Jordi Dachs

An updated climatology of surface dimethlysulfide concentrations and emission fluxes in the global ocean

[1] The potentially significant role of the biogenic trace gas dimethylsulfide (DMS) in determining the Earth’s radiation budget makes it necessary to accurately reproduce seawater DMS distribution and quantify its global flux across the sea/air interface. Following a threefold increase of data (from 15,000 to over 47,000) in the global surface ocean DMS database over the last decade, new global monthly climatologies of surface ocean DMS concentration and sea‐to‐air emission flux are presented as updates of those constructed 10 years ago. Interpolation/extrapolation techniques were applied to project the discrete concentration data onto a first guess field based on Longhurst’s biogeographic provinces. Further objective analysis allowed us to obtain the final monthly maps. The new climatology projects DMS concentrations typically in the range of 1–7 nM, with higher levels occurring in the high latitudes, and with a general trend toward increasing concentration in summer. The increased size and distribution of the observations in the DMS database have produced in the new climatology substantially lower DMS concentrations in the polar latitudes and generally higher DMS concentrations in regions that were severely undersampled 10 years ago, such as the southern Indian Ocean. Using the new DMS concentration climatology in conjunction with state‐of‐the‐art parameterizations for the sea/air gas transfer velocity and climatological wind fields, we estimate that 28.1 (17.6–34.4) Tg of sulfur are transferred from the oceans into the atmosphere annually in the form of DMS. This represents a global emission increase of 17% with respect to the equivalent calculation using the previous climatology. This new DMS climatology represents a valuable tool for atmospheric chemistry, climate, and Earth System models.

Mass budget and dynamics of polycyclic aromatic hydrocarbons in the Mediterranean Sea

A mass budget was constructed to examine the status and dynamics of polycyclic aromatic hydrocarbons (PAHs) in the western Mediterranean Sea. Using gas chromatography-mass spectrometry, 11 PAHs have been quantified in atmospheric aerosols, rivers and seawater, sediment cores and sediment trap samples. Total PAH concentrations in Mediterranean aerosols range from 0.2 to 2 ng m−3, with 50–70% associated with the sub-micron particles. Maximum PAH concentrations were observed in winter when the concentrations were double those recorded in the spring. Total PAH inputs from the atmosphere were estimated to be from 35 to 70 t year−1 with a mean value of 47.5 t year−1 (wet/dry mean ratio of ∼2–3). Atmospherically-deposited PAH are dominated by the benzofluoranthenes. The total PAH riverine inputs amount to about 5.3−33 t year−1 from the Rhone river and 1.3 t year−1 from the Ebro river. The difference in these riverine fluxes is due to differences in annual water discharges and upstream land use. The total PAH accumulation rate in surficial sediments in the whole basin is estimated at 182 t year−1. Nearly 50% of the total PAHs accumulate in the 0–200 m water depth area supporting the importance of the coastal zone as a trap of terrigenous material and associated contaminants. Sediment trap experiments gave a mean residence time in the water column of total PAH (considering only particle settling) of 11 years, with higher residence times for high molecular weight PAHs. This supports the hypothesis that lower molecular weight PAHs are more efficiently removed from the water column. Water exchange resulted in a net outflow of 20 t year−1 and 2 t year−1 through the Gibraltar and Sicilian Straits, respectively. Atmospheric deposition and the Rhone River are the major contributors of PAH in the western Mediterranean. Sedimentation was identified as the major net output of PAH.

Past, Present, and Future Controls on Levels of Persistent Organic Pollutants in the Global Environment

Understanding the legacy of persistent organic pollutants requires studying the transition from primary to secondary source control.

Aerosol inputs enhance new production in the subtropical northeast Atlantic

Received 21 November 2005; revised 13 May 2006; accepted 30 June 2006; published 10 November 2006. [1] Atmospheric deposition is an important source of limiting nutrients to the ocean, potentially stimulating oceanic biota. Atmospheric inputs can also deliver important amounts of organic matter, which may fuel heterotrophic activity in the ocean. The effect of atmospheric dry aerosol deposition on the metabolic balance and net production of planktonic communities remains unresolved. Here we report high inputs of aerosol-bound N, Si, P, Fe and organic C to the subtropical NE Atlantic and experimentally demonstrate these inputs to stimulate autotrophic abundance and metabolism far beyond the modest stimulation of heterotrophic processes, thereby enhancing new production. Aerosol dry deposition was threefold to tenfold higher in the coastal ocean than in the open ocean, and supplied high average (±SE) inputs of organic C (980 ± 220 mmol C m 2 d 1 ), total N (280 ± 70 mmol N m 2 d 1 ), Si (211 ± 39 mmol Si m 2 d 1 ), and labile Fe (1.01 ± 0.19 mmol Fe m 2 d 1 ), but low amounts of total P (8 ± 1.6 mmol P m 2 d 1 ) to the region during the study. Experimental aerosol inputs to oceanic planktonic communities from the studied area resulted, at the highest doses applied, in a sharp increase in phytoplankton biomass (sevenfold) and production (tenfold) within 4 days, with the community shifting from a dominance of picocyanobacteria to one of diatoms. In contrast, bacterial abundance and production showed little response. Primary production showed a much greater increase in response to aerosol inputs than community respiration did, so that the P/R ratio increased from around 0.95 in the ambient waters, where communities were close to metabolic balance, to 3.3 at the highest nutrient inputs, indicative of a high excess production and a potential for substantial net CO2 removal by the community in response to aerosol inputs. These results showed that aerosol inputs are major vectors of nutrient and carbon inputs, which can, during high depositional events, enhance new production in the NE subtropical Atlantic Ocean.

