Identification et distribution des grandes masses d'eau dans les mers du Labrador et d'Irminger

1994 ◽  
Vol 31 (1) ◽  
pp. 5-13 ◽  
Author(s):  
Marc Lucotte ◽  
Claude Hillaire-Marcel
Keyword(s):  
Deep Water ◽  
Water Mass ◽  
Transfer Functions ◽  
Sea Water ◽  
Water Masses ◽  
Labrador Sea ◽  
Western Boundary ◽  
Boundary Current ◽  
North East ◽  
Continental Slopes

The main deep water masses present at the time of the CSS Hudson cruises in Labrador and Irminger seas in June 1990 and October–November 1991 have been identified using characteristic temperatures (T) and salinities (S). The purpose of this study was to establish the transfer functions between micropaleontological assemblages of top sediments and thermohaline characteristics of water masses. The water mass at the top of the Labrador Sea (Labrador Sea Water, LSW) is formed after intense movements of winter convection in the first 900-m depth of the water column. Below that depth, the LSW parameters reach a double minimum (S ≈ 34.80 and T ≈ 2.9 °C). Only the sediments located on the continental slopes of Greenland and Labrador between depths of 500 and 1500 m are in contact with the LSW. Below the LSW, the superior fraction of the North East Atlantic Deep Water (NEADW1) is characterized by a temperature maximum (≈ 3.3 °C) and, as such, is distinguishable from the inferior fraction (NEADW2). The latter is characterized by a maximum S (≈ 34, 90) when compared with other intermediary and deep water masses. In contrast to the NEADW1 that freely circulates over the Reykjanes Ridge, the NEADW2 must flow through the Charlie Gibbs Fracture Zone to go from the northeastern Atlantic to the Irminger Sea. The NEADW 1 and 2 respectively bathe the ridge section less than 2000 m deep and the European abyssal basins. On the contrary, the majority of the deep sediments of the Labrador and Irminger seas are in contact with the cold (T < 2.6 °C) and salty (≈ 34.85) Denmark Strait Overflow Water. Although this water mass is normally found at depths exceeding 2700 m in pelagic environments, it can be found at less than 2000-m depth on the bottom of the continental slopes of Greenland and Labrador, where it is carried by the strong Deep Northern Boundary Current and Western Boundary Undercurrent. The presence of the NEADW 1 and 2 on the sediments is then restricted to narrow bands on the same continental slopes, between depths of 1800 and 2200 m.

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 Water mass distributions and transports for the 2014 GEOVIDE cruise in the North Atlantic

2017 ◽  
Author(s):  
Maribel I. García-Ibáñez ◽  
Fiz F. Pérez ◽  
Pascale Lherminier ◽  
Patricia Zunino ◽  
Paul Tréguer
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Sea Water ◽  
Water Levels ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Intermediate Water ◽  
North East ◽  
Relative Contribution

Abstract. We present the distribution of water masses along the GEOTRACES-GA01 section during the GEOVIDE cruise, which crossed the subpolar North Atlantic Ocean and the Labrador Sea in the summer of 2014. The water mass structure resulting from an extended Optimum MultiParameter (eOMP) analysis provides the framework for interpreting the observed distributions of trace elements and their isotopes. Central Waters and Subpolar Mode Waters (SPMW) dominated the upper part of the GEOTRACES-GA01 section in 2014. At intermediate depths, the dominant water mass was Labrador Sea Water, while the deep parts of the section were filled by Iceland–Scotland Overflow Water (ISOW) and North East Atlantic Deep Water. We also evaluate the water mass volume transports across the 2014 OVIDE line (Portugal to Greenland section) by combining the water mass fractions resulting from the eOMP analysis with the absolute geostrophic velocity field estimated through a box inverse model. This allowed us to assess the relative contribution of each water mass to the transport across the section. Finally, we discuss the changes in the distribution and transport of water masses between the 2014 OVIDE line and the 2002–2010 mean state. At the upper and intermediate water levels, colder end-member of the water masses replaced the warmer ones in 2014 with respect to 2002–2010, in agreement with the observed cooling of the surface and intermediate waters. Below 2000 dbar, ISOW increased its contribution in 2014 with respect to 2002–2010, increase related to the observed salinization since 2002. We also observed an increase in SPMW in the East Greenland Irminger Current in 2014 with respect to 2002–2010, which supports the recent deep convection events in the Irminger Sea. The assessment of the relative contribution of each water mass to the Atlantic Meridional Overturning Circulation (AMOC) across the OVIDE line allows identifying the water masses involved in the increase in the AMOC intensity from 2002–2010 to 2014. The increase in the AMOC intensity is related to the increase in the northward transport of the Central Waters in its upper limb, and to the increase in the southward flow of SPMW of the Irminger Basin and ISOW in its lower limb.

