Search

Antarctica is an ideal analogue for studying the limits of life. Despite severe temperature fluctuations and desiccating conditions, life is commonly found colonizing the structural cavities within Antarctic rocks (i.e., endoliths). Previous studies have speculated that the slow cycling of endoliths in the McMurdo Dry Valleys may be the limit of life on Earth. However, very little is known about the in situ activities of these communities-especially in regions outside the McMurdo Dry Valleys where endoliths are thought to be cycling carbon very slowly (e.g., hundreds of years). Here, we show that East Antarctic endoliths found on nunataks are cycling carbon quickly and are therefore quite active. Through radiocarbon (14C) analyses of the viable cell membrane (as phospholipid-derived fatty acids [PLFA]), we found that the Δ14C composition of these microbial communities was on average predominantly modern, with a few samples signaling older carbon in the system. These findings indicate that endoliths inhabiting inland Antarctic nunataks are cycling carbon on decadal timescales, which support the notion that endoliths in Antarctica are cycling carbon quickly. This work provides new insights into the potential variability of Antarctic endolith activities and demonstrates that, despite the climatic extremes that exist farther inland on the most inhospitable continent on Earth, indigenous life can thrive.

Cryoconite holes are depressions in glacial ice surfaces filled with dark debris that reduce albedo. The relative contributions of combustion and microbial carbon to cryoconite carbon are currently not known. To constrain cryoconite organic carbon composition and carbon sources to microorganisms living on glacier surfaces, measurements of bulk organic carbon and microbial phospholipid fatty acids (PLFAs) from supraglacial cryoconite sediment within the ablation zones of Spencer and Matanuska glaciers in southern Alaska were coupled with radiocarbon (14C) analyses. The 14C content of bulk cryoconite organic carbon on both glaciers was depleted relative to the modern atmosphere, while the PLFAs contained carbon that was recently in equilibrium with the atmosphere. Because the bulk cryoconite material is isotopically distinct from the PLFAs, these results indicate that cryoconite organic carbon is not bioavailable to the microbes. Instead, modern carbon in the microbes suggests that carbon is being quickly cycled by them within the cryoconite. Biomarker and stable isotope analyses of cryoconite organic carbon points to fresh carbon inputs to cryoconite and indicates that combusted fossil carbon is a not a major component of cryoconite organic carbon. Trace element analyses of the bulk cryoconite show crustal inputs and no evidence for excess metals associated with recent combustions sources, indicating that the aged bulk cryoconite organic carbon is likely of rock origin (e.g., shale). This study highlights that microbes in cryoconite holes on these glaciers are fixing atmospheric carbon and not using the aged carbon surrounding them.

Stormwater detention ponds are widely utilized as control structures to manage runoff during storm events. These ponds also represent biogeochemical hotspots, where carbon (C) and nutrients can be processed and buried in sediments. This study quantified C and nutrient [nitrogen (N) and phosphorus (P)] sources and burial rates in 14 stormwater detention ponds representative of typical residential development in coastal South Carolina. Bulk sediment accumulation was directly correlated with catchment impervious surface coverage (R2 = 0.90) with sediment accumulation rates ranging from 0.06 to 0.50 cm y−1. These rates of sediment accumulation and consequent pond volume loss were lower than anticipated based on maintenance guidelines provided by the State. N-alkanes were used as biomarkers of sediment source; the derived terrestrial aquatic ratio (TARHC) index was strongly correlated with sediment accumulation rate (R2 = 0.71) which, in conjunction with high C/N ratios (16–33), suggests that terrestrial biomass drives this sediment accumulation, with relatively minimal contributions from algal derived material. This is counter to expectations that were based on the high algal productivity generally observed in stormwater ponds and previous studies of natural lakes. Sediment C and nutrient concentrations were consistent among ponds, such that differences in burial rates were a simple function of bulk sediment accumulation rate. These burial rates (C: 8.7–161 g m−2 y−1, N: 0.65–6.4 g m−2 y−1, P: 0.238–4.13 g m−2 y−1) were similar to those observed in natural lake systems, but lower than those observed in reservoirs or impoundments. Though individual ponds were small in area (930–41,000 m2), they are regionally abundant and, when mean burial rates are extrapolated to the regional scale (≈ 21,000 ponds), ultimately sequester 2.0 × 109 g C y−1, 9.5 × 107 g N y−1, and 3.7 × 107 g P y−1 in the coastal region of South Carolina alone. Stormwater ponds represent a relatively new but increasingly significant feature of the coastal landscape and, thus, are a key component in understanding how urbanization alters the transport and transformations of C and nutrients between terrestrial uplands and downstream receiving waters.

