A5029779082- Marine and coastal ecosystems
- Isotope Analysis in Ecology
- Groundwater and Isotope Geochemistry
- Methane Hydrates and Related Phenomena
- Geology and Paleoclimatology Research
- Arctic and Antarctic ice dynamics
- Wastewater Treatment and Nitrogen Removal
- Microbial Community Ecology and Physiology
- Atmospheric chemistry and aerosols
- Marine Biology and Ecology Research
- Atmospheric and Environmental Gas Dynamics
- Ocean Acidification Effects and Responses
- Marine and fisheries research
- Soil and Water Nutrient Dynamics
- Radioactive contamination and transfer
- Geological Studies and Exploration
- Nuclear Physics and Applications
- Atmospheric Ozone and Climate
- Marine Bivalve and Aquaculture Studies
- Oceanographic and Atmospheric Processes
- Coral and Marine Ecosystems Studies
- Chemical Reactions and Isotopes
- Chemical Thermodynamics and Molecular Structure
- Geochemistry and Elemental Analysis
- Single-cell and spatial transcriptomics
University of Connecticut
2015-2025
Johns Hopkins Medicine
2023-2024
Johns Hopkins University
2023-2024
Cancer Research Center
2023-2024
University of British Columbia
2003-2023
University of Washington
2022
Princeton University
2003-2014
University of California, San Diego
2004
Université du Québec à Montréal
2000
Université de Montréal
2000
We report the first measurements of coupled nitrogen (N) and oxygen (O) isotopic variations nitrate (NO ) during its assimilation by laboratory cultures marine phytoplankton derive N O kinetic isotope effects for three species diatoms ( Thalassiosira weissflogii , oceanica pseudonana a coccolithophorid Emiliana huxleyi ). Large interspecies intraspecies in were observed. The effect associated with consumption was consistently close to effect, such that 18 O/ 16 15 N/ 14 varied ratio ~1 : 1,...
We report the first measurements of coupled nitrogen (N) and oxygen (O) isotope fractionation nitrate by laboratory cultures denitrifying bacteria. Two seawater strains ( Pseudomonas stutzeri , Ochrobactrum sp.) three freshwater Paracoccus denitrificans chlororaphis Rhodobacter sphaeroides ) were examined. Among four facultative anaerobic denitrifiers, N O effects variable, ranging from 5‰ to 25‰, with evidence for a drop in as concentrations approached halfsaturation constant transport....
Water column depth profiles along the North Pacific margin from Point Conception to tip of Baja California indicate elevation nitrate (NO 3 − ) 15 N/ 14 N and 18 O/ 16 O associated with denitrification in oxygen‐deficient thermocline waters eastern tropical Pacific. The increase δ is up 3‰ greater than N, whereas our experiments denitrifier cultures seawater medium a 1:1 NO during consumption. Moreover, maximum somewhat shallower N. These two observations can be summarized as an “anomaly”...
Abstract In environmental water samples that contain both nitrate (NO ) and nitrite ), isotopic analysis of alone by all currently available methods requires pretreatment to remove nitrite. Sulfamic acid addition, used previously for this purpose (Wu JP, Calvert SE, Wong CS. Deep‐Sea Research Part I – Oceanographic Papers 1997; 44: 287), is shown here be compatible with the denitrifier method N O isotope nitrate. at a pH ∼1.7 reduces 2 . Samples are then neutralized base prior analysis,...
We report on the contamination of commercial 15-nitrogen (15N) N2 gas stocks with 15N-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. 15N2 is used to estimate fixation rates from incubations environmental samples by monitoring incorporation isotopically labeled into organic matter. However, microbial assimilation bioavailable 15N-labeled contaminants, nitrate, liable lead inflation or false detection rates. procured three major suppliers was analyzed for presence these...
Significance Stable isotopes of nitrate have long provided a tool for tracking environmental sources and biological transformations. However, divergent interpretations fundamental isotope systematics exist among disciplinary divisions. In an effort to transcend boundaries terrestrial marine biogeochemistry, we use quantitative model coupled nitrogen oxygen founded on benchmarks established from microbial cultures, reconcile decades isotopic measurements in freshwater seawater move toward...
Prokaryotic microbes play a critical role in oceanic Fe cycling. They contain most of the biogenic offshore waters and are responsible for large portion uptake by plankton community. In subarctic North Pacific, surface populations heterotrophic species assimilate more than 50% dissolved thus compete directly with phytoplankton this limiting resource. oligotrophic tropical subtropical waters, photosynthetic bacteria become important cycling as number unicellular cyanobacteria increases...
We studied the nitrogen biogeochemistry of ice‐covered eastern Bering Sea shelf using isotope ratios ( 15 N/ 14 N and 18 O/ 16 O) NO 3 − other species. The late winter on decreases inshore is inversely correlated with bottom water [NH 4 + ], consistent an input low‐ from partial nitrification NH remineralized sediments. An increase in total dissolved (TDN) suggests that (1) sediment‐derived elevated due to same yields , (2) N‐deplete within sediments denitrified 2 . proportion newly...
