Oliver Wurl

A marine biogenic source of atmospheric ice-nucleating particles

The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice. Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea–air interface or sea surface microlayer. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.

Practical guidelines for the analysis of seawater

Sampling and Sample Treatments, O. Wurl Analysis of Dissolved and Particulate Organic Carbon with the HTCO Technique, O. Wurl and T.M. Sin Spectrophotometric and Chromatographic Analysis of Carbohydrates in Marine Samples, C. Panagiotopoulos and O. Wurl The Analysis of Amino Acids in Seawater, T. Dittmar, J. Cherrier, and K.-U. Ludwichowski Optical Analysis of Chromophoric Dissolved Organic Matter, N.B. Nelson and P.G. Coble Isotope Composition of Organic Matter in Seawater, L. Guo and M.-Y. Sun Determination of Marine Gel Particles, A. Engel Nutrients in Seawater Using Segmented Flow Analysis, A. Aminot, R. Kerouel, and S.C. Coverly Dissolved Organic and Particulate Nitrogen and Phosphorous, G. Kattner Pigment Applications in Aquatic Systems, K.H. Wiltshire Determination of DMS, DMSP, and DMSO in Seawater, J. Stefels Determination of Iron in Seawater, A.R. Bowie and M.C. Lohan Radionuclide Analysis in Seawater, M. Baskaran, G.-H. Hong, and P.H. Santschi Sampling and Measurements of Trace Metals in Seawater, S.G. Sander, K. Hunter, and R. Frew Trace Analysis of Selected Persistent Organic Pollutants in Seawater, O. Wurl Pharmaceutical Compounds in Estuarine and Coastal Waters, J.L. Zhou and Z. Zhang Appendix A: First Aid for Common Problems with Typical Analytical Instruments Appendix B: Chemical Compatibilities and Physical Properties of Various Materials Appendix C: Water Purification Technologies Index

Flow system device for the on-line determination of total mercury in seawater

The instrumental set-up for the on-line sampling, digestion and quantification of total mercury in seawater is described. Based on a flow system and cold vapour atomic absorption spectrometry (CVAAS) detection limit was improved by a gold amalgam preconcentration to 0.5 ng l(-1). The manifold design was optimized by the variation of the gas flow, length of reaction coils, shape and material of the gas-liquid separator and flow rate of the reductant. A calibration following the equations p=0.039c+0.0813 (p, peak area; c, concentration) and a correlation coefficient of r=0.9996 was obtained. The relative standard deviation of three measurements of 0.5 ng l(-1) Hg(2+) was 3.8%. The long-time (12 h) reproducibility was 6.2% RSD (n=25) of 0.5 ng l(-1) Hg(2+). With a recovery rate >90% mercury can be determined after on-line UV digestion. For a complete analysis, 6 min is required. The technique is fast, simple to handle and robust. The apparatus is designed for the use on research vessels under sea conditions.

Sea Surface Scanner (S3): A Catamaran for High-Resolution Measurements of Biogeochemical Properties of the Sea Surface Microlayer

AbstractThis paper describes a state-of-the-art research catamaran to investigate processes such as air–sea gas exchange, heat exchange, surface blooms, and photochemistry at the sea surface microlayer (SML) with high-resolution measurements of 0.1-Hz frequency. As the boundary layer between the ocean and the atmosphere, the SML covers 70% of Earth. The remote-controlled Sea Surface Scanner is based on a glass disk sampler to automate the sampling of the thin SML, overcoming the disadvantages of techniques such as low volume sampling and ex situ measurement of the SML. A suite of in situ sensors for seven biogeochemical parameters (temperature, pH, dissolved oxygen, salinity, chromophoric dissolved organic matter, chlorophyll-a, and photosynthetic efficiency) was implemented to characterize the SML in reference to the mixed bulk water. The Sea Surface Scanner has the capability to collect 24 discrete water samples with a volume of 1 L each for further laboratory analysis. Meteorological parameters such as...

High wind speeds prevent formation of a distinct bacterioneuston community in the sea-surface microlayer

Abstract The sea-surface microlayer (SML) at the boundary between atmosphere and hydrosphere represents a demanding habitat for bacteria. Wind speed is a crucial but poorly studied factor for its physical integrity. Increasing atmospheric burden of CO2, as suggested for future climate scenarios, may particularly act on this habitat at the air–sea interface. We investigated the effect of increasing wind speeds and different pCO2 levels on SML microbial communities in a wind-wave tunnel, which offered the advantage of low spatial and temporal variability. We found that enrichment of bacteria in the SML occurred solely at a U10 wind speed of ≤5.6 m s−1 in the tunnel and ≤4.1 m s−1 in the Baltic Sea. High pCO2 levels further intensified the bacterial enrichment in the SML during low wind speed. In addition, low wind speed and pCO2 induced the formation of a distinctive bacterial community as revealed by 16S rRNA gene fingerprints and influenced the presence or absence of individual taxonomic units within the SML. We conclude that physical stability of the SML below a system-specific wind speed threshold induces specific bacterial communities in the SML entailing strong implications for ecosystem functioning by wind-driven impacts on habitat properties, gas exchange and matter cycling processes.