An increasing number of studies from high latitude settings use the stable hydrogen isotope ratio (δ2H) of plant leaf waxes to quantify changes in past precipitation. Calibration of modern vegetation and source water use from these landscapes is important to more accurately reconstruct past hydroclimate variability using sedimentary leaf wax δ2H values. Here, we determine plant-water fractionations from 12 sites along a south-north transect in central Alaska, from Fairbanks to Deadhorse (64-70°N). We characterize the δ2H values of n-alkanes and n-alkanoic acids from modern plants and their xylem and leaf water δ2H values, as well as plant source water using surface soils, a soil core, and previously collected meteoric water data from the region. We find both transpiration (eLW/XW) and biosynthetic (ewax/LW) fractionation are sensitive to environmental controls with latitude, with increased leaf transpiration and biosynthetic fractionation to the north, potentially due to increased summer sunlight hours. Soil water δ2H values show near linear 2H enrichment toward the surface associated with evaporation, with the δ2H value ∼40 cm matching mean annual precipitation (MAP). Average net fractionation was calculated using xylem water and chain length weighted wax δ2H values (ewax/XW) and we find nearly the same mean values for both n-alkanes, −112 ± 27‰, and n-alkanoic acids, −110 ± 23‰, from 12 common high latitude vascular plants. To provide the range of likely net fractionations along this transect, we also calculate the average net fractionation using MAP, finding values are less negative than using xylem waters (ewax/MAP, −89 ± 28‰ for n-alkanes, and −86 ± 24‰ for n-alkanoic acids). To compare across studies, we determined the average ewax/MAP of n-alkanes from all available high latitude calibration studies and found more 2H enriched (smaller fractionations) for C27 (-87 ± 29‰), C29 (-87 ± 32‰), and C31 (-91 ± 31‰) than those of global ewax/MAP homolog averages. This new work in Alaska contributes to our growing understanding of plant water-wax fractionation in the high latitudes and is potentially important for the use of sedimentary δ2H values for paleoprecipitation estimates.

Heavily weathered petroleum residues from the Deepwater Horizon (DwH) disaster continue to be found on beaches along the Gulf of Mexico as oiled-sand patties. Here, we demonstrate the ongoing biodegradation of weathered Macondo Well (MW) oil residues by tracing oil-derived carbon into active microbial biomass using natural abundance radiocarbon (14C). Oiled-sand patties and non-oiled sand were collected from previously studied beaches in Mississippi, Alabama, and Florida. Phospholipid fatty acid (PLFA) analyses illustrated that microbial communities present in oiled-sand patties were distinct from non-oiled sand. Depleted 14C measurements of PLFA revealed that microbes on oiled-sand patties were assimilating MW oil residues five years post-spill. In contrast, microbes in non-oiled sand assimilated recently photosynthesized carbon. These results demonstrate ongoing biodegradation of weathered oil in sand patties and the utility of 14C PLFA analysis to track the biodegradation of MW oil residues long after other indicators of biodegradation are no longer detectable.

Microbial communities play key roles in remediation and reclamation of contaminated environments via biogeochemical cycling of organic and inorganic components. Understanding the trends in in situ microbial community abundance, metabolism and carbon sources is therefore a crucial component of effective site management. The focus of this study was to use radiocarbon analysis to elucidate the carbon sources driving microbial metabolism within the first pilot Wetland reclamation project in the Alberta oil sands region where the observation of H2S had indicated the occurrence of microbial sulphate reduction. The reclamation project involved construction of a three compartment system consisting of a freshwater wetland on top of a sand cap overlying a composite tailings (CT) deposit. Radiocarbon analysis demonstrated that both dissolved and sediment associated organic carbon associated with the deepest compartments (the CF and sand cap) was primarily fossil (Delta C-14 = -769 to -955 parts per thousand) while organic carbon in the overlying peat was hundreds to thousands of years old (Delta C-14 = -250 to -350 parts per thousand). Radiocarbon contents of sediment associated microbial phospholipid fatty acids (PLFA) were consistent with the sediment bulk organic carbon pools (Peat: Delta C-14(PLFA) = 257 parts per thousand; Sand cap Delta C-14(PLFA) = -805 parts per thousand) indicating that these microbes were using sediment associated carbon. In contrast, microbial PLFA grown on biofilm units installed in wells within the deepest compartments contained much more modern carbon that the associated bulk carbon pools. This implied that the transfer of relatively more modern carbon was stimulating the microbial community at depth within the system. Correlation between cellular abundance estimates based on PLFA concentrations and the Delta C-14(PLFA) indicated that the utilization of this more modern carbon was stimulating the microbial community at depth. These results highlight the importance of understanding the occurrence and potential outcomes of the introduction of relatively bioavailable carbon to mine wastes in order to predict and manage the performance of reclamation strategies.

