scholarly journals How Does Labrador Sea Water Enter the Deep Western Boundary Current?

2008 ◽  
Vol 38 (5) ◽  
pp. 968-983 ◽  
Author(s):  
Jaime B. Palter ◽  
M. Susan Lozier ◽  
Kara L. Lavender
Keyword(s):  
Heat Flux ◽  
Water Mass ◽  
Sea Water ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Western Boundary ◽  
Boundary Current ◽  
Deep Western Boundary Current ◽  
Labrador Sea Water

Abstract Labrador Sea Water (LSW), a dense water mass formed by convection in the subpolar North Atlantic, is an important constituent of the meridional overturning circulation. Understanding how the water mass enters the deep western boundary current (DWBC), one of the primary pathways by which it exits the subpolar gyre, can shed light on the continuity between climate conditions in the formation region and their downstream signal. Using the trajectories of (profiling) autonomous Lagrangian circulation explorer [(P)ALACE] floats, operating between 1996 and 2002, three processes are evaluated for their role in the entry of Labrador Sea Water in the DWBC: 1) LSW is formed directly in the DWBC, 2) eddies flux LSW laterally from the interior Labrador Sea to the DWBC, and 3) a horizontally divergent mean flow advects LSW from the interior to the DWBC. A comparison of the heat flux associated with each of these three mechanisms suggests that all three contribute to the transformation of the boundary current as it transits the Labrador Sea. The formation of LSW directly in the DWBC and the eddy heat flux between the interior Labrador Sea and the DWBC may play leading roles in setting the interannual variability of the exported water mass.

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 The arrival of recently formed Labrador sea water in the Deep Western Boundary Current at 26.5°N

1998 ◽  
Vol 25 (13) ◽  
pp. 2249-2252 ◽  
Author(s):  
Robert L. Molinari ◽  
Rana A. Fine ◽  
W. Douglas Wilson ◽  
Ruth G. Curry ◽  
Jeff Abell ◽  
...  
Keyword(s):  
Sea Water ◽  
Western Boundary Current ◽  
Labrador Sea ◽  
Western Boundary ◽  
Boundary Current ◽  
Deep Western Boundary Current ◽  
Labrador Sea Water

scholarly journals Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

2016 ◽  
Author(s):  
Christopher S. Meinen ◽  
Silvia L. Garzoli ◽  
Renellys C. Perez ◽  
Edmo Campos ◽  
Alberto R. Piola ◽  
...  
Keyword(s):  
Volume Transport ◽  
Horizontal Resolution ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Time Variability ◽  
Western Boundary ◽  
Boundary Current ◽  
Meridional Heat Transport ◽  
Data Set ◽  
Deep Western Boundary Current

Abstract. The Deep Western Boundary Current (DWBC) at 34.5° S in the South Atlantic carries a significant fraction of the cold deep limb of the Meridional Overturning Circulation (MOC), and therefore its variability affects both the meridional heat transport and the regional and global climate. Nearly six years of observations from a line of pressure-equipped inverted echo sounders (PIES) have yielded an unprecedented data set for studying the characteristics of the time-varying DWBC volume transport at 34.5° S. Furthermore, the horizontal resolution of the observing array was greatly improved in December 2012 with the addition of two current-and-pressure-equipped inverted echo sounders (CPIES) at the midpoints of three of the existing sites. Regular hydrographic sections along the PIES/CPIES line confirm the presence of recently-ventilated North Atlantic Deep Water carried by the DWBC. The time-mean absolute geostrophic transport integrated within the DWBC layer, defined between 800–4800 dbar, and within longitude bounds of 51.5° W to 44.5° W is −15 Sv (1 Sv = 106 m3 s−1; negative indicates southward flow). The observed peak-to-peak range in volume transport using these integration limits is from −89 Sv to +50 Sv, and the temporal standard deviation is 23 Sv. Testing different vertical integration limits based on time-mean water-mass property levels yields small changes to these values, but no significant alteration to the character of the transport time series. The time-mean southward DWBC flow at this latitude is confined west of 49.5° W, with recirculations dominating the flow further offshore. As with other latitudes where the DWBC has been observed for multiple years, the time variability greatly exceeds the time-mean, suggesting the presence of strong coherent vortices and/or Rossby Wave-like signals propagating to the boundary from the interior.

