Detection and structural identification of dissolved organic matter in Antarctic glacial ice at natural abundance by SPR-W5-WATERGATE 1H NMR spectroscopy

Slice through the water-Exploring the fundamental challenge of water suppression for benchtop NMR systems

Benchtop NMR provides improved accessibility in terms of cost, space, and technical expertise. In turn, this encourages new users into the field of NMR spectroscopy. Unfortunately, many interesting samples in education and research, from beer to whole blood, contain significant amounts of water that require suppression in 1H NMR in order to recover sample information. However, due to the significant reduction in chemical shift dispersion in benchtop NMR systems, the sample signals are much closer to the water resonance compared to those in a corresponding high-field NMR spectrum. Therefore, simply translating solvent suppression experiments intended for high-field NMR instruments to benchtop NMR systems without careful consideration can be problematic. In this study, the effectiveness of several popular water suppression schemes was evaluated for benchtop NMR applications. Emphasis is placed on pulse sequences with no, or few, adjustable parameters making them easy to implement. These fall into two main categories: (1) those based on Pre-SAT including Pre-SAT, PURGE, NOESY-PR, and g-NOESY-PR and (2) those based on binomial inversion including JRS and W5-WATERGATE. Among these schemes, solvent suppression sequences based on Pre-SAT offer a general approach for easy solvent suppression for samples with higher analyte concentrations (sucrose standard and Redbull™). However, for human urine, binomial-like sequences were required. In summary, it is demonstrated that highly efficient water suppression approaches can be implemented on benchtop NMR systems in a simple manner, despite the limited spectral dispersion, further illustrating the potential for widespread implementation of these approaches in education and research.

HR-MAS DREAMTIME NMR for Slow Spinning ex Vivo and in Vivo Samples

HR-MAS NMR is a powerful tool, capable of monitoring molecular changes in intact heterogeneous samples. However, one of the biggest limitations of 1H NMR is its narrow spectral width which leads to considerable overlap in complex natural samples. DREAMTIME NMR is a highly selective technique that allows users to isolate suites of metabolites from congested spectra. This permits targeted metabolomics by NMR and is ideal for monitoring specific processes. To date, DREAMTIME has only been employed in solution-state NMR, here it is adapted for HR-MAS applications. At high spinning speeds (>5 kHz), DREAMTIME works with minimal modifications. However, spinning over 3-4 kHz leads to cell lysis, and if maintaining sample integrity is necessary, slower spinning (<2.5 kHz) is required. Very slow spinning (≤500 Hz) is advantageous for in vivo analysis to increase organism survival; however, sidebands from water pose a problem. To address this, a version of DREAMTIME, termed DREAMTIME-SLOWMAS, is introduced. Both techniques are compared at 2500, 500, and 50 Hz, using ex vivo worm tissue. Following this, DREAMTIME-SLOWMAS is applied to monitor key metabolites of anoxic stress in living shrimp at 500 Hz. Thus, standard DREAMTIME works well under MAS conditions and is recommended for samples reswollen in D2O or spun >2500 Hz. For slow spinning in vivo or intact tissue samples, DREAMTIME-SLOWMAS provides an excellent way to target process-specific metabolites while maintaining sample integrity. Overall, DREAMTIME should find widespread application wherever targeted molecular information is required from complex samples with a high degree of spectral overlap.

Ocean-atmosphere interactions: Different organic components across Pacific and Southern Oceans

Sea spray aerosol (SSA) particles strongly influence clouds and climate but the potential impact of ocean microbiota on SSA fluxes is still a matter of active research. Here-by means of in situ ship-borne measurements-we explore simultaneously molecular-level chemical properties of organic matter (OM) in oceans, sea ice, and the ambient PM_2.5 aerosols along a transect of 15,000 km from the western Pacific Ocean (36°13'N) to the Southern Ocean (75°15'S). By means of orbitrap mass spectrometry and optical characteristics, lignin-like material (24 ± 5 %) and humic material (57 ± 8 %) were found to dominate the pelagic Pacific Ocean surface, while intermediate conditions were observed in the Pacific-Southern Ocean waters. In the marine atmosphere, we found a gradient of features in the aerosol: lignin-like material (31 ± 9 %) dominating coastal areas and the pelagic Pacific Ocean, whereas lipid-like (23 ± 16 %) and protein-like (11 ± 10 %) OM controlled the sympagic Southern Ocean (sea ice-influence). The results of this study showed that the OM composition in the ocean, which changes with latitude, affects the OM in aerosol compositions in the atmosphere. This study highlights the importance of the global-scale OM monitoring of the close interaction between the ocean, sea ice, and the atmosphere. Sympagic primary marine aerosols in polar regions must be treated differently from other pelagic-type oceans.