We report measurements of oceanic black carbon (BC) to determine the sources of BC to abyssal marine sediments in the northeast Pacific Ocean. We find that the average 14C age of BC is older (by 6200 ± 2200 14C years) than that of the concurrently deposited non-BC sedimentary organic carbon. We investigate sources of aged BC to sediments by measuring a sample of sinking particulate organic carbon (POC) and find that POC may provide the main transport mechanism of BC to sediments. We suggest that aged BC is incorporated into POC from a combination of resuspended sediments and sorption of ancient dissolved organic carbon BC onto POC. Our BC flux estimate represents ~8–16% of the global burial flux of organic carbon to abyssal sediments and constitutes a minimum long-term removal estimate of 6–32% of biomass-derived BC using the present day emission flux.

The hyperarid core of the Atacama Desert is one of the driest and most inhospitable places on Earth, where life is most commonly found in the interior of rocks (i.e., endolithic habitats). Due to the extreme dryness, microbial activity in these habitats is expected to be low; however, the rate of carbon cycling within these microbial communities remains unknown. We address this issue by characterizing the isotopic composition (13C and 14C) of phospholipid fatty acids (PLFA) and glycolipid fatty acids (GLFA) in colonized rocks from four different sites inside the hyperarid core. δ13C results suggest that autotrophy and/or quantitative conversion of organic matter to CO2 are the dominant processes occurring with the rock. Most Δ14C signatures of PLFA and GLFA were consistent with modern atmospheric CO2, indicating that endoliths are using atmospheric carbon as a primary carbon source and are also cycling carbon quickly. However, at one site the PLFA contained 14C from atmospheric nuclear weapons testing that occurred during the 1950s and 1960s, indicating a decadal rate of carbon cycling. At the driest site (Yungay), based on the relative abundance and 14C content of GLFA and PLFA, there was evidence of possible preservation. Hence, in low-moisture conditions, glycolipids may persist while phospholipids are preferentially hydrolyzed. Key Words: Endoliths—Extremophile—Carbon isotopes—Radiocarbon—Lipids. Astrobiology 13, 607–616.

This chapter reviews how radiocarbon (14C) in dissolved inorganic carbon (DIC) has been used to determine the cycling time of water within the world ocean, and how 14C in dissolved organic carbon (DOC) is being used to reveal the sources and cycling of this largest organic carbon pool in the ocean. In addition, recent studies that reveal the concentration and 14C values of black carbon in DOC in the oceans are presented.

This chapter presents an overview of the steps required to prepare a sample for radiocarbon (14C) measurement by accelerator mass spectrometry (AMS). These include: (1) collection of an appropriate sample that can answer the question being asked; (2) pretreatment of samples to isolate a the most representative fraction of the bulk carbon (C) or to separate total C into different components; (3) conversion of C in the sample to CO2 and/or graphite for measurement by AMS; and (4) assessing errors, especially those associated with 14C contamination that occur during processing.

Isotopic analysis of cellular biomass has greatly improved our understanding of carbon cycling in the environment. Compound specific radiocarbon analysis (CSRA) of cellular biomass is being increasingly applied in a number of fields. However, it is often difficult to collect sufficient cellular biomass for analysis from oligotrophic waters because easy-to-use filtering methods that are free of carbon contaminants do not exist. The goal of this work was to develop a new column based filter to autonomously collect high volume samples of biomass from oligotrophic waters for CSRA using material that can be baked at 450 °C to remove potential organic contaminants. A series of filter materials were tested, including uncoated sand, ferrihydrite-coated sand, goethite-coated sand, aluminum-coated sand, uncoated glass wool, ferrihydrite-coated glass wool, and aluminum-coated glass wool, in the lab with 0.1 and 1.0 μm microspheres and Escherichia coli . Results indicated that aluminum-coated glass wool was the most efficient filter and that the retention capacity of the filter far exceeded the biomass requirements for CSRA. Results from laboratory tests indicate that for oligotrophic waters with 1 × 10 5 cells ml − 1 , 117 l of water would need to be filtered to collect 100 μg of PLFA for bulk PLFA analysis and 2000 l for analysis of individual PLFAs. For field sampling, filtration tests on South African mine water indicated that after filtering 5955 l, 450 μg of total PLFAs were present, ample biomass for radiocarbon analysis. In summary, we have developed a filter that is easy to use and deploy for collection of biomass for CSRA including total and individual PLFAs.

