Counteracting contributions of the Upper and Lower Meridional Overturning Limbs to the North Atlantic Nutrient Budgets: enhanced imbalance in 2010

Type Article
Date 2021-06
Language English
Author(s) Carracedo LidiaORCID1, 2, Mercier HerleORCID8, McDonagh E.ORCID2, 3, Rosón G.ORCID4, Sanders R.2, 3, Moore C.M.5, Torres‐valdés S.ORCID6, Brown P.ORCID2, Lherminier PascaleORCID1, Pérez Ff7
Affiliation(s) 1 : University of Brest CNRS Ifremer IRD Laboratoire d'Océanographie Physique et Spatiale (LOPS) IUEM Centre Ifremer de Bretagne F‐29280 Plouzané ,France
2 : National Oceanography Centre (NOC) SouthamptonSO14 3ZH, UK
3 : NORCE Norwegian Research Centre Bjerknes Centre for Climate Research Bergen, Norway
4 : Faculty of Marine Sciences University of Vigo Campus Lagoas‐Marcosende 36200 Vigo ,Spain
5 : School of Ocean and Earth Science National Oceanography Centre University of Southampton SouthamptonSO14 3ZH ,UK
6 : Alfred Wegener Institute Am Handelshafen 12 27570 Bremerhaven, Germany
7 : Instituto de Investigaciones Marinas CSIC 36208 Vigo, Spain
8 : University of Brest CNRS Ifremer IRD Laboratoire d'Océanographie Physique et Spatiale (LOPS) IUEM Centre Ifremer de Bretagne F‐29280 Plouzané ,France
Source Global Biogeochemical Cycles (0886-6236) (American Geophysical Union (AGU)), 2021-06 , Vol. 35 , N. 6 , P. e2020GB006898 (26p.)
DOI 10.1029/2020GB006898
Keyword(s) Carbon cycle, North Atlantic, Nutrient and oxygen transports, Nutrient budgets, Nutrient cycles, Overturning circulation
Abstract

The North Atlantic Basin is a major sink for atmospheric carbon dioxide (CO2) due in part to the extensive plankton blooms which form there supported by nutrients supplied by the three‐dimensional ocean circulation. Hence, changes in ocean circulation and/or stratification may influence primary production and biological carbon export. In this study, we assess this possibility by evaluating inorganic nutrient budgets for 2004 and 2010 in the North Atlantic based on observations from the transatlantic A05‐24.5°N and the Greenland‐Portugal OVIDE hydrographic sections, to which we applied a box inverse model to solve the circulation and estimate the across‐section nutrient transports. Full water column nutrient budgets were split into upper and lower meridional overturning circulation (MOC) limbs. According to our results, anomalous circulation in early 2010, linked to negative‐NAO conditions, led to an enhanced northward advection of more nutrient‐rich waters by the upper overturning limb, which resulted in a significant nitrate and phosphate convergence north of 24.5N. Combined with heaving of the isopycnals, this 'extreme circulation event' in 2010 favoured an enhancement of the nutrient consumption (5.7 ± 4.1 kmol‐P s‐1) and associated biological CO2 uptake (0.25 ± 0.18 Pg‐C yr−1, upper‐bound estimate), which represents a 50% of the mean annual sea–air CO2 flux in the region. Our results also suggest a transient state of deep silicate divergence in both years. Both results are indicative of a MOC‐driven modulation of the biological carbon uptake (by the upper MOC limb) and nutrient inventories (by the lower MOC limb) in the North Atlantic.

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Carracedo Lidia, Mercier Herle, McDonagh E., Rosón G., Sanders R., Moore C.M., Torres‐valdés S., Brown P., Lherminier Pascale, Pérez Ff (2021). Counteracting contributions of the Upper and Lower Meridional Overturning Limbs to the North Atlantic Nutrient Budgets: enhanced imbalance in 2010. Global Biogeochemical Cycles, 35(6), e2020GB006898 (26p.). Publisher's official version : https://doi.org/10.1029/2020GB006898 , Open Access version : https://archimer.ifremer.fr/doc/00689/80086/