Microstructure measurements and estimates of entrainment in the Denmark Strait overflow plume

Пака, В. Т.; Zhurbas, Victor; Rudels, Bert; Quadfasel, Detlef; Корж, А. О.; Delisi, Donald P.

doi:10.5194/os-9-1003-2013

Cited by 14 publications

(42 citation statements)

References 37 publications

(56 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…This hypothesis was supported by microstructure measurements by Paka et al . [], who concluded that vertical turbulent mixing is not the major process controlling entrainment in the DSOW plume at ∼200 km from the sill. Detailed process studies on the entrainment in the region close to the sill of Denmark Strait are lacking; it is therefore still unclear which process dominates the entrainment in this specific region.…”

Section: Introductionmentioning

confidence: 99%

On the origin and propagation of Denmark Strait overflow water anomalies in the Irminger Basin

et al. 2015

View full text Add to dashboard Cite

Denmark Strait Overflow Water (DSOW) supplies the densest contribution to North Atlantic Deep Water and is monitored at several locations in the subpolar North Atlantic. Hydrographic (temperature and salinity) and velocity time series from three multiple-mooring arrays at the Denmark Strait sill, at 180 km downstream (south of Dohrn Bank) and at a further 320 km downstream on the east Greenland continental slope near Tasiilaq (formerly Angmagssalik), were analyzed to quantify the variability and track anomalies in DSOW in the period [2007][2008][2009][2010][2011][2012]. No long-term trends were detected in the time series, while variability on time scales from interannual to weekly was present at all moorings. The hydrographic time series from different moorings within each mooring array showed coherent signals, while the velocity fluctuations were only weakly correlated. Lagged correlations of anomalies between the arrays revealed a propagation from the sill of Denmark Strait to the Angmagssalik array in potential temperature with an average propagation time of 13 days, while the correlations in salinity were low. Entrainment of warm and saline Atlantic Water and fresher water from the East Greenland Current (via the East Greenland Spill Jet) can explain the whole range of hydrographic changes in the DSOW measured downstream of the sill. Changes in the entrained water masses and in the mixing ratio can thus strongly influence the salinity variability of DSOW. Fresh anomalies found in downstream measurements of DSOW within the Deep Western Boundary Current can therefore not be attributed to Arctic climate variability in a straightforward way.

show abstract

Section: Introductionmentioning

confidence: 99%

On the origin and propagation of Denmark Strait overflow water anomalies in the Irminger Basin

et al. 2015

View full text Add to dashboard Cite

show abstract

“…The data measured along AUV leg 7 were taken for the upper integration limit. To our minds, the main source of errors of the calculated entrainment rates lies in linear vertical interpolation between the measured dissipation rates, because the vertical profiles of ε are known to be highly variable (patchy) due to turbulence intermittency [e.g., Paka et al ., ]. For this reason, it is hardly expected that the accuracy of the w e estimates is better than one order of magnitude.…”

Section: Resultsmentioning

confidence: 99%

“…Second, based on measurements of dissipation of turbulent kinetic energy (hereafter simply referred to as dissipation) in the DSO plume at 200 km downstream of the sill, Paka et al . [] computed much smaller entrainment rates than required to explain the rapid warming of the plume observed by Voet and Quadfasel []. Paka et al .…”

Section: Introductionmentioning

confidence: 99%

“…Paka et al . [] therefore speculated that lateral mixing rather than vertical mixing should be the main driver of the plume modification in the first 200 km downstream of the sill. Since reliable estimates of neither vertical mixing nor lateral mixing exist in this distance interval, the question which of the two components drives the bulk of the warming in this region [see also Jochumsen et al ., ] is still unresolved.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Enhanced turbulence driven by mesoscale motions and flow‐topography interaction in the Denmark Strait Overflow plume

et al. 2016

View full text Add to dashboard Cite

The Denmark Strait Overflow (DSO) contributes roughly half to the total volume transport of the Nordic overflows. The overflow increases its volume by entraining ambient water as it descends into the subpolar North Atlantic, feeding into the deep branch of the Atlantic Meridional Overturning Circulation. In June 2012, a multiplatform experiment was carried out in the DSO plume on the continental slope off Greenland (180 km downstream of the sill in Denmark Strait), to observe the variability associated with the entrainment of ambient waters into the DSO plume. In this study, we report on two high‐dissipation events captured by an autonomous underwater vehicle (AUV) by horizontal profiling in the interfacial layer between the DSO plume and the ambient water. Strong dissipation of turbulent kinetic energy of O( 10−6) W kg−1 was associated with enhanced small‐scale temperature variance at wavelengths between 0.05 and 500 m as deduced from a fast‐response thermistor. Isotherm displacement slope spectra reveal a wave number‐dependence characteristic of turbulence in the inertial‐convective subrange ( k1/3) at wavelengths between 0.14 and 100 m. The first event captured by the AUV was transient, and occurred near the edge of a bottom‐intensified energetic eddy. Our observations imply that both horizontal advection of warm water and vertical mixing of it into the plume are eddy‐driven and go hand in hand in entraining ambient water into the DSO plume. The second event was found to be a stationary feature on the upstream side of a topographic elevation located in the plume pathway. Flow‐topography interaction is suggested to drive the intense mixing at this site.

show abstract

“…Following the methods outlined in previous overflow plume studies (e.g., Arneborg et al, 2007;Paka et al, 2013;Zhurbas et al, 2016), the integrated entrainment rate (w layer ) was calculated as:…”

Section: Data Set Sources and Processingmentioning

confidence: 99%

Entrainment and Energy Transfer Variability Along the Descending Path of the Denmark Strait Overflow Plume

2018

View full text Add to dashboard Cite

The descent of the Denmark Strait overflow plume is an important process in the Atlantic Meridional Overturning Circulation. Downstream of the sill, the plume entrains ambient water, increasing its volume transport. The entrainment and related transfer of energy can be driven by vertical or horizontal turbulent mixing, and varies spatially, as the plume descends, and temporally, as the volume transport at the sill changes. Using over 30 years of profile data, this spatial and temporal variability in the first 200 km downstream of the sill was investigated. Dissipation and entrainment rates were derived from Thorpe scales, and each profile was identified as either a low‐ or high‐transport flow, defined as below or above‐average volume transport at the sill. In the first 175 km flow type explains most of the variability in entrainment and dissipation rates, with high‐transport flow producing order of magnitude higher rates. Sections crossing the plume and yo‐yo casts (continuous profiling) indicate that dissipation and entrainment are likely driven by the formation of shear instabilities in the interfacial layer, when the vertical velocity shear overcomes the stratification. This vertical turbulent mixing explains most of the variability within the first 175 km, suggesting horizontal turbulent mixing processes may not play as important a role in this region. The importance of temporal flow variability means that further improvements to our understanding of plume dynamics in the Denmark Strait will require a novel observational approach to fully account for spatial and temporal contributions.

show abstract

Microstructure measurements and estimates of entrainment in the Denmark Strait overflow plume

Cited by 14 publications

References 37 publications

On the origin and propagation of Denmark Strait overflow water anomalies in the Irminger Basin

On the origin and propagation of Denmark Strait overflow water anomalies in the Irminger Basin

Enhanced turbulence driven by mesoscale motions and flow‐topography interaction in the Denmark Strait Overflow plume

Entrainment and Energy Transfer Variability Along the Descending Path of the Denmark Strait Overflow Plume

Contact Info

Product

Resources

About