Vertical fluxes of polycyclic aromatic hydrocarbons and organochlorine compounds in the western Alboran Sea (southwestern Mediterranean)

Time-series samples of sinking particles were collected in the Alboran Sea with sediment traps moored at three water column depths (250, 500 and 750 m) between February and May 1992. The samples were analyzed for individual polychlorobiphenyl congeners (i.e. PCBs IUPAC no.: 28, 52, 101, 118, 153, 138 and 180), chlorinated pesticides (DDE and Lindane) and individual polycyclic aromatic hydrocarbons (PAHs; 3–6 aromatic rings). Average concentrations of PCB and total PAHs were 78.9 ng g− (range: 27.3–212) as Clophen A40 equivalents and 1176 ng g− (range: 104–2780), respectively. The 1,1-dichloro-2,2-bis(p-chlorophenyl)ethene (4,4′-DDE) and 1,2,3,4,5,6-hexachlorocyclohexane (γ-HCH) were the only chlorinated pesticides identified throughout the sampling period, with respective concentrations of 6.6 ng g− (range 1.1–15) and 16.8 ng g− (range 5.4–48). Corresponding fluxes of PCBs (as Clophen A40 equivalents) and PAHs were 15.1 ng m−2 d−1 (range: 6.9–24.9) and 225 ng m−2 d−1 (range: 15–625). Contaminant fluxes were analyzed with other collective fluxes obtained from the same samples (i.e. fecal pellets, mass and organic carbon); while higher molecular weight PAHs (MW > 228 daltons) exhibited a strong correlation with the mass fluxes (r2 = 90.7%, p < 0.001, n = 18), the lower molecular weight compounds (MW < 202 daltons) covaried with organic carbon and fecal pellet fluxes (r2 = 76.4%, p < 0.001, n = 18). The ΣPCB fluxes covaried with organic carbon, and fecal pellet fluxes and depth (r2 = 97.6%, p < 0.001, n = 9). The 4,4′-DDE only covaried with fluxes of organic carbon (r2 = 85.87%, p < 0.001) and γ-HCH with the fecal pellets fluxes and depth (r2 = 85.2% and p = 0.001, n = 9). Comparison with similar data from the northwestern Mediterranean and other oceans suggests that the Alboran Sea is a relatively clean environment primarily due to its relative remoteness from input terrigenous sources.

PCBs in the western Mediterranean. Temporal trends and mass balance assessment

Comparison of data reported for polychlorinated biphenyl (PCB) concentrations in different environmental compartments of the western Mediterranean (dissolved and particulate phases of water, sediment and biota) over the last two decades shows a substantial decline in PCB concentrations, which coincides with legislated restrictions in the use of these compounds. Nevertheless, localised chronic (“hotspot”) contamination continues, which underscores the importance of these compounds as environmental contaminants in certain specific areas of the region. Data on depositional fluxes are used to estimate and model transport processes to investigate the fate of these chemicals in the study area. A tentative mass balance of the compounds suggests that dry and wet deposition (12 t year−1) account for most of the input. This comparess with approximately 1 t year−1 discharged from rivers and sewage outfalls into coastal environments. Sedimentation is estimated to remove 5 t year−1 from the water column. Losses through volatilization are difficult to model owing to the critical dependance within calculations on atmospheric and dissolved seawater concentrations, for which very few data exist.