Annual samples from two Palmyra Atoll corals ( Porites lutea ) that lived during the past 110 years were analyzed for radiocarbon (Δ 14 C) and δ 18 O. The Δ 14 C values decreased 7.6‰ from 1896 to 1953, similar to other coral records from the tropical and subtropical Pacific. Δ 14 C values rose from ∼−60‰ to ∼+110‰ by 1980 due to the input of bomb radiocarbon from the atmosphere. Elevated Δ 14 C values were observed for the mid- to late-1950s, suggesting early input of bomb radiocarbon, possibly from the largest Marshall Islands bomb tests in 1954. Secondary aragonite precipitation was identified in a portion of one core using scanning electron microscopy and X-radiography, and was responsible for high δ 18 O and δ 13 C values and a correlation between them. The Δ 14 C results were more resistant to alteration, except when contamination was from the bomb era (>1956).

The SOLAS air–sea gas exchange experiment (SAGE) was a multiple-objective study investigating gas-transfer processes and the influence of iron fertilisation on biologically driven gas exchange in high-nitrate low-silicic acid low-chlorophyll (HNLSiLC) Sub-Antarctic waters characteristic of the expansive subpolar zone of the southern oceans. This paper provides a general introduction and summary of the main experimental findings. The release site was selected from a pre-voyage desktop study of environmental parameters to be in the south-west Bounty Trough (46.5°S 172.5°E) to the south-east of New Zealand and the experiment was conducted between mid-March and mid-April 2004. In common with other mesoscale iron addition experiments (FeAX’s), SAGE was designed as a Lagrangian study, quantifying key biological and physical drivers influencing the air–sea gas exchange processes of CO2, DMS and other biogenic gases associated with an iron-induced phytoplankton bloom. A dual tracer SF6/3He release enabled quantification of both the lateral evolution of a labelled volume (patch) of ocean and the air–sea tracer exchange at tenths of kilometer scale, in conjunction with the iron fertilisation. Estimates from the dual-tracer experiment found a quadratic dependency of the gas exchange coefficient on windspeed that is widely applicable and describe air–sea gas exchange in strong wind regimes. Within the patch, local and micrometeorological gas exchange process studies (100 m scale) and physical variables such as near-surface turbulence, temperature microstructure at the interface, wave properties and windspeed were quantified to further assist the development of gas exchange models for high-wind environments. There was a significant increase in the photosynthetic competence (Fv/Fm) of resident phytoplankton within the first day following iron addition, but in contrast to other FeAX’s, rates of net primary production and column-integrated chlorophyll a concentrations had only doubled relative to the unfertilised surrounding waters by the end of the experiment. After 15 days and four iron additions totalling 1.1 ton Fe2+, this was a very modest response compared to other mesoscale iron enrichment experiments. An investigation of the factors limiting bloom development considered co-limitation by light and other nutrients, the phytoplankton seed-stock and grazing regulation. Whilst incident light levels and the initial Si:N ratio were the lowest recorded in all FeAXs to date, there was only a small seed-stock of diatoms (less than 1% of biomass) and the main response to iron addition was by the picophytoplankton. A high rate of dilution of the fertilised patch relative to phytoplankton growth rate, the greater than expected depth of the surface mixed layer and microzooplankton grazing were all considered as factors that prevented significant biomass accumulation. In line with the limited response, the enhanced biological draw-down of pCO2 was small and masked by a general increase in pCO2 due to mixing with higher pCO2 waters. The DMS precursor DMSP was kept in check through grazing activity and in contrast to most FeAX’s dissolved dimethylsulfide (DMS) concentration declined through the experiment. SAGE is an important low-end member in the range of responses to iron addition in FeAX’s. In the context of iron fertilisation as a geoengineering tool for atmospheric CO2 removal, SAGE has clearly demonstrated that a significant proportion of the low iron ocean may not produce a phytoplankton bloom in response to iron addition.

