scholarly journals Turbulence and hypoxia contribute to dense biological scattering layers in a Patagonian fjord system

Ocean Science ◽  
2018 ◽  
Vol 14 (5) ◽  
pp. 1185-1206 ◽  
Author(s):  
Iván Pérez-Santos ◽  
Leonardo Castro ◽  
Lauren Ross ◽  
Edwin Niklitschek ◽  
Nicolás Mayorga ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Water Column ◽  
Turbulent Kinetic Energy ◽  
Tidal Flow ◽  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Marine Species ◽  
Eddy Diffusivity ◽  
Diel Vertical Migrations

Abstract. The aggregation of plankton species along fjords can be linked to physical properties and processes such as stratification, turbulence and oxygen concentration. The goal of this study is to determine how water column properties and turbulent mixing affect the horizontal and vertical distributions of macrozooplankton along the only northern Patagonian fjord known to date, where hypoxic conditions occur in the water column. Acoustic Doppler current profiler moorings, scientific echo-sounder transects and in situ plankton abundance measurements were used to study macrozooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel in Chilean Patagonia. The dissipation of turbulent kinetic energy was quantified through vertical microstructure profiles collected throughout time in areas with high macrozooplankton concentrations. The acoustic records and in situ macrozooplankton data revealed diel vertical migrations (DVM) of siphonophores, chaetognaths and euphausiids. In particular, a dense biological backscattering layer was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic boundary layer (∼100 m), which limited the vertical distribution of most macrozooplankton and their DVM, generating a significant reduction of habitat. Aggregations of macrozooplankton and fishes were most abundant around a submarine sill in Jacaf Channel. In this location macrozooplankton were distributed throughout the water column (0 to ∼200 m), with no evidence of a hypoxic boundary due to the intense mixing near the sill. In particular, turbulence measurements taken near the sill indicated high dissipation rates of turbulent kinetic energy (ε∼10-5 W kg−1) and vertical diapycnal eddy diffusivity (Kρ∼10-3 m2 s−1). The elevated vertical mixing ensures that the water column is well oxygenated (3–6 mL L−1, 60 %–80 % saturation), creating a suitable environment for macrozooplankton and fish aggregations. Turbulence induced by tidal flow over the sill apparently enhances the interchange of nutrients and oxygen concentrations with the surface layer, creating a productive environment for many marine species, where the prey–predator relationship might be favored.

scholarly journals Turbulence and hypoxia contribute to dense zooplankton scattering layers in Patagonian Fjord System

2017 ◽  
Author(s):  
Iván Pérez-Santos ◽  
Leonardo Castro ◽  
Nicolás Mayorga ◽  
Lauren Ross ◽  
Luis Cubillos ◽  
...  
Keyword(s):  
Water Column ◽  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Eddy Diffusivity ◽  
Future Research ◽  
Dense Layer ◽  
The North ◽  
Diel Vertical Migrations ◽  
And Migration

Abstract. The Puyuhuapi Fjord is an atypical fjord, with two mouths, located in northern Patagonia (44.7° S). One mouth lies to the south, close to the Pacific Ocean, whilst the second connects with the Jacaf Channel to the north where a shallow sill inhibits deep water ventilation contributing to the hypoxic conditions below ~ 100 m depth. Acoustic Doppler Current Profiler moorings, scientific echo sounder transects, and in-situ abundance measurements were used to study zooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel. The acoustic records and in-situ zooplankton data revealed diel vertical migrations of siphonophores, euphausiids and copepods. A dense layer of zooplankton was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic layer (~ 100 m), which acted as a physic-chemical barrier to the distribution and migration of the zooplankton. Aggregations of zooplankton and fishes were generally more abundant around the sill in Jacaf Channel than anywhere within Puyuhuapi Fjord. In particular, zooplanktons were distributed throughout the entire water column to ~ 200 m depth, with no evidence of a hypoxic boundary. Turbulence measurements taken near the sill in the Jacaf Channel indicated high turbulent kinetic energy dissipation rates (ε ~ 10−4 W kg−1) and vertical diapycnal eddy diffusivity (Kρ ~ 10−2 m2 s−1) values. These elevated vertical mixing ensures that the water column well oxygenated and promotes zooplanktons aggregation. The sill region represents a major topographic contrast between the two fjords, and we suggest that this is an feature for future research on carbon export and fluxes in these fjords.

