scholarly journals Ventilation variability of Labrador Sea Water and its impact on oxygen and anthropogenic carbon: a review

2017 ◽  
Vol 375 (2102) ◽  
pp. 20160321 ◽  
Author(s):  
Monika Rhein ◽  
Reiner Steinfeldt ◽  
Dagmar Kieke ◽  
Ilaria Stendardo ◽  
Igor Yashayaev
Keyword(s):  
Time Scales ◽  
North Atlantic ◽  
Sea Water ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Southern Boundary ◽  
Rate Of Increase ◽  
Anthropogenic Carbon ◽  
Warming World ◽  
Labrador Sea Water

Ventilation of Labrador Sea Water (LSW) receives ample attention because of its potential relation to the strength of the Atlantic Meridional Overturning Circulation (AMOC). Here, we provide an overview of the changes of LSW from observations in the Labrador Sea and from the southern boundary of the subpolar gyre at 47° N. A strong winter-time atmospheric cooling over the Labrador Sea led to intense and deep convection, producing a thick and dense LSW layer as, for instance, in the early to mid-1990s. The weaker convection in the following years mostly ventilated less dense LSW vintages and also reduced the supply of oxygen. As a further consequence, the rate of uptake of anthropogenic carbon by LSW decreased between the two time periods 1996–1999 and 2007–2010 in the western subpolar North Atlantic. In the eastern basins, the rate of increase in anthropogenic carbon became greater due to the delayed advection of LSW that was ventilated in previous years. Starting in winter 2013/2014 and prevailing at least into winter 2015/2016, production of denser and more voluminous LSW resumed. Increasing oxygen signals have already been found in the western boundary current at 47° N. On decadal and shorter time scales, anomalous cold atmospheric conditions over the Labrador Sea lead to an intensification of convection. On multi-decadal time scales, the ‘cold blob’ in the subpolar North Atlantic projected by climate models in the next 100 years is linked to a weaker AMOC and weaker convection (and thus deoxygenation) in the Labrador Sea. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.

scholarly journals Local and Downstream Relationships between Labrador Sea Water Volume and North Atlantic Meridional Overturning Circulation Variability

2019 ◽  
Vol 32 (13) ◽  
pp. 3883-3898 ◽  
Author(s):  
Feili Li ◽  
M. Susan Lozier ◽  
Gokhan Danabasoglu ◽  
Naomi P. Holliday ◽  
Young-Oh Kwon ◽  
...  
Keyword(s):  
Time Scales ◽  
North Atlantic ◽  
Sea Water ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Labrador Sea ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
Labrador Sea Water

Abstract While it has generally been understood that the production of Labrador Sea Water (LSW) impacts the Atlantic meridional overturning circulation (MOC), this relationship has not been explored extensively or validated against observations. To explore this relationship, a suite of global ocean–sea ice models forced by the same interannually varying atmospheric dataset, varying in resolution from non-eddy-permitting to eddy-permitting (1°–1/4°), is analyzed to investigate the local and downstream relationships between LSW formation and the MOC on interannual to decadal time scales. While all models display a strong relationship between changes in the LSW volume and the MOC in the Labrador Sea, this relationship degrades considerably downstream of the Labrador Sea. In particular, there is no consistent pattern among the models in the North Atlantic subtropical basin over interannual to decadal time scales. Furthermore, the strong response of the MOC in the Labrador Sea to LSW volume changes in that basin may be biased by the overproduction of LSW in many models compared to observations. This analysis shows that changes in LSW volume in the Labrador Sea cannot be clearly and consistently linked to a coherent MOC response across latitudes over interannual to decadal time scales in ocean hindcast simulations of the last half century. Similarly, no coherent relationships are identified between the MOC and the Labrador Sea mixed layer depth or the density of newly formed LSW across latitudes or across models over interannual to decadal time scales.

scholarly journals Mean circulation and EKE distribution in the Labrador Sea Water level of the subpolar North Atlantic

