A whirling ecosystem in the equatorial Atlantic

Menkès, Christophe E.

doi:10.1029/2001gl014576

Cited by 76 publications

(90 citation statements)

References 21 publications

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“…It would suggest that, to achieve similarly strong negative oxygen anomalies, the oxygen consumption in the eddies south of 12 • N must be even stronger than in the ACMEs further north. Pronounced productivity patterns in tropical instability waves and vortices have been reported in the past (Menkes et al, 2002) but were not connected to low-oxygen eddies before.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, the generation mechanism of the southern eddies is not obvious. The eddy generation could be related to the presence of strong tropical instabilities in that region (Menkes et al, 2002;von Schuckmann et al, 2008). However, in particular the generation of ACMEs is complex and has been subject of scientific interest for several decades already (D'Asaro, 1988;McWilliams, 1985).…”

Section: Discussionmentioning

confidence: 99%

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Characterization of “dead-zone” eddies in the eastern tropical North Atlantic

Schütte¹,

Karstensen²,

Krahmann³

et al. 2016

Biogeosciences

102

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Abstract. Localized open-ocean low-oxygen "dead zones" in the eastern tropical North Atlantic are recently discovered ocean features that can develop in dynamically isolated water masses within cyclonic eddies (CE) and anticyclonic modewater eddies (ACME). Analysis of a comprehensive oxygen dataset obtained from gliders, moorings, research vessels and Argo floats reveals that "dead-zone" eddies are found in surprisingly high numbers and in a large area from about 4 to 22 • N, from the shelf at the eastern boundary to 38 • W. In total, 173 profiles with oxygen concentrations below the minimum background concentration of 40 µmol kg −1 could be associated with 27 independent eddies (10 CEs; 17 ACMEs) over a period of 10 years. Lowest oxygen concentrations in CEs are less than 10 µmol kg −1 while in ACMEs even suboxic (< 1 µmol kg −1 ) levels are observed. The oxygen minimum in the eddies is located at shallow depth from 50 to 150 m with a mean depth of 80 m. Compared to the surrounding waters, the mean oxygen anomaly in the core depth range (50 and 150 m) for CEs (ACMEs) is −38 (−79) µmol kg −1 . North of 12 • N, the oxygen-depleted eddies carry anomalously low-salinity water of South Atlantic origin from the eastern boundary upwelling region into the open ocean. Here water mass properties and satellite eddy tracking both point to an eddy generation near the eastern boundary. In contrast, the oxygen-depleted eddies south of 12 • N carry weak hydrographic anomalies in their cores and seem to be generated in the open ocean away from the boundary. In both regions a decrease in oxygen from east to west is identified supporting the en-route creation of the low-oxygen core through a combination of high productivity in the eddy surface waters and an isolation of the eddy cores with respect to lateral oxygen supply. Indeed, eddies of both types feature a cold sea surface temperature anomaly and enhanced chlorophyll concentrations in their center. The low-oxygen core depth in the eddies aligns with the depth of the shallow oxygen minimum zone of the eastern tropical North Atlantic. Averaged over the whole area an oxygen reduction of 7 µmol kg −1 in the depth range of 50 to 150 m (peak reduction is 16 µmol kg −1 at 100 m depth) can be associated with the dispersion of the eddies. Thus the locally increased oxygen consumption within the eddy cores enhances the total oxygen consumption in the open eastern tropical North Atlantic Ocean and seems to be an contributor to the formation of the shallow oxygen minimum zone.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Characterization of “dead-zone” eddies in the eastern tropical North Atlantic

Schütte¹,

Karstensen²,

Krahmann³

et al. 2016

Biogeosciences

102

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“…TIVs have a complex three-dimensional circulation from the surface down to the thermocline [Kennan and Flament, 2000]. At the leading western edge of the vortex, the flow decelerates, resulting in convergence and downwelling [Menkes et al, 2002]. As the flow recirculates anticyclonically, upwelling occurs from the trailing east edge to the core of the vortex [Dutrieux et al, 2008].…”

Section: The Propagation Of Tiws In 2010mentioning

confidence: 99%

SMOSSea Surface Salinity signals of tropical instability waves

Yin

Boutin

Reverdin

et al. 2014

J. Geophys. Res. Oceans

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“…These are within the range of previous estimates from observations and models. The beams are modulated annually, as in the observations, because of the annual cycle of the upper-ocean instabilities that generate them (e.g., Menkes et al 2002;Lyman et al 2007). Because few observations are available, however, we do not know if the beams in these models have a realistic structure.…”

Section: ) Yanai Beammentioning

confidence: 99%

Deep Equatorial Ocean Circulation Induced by a Forced–Dissipated Yanai Beam*

Ascani

Firing

Dutrieux

et al. 2010

Journal of Physical Oceanography

100

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A complex pattern of zonal currents below the thermocline has been observed in the equatorial Pacific and Atlantic Oceans. The currents have typical speeds from 10 to 15 cm s 21 and extend as deep as 2500 m. Their structure can be divided into two overlapping parts: the equatorial deep jets (EDJs), centered on the equator and alternating in the vertical with a wavelength of several hundred meters, and the Equatorial Intermediate Current system (EICS), composed of currents with large vertical scale and alternating with latitude over several degrees on either side of the equator. The strongest EICS current is a westward flow on the equator flanked by eastward currents at 28N and 28S.In the present study, the authors use idealized numerical simulations and analytical solutions to demonstrate that the EICS currents within 2.58 from the equator could result from the self-advection with dissipation of a downward-propagating beam of monthly periodic Yanai (Rossby gravity) waves. The zonally restricted beam is generated in the eastern part of the basin by instabilities of the swift near-surface equatorial currents. For a weak Yanai wave amplitude and no dissipation, mean Eulerian currents resembling the three strongest EICS currents are obtained but only within the beam; in this case, the Eulerian flow is balanced by the waveinduced Stokes drift, yielding a zero-mean Lagrangian flow, and the water parcels conserve their potential vorticity (PV) and are stationary over a wave cycle. For larger amplitudes, the Yanai waves break, losing their energy to small vertical scales where it is dissipated. This dissipation changes the mean (wave averaged) PV of a water parcel within the beam, allowing the parcel to have a persistent equatorward drift across PV contours. This can be viewed as a wave-induced Sverdrup transport; by continuity and by virtue of the westward group velocity of long Rossby waves, this Lagrangian-mean meridional flow requires a Lagrangian-mean zonal flow within and to the west of the beam, with a meridional structure consistent with the three strongest EICS currents. This mechanism of EICS formation is active in some ocean general circulation models; its importance in the ocean remains to be evaluated.

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A whirling ecosystem in the equatorial Atlantic

Cited by 76 publications

References 21 publications

Characterization of “dead-zone” eddies in the eastern tropical North Atlantic

Characterization of “dead-zone” eddies in the eastern tropical North Atlantic

SMOSSea Surface Salinity signals of tropical instability waves

Deep Equatorial Ocean Circulation Induced by a Forced–Dissipated Yanai Beam*

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