Fs) have focused on the terrestrial sink, thereby neglecting deposition to the oceans and atmospheric losses. In this study, the atmospheric sink of polychlorinated dioxins and furans (PCDD/Fs) was calculated on the basis of their presence in soils. OH radical ([OH]) depletion reactions compete with atmospheric deposition fluxes for the fate of atmospheric PCDD/Fs. Three different steady state scenarios were considered: scenario A was a one-box atmosphere with globally averaged [OH], temperature (T), atmospheric lifetime (tlife), and a constant gas-particle partitioning (Φ); in scenario B, [OH], T, and Φ were averaged in a multibox atmosphere, with a constant tlife; and in scenario C, tlife was varied. In scenario A the strength of the atmospheric sink was 2400–2800 kg/yr; in scenario B it was ∼2100 kg/yr; in scenario C, it was ∼1,800 kg/yr (tlife = 5.4 days) to ∼2,800 kg/yr (tlife = 14 days). The majority of the atmospheric sink was due to the depletion of Cl4DFs (1300–1400 kg/yr), followed by Cl4DDs (360–380 kg/yr) and Cl5DFs (230–240 kg/yr). On a global scale, major sinks for PCDD/Fs are the deposition to terrestrial soils and the oceans. For Cl6–8DDs, deposition to soils outweighs depletion reactions in the atmosphere and ocean uptake. The more volatile Cl4–5DD/Fs, however, are true “multimedia” compounds, with their estimated atmospheric sink being roughly as important as the terrestrial sink (in the case of Cl5DD/Fs) or outweighing it (e.g., Cl4DD/Fs).