Pairing ΔN2/Ar and N* tracers to observe denitrification in the Canada Basin




Reeve, Jennifer L.

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Our understanding of the global marine xed nitrogen budget has undergone rapid growth, and as a result there is debate as to whether or not it is balanced. The Arctic plays a disproportionately large role in the sink terms of this budget. This paper works to understand the role of the Canada Basin in the nitrogen cycle. We utilize two tracers of denitri cation: N2/Ar, a dissolved gas tracer, and N*, a nutrient ratio tracer. We aim to quantify the current state of nitrogen cycling in the Canada Basin, and determine its role in the global cycle. Our paired tracer method provides support for shelf denitri cation rates while providing an estimate of ventilation in the same water mass, and provides an estimate for deep benthic denitri cation rates. We observe a disconnect between N2/Ar and N* in the Paci c Upper Halocline Layer (PUHL), wherein the excess N2/Ar we expect from N* is nearly 250% larger than the excess we observe. Our calculations suggest that an approximate steady state between benthic denitri cation and gas exchange on the Chukchi shelf maintains this disconnect. Our measurements of the PUHL support the shelf denitri cation rates reported from direct measurements, and can predict wind speeds required for ventilation within a factor of two. A 1D diffusion model of the old deep waters of the Canada Basin supports benthic denitri cation rates of 0.095-0.15 Tg N y-1. Benthic denitri cation rates determined from the model are on the low end of rates in other deep basins. Our results suggest additional measurements of these tracers in the Canada Basin and surrounding areas would help to constrain both the physical and biological processes controlling nitrogen cycling.



chemical oceanography, nitrogen, denitrification, Arctic, Canada Basin, N*, dissolved gases, ΔN2/Ar, marine nitrogen cycle