Starting with the work of Ben Houlton, we have collaborated with the group of Lars Hedin in the Department of Ecology and Evolutionary Biology in isotope studies of terrestrial N cycling. We have also worked on the nitrate N and O isotopes in rain, snow, and ice as tracers of reactive nitrogen sources and processing in the modern and ancient atmosphere.
References
12 Publications
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Nitrogen in Past Marine Environments
This chapter reviews the ongoing efforts to use sediment and ice core records to understand the dynamics of oceanic fixed nitrogen (N), focusing on recent glacial-interglacial cycles. Research has, up to this point, followed the reductionist approach of trying to reconstruct either changes in the ocean N budget (largely through low latitude…
Consistent relationship between global climate and surface nitrate utilization in the western subarctic Pacific throughout the last 500 ka
The open subarctic Pacific is, at present, a high nitrate low chlorophyll (HNLC) region, where nitrate is perennially abundant at the surface. Theoretically, the HNLC status of this region is subject to modification by ocean circulation and/or micronutrient supply, with implications for the effectiveness of the biological pump and hence carbon…
Carbon dioxide release from the North Pacific abyss during the last deglaciation
Atmospheric carbon dioxide concentrations were significantly lower during glacial periods than during intervening interglacial periods, but the mechanisms responsible for this difference remain uncertain. Many recent explanations call on greater carbon storage in a poorly ventilated deep ocean during glacial periods, but direct evidence regarding…
Insights into anthropogenic nitrogen deposition to the North Atlantic investigated using the isotopic composition of aerosol and rainwater nitrate
Identifying the dominant sources of atmospheric reactive nitrogen (N r) is critical for determining the influence of anthropogenic emissions on Nr deposition, especially in marine ecosystems. To test the influence of anthropogenic versus marine air masses, samples were collected in Bermuda, where seasonal atmospheric circulation patterns lead to…
Coupled nitrification-denitrification in sediment of the eastern Bering Sea shelf leads to 15N enrichment of fixed N in shelf waters
We studied the nitrogen biogeochemistry of the ice-covered eastern Bering Sea shelf using the isotope ratios (15N/14N and 18O/16O) of NO3- and other N species. The 15N/14N of late winter NO3 - on the shelf decreases inshore and is inversely correlated with bottom water [NH4+], consistent with an input of low- 15N/14N NO3- from partial…
N and O isotope effects during nitrate assimilation by unicellular prokaryotic and eukaryotic plankton cultures
In order to provide biological systematics from which to interpret nitrogen (N) and oxygen (O) isotope ratios of nitrate (15N/14N, 18O/16O, respectively) in the environment, we previously investigated the isotopic fractionation of nitrate during its assimilation by mono-cultures of eukaryotic algae (Granger et al., 2004). In this study, we…
Removal of nitrite with sulfamic acid for nitrate N and O isotope analysis with the denitrifier method
In environmental water samples that contain both nitrate (NO 3-) and nitrite (NO2-), isotopic analysis of nitrate 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 - Oceanographie Research Papers 1997; 44…
Nitrogen and oxygen isotope fractionation during dissimilatory nitrate reduction by denitrifying bacteria
We report the first measurements of coupled nitrogen (N) and oxygen (O) isotope fractionation of nitrate by laboratory cultures of denitrifying bacteria. Two seawater strains (Pseudomonas stutzeri, Ochrobactrum sp.) and three freshwater strains (Paracoccus denitrificans, Pseudomonas chlororaphis, Rhodobacter sphaeroides) were examined. Among four…
A method for nitrite removal in nitrate N and O isotope analyses
We describe a method to remove nitrite from seawater and freshwater samples to determine the nitrogen (N) and oxygen (O) isotopic composition of nitrate in aqueous samples (15N/14N and 18O/16O, respectively). This method is simple, inexpensive, and effective in the removal of nitrite without compromising the natural N and O isotopic composition of…
Coupled nitrogen and oxygen isotope fractionation of nitrate during assimilation by cultures of marine phytoplankton
We report the first measurements of coupled nitrogen (N) and oxygen (O) isotopic variations of nitrate (NO3-) during its assimilation by laboratory cultures of marine phytoplankton and derive the N and O kinetic isotope effects for nitrate assimilation by three species of diatoms (Thalassiosira weissflogii, Thalassiosira oceanica, and…
On the Properties of the Arctic Halocline and Deep Water Masses of the Canada Basin from Nitrate Isotope Ratios
Nitrogen is a limiting nutrient for primary production in the western Arctic Ocean. Measurements of the nitrogen (15N/14N) and oxygen (18O/16O) isotope ratios of nitrate in the southeastern Beaufort Sea provide insight into biogeochemical cycling of nitrogen in the western Arctic Ocean. Nitrate O isotope ratios in the Pacific halocline evidence a…
The proportion of remineralized nitrate on the ice-covered eastern Bering Sea shelf evidenced from the oxygen isotope ratio of nitrate
We present measurements of nitrate and its natural abundance oxygen isotope composition (18O/16O) in the water column of the broad and shallow eastern Bering Sea shelf in the late winter and early spring of 2007 and 2008. In both years, nitrate concentrations showed a characteristic decrease, from 25 μM at the slope to ≤5 μM inshore. The 18O/16O…