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Ocean Circulation Causes Strong Variability in the Mid‐Atlantic Bight Nitrogen Budget
Author(s) -
Friedrichs Marjorie A. M.,
StLaurent Pierre,
Xiao Yongjin,
Hofmann Eileen,
Hyde Kimberly,
Mannino Antonio,
Najjar Raymond G.,
Narváez Diego A.,
Signorini Sergio R.,
Tian Hanqin,
Wilkin John,
Yao Yuanzhi,
Xue Jianhong
Publication year - 2019
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2018jc014424
Subject(s) - biogeochemical cycle , environmental science , ocean gyre , continental shelf , oceanography , biogeochemistry , nitrogen , nutrient , current (fluid) , nitrogen cycle , new production , ocean current , climatology , atmospheric sciences , geology , ecology , phytoplankton , subtropics , biology , chemistry , organic chemistry
Understanding of nitrogen cycling on continental shelves, a critical component of global nutrient cycling, is hampered by limited observations compared to the strong variability on a wide range of time and space scales. Numerical models have the potential to partially alleviate this issue by filling spatiotemporal data gaps and hence resolving annual area‐integrated nutrient fluxes. In this study, a three‐dimensional biogeochemical‐circulation model was implemented to simulate the Mid‐Atlantic Bight (MAB) nitrogen budget. Model results demonstrate that, on average, MAB net community production (NCP) was positive (+0.27 Tg N/year), indicating net autotrophy. Interannual variability in NCP was strong, with annual values ranging between 0.19 and 0.41 Tg N/year. Along‐shelf and across‐shelf horizontal transport fluxes were the other dominant terms in the nitrogen budget and were primarily responsible for this NCP variability. The along‐shelf current transported nitrogen from the north (0.65 Tg N/year) into the MAB, supplementing the nitrogen entering from terrestrial inputs (0.27 Tg N/year). However, NCP was highest in the year when total water volume transport and inorganic nitrogen input was strongest across the continental slope in the southern MAB, rather than when terrestrial inputs were greatest. Interannual variability of NCP appears to be linked to changes in the positions of the Gulf Stream and Slope Water Gyre. Overall, the strong spatiotemporal variability of the nitrogen fluxes highlights the importance of observations throughout all seasons and multiple years in order to accurately resolve the current status and future changes of the MAB nitrogen budget.