Wind forcing of salinity anomalies in the Denmark Strait overflow

Hall, Sarah B.; Dye, Stephen; Heywood, Karen J.; Wadley, Martin R.

doi:10.5194/osd-8-1403-2011

Cited by 5 publications

(14 citation statements)

References 24 publications

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“…Given a nominal distance of 1500 km, this equates to a mean advective velocity of ∼15 cm s – 1 from the Fram Strait to our moorings. This compares reasonably well with previous measurements of velocities in the East Greenland Current [ Dickson et al ., ; Hall et al ., ]. We therefore argue that the seasonal export of freshwater from Fram Strait is likely to be a significant driver of the winter deepening of the Polar layer in the East Greenland Coastal Current.…”

Section: Discussionmentioning

confidence: 91%

Moored observations of synoptic and seasonal variability in the East Greenland Coastal Current

2014

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We present a year-round assessment of the hydrographic variability within the East Greenland Coastal Current on the Greenland shelf from five synoptic crossings and 4 years of moored hydrographic data. From the five synoptic sections the current is observed as a robust, surface intensified flow with a total volume transport of 0.66 6 0.18 Sv and a freshwater transport of 42 6 12 mSv. The moorings showed heretofore unobserved variability in the abundance of Polar and Atlantic water masses in the current on synoptic scales. This is exhibited as large vertical displacement of isotherms (often greater than 100 m). Seasonally, the current is hemmed into the coast during the fall by a full depth Atlantic Water layer that has penetrated onto the inner shelf. The Polar Water layer in the current then thickens through the winter and spring seasons increasing the freshwater content in the current; the timing implies that this is probably driven by the seasonally varying export of freshwater from the Arctic and not the local runoff from Greenland. The measured synoptic variability is enhanced during the winter and spring period due to a lower halocline and a concurrent enhancement in the along-coast wind speed. The local winds force much of the high-frequency variability in a manner consistent with downwelling, but variability distinct from downwelling is also visible.

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Section: Discussionmentioning

confidence: 91%

Moored observations of synoptic and seasonal variability in the East Greenland Coastal Current

2014

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“…Hall et al . [] also connected fresh events at Angmagssalik with upstream atmospheric forcing arguing that they are caused by northerly wind anomalies north of Denmark Strait generating higher volume flux of EGC water to the sill rather than by changes in the properties of this source water. This is directly compatible with our finding that it is the amount of EGC water rather than its property anomalies that drives salinity variability in the DSOW plume.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…This conclusion of Hall et al . [] was based on a global model in which entrainment processes are underestimated (although they are eddy‐resolving) and downstream overflow water is often represented at wrong depth levels [e.g., Xu et al ., ]. Additionally, our work places the processes responsible for the anomalies to locations south of the Denmark Strait sill.…”

Section: Summary and Discussionmentioning

confidence: 99%

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

et al. 2015

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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.

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“…Other long term observations of the overflow transport and properties are based on downstream mooring arrays [e.g., Dickson and Brown , 1994; Dickson et al , 2008; Hall et al , 2011], giving mean transport values of 4.0 ± 0.4 Sv for density anomalies above σ θ = 27.85 kg m −3 . These observations are focused on the overflow plume in the Irminger Basin, which descends from Denmark Strait to 2500–3000 m depth near Cape Farewell [ van Aken and de Jong , 2012].…”

Section: Introductionmentioning

confidence: 99%

Variability of the Denmark Strait overflow: Moored time series from 1996–2011

Jochumsen¹,

Quadfasel²,

Valdimarsson³

et al. 2012

J. Geophys. Res.

111

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[1] The Denmark Strait overflow provides about half of the total dense water overflow from the Nordic Seas into the North Atlantic Ocean. The velocity of the overflow has been monitored in the Strait with two moored Acoustic Doppler Current Profilers since 1996 with several interruptions due to mooring losses or instrument failure. So far, overflow transports were only calculated when data from both moorings were available. In this work, we introduce a linear model to fill gaps in the time series when data from only one instrument is available. The mean overflow transport is 3.4 Sv and exhibits a variance of 2.0 Sv 2 . No significant trend was detected in the time series. The highest variability in the transport is associated with the passage of mesoscale eddies with time scales of 2-10 days (associated with a variance of 1.5 Sv 2 ). Seasonal variability is weak and explains less than 5% of the variance in all time series, which is in contrast to the strong seasonal cycle found in high resolution model simulations. Interannual variability is on the order of 10% of the mean. A relation to atmospheric forcing such as the local wind stress curl, as well as to larger scale phenomena, e.g. the North Atlantic Oscillation, is not detected. Since 2005 data from moored temperature, conductivity and pressure recorders have been available as well, monitoring the hydrographic variability at the bottom of Denmark Strait. In recent years the temperature time series of the Denmark Strait overflow revealed a cooling, while the salinity stayed nearly constant.

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Wind forcing of salinity anomalies in the Denmark Strait overflow

Cited by 5 publications

References 24 publications

Moored observations of synoptic and seasonal variability in the East Greenland Coastal Current

Moored observations of synoptic and seasonal variability in the East Greenland Coastal Current

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

Variability of the Denmark Strait overflow: Moored time series from 1996–2011

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