A5081670746- Marine and coastal ecosystems
- Isotope Analysis in Ecology
- Geology and Paleoclimatology Research
- Marine Biology and Ecology Research
- Groundwater and Isotope Geochemistry
- Methane Hydrates and Related Phenomena
- Microbial Community Ecology and Physiology
- Marine Bivalve and Aquaculture Studies
- Oceanographic and Atmospheric Processes
- Ocean Acidification Effects and Responses
- Wastewater Treatment and Nitrogen Removal
- Marine and environmental studies
- Marine and coastal plant biology
- Atmospheric and Environmental Gas Dynamics
- Soil and Water Nutrient Dynamics
- Radioactive contamination and transfer
- Marine and fisheries research
- Geological formations and processes
- Arctic and Antarctic ice dynamics
- Marine animal studies overview
- Water Quality Monitoring and Analysis
- Paleontology and Stratigraphy of Fossils
- Cardiovascular and Diving-Related Complications
- Hydrocarbon exploration and reservoir analysis
- Peatlands and Wetlands Ecology
University of Massachusetts Dartmouth
2016-2025
Dartmouth College
2012-2016
Israel Oceanographic and Limnological Research
2007
Yale University
2007
Woods Hole Oceanographic Institution
1990-2004
Duke University
2004
University of California, Santa Barbara
2004
Moss Landing Marine Laboratories
2004
Monterey Bay Aquarium Research Institute
2004
University of South Carolina
1999
In two contrasting regions of the ocean, equatorial Pacific and southern δ 15 N core top sediments were strongly related to [NO 3 − ] in surface waters. With distance from equator Pacific, increased 7‰ 16‰ as decreased 8μM < 0.1 μM. Going 60° 30° S SE Indian Ocean, 5‰ 11‰ 25μM These results are strong evidence that sedimentary these is recording increasing isotopic enrichment near‐surface NO with its depletion by phytoplankton. case values for sinking particles collected at 150 m matched...
We present a novel method for nitrogen and oxygen natural isotopic abundance analysis of nitrate nitrite seawater freshwater at environmental concentrations. The involves the reduction to using spongy cadmium with further nitrous oxide sodium azide in an acetic acid buffer. For separate analysis, step is simply bypassed. Nitrous purged from water sample trapped cryogenically automated system subsequent release into gas chromatography column. isolated then analyzed on continuous flow isotope...
The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas the ocean and may have been an important factor variation concentration atmospheric carbon dioxide glacial cycles. effect Southern Ocean particularly because its area abundant nitrate, yet iron-enhanced growth phytoplankton be differentially expressed between with high silicic acid south low north, where diatom limited by both iron. Two mesoscale experiments,...
We have adapted the "ammonia diffusion" method of nitrate extraction for natural-abundance level nitrogen isotopic measurement oceanic nitrate. The involves: (1) sample concentration (by boiling or evaporation); (2) conversion to ammonia using Devarda's alloy; and (3) gas-phase diffusion onto an acidified glass fiber disk which is sandwiched between two porous Teflon membranes. investigated conditions necessary effect complete recovery from natural seawater samples use alloy under these...
The utility of 15 N isotope dilution models for the calculation uptake and remineralization NH 4 + by marine phytoplankton was examined in light model limitations when applied to field data either ambient levels border on our limit detection or there is no statistically significant difference between at beginning end an incubation. Through specific examples laboratory we show that are a function both analytical error inherent methodology changes rates over course given experiment. We propose...
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...
We report nitrogen isotope data for nitrate from transects of hydrocast and surface samples collected in the eastern Indian Pacific sectors Southern Ocean, focusing here on upper water column to study effect consumption by phytoplankton. The δ 15 N increases 1–2‰ deep into Antarctic summertime layer, due kinetic isotopic fractionation during uptake. Estimation uptake depth profiles yields values range 5–6‰ east sector 4–5‰ sector. Surface transect also yield 4–5‰. major uncertainty...
We report analyses of the nitrogen isotopic composition nitrate in eastern Indian and Pacific sectors Southern Ocean. In this paper, we focus on subsurface data as well from deep waters other ocean basins. Nitrate δ 15 N is relatively invariant much abyssal (i.e., below 2.5 km), with a value 4.8±0.2‰ observed Lower Circumpolar Deep Water, North Atlantic central water. The invariance stems fundamentally completeness utilization most global surface ocean, Ocean being an important exception....
Treatment of diatom microfossils from Southern Ocean sediments with hot perchloric acid leaves a “diatom‐bound” N fraction which is 0–4‰ lower in δ 15 than the bulk sediment, typically 3‰ recent Antarctic ooze. Results surface indicate that early diagenetic changes sediment content and are not reflected diatom‐bound N, suggesting physically protected diagenesis by microfossil matrix. A meridional transect multicores Indian sector shows northward increase like sedimentary varies nitrate...
We have measured the carbon isotopic composition of particulate organic matter suspended in surface waters (POM) between 59°S and 30°S SW Indian Ocean during austral summer. In an attempt to further document pattern causes covariance POC‐δ 13 C [CO 2aq ], we concurrently water pCO 2 , temperature, salinity, nitrate concentration, POM chlorophyll a δ total dissolved inorganic carbon. While found previously reported general negative correlation also observed prominent maximum region...
Nitrogen stable-isotope compositions (delta15N) can help track denitrification and N2O production in the environment, as knowledge of isotopic discrimination, or isotope effect, inherent to denitrification. However, effects associated with a function dissolved-oxygen concentration their influence on composition are not known. We developed simple steady-state reactor allow measurement Paracoccus denitrificans. With [dO2] between 0 1.2 microM, N NO3- reduction were constant at 28.6 per...
We present a new nitrogen isotope model incorporated into the three‐dimensional ocean component of global Earth system climate designed for millennial timescale simulations. The includes prognostic tracers two stable isotopes, 14 N and 15 N, in nitrate (NO 3 − ), phytoplankton, zooplankton, detritus variables marine ecosystem model. effects algal NO uptake, fixation, water column denitrification, zooplankton excretion are considered as well removal by sedimentary denitrification. A database...