Net primary production in the Gulf Stream sustained by quasi‐geostrophic vertical exchanges

Pascual, Ananda; Ruiz, Simón; Nardelli, Bruno Buongiorno; Guinehut, S.; Iudicone, Daniele; Tintoré, Joaquı́n

doi:10.1002/2014gl062569

Cited by 30 publications

(29 citation statements)

References 60 publications

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“…Different processes, operating on the sub-mesoscale, have been identified as being responsible for intense vertical velocities within eddies. However, the exact details are a topic that has been under debate for more than a decade (see Klein and Lapeyre, 2009;Lévy et al, 2012;Gaube et al, 2014;Pascual et al, 2015, for further references). Also, the trapping of surface waters by eddies should play a role (d'Ovidio et al, 2013).…”

Section: Respiration In Isolated Eddiesmentioning

confidence: 99%

“…The data at hand do not allow for conclusions to be made on nutrient pathways within eddies, nor can we estimate productivity. However, a bulk estimate for the vertical velocity across the eddies can be done, making use of an approach based on wind stress variations generated by wind/surface current shear (Martin and Richards, 2001;McGillicuddy et al, 2007;Pascual et al, 2015). In brief, on one side of the eddy, where the wind blows against the eddy rotation, the wind stress is elevated while the contrary happens on the opposite side.…”

Section: Respiration In Isolated Eddiesmentioning

confidence: 99%

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Open ocean dead zones in the tropical North Atlantic Ocean

et al. 2015

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Abstract.Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low ( < 2 µmol kg −1 ) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 µmol kg −1 . The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day −1 , from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

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Section: Respiration In Isolated Eddiesmentioning

confidence: 99%

Section: Respiration In Isolated Eddiesmentioning

confidence: 99%

Open ocean dead zones in the tropical North Atlantic Ocean

et al. 2015

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“…f is the Coriolis parameter and g is gravity. Vertical velocity is estimated using the quasi-geostrophic approximation by integrating the QG omega equation, presented here in its Q vector formulation (Hoskins et al, 1978;Tintoré et al, 1991;Buongiorno Nardelli et al, 2012;Pascual et al, 2015):…”

Section: Computation Of 3-d Velocitymentioning

confidence: 99%

“…In this context, we aim to estimate the importance of horizontal and vertical mesoscale motions on nutrient redistribution through the application of quasi-geostrophic (QG) theory to an observation-based product (Buongiorno Nardelli et al, 2012;Pascual et al, 2015). In particular, we aim to investigate the influence of derived horizontal and vertical ve-locities on ocean nitrate uptake in the southeast Pacific (SEP) through the use of a Lagrangian particle-tracking code.…”

Section: Introductionmentioning

confidence: 99%

Impact of vertical and horizontal advection on nutrient distribution in the southeast Pacific

et al. 2016

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Abstract. An innovative approach is used to analyze the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the redistribution and uptake of nitrate in the southeast Pacific (SEP). A total of 12 years of vertical and horizontal currents are derived from an observationbased estimate of the ocean state. Horizontal velocities are obtained through the application of thermal wind balance to weekly temperature and salinity fields. Vertical velocities are estimated by integration of the QG omega equation. Seasonal variability of the synthetic vertical velocity and kinetic energy associated with the horizontal currents is coincident, with peaks in austral summer (November-December) in accord with published observations. The impact of vertical velocity on SEP nitrate uptake rates is assessed by using two Lagrangian particle tracking experiments that differ according to vertical forcing (ω = ω QG vs. ω = 0). From identical initial distributions of nitrate-tagged particles, the Lagrangian results show that vertical motions induce local increases in nitrate uptake reaching up to 30 %. Such increases occur in low uptake regions with high mesoscale activity. Despite being weaker than horizontal currents by a factor of up to 10 −4 , vertical velocity associated with mesoscale activity is demonstrated to make an important contribution to nitrate uptake, hence productivity, in low uptake regions.

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“…Buongiorno Nardelli et al (2012) carried out the first attempt to apply the quasigeostrophic (QG) approximation to the observation-based product in order to map 3D mesoscale dynamics. Pascual et al (2015) and Barceló-Llull et al (2016) derive the QG mesoscale vertical velocity from the ARMOR3D fields in order to analyze its distribution in different regions of the global ocean as well as its contribution to nutrient advection and phytoplankton growth. Mason et al (2017) construct eddy-centric composites of tracers, geostrophic currents and QG vertical velocity diagnosed from ARMOR3D in the energetic Brazil-Malvinas Confluence region.…”

Section: Introductionmentioning

confidence: 99%

Comparing a Multivariate Global Ocean State Estimate With High-Resolution in Situ Data: An Anticyclonic Intrathermocline Eddy Near the Canary Islands

et al. 2018

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The provision of high-resolution in situ oceanographic data is key for the ongoing verification, validation and assessment of operational products, such as those provided by the Copernicus Marine Core Service (CMEMS). Here we analyze the ability of ARMOR3D-a multivariate global ocean state estimate that is available from CMEMS-to reconstruct a mesoscale anticyclonic intrathermocline eddy that was previously sampled with high-resolution independent in situ observations. ARMOR3D is constructed by merging remote sensing observations with in situ vertical profiles of temperature and salinity obtained primarily from the Argo network. In situ data from CTDs and an Acoustic Doppler Current Profiler were obtained during an oceanographic cruise near the Canary Islands (Atlantic ocean). The analysis of the ARMOR3D product using the in situ data is done over (i) a high-resolution meridional transect crossing the eddy center and (ii) a three-dimensional grid centered on the eddy center. An evaluation of the hydrographic eddy signature and derived dynamical variables, namely geostrophic velocity, vertical vorticity and quasi-geostrophic (QG) vertical velocity, demonstrates that the ARMOR3D product is able to reproduce the vertical hydrographic structure of the independently sampled eddy below the seasonal pycnocline, with the caveat that the flow is surface intensified and the seasonal pycnocline remains flat. Maps of ARMOR3D density show the signature of the eddy, and agreement with the elliptical eddy shape seen in the in situ data. The major eddy axes are oriented NW-SE in both data sets. The estimated radius for the in situ eddy is ∼46 km; the ARMOR3D radius is significantly larger at ∼ 92 km and is considered an overestimation that is inherited from an across-track altimetry sampling issue. The ARMOR3D geostrophic flow is underestimated by a factor of 2, with maxima of 0.11 (−0.19) m s −1 at the surface, which implies an underestimation of the local Rossby number by a factor of 3. Both the in situ and ARMOR3D eddies have decelerating flows at their northern edges. The ARMOR3D QG vertical velocity distribution has upwelling/downwelling cells located along the eddy periphery and similar magnitudes to the in situ-derived QG vertical velocity.

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Net primary production in the Gulf Stream sustained by quasi‐geostrophic vertical exchanges

Cited by 30 publications

References 60 publications

Open ocean dead zones in the tropical North Atlantic Ocean

Open ocean dead zones in the tropical North Atlantic Ocean

Impact of vertical and horizontal advection on nutrient distribution in the southeast Pacific

Comparing a Multivariate Global Ocean State Estimate With High-Resolution in Situ Data: An Anticyclonic Intrathermocline Eddy Near the Canary Islands

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