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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-87
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-87
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 20 Mar 2020

Submitted as: research article | 20 Mar 2020

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This preprint is currently under review for the journal BG.

Contrasting decadal trends of subsurface excess nitrate in the western and eastern North Atlantic Ocean

Jin-Yu Terence Yang1,2, Kitack Lee1, Jia-Zhong Zhang3, Ji-Young Moon1, Joon-Soo Lee4, In-Seong Han4, and Eunil Lee5 Jin-Yu Terence Yang et al.
  • 1Division of Environmental Sciences and Engineering, Pohang University of Science and Technology, Pohang 37673, Korea
  • 2State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
  • 3National Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratory, Miami, FL 33149, USA
  • 4Ocean Climate and Ecology Research Division, National Institute of Fisheries Science, Busan 46083, Korea
  • 5Ocean Research Division, Korea Hydrographic and Oceanographic Agency, Busan 49111, Korea

Abstract. Temporal variations in excess nitrate (DINxs) relative to phosphate were evaluated using datasets derived from repeated measurements along meridional and zonal transects in the upper (200–600 m) North Atlantic (NAtl) between the 1980s and 2010s. The analysis revealed that the DINxs trend in the western NAtl differed from that in the eastern NAtl. In the western NAtl, which has been subject to atmospheric nitrogen deposition (AND) from the USA, the subsurface DINxs concentrations have increased over the last two decades. This increase was associated with the increase in AND measured along the US east coast, with a mean lag period of 15 years. This time lag was approximately equivalent to the time elapsed since the subsurface waters in the western NAtl were last in contact with the atmosphere (the ventilation age). Our finding provides an evidence that the DINxs dynamics in the western NAtl in recent years has been affected by anthropogenic nitrogen inputs, although this influence is weak relative to that in the North Pacific. In contrast, a decreasing trend in subsurface DINxs was observed after the 2000s in the eastern NAtl, particularly in the high latitudes. This finding may be associated with a possible decline of tropical N2 fixation and the weakening of the Atlantic meridional overturning circulation, although more time-resolved data on nutrients and meridional circulation are needed to assess this hypothesis. Our results highlight the importance of both anthropogenic and climate forcing in impacting the nutrient dynamics in the upper NAtl.

Jin-Yu Terence Yang et al.

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Jin-Yu Terence Yang et al.

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