Elevated 15N/14N in particulate organic matter, zooplankton, and diatom frustule-bound nitrogen in the ice-covered water column of the Bering Sea eastern shelf

Morales, Laura V.; Granger, Julie; Chang, Bonnie X.; Prokopenko, Maria G.; Plessen, Birgit; Gradinger, Rolf; Sigman, Daniel M.

doi:10.1016/j.dsr2.2014.05.008

Cited by 39 publications

(34 citation statements)

References 58 publications

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“…Indeed, Granger et al () and Brown et al () reported that the δ 15 N of reactive N on the Bering and Chukchi shelves increases progressively in proportion to N loss recorded by N* in the water column, ascribing the increase to coupled nitrification‐denitrification in shelf sediments: Nitrogen isotopic discrimination of reactive N occurs during nitrification of ammonium to NO 3 − in sediments, resulting in 15 N enrichment of benthic ammonium and the production of 15 N‐deplete NO 3 − . The 15 N‐deplete nitrate is denitrified to N 2 in underlying sediments, whereas the 15 N‐enriched ammonium is released to the water column (Granger et al, ; Morales et al, ). Complete nitrification of water‐column ammonium then yields 15 N‐enriched, 18 O‐deplete NO 3 − , consistent with the signal observed downstream in PWW.…”

Section: Discussionmentioning

confidence: 99%

On the Properties of the Arctic Halocline and Deep Water Masses of the Canada Basin from Nitrate Isotope Ratios

et al. 2018

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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 highly regenerated reservoir. Coincident peaks in nutrient concentrations and reduced dissolved oxygen concentrations suggest that nitrate accrues from organic matter remineralization in bottom waters of the Chukchi shelf and that these ventilate the basin predominantly in summer, when isolated from the atmosphere. Preformed nitrate in Pacific Winter Water lacks 18O/16O elevation from nitrate assimilation, contrasting with preformed nitrate in other ocean regions. A reactive N deficit and elevated nitrate N isotope ratios in the Pacific halocline further indicate substantial N loss to coupled nitrification‐denitrification in shelf sediments upstream. In the Atlantic Water below, nitrate isotope ratios identify two distinct waters entering the Arctic at Fram Strait, from (1) the surface West Spitsbergen Current, bearing isotopic signatures akin to North Atlantic waters, and (2) deeper inflows of waters ventilated in the Nordic Seas, transporting nitrate O isotope ratios indicative of regenerated nitrate. Poorly ventilated Canada Basin Deep Water shows evidence of nominal accrual of remineralized products, and nitrate isotope ratios suggest an influence of slow benthic denitrification on the sea floor. The observations reveal that shelf processes have a disproportionate influence on tracer properties of the Pacific halocline, while those in Atlantic Water are dominated by processes in the Nordic Seas.

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Section: Discussionmentioning

confidence: 99%

On the Properties of the Arctic Halocline and Deep Water Masses of the Canada Basin from Nitrate Isotope Ratios

et al. 2018

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“…But it could presumably occur in individual basins, as proposed for late Archean lakes (Thomazo et al, 2011). It may be recognizable by a large scatter in sedimentary δ 15 N data as in the modern Bering Sea where organic N ranges from +2‰ to +18‰ (Morales et al, 2014). This scatter may result from fluctuations between complete and incomplete nitrification over short timescales.…”

Section: A Primer On Nitrogen Isotopes In Geological Samplesmentioning

confidence: 97%

“…One would thus expect it to go to completion in most cases without leaving an isotopic trace in the geologic record. However, incomplete nitrification has been reported from sediments in the Bering Sea where biomass becomes increasingly heavy from assimilation of the residual NH 4 + (Granger et al, 2011;Morales et al, 2014). The light NO 2 -was lost by subsequent denitrification.…”

Section: A Primer On Nitrogen Isotopes In Geological Samplesmentioning

confidence: 99%

The evolution of Earth's biogeochemical nitrogen cycle

Stüeken

Kipp

Koehler

et al. 2016

Earth-Science Reviews

310

287

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Nitrogen is an essential nutrient for all life on Earth and it acts as a major control on biological productivity in the modern ocean. Accurate reconstructions of the evolution of life over the course of the last four billion years therefore demand a better understanding of nitrogen bioavailability and speciation through time. The biogeochemical nitrogen cycle has evidently been closely tied to the redox state of the ocean and atmosphere. Multiple lines of evidence indicate that the Earth"s surface has passed in a non-linear fashion from an anoxic state in the Hadean to an oxic state in the later Phanerozoic. It is therefore likely that the nitrogen cycle has changed markedly over time, with potentially severe implications for the productivity and evolution of the biosphere. Here we compile nitrogen isotope data from the literature and review our current understanding of the evolution of the nitrogen cycle, with particular emphasis on the Precambrian. Combined with recent work on redox conditions, trace metal availability, sulfur and iron cycling on the early Earth, we then use the nitrogen isotope record as a platform to test existing and new hypotheses about biogeochemical pathways that may have controlled nitrogen availability through time. Among other things, we conclude that (a) abiotic nitrogen sources were likely insufficient to sustain a large biosphere, thus favoring an early origin of biological N 2 fixation, (b) evidence of nitrate in the Neoarchean and Paleoproterozoic confirm current views of increasing surface oxygen levels at those times, (c) abundant ferrous iron and sulfide in the midPrecambrian ocean may have affected the speciation and size of the fixed nitrogen reservoir, and (d) nitrate availability alone was not a major driver of eukaryotic evolution.

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“…Microzooplankton biomass increases seasonally, and at least part of that increase is linked to the variability of mesozooplankton grazing control on microzooplankton during winter and spring. In contrast to experimental grazing observations, Morales et al (2014), present stable isotope data that suggests mesozooplankton preferentially graze on diatoms and other primary producers, and that there is little to no evidence of grazing at more than one trophic level. This apparent lack of grazing control leads to increased microzooplankton biomass from spring to summer, consistent with the findings of Stoecker et al (2014b) who observed that microzooplankton biomass was equal to or greater than phytoplankton biomass.…”

Section: Zooplanktonmentioning

confidence: 54%

“…For example, in an analysis of the mooring chlorophyll fluorescence time-series, Sigler et al (2014) observed that the timing of the open water spring bloom was dependent upon stratification. This pattern of physical control, tied to the presence or absence of sea ice, leads to a variable time period between the fall blooms in one year and the spring bloom in the subsequent year and is hypothesized to have important implications for the flow of energy to mesozooplankton in the spring (Morales et al, 2014;Sigler et al, 2014) and for 'refueling' in the fall. Sigler et al (2014) also suggest that the presence or absence of sea ice impacts the magnitude of the spring bloom, where ice algal production may reduce the nutrient content of the upper water column by consumption and rapid export to the benthos, thus leading to lower chlorophyll and primary production in the subsequent open-water spring bloom and summer period.…”

Section: Phytoplankton and Primary Productionmentioning

confidence: 99%