Radiocarbon ((14)C) is a radioactive isotope that is useful for determining the age and cycling of carbon-based materials in the Earth system. Compound specific radiocarbon analysis (CSRA) provides powerful insight into the turnover of individual components that make up the carbon cycle. Extraneous or nonspecific background carbon (C(ex)) is added during sample processing and subsequent isolation of CSRA samples. Here, we evaluate the quantity and radiocarbon signature of C(ex) added from two sources: preparative capillary gas chromatography (PCGC, C(PCGC)) and chemical preparation of CSRA of black carbon samples (C(chemistry)). We evaluated the blank directly using process blanks and indirectly by quantifying the difference in the isotopic composition between processed and unprocessed samples for a range of sample sizes. The direct and indirect assessment of C(chemistry+PCGC) agree, both in magnitude and radiocarbon value (1.1 +/- 0.5 microg of C, fraction modern = 0.2). Half of the C(ex) is introduced before PCGC isolation, likely from coeluting compounds in solvents used in the extraction method. The magnitude of propagated uncertainties of CSRA samples are a function of sample size and collection duration. Small samples collected for a brief amount of time have a smaller propagated (14)C uncertainty than larger samples collected for a longer period of time. CSRA users are cautioned to consider the magnitude of uncertainty they require for their system of interest, to frequently evaluate the magnitude of C(ex) added during sampling processing, and to avoid isolating samples < or = 5 microg of carbon.

The incorporation of fullerenes and carbon nanotubes into electronic, optical and consumer products will inevitably lead to the presence of these anthropogenic compounds in the environment. To date, there have been few studies isolating these materials from environmental matrices. Here we report a method commonly used to quantify black carbon (BC) in soils, the benzene polycarboxylic acid (BPCA) method, for measurement of two types of single walled carbon nanotubes (SWCNTs), two types of fullerenes and two forms of soot. The distribution of BC products (BPCAs) from the high pressure and high temperature oxidation illustrates the condensed nature of these compounds because they form predominantly fully substituted mellitic acid (B6CA). The conversion of carbon nanoparticles to BPCAs was highest for fullerenes (average of 23.2+/-4.0% C recovered for both C(60) and C(70)) and lowest for non-functionalized SWCNTs (0.5+/-0.1% C). The recovery of SWCNTs was 10 times higher when processed through a cation-exchange column, indicating the presence of metals in SWCNTs compromises the oxidation chemistry. While mixtures of SWCNTs, soot and sediment revealed small losses of black carbon during sample processing, the method is suitable for quantifying total BC. The BPCA distribution of mixtures did not agree with theoretical mixtures using model polyaromatic hydrocarbons, suggesting the presence of a matrix effect. Future work is required to quantify different types of black carbon within the same sample.

The photochemical oxidation of colored, dissolved organic matter (CDOM) is important for carbon cycling in the ocean. This oxidation process produces a number of products, including carbon monoxide (CO). While the photochemical production efficiency of CO (apparent quantum yield, AQY, defined in terms of CDOM absorbance) has been reported to be similar for many water types, a full evaluation of the observed natural variability in CO AQY requires additional study. Here we use a polychromatic irradiation system to determine twenty AQY spectra at sea on fresh samples ranging from the near coastal waters of the Gulf of Maine to the offshore waters of the Northwest Atlantic. Despite the geographic variability of these marine samples the AQY of CO production in the Gulf of Maine and Northwest Atlantic exhibited only a small degree of variability, none of which was not correlated with measured environmental parameters. Consequently, a single aggregate AQY spectrum ϕ λ = e (−(9.134+0.0425( λ −290)))+ e (−(11.316+0.0142( λ −290))) was found to adequately represent the entire data set. Significantly, the accuracy of an AQY spectrum determined using this multispectral/statistical technique was confirmed with data obtained from a monochromatic irradiation technique on a single open ocean sample. Taken together, the AQY spectra determined in this study were similar in magnitude and shape to those previously published for marine samples and, overall, were somewhat lower than those previously reported for freshwater studies.

