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 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 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 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.

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

scholarly journals Cold-water corals in the Subpolar North Atlantic Ocean exposed to aragonite undersaturation if Paris 2 ºC is not met

2021 ◽  
Author(s):  
Maribel I. García-Ibáñez ◽  
Nicholas R. Bates ◽  
Dorothee C.E. Bakker ◽  
Marcos Fontela ◽  
Antón Velo
Keyword(s):  
Atlantic Ocean ◽  
Water Column ◽  
North Atlantic ◽  
Cold Water ◽  
Sea Water ◽  
North Atlantic Ocean ◽  
Labrador Sea ◽  
Entire Water Column ◽  
Intermediate Waters ◽  
Labrador Sea Water

<p>The uptake of carbon dioxide (CO<sub>2</sub>) from the atmosphere is changing the ocean’s chemical state. Such changes, commonly known as ocean acidification, include reduction in pH and the carbonate ion concentration ([CO<sub>3</sub><sup>2-</sup>]), which in turn lowers oceanic saturation states (Ω) for calcium carbonate (CaCO<sub>3</sub>) minerals. The Ω values for aragonite (Ω<sub>aragonite</sub>; one of the main CaCO<sub>3</sub> minerals formed by marine calcifying organisms) influence the calcification rate and geographic distribution of cold-water corals (CWCs), important for biodiversity. In this work we use high-quality data of inorganic carbon measurements, collected on thirteen cruises along the same track during 1991–2018, to determine the long-term trends in Ω<sub>aragonite</sub> in the Irminger and Iceland Basins of the North Atlantic Ocean, providing the first trends of Ω<sub>aragonite</sub> in the deep waters of these basins. The entire water column of both basins showed significant negative Ω<sub>aragonite</sub> trends between -0.0015 ± 0.0002 and -0.0061 ± 0.0016 per year. The decrease in Ω<sub>aragonite</sub> in the intermediate waters, where nearly half of the CWC reefs of the study region are located, caused the Ω<sub>aragonite</sub> isolines to migrate upwards rapidly at a rate between 6 and 34 m per year. The main driver of the observed decline in Ω<sub>aragonite</sub> in the Irminger and Iceland Basins was the increase in anthropogenic CO<sub>2</sub>. But this was partially offset by increases in salinity (in Subpolar Mode Water), enhanced ventilation (in upper Labrador Sea Water) and increases in alkalinity (in classical Labrador Sea Water, cLSW; and overflow waters). We also found that water mass aging reinforced the Ω<sub>aragonite</sub> decrease in cLSW. Based on the observed Ω<sub>aragonite</sub> trends, we project that the entire water column of the Irminger and Iceland Basins will likely be undersaturated for aragonite when in equilibrium with an atmospheric mole fraction of CO<sub>2</sub> (xCO<sub>2</sub>) of ~860 ppmv, corresponding to climate model projections for the end of the century based on the highest CO<sub>2</sub> emission scenarios. However, intermediate waters will likely be aragonite undersaturated when in equilibrium with an atmospheric xCO<sub>2</sub> of ~600 ppmv, an xCO<sub>2</sub> level slightly above that corresponding to 2 ºC warming, thus exposing CWCs inhabiting the intermediate waters to undersaturation for aragonite.</p>

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>

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