scholarly journals On the Cascading of Dense Shelf Waters in the Irminger Sea

2012 ◽  
Vol 42 (12) ◽  
pp. 2254-2267 ◽  
Author(s):  
Anastasia Falina ◽  
Artem Sarafanov ◽  
Herlé Mercier ◽  
Pascale Lherminier ◽  
Alexey Sokov ◽  
...  
Keyword(s):  
Continental Slope ◽  
Western Boundary ◽  
Boundary Current ◽  
East Greenland ◽  
Low Salinity ◽  
East Greenland Current ◽  
Irminger Sea ◽  
Deep Western Boundary Current ◽  
Deep Waters ◽  
Denmark Strait

Abstract Hydrographic data collected in the Irminger Sea in the 1990s–2000s indicate that dense shelf waters carried by the East Greenland Current south of the Denmark Strait intermittently descend (cascade) down the continental slope and merge with the deep waters originating from the Nordic Seas overflows. Repeat measurements on the East Greenland shelf at ~200 km south of the Denmark Strait (65°–66°N) reveal that East Greenland shelf waters in the Irminger Sea are occasionally as dense (σ0 > 27.80) as the overflow-derived deep waters carried by the Deep Western Boundary Current (DWBC). Clear hydrographic traces of upstream cascading of dense shelf waters are found over the continental slope at 64.3°N, where the densest plumes (σ0 > 27.80) originating from the shelf are identified as distinct low-salinity anomalies in the DWBC. Downstream observations suggest that dense fresh waters descending from the shelf in the northern Irminger Sea can be distinguished in the DWBC up to the latitude of Cape Farewell (~60°N) and that these waters make a significant contribution to the DWBC transport.

Observed Denmark Strait Overflow Cyclones around Greenland

2021 ◽  
Author(s):  
Sijia Zou ◽  
Amy Bower ◽  
Heather Furey ◽  
Robert Pickart ◽  
Loïc Houpert ◽  
...  
Keyword(s):  
Continental Slope ◽  
Potential Vorticity ◽  
Small Radius ◽  
Rossby Number ◽  
Western Boundary ◽  
Boundary Current ◽  
Boundary Currents ◽  
Irminger Sea ◽  
Deep Western Boundary Current ◽  
Denmark Strait

<div> <p>Abundant cyclonic eddies are observed to travel along the Deep Western Boundary Current around Greenland by Lagrangian floats, hydrographic stations and moorings. Most of the cyclones have intensified rotations below the surface (700-1000 dbar), with maximum azimuthal velocities of ~30 cm/s at radii of ~10 km. The swift rotation and small radius lead to a relatively large Rossby number (~0.4), suggesting important contributions from the ageostrophic terms. The subsurface rotational core is also characterized with a local (both vertically and horizontally) potential vorticity (PV) maximum, which is associated with the pinching of isopycnals towards the mid-depths (i.e. high stratification). The PV structure suggests the origin of the cyclone as the Denmark Strait Overflow Cyclone. The latter is known to be formed by vortex stretching southwest of the Denmark Strait, where outflow waters with high PV from the sill descends the continental slope into the low PV Irminger Sea. Finally, we show that these cyclones can influence the boundary currents around Greenland by introducing property anomalies that originate from the Denmark Strait.</p> </div>

scholarly journals The East Greenland Spill Jet*

2005 ◽  
Vol 35 (6) ◽  
pp. 1037-1053 ◽  
Author(s):  
Robert S. Pickart ◽  
Daniel J. Torres ◽  
Paula S. Fratantoni
Keyword(s):  
Gulf Stream ◽  
Current System ◽  
Vertical Mixing ◽  
Relative Vorticity ◽  
Boundary Current ◽  
Velocity Measurements ◽  
East Greenland ◽  
Irminger Sea ◽  
Denmark Strait ◽  
Vorticity Analysis

Abstract High-resolution hydrographic and velocity measurements across the East Greenland shelf break south of Denmark Strait have revealed an intense, narrow current banked against the upper continental slope. This is believed to be the result of dense water cascading over the shelf edge and entraining ambient water. The current has been named the East Greenland Spill Jet. It resides beneath the East Greenland/Irminger Current and transports roughly 2 Sverdrups of water equatorward. Strong vertical mixing occurs during the spilling, although the entrainment farther downstream is minimal. A vorticity analysis reveals that the increase in cyclonic relative vorticity within the jet is partly balanced by tilting vorticity, resulting in a sharp front in potential vorticity reminiscent of the Gulf Stream. The other components of the Irminger Sea boundary current system are described, including a presentation of absolute transports.

