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- Title
Increases in Benthic Particulate Export and Sedimentary Denitrification in the Northern Chukchi Sea Tied to Under‐Ice Primary Production.
- Authors
Payne, C. M.; Arrigo, K. R.
- Abstract
Changing sea ice conditions have led to increases in net primary production (NPP) in the northern Chukchi Sea, driven in part by massive under‐ice phytoplankton blooms. These blooms increase particle export to the sediments and could affect the rate of sedimentary denitrification. We use a 1‐D coupled ecosystem model forced with satellite‐derived sea ice conditions to quantify changes in particle export, nitrification, and denitrification on the northern Chukchi shelf. Between 1988 and 2018, increases in annual NPP drove secular increases in particle export to the benthos (1.8 ± 0.8 mmol m−2 yr−1), water‐column and sedimentary nitrification (1.2 ± 0.4 and 1.1 ± 0.4 mmol m−2 yr−1, respectively), and sedimentary denitrification rates (1.3 ± 0.5 mmol m−2 yr−1). Increased annual export to the benthos and denitrification were driven by higher rates early in the year (from January to June) and are highest in years where under‐ice blooms (UIBs) dominate. Greater denitrification rates in the northern Chukchi Sea would likely reduce NPP in downstream regions such as the Greenland Sea and promote greater N2 fixation in the North Atlantic. Furthermore, sea ice loss and a change in advection of nitrogen (N)‐replete waters through the Bering Strait will likely increase winter N concentrations in the northern Chukchi Sea. Through N sensitivity experiments, we found that 30% of all added N was lost through denitrification, diminishing the N supply available downstream of the Chukchi Sea. Thus, increased particle export associated with UIBs has the potential to markedly alter the N cycle both in the northern Chukchi Sea and in adjacent waters. Plain Language Summary: As sea ice has thinned and retreated, phytoplankton blooms have changed in the Arctic Ocean. In the Chukchi Sea, large phytoplankton blooms have shifted earlier in the year and are even generated when the ocean is covered in sea ice, a period previously assumed to be too light‐limited to allow for blooms. We use a 1‐D model to understand how changes in phytoplankton productivity could influence the nitrogen (N) cycle in the northern Chukchi Sea. We found that increasing under‐ice blooms (UIB) have led to increases in the export of particles to the sediments, which has subsequently led to an increase in both N recycling (nitrification) and N loss (denitrification) in the sediments. The increases in N loss in the region would likely negatively affect downstream ecosystems, where there could be less N available. We also investigated how a change in N supply to the region might affect phytoplankton blooms and the N cycle. We found that 30% of all added N was lost through denitrification, which would also diminish the N available downstream of the Chukchi Sea. By increasing the export of particles to the seafloor, UIBs can markedly alter the N cycle both in the Chukchi Sea and in downstream waters. Key Points: Secular increases in particulate export and sedimentary denitrification (1988–2018) are correlated with increases in total annual NPPExport and denitrification are highest in years with dominant under‐ice NPP; increases from January‐June drive the increasing secular trendsIncreases in winter N concentrations contribute to further increases in denitrification, possibly affecting downstream NPP
- Subjects
CHUKCHI Sea; BENTHIC zone; SEA ice; DENITRIFICATION; NITRIFICATION
- Publication
Journal of Geophysical Research. Oceans, 2022, Vol 127, Issue 2, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2021JC018110