Production of atmospheric sulfur by oceanic plankton: biogeochemical, ecological and evolutionary links

Biological production of the volatile compound dimethylsulfide in the ocean is the main natural source of tropospheric sulfur on a global scale, with important consequences for the radiative balance of the Earth. In the late 1980s, a Gaian feedback link between marine phytoplankton and climate through the release of atmospheric sulfur was hypothesized. However, the idea of microalgae producing a substance that could regulate climate has been criticized on the basis of its evolutionary feasibility. Recent advances have shown that volatile sulfur is a result of ecological interactions and transformation processes through planktonic food webs. It is, therefore, not only phytoplankton biomass, taxonomy or activity, but also food-web structure and dynamics that drive the oceanic production of atmospheric sulfur. Accordingly, the viewpoint on the ecological and evolutionary basis of this amazing marine biota-atmosphere link is changing.

Linking the composition of bacterioplankton to rapid turnover of dissolved dimethylsulphoniopropionate in an algal bloom in the North Sea

The algal osmolyte, dimethylsulphoniopropionate (DMSP), is abundant in the surface oceans and is the major precursor of dimethyl sulphide (DMS), a gas involved in global climate regulation. Here, we report results from an in situ Lagrangian study that suggests a link between the microbially driven fluxes of dissolved DMSP (DMSPd) and specific members of the bacterioplankton community in a North Sea coccolithophore bloom. The bacterial population in the bloom was dominated by a single species related to the genus Roseobacter, which accounted for 24% of the bacterioplankton numbers and up to 50% of the biomass. The abundance of the Roseobacter cells showed significant paired correlation with DMSPd consumption and bacterioplankton production, whereas abundances of other bacteria did not. Consumed DMSPd (28 nM day(-1)) contributed 95% of the sulphur and up to 15% of the carbon demand of the total bacterial populations, suggesting the importance of DMSP as a substrate for the Roseobacter-dominated bacterioplankton. In dominating DMSPd flux, the Roseobacter species may exert a major control on DMS production. DMSPd turnover rate was 10 times that of DMS (2.7 nM day(-1)), indicating that DMSPd was probably the major source of DMS, but that most of the DMSPd was metabolized without DMS production. Our study suggests that single species of bacterioplankton may at times be important in metabolizing DMSP and regulating the generation of DMS in the sea.

Characterization of novel di- and tricarboxylic acids in fine tropical aerosols

Three unknown di- and tricarboxylic acids were characterized in the fine size fraction of aerosols which were collected during the wet season in the Amazon basin (Rondonia, Brazil). For the structural characterization of the methyl esters of these unknown compounds, mass spectrometry with electron ionization (EI) and tandem mass spectral techniques combined with gas chromatographic (GC) separation were employed. Fragment and parent ion spectra were recorded during elution of the GC peaks by linked scanning of the B and E sectors in combination with high-energy collision-induced dissociation. The fragmentation patterns of significant ions in the first-order EI spectra were also obtained for nonanedioic acid, which was examined as a model compound. The compounds were tentatively identified as 4-acetyloxyheptanedioic acid and cis and trans isomers of 5-hexene-1,1,6-tricarboxylic acid. Since there were indications of biomass burning during the aerosol sampling the di- and tricarboxylic acids characterized in the present work could be markers for biomass burning. Furthermore, the characterization of di- and tricarboxylic acids in the fine size fraction of atmospheric aerosols may be important for assessing the effects of organic aerosols in cloud formation.

Structural elucidation of monoterpene oxidation products by ion trap fragmentation using on-line atmospheric pressure chemical ionisation mass spectrometry in the negative ion mode

Based on ion trap mass spectrometry, an on-line method is described which provides valuable information on the molecular composition of structurally complex organic aerosols. The investigated aerosols were generated from the gas-phase ozonolysis of various C(10)H(16)-terpenes (alpha-pinene, beta-pinene, 3-carene, sabinene, limonene), and directly introduced into the ion source of the mass spectrometer. Negative ion chemical ionisation at atmospheric pressure (APCI(-)) enabled the detection of multifunctional carboxylic acid products by combining inherent sensitivity and molecular weight information. Sequential low-energy collision-induced product ion fragmentation experiments (MS(n)) were performed in order to elucidate characteristic decomposition pathways of the compounds. Dicarboxylic acids, oxocarboxylic acids and hydroxyketocarboxylic acid products could be clearly distinguished by multistage on-line MS. Furthermore, sabinonic acid and two C(9)-ether compounds were tentatively identified for the first time by applying on-line APCI(-)-MS(n).

Ecological significance of compatible solute accumulation by micro-organisms: from single cells to global climate

The osmoadaptation of most micro-organisms involves the accumulation of K(+) ions and one or more of a restricted range of low molecular mass organic solutes, collectively termed 'compatible solutes'. These solutes are accumulated to high intracellular concentrations, in order to balance the osmotic pressure of the growth medium and maintain cell turgor pressure, which provides the driving force for cell extension growth. In this review, I discuss the alternative roles which compatible solutes may also play as intracellular reserves of carbon, energy and nitrogen, and as more general stress metabolites involved in protection of cells against other environmental stresses including heat, desiccation and freezing. Thus, the evolutionary selection for the accumulation of a specific compatible solute may not depend solely upon its function during osmoadaptation, but also upon the secondary benefits its accumulation provides, such as increased tolerance of other environmental stresses prevalent in the organism's niche or even anti-herbivory or dispersal functions in the case of dimethylsulfoniopropionate (DMSP). In the second part of the review, I discuss the ecological consequences of the release of compatible solutes to the environment, where they can provide sources of compatible solutes, carbon, nitrogen and energy for other members of the micro-flora. Finally, at the global scale the metabolism of specific compatible solutes (betaines and DMSP) in brackish water, marine and hypersaline environments may influence global climate, due to the production of the trace gases, methane and dimethylsulfide (DMS) and in the case of DMS, also couple the marine and terrestrial sulfur cycles.