2018 ◽  
Author(s):  
Jürgen Fischer ◽  
Johannes Karstensen ◽  
Marilena Oltmanns ◽  
Sunke Schmidtko
Keyword(s):  
Flow Field ◽  
North Atlantic ◽  
Sea Water ◽  
Labrador Sea ◽  
Mean Flow ◽  
Southern Boundary ◽  
Mapping Algorithms ◽  
Iceland Basin ◽  
Irminger Sea ◽  
Labrador Sea Water

Abstract. A long term mean flow field for the subpolar North Atlantic region with a horizontal resolution of approximately 25 km is created by gridding Argo-derived velocity vectors using two different topography following interpolation schemes. The 10-d float displacements in the typical drift depths of 1000 m to 1500 m represent the flow in the Labrador Sea Water density range. Both mapping algorithms separate the flow field into potential vorticity (PV) conserving, i.e. topography following contribution and a deviating part, which we define as the eddy contribution. To verify the significance of the separation, we compare the mean flow and the eddy kinetic energy (EKE), derived from both mapping algorithms, with those obtained from multiyear mooring observations. The PV-conserving mean flow is characterized by stable boundary currents along all major topographic features including shelf breaks and basin-interior topographic ridges such as the Reykjanes Ridge or the Rockall Plateau. Mid-basin northward advection pathways from the northeastern Labrador Sea into the Irminger Sea and from the Mid Atlantic Ridge region into the Iceland basin are well-resolved. An eastward flow is present across the southern boundary of the subpolar gyre near 52° N, the latitude of the Charlie Gibbs Fracture Zone. The mid-depth EKE field resembles most of the satellite-derived surface EKE field. However, noticeable differences exist along the northward advection pathways in the Irminger Sea and the Iceland basin, where the deep EKE exceeds the surface EKE field. Further, the ratio between mean flow and the square root of the EKE, the Peclet Number, reveals distinct advection-dominated regions as well as basin interior regimes in which mixing is prevailing.

scholarly journals Mean circulation and EKE distribution in the Labrador Sea Water level of the subpolar North Atlantic

Ocean Science ◽  
2018 ◽  
Vol 14 (5) ◽  
pp. 1167-1183 ◽  
Author(s):  
Jürgen Fischer ◽  
Johannes Karstensen ◽  
Marilena Oltmanns ◽  
Sunke Schmidtko
Keyword(s):  
Flow Field ◽  
North Atlantic ◽  
Sea Water ◽  
Labrador Sea ◽  
Mean Flow ◽  
Southern Boundary ◽  
Mapping Algorithms ◽  
Iceland Basin ◽  
Irminger Sea ◽  
Labrador Sea Water

Abstract. A long-term mean flow field for the subpolar North Atlantic region with a horizontal resolution of approximately 25 km is created by gridding Argo-derived velocity vectors using two different topography-following interpolation schemes. The 10-day float displacements in the typical drift depths of 1000 to 1500 m represent the flow in the Labrador Sea Water density range. Both mapping algorithms separate the flow field into potential vorticity (PV) conserving, i.e., topography-following contribution and a deviating part, which we define as the eddy contribution. To verify the significance of the separation, we compare the mean flow and the eddy kinetic energy (EKE), derived from both mapping algorithms, with those obtained from multiyear mooring observations. The PV-conserving mean flow is characterized by stable boundary currents along all major topographic features including shelf breaks and basin-interior topographic ridges such as the Reykjanes Ridge or the Rockall Plateau. Mid-basin northward advection pathways from the northeastern Labrador Sea into the Irminger Sea and from the Mid-Atlantic Ridge region into the Iceland Basin are well-resolved. An eastward flow is present across the southern boundary of the subpolar gyre near 52∘ N, the latitude of the Charlie Gibbs Fracture Zone (CGFZ). The mid-depth EKE field resembles most of the satellite-derived surface EKE field. However, noticeable differences exist along the northward advection pathways in the Irminger Sea and the Iceland Basin, where the deep EKE exceeds the surface EKE field. Further, the ratio between mean flow and the square root of the EKE, the Peclet number, reveals distinct advection-dominated regions as well as basin-interior regimes in which mixing is prevailing.

