scholarly journals Modification of turbulent dissipation rates by a deep Southern Ocean eddy

2015 ◽  
Vol 42 (9) ◽  
pp. 3450-3457 ◽  
Author(s):  
K. L. Sheen ◽  
J. A. Brearley ◽  
A. C. Naveira Garabato ◽  
D. A. Smeed ◽  
L. St. Laurent ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Turbulent Dissipation ◽  
Dissipation Rates

scholarly journals Rates and mechanisms of turbulent dissipation and mixing in the Southern Ocean: Results from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES)

2013 ◽  
Vol 118 (6) ◽  
pp. 2774-2792 ◽  
Author(s):  
K. L. Sheen ◽  
J. A. Brearley ◽  
A. C. Naveira Garabato ◽  
D. A. Smeed ◽  
S. Waterman ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Turbulent Dissipation ◽  
Isopycnal Mixing

scholarly journals LAGRANGIAN MEASUREMENTS OF TURBULENT DISSIPATION OVER A SHALLOW TIDAL FLAT FROM PULSE COHERENT ACOUSTIC DOPPLER PROFILERS

2012 ◽  
Vol 1 (33) ◽  
pp. 49 ◽  
Author(s):  
Julia C Mullarney ◽  
Stephen M Henderson
Keyword(s):  
High Resolution ◽  
Tidal Flat ◽  
Order Structure ◽  
Measured Velocity ◽  
Near Surface ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
Surface Drifters ◽  
Freshwater Plume ◽  
Lagrangian Measurements

We present high resolution (25 mm spatial, 8 Hz temporal) profiles of velocity measured over a shallow tidal flat using pulse-coherent Acoustic Doppler Profilers mounted on surface drifters. The use of Lagrangian measurements mitigated the problem of resolving velocity ambiguities, a problem which often limits the application of high-resolution pulse-coherent profilers. Turbulent dissipation rates were estimated from second-order structure functions of measured velocity. Drifters were advected towards, and subsequently trapped on, a convergent surface front which marked the edge of a freshwater plume. Measured dissipation rates increased as a drifter deployed within the plume approached the front. A drifter then propagated with and along the front as the fresh plume spread across the tidal flats. Near-surface turbulent dissipation measured at the front roughly matched a theoretical mean-shear-cubed relationship, whereas dissipation measured in the stratified plume behind the front was suppressed. After removal of estimates affected by surface waves, near-bed dissipation matched the velocity cubed relationship, although scatter was substantial. Dissipation rates appeared to be enhanced when the drifter propagated across small subtidal channels.

Mixing Rates and Bottom Drag in Bering Strait

2020 ◽  
Vol 50 (3) ◽  
pp. 809-825
Author(s):  
Nicole Couto ◽  
Matthew H. Alford ◽  
Jennifer MacKinnon ◽  
John B. Mickett
Keyword(s):  
Friction Velocity ◽  
The Arctic ◽  
Bering Strait ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
The Pacific ◽  
Mixing Rates ◽  
The Pacific Ocean ◽  
High Turbulence ◽  
Property Changes

AbstractThree shipboard survey lines were occupied in Bering Strait during autumn of 2015, where high-resolution measurements of temperature, salinity, velocity, and turbulent dissipation rates were collected. These first-reported turbulence measurements in Bering Strait show that dissipation rates here are high even during calm winds. High turbulence in the strait has important implications for the modification of water properties during transit from the Pacific Ocean to the Arctic Ocean. Measured diffusivities averaging 2 × 10−2 m2 s−1 are capable of causing watermass property changes of 0.1°C and 0.1 psu during the ~1–2-day transit through the narrowest part of the strait. We estimate friction velocity using both the dissipation and profile methods and find a bottom drag coefficient of 2.3 (±0.4) × 10−3. This result is smaller than values typically used to estimate bottom stress in the region and may improve predictions of transport variability through Bering Strait.

Subducting filaments at fronts in the Alboran Sea: Physical, turbulent and biological evidences.

2020 ◽  
Author(s):  
Francesco Marcello Falcieri ◽  
Mathieu Dever ◽  
Mara Freilich ◽  
Annalisa Griffa ◽  
Katrin Schroeder ◽  
...  
Keyword(s):  
Western Mediterranean ◽  
Point Of View ◽  
Surface Mixed Layer ◽  
Alboran Sea ◽  
Vertical Exchange ◽  
Turbulent Dissipation ◽  
Oceanic Fronts ◽  
Dissipation Rates ◽  
Research Initiative ◽  
Alborán Sea

<p>Submesoscale instabilities along oceanic fronts can cause water mass intrusions from the surface mixed layer into the stratified pycnocline. These are important drivers of vertical exchange that have a potentially significant impact on the transfer of physical properties and biological tracers.</p><p>The CALYPSO (Coherent Lagrangian Pathways from the Surface Ocean to Interior) ONR research initiative focuses on observing and understanding coherent vertical pathways by which vertical exchange occurs. The Alboran Sea (located in the south-western Mediterranean, east of Gibraltar) is well known for its strong density fronts and eddies. During a research cruise, onboard <em>R/V Pourquoi Pas? </em>in early April 2019<em>,</em> we found that fronts in this area support the generation of subducting filaments. Several types of observations (using CTD, uCTD, microstructure profiles, drifters and floats) were collected along numerous cross-front transects over a period of two weeks.</p><p>The analysis of the temperature profiles highlighted the presence of several intruding filaments moving along isopycnal surfaces in the proximity of the frontal area. The intrusion signal was also clearly visible in biophysical properties with elevated Chlorophyll-a concentrations, well below the deep chlorophyll maximum, in conjunction with high dissolved oxygen values. From a microstructure point of view, the upper and lower limits of the subducting filaments exhibited high turbulent dissipation rates, with values of O(10<sup>-7</sup>) W/m<sup>2</sup>. These dissipation rates are higher than what is generally observed at such depths and point to enhanced mixing activity at the boundaries of the intrusions even along isopycnal surfaces.</p>

scholarly journals Chemical Signaling in the Turbulent Ocean—Hide and Seek at the Kolmogorov Scale

