On the hydrography of Denmark Strait (original) (raw)
Related papers
Sources to the East Greenland Current and its contribution to the Denmark Strait Overflow
Progress in Oceanography, 2008
Data from the East Greenland Current in 2002 are evaluated using optimum multiparameter analysis. The current is followed from north of Fram Strait to the Denmark Strait Sill and the contributions of different source waters, in mass fractions, are deduced. From the results it can be concluded that, at least in spring 2002, the East Greenland Current was the main source for the waters found at the Denmark Strait Sill, contributing to the overflow into the North Atlantic. The East Greenland Current carried water masses from different source regions in the Arctic Ocean, the West Spitsbergen Current and the Greenland Sea. The results agree well with the known circulation of the western Nordic Seas but also add knowledge both to the quantification and to the mixing processes, showing the importance of the locally formed Greenland Sea Arctic Intermediate Water for the East Greenland Current and the Denmark Strait.
Frontogenesis and variability in Denmark Strait and its influence on overflow water
Journal of Physical Oceanography
A high-resolution numerical model, together with in situ and satellite observations, is used to explore the nature and dynamics of the dominant high-frequency (from one day to one week) variability in Denmark Strait. Mooring measurements in the center of the strait reveal that warm water “flooding events” occur, whereby the North Icelandic Irminger Current (NIIC) propagates offshore and advects subtropical-origin water northward through the deepest part of the sill. Two other types of mesoscale processes in Denmark Strait have been described previously in the literature, known as “boluses” and “pulses,” associated with a raising and lowering of the overflow water interface. Our measurements reveal that flooding events occur in conjunction with especially pronounced pulses. The model indicates that the NIIC hydrographic front is maintained by a balance between frontogenesis by the large-scale flow and frontolysis by baroclinic instability. Specifically, the temperature and salinity t...
On the origin and propagation of Denmark Strait overflow water anomalies in the Irminger Basin
Journal of Geophysical Research: Oceans, 2015
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 2007-2012. 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. Downstream of Denmark Strait, entrainment warms the overflow and hence decreases its density. Nevertheless, DSOW remains the densest water mass in the Irminger Sea with temperatures below 2 C, descending to more than 2000 m depth. Here it is overlain by Iceland Scotland Overflow Water (ISOW), which also influences the less dense portion of the plume by isopycnal mixing. The average overflow water transport at the sill of Denmark Strait is around 3.4 Sv [Jochumsen et al., 2012], which increases further downstream to 10.7 Sv near Angmagssalik due to entrainment and the combination with ISOW [Dickson et al., 2008].
Revised circulation scheme north of the Denmark Strait
Deep Sea Research Part I: Oceanographic Research Papers, 2013
The circulation and water mass transports north of the Denmark Strait are investigated using recently collected and historical in situ data along with an idealized numerical model and atmospheric reanalysis fields. Emphasis is placed on the pathways of dense water feeding the Denmark Strait Overflow Water plume as well as the upper-layer circulation of freshwater. It is found that the East Greenland Current (EGC) bifurcates at the northern end of the Blosseville Basin, some 450 km upstream of the Denmark Strait, advecting overflow water and surface freshwater away from the boundary. This "separated EGC" flows southward adjacent to the previously identified North Icelandic Jet, indicating that approximately 70% of the Denmark Strait Overflow Water approaches the sill along the Iceland continental slope. Roughly a quarter of the freshwater transport of the EGC is diverted offshore via the bifurcation. Two hypotheses are examined to explain the existence of the separated EGC. The atmospheric fields demonstrate that flow distortion due to the orography of Greenland imparts significant vorticity into the ocean in this region. The negative wind stress curl, together with the closed bathymetric contours of the Blosseville Basin, is conducive for spinning up an anti-cyclonic gyre whose offshore branch could represent the separated EGC. An idealized numerical simulation suggests instead that the current is primarily eddy-forced. In particular, baroclinic instability of the model EGC spawns large anti-cyclones that migrate offshore and coalesce upon reaching the Iceland continental slope, resulting in the separated EGC. Regardless of the formation mechanism, the recently obtained shipboard data and historical hydrography both indicate that the separated EGC is a permanent feature of the circulation north of the Denmark Strait.
