UV Photochemical Oxidation and Extraction of Marine Dissolved Organic Carbon at UC Irvine: Status, Surprises, and Methodological Recommendations

Radiocarbon ◽  
2019 ◽  
Vol 61 (5) ◽  
pp. 1603-1617 ◽  
Author(s):  
Brett D Walker ◽  
Steven R Beaupré ◽  
Sheila Griffin ◽  
Ellen R M Druffel
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Small Sample ◽  
Photochemical Oxidation ◽  
Comparison Study ◽  
Trap Design ◽  
Design Efficiency ◽  
System Parameters ◽  
Carbon Isotopic ◽  
Overall Efficiency

ABSTRACTThe first ultraviolet photochemical oxidation (UVox) extraction method for marine dissolved organic carbon (DOC) as CO2 gas was established by Armstrong and co-workers in 1966. Subsequent refinement of the UVox technique has co-evolved with the need for high-precision isotopic (Δ14C, δ13C) analysis and smaller sample size requirements for accelerator mass spectrometry radiocarbon (AMS 14C) measurements. The UVox line at UC Irvine was established in 2004 and the system reaction kinetics and efficiency for isolating seawater DOC rigorously tested for quantitative isolation of ∼1 mg C for AMS 14C measurements. Since then, improvements have been made to sampling, storage, and UVox methods to increase overall efficiency. We discuss our progress, and key UVox system parameters for optimizing precision, accuracy, and efficiency, including (1) ocean to reactor: filtration, storage and preparation of DOC samples, (2) cryogenic trap design, efficiency and quantification of CO2 break through, and (3) use of isotopic standards, blanks and small sample graphitization techniques for the correction of DOC concentrations and Fm values with propagated uncertainties. New DOC UVox systems are in use at many institutions. However, rigorous assessment of quantitative UVox DOC yields and blank contributions, DOC concentrations and carbon isotopic values need to be made. We highlight the need for a community-wide inter-comparison study.

scholarly journals Dissolved organic carbon lability and stable isotope shifts during microbial decomposition in a tropical river system

2015 ◽  
Vol 12 (15) ◽  
pp. 12761-12782
Author(s):  
N. Geeraert ◽  
F. O. Omengo ◽  
G. Govers ◽  
S. Bouillon
Keyword(s):  
Stable Isotope ◽  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Isotope Composition ◽  
River System ◽  
Photochemical Oxidation ◽  
Microbial Decomposition ◽  
Tana River ◽  
Incubation Experiments ◽  
Microbial Consumption

Abstract. A significant amount of carbon is transported to the ocean as dissolved organic carbon (DOC) in rivers. During transport, it can be transformed through microbial consumption and photochemical oxidation. In dark incubation experiments with water from the Tana River, Kenya, we examined the consumption of DOC through microbial decomposition and the associated change in its carbon stable isotope composition (δ13C). In 15 of the 18 incubations, DOC concentrations decreased significantly by 10 to 60 %, with most of the decomposition taking place within the first 24–48 h. After 8 days, the remaining DOC was up to 3 ‰ more depleted in 13C compared with the initial pool, and the change in δ13C correlated strongly with the fraction of DOC remaining. We propose that the shift in δ13C is consistent with greater microbial lability of DOC originating from herbaceous C4 vegetation than DOC derived from woody C3 vegetation in the semi-arid lower Tana. The findings complement earlier data that riverine C sources do not necessarily reflect their proportion in the catchment: besides spatial distribution, also processing within the river can further influence the riverine δ13C.

scholarly journals Isotopic and chromatographic fingerprinting of the sources of dissolved organic carbon in a shallow coastal aquifer

2020 ◽  
Vol 24 (4) ◽  
pp. 2167-2178 ◽  
Author(s):  
Karina T. Meredith ◽  
Andy Baker ◽  
Martin S. Andersen ◽  
Denis M. O'Carroll ◽  
Helen Rutlidge ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Coastal Aquifer ◽  
Carbon Isotopic Composition ◽  
Median Concentration ◽  
Carbon Isotopic ◽  
Groundwater Samples ◽  
Doc Concentration ◽  
Geochemical Analyses ◽  
Terrestrial Subsurface

Abstract. The terrestrial subsurface is the largest source of freshwater globally. The organic carbon contained within it and processes controlling its concentration remain largely unknown. The global median concentration of dissolved organic carbon (DOC) in groundwater is low compared to surface waters, suggesting significant processing in the subsurface. Yet the processes that remove this DOC in groundwater are not fully understood. The purpose of this study was to investigate the different sources and processes influencing DOC in a shallow anoxic coastal aquifer. Uniquely, this study combines liquid chromatography organic carbon detection with organic (δ13CDOC) carbon isotope geochemical analyses to fingerprint the various DOC sources that influence the concentration, carbon isotopic composition, and character with respect to distance from surface water sources, depth below surface, and inferred groundwater residence time (using 3H activities) in groundwater. It was found that the average groundwater DOC concentration was 5 times higher (5 mg L−1) than the global median concentration and that the concentration doubled with depth at our site, but the chromatographic character did not change significantly. The anoxic saturated conditions of the aquifer limited the rate of organic matter processing, leading to enhanced preservation and storage of the DOC sources from peats and palaeosols contained within the aquifer. All groundwater samples were more aromatic for their molecular weight in comparison to other lakes, rivers and surface marine samples studied. The destabilization or changes in hydrology, whether by anthropogenic or natural processes, could lead to the flux of up to 10 times more unreacted organic carbon from this coastal aquifer compared to deeper inland aquifers.

