Prefrontal bore mixing

Haren, Hans van; Duineveld, G.C.A.; Stigter, Henko de

doi:10.1002/2017gl074384

Cited by 4 publications

(9 citation statements)

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“…1). The turbulence expansion occurs in the tidal phase 1 to 2 h before 'pre-frontal bore mixing', the recently reported large near-homogenization that pushes a stratification anomaly to very near the seafloor just before frontal bores propagate on-slope (van Haren et al 2017). While the here reported process of turbulence expansion is reminiscent of an internal hydraulic jump, the previously reported process of pre-frontal mixing is not associated with an internal hydraulic jump.…”

Section: Introductioncontrasting

confidence: 43%

“…A major separator is visible around z ¼ À1900 m, where both the w-and the v-(also u-)components change their patterns. It was suggested by van Haren et al (2017) that this was associated with the flow over the top of Rainbow Ridge, which is found at this depth.…”

Section: One-day Variabilitymentioning

confidence: 78%

“…The phase in the tide with most vertical isotherms, i.e. weakest density stratification, is associated with pre-frontal mixing described in van Haren et al (2017), occurring around day 183.8 and day 184.3 in Fig. 3, and with near-bottom frontal bore motions (e.g.…”

Section: One-day Variabilitymentioning

confidence: 89%

“…It was suggested by van Haren et al (2017) that the turbulence associated with pre-frontal mixing is not a result from hydraulic control of the tidal flow over the ridge. This was because bN % 1.5r M2 , <2-3r M2 or not enough time for the vertical signal to propagate before the tide reversal, e.g.…”

Section: Discussionmentioning

confidence: 99%

“…The local bottom-slope is b % 0.22 ¼ 13 . Semidiurnal lunar M 2 tidal motions dominate currents, having near-bottom polarized ellipses with cross-slope amplitude of v ¼ 0.15 m s À1 and along-slope amplitude of u ¼ 0.10 m s À1 , and near-circular polarization of u, v ¼ 0.10 m s À1 at 150 mab (van Haren et al, 2017).…”

Section: Methodsmentioning

confidence: 99%

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Off-bottom turbulence expansions of unbounded flow over a deep-ocean ridge

Haren

2019

Tellus A: Dynamic Meteorology and Oceanography

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ISSN: (Print) 1600-0870 (Online) Journal homepage: https://www.tandfonline.com/loi/zela20 Off-bottom turbulence expansions of unbounded flow over a deep-ocean ridge Hans van Haren To cite this article: Hans van Haren (2019) Off-bottom turbulence expansions of unbounded flow over a deep-ocean ridge, Tellus A: Dynamic Meteorology and Oceanography, 71:1, 1653137,ABSTRACT Internal wave breaking upon sloping seafloors is a potential source of turbulent mixing in the deep-ocean, but we lack details on off-bottom breaking. Turbulence processes are relevant for the dispersal away from the seafloor of suspended materials like those emanating from thermal vents and artificial mining activities. For the present study, high-resolution temperature sensors have been moored up to 406 m above a slope of a 2000 m deep crest of the Mid-Atlantic Ridge. In addition to familiar observations of on-slope propagating highly nonlinear bores dominating turbulent mixing near and in contact with a sloping seafloor, the present observations show occasionally larger than 100 m tall turbulence expansions between 100 and 250 m above the seafloor at the transition from on-to off-slope flow. The details of such turbulence expansion are reminiscent of an asymmetric quasi-mode-2 internal hydraulic jump, with some specific differences compared with near-surface hydraulic jumps. As the expansion is generated at the transition from weak to steep edge of a saw-tooth internal tidal wave, it leads turbulence and stratification in two directions: One down to the seafloor in the direction of tidal phase propagation; the other more horizontally and slightly upward associated with near-homogeneous overturning remaining well away from the seafloor while preceding and sharpening near-bottom frontal bores. The mean turbulence dissipation rates O(10 À8 -10 À7 m 2 s À3 ) associated with these expansions are half an order of magnitude less than those of on-slope propagating near-bottom bores, while about equal in duration. As for bores, their appearance, intensity and timing vary every tidal cycle.

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Section: Introductioncontrasting

confidence: 43%

Section: One-day Variabilitymentioning

confidence: 78%

Section: One-day Variabilitymentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Off-bottom turbulence expansions of unbounded flow over a deep-ocean ridge

Haren

2019

Tellus A: Dynamic Meteorology and Oceanography

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Processes Driving Iron and Manganese Dispersal From the TAG Hydrothermal Plume (Mid-Atlantic Ridge): Results From a GEOTRACES Process Study

et al. 2020

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Hydrothermal vents are a recognized source of trace elements to the ocean inventory. Nevertheless, the contribution of slow-spreading ridges remains poorly resolved. To address this, high-resolution dissolved (<0.45 µm) iron (dFe) and manganese (dMn) samples were collected during the GEOTRACES HERMINE GApr07 process study at the Mid Atlantic Ridge. Samples were collected at nine stations, from the TAG vent site to 75 km south-southwest following the neutrally buoyant plume. Concentrations of dMn and dFe ranged from 71 ± 6 and 51 ± 2 nmol kg −1 right above the vent site to 0.43 ± 0.01 and 1.56 ± 0.02 nmol kg −1 at the most distal station, respectively. Using a 5-box model coupled with our data, we show that as the plume traveled away from the vent, aggregation processes controlled dFe concentrations in the first 2 km, with an aggregation rate averaging between 8.0 ± 0.6 and 0.11 ± 0.04 nmol L −1 d −1 , respectively in the first and second kilometer. Aggregation, likely of small colloidal particles, led to partitioning of the size fractionated Fe pool, as 6% of the dFe was moved into the particulate size fraction. Further away, disaggregation processes became more prevalent, with rates ranging from 0.27 ± 0.02 to 0.008 ± 0.001 nmol L −1 d −1 , enriching the dFe pool by 10%. The computed decrease of hydrothermal Fe within the neutrally buoyant plume was likely caused by flocculation of small Fe oxyhydroxide particles. This process resulted in Fe aggregate formation with radii estimated to range between 14 and 20 µm in the first km from TAG. Between 2 and 30 km from the vent site, the radii ranged between 2 and 4 µm.

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Philosophy and Application of High-Resolution Temperature Sensors for Stratified Waters

Haren

2018

Sensors

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Every application may have its specifically designed sensor. For studying the effects of short-term temperature variations on life in water, a high-resolution sensor has been designed with low noise level <0.1 mK. Pro and cons of the design include its adequacy for use in large heat-capacity environments like water but less in air. The sensor can be used under high static environmental pressure of >1000 Bar (>108 N m−2) in the deepest ocean regions. Its response time of 0.5 s in water allows quantitative studies of internal wave turbulent mixing effects, e.g., on the redistribution of matter and on nearly completely submerged human bodies. In a chain of >100 sensors, clocks are synchronized to sample within 0.02 s and a verified range of 600 m.

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Prefrontal bore mixing

Cited by 4 publications

References 33 publications

Off-bottom turbulence expansions of unbounded flow over a deep-ocean ridge

Off-bottom turbulence expansions of unbounded flow over a deep-ocean ridge

Processes Driving Iron and Manganese Dispersal From the TAG Hydrothermal Plume (Mid-Atlantic Ridge): Results From a GEOTRACES Process Study

Philosophy and Application of High-Resolution Temperature Sensors for Stratified Waters

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