Determinants of Microbial-Derived Dissolved Organic Matter Diversity in Antarctic Lakes

Identifying drivers of the molecular composition of dissolved organic matter (DOM) is essential to understand the global carbon cycle, but an unambiguous interpretation of observed patterns is challenging due to the presence of confounding factors that affect the DOM composition. Here, we show, by combining ultrahigh-resolution mass spectrometry and nuclear magnetic resonance spectroscopy, that the DOM molecular composition varies considerably among 43 lakes in East Antarctica that are isolated from terrestrial inputs and human influence. The DOM composition in these lakes is primarily driven by differences in the degree of photodegradation, sulfurization, and pH. Remarkable molecular beta-diversity of DOM was found that rivals the dissimilarity between DOM of rivers and the deep ocean, which was driven by environmental dissimilarity rather than the spatial distance. Our results emphasize that the extensive molecular diversity of DOM can arise even in one of the most pristine and organic matter source-limited environments on Earth, but at the same time the DOM composition is predictable by environmental variables and the lakes' ecological history.

Improved fractionation method using amphipathic NDAM for the efficient separation of disinfection by-product precursors in natural organic matter

The hydrophilic substances in natural organic matter (NOM) are the main precursor of disinfection by-products (DBPs) formed during disinfection processes. The fractionation of the components in NOM based on hydrophilicity contributes to elaborating the behavior of NOM during disinfection. However, the traditional NOM fractionation method using two hydrophobic resins of DAX-8 and XAD-4 lays emphasis on the separation of hydrophobic substances, limiting the thorough study of the hydrophilic components in NOM. In this work, the amphiphilic resin NDAM was employed as a replacement of XAD-4 to realize more thorough separation of the hydrophilic substances. Compared with the divinylbenzene (DVB) structure of XAD-4, the NDAM possesses a more hydrophilic skeleton of N-vinylpyrrolidone (NVP) and DVB which favors the adsorption of hydrophilic components in NOM. The two fractionation methods of DAX-8 + XAD-4 and DAX-8 + NDAM were applied to fractionate NOM, and the obtained fractions were characterized via fluorescence spectra, UV spectra, acid-base titration, the partition coefficients of aqueous two-phase systems(ATPs), and 1H nuclear magnetic resonance (1H-NMR). The results showed that the transphilic fractions separated by XAD-4 accounted for 11.09% of NOM, while the proportion increased to 20.33% with the method of NDAM fractionation. Besides, the hydrophilic components enriched by NDAM not only have more π-conjugated systems and more aromatic structure but also contain more oxygen-containing and nitrogen-containing functional groups. In addition, the hydrophilic fractions separated by NDAM contained more DBP precursors. The NDAM separates more NOM which can produce bromine-containing DBPs into HPIA, and the DBP productivity of HPIN is significantly higher than that of XAD-4. In general, the NOM fractionation method proposed in this study utilizing NDAM resin could fractionate the hydrophilic fractions in NOM more thoroughly, showing application potential in the analysis and control of DBPs formed from NOM.

