Subseasonal Coastal‐Trapped Wave Propagations in the Southeastern Pacific and Atlantic Oceans: 1. A New Approach to Estimate Wave Amplitude

Illig, Séréna; Cadier, Emeline; Bachèlery, Marie‐Lou; Kersalé, Marion

doi:10.1029/2017jc013539

Cited by 27 publications

(54 citation statements)

References 79 publications

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“…Thus, seasonal changes in DO over the continental shelf seem to be more tightly related to the annual upwelling cell than to the drivers that control DO in the OMZ core. Nevertheless, different ship‐based, monthly, time series from northern and central Chile show also large month to month and interannual variability of the oxycline not well related to the local upwelling favorable winds, but to coastally trapped waves of equatorial origin, which may largely disturb the pycnocline, as well as the oxycline and the PCUC (Shaffer et al, , Morales et al, ; Ulloa et al, ; Illig, Cadier , et al, ; Illig, Bachèlery, & Cadier, ). Thus, the dynamics of the OMZ over the continental shelf seems to be different from that described here for the core of the OMZ.…”

Section: Discussionmentioning

confidence: 99%

“…The PCUC undergoes large variability at a wide range of timescales, standing out the intraseasonal one (from about 20 to 90 days) and the interannual that characterize the El Niño‐La Niña cycles (e.g. Shaffer et al, , ; Pizarro et al, , ; Dewitte et al, ; Illig, Bachèlery, et al, Illig, Cadier, et al, ). To date, the paucity of DO data has prevented a thorough assessment of the temporal variability of the OMZ off Chile associated with temporal and spatial changes of the PCUC.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal Variability of the Southern Tip of the Oxygen Minimum Zone in the Eastern South Pacific (30°‐38°S): A Modeling Study

et al. 2019

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We investigate the seasonal variability of the southern tip (30°-38°S) of the eastern South Pacific oxygen minimum zone (OMZ) based on a high horizontal resolution (1/12°) regional coupled physical-biogeochemical model simulation. The simulation is validated by available in situ observations and the OMZ seasonal variability is documented. The model OMZ, bounded by the contour of 45 μM, occupies a large volume (4.5x10 4 km 3 ) during the beginning of austral winter and a minimum (3.5x10 4 km 3 ) at the end of spring, just 1 and 2 months after the southward transport of the Peru-Chile Undercurrent (PCUC) is maximum and minimum, respectively. We showed that the PCUC significantly impacts the alongshore advection of dissolved oxygen (DO) modulating the OMZ seasonal variability. However, zonal transport of DO by meridionally alternating zonal jets and mesoscale eddy fluxes play also a major role in the seasonal and spatial variability of the OMZ. Consistently, a DO budget analysis reveals a significant contribution of advection terms to the rate of change of DO and the prominence of mesoscale variability within the seasonal cycle of these terms. Biogeochemical processes and horizontal and vertical mixing, associated with subgrid scale processes, play only a secondary role in the OMZ seasonal cycle. Overall, our study illustrates the interplay of mean and (mesoscale) eddy-induced transports of DO in shaping the OMZ and its seasonal cycle off Central Chile.Plain Language Summary Dissolved oxygen in the ocean strongly impacts most marine ecosystems. Its distribution depends mainly on physical and biogeochemical processes. In the eastern South Pacific, water with very low oxygen is present at intermediate depths (100-800 m). This oxygen minimum zone (OMZ) is associated with a regional water mass called Equatorial Subsurface Water which is transported southward along the coast by the Peru-Chile Undercurrent. Here, using a physical/biogeochemical model we investigate the main mechanisms controlling the seasonal variability of the OMZ off central Chile. We found that the total volume of the low-oxygen waters is reduced by 25% during spring. This seasonal change is closely related to changes in the water mass composition and is mainly driven by changes in the undercurrent transport, but zonal currents and eddy fluxes, largely related to mesoscale variability, play also a major role in the seasonal and spatial variability of the OMZ, while biogeochemical and mixing processes play only a secondary role.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Seasonal Variability of the Southern Tip of the Oxygen Minimum Zone in the Eastern South Pacific (30°‐38°S): A Modeling Study

et al. 2019

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“…To interpret the observed flow variability along the Peruvian coast in terms of CTW, the cross-shore-depth structure of 185 CTWs was determined by considering the linear, hydrostatic, inviscid, and Boussinesq approximated equations of motion on an f-plane using local bathymetry and stratification (Brink, 1982;1989;Illig et al, 2018a). For alongshore scales larger than cross-shore scales and horizontally uniform stratification, cross-shore-vertical mode structures (eigenfunctions) and corresponding phase velocities (eigenvalues) solutions can be obtained from the simplified set of equations by using a resonance iteration approach (Brink, 1982;Brink and Chapman, 1987).…”