scholarly journals Turbulent Exchange Characteristics in the Hypolimnion Layer of Lake Ontario

2001 ◽  
Vol 32 (1) ◽  
pp. 13-28 ◽  
Author(s):  
Messon B. Gbah ◽  
Y.R. Rao ◽  
Raj C. Murthy
Keyword(s):  
Kinetic Energy ◽  
Water Column ◽  
Sediment Resuspension ◽  
Surface Wind ◽  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Lake Ontario ◽  
Mean Flow ◽  
Turbulent Structures ◽  
Nepheloid Layer

Flow regime and turbulence characteristics in a hypolimnion of Lake Ontario are determined using time series current measurements from a vertical string of moored current meters and a bottom mounted Acoustic Doppler Current Profiler (ADCP). The diffusion and turbulent structures of the water column are parameterised in terms of horizontal exchange coefficients for momentum (Kx and Ky) during these deployments. The analysis suggests that the structure of the turbulent fluctuations is isotropic. The kinetic energy and horizontal exchange coefficients decrease with depth. The mean flow at all moorings appears to be strongly correlated with the zonal surface wind stress. Fifteen to twenty metres above the bottom, the flow is marked by an increase in kinetic energy, turbulence intensities, and eddy viscosity coefficients. Strong episodic wind impulse decreases horizontal exchange coefficients through the water column but probably enhances the vertical mixing due to increase in current shear. It is suggested that the associated current-induced sediment resuspension may contribute to the establishment and maintenance of a Nepheloid layer in Lake Ontario.

scholarly journals Quantifying Suspended Sediment using Acoustic Doppler Current Profiler in Tidung Island Seawaters

2021 ◽  
Vol 29 (1) ◽  
Author(s):  
Henry Munandar Manik ◽  
Randi Firdaus
Keyword(s):  
Water Column ◽  
Suspended Sediment ◽  
Suspended Solids ◽  
Acoustic Doppler Current Profiler ◽  
Sediment Concentration ◽  
In Situ Measurement ◽  
Ocean Current ◽  
Echo Intensity ◽  
Current Profiler

Tidung Island, located near Jakarta Bay, is a tourism and conservation area. It is necessary to keep these seawaters unpolluted. To calculate the level of pollution, it is necessary to know the sediment concentration. Quantifying concentration suspended sediment is important for knowledge of sediment transport. Researchers usually use water sample analysis and optical method for quantifying suspended sediment in seawater. Less accuracies of these methods are due to under sample of seawater and the existence of biological fouling. One promising method to measure concentration of suspended sediment is using Acoustic Doppler Current Profiler (ADCP). ADCP is usually used by oceanographer and hydrographer to measure ocean current. In this research, ADCP with 300 kHz operating frequency was used effectively to measure suspended sediment concentration (SSC) and ocean current simultaneously. The echo intensity received from suspended sediment was computed using sonar equations to quantify SSC. The empirical equation between echo intensity and SSC was found. The SSC value obtained by ADCP was also compared with in situ measurement. The result showed that quantified SSC value obtained by ADCP was nearly equal with SSC obtained from in situ measurement with coefficient correlation of 0.98. The high concentration ranged from 55 mg/L to 80 mg/L at the surface layer to a depth 12 m, moderate concentration ranged from 45 mg/L to 55 mg/L at a depth 12 m to 40 m, and low concentration less than 45 mg/L at a depth greater than 40 m. The distribution of SSC was correlated with ocean current condition. In small currents, suspended solids will settle faster so that the concentration in the water column will decrease. Conversely, if the velocity is high, suspended solids will continue to float carried by the current in the water column so that the concentration is high.

scholarly journals Measurements of Enhanced Turbulent Mixing near Highways

2012 ◽  
Vol 51 (9) ◽  
pp. 1618-1632 ◽  
Author(s):  
Mark Gordon ◽  
Ralf M. Staebler ◽  
John Liggio ◽  
Paul Makar ◽  
Shao-Meng Li ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Traffic Flow ◽  
Power Law ◽  
Vertical Mixing ◽  
Weather Forecast ◽  
Early Morning ◽  
Highway Traffic ◽  
Vertical Diffusion ◽  
Global Environmental