NMR spectroscopy of wastewater: A review, case study, and future potential

NMR spectroscopy is arguably the most powerful tool for the study of molecular structures and interactions, and is increasingly being applied to environmental research, such as the study of wastewater. With over 97% of the planet's water being saltwater, and two thirds of freshwater being frozen in the ice caps and glaciers, there is a significant need to maintain and reuse the remaining 1%, which is a precious resource, critical to the sustainability of most life on Earth. Sanitation and reutilization of wastewater is an important method of water conservation, especially in arid regions, making the understanding of wastewater itself, and of its treatment processes, a highly relevant area of environmental research. Here, the benefits, challenges and subtleties of using NMR spectroscopy for the analysis of wastewater are considered. First, the techniques available to overcome the specific challenges arising from the nature of wastewater (which is a complex and dilute matrix), including an examination of sample preparation and NMR techniques (such as solvent suppression), in both the solid and solution states, are discussed. Then, the arsenal of available NMR techniques for both structure elucidation (e.g., heteronuclear, multidimensional NMR, homonuclear scalar coupling-based experiments) and the study of intermolecular interactions (e.g., diffusion, nuclear Overhauser and saturation transfer-based techniques) in wastewater are examined. Examples of wastewater NMR studies from the literature are reviewed and potential areas for future research are identified. Organized by nucleus, this review includes the common heteronuclei (¹³C, ¹⁵N, ¹⁹F, ³¹P, ²⁹Si) as well as other environmentally relevant nuclei and metals such as ²⁷Al, ⁵¹V, ²⁰⁷Pb and ¹¹³Cd, among others. Further, the potential of additional NMR methods such as comprehensive multiphase NMR, NMR microscopy and hyphenated techniques (for example, LC-SPE-NMR-MS) for advancing the current understanding of wastewater are discussed. In addition, a case study that combines natural abundance (i.e. non-concentrated), targeted and non-targeted NMR to characterize wastewater, along with in vivo based NMR to understand its toxicity, is included. The study demonstrates that, when applied comprehensively, NMR can provide unique insights into not just the structure, but also potential impacts, of wastewater and wastewater treatment processes. Finally, low-field NMR, which holds considerable future potential for on-site wastewater monitoring, is briefly discussed. In summary, NMR spectroscopy is one of the most versatile tools in modern science, with abilities to study all phases (gases, liquids, gels and solids), chemical structures, interactions, interfaces, toxicity and much more. The authors hope this review will inspire more scientists to embrace NMR, given its huge potential for both wastewater analysis in particular and environmental research in general.

Dissolved Organic Matter Processing in Pristine Antarctic Streams

Accelerated glacier melt and runoff may lead to inputs of labile dissolved organic matter (DOM) to downstream ecosystems and stimulate the associated biogeochemical processes. However, still little is known about glacial DOM composition and its downstream processing before entering the ocean, although the function of DOM in food webs and ecosystems largely depends on its composition. Here, we employ a set of molecular and optical techniques (UV-vis absorption and fluorescence spectroscopy, ¹H NMR, and ultrahigh-resolution mass spectrometry) to elucidate the composition of DOM in Antarctic glacial streams and its downstream change. Glacial DOM consisted largely of a mixture of small microbial-derived biomolecules. ¹H NMR analysis of bulk water revealed that these small molecules were processed downstream into more complex, structurally unrecognizable molecules. The extent of processing varied between streams. By applying multivariate statistical (compositional data) analysis of the DOM molecular data, we identified molecular compounds that were tightly associated and moved in parallel in the glacial streams. Lakes in the middle of the flow paths enhanced water residence time and allowed for both more DOM processing and production. In conclusion, downstream processing of glacial DOM is substantial in Antarctica and affects the amounts of biologically labile substrates that enter the ocean.

Direct noninvasive 1 H NMR analysis of stream water DOM: Insights into the effects of lyophilization compared with whole water

NMR spectroscopy is widely used in the field of aquatic biogeochemistry to examine the chemical structure of dissolved organic matter (DOM). Most aquatic DOM analyzed by proton NMR (¹ H NMR) is concentrated mainly by freeze-drying prior to analysis to combat low concentrations, frequently <100 μM C, and eliminate interference from water. This study examines stream water with low dissolved organic carbon content by ¹ H NMR with a direct noninvasive analysis of whole water using a water-suppression technique. Surface waters, collected from the headwaters of the Rio Tempisquito, Costa Rica, were examined directly, and the spectral characteristics were compared with those of the traditional preanalysis freeze-drying approach revealing significant differences in the relative intensity of peaks between the whole water and freeze-dried DOM. The freeze-dried DOM required less time to obtain quality spectra, but several peaks were missing compared with the spectra of whole water DOM; notably the most dominant peak in the spectrum constituting roughly 10% of the DOM. The stream water DOM showed an increase in the relative intensity of aliphatic methyl and methylene groups and a decrease in carbonyl, carboxyl, and carbohydrate functionalities after freeze-drying. The results of this study show that freeze-drying alters the original composition of DOM and thus freeze-dried DOM may not represent the original DOM. The information gained from whole water analysis of stream water DOM in a noninvasive fashion outweighs the attraction of reduced analysis times for preconcentrated samples, particularly for studies interested in investigating the low molecular weight fraction of DOM.

