Internal Tide Cycle and Topographic Scattering Over the North Mid‐Atlantic Ridge

Lahaye, Noé; Gula, Jonathan; Roullet, Guillaume

doi:10.1029/2020jc016376

Cited by 10 publications

(11 citation statements)

References 92 publications

(153 reference statements)

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“…The modal amplitude of the velocity fields u , v is obtained by projecting the observed fields onto the different modes computed from the averaged N 2 for each vertical profile (Lahaye et al., 2020). This is preferred over resolving a least‐square problem, which sometimes leads to unrealistic modal amplitudes into the high modes.…”

Section: Methodsmentioning

confidence: 99%

“…The time variability of the modal content, assessed between the ship's outbound and inbound, also appears to be important with no clear symmetry with respect to the section westernmost edge. This small-scale variability of the modal content in space and time has been represented in the rift valley of the MAR in a high-resolution regional model (Lahaye et al, 2020) but had never been documented with in situ data. It could be interpreted as enhanced energy transfer between modes through topographic scattering (Lahaye et al, 2020).…”

Section: Observation Of the Internal Tide Beammentioning

confidence: 99%

“…This small-scale variability of the modal content in space and time has been represented in the rift valley of the MAR in a high-resolution regional model (Lahaye et al, 2020) but had never been documented with in situ data. It could be interpreted as enhanced energy transfer between modes through topographic scattering (Lahaye et al, 2020). Note that this small-scale variability in the high modes could also be explained by localized variations in N 2 that change the high-mode shapes between neighboring profiles (Figures 2d and 2e).…”

Section: Observation Of the Internal Tide Beammentioning

confidence: 99%

“…The seafloor topography of the Mid‐Atlantic Ridge (MAR) is mostly subcritical for semidiurnal tides, and linear theories predict quantitatively well the barotropic‐to‐baroclinic energy conversion compared to moored observations of energy fluxes (St Laurent & Nash, 2004; Vic, Naveira Garabato, et al., 2018), and results from primitive‐equation (hence non linear) regional and global models (Buijsman et al., 2020; Lahaye et al., 2020; Zilberman et al., 2009). However, those models use seafloor topographies that do not, or partially, resolve the ≈10‐km scales typical of abyssal hills, which populate slow‐spreading mid‐ocean ridges (Goff, 2010; Goff & Arbic, 2010) and often feature supercritical slopes (Melet et al., 2013).…”

Section: Introductionmentioning

confidence: 99%

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Observed Structure of an Internal Tide Beam Over the Mid‐Atlantic Ridge

Vic

Ferron

2023

JGR Oceans

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Internal tides are key players in ocean dynamics above mid‐ocean ridges. The generation and propagation of internal tides over the Mid‐Atlantic Ridge (MAR) have been studied through theoretical and numerical models, as well as through moored, that is, one‐dimensional, observations. Yet, observations remain sparse and often restricted to the vertical direction. Here we report on the first two‐dimensional in situ observation of an internal tide beam sampled by a shipboard acoustic Doppler current profiler through a vertical section over the MAR. The beam is generated by the interaction of the barotropic tidal current with a supercritical abyssal hill that sits in the rift valley of the MAR. A vertical mode decomposition is carried out to characterize the spatio‐temporal variability of the beam. Although the modal content of the velocity field is dominated by modes 1 to 3, higher modes display localized and not persistent bursts of energy. The use of an analytical theory for linear internal waves allows us to rationalize the observed velocity field and interpret it as the superposition of modal waves generated on the hill and propagating in the same direction. The observed beam is qualitatively reconstructed as the superposition of waves of modes 2 to 6. The velocity field was sampled seven times across the same section and displayed qualitatively different patterns, unveiling the complexity of the dynamics above the MAR. A ray tracing of modal waves shows that the refraction by mesoscale currents could explain the observed variability of the tidal beam.

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Section: Methodsmentioning

confidence: 99%

Section: Observation Of the Internal Tide Beammentioning

confidence: 99%

Section: Observation Of the Internal Tide Beammentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Observed Structure of an Internal Tide Beam Over the Mid‐Atlantic Ridge

Vic

Ferron

2023

JGR Oceans

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“…Although the astronomical (tidal) forcing is now easily predicted and appears to be remarkably in-phase with the local tidal energy density over ridges (Vic et al, 2021), the spatiotemporal variability of mixing remains poorly quantified, due to sparse data. Studies conducted these last decades highlighted key processes associated with internal tides, including their interactions with seafloor topography and background currents, leading to dynamical modifications of the mean state of the deep ocean (Thomson et al, 1990;Thomson et al, 2003;Lahaye et al, 2019;Lahaye et al, 2020).…”

Section: Water Column: Deep Circulation Fluid Dispersal and Connectivitymentioning

confidence: 99%

Integrating Multidisciplinary Observations in Vent Environments (IMOVE): Decadal Progress in Deep-Sea Observatories at Hydrothermal Vents

et al. 2022

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The unique ecosystems and biodiversity associated with mid-ocean ridge (MOR) hydrothermal vent systems contrast sharply with surrounding deep-sea habitats, however both may be increasingly threatened by anthropogenic activity (e.g., mining activities at massive sulphide deposits). Climate change can alter the deep-sea through increased bottom temperatures, loss of oxygen, and modifications to deep water circulation. Despite the potential of these profound impacts, the mechanisms enabling these systems and their ecosystems to persist, function and respond to oceanic, crustal, and anthropogenic forces remain poorly understood. This is due primarily to technological challenges and difficulties in accessing, observing and monitoring the deep-sea. In this context, the development of deep-sea observatories in the 2000s focused on understanding the coupling between sub-surface flow and oceanic and crustal conditions, and how they influence biological processes. Deep-sea observatories provide long-term, multidisciplinary time-series data comprising repeated observations and sampling at temporal resolutions from seconds to decades, through a combination of cabled, wireless, remotely controlled, and autonomous measurement systems. The three existing vent observatories are located on the Juan de Fuca and Mid-Atlantic Ridges (Ocean Observing Initiative, Ocean Networks Canada and the European Multidisciplinary Seafloor and water column Observatory). These observatories promote stewardship by defining effective environmental monitoring including characterizing biological and environmental baseline states, discriminating changes from natural variations versus those from anthropogenic activities, and assessing degradation, resilience and recovery after disturbance. This highlights the potential of observatories as valuable tools for environmental impact assessment (EIA) in the context of climate change and other anthropogenic activities, primarily ocean mining. This paper provides a synthesis on scientific advancements enabled by the three observatories this last decade, and recommendations to support future studies through international collaboration and coordination. The proposed recommendations include: i) establishing common global scientific questions and identification of Essential Ocean Variables (EOVs) specific to MORs, ii) guidance towards the effective use of observatories to support and inform policies that can impact society, iii) strategies for observatory infrastructure development that will help standardize sensors, data formats and capabilities, and iv) future technology needs and common sampling approaches to answer today’s most urgent and timely questions.

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