Evaluation of global ocean model on simulating deep western boundary current in the Pacific

2020 ◽  
Author(s):  
Huichang Jiang ◽  
Hongzhou Xu
Keyword(s):  
Spatial Structure ◽  
Water Mass ◽  
Volume Transport ◽  
Ocean Model ◽  
Western Boundary Current ◽  
Global Ocean ◽  
Western Boundary ◽  
Boundary Current ◽  
Deep Western Boundary Current ◽  
The Pacific

<p>As an important branch of the global overturning circulation, the deep western boundary current (DWBC) in the Pacific was poorly understood due to sparse observations. Six state-of-the-art global ocean model outputs were used herein to evaluate their performance for simulating the DWBC in the Melanesian Basin (MB) and Central Pacific Basin (CPB). These model outputs were compared to the historical observations, in aspects of water-mass characteristics, spatial structure and meridional volume transport of the DWBC, and seasonal variation. The results showed that most of the models reproduced the DWBC in the two basins well. Besides OFES with obvious cold and salty biases, the other models had minor deviations of the temperature and salinity in the deep layer. These models can reconstruct the spatial structure of the DWBC in detail and simulate appropriate transports of the eastern branch DWBC, ranging from 6.36 Sv to 8.55 Sv. But the western branch DWBC was underestimated in the models except HYCOM (4.48 Sv). HYCOM performed best for the DWBC with a whole transport of 12.84 Sv. Analysis of the temperature and salinity from Levitus data demonstrates the existence of annual and semi-annual cycles in the deep water of the MB and CPB, respectively, with warmer and saltier water mass in summer and autumn. Overall, the six models have good abilities to simulate the seasonal variations of temperature and volume transport of the DWBC in the Pacific. The seasonal signals probably originated from the DWBC upstream and propagated along its pathway.</p>

Deep Atlantic Ocean Warming Facilitated by the Deep Western Boundary Current and Equatorial Kelvin Waves

2018 ◽  
Vol 31 (20) ◽  
pp. 8541-8555 ◽  
Author(s):  
Min Zhang ◽  
Zhaohua Wu ◽  
Fangli Qiao
Keyword(s):  
Atlantic Ocean ◽  
Heat Storage ◽  
Western Boundary Current ◽  
Ocean Warming ◽  
Labrador Sea ◽  
Western Boundary ◽  
Boundary Current ◽  
Narrow Strip ◽  
Surface Warming ◽  
Deep Western Boundary Current

Increased heat storage in deep oceans has been proposed to account for the slowdown of global surface warming since the end of the twentieth century. How the imbalanced heat at the surface has been redistributed to deep oceans remains to be elucidated. Here, the evolution of deep Atlantic Ocean heat storage since 1950 on multidecadal or longer time scales is revealed. The anomalous heat in the deep Labrador Sea was transported southward by the shallower core of the deep western boundary current (DWBC). Upon reaching the equator around 1980, this heat transport route bifurcated into two, with one continuing southward along the DWBC and the other extending eastward along a narrow strip (about 4° width) centered at the equator. In the 1990s and 2000s, meridional diffusion helped to spread warming in the tropics, making the eastward equatorial warming extension have a narrow head and wider tail. The deep Atlantic Ocean warming since 1950 had overlapping variability of approximately 60 years. The results suggest that the current basinwide Atlantic Ocean warming at depths of 1000–2000 m can be traced back to the subsurface warming in the Labrador Sea in the 1950s. An inference from these results is that the increased heat storage in the twenty-first century in the deep Atlantic Ocean is unlikely to partly account for the atmospheric radiative imbalance during the last two decades and to serve as an explanation for the current warming hiatus.

scholarly journals Wind-Forced Variability of the Remote Meridional Overturning Circulation

2020 ◽  
Vol 50 (2) ◽  
pp. 455-469 ◽  
Author(s):  
Michael A. Spall ◽  
David Nieves
Keyword(s):  
Wind Stress ◽  
Rossby Wave ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Western Boundary ◽  
Boundary Current ◽  
Overturning Circulation ◽  
Deep Western Boundary Current ◽  
Wave Basin ◽  
Meridional Overturning

AbstractThe mechanisms by which time-dependent wind stress anomalies at midlatitudes can force variability in the meridional overturning circulation at low latitudes are explored. It is shown that winds are effective at forcing remote variability in the overturning circulation when forcing periods are near the midlatitude baroclinic Rossby wave basin-crossing time. Remote overturning is required by an imbalance in the midlatitude mass storage and release resulting from the dependence of the Rossby wave phase speed on latitude. A heuristic theory is developed that predicts the strength and frequency dependence of the remote overturning well when compared to a two-layer numerical model. The theory indicates that the variable overturning strength, relative to the anomalous Ekman transport, depends primarily on the ratio of the meridional spatial scale of the anomalous wind stress curl to its latitude. For strongly forced systems, a mean deep western boundary current can also significantly enhance the overturning variability at all latitudes. For sufficiently large thermocline displacements, the deep western boundary current alternates between interior and near-boundary pathways in response to fluctuations in the wind, leading to large anomalies in the volume of North Atlantic Deep Water stored at midlatitudes and in the downstream deep western boundary current transport.

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