High-Resolution Magic Angle Spinning (HR-MAS) NMR-Based Fingerprints Determination in the Medicinal Plant Berberis laurina

Berberis laurina (Berberidaceae) is a well-known medicinal plant used in traditional medicine since ancient times; however, it is scarcely studied to a large-scale fingerprint. This work presents a broad-range fingerprints determination through high-resolution magical angle spinning (HR-MAS) nuclear magnetic resonance (NMR) spectroscopy, a well-established flexible analytical method and one of most powerful "omics" platforms. It had been intended to describe a large range of chemical compositions in all plant parts. Beyond that, HR-MAS NMR allowed the direct investigation of botanical material (leaves, stems, and roots) in their natural, unaltered states, preventing molecular changes. The study revealed 17 metabolites, including caffeic acid, and berberine, a remarkable alkaloid from the genus Berberis L. The metabolic pattern changes of the leaves in the course of time were found to be seasonally dependent, probably due to the variability of seasonal and environmental trends. This metabolites overview is of great importance in understanding plant (bio)chemistry and mediating plant survival and is influenceable by interacting environmental means. Moreover, the study will be helpful in medicinal purposes, health sciences, crop evaluations, and genetic and biotechnological research.

Metabolic Profiling Using In Vivo High Field Flow NMR

In vivo NMR (nuclear magnetic resonance) has the potential to monitor and record metabolic flux in close to real time, which is essential for better understanding the toxic mode of action of a contaminant and deciphering complex interconnected stress-induced pathways impacted inside an organism. Here, we describe how to construct and use a simple flow system to keep small aquatic organisms alive inside the NMR spectrometer. In living organisms, magnetic susceptibility distortions lead to severe broadening in conventional NMR. Two main approaches can be employed to overcome this issue: (1) use a pulse sequence to reduce the distortions, or (2) employ multidimensional NMR in combination with isotopic enrichment to provide the spectral dispersion required to separate peaks from overlapping resonances. Both approaches are discussed, and protocols for both approaches are provided here in the context of small aquatic organisms.

Improvements in lipid suppression for 1 H NMR-based metabolomics: Applications to solution-state and HR-MAS NMR in natural and in vivo samples

Proton nuclear magnetic resonance (NMR) spectra of intact biological samples often show strong contributions from lipids, which overlap with signals of interest from small metabolites. Pioneering work by Diserens et al. demonstrated that the relative differences in diffusivity and relaxation of lipids versus small metabolites could be exploited to suppress lipid signals, in high-resolution magic angle spinning (HR-MAS) NMR spectroscopy. In solution-state NMR, suspended samples can exhibit very broad water signals, which are challenging to suppress. Here, improved water suppression is incorporated into the sequence, and the Carr-Purcell-Meiboom-Gill sequence (CPMG) train is replaced with a low-power adiabatic spinlock that reduces heating and spectral artefacts seen with longer CPMG filters. The result is a robust sequence that works well in both HR-MAS as well as static solution-state samples. Applications are also extended to include in vivo organisms. For solution-state NMR, samples containing significant amount of fats such as milk and hemp hearts seeds are used to demonstrate the technique. For HR-MAS, living earthworms (Eisenia fetida) and freshwater shrimp (Hyalella azteca) are used for in vivo applications. Lipid suppression techniques are essential for non-invasive NMR-based analysis of biological samples with a high-lipid content and adds to the suite of experiments advantageous for in vivo environmental metabolomics.

In-Vivo NMR Spectroscopy: A Powerful and Complimentary Tool for Understanding Environmental Toxicity

Part review, part perspective, this article examines the applications and potential of in-vivo Nuclear Magnetic Resonance (NMR) for understanding environmental toxicity. In-vivo NMR can be applied in high field NMR spectrometers using either magic angle spinning based approaches, or flow systems. Solution-state NMR in combination with a flow system provides a low stress approach to monitor dissolved metabolites, while magic angle spinning NMR allows the detection of all components (solutions, gels and solids), albeit with additional stress caused by the rapid sample spinning. With in-vivo NMR it is possible to use the same organisms for control and exposure studies (controls are the same organisms prior to exposure inside the NMR). As such individual variability can be reduced while continual data collection over time provides the temporal resolution required to discern complex interconnected response pathways. When multidimensional NMR is combined with isotopic labelling, a wide range of metabolites can be identified in-vivo providing a unique window into the living metabolome that is highly complementary to more traditional metabolomics studies employing extracts, tissues, or biofluids.

