Export of newly oxygenated Labrador Sea Water at 53N

2021 ◽  
Author(s):  
Jannes Koelling ◽  
Dariia Atamanchuk ◽  
Johannes Karstensen ◽  
Douglas W.R. Wallace
Keyword(s):  
Sea Water ◽  
Deep Convection ◽  
Sudden Change ◽  
Deep Ocean ◽  
Labrador Sea ◽  
Low Oxygen ◽  
Boundary Current ◽  
Convective Mixing ◽  
Future Work ◽  
Labrador Sea Water

<div> <p>Most of the life-sustaining oxygen found in the global deep ocean is supplied in one of only a handful of key regions around the globe, such as the Labrador Sea in the subpolar North Atlantic. Here, oxygen is supplied directly to the deep ocean during the formation of Labrador Sea Water (LSW), when convective mixing continuously brings low-oxygen deep water towards the surface and into contact with the atmosphere. The continuous exchange between the surface and deep ocean during convection can bring newly oxygenated waters as deep as 2000m. Although the associated oxygen uptake has been observed and quantified, and the resulting oxygen-rich water mass in the deep ocean is readily detected throughout the Atlantic Ocean, relatively little is known about the exact mechanisms and timing of its export out of the basin.</p> </div><div> <p>In this talk, we will present a novel dataset of oxygen sensors deployed within the boundary current at the exit of the Labrador Sea to investigate oxygen variability in the deep ocean. This is the first time that a continuous time series of oxygen has been collected in the boundary current of the Labrador Sea, with a total of 10 sensors deployed on 4 moorings from 2016 to 2020. The sensors at 600m depth show a sudden change in oxygen, temperature, and salinity in the spring, which we discuss in relation to deep convection in the interior. We also use data from Argo floats to analyse export pathways from the convection region to the location of the moorings. Our results give new insights into how the oxygen taken up in the central Labrador Sea subsequently spreads into the global deep ocean, and lay the basis for future work on quantifying variability of oxygen transport at the exit of the Labrador Sea.</p> </div>

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 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 Oxygen export to the deep ocean following Labrador Sea Water formation

2021 ◽  
Author(s):  
Jannes Koelling ◽  
Dariia Atamanchuk ◽  
Johannes Karstensen ◽  
Patricia Handmann ◽  
Douglas W. R. Wallace
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
Sea Water ◽  
Deep Ocean ◽  
Water Layer ◽  
Labrador Sea ◽  
Boundary Current ◽  
The North ◽  
Deep Water Layer

Abstract. The Labrador Sea in the North Atlantic Ocean is one of the few regions globally where oxygen from the atmosphere can reach the deep ocean directly. This is the result of wintertime convection, which homogenizes the water column to a depth of up to 2000 m, and brings deep water undersaturated in oxygen into contact with the atmosphere. In this study, we analyze how the intense oxygen uptake during Labrador Sea Water (LSW) formation affects the properties of the outflowing deep western boundary current, which ultimately feeds the upper part of the North Atlantic Deep Water layer in much of the Atlantic Ocean. Seasonal cycles of oxygen concentration, temperature, and salinity from a two-year time series collected by sensors moored at 600 m nominal depth in the outflowing boundary current at 53° N show that LSW is primarily exported in the months following the onset of convection, from March to August. During the rest of the year, properties of the outflow resemble those of Irminger Water, which enters the basin with the boundary current from the Irminger Sea. The input of newly ventilated LSW increases the oxygen concentration from 298 μmol L−1 in January to a maximum of 306 μmol L−1 in April. As a result of this LSW input, 1.57 × 1012 mol year−1 of oxygen are added to the outflowing boundary current, mostly during summer, equivalent to 49 % of the wintertime uptake from the atmosphere in the interior of the basin. The export of oxygen from the subpolar gyre associated with this direct southward pathway of LSW is estimated to supply about 71 % of the oxygen consumed annually in the upper North Atlantic Deep Water layer in the Atlantic Ocean between the equator and 50° N. Our results show that the formation of LSW is important for replenishing oxygen to the deep oceans, meaning that possible changes in its formation rate and ventilation due to climate change could have wide-reaching impacts on marine life.

