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Nitrogen cycling in the ocean: From genes to ecosystems and from the past to the future
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Insights on Halocline Ventilation in the Western Arctic from Nitrate Isotope Ratios (Invited)
Monday 7th @ 1330-1350, Multifunction Hall
Julie Granger* , University of Connecticut
Presenter Email: julie.granger@uconn.edu |
| 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. Pre-formed nitrate in the Halocline lacks a 18O/16O enrichment from nitrate assimilation, contrasting preformed nitrate in other ocean basins. 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. The observations reveal that shelf processes have a disproportionate influence on tracer properties of the Pacific Halocline. |
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