Studies in the Modern Ocean

CTD/hydrocast package descending into the Southern Ocean. Photo Kenemy

The CTD/hydrocast package descending into the Southern Ocean water column from the deck of the South African research icebreaker S.A. Agulhas II, sailing from Cape Town to the Antarctic winter ice edge. Photo: Preston Cosslett Kemeny ’15

 

References

9 Publications
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Dissolved organic nitrogen (DON) is the dominant form of fixed nitrogen in most low and middle latitude ocean surface waters. Here, we report measurements of DON isotopic composition (δ15N) from the west South China Sea (SCS), with the goal of providing new insight into DON cycling. The concentration of DON in the surface ocean is correlated (r =…
We have developed a transportable spectroscopic nitrogen isotopic analyzer. The spectrometer is based on dual-modulation Faraday rotation spectroscopy of nitric oxide isotopologues with near shot-noise limited performance and baseline-free operation. Noise analysis indicates minor isotope (15NO) detection sensitivity of 0.36 ppbv·Hz−1/2,…

We present a dual-modulation Faraday rotation spectrometer with in-line optical subtraction for differential measurement of nitric oxide (NO) isotopologues. In-situ sample referencing is accomplished via differential dual-cell measurements, with 3.1 ppbv/rt(Hz) (15NO) sensitivity through 15 cm optical path length. Our system operates at 1.9x…

(Figure Presented) Figure 4. Cycle of biologically driven N transformations that occur in natural and human-influenced terrestrial and marine environments. Nitrogen (N2) fixation (step 1) and N assimilation (from ammonium, nitrate, or organic N, step 2) are anabolic processes, whereas mineralization (step 3), nitrification (steps 4−6), DNRA (steps 7,…
Nitrogen (N) is used in many of life s fundamental biomolecules, and it is also a participant in environmental redox chemistry. Biogeochemical processes control the amount and form of N available to organisms ("fixed"N). These interacting processes result in N acting as the proximate limiting nutrient in most surface environments. Here, we review…
Biological nitrogen fixation constitutes the main input of fixed nitrogen to Earth s ecosystems, and its isotope effect is a key parameter in isotope-based interpretations of the N cycle. The nitrogen isotopic composition (δ15N) of newly fixed N is currently believed to be∼-10/00, based on measurements of organic matter from diazotrophs using…
We present real-time optical polarization subtraction for calibration of Faraday rotation spectra. Noise analysis yields minor isotope sensitivity of 3.0 ppbv·Hz-1/2 and 1.7×10-8 rad·Hz-1/2 noise-equivalent angle. Sub-permil ratiometric precision is achieved at integration times >100 s. © 2016 OSA.
A dual-modulation Faraday rotation spectrometer is employed for isotopic ratiometry of nitric oxide (NO) converted from nitrate/nitrite. Excellent linearity of measured NO to dissolved nitrate is demonstrated. Ratiometry of IAEA-NO-3 standards indicates 3 % accuracy. © 2014 OSA.
A dual-modulation Faraday rotation spectrometer is employed for isotopic ratiometry of nitric oxide (NO) converted from nitrate/nitrite. Excellent linearity of measured NO to dissolved nitrate is demonstrated. Ratiometry of IAEA-NO-3 standards indicates ∼3 % accuracy. © 2014 Optical Society of America.