AbstractIn August and September of 2010, measurements of turbulent fluxes and turbulent kinetic energy were made on highways in the Toronto area (Ontario, Canada). In situ turbulence measurements were made with a mobile laboratory while driving on the highway with traffic. Results demonstrate that the turbulent kinetic energy (TKE) spectrum is significantly enhanced on and near the highway by traffic for frequencies above 0.015 Hz. The decay of TKE with distance behind vehicles is well approximated by power-law curves. The strongest increase in TKE is seen while following heavy-duty trucks, primarily for frequencies above 0.7 Hz. From these results, a parameterization of on-road TKE enhancement is developed that is based on vehicle type and traffic-flow rate. TKE with distance downwind of the highway also decays following a power law. The enhancement of roadside TKE is shown to be strongly dependent on traffic flow. The effect of vehicle-induced turbulence on vertical mixing was studied by comparing parameterized TKE enhancement with the typical TKE predictions from the Global Environmental Multiscale weather forecast to predict the potential increase in vertical diffusion that results from highway traffic. It is demonstrated that this increase in TKE by traffic may be locally significant, especially in the early morning.

scholarly journals Assessing the turbulent kinetic energy budget in an energetic tidal flow from measurements of coupled ADCPs

2020 ◽  
Vol 378 (2178) ◽  
pp. 20190496 ◽  
Author(s):  
Maxime Thiébaut ◽  
Jean-François Filipot ◽  
Christophe Maisondieu ◽  
Guillaume Damblans ◽  
Rui Duarte ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Production Rate ◽  
Tidal Flow ◽  
Tidal Energy ◽  
Reynolds Stresses ◽  
Common Assumption ◽  
Non Local ◽  
Tke Dissipation Rate ◽  
Acoustic Doppler Current Profilers

Two coupled four-beam acoustic Doppler current profilers were used to provide simultaneous and independent measurements of the turbulent kinetic energy (TKE) dissipation rate ε and the TKE production rate P over a 36 h long period at a highly energetic tidal energy site in the Alderney Race. The eight-beam arrangement enabled the evaluation of the six components of the Reynolds stress tensor which allows for an improved estimation of the TKE production rate. Depth-time series of ε, P and the Reynolds stresses are provided. The comparison between ε and P was performed by calculating individual ratios of ε corresponding to P . The depth-averaged ratio ε / P averaged over whole flood and ebb tide were found to be 2.2 and 2.8 respectively, indicating that TKE dissipation exceeds TKE production. It is shown that the term of diffusive transport of TKE is significant. As a result, non-local transport is important to the TKE budget and the common assumption of a local balance, i.e. a balance between production and dissipation, is not valid at the measurement site. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

Onset of stratification in a mixed layer subjected to a stabilizing buoyancy flux

1995 ◽  
Vol 304 ◽  
pp. 27-46 ◽  
Author(s):  
Y. Noh ◽  
H. J. S. Fernando
Keyword(s):  
Numerical Model ◽  
Kinetic Energy ◽  
Laboratory Experiment ◽  
Water Column ◽  
Turbulent Kinetic Energy ◽  
Energy Flux ◽  
Mixed Layer ◽  
Mixed State ◽  
Buoyancy Flux ◽  
Tidal Front

The formation of a thermocline in a water column, in which shear-free turbulence is generated both at the surface and bottom, and a stabilizing buoyancy flux is imposed at the surface, is studied using a laboratory experiment and a numerical model with the aim of understanding the formation of a tidal front in coastal seas. The results show that the formation of a thermocline, which always occurs in the absence of bottom mixing, is inhibited and the water column maintains a vertically mixed state, when bottom mixing becomes sufficiently strong. It is found from both experimental and numerical results that the criterion for the formation of a thermocline is determined by the balance between the rate of work that is necessary to maintain a mixed state against the formation of stratification by the buoyancy flux and the turbulent kinetic energy flux from the bottom supplied to the depth of thermocline formation. The depth of the thermocline, when it is formed, is found to decrease with bottom mixing.