Environmental Nuclear Magnetic Resonance Spectroscopy: An Overview and a Primer

NMR spectroscopy is a versatile tool for the study of structure and interactions in environmental media such as air, soil, and water as well as monitoring the metabolic responses of living organisms to an ever changing environment. Part review, part perspective, and part tutorial, this Feature is aimed at nonspecialists who are interested in learning more about the potential and impact of NMR spectroscopy in environmental research.

Analysis of DOM phototransformation using a looped NMR system integrated with a sunlight simulator

Photochemical transformation plays an important role in functionalizing and degrading dissolved organic matter (DOM), producing one of the most complex mixtures known. In this study, using a flow-based design, nuclear magnetic resonance (NMR) spectroscopy is directly interfaced with a sunlight simulator enabling the study of DOM photodegradation in situ with high temporal resolution over 5 days. Samples from Suwannee River (Florida), Nordic Reservoir (Norway), and Pony Lake (Antarctic) are studied. Phototransformation of DOM is dominated by the degradation of aromatics and unsaturated structures (many arising from lignin) into carboxylated and hydroxylated products. To assess longer term changes, the samples were continuously irradiated for 17.5 days, followed by the identification a wide range of compounds and assessment of their fate using off-line 2D-NMR. This study demonstrates the applicability of the looped system to follow degradation in a non-targeted fashion (the mixture as a whole) and target analysis (tracing specific metabolites), which holds great potential to study the fate and transformation of contaminants and nutrients in the presence of DOM. It also demonstrates that components that remain unresolved in 1D NMR can be identified using 2D methods.

Molecular Insights on Dissolved Organic Matter Transformation by Supraglacial Microbial Communities

Snow overlays the majority of Antarctica and is an important repository of dissolved organic matter (DOM). DOM transformations by supraglacial microbes are not well understood. We use ultrahigh resolution mass spectrometry to elucidate molecular changes in snowpack DOM by in situ microbial processes (up to 55 days) in a coastal Antarctic site. Both autochthonous and allochthonous DOM is highly bioavailable and is transformed by resident microbial communities through parallel processes of degradation and synthesis. DOM thought to be of a more refractory nature, such as dissolved black carbon and carboxylic-rich alicyclic molecules, was also rapidly and extensively reworked. Microbially reworked DOM exhibits an increase in the number and magnitude of N-, S-, and P-containing formulas, is less oxygenated, and more aromatic when compared to the initial DOM. Shifts in the heteroatom composition suggest that microbial processes may be important in the cycling of not only C, but other elements such as N, S, and P. Microbial reworking also produces photoreactive compounds, with potential implications for DOM photochemistry. Refined measurements of supraglacial DOM and their cycling by microbes is critical for improving our understanding of supraglacial DOM cycling and the biogeochemical and ecological impacts of DOM export to downstream environments.

Comprehensive multiphase NMR applied to a living organism

Comprehensive multiphase (CMP) NMR is a novel technology that integrates all the hardware from solution-, gel- and solid-state into a single NMR probe, permitting all phases to be studied in intact samples. Here comprehensive multiphase (CMP) NMR is used to study all components in a living organism for the first time. This work describes 4 new scientific accomplishments summarized as: (1) CMP-NMR is applied to a living animal, (2) an effective method to deliver oxygen to the organisms is described which permits longer studies essential for in-depth NMR analysis in general, (3) a range of spectral editing approaches are applied to fully differentiate the various phases solutions (metabolites) through to solids (shell) (4) 13C isotopic labelling and multidimensional NMR are combined to provide detailed assignment of metabolites and structural components in vivo. While not explicitly studied here the multiphase capabilities of the technique offer future possibilities to study kinetic transfer between phases (e.g. nutrient assimilation, contaminant sequestration), molecular binding at interfaces (e.g. drug or contaminant binding) and bonding across and between phases (e.g. muscle to bone) in vivo. Future work will need to focus on decreasing the spinning speed to reduce organism stress during analysis.