On-line characterization of organic aerosols formed from biogenic precursors using atmospheric pressure chemical ionization mass spectrometry

A method to investigate the chemical composition of organic aerosols formed from biogenic hydrocarbon oxidation using atmospheric pressure chemical ionization mass spectrometry (APCI/MS) is described. The method involves the direct introduction of aerosol particles into the ion source of the mass spectrometer. Using this technique, reaction monitoring experiments of alpha-pinene ozonolysis show the formation of hetero- and homomolecular cluster anions (dimers) of the primary oxidation products (multifunctional carboxylic acids). Since the formation of dimers plays a profound role in new particle formation processes by homogeneous nucleation in the atmosphere and, at the same time, is an intrinsic feature of APCI, it is essential to differentiate between both processes when on-line APCI/MS is applied. In this paper, we compare the results from the investigations of organic aerosols and artificially generated dimer cluster ions of the same compounds using identical ionization conditions. The clusters and their formation processes are characterized by varying the analyte concentration, investigating the thermal stability of dimers, and studying collisional activation properties of both ion species. The investigations show a significant difference in ion stability: dimer anions measured on-line have an estimated stability that is 20 kJ mol(-1) higher than that of the corresponding artificially generated cluster ions. Hence, the technique provides the possibility to accurately characterize dimers as ionized reaction products from biogenic hydrocarbon oxidation and allows an insight into the process of new-particle formation by homogeneous nucleation.

Seasonal patterns of terpene content and emission from seven Mediterranean woody species in field conditions

The seasonal pattern of terpene content and emission by seven Mediterranean woody species was studied under field conditions. Emission rates were normalized at 30°C and 1000 μmol·m·s PFD (photosynthetic photon flux density). Bupleurum fruticosum, Pinus halepensis, and Cistus albidus stored large amounts of terpenes (0.01-1.77% [dry matter]) with maximum values in autumn and minimum values in spring. They emitted large amounts of terpenes (2-40 μg·g DM·h), but with no clear seasonal trend except for Cistus albidus, which had maximum values in spring and minimum values in autumn. The nonstoring species Arbutus unedo, Erica arborea, Quercus coccifera and Quercus ilex also emitted large amounts of terpenes (0-40 μg·g DM·h) and also tended to present maximum emission rates in spring, although this trend was significant only for A. unedo. At the seasonal scale, emission rates did not follow changes in photosynthetic rates; instead, they mostly followed changes in temperature. From autumn to spring, the least volatile monoterpenes such as limonene were emitted at highest rates, whereas the most volatile monoterpenes such as α-pinene and β-pinene were the most emitted in summer. The monoterpene emission rates represented a greater percentage of the photosynthetic carbon fixation in summer (from 0.51% in Arbutus unedo to 5.64% in Quercus coccifera) than in the rest of the seasons. All these seasonality trends must be considered when inventorying and modeling annual emission rates in Mediterranean ecosystems.

Airborne minerals and related aerosol particles: effects on climate and the environment

Aerosol particles are ubiquitous in the troposphere and exert an important influence on global climate and the environment. They affect climate through scattering, transmission, and absorption of radiation as well as by acting as nuclei for cloud formation. A significant fraction of the aerosol particle burden consists of minerals, and most of the remainder- whether natural or anthropogenic-consists of materials that can be studied by the same methods as are used for fine-grained minerals. Our emphasis is on the study and character of the individual particles. Sulfate particles are the main cooling agents among aerosols; we found that in the remote oceanic atmosphere a significant fraction is aggregated with soot, a material that can diminish the cooling effect of sulfate. Our results suggest oxidization of SO2 may have occurred on soot surfaces, implying that even in the remote marine troposphere soot provided nuclei for heterogeneous sulfate formation. Sea salt is the dominant aerosol species (by mass) above the oceans. In addition to being important light scatterers and contributors to cloud condensation nuclei, sea-salt particles also provide large surface areas for heterogeneous atmospheric reactions. Minerals comprise the dominant mass fraction of the atmospheric aerosol burden. As all geologists know, they are a highly heterogeneous mixture. However, among atmospheric scientists they are commonly treated as a fairly uniform group, and one whose interaction with radiation is widely assumed to be unpredictable. Given their abundances, large total surface areas, and reactivities, their role in influencing climate will require increased attention as climate models are refined.

Gaia and natural selection

Evidence indicates that the Earth self-regulates at a state that is tolerated by life, but why should the organisms that leave the most descendants be the ones that contribute to regulating their planetary environment? The evolving Gaia theory focuses on the feedback mechanisms, stemming from naturally selected traits of organisms, that could generate such self-regulation.

Nutrient Biogeochemistry of the Coastal Zone

The coastal seas are one of the most valuable and vulnerable of Earth's habitats. Significant inputs of nutrients to the coastal zone arrive via rivers, groundwater, and the atmosphere. Nutrient fluxes through these routes have been increased by human activity. In addition, the N:P:Si ratios of these inputs have been perturbed, and many coastal management practices exacerbate these perturbations. There is evidence of impacts arising from these changes (in phytoplankton numbers and relative species abundance, and deep-water oxygen declines) in areas of restricted water exchange. Elsewhere, the nutrient fluxes through the coastal zone appear to be still dominated by large inputs from the open ocean, and there is little evidence of anthropogenic perturbations.