scholarly journals Can vertical mixing from turbulent kinetic energy mitigate coral bleaching? An application of high frequency ocean radar

2010 ◽  
Author(s):  
Diane D. DiMassa ◽  
Malcolm L. Heron ◽  
Alessandra Mantovanelli ◽  
Scott F. Heron ◽  
Craig Steinberg
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Coral Bleaching ◽  
High Frequency ◽  
Vertical Mixing ◽  
Ocean Radar

scholarly journals Using an ADCP to Estimate Turbulent Kinetic Energy Dissipation Rate in Sheltered Coastal Waters

2015 ◽  
Vol 32 (2) ◽  
pp. 318-333 ◽  
Author(s):  
A. D. Greene ◽  
P. J. Hendricks ◽  
M. C. Gregg
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Cell Size ◽  
Dissipation Rate ◽  
Puget Sound ◽  
Acoustic Doppler Current Profiler ◽  
Energy Dissipation Rate ◽  
Integral Scale ◽  
Thorpe Scale

AbstractTurbulent microstructure and acoustic Doppler current profiler (ADCP) data were collected near Tacoma Narrows in Puget Sound, Washington. Over 100 coincident microstructure profiles have been compared to ADCP estimates of turbulent kinetic energy dissipation rate (ϵ). ADCP dissipation rates were calculated using the large-eddy method with theoretically determined corrections for sensor noise on rms velocity and integral-scale calculations. This work is an extension of Ann Gargett’s approach, which used a narrowband ADCP in regions with intense turbulence and strong vertical velocities. Here, a broadband ADCP is used to measure weaker turbulence and achieve greater horizontal and vertical resolution relative to the narrowband ADCP. Estimates of ϵ from the Modular Microstructure Profiler (MMP) and broadband ADCP show good quantitative agreement over nearly three decades of dissipation rate, 3 × 10−8–10−5 m2 s−3. This technique is most readily applied when the turbulent velocity is greater than the ADCP velocity uncertainty (σ) and the ADCP cell size is within a factor of 2 of the Thorpe scale. The 600-kHz broadband ADCP used in this experiment yielded a noise floor of 3 mm s−1 for 3-m vertical bins and 2-m along-track average (≈four pings), which resulted in turbulence levels measureable with the ADCP as weak as 3 × 10−8 m2 s−3. The value and trade-off of changing the ADCP cell size, which reduces noise but also changes the ratio of the Thorpe scale to the cell size, are discussed as well.

scholarly journals Observations of Near-Surface Mixing Behind a Headland

2020 ◽  
Vol 8 (2) ◽  
pp. 68
Author(s):  
Preston Spicer ◽  
Kimberly Huguenard
Keyword(s):  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Bottom Layer ◽  
Eddy Diffusivity ◽  
Vertical Shear ◽  
Small Island ◽  
Streamwise Vorticity ◽  
Near Surface ◽  
Surface Mixing ◽  
Complex Features

Field observations were collected near the mouth of the Bagaduce River, Maine, in order to understand how complex features affect the intratidal and lateral variability of turbulence and vertical mixing. The Bagaduce River is a low-inflow, macrotidal estuary that features tidal islands, tidal flats and sharp channel bends. Profiles of salinity, temperature, and turbulent kinetic energy dissipation (ε) were collected for a tidal cycle across the estuary with a microstructure profiler. Lateral distributions of current velocities were obtained with an acoustic doppler current profiler. Results showed intratidal asymmetries in bottom-generated vertical eddy diffusivity and viscosity, with larger values occurring on ebb (Kz: 10−2 m2; Az: 10−2 m2/s) compared to flood (Kz: 10−5 m2/s; Az: 10−4 m2/s). Bottom-generated mixing was moderated by the intrusion of stratified water on flood, which suppressed mixing. Elevated mixing (Kz: 10−3 m2; Az: 10−2.5 m2/s) occurred in the upper water column in the lee of a small island and was decoupled from the bottom layer. The near-surface mixing was a product of an eddy formed downstream of a headland, which tended to reinforce vertical shear by laterally straining streamwise velocities. These results are the first to show near-surface mixing caused by vertical vorticity induced by an eddy, rather than previously reported streamwise vorticity associated with lateral circulation.

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