Extracellular carbonic anhydrase: Method development and its application to natural seawater

Abstract We developed an effective fluorometric technique to quantify extracellular carbonic anhydrase (eCA) present in natural seawater samples. The technique includes the separation of eCA from cells to achieve low detection limits through high signal : noise ratios. eCA was efficiently extracted from cell membranes by treatment with 0.1 M phosphate buffer containing 2.5 M NaCl. The free eCA specifically forms a fluorescent complex with dansylamide, and the detection limit of the complex is below 0.1 nM. We applied the technique to samples from different culture solutions and natural seawater collected from the Baltic Sea. We observed eCA concentrations to be in the range of 0.10–0.67 nM in natural seawater. The data indicated that this technique is very sensitive, accurate, and feasible for routine and shipboard measurement of eCA from natural seawater. It is therefore an effective and rapid tool to investigate the carbon acquisition of phytoplankton both in mono culture as well natural communities.

Chapter 15 Persistent Organic Pollutants in Singapore's Marine Environment

Abstract Singapore is one of the busiest ports in the world and has many shipyards, petroleum refineries and pharmaceutical manufacturing plants are located on its coastline. Data on the prevalence of persistent organic pollutants (POPs) in Singapores coastal ecosystems are therefore important in order to support research on the potential threats to the local marine environment and human health. This chapter presents data on the prevalence of POPs in the seawater, sediments, biota and mangrove habitats of Singapore. Data are presented for a range of POPs including polycyclic aromatic hydrocarbons (PAHs), organochlorine compounds (OCPs), polychlorinated biphenyls and polybrominated diphenyl ethers (PBDEs). Local studies confirm the ubiquity of POPs in the marine environment of Singapore. The prevailing ocean currents in the region govern the fate and transport of POPs in coastal waters, where the presence of localized high levels of POPs is likely to be a function of local shipping and industrial discharges. Land reclamation activities may also be a factor in the prevalence of POPs in seawater, where compounds are released from sediments and transported to the water column by seabed dredging. The land area under agricultural use in Singapore is negligible, and there is no direct application of OCPs in the country. However, pesticides may be easily transported through the atmosphere following volatilization from soil, and the presence of OCPs in Singapores marine waters is likely to be a function of their use in neighbouring countries, with subsequent atmospheric transport and deposition. A biomagnification phenomenon was observed amongst the species collected and analysed from mangrove sites, but levels of POPs were not found to exceed relevant food safety standards. However, PCB concentrations in mangrove fish muscles were found to be higher than mean levels of PCBs found in seafood commonly consumed in Singapore. Overall, available data on the prevalence, fate and transfer of POPs in Singapores marine environment highlights the ubiquity of these pollutants, and supports the need for a greater awareness on their fate, transport and bioaccumulation in local ecosystems.

High-resolution observations on enrichment processes in the sea-surface microlayer

For decades, researchers assumed that enrichment of dissolved organic matter (DOM) in the sea surface microlayer (SML) is solely controlled by changes in the DOM concentration at this uppermost thin boundary layer between the ocean and the atmosphere. We conducted high-resolution observations of fluorescent-DOM (FDOM) at 13 stations in the coastal and open Atlantic Ocean to understand the enrichment processes. Results show that FDOM enrichment in the SML varied between 0.8 and 2.0 (in comparison to the concentrations in the underlying water; ULW), and FDOM enrichment is a common feature of the SML despite the varied distances to the terrestrial sources. At six stations, the FDOM concentration in the SML was less variable over the sampling period (>5 h) compared to FDOM concentrations in the ULW characterized with sudden changes. Even so we observed slightly lower enrichments with increasing wind speeds and solar radiation, changes in ULW concentrations forced the enrichment to change. In addition, we found evidences for the occurrence of photochemical degradation of FDOM in near-shore SML with implications on coastal carbon cycling. Overall, the results show that the processes leading to the enrichment of DOM in the SML are more complex than previously assumed. Given the importance of the organic-rich SML as a diffusion layer in the air–sea exchange of climate-relevant gases and heat, understanding the layer’s enrichment processes is crucial.

Warming and Inhibition of Salinization at the Ocean's Surface by Cyanobacteria

Abstract This paper describes high‐resolution in situ observations of temperature and, for the first time, of salinity in the uppermost skin layer of the ocean, including the influence of large surface blooms of cyanobacteria on those skin properties. In the presence of the blooms, large anomalies of skin temperature and salinity of 0.95°C and −0.49 practical salinity unit were found, but a substantially cooler (−0.22°C) and saltier skin layer (0.19 practical salinity unit) was found in the absence of surface blooms. The results suggest that biologically controlled warming and inhibition of salinization of the oceans surface occur. Less saline skin layers form during precipitation, but our observations also show that surface blooms of Trichodesmium sp. inhibit evaporation decreasing the salinity at the oceans surface. This study has important implications in the assessment of precipitation over the ocean using remotely sensed salinity, but also for a better understanding of heat exchange and the hydrologic cycle on a regional scale.

Enrichment of Extracellular Carbonic Anhydrase in the Sea Surface Microlayer and Its Effect on Air-Sea CO2 Exchange: Enrichment of eCA in the SML

This paper describes the quantification of extracellular carbonic anhydrase (eCA) concentrations in the sea surface microlayer (SML), the boundary layer between the ocean and the atmosphere of the Indo-West Pacific. We demonstrated that the SML is enriched with eCA by 1.5 ± 0.7 compared to the mixed underlying water. Enrichment remains up to a wind speed of 7 m s 1 (i.e., under typical oceanic conditions). As eCA catalyzes the interconversion of HCO3 and CO2, it has been hypothesized that its enrichment in the SML enhances the air-sea CO2 exchange. We detected concentrations in the range of 0.12 to 0.76 nM, which can enhance the exchange by up to 15% based on the model approach described in the literature.