Measurements of underwater light fields and available quantum yield spectra were used to calculate photochemical removal rates of DMS for surface waters of the northeast subarctic Pacific during the SERIES mesoscale iron-fertilization experiment in July 2002. We observed that the UV portion of the solar spectrum was most important in inducing DMS photo-oxidation, and calculated that UV-B accounted for more than 20% and UV-A for more than 68% of the total DMS photo-oxidation near the sea surface. Vertically resolved rates showed that most (>90%) of the DMS photo-oxidation occurs in the upper 15 m of the water column. During the study, calculated rates of DMS photo-oxidation, just below the ocean's surface ranged from 0.34 to 5.9 μmol m−3 d−1. As the study progressed, an initial increase in photo-oxidation rates occurred within the iron-enriched patch and this was followed by a dramatic decrease in rates, whereas little change was observed outside the patch. Changes in DMS concentrations and decreases in the photochemical removal efficiency for DMS were the dominant factors explaining the variation in the DMS photo-oxidation rates. The turnover rate constants for DMS photo-oxidation, calculated for the upper mixed layer (UML) of the water column, (0.03–0.25 d−1) were in the range of those previously published and were at times higher than those calculated for biological consumption of DMS during SERIES. Our results suggest that iron fertilization of an oceanic patch in the northeast Pacific Ocean considerably altered the photochemical removal rates and turnover rate constants of DMS.

Partial pressures of carbon dioxide (pCO2) were measured in river and coastal waters on two cruises in November 1999 and June 2000 on the Southwest Florida Shelf. Supersaturation with respect to the atmosphere was observed for most river and near-shore waters in November 1999. pCO2 ranged from 403 μatm in the Gulf of Mexico to 1280 μatm in the Shark River. The coastal waters of the Southwest Florida Shelf had unusually low salinities at this time due to high inputs of freshwater runoffs after Hurricane Irene. In general, pCO2 levels decreased with increasing salinity, but at different gradients for the different river systems. In June 2000, salinity gradients were considerably reduced during this drought year, with hypersalinity indicating reduced freshwater inputs. However, high pCO2 levels were still observed in and near the mouth of the Shark River (pCO2=383–1280 μatm). A positive correlation of pCO2 levels with colored dissolved organic matter (CDOM) and chlorophyll was observed in all systems examined. CO2 in natural waters may be produced from the photochemical degradation of CDOM, microbial respiration or via shifts in the carbonate equilibrium. Some evidence for a small contribution from photochemical production was observed in the Shark River mouth in a dry season diel study, but not in the wet season. Differences between the rivers are primarily attributed to the significantly higher total alkalinity and lower pH values in the Shark River, and associated higher pCO2 levels. In general, spatial variability in pCO2 is dominated by the chemical characteristics of the river inputs, with temporal variability modulated by changes in pH, photochemical production in low flow seasons and draw down by primary production.

A headspace analysis system with well demonstrated precision and accuracy for measuring carbon monoxide (CO) in natural waters and for CO incubation experiments is described. High water/gas volume ratios are accurately set by injecting known volumes of CO-free air into known volumes of water in glass syringes. CO in equilibrated headspace gas is separated chromatographically and quantified by a mercuric oxide reduction detector. A water/gas ratio of ∼7 is sensitive and precise enough for determining low-level CO; sensitivity can be increased by raising the water/gas ratio. At a water/gas ratio of 7 (40 ml total), the analytical blank, precision, and accuracy are 0.02 nM (nanomolar), ±0.018 nM±2%, and better than ±10%, respectively. Recovery of CO from the water phase is ∼88%. The system is efficient, simple, convenient, rapid and robust; it responds linearly up to ∼12 nM, and can process ∼8–12 samples/h. Several applications are illustrated: studies elucidating subtle CO-contamination artifacts, microbial oxidation incubations, and an oceanic profile. Validated low-contamination sampling methods are presented, and contamination control measures are recommended. A detailed 0–200-m profile at BATS in summer shows less “deep” CO than previously reported, but there is CO well below the seasonal mixed layer (ML) and even at the 1% light level.

Photostabilization of phenosafranin dye on poly(styrenesulfonate)-capped TiO2 nanoparticles has been investigated using diffuse reflectance spectroscopy. The dye degrades oxidiatively on a native TiO2 surface under visible light excitation as the excited dye participates in the charge injection process. The interaction of the dye with the semiconductor surface can be significantly reduced by capping the TiO2 particles first with poly(styrenesulfonate). The increase in fluorescence emission and decrease in dye degradation rate with increasing polymer capping suggest the protective role of poly(styrenesulfonate) capping. Diffuse reflectance laser flash photolysis studies further elucidate surface photochemical processes of phenosafranin on native and polymer-capped TiO2 nanoparticles.