Fates and Travel Times of Denmark Strait Overflow Water in the Irminger Basin
Journal of Physical Oceanography, 2013
The Denmark Strait Overflow (DSO) supplies about one third of the North Atlantic Deep 6 Water and is critical to the global thermohaline circulation. Knowledge of the pathways of 7 DSO through the Irminger Basin and its transformation there is still incomplete however. We 8 deploy over 10,000 Lagrangian particles at Denmark Strait in a high resolution ocean model 9 to study these issues. The particle trajectories show that: First, the mean-position and 10 potential density of dense waters cascading over the Denmark Strait sill evolve consistently 11 with hydrographic observations. These sill particles transit the Irminger basin to the Spill Jet 12 section (65.25 o N) in 5-7 days and to the Angmagssalik section (63.5 o N) in two-three weeks. 13 Second, the dense water pathways on the continental shelf are consistent with observations 14 and particles released on the shelf in the Strait constitute a significant fraction of the dense 15 water particles recorded at the Angmagssalik section within 60 days (∼ 25%). Some particles 16 circulate on the shelf for several weeks before they spill off the shelf break and join the 17 overflow from the sill. Third, there are two places where the water density following particle 18 trajectories decreases rapidly due to intense mixing: southwest of the sill and southwest of 19 the Kangerdlugssuaq Trough on the continental slope. After transformation in these places, 20 the overflow particles exhibit a wide range of densities. 21 1 23 waters formed in the Arctic Ocean and the Nordic Seas. The dense waters pass through the 24 Irminger Basin toward the North Atlantic where they supply about one third of the North 25 Atlantic Deep Water, a major component of the global thermohaline circulation (Dickson 26 and Brown 1994). The DSO transmits the climate signals from its source regions, modified 27 en route by mixing and entrainment, and affects the properties throughout the water column 28 in the North Atlantic (Dickson et al. 2008; Yashayaev and Dickson 2008). 29 The 620-m deep Denmark Strait (DS) sill is the main gateway for dense waters exiting 30 the Greenland Sea to the Irminger Basin and is a key location for observing the DSO at 31 the start of its transit to the North Atlantic (Dickson et al. 2008). Measurements show that 32 the dense overflow through the sill is fast (speeds frequently exceed 1 m/s) and occurs as 33 pulses of dense water (referred to as boluses) cascading to the deep water south of the sill 34 at intervals of 2-5 days. On longer timescales, DSO appears as a steadier and hydraulically 35 controlled flow with a mean transport of approximately 3 Sv (1 Sv = 10 6 m 3 s −1 ; Käse and 36 Oschlies 2000; Macrander et al. 2007; Jochumsen et al. 2012). DSO temperature and salinity 37 vary on a timescale of a few-days, owing to mesoscale activity and intense mixing processes 38 near the sill (Rudels et al. 1999; Tanhua et al. 2005). The seasonal signals in the DSO 39 transport and properties are weak (Dickson and Brown 1994; Jochumsen et al. 2012). The 40 overflow composition exhibits interannual-to-decadal variations, however, most likely linked 41 to changes in the upstream source waters or pathways (Rudels et al. 2002a). These changes 42 in turn are possibly linked to atmospheric forcing and in particular to variations in the North 43 Atlantic Oscillation (Yashayaev and Dickson 2008; Serra et al. 2010).
Journal of Geophysical Research: Oceans
We present measurements from two shipboard surveys conducted in summer 2012 that sampled the rim current system around the Nordic Seas from Fram Strait to Denmark Strait. The data reveal that, along a portion of the western boundary of the Nordic Seas, the East Greenland Current (EGC) has three distinct components. In addition to the well-known shelfbreak branch, there is an inshore branch on the continental shelf as well as a separate branch offshore of the shelfbreak. The inner branch contributes significantly to the overall freshwater transport of the rim current system, and the outer branch transports a substantial amount of Atlantic-origin Water equatorward. Supplementing our measurements with historical hydrographic data, we argue that the offshore branch is a direct recirculation of the western branch of the West Spitsbergen Current in Fram Strait. The total transport of the shelfbreak EGC (the only branch sampled consistently in all of the sections) decreased toward Denmark Strait. The estimated average transport of dense overflow water (r h > 27.8 kg/m 3 and h > 08C) in the shelfbreak EGC was 2.8 6 0.7 Sv, consistent with previous moored measurements. For the three sections that crossed the entire EGC system the freshwater flux, relative to a salinity of 34.8, ranged from 127 6 13 to 81 6 8 mSv. The hydrographic data reveal that, between Fram Strait and Denmark Strait, the core of the Atlantic-origin Water in the shelfbreak EGC cools and freshens but changes very little in density.