scholarly journals Changes in the Deep Western Boundary Current at 53°N

2012 ◽  
Vol 42 (7) ◽  
pp. 1207-1216 ◽  
Author(s):  
Paul G. Myers ◽  
Nilgun Kulan
Keyword(s):  
Sea Water ◽  
Water Layer ◽  
Western Boundary Current ◽  
Labrador Sea ◽  
Western Boundary ◽  
Boundary Current ◽  
Deep Western Boundary Current ◽  
Denmark Strait ◽  
Labrador Sea Water

Abstract Southward transports in the deep western boundary current across 53°N, over 1949–99, are determined from a historical reconstruction. Long-term mean transports, for given water masses, for net southward transport (the southward component of the transport not including recirculation given in parentheses) are 4.7 ± 2.3 Sv (5.1 ± 2.4 Sv) (Sv ≡ 106 m3 s−1) for the Denmark Strait Overflow Water, 6.1 ± 2.7 Sv (6.8 ± 1.7 Sv) for the Iceland–Scotland Overflow Water, 6.5 ± 2.6 Sv (7.1 ± 1.8 Sv) for classical Labrador Sea Water, and 2.3 ± 1.9 Sv (2.7 ± 3.4 Sv) for upper Labrador Sea Water. The estimates take into account seasonal and interannual variability of the isopycnal positions and suggest the importance of including this factor. A strong correlation, 0.91, is found between variability of the total and baroclinic transports (with the barotropic velocity removed) at the annual time scale. This correlation drops to 0.32 if the baroclinic transports are, instead, computed based upon the use of a fixed level of no motion at 1400 m. The Labrador Sea Water layer shows significant variability and enhanced transport during the 1990s but no trend. The deeper layers do show a declining (but nonstatistically significant) trend over the period analyzed, largest in the ISOW layer. The Iceland–Scotland Overflow Water presents a 0.029 Sv yr−1 decline or 1.5 Sv over the 50-yr period, an 18%–22% decrease in its mean transport.

scholarly journals Variability in the Internal Wave Field Induced by the Atlantic Deep Western Boundary Current at 16°N

2014 ◽  
Vol 44 (2) ◽  
pp. 492-516 ◽  
Author(s):  
Janna Köhler ◽  
Christian Mertens ◽  
Maren Walter ◽  
Uwe Stöber ◽  
Monika Rhein ◽  
...  
Keyword(s):  
Internal Wave ◽  
Wave Field ◽  
Continental Slope ◽  
Internal Waves ◽  
Vertical Mixing ◽  
Low Frequency ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Deep Western Boundary Current

Abstract Five years of continuous mooring data combined with conductivity–temperature–depth (CTD)/lowered acoustic Doppler current profiler (LADCP) measurements from five cruises are used to investigate the influence of the deep western boundary current (DWBC) on the internal wave field and associated vertical mixing at the continental slope at 16°N in the western Atlantic. The mooring data include 2-hourly rotor current-meter measurements and temperature/conductivity time series with a high temporal resolution of 5–20 min. Thus, the data resolve time scales ranging from the low-frequency variability of the large-scale DWBC that generates internal waves due to interactions with the topography to frequencies greater than that of internal waves that are associated with vertical mixing. Estimates of the vertical mixing induced by the breaking of the observed internal waves show elevated diapycnal diffusivities of up to 10−3 ± 0.4 × 10−3 m2 s−1 in the bottommost 1500 m during times of a strong DWBC (maximum velocities at the mooring site up to 50 cm s−1) whereas vertical mixing rates are about an order of magnitude lower (1.6 × 10−4 ± 0.6 × 10−4 m2 s−1) during weak flow. During periods of a strong DWBC, spectra of horizontal velocity and internal wave available potential energy change substantially at depths below 1200 m and show a strong increase in variance particularly in the near-inertial frequency band. Low-frequency, near-inertial waves generated by topography/DWBC interaction on the slope to the west of the moorings can potentially cause this observed wave intensification; ray paths estimated for these waves agree well with the observed spectral changes at different depths. Variability in the high-frequency range, considered as a proxy for turbulent mixing, is significantly correlated with the DWBC strength above the continental slope.

scholarly journals Transport Variability of the Irminger Sea Deep Western Boundary Current From a Mooring Array

2019 ◽  
Vol 124 (5) ◽  
pp. 3246-3278 ◽  
Author(s):  
J. E. Hopkins ◽  
N. P. Holliday ◽  
D. Rayner ◽  
L. Houpert ◽  
I. Le Bras ◽  
...  
Keyword(s):  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Irminger Sea ◽  
Deep Western Boundary Current

scholarly journals Midlatitude–Equatorial Dynamics of a Grounded Deep Western Boundary Current. Part I: Midlatitude Flow and the Transition to the Equatorial Region

2015 ◽  
Vol 45 (10) ◽  
pp. 2457-2469 ◽  
Author(s):  
Gordon E. Swaters
Keyword(s):  
Bottom Topography ◽  
Zonal Flow ◽  
Ocean Basin ◽  
Equatorial Region ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Qualitative Properties ◽  
Deep Western Boundary Current ◽  
The Tropics