Microbial communities associated with Antarctic snow pack and their biogeochemical implications

Snow ecosystems represent a large part of the Earth's biosphere and harbour diverse microbial communities. Despite our increased knowledge of snow microbial communities, the question remains as to their functional potential, particularly with respect to their role in adapting to and modifying the specific snow environment. In this work, we investigated the diversity and functional capabilities of microorganisms from 3 regions of East Antarctica, with respect to compounds present in snow and tested whether their functional signature reflected the snow environment. A diverse assemblage of bacteria (Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, Deinococcus-Thermus, Planctomycetes, Verrucomicrobia), archaea (Euryarchaeota), and eukarya (Basidiomycota, Ascomycota, Cryptomycota and Rhizaria) were detected through culture-dependent and -independent methods. Although microbial communities observed in the three snow samples were distinctly different, all isolates tested produced one or more of the following enzymes: lipase, protease, amylase, β-galactosidase, cellulase, and/or lignin modifying enzyme. This indicates that the snow pack microbes have the capacity to degrade organic compounds found in Antarctic snow (proteins, lipids, carbohydrates, lignin), thus highlighting their potential to be involved in snow chemistry.

Development of an in Situ NMR Photoreactor To Study Environmental Photochemistry

Photochemistry is a key environmental process directly linked to the fate, source, and toxicity of pollutants in the environment. This study explores two approaches for integrating light sources with nuclear magnetic resonance (NMR) spectroscopy: sample irradiation using a "sunlight simulator" outside the magnet versus direct irradiation of the sample inside the magnet. To assess their applicability, the in situ NMR photoreactors were applied to a series of environmental systems: an atmospheric pollutant (p-nitrophenol), crude oil extracts, and groundwater. The study successfully illustrates that environmentally relevant aqueous photochemical processes can be monitored in situ and in real time using NMR spectroscopy. A range of intermediates and degradation products were identified and matched to the literature. Preliminary measurements of half-lives were also obtained from kinetic curves. The sunlight simulator was shown to be the most suitable model to explore environmental photolytic processes in situ. Other light sources with more intense UV output hold potential for evaluating UV as a remediation alternative in areas such as wastewater treatment plants or oil spills. Finally, the ability to analyze the photolytic fate of trace chemicals at natural abundance in groundwater, using a cryogenic probe, demonstrates the viability of NMR spectroscopy as a powerful and complementary technique for environmental applications in general.

Non-targeted analyses of organic compounds in urban wastewater

A large number of organic pollutants that cause damage to the ecosystem and threaten human health are transported to wastewater treatment plants (WWTPs). The problems regarding water pollution in Latin America have been well documented, and there is no evidence of substantive efforts to change the situation. In the present work, two methods to study wastewater samples are employed: non-targeted 1D ((13)C and (1)H) and 2D NMR spectroscopic analysis to characterize the largest possible number of compounds from urban wastewater and analysis by HPLC-(UV/MS)-SPE-ASS-NMR to detect non-specific recalcitrant organic compounds in treated wastewater without the use of common standards. The set of data is composed of several compounds with the concentration ranging considerably with treatment and seasonality. An anomalous discharge, the influence of stormwater on the wastewater composition and the presence of recalcitrant compounds (linear alkylbenzene sulfonate surfactant homologs) in the effluent were further identified. The seasonal variations and abnormality in the composition of organic compounds in sewage indicated that the procedure that was employed can be useful in the identification of the pollution source and to enhance the effectiveness of WWTPs in designing preventive action to protect the equipment and preserve the environment.

Origin and sources of dissolved organic matter in snow on the East Antarctic ice sheet

Polar ice sheets hold a significant pool of the world's carbon reserve and are an integral component of the global carbon cycle. Yet, organic carbon composition and cycling in these systems is least understood. Here, we use ultrahigh resolution mass spectrometry to elucidate, at an unprecedented level, molecular details of dissolved organic matter (DOM) in Antarctic snow. Tens of thousands of distinct molecular species are identified, providing clues to the nature and sources of organic carbon in Antarctica. We show that many of the identified supraglacial organic matter formulas are consistent with material from microbial sources, and terrestrial inputs of vascular plant-derived materials are likely more important sources of organic carbon to Antarctica than previously thought. Black carbon-like material apparently originating from biomass burning in South America is also present, while a smaller fraction originated from soil humics and appears to be photochemically or microbially modified. In addition to remote continental sources, we document signals of oceanic emissions of primary aerosols and secondary organic aerosol precursors. The new insights on the diversity of organic species in Antarctic snowpack reinforce the importance of studying organic carbon associated with the Earth's polar regions in the face of changing climate.