Measurements of the stable isotope ratios nitrogen (15N/14N) and oxygen (18O/16O) in nitrate (NO3-) enable identification sources, dispersal, fate natural contaminant NO3- aquatic environments. The 18O/16O produced by nitrification is often assumed to reflect proportional contribution atom water, molecular oxygen, a 2:1 ratio. Culture seawater incubations, however, indicate isotopic equilibration between nitrite (NO2-) kinetic effects for incorporation, which modulate NO3-18O/16O during...
Recent studies demonstrate that dissolved iron in seawater is bound to strong organic complexes have stability constants comparable those of microbial chelates. We examined acquisition by seven strains heterotrophic marine bacteria from a number siderophore–iron complexes, including desferrioxamine B (DFB) and siderophores partially purified iron‐limited cultures. Hydroxamate were detected the supernatants four strains, one which also produced catechol. All transported regardless whether or...
Three strains of heterotrophic denitrifying bacteria were cultured in artificial seawater medium under trace metal clean conditions to investigate their physiological response changes copper concentration. Decreasing the concentration cultures Pseudomonas stutzeri and Paracoccus denitrificans resulted accumulation nitrous oxide (N 2 O) gas compared copper‐replete cessation growth before complete denitrification dinitrogen. Correspondingly, activity enzyme reductase, measured for P. cultures,...
In order to (i) establish the biological systematics necessary interpret nitrogen (N) and oxygen (O) isotope ratios of nitrate ((15)N/(14)N (18)O/(16)O) in environment (ii) investigate potential for isotopes elucidate mechanism a key N cycle enzyme, we measured O effects ((15)ε (18)ε) reduction by two assimilatory eukaryotic reductase (eukNR) enzymes. The (15)ε purified extracts NADPH eukNR from fungus Aspergillus niger NADH cell homogenates marine diatom Thalassiosira weissflogii were...
Abstract Nitrogen is a limiting nutrient for primary production in the western Arctic Ocean. Measurements of nitrogen ( 15 N/ 14 N) and oxygen 18 O/ 16 O) isotope ratios nitrate southeastern Beaufort Sea provide insight into biogeochemical cycling Nitrate O Pacific halocline evidence highly regenerated reservoir. Coincident peaks concentrations reduced dissolved suggest that accrues from organic matter remineralization bottom waters Chukchi shelf these ventilate basin predominantly summer,...
Abstract Salinity-driven density stratification of the upper Arctic Ocean isolates sea-ice cover and cold, nutrient-poor surface waters from underlying warmer, nutrient-rich waters. Recently, has strengthened in western but weakened eastern Arctic; it is unknown if these trends will continue. Here we present foraminifera-bound nitrogen isotopes sediments since 35,000 years ago to reconstruct past changes nutrient sources degree consumption waters, latter reflecting stratification. During...
[1] The oxygen triple-isotope composition of dissolved O2 provides an integrative method to estimate the rates Gross Photosynthetic Production (GPP) in upper ocean, and combined with estimates Net Community (NCP) yields net-to-gross (NCP/GPP) production ratios. However, derivations GPP from measurements have involved some mathematical approximations. We derive exact expression for calculating GPP, show that small errors associated approximations result a relative error up ∼38% ∼50% N/G. In...
Abstract To provide mechanistic constraints to interpret nitrogen (N) and oxygen (O) isotope ratios of nitrate ( ), 15 N/ 14 N 18 O/ 16 O, in the environment, we measured enzymatic O effects ε ε) during its reduction by reductase enzymes, including (1) a prokaryotic respiratory reductase, Nar , from heterotrophic denitrifier Paracoccus denitrificans (2) eukaryotic assimilatory reductases, eukNR Pichia angusta Arabidopsis thaliana (3) periplasmic Nap photoheterotroph Rhodobacter sphaeroides ....
The cyclic growth and decay of continental ice sheets can be reconstructed from the history global sea level. Sea level is relatively well constrained for Last Glacial Maximum (LGM, 26,500 to 19,000 y ago, 26.5 19 ka) ensuing deglaciation. However, sea-level estimates period ice-sheet before LGM vary by > 60 m, an uncertainty comparable equivalent contemporary Antarctic Ice Sheet. Here, we constrain prior reconstructing flooding shallow Bering Strait since 46 ka. Using a geochemical proxy...
We describe a method to remove nitrite from seawater and freshwater samples determine the nitrogen (N) oxygen (O) isotopic composition of nitrate in aqueous (15N/14N 18O/16O, respectively). This is simple, inexpensive, effective removal without compromising natural N O nitrate. Moreover, nontoxic compatible with "denitrifier method" for isotope analysis. Nitrite removed solution by reduction nitric oxide (NO) gas using ascorbic acid at pH ~3.5. The NO produced continually degassed an inert...