Identification and quantification of the North Atlantic Deep Water pathways

2021 ◽  
Author(s):  
Philippe Miron ◽  
Maria J. Olascoaga ◽  
Francisco J. Beron-Vera ◽  
Kimberly L. Drouin ◽  
M. Susan Lozier
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Sea Water ◽  
Lower Layer ◽  
North Atlantic Deep Water ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Western Boundary ◽  
The North ◽  
The North Atlantic

<p>The North Atlantic Deep Water (NADW) flows equatorward along the Deep Western Boundary Current (DWBC) as well as interior pathways and is a critical part of the Atlantic Meridional Overturning Circulation. Its upper layer, the Labrador Sea Water (LSW), is formed by open-ocean deep convection in the Labrador and Irminger Seas while its lower layers, the Iceland–Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW), are formed north of the Greenland–Iceland–Scotland Ridge.</p><p>In recent years, more than two hundred acoustically-tracked subsurface floats have been deployed in the deep waters of the North Atlantic.  Studies to date have highlighted water mass pathways from launch locations, but due to limited float trajectory lengths, these studies have been unable to identify pathways connecting  remote regions.</p><p>This work presents a framework to explore deep water pathways from their respective sources in the North Atlantic using Markov Chain (MC) modeling and Transition Path Theory (TPT). Using observational trajectories released as part of OSNAP and the Argo projects, we constructed two MCs that approximate the lower and upper layers of the NADW Lagrangian dynamics. The reactive NADW pathways—directly connecting NADW sources with a target at 53°N—are obtained from these MCs using TPT.</p><p>Preliminary results show that twenty percent more pathways of the upper layer(LSW) reach the ocean interior compared to  the lower layer (ISOW, DSOW), which mostly flows along the DWBC in the subpolar North Atlantic. Also identified are the Labrador Sea recirculation pathways to the Irminger Sea and the direct connections from the Reykjanes Ridge to the eastern flank of the Mid–Atlantic Ridge, both previously observed. Furthermore, we quantified the eastern spread of the LSW to the area surrounding the Charlie–Gibbs Fracture Zone and compared it with previous analysis. Finally, the residence time of the upper and lower layers are assessed and compared to previous observations.</p>

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.

Using reconstructed Irminger Water changes within the past three decades to connect the West Greenland shelf to the production of Labrador Sea Water

2021 ◽  
Author(s):  
Kevin Niklas Wiegand ◽  
Dagmar Kieke ◽  
Paul G. Myers
Keyword(s):  
Time Series ◽  
Sea Water ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Labrador Sea ◽  
The West ◽  
West Greenland ◽  
The Past ◽  
Local Water ◽  
Labrador Sea Water

<p>In this study we analyze the exchange processes between the West Greenland shelf and the Labrador Sea. This region is affected by warm and saline waters originating from the subtropical North Atlantic, as well as cold and fresh waters from the Arctic and the Greenland Ice Sheet. Heat and freshwater both impact the local formation of Labrador Sea Water (LSW) that itself is a major contributor to the Atlantic Meridional Overturning Circulation.</p><p>We use the ARMOR3D large-scale hydrographic data set from the Copernicus Marine Environmental Monitoring Service (CMEMS) and validate it with ship-based measurements in the period between 1993 to 2018. By extracting cross-shelf sections from ARMOR3D for various locations around Greenland, we reconstruct time series of local water masses like the Irminger Water (IW) for the past three decades. Previous studies from the West Greenland shelf have shown that IW properties are locally anti-correlated to changes in LSW. We analyze the interannual and decadal variability of these IW time series and compare them towards hydrographic changes observed in the interior Labrador Sea.</p><p>Since ARMOR3D allows us to investigate interannual and decadal changes along cross-shelf sections, the goal of this study is to unravel the complex connection between changes in the shelf regions around Greenland and the interior Labrador Sea, especially the local water mass production.</p>

Spreading of Labrador Sea Water in the eastern North Atlantic

1998 ◽  
Vol 103 (C5) ◽  
pp. 10223-10239 ◽  
Author(s):  
Jérôme Paillet ◽  
Michel Arhan ◽  
Michael S. McCartney
Keyword(s):  
North Atlantic ◽  
Sea Water ◽  
Labrador Sea ◽  
Eastern North Atlantic ◽  
Labrador Sea Water
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