Bio-organic materials in the atmosphere and snow: measurement and characterization

Bio-organic chemicals are ubiquitous in the Earth's atmosphere and at air-snow interfaces, as well as in aerosols and in clouds. It has been known for centuries that airborne biological matter plays various roles in the transmission of disease in humans and in ecosystems. The implication of chemical compounds of biological origins in cloud condensation and in ice nucleation processes has also been studied during the last few decades, and implications have been suggested in the reduction of visibility, in the influence on oxidative potential of the atmosphere and transformation of compounds in the atmosphere, in the formation of haze, change of snow-ice albedo, in agricultural processes, and bio-hazards and bio-terrorism. In this review we critically examine existing observation data on bio-organic compounds in the atmosphere and in snow. We also review both conventional and cutting-edge analytical techniques and methods for measurement and characterisation of bio-organic compounds and specifically for microbial communities, in the atmosphere and snow. We also explore the link between biological compounds and nucleation processes. Due to increased interest in decreasing emissions of carbon-containing compounds, we also briefly review (in an Appendix) methods and techniques that are currently deployed for bio-organic remediation.

Molecular characterization of dissolved organic matter in glacial ice: coupling natural abundance 1H NMR and fluorescence spectroscopy

Glaciers and ice sheets are the second largest freshwater reservoir in the global hydrologic cycle, and the onset of global climate warming has necessitated an assessment of their contributions to sea-level rise and the potential release of nutrients to nearby aquatic environments. In particular, the release of dissolved organic matter (DOM) from glacier melt could stimulate microbial activity in both glacial ecosystems and adjacent watersheds, but this would largely depend on the composition of the material released. Using fluorescence and (1)H NMR spectroscopy, we characterize DOM at its natural abundance in unaltered samples from a number of glaciers that differ in geographic location, thermal regime, and sample depth. Parallel factor analysis (PARAFAC) modeling of DOM fluorophores identifies components in the ice that are predominantly proteinaceous in character, while (1)H NMR spectroscopy reveals a mixture of small molecules that likely originate from native microbes. Spectrofluorescence also reveals a terrestrial contribution that was below the detection limits of NMR; however, (1)H nuclei from levoglucosan was identified in Arctic glacier ice samples. This study suggests that the bulk of the DOM from these glaciers is a mixture of biologically labile molecules derived from microbes.

Direct hydrodynamic radius measurement on dissolved organic matter in natural waters using diffusion NMR

Dissolved organic matter from natural waters is a complex mixture of various chemical components, which play vital roles in many environmental processes such as the global carbon cycle and the fate of many key anthropogenic pollutants. Despite its environmental significance, dissolved organic matter in natural form has never been studied using nuclear magnetic resonance based hydrodynamic radius measurements due to its extremely low concentration (e.g., a few mg/L) in natural waters. In this study, NMR-based hydrodynamic radius measurements were performed directly on unconcentrated pond, river, and sea waters. The key chemical components of the dissolved organic matters from different sources were identified as carbohydrates, carboxyl-rich alicyclic molecules, and aliphatic molecules. By using the Stokes-Einstein-Sutherland equation, the average hydrodynamic radii of the three key components were calculated.

Organic carbon in Antarctic snow: spatial trends and possible sources

Organic carbon records in Antarctic snow are sparse despite the fact that it is of great significance to global carbon dynamics, snow photochemistry, and air-snow exchange processes. Here, surface snow total organic carbon (TOC) along with sea-salt Na(+), dust, and microbial load of two geographically distinct traverses in East Antarctica are presented, viz. Princess Elizabeth Land (PEL, coast to 180 km inland, Indian Ocean sector) and Dronning Maud Land (DML, ∼110-300 km inland, Atlantic Ocean sector). TOC ranged from 88 ± 4 to 928 ± 21 μg L(-1) in PEL and 13 ± 1 to 345 ± 6 μg L(-1) in DML. TOC exhibited considerable spatial variation with significantly higher values in the coastal samples (p < 0.001), but regional variation was insignificant within the two transects beyond 100 km (p > 0.1). Both distance from the sea and elevation influenced TOC concentrations. TOC also showed a strong positive correlation with sea-salt Na(+) (p < 0.001). In addition to marine contribution, in situ microorganisms accounted for 365 and 320 ng carbon L(-1) in PEL and DML, respectively. Correlation with dust suggests that crustal contribution of organic carbon was marginal. Though TOC was predominantly influenced by marine sources associated with sea-spray aerosols, local microbial contributions were significant in distant locations having minimal sea-spray input.