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

&lt;p&gt;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&amp;#8211;Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW), are formed north of the Greenland&amp;#8211;Iceland&amp;#8211;Scotland Ridge.&lt;/p&gt;&lt;p&gt;In recent years, more than two hundred acoustically-tracked subsurface floats have been deployed in the deep waters of the North Atlantic. &amp;#160;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 &amp;#160;remote regions.&lt;/p&gt;&lt;p&gt;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&amp;#8212;directly connecting NADW sources with a target at 53&amp;#176;N&amp;#8212;are obtained from these MCs using TPT.&lt;/p&gt;&lt;p&gt;Preliminary results show that twenty percent more pathways of the upper layer(LSW) reach the ocean interior compared to &amp;#160;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&amp;#8211;Atlantic Ridge, both previously observed. Furthermore, we quantified the eastern spread of the LSW to the area surrounding the Charlie&amp;#8211;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.&lt;/p&gt;

scholarly journals Water mass distributions and transports for the 2014 GEOVIDE cruise in the North Atlantic

2018 ◽  
Vol 15 (7) ◽  
pp. 2075-2090 ◽  
Author(s):  
Maribel I. García-Ibáñez ◽  
Fiz F. Pérez ◽  
Pascale Lherminier ◽  
Patricia Zunino ◽  
Herlé Mercier ◽  
...  
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Water Levels ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
Labrador Sea ◽  
Intermediate Water ◽  
North East ◽  
The North ◽  
The North Atlantic

Abstract. We present the distribution of water masses along the GEOTRACES-GA01 section during the GEOVIDE cruise, which crossed the subpolar North Atlantic Ocean and the Labrador Sea in the summer of 2014. The water mass structure resulting from an extended optimum multiparameter (eOMP) analysis provides the framework for interpreting the observed distributions of trace elements and their isotopes. Central Waters and Subpolar Mode Waters (SPMW) dominated the upper part of the GEOTRACES-GA01 section. At intermediate depths, the dominant water mass was Labrador Sea Water, while the deep parts of the section were filled by Iceland–Scotland Overflow Water (ISOW) and North-East Atlantic Deep Water. We also evaluate the water mass volume transports across the 2014 OVIDE line (Portugal to Greenland section) by combining the water mass fractions resulting from the eOMP analysis with the absolute geostrophic velocity field estimated through a box inverse model. This allowed us to assess the relative contribution of each water mass to the transport across the section. Finally, we discuss the changes in the distribution and transport of water masses between the 2014 OVIDE line and the 2002–2010 mean state. At the upper and intermediate water levels, colder end-members of the water masses replaced the warmer ones in 2014 with respect to 2002–2010, in agreement with the long-term cooling of the North Atlantic Subpolar Gyre that started in the mid-2000s. Below 2000 dbar, ISOW increased its contribution in 2014 with respect to 2002–2010, with the increase being consistent with other estimates of ISOW transports along 58–59° N. We also observed an increase in SPMW in the East Greenland Irminger Current in 2014 with respect to 2002–2010, which supports the recent deep convection events in the Irminger Sea. From the assessment of the relative water mass contribution to the Atlantic Meridional Overturning Circulation (AMOC) across the OVIDE line, we conclude that the larger AMOC intensity in 2014 compared to the 2002–2010 mean was related to both the increase in the northward transport of Central Waters in the AMOC upper limb and to the increase in the southward flow of Irminger Basin SPMW and ISOW in the AMOC lower limb.

