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Spatial and temporal occurrence of preformed nitrate anomalies in the subtropical North Pacific and North Atlantic oceans.

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Title: Spatial and temporal occurrence of preformed nitrate anomalies in the subtropical North Pacific and North Atlantic oceans.
Authors: Smyth, Adam J.1,2 (AUTHOR) ajsmyth17@gmail.com, Letscher, Robert T.1,2 (AUTHOR)
Source: Marine Chemistry. May2023, Vol. 252, pN.PAG-N.PAG. 1p.
Subjects: Euphotic zone, Ocean, Ocean circulation, Nitrates, Dissolved organic matter, Organic compounds
Abstract: Preformed nitrate (PreNO 3) was formulated to act as a conservative tracer of ocean circulation after accounting for the stoichiometry of marine biochemical reactions involving oxygen and nitrate. However, PreNO 3 anomalies (e.g. negative values) have been identified within the shallow subsurface of the subtropical ocean which still have yet to be fully explained. The mechanisms proposed to drive the formation of PreNO 3 anomalies include: vertical export and remineralization of N-poor dissolved organic matter (DOM) or transparent exopolymer particles (TEP), and the actions of vertically migrating phytoplankton. In this study we use observations from the subtropical Pacific and Atlantic Oceans taken by twenty Biogeochemical Argo profiling floats to assess the spatiotemporal variability of negative subsurface and positive euphotic zone PreNO 3 anomalies and their formation rates. After explicitly accounting for the magnitude of DOM cycling, residual euphotic zone positive PreNO 3 anomalies and subsurface negative PreNO 3 anomalies are consistently observed between 40°S and 40°N. The seasonal timing of euphotic zone positive residual PreNO 3 anomaly formation in relation to subsurface negative residual PreNO 3 anomalies suggests that both vertically migrating phytoplankton and the remineralization of N-deficient TEP likely contribute to the formation of residual PreNO 3 anomalies, but with regional variance suggesting a potentially larger role for migrating phytoplankton in the North Pacific and TEP processes in the North Atlantic. Since migrators include large diatoms that produce ballasted organic matter while TEP may only sink shallowly before remineralization, further investigation into the mechanisms generating PreNO 3 anomalies and their quantitative significance is needed to assess the future trajectory of the biological carbon pump in an expanding subtropical ocean ecosystem. • PreNO 3 anomalies persist seasonally in the BGC-Argo PreNO 3 record. • Euphotic zone positive PreNO 3 anomalies are observed throughout the subtropical ocean. • Subsurface negative PreNO 3 anomalies are present in most of the subtropical ocean. • Formation of PreNO 3 anomalies span monthly to annual timescales [ABSTRACT FROM AUTHOR]
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Abstract:Preformed nitrate (PreNO 3) was formulated to act as a conservative tracer of ocean circulation after accounting for the stoichiometry of marine biochemical reactions involving oxygen and nitrate. However, PreNO 3 anomalies (e.g. negative values) have been identified within the shallow subsurface of the subtropical ocean which still have yet to be fully explained. The mechanisms proposed to drive the formation of PreNO 3 anomalies include: vertical export and remineralization of N-poor dissolved organic matter (DOM) or transparent exopolymer particles (TEP), and the actions of vertically migrating phytoplankton. In this study we use observations from the subtropical Pacific and Atlantic Oceans taken by twenty Biogeochemical Argo profiling floats to assess the spatiotemporal variability of negative subsurface and positive euphotic zone PreNO 3 anomalies and their formation rates. After explicitly accounting for the magnitude of DOM cycling, residual euphotic zone positive PreNO 3 anomalies and subsurface negative PreNO 3 anomalies are consistently observed between 40°S and 40°N. The seasonal timing of euphotic zone positive residual PreNO 3 anomaly formation in relation to subsurface negative residual PreNO 3 anomalies suggests that both vertically migrating phytoplankton and the remineralization of N-deficient TEP likely contribute to the formation of residual PreNO 3 anomalies, but with regional variance suggesting a potentially larger role for migrating phytoplankton in the North Pacific and TEP processes in the North Atlantic. Since migrators include large diatoms that produce ballasted organic matter while TEP may only sink shallowly before remineralization, further investigation into the mechanisms generating PreNO 3 anomalies and their quantitative significance is needed to assess the future trajectory of the biological carbon pump in an expanding subtropical ocean ecosystem. • PreNO 3 anomalies persist seasonally in the BGC-Argo PreNO 3 record. • Euphotic zone positive PreNO 3 anomalies are observed throughout the subtropical ocean. • Subsurface negative PreNO 3 anomalies are present in most of the subtropical ocean. • Formation of PreNO 3 anomalies span monthly to annual timescales [ABSTRACT FROM AUTHOR]
ISSN:03044203
DOI:10.1016/j.marchem.2023.104248