Biological Pump Control of the Fate and Distribution of Hydrophobic Organic Pollutants in Water and Plankton

The goal of this study was to experimentally assess the coupling between primary producer biomass dynamics and the distribution and fate of persistent organic pollutants (POPs) in a lake pelagic ecosystem. This was done by following the short-term evolution of polychlorinated biphenyl (PCB) concentrations in water and biota (phytoplankton and zooplankton) and the variability of bioconcentration (BCF), biomagnification (BMF), and bioaccumulation (BAF) factors during the development of a typical spring ecological progression in which the phytoplankton bloom is followed by a peak in the zooplankton abundance. The bulk of compounds with log K(OW) > 6.5 in the lake epilimnion was mainly associated with primary producer biomass. The phytoplankton biological pump was a major driver of POP export from the epilimnion, causing the decline of dissolved-phase concentrations. The BCF of phytoplankton for the more hydrophobic PCBs showed minima during the period of biomass climax. The concentration in the zooplankton of all selected PCBs sharply declined from March to May, with BAFs having minima in the post algal bloom phase. Biomagnification occurred during the pre algal bloom and algal bloom phases but appeared to be absent during the post algal bloom. This study highlights the occurrence of a prompt and complex response in the fate and distribution of POPs to dynamic biogeochemical control. Within the frame of the ecological succession, phytoplankton and zooplankton biomass dynamics produced bioaccumulation metrics varying over 1-2 orders of magnitude in the time frame of a few weeks and resulted in reduced trophic web exposure.

Polycyclic aromatic hydrocarbons (PAHs) in the Mediterranean Sea: Atmospheric occurrence, deposition and decoupling with settling fluxes in the water column

∑(30)PAH gas phase concentrations (13-86 and 22-40 ng m(-3) in the Mediterranean and Black Seas, respectively) dominated the atmospheric levels due to the high contribution of phenanthrene, dibenzothiophene and their alkylated derivates. The high variability of PAH atmospheric concentrations in the different sub-basins is due to several factors (i.e. air-mass trajectory, proximity to sources and losses by deposition). The ∑(30)PAH atmospheric deposition (dominated by low MW PAH net air-water diffusive fluxes) is estimated to be ~3100 ton y(-1) (Mediterranean) and ~500 ton y(-1) (Black Sea). Net volatilization for certain PAHs was estimated. Deposition fluxes (1-2 orders of magnitude higher than reported PAH settling fluxes in the water column) confirm an important depletion/sink of water column PAH in the photic zone, especially for low MW PAHs. Degradation processes in the water column may be responsible for this decoupling. Conversely, high MW PAHs dry deposition fluxes are similar to their settling fluxes.

Persistent Organic Pollutants in Mediterranean Seawater and Processes Affecting their Accumulation in Plankton

The Mediterranean and Black Seas are unique marine environments subject to important anthropogenic pressures due to riverine and atmospheric inputs of organic pollutants. Here, we report the results obtained during two east-west sampling cruises in June 2006 and May 2007 from Barcelona to Istanbul and Alexandria, respectively, where water and plankton samples were collected simultaneously. Both matrixes were analyzed for hexaclorochyclohexanes (HCHs), hexachlorobenzene (HCB), and 41 polychlorinated biphenyl (PCB) congeners. The comparison of the measured HCB and HCHs concentrations with previously reported dissolved phase concentrations suggests a temporal decline in their concentrations since the 1990s. On the contrary, PCB seawater concentrations did not exhibit such a decline, but show a significant spatial variability in dissolved concentrations with lower levels in the open Western and South Eastern Mediterranean, and higher concentrations in the Black, Marmara, and Aegean Seas and Sicilian Strait. PCB and OCPs (organochlorine pesticides) concentrations in plankton were higher at lower plankton biomass, but the intensity of this trend depended on the compound hydrophobicity (K(OW)). For the more persistent PCBs and HCB, the observed dependence of POP concentrations in plankton versus biomass can be explained by interactions between air-water exchange, particle settling, and/or bioaccumulation processes, whereas degradation processes occurring in the photic zone drive the trends shown by the more labile HCHs. The results presented here provide clear evidence of the important physical and biogeochemical controls on POP occurrence in the marine environment.

Ubiquitous Net Volatilization of Polycyclic Aromatic Hydrocarbons from Soils and Parameters Influencing Their Soil−Air Partitioning

Soils are a major reservoir of organic pollutants, and soil-air partitioning and exchange are key processes controlling the regional fate of pollutants. Here, we report and discuss the soil concentrations of polycyclic aromatic hydrocarbons (PAHs), their soil fugacities, the soil-air partition coefficients (K(SA)) and soil-air gradients for rural and semirural soils, in background areas of N-NE Spain and N-NW England. Different sampling campaigns were carried out to assess seasonal variability and differences between sampling sites. K(SA) values were dependent on soil temperature and soil organic quantity and type. Soil fugacities of phenanthrene and its alkyl homologues were 1-2 orders of magnitude higher than their ambient air fugacities for all sampling sites and periods. The soil to air fugacity ratio was correlated with soil temperature and soil redox potential. Similar trends for other PAHs were found but with lower fugacity ratios. The ubiquitous source of PAHs from background soils to the atmosphere found in all temperate regions in different seasons provides an indirect evidence of potential in situ generation of two to four ring PAHs and their alkyl homologues in the surface soil. We discuss this hypothetical biogenic source and other potential processes that could drive the high soil to air fugacity ratios of some PAHs.