Extraneous carbon (Cex) added during chemical processing and isolation of black carbon (BC) in environmental matrices was quantified to assess its impact on compound specific radiocarbon analysis (CSRA). Extraneous carbon is added during the multiple steps of BC extraction, such as incomplete removal of solvents, and carbon bleed from the gas chromatographic and cation columns. We use 2 methods to evaluate the size and Δ14C values of Cex in BC in ocean sediments that require additional pretreatment using a cation column with the benzene polycarboxylic acid (BPCA) method. First, the direct method evaluates the size and Δ14C value of Cex directly from the process blank, generated by processing initially empty vials through the entire method identically to the treatment of a sample. Second, the indirect method quantifies Cex as the difference between processed and unprocessed (bulk) Δ14C values in a variety of modern and 14C-free or “dead” BC standards. Considering a suite of hypothetical marine sedimentary samples of various sizes and Δ14C values and BC Ring Trial standards, we compare both methods of corrections and find agreement between samples that are >50 μg C. Because Cex can profoundly influence the measured Δ14C value of compound specific samples, we strongly advocate the use of multiple types of process standards that match the sample size to assess Cex and investigate corrections throughout extensive sample processing.

The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has developed protocols for analyzing radiocarbon in samples as small as ∼0.001 mg of carbon (C). Mass-balance background corrections for modern and 14C-dead carbon contamination (MC and DC, respectively) can be assessed by measuring 14C-free and modern standards, respectively, using the same sample processing techniques that are applied to unknown samples. This approach can be validated by measuring secondary standards of similar size and 14C composition to the unknown samples. Ordinary sample processing (such as ABA or leaching pretreatment, combustion/graphitization, and handling) introduces MC contamination of ∼0.6 ± 0.3 μg C, while DC is ∼0.3 ± 0.15 μg C. Today, the laboratory routinely analyzes graphite samples as small as 0.015 mg C for external submissions and ≅0.001 mg C for internal research activities with a precision of ∼1% for ∼0.010 mg C. However, when analyzing ultra-small samples isolated by a series of complex chemical and chromatographic methods (such as individual compounds), integrated procedural blanks may be far larger and more variable than those associated with combustion/graphitization alone. In some instances, the mass ratio of these blanks to the compounds of interest may be so high that the reported 14C results are meaningless. Thus, the abundance and variability of both MC and DC contamination encountered during ultra-small sample analysis must be carefully and thoroughly evaluated. Four case studies are presented to illustrate how extraction chemistry blanks are determined.

GEOPHYSICAL RESEARCH LETTERS, VOL. 37, L16601, doi:10.1029/2010GL043963, 2010 Aged black carbon identified in marine dissolved organic carbon L. A. Ziolkowski 1,2 and E. R. M. Druffel 1 Received 13 May 2010; revised 17 June 2010; accepted 1 July 2010; published 17 August 2010. [ 1 ] Produced on land by incomplete combustion of organic matter, black carbon (BC) enters the ocean by aerosol and river deposition. It has been postulated that BC resides in the marine dissolved organic carbon (DOC) pool before sedimentary deposition and may attribute to its great 14 C age (1500–6500 14 C years). Here we report the first radiocarbon measurements of BC in high molecular weight DOC (UDOM). BC exported from rivers is highly aromatic and 50,000 years (the detection limit). In contrast, BC recently produced from biomass burning has a C content equal to that in the contemporary biosphere C (D 14 C = 0 to 200‰). Here we present the distribution of BPCAs in conjunction with radiocarbon measurements of Auxiliary materials are available in the HTML. doi:10.1029/ 2010GL043963. L16601 1 of 4

We report compound-specific radiocarbon analyses of organic matter in ocean sediments from the northeast Pacific Ocean. Chemical extractions and a preparative capillary gas chromatograph (PCGC) were used to isolate phospholipid fatty acids (PLFA) and n-alkanes from 3 cores collected off the coast of California, USA. Mass of samples for accelerator mass spectrometry (AMS) 14C analysis ranged from 13–100 μg C. PLFA extracted from anaerobic sediments in the Santa Barbara Basin (595 m depth) had modern Δ14C values (–20 to +54‰), indicating bacterial utilization of surface-produced, post-bomb organic matter. Lower Δ14C values were obtained for n-alkanes and PLFA from coast (92 m depth) and continental slope (1866 m) sediments, which reflect sources of old organic matter and bioturbation. We present a brief analysis of the blank carbon introduced to samples during chemical processing and PCGC isolation.