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 54
Author(s):  
Erik Selander ◽  
Sam T. Fredriksson ◽  
Lars Arneborg
Keyword(s):  
Steady State ◽  
Chemical Cues ◽  
Chemical Properties ◽  
Strong Wind ◽  
Mate Finding ◽  
Surrounding Water ◽  
Near Surface ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
Kolmogorov Scale

Chemical cues and signals mediate resource acquisition, mate finding, and the assessment of predation risk in marine plankton. Here, we use the chemical properties of the first identified chemical cues from zooplankton together with in situ measurements of turbulent dissipation rates to calculate the effect of turbulence on the distribution of cues behind swimmers as well as steady state background concentrations in surrounding water. We further show that common zooplankton (copepods) appears to optimize mate finding by aggregating at the surface in calm conditions when turbulence do not prevent trail following. This near surface environment is characterized by anisotropic turbulence and we show, using direct numerical simulations, that chemical cues distribute more in the horizontal plane than vertically in these conditions. Zooplankton may consequently benefit from adopting specific search strategies near the surface as well as in strong stratification where similar flow fields develop. Steady state concentrations, where exudation is balanced by degradation develops in a time scale of ~5 h. We conclude that the trails behind millimeter-sized copepods can be detected in naturally occurring turbulence below the wind mixed surface layer or in the absence of strong wind. The trails, however, shorten dramatically at high turbulent dissipation rates, above ~10−3 cm2 s−3 (10−7 W kg−1)

scholarly journals On Turbulence Production by Swimming Marine Organisms in the Open Ocean and Coastal Waters

2010 ◽  
Vol 40 (9) ◽  
pp. 2107-2121 ◽  
Author(s):  
Shani Rousseau ◽  
Eric Kunze ◽  
Richard Dewey ◽  
Kevin Bartlett ◽  
John Dower
Keyword(s):  
Reynolds Numbers ◽  
Marine Organisms ◽  
Vertical Shear ◽  
Acoustic Backscatter ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
Saanich Inlet ◽  
Acoustic Profile ◽  
Turbulence Production ◽  
O 10

Abstract Microstructure and acoustic profile time series were collected near Ocean Station P in the eastern subarctic North Pacific and in Saanich Inlet at the south end of Vancouver Island, British Columbia, Canada, to examine production of turbulent dissipation by swimming marine organisms. At Ocean Station P, although a number of zooplankton species are large enough to generate turbulence with Reynolds numbers Re > 1000, biomass densities are typically less than 103 individuals per cubic meter (<0.01% by volume), and turbulent kinetic energy dissipation rates ɛ were better correlated with 16-m vertical shear than acoustic backscatter layers. In Saanich Inlet, where krill densities are up to 104 individuals per cubic meter (0.1% by volume), no dramatic elevation of dissipation rates ɛ was associated with dusk and dawn vertical migrations of the acoustic backscatter layer. Dissipation rates are a factor of 2 higher [〈ɛ〉 = 1.4 × 10−8 W kg−1, corresponding to buoyancy Re = 〈ɛ〉/(νN 2) ∼ 140] in acoustic backscatter layers than in acoustically quiet waters, regardless of whether they are vertically migrating. The O(1 m) thick turbulence patches have vertical wavenumber spectra for microscale shear commensurate with the Nasmyth model turbulence spectrum. However, the turbulence bursts of O(10−5 W kg−1) proposed to occur in such dense swarms appear to be rare. Thus far, intense turbulent bursts have been found infrequently, even in very dense aggregations O(104 individuals per cubic meter) characteristic of coastal and high-latitude environs. Based on sampling to date, this corresponds to a frequency of occurrence of less than 4%, suggesting that turbulence production by the marine biosphere is not efficient.

scholarly journals Turbulent Length Scales in a Fast-flowing, Weakly Stratified, Strait: Cook Strait, New Zealand

2017 ◽  
Author(s):  
Craig L. Stevens
Keyword(s):  
New Zealand ◽  
Full Range ◽  
Turbulent Energy ◽  
Flow Speed ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
Cook Strait ◽  
Flow Speeds ◽  
Ozmidov Scale ◽  
Thorpe Scale

Abstract. There remains much to be learned about the full range of turbulent motions in the ocean. Here we consider turbulence and overturn scales in the relatively shallow, weakly stratified, fast-flowing tidal flows of Cook Strait, New Zealand. With flow speeds reaching 3 m s−1 in a water column of ~ 300 m depth the location is heuristically known to be highly turbulent. Dissipation rates of turbulent kinetic energy ε along with the Thorpe scale, LT, are described. Thorpe scales, often as much as one quarter of the water depth, are compared with dissipation rates and background flow speed. Turbulent energy dissipation rates ε are modest but high for oceans, around 5 × 10–5 W kg−1. Comparison of the buoyancy-limit Ozmidov scale LOz suggest the Cook Strait data lie for the majority of the time in the LOz > LT regime, but not universally. Also, comparison of direct and LT -based estimates of ε exhibit reasonable similarity.

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