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

Mesoscale Eddies in the Labrador Sea and Their Contribution to Convection and Restratification

2008 ◽  
Vol 38 (8) ◽  
pp. 1617-1643 ◽  
Author(s):  
Jérôme Chanut ◽  
Bernard Barnier ◽  
William Large ◽  
Laurent Debreu ◽  
Thierry Penduff ◽  
...  
Keyword(s):  
Deep Convection ◽  
Labrador Sea ◽  
Central Basin ◽  
Barotropic Instability ◽  
Boundary Current ◽  
The West ◽  
Simultaneous Generation ◽  
Near Surface ◽  
West Greenland ◽  
Convective Mixing

Abstract The cycle of open ocean deep convection in the Labrador Sea is studied in a realistic, high-resolution (4 km) regional model, embedded in a coarser (⅓°) North Atlantic setup. This configuration allows the simultaneous generation and evolution of three different eddy types that are distinguished by their source region, generation mechanism, and dynamics. Very energetic Irminger Rings (IRs) are generated by barotropic instability of the West Greenland and Irminger Currents (WGC/IC) off Cape Desolation and are characterized by a warm, salty subsurface core. They densely populate the basin north of 58°N, where their eddy kinetic energy (EKE) matches the signal observed by satellite altimetry. Significant levels of EKE are also found offshore of the West Greenland and Labrador coasts, where boundary current eddies (BCEs) are spawned by weakly energetic instabilities all along the boundary current system (BCS). Baroclinic instability of the steep isopycnal slopes that result from a deep convective overturning event produces convective eddies (CEs) of 20–30 km in diameter, as observed and produced in more idealized models, with a distinct seasonal cycle of EKE peaking in April. Sensitivity experiments show that each of these eddy types plays a distinct role in the heat budget of the central Labrador Sea, hence in the convection cycle. As observed in nature, deep convective mixing is limited to areas where adequate preconditioning can occur, that is, to a small region in the southwestern quadrant of the central basin. To the east, west, and south, BCEs flux heat from the BCS at a rate sufficient to counteract air–sea buoyancy loss. To the north, this eddy flux alone is not enough, but when combined with the effects of Irminger Rings, preconditioning is effectively inhibited here too. Following a deep convective mixing event, the homogeneous convection patch reaches as deep as 2000 m and a horizontal scale on the order of 200 km, as has been observed. Both CEs and BCEs are found to play critical roles in the lateral mixing phase, when the patch restratifies and transforms into Labrador Sea Water (LSW). BCEs extract the necessary heat from the BCS and transport it to the deep convection site, where it fluxed into convective patches by CEs during the initial phase. Later in the phase, BCE heat flux maintains and strengthens the restratification throughout the column, while solar heating establishes a near-surface seasonal stratification. In contrast, IRs appear to rarely enter the deep convection region. However, by virtue of their control on the surface area preconditioned for deep convection and the interannual variability of the associated barotropic instability, they could have an important role in the variability of LSW.

scholarly journals The Nature of Eddy Kinetic Energy in the Labrador Sea: Different Types of Mesoscale Eddies, Their Temporal Variability, and Impact on Deep Convection

2019 ◽  
Vol 49 (8) ◽  
pp. 2075-2094 ◽  
Author(s):  
Jan K. Rieck ◽  
Claus W. Böning ◽  
Klaus Getzlaff
Keyword(s):  
Kinetic Energy ◽  
Temporal Variability ◽  
Decadal Variability ◽  
Deep Convection ◽  
Deep Ocean ◽  
Temporal Variations ◽  
Heat Fluxes ◽  
Eddy Kinetic Energy ◽  
Labrador Sea ◽  
Boundary Current

AbstractOceanic eddies are an important component in preconditioning the central Labrador Sea (LS) for deep convection and in restratifying the convected water. This study investigates the different sources and impacts of eddy kinetic energy (EKE) and its temporal variability in the LS with the help of a 52-yr-long hindcast simulation of a 1/20° ocean model. Irminger Rings (IR) are generated in the West Greenland Current (WGC) between 60° and 62°N, mainly affect preconditioning, and limit the northward extent of the convection area. The IR exhibit a seasonal cycle and decadal variations linked to the WGC strength, varying with the circulation of the subpolar gyre. The mean and temporal variations of IR generation can be attributed to changes in deep ocean baroclinic and upper-ocean barotropic instabilities at comparable magnitudes. The main source of EKE and restratification in the central LS are convective eddies (CE). They are generated by baroclinic instabilities near the bottom of the mixed layer during and after convection. The CE have a middepth core and reflect the hydrographic properties of the convected water mass with a distinct minimum in potential vorticity. Their seasonal to decadal variability is tightly connected to the local atmospheric forcing and the associated air–sea heat fluxes. A third class of eddies in the LS are the boundary current eddies shed from the Labrador Current (LC). Since they are mostly confined to the vicinity of the LC, these eddies appear to exert only minor influence on preconditioning and restratification.