AbstractA comprehensive theoretical study of the nonlinear hemispheric-scale midlatitude and cross-equatorial steady-state dynamics of a grounded deep western boundary current is given. The domain considered is an idealized differentially rotating, meridionally aligned basin with zonally varying parabolic bottom topography so that the model ocean shallows on both the western and eastern sides of the basin. Away from the equator, the flow is governed by nonlinear planetary geostrophic dynamics on sloping topography in which the potential vorticity equation can be explicitly solved. As the flow enters the equatorial region, it speeds up and becomes increasingly nonlinear and passes through two distinguished inertial layers referred to as the “intermediate” and “inner” inertial equatorial boundary layers, respectively. The flow in the intermediate equatorial region is shown to accelerate and turn eastward, forming a narrow equatorial jet. The qualitative properties of the solution presented are consistent with the known dynamical characteristics of the deep western boundary currents as they flow from the midlatitudes into the tropics. The predominately zonal flow across the ocean basin in the inner equatorial region (and its exit from the equatorial region) is determined in Part II of this study.

scholarly journals Atlantic transport variability at 25° N in six hydrographic sections

Ocean Science ◽  
2012 ◽  
Vol 8 (4) ◽  
pp. 497-523 ◽  
Author(s):  
C. P. Atkinson ◽  
H. L. Bryden ◽  
S. A. Cunningham ◽  
B. A. King
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Decadal Variability ◽  
Potential Temperature ◽  
Deep Ocean ◽  
Velocity Shear ◽  
Western Boundary ◽  
Boundary Current ◽  
Annual Average ◽  
Deep Western Boundary Current

Abstract. In January and February 2010, a sixth transatlantic hydrographic section was completed across 25° N, extending the hydrographic record at this latitude to over half a century. In combination with continuous transport measurements made since 2004 at 26.5° N by the Rapid-WATCH project, we reassess transport variability in the 25° N hydrographic record. Past studies of transport variability at this latitude have assumed transport estimates from each hydrographic section to represent annual average conditions. In this study the uncertainty in this assumption is assessed through use of Rapid-WATCH observations to quantify sub-seasonal and seasonal transport variability. Whilst in the upper-ocean no significant interannual or decadal transport variability are identified in the hydrographic record, in the deep ocean transport variability in both depth and potential temperature classes suggests some interannual or decadal variability may have occurred. This is particularly striking in the lower North Atlantic Deep Water where southward transports prior to 1998 were greater than recent transports by several Sverdrups. Whilst a cooling and freshening of Denmark Straits Overflow Water has occurred which is coincident with these transport changes, these water mass changes appear to be density compensated. Transport changes are the result of changing velocity shear in the vicinity of the Deep Western Boundary Current.

scholarly journals Wind forcing of salinity anomalies in the Denmark Strait overflow

Ocean Science ◽  
2011 ◽  
Vol 7 (6) ◽  
pp. 821-834 ◽  
Author(s):  
S. Hall ◽  
S. R. Dye ◽  
K. J. Heywood ◽  
M. R. Wadley
Keyword(s):  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Mixing Processes ◽  
East Greenland ◽  
The North ◽  
East Greenland Current ◽  
Denmark Strait ◽  
Salinity Anomaly

Abstract. The overflow of dense water from the Nordic Seas to the North Atlantic through Denmark Strait is an important part of the global thermohaline circulation. The salinity of the overflow plume has been measured by an array of current meters across the continental slope off the coast of Angmagssalik, southeast Greenland since September 1998. During 2004 the salinity of the overflow plume changed dramatically; the entire width of the array (70 km) freshened between January 2004 and July 2004, with a significant negative salinity anomaly of about 0.06 in May. The event in May represents a fresh anomaly of over 3 standard deviations from the mean since recording began in 1998. The OCCAM 1/12° Ocean General Circulation Model not only reproduces the 2004 freshening event (r=0.96, p<0.01), but also correlates well with salinity observations over a previous 6 year period (r=0.54, p<0.01), despite the inevitable limitations of a z-coordinate model in representing the mixing processes at and downstream of the Denmark Strait sill. Consequently the physical processes causing the 2004 anomaly and prior variability in salinity are investigated using the model output. Our results reject the hypotheses that the anomaly is caused by processes occurring between the overflow sill and the moorings, or by an increase in upstream net freshwater input. Instead, we show that the 2004 salinity anomaly is caused by an increase in volume flux of low salinity water, with a potential density greater than 27.60 kg m−3, flowing towards the Denmark Strait sill in the East Greenland Current. This is caused by an increase in southward wind stress upstream of the sill at around 75° N 20° W four and a half months earlier, and an associated strengthening of the East Greenland Current.

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