The Distribution and Stable Carbon Isotopic Composition of Dissolved Organic Carbon in Estuaries

Estuaries ◽  
1994 ◽  
Vol 17 (1) ◽  
pp. 111 ◽  
Author(s):  
Bruce Peterson ◽  
Brian Fry ◽  
Meredith Hullar ◽  
Susan Saupe ◽  
Richard Wright
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Isotopic Composition ◽  
Carbon Isotopic Composition ◽  
Stable Carbon ◽  
Carbon Isotopic

scholarly journals Isotopic and chromatographic fingerprinting of the sources of dissolved organic carbon in a shallow coastal aquifer

2019 ◽  
Author(s):  
Karina T. Meredith ◽  
Andy Baker ◽  
Martin S. Andersen ◽  
Denis M. O'Carroll ◽  
Helen Rutlidge ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Coastal Aquifer ◽  
Carbon Isotopic Composition ◽  
Natural Processes ◽  
Median Concentration ◽  
Carbon Isotopic ◽  
Groundwater Samples ◽  
Doc Concentration ◽  
Geochemical Analyses

Abstract. The terrestrial sub-surface is the largest source of freshwater globally. The organic carbon contained within it and processes controlling its concentration remain largely unknown. The global median concentration of dissolved organic carbon in groundwater is low compared to surface waters suggesting significant processing in the subsurface. Yet the processes that remove this dissolved organic carbon (DOC) in groundwater are not fully understood. The purpose of this study was to investigate the different sources and processes influencing DOC in a shallow anoxic coastal aquifer. Uniquely, this study combines liquid chromatography organic carbon detection with inorganic (δ13CDIC) and organic (δ13CDOC) carbon isotope geochemical analyses, to fingerprint the various DOC sources that influence the concentration, carbon isotopic composition and character with distance from surface water sources, depth below surface and groundwater residence time (using 3H) in groundwater. It was found that the average groundwater DOC concentration was five times higher (5 mg L−1) than the global median concentration and it doubled with depth, but the chromatographic character did not change significantly. The anoxic saturated conditions of the aquifer have limited the rate of organic matter processing leading to enhanced preservation and storage of the sources such as peats and palaeosols. All groundwater samples are more aromatic for their molecular weight in comparison to lakes and rivers and surface marine samples. The destabilisation or changes in hydrology, whether by anthropogenic or natural processes could lead to the flux of up to ten times more unreacted organic carbon from this coastal aquifer than compared to deeper inland aquifers.

scholarly journals Yucca Mountain Area Saturated Zone Dissolved Organic Carbon Isotopic Data

2007 ◽  
Author(s):  
James Thomas ◽  
David Decker ◽  
Gary Patterson ◽  
Zell Peterman ◽  
Todd Mihevc ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Yucca Mountain ◽  
Saturated Zone ◽  
Isotopic Data ◽  
Mountain Area ◽  
Carbon Isotopic

RADIOCARBON IN DISSOLVED ORGANIC CARBON BY UV OXIDATION: PROCEDURES AND BLANK CHARACTERIZATION AT NOSAMS

Radiocarbon ◽  
2020 ◽  
pp. 1-18
Author(s):  
Li Xu ◽  
Mark L Roberts ◽  
Kathryn L Elder ◽  
Mark D Kurz ◽  
Ann P McNichol ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Photochemical Oxidation ◽  
Oxidation Method ◽  
Procedural Blank ◽  
Ocean Sciences ◽  
Mass Spectrometry Facility ◽  
Best Fit ◽  
Uv Oxidation

ABSTRACT This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ13C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring results in line with accepted values. The application of a best-fit mass-balance correction yielded a procedural blank of 22.0 ± 6.0 µg C with Fm of 0.30 ± 0.20 and δ13C of –32.0 ± 3.0‰ for this period, which was notably higher and more variable than previously reported. Changes to the procedure, specifically elimination of higher organic carbon reagents and improved sample and reactor handling, reduced the blank to 11.0 ± 2.75 µg C, with Fm of 0.14 ± 0.10 and δ13C of –31.0 ± 5.5‰. A thorough determination of the entire sample processing blank is required to ensure accurate isotopic compositions of seawater DOC using the UV oxidation method. Additional efforts are needed to further reduce the procedural blank so that smaller DOC samples can be analyzed, and to increase sample throughput.

Sign in / Sign up

Export Citation Format

Share Document