Nitrogen fixation at the Mid‐Atlantic Bight shelfbreak and transport of newly fixed nitrogen to the Slope Sea

Selden, C. R.; Mulholland, M. R.; Crider, K. E.; Clayton, S.; Macías‐Tapia, A.; Bernhardt, P.; McGillicuddy, D. J.; Zhang, W. G.; Chappell, P. D.. 2024 Nitrogen fixation at the Mid‐Atlantic Bight shelfbreak and transport of newly fixed nitrogen to the Slope Sea. Journal of Geophysical Research: Oceans, 129 (4).

Before downloading, please read NORA policies.
©2024. The Authors.
JGR Oceans - 2024 - Selden - Nitrogen Fixation at the Mid‐Atlantic Bight Shelfbreak and Transport of Newly Fixed Nitrogen.pdf - Published Version
Available under License Creative Commons Attribution 4.0.

Download (1MB) | Preview


Continental shelves contribute a large fraction of the ocean's new nitrogen (N) via N2 fixation; yet, we know little about how physical processes at the ocean's margins shape diazotroph biogeography and activity. Here, we test the hypothesis that frontal mixing favors N2 fixation at the Mid-Atlantic Bight shelfbreak. Using the 15N2 bubble release method, we measured N2 fixation rates on repeat cross-frontal transects in July 2019. N2 fixation rates in shelf waters (median = 5.42 nmol N L−1 d−1) were higher than offshore (2.48 nmol N L−1 d−1) but did not significantly differ front frontal waters (8.42 nmol N L−1 d−1). However, specific N2 uptake rates, indicative of the relative contribution of diazotroph-derived N to particulate N turnover, were significantly higher in frontal waters, suggesting that diazotroph-derived N is of greater importance in supporting productivity there. This study furthered captured an ephemeral shelf-water streamer, which resulted from the impingement of a warm core ring on the shelf. The streamer transported shelf-water diazotrophs (including UCYN-A and Richelia spp., as assessed by qPCR) offshore with sustained high N2 fixation rates. This feature injected >50 metric tons d−1 of newly fixed N to the Slope Sea—a rate equivalent to ∼4% of the total N flux estimated for the entire Mid-Atlantic Bight. As intrusions of Gulf Stream meanders and eddies onto the shelf are increasing in frequency due to climate change, episodic lateral fluxes of new N into the Slope Sea may become increasingly important to regional budgets and ecosystem productivity.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 2169-9275
Additional Keywords: N2 fixation, diazotroph, front, Gulf Stream, Mid-Atlantic Bight, warm-core ring, streamer
Date made live: 25 Apr 2024 14:50 +0 (UTC)

Actions (login required)

View Item View Item

Document Downloads

Downloads for past 30 days

Downloads per month over past year

More statistics for this item...