LIMNOLOGY and OCEANOGRAPHY: METHODS Limnol. Oceanogr.: Methods 9, 2011, 140–149 © 2011, by the American Society of Limnology and Oceanography, Inc. Quantification of black carbon in marine systems using the benzene polycarboxylic acid method: a mechanistic and yield study L. A. Ziolkowski 1,2 *, A.R. Chamberlin 3 , J. Greaves 3 , and E.R.M. Druffel 1 Department of Earth System Science, University of California Irvine, Irvine, CA 92697 Origins Institute, McMaster University, Hamilton, Ontario L8S 4L8 Department of Chemistry, University of California Irvine, Irvine, CA 92697 Abstract Quantification of black carbon (BC), carbonaceous material of pyrogenic origin, has typically required either chemical or thermal oxidation methods for isolation from heterogeneous matrices, such as sediment or soil. The benzene polycarboxylic acid (BPCA) method involves chemical oxidation of aromatic structures, such as those in BC, into BPCAs. We revised the BPCA method with the intent to quantify BC in marine dissolved organic carbon (DOC). As part of this work, we evaluated the mechanism and yield of the method using nine polycyclic aromatic hydrocarbons (PAHs) and six BC reference materials. After 8 h of oxidation at 180°C, the average car- bon yield was 26 ± 7% C and was not correlated to the molecular weight of the PAH oxidized. The majority of observed BPCAs were nitrated, which has serious implications for the quantification of BC. Smaller PAHs favor the formation of less substituted BPCAs, whereas larger PAHs, such as coronene, favor the formation of more fully substituted BPCAs. Time-course experiments revealed variations of BPCA distributions over time, favoring less substituted BPCAs with longer oxidation times, whereas the carbon yield exhibited little variation. No decarboxylation of fully substituted mellitic acid (B6CA) was observed during time course experiments. Using the model compound anthracene, a potential internal standard, we propose a mechanism for the oxidation reaction based on time-course experiment data. Quantification of BC in reference materials revealed that this revision of the BPCA method is significantly more efficient than previous versions and is effective for quanti- fying both char and soot BC. and quantifying BC (Masiello 2004). Various techniques are used to quantify BC isolated from environmental matrices including thermal oxidation (Gustafsson et al. 1997), chemi- cal oxidation (nitric acid: Glaser et al. 1998; Brodowski et al. 2005; and acid dichromate: Wolbach and Anders 1989) and mild chemical or photo-oxidation (NaClO, Simpson and Hatcher 2004; and ultra-violet radiation, Skjemstad et al. 1996) followed by NMR. The benzene polycarboxylic acid (BPCA) method (Glaser et al. 1998; Brodowski et al. 2005) converts BC to benzene rings that are substituted with various numbers (2-6) of carboxylic acid groups. Assuming that the aromatic carbon within the sample is BC and additional carbon is neither added nor exchanged, this method provides both yield and general struc- tural information about the BC. Nitric acid oxidizes the BC structure to BPCAs in which a single aromatic ring from the BC is preserved and is substituted with carboxylic acids derived from adjacent rings or side chains. This method retains the carbon from the molecular structure, which is essential for subsequent isotopic abundance assays such as Black carbon (BC) particles are byproducts of combustion processes that can be defined by a broad range of characteris- tics. Sizes range from nanometer soot particles to millimeter pieces of charcoal. Chemically, BC has a condensed, highly aromatic structure (Fig. 1). Environmental scientists are inter- ested in isolating BC from organic matrices, such as soils and sediments, to address questions regarding the time scales of carbon storage in the Earth system. The wide ranges of physi- cal and chemical characteristics of both BC and heterogeneous matrices in which it is found pose challenges when isolating *Corresponding author: E-mail: lorized@gmail.com Acknowledgments The authors would like to thank Sheila Griffin and Claudia Green for their help with this work. Black carbon reference materials were a gift of M.W.I. Schmidt and D. M. Smith. This manuscript benefitted from com- ments from Associate Editor Elizabeth Minor and two anonymous reviewers. We acknowledge funding from the NSF Chemical Oceanography Program. DOI 10:4319/lom.2011.9.140