scholarly journals Introducing LAB60: A 1∕60° NEMO 3.6 numerical simulation of the Labrador Sea

2020 ◽  
Vol 13 (10) ◽  
pp. 4959-4975
Author(s):  
Clark Pennelly ◽  
Paul G. Myers
Keyword(s):  
High Resolution ◽  
North Atlantic ◽  
Sea Water ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Labrador Sea ◽  
The North ◽  
Passive Tracers ◽  
Set Up ◽  
Labrador Sea Water

Abstract. A high-resolution coupled ocean–sea ice model is set up within the Labrador Sea. With a horizontal resolution of 1∕60∘, this simulation is capable of resolving the multitude of eddies that transport heat and freshwater into the interior of the Labrador Sea. These fluxes strongly govern the overall stratification, deep convection, restratification, and production of Labrador Sea Water. Our regional configuration spans the full North Atlantic and Arctic; however, high resolution is only applied in smaller nested domains within the North Atlantic and Labrador Sea. Using nesting reduces computational costs and allows for a long simulation from 2002 to the near present. Three passive tracers are also included: Greenland runoff, Labrador Sea Water produced during convection, and Irminger Water that enters the Labrador Sea along Greenland. We describe the configuration setup and compare it against similarly forced lower-resolution simulations to better describe how horizontal resolution impacts the representation of the Labrador Sea in the model.

scholarly journals On the Linkage between Labrador Sea Water Volume and Overturning Circulation in the Labrador Sea: A Case Study on Proxies

2018 ◽  
Vol 31 (13) ◽  
pp. 5225-5241 ◽  
Author(s):  
Feili Li ◽  
M. Susan Lozier
Keyword(s):  
North Atlantic ◽  
Sea Water ◽  
Deep Ocean ◽  
Ocean Model ◽  
Labrador Sea ◽  
Water Volume ◽  
Overturning Circulation ◽  
Robust Estimates ◽  
Labrador Sea Water

Although proxies have generally been used to study deep ocean convection and overturning circulation in the Labrador Sea, their efficacy has not been explicitly evaluated because observations that directly measure those variables are scarce. In this study, the volume of newly formed Labrador Sea Water (LSW) and the overturning circulation in the Labrador Sea are estimated using observational data and output from a high-resolution ocean model and then compared to proxies used to represent those variables. The comparisons reveal the limitations of proxies, highlighting the desirability of robust estimates derived from direct monitoring in the region [i.e., from Argo and Overturning in the Subpolar North Atlantic Program (OSNAP)]. A linkage among LSW formation, overturning circulation in the Labrador Sea, and the export of LSW from the basin on interannual time scales is found in the model.

scholarly journals Introducing LAB60: A 1/60° NEMO 3.6 numerical simulation of the Labrador Sea

2020 ◽  
Author(s):  
Clark Pennelly ◽  
Paul G. Myers
Keyword(s):  
Numerical Simulation ◽  
Sea Water ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Labrador Sea ◽  
Computational Costs ◽  
Passive Tracers ◽  
Set Up ◽  
Ice Model ◽  
Labrador Sea Water

Abstract. A high-resolution coupled ocean-sea ice model is set up within the Labrador Sea. With a horizontal resolution of 1/60°, this simulation is capable of resolving the multitude of eddies which transport heat and freshwater into the interior of the Labrador Sea. The transport of these fluxes strongly governs the overall stratification, deep convection, and subsequent production of Labrador Sea Water. We implement nested domains within our regional configuration to reduce computational costs, allowing for a simulation that spans over 10 years. Three passive tracers are also included: Greenland runoff, Labrador Sea Water produced during convection, and Irminger Water which enters the Labrador Sea along Greenland. We describe the configuration setup and compare against similarly forced lower-resolution simulations to better describe how horizontal resolution impacts the Labrador Sea.

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