ORCID
0000-0002-8035-7338 (Zhu), 0000-0001-5212-6228 (Chappell), 0009-0002-6834-8508 (Crider), 0000-0001-7473-4873 (Clayton)
Document Type
Article
Publication Date
2024
DOI
10.1002/lno.12678
Publication Title
Limnology & Oceanography
Volume
69
Issue
10
Pages
2406-2421
Abstract
Observations and model studies suggest that front dynamics can enhance phytoplankton productivity. This study tested whether frontal systems also increase the abundance of nitrifying microbes and nitrogen recycling during repeat sampling transects across the Mid‐Atlantic Bight shelfbreak in July 2019. We measured ammonium concentrations, nitrate dual isotopes (δ15N, δ18O), and ammonia monooxygenase subunit A (amoA) genes of ammonia‐oxidizing archaea (AOA) and bacteria (AOB). In subsurface shelf waters, ammonium concentrations exceeded 2 μmol L−1, due to a temporary imbalance in regeneration from sinking particles and subsequent nitrification. The inverse correlation between nitrate δ15N values and ammonium concentrations confirmed nitrate was partially or entirely from local nitrification on the shelf. In contrast, the shelfbreak frontal zone and slope sea subsurface waters had much lower ammonium concentrations (0.1–0.2 μmol L−1) due to tight coupling between ammonium regeneration and nitrification. The deviation of nitrate δ15N and δ18O from algal uptake‐driven 1 : 1 ratio suggests concurrent nitrification in the euphotic zone. The shelfbreak front acted as an ecological boundary where AOA and AOB amoA gene numbers were partitioned, with AOAs abounding in slope waters and AOBs in shelf waters, likely due to ammonium availability. At certain slope stations, deep‐water nutrient inputs via isopycnal lifting induced by Gulf Stream intrusions caused unexpectedly high phytoplankton biomass, which doubled nitrifier abundance and potentially stimulated both ammonium regeneration and nitrification. These findings demonstrate distinct distributions of nitrifying microbes along the salinity gradient from shelf to slope and highlight the significant influence of coastal ocean‐western boundary current interactions on nitrogen biogeochemistry.
Rights
© 2024
This is an open access article under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Data Availability
The CTD and bottle data are available on the BCO-DMO project page https://bco-dmo.org/project/748894. The nitrate dual isotopes, nitrifiers gene abundance, and DOC and DON data can be accessed in Supporting Information Data S1 .
Original Publication Citation
Zhu, Y., Mulholland, M. R., Selden, C. R., McGillicuddy, D. J., Jr., Mottram, J., Chappell, P. D., Zhang, W. G., Granger, J., Crider, K. E., Meyer, M. G., Bernhardt, P. W., Oliver, H., & Clayton, S. (2024). Contrasting nitrogen dynamics across the Mid‐Atlantic Bight shelfbreak front: Insights from nitrate dual isotopes and nitrifier gene abundance. Limnology & Oceanography, 69(10), 2406-2421. https://doi.org/10.1002/lno.12678
Repository Citation
Zhu, Yifan; Mulholland, Margaret R.; Selden, Corday R.; McGillicuddy, Dennis J. Jr.; Mottram, Josie; Chappell, P. Dreux; Zhang, Weifang Gordon; Granger, Julie; Crider, Katherine E.; Meyer, Meredith G.; Bernhardt, Peter W.; Oliver, Hilde; and Clayton, Sophie, "Contrasting Nitrogen Dynamics Across the Mid-Atlantic Bight Shelfbreak Front: Insights from Nitrate Dual Isotopes and Nitrifier Gene Abundance" (2024). OES Faculty Publications. 521.
https://digitalcommons.odu.edu/oeas_fac_pubs/521
Data S1. Supporting Information.
Zhu-2024-ContrastingNitrogenDynamicsS2.xlsx (60 kB)
Data S2. Supporting Information.