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 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 Water masses in the Atlantic Ocean: characteristics and distributions

Ocean Science ◽  
2021 ◽  
Vol 17 (2) ◽  
pp. 463-486
Author(s):  
Mian Liu ◽  
Toste Tanhua
Keyword(s):  
Atlantic Ocean ◽  
Deep Water ◽  
Bottom Water ◽  
Water Mass ◽  
Sea Water ◽  
Weddell Sea ◽  
Water Masses ◽  
Global Ocean ◽  
Intermediate Water ◽  
The North

Abstract. A large number of water masses are presented in the Atlantic Ocean, and knowledge of their distributions and properties is important for understanding and monitoring of a range of oceanographic phenomena. The characteristics and distributions of water masses in biogeochemical space are useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples. Here, we define the characteristics of the major water masses in the Atlantic Ocean as source water types (SWTs) from their formation areas, and map out their distributions. The SWTs are described by six properties taken from the biased-adjusted Global Ocean Data Analysis Project version 2 (GLODAPv2) data product, including both conservative (conservative temperature and absolute salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) properties. The distributions of these water masses are investigated with the use of the optimum multi-parameter (OMP) method and mapped out. The Atlantic Ocean is divided into four vertical layers by distinct neutral densities and four zonal layers to guide the identification and characterization. The water masses in the upper layer originate from wintertime subduction and are defined as central waters. Below the upper layer, the intermediate layer consists of three main water masses: Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Water (MW). The North Atlantic Deep Water (NADW, divided into its upper and lower components) is the dominating water mass in the deep and overflow layer. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW). The Antarctic Bottom Water (AABW) is the only natural water mass in the bottom layer, and this water mass is redefined as Northeast Atlantic Bottom Water (NEABW) in the north of the Equator due to the change of key properties, especially silicate. Similar with NADW, two additional water masses, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea region in order to understand the origin of AABW.

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 Equatorward Pathways of Solomon Sea Water Masses and Their Modifications

2011 ◽  
Vol 41 (4) ◽  
pp. 810-826 ◽  
Author(s):  
Angélique Melet ◽  
Jacques Verron ◽  
Lionel Gourdeau ◽  
Ariane Koch-Larrouy
Keyword(s):  
Water Column ◽  
Water Mass ◽  
Sea Water ◽  
Southern Oscillation ◽  
Equatorial Pacific ◽  
Water Masses ◽  
Internal Tides ◽  
Tidal Mixing ◽  
Western Boundary ◽  
Potential Influence

Abstract The Solomon Sea is a key region of the southwest Pacific Ocean, connecting the thermocline subtropics to the equator via western boundary currents (WBCs). Modifications to water masses are thought to occur in this region because of the significant mixing induced by internal tides, eddies, and the WBCs. Despite their potential influence on the equatorial Pacific thermocline temperature and salinity and their related impact on the low-frequency modulation of El Niño–Southern Oscillation, modifications to water masses in the Solomon Sea have never been analyzed to our knowledge. A high-resolution model incorporating a tidal mixing parameterization was implemented to depict and analyze water mass modifications and the Solomon Sea pathways to the equator in a Lagrangian quantitative framework. The main routes from the Solomon Sea to the equatorial Pacific occur through the Vitiaz and Solomon straits, in the thermocline and intermediate layers, and mainly originate from the Solomon Sea south inflow and from the Solomon Strait itself. Water mass modifications in the model are characterized by a reduction of the vertical temperature and salinity gradients over the water column: the high salinity of upper thermocline water [Subtropical Mode Water (STMW)] is eroded and exported toward surface and deeper layers, whereas a downward heat transfer occurs over the water column. Consequently, the thermocline water temperature is cooled by 0.15°–0.3°C from the Solomon Sea inflows to the equatorward outflows. This temperature modification could weaken the STMW anomalies advected by the subtropical cell and thereby diminish the potential influence of these anomalies on the tropical climate. The Solomon Sea water mass modifications can be partially explained (≈60%) by strong diapycnal mixing in the Solomon Sea. As for STMW, about a third of this mixing is due to tidal mixing.

Sign in / Sign up

Export Citation Format

Share Document