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Counteracting contributions of the upper and lower meridional overturning limbs to the North Atlantic nutrient budgets: enhanced imbalance in 2010

Counteracting contributions of the upper and lower meridional overturning limbs to the North Atlantic nutrient budgets: enhanced imbalance in 2010
Counteracting contributions of the upper and lower meridional overturning limbs to the North Atlantic nutrient budgets: enhanced imbalance in 2010
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 24.5°N. Combined with heaving of the isopycnals, this 'extreme circulation event' in 2010 favoured an enhancement of the nutrientconsumption (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)
45 in the North Atlantic.
Carbon cycle, North Atlantic, Nutrient and oxygen transports, Nutrient budgets, Nutrient cycles, Overturning circulation
0886-6236
Carracedo, L.I.
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Mercier, H.
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McDonagh, E.
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Rosón, G.
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Sanders, R.
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Moore, Christopher
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Torres‐Valdés, S.
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Brown, P.
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Lherminier, P.
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Pérez, F.F.
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Carracedo, L.I.
bec89e77-2127-4792-982b-d5aaea471ccd
Mercier, H.
a41884c5-8915-45e1-b1d7-388248f69505
McDonagh, E.
d86c507f-6018-47da-882e-1192068709e0
Rosón, G.
1c377389-c80f-4b73-aa66-5f81d357abbc
Sanders, R.
a70fab9e-0090-499e-b33d-d0b2ecbef532
Moore, Christopher
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Torres‐Valdés, S.
61640a2f-880e-4da0-80ec-5a2b506f1703
Brown, P.
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Lherminier, P.
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Pérez, F.F.
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Carracedo, L.I., Mercier, H., McDonagh, E., Rosón, G., Sanders, R., Moore, Christopher, Torres‐Valdés, S., Brown, P., Lherminier, P. and Pérez, F.F. (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]. (doi:10.1029/2020GB006898).

Record type: Article

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 24.5°N. Combined with heaving of the isopycnals, this 'extreme circulation event' in 2010 favoured an enhancement of the nutrientconsumption (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)
45 in the North Atlantic.

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Carracedo_etal_GBC - Accepted Manuscript
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e-pub ahead of print date: 14 April 2021
Published date: 21 April 2021
Keywords: Carbon cycle, North Atlantic, Nutrient and oxygen transports, Nutrient budgets, Nutrient cycles, Overturning circulation

Identifiers

Local EPrints ID: 449171
URI: http://eprints.soton.ac.uk/id/eprint/449171
ISSN: 0886-6236
PURE UUID: 8a4a6882-3adf-4254-95a4-8d1b677f6421
ORCID for Christopher Moore: ORCID iD orcid.org/0000-0002-9541-6046

Catalogue record

Date deposited: 18 May 2021 16:33
Last modified: 26 Nov 2021 02:42

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Contributors

Author: L.I. Carracedo
Author: H. Mercier
Author: E. McDonagh
Author: G. Rosón
Author: R. Sanders
Author: S. Torres‐Valdés
Author: P. Brown
Author: P. Lherminier
Author: F.F. Pérez

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