Section: Theoretical Coastal Trapped Wave Structurementioning

confidence: 99%

“…These solutions have been used successfully in previous analyses of CTW structures in observational and model data (e.g. Brink et al, 1982;Pietri et al, 2014;Illig et al, 2018a).…”

Section: Theoretical Coastal Trapped Wave Structurementioning

confidence: 99%

Influence of intraseasonal eastern boundary circulation variability on hydrography and biogeochemistry off Peru

Lüdke¹,

Dengler²,

Sommer³

et al. 2019

Preprint

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The Peruvian Upwelling System is characterized by high primary productivity fuelled by the supply of nutrients in a highly dynamic boundary circulation. The intraseasonal evolution of the physical and biogeochemical properties is 10 analysed based on shipboard observations and remote sensing conducted between April and June 2017 off central Peru. The poleward transport in the subsurface Peru Chile Undercurrent was highly variable and strongly intensified between mid and end of May. This intensification was likely caused by a first baroclinic mode downwelling coastal trapped wave excited at the equator at about 95°W that propagated poleward along the South American coast. The intensified poleward flow shortens the time of water mass advection from the equatorial current system to the study site. The impact of the anomalous advection 15 is mostly noticed in the nitrogen cycle because during the shorter time needed for poleward advection less fixed nitrogen loss occurs within the waters. This causes a strong increase of nitrate concentrations and a decrease in the nitrogen deficit. These changes suggest that the advection caused by the coastal trapped wave supersedes the simultaneous effect of anomalous downwelling in terms of nutrient response.

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“…Given the lack of an adequate observation network in the two systems, our approach relies on the numerical experimentation with twin regional ocean general circulation model configurations of the southeastern Pacific and Atlantic Oceans. We benefit from the CTW amplitude extraction methodology developed in the companion paper (Illig et al, ), which showed good skills in estimating CTW characteristics from regional ocean models. Our results will be tested using sensitivity experiments with twin configurations of a simple multimode linear CTW model of the two coastal systems.…”

Section: Introductionmentioning

confidence: 99%

Subseasonal Coastal‐Trapped Wave Propagations in the Southeastern Pacific and Atlantic Oceans: 2. Wave Characteristics and Connection With the Equatorial Variability

2018

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The objective of this study is to compare the characteristics of the oceanic teleconnection with the linear equatorial dynamics of two upwelling systems along the southwestern South American and African continents at subseasonal time scales (<120 days). Altimetric data analysis shows that the coastal variability remains coherent with the equatorial signal until 27°S in the southeastern Pacific (SEP), while in the southeastern Atlantic (SEA) it fades out south of 12°S. To explain this striking difference, our methodology is based on the experimentation with twin regional model configurations of the SEP and SEA Oceans. The estimation of free Coastal‐Trapped Waves (CTWs) modal structures and associated contribution to coastal variability allows inferring and comparing the characteristics of each CTW mode in the two systems; namely, their forcings, amplitude, dissipation rate, and scattering. Results show that the Pacific subseasonal equatorial forcing is only 20% larger than in the Atlantic, but important differences in the relative contribution of each baroclinic mode are reported. The first baroclinic mode dominates the eastern equatorial Pacific variability, while in the eastern equatorial Atlantic, the second mode is the most energetic. This leads to a drastic increase in the dissipation and scattering of the remotely forced CTW in the SEA sector, compared to the coastal SEP. Concomitantly, south of 15°S, the subseasonal coastal wind stress forcing is substantially more energetic in the SEA and participates in breaking the link between the equatorial forcing and the coastal variability. Our results are consistent with the solutions of a simple multimode CTW model.

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Subseasonal Coastal‐Trapped Wave Propagations in the Southeastern Pacific and Atlantic Oceans: 1. A New Approach to Estimate Wave Amplitude

Cited by 27 publications

References 79 publications

Seasonal Variability of the Southern Tip of the Oxygen Minimum Zone in the Eastern South Pacific (30°‐38°S): A Modeling Study

Seasonal Variability of the Southern Tip of the Oxygen Minimum Zone in the Eastern South Pacific (30°‐38°S): A Modeling Study

Influence of intraseasonal eastern boundary circulation variability on hydrography and biogeochemistry off Peru

Subseasonal Coastal‐Trapped Wave Propagations in the Southeastern Pacific and Atlantic Oceans: 2. Wave Characteristics and Connection With the Equatorial Variability

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