Water masses in the Atlantic Ocean: characteristics and distributions

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.

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Characteristics of Water Masses in the Atlantic Ocean based on GLODAPv2 data

10.5194/os-2018-139 ◽

2019 ◽

Cited By ~ 1

Author(s):

Mian Liu ◽

Toste Tanhua

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Deep Water ◽

Bottom Water ◽

South Atlantic ◽

Weddell Sea ◽

Water Masses ◽

Intermediate Water ◽

South Atlantic Central Water ◽

The North

Abstract. The characteristics of the main water masses in the Atlantic Ocean are investigated and defined as Source Water Types (SWTs) from their formation area by six key properties based on the GLODAPv2 observational data. These include both conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) variables. For this we divided the Atlantic Ocean into four vertical layers by distinct potential densities in the shallow and intermediate water column, and additionally by concentration of silicate in the deep waters. The SWTs in the upper/central water layer originates from subduction during winter and are defined as central waters, formed in four distinct areas; East North Atlantic Central water (ENACW), West North Atlantic Central Water (WNACW), East South Atlantic Central Water (ESACW) and West South Atlantic Central Water (WSACW). Below the upper/central layer the intermediate layer consist of three main SWTs; Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Overflow Water (MOW). The North Atlantic Deep Water (NADW) is the dominating SWT in the deep and overflow layer, and is divided into upper and lower NADW based on the different origins and properties. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). Antarctic Bottom Water (AABW) is the only natural SWT in the bottom layer and this SWT is redefined as North East Atlantic Bottom Water (NEABW) in the north of equator due to the change of key properties, especial silicate. Similar with NADW, two additional SWTS, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea in order to understand the origin of AABW. The definition of water masses in biogeochemical space is useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples.

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Distribution of Water Masses in the Atlantic Ocean based on GLODAPv2

10.5194/os-2018-140 ◽

2019 ◽

Author(s):

Mian Liu ◽

Toste Tanhua

Keyword(s):

Atlantic Ocean ◽

Bottom Water ◽

Water Mass ◽

Potential Temperature ◽

Weddell Sea ◽

Water Masses ◽

General Distribution ◽

Intermediate Water ◽

The North ◽

The Antarctic

Abstract. The distribution of the main water masses in the Atlantic Ocean are investigated with the Optimal Multi-Parameter (OMP) method. The properties of the main water masses in the Atlantic Ocean are described in a companion article; here these definitions are used to map out the general distribution of those water masses. Six key properties, including conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate), are incorporated into the OMP analysis to determine the contribution of the water masses in the Atlantic Ocean based on the GLODAP v2 observational data. To facilitate the analysis the Atlantic Ocean is divided into four vertical layers based on potential density. Due to the high seasonal variability in the mixed layer, this layer is excluded from the analysis. Central waters are the main water masses in the upper/central layer, generally featuring high potential temperature and salinity and low nutrient concentrations and are easily distinguished from the intermediate water masses. In the intermediate layer, the Antarctic Intermediate Water (AAIW) from the south can be detected to ~30 °N, whereas the Subarctic Intermediate Water (SAIW), having similarly low salinity to the AAIW flows from the north. Mediterranean Overflow Water (MOW) flows from the Strait of Gibraltar as a high salinity water. NADW dominates the deep and overflow layer both in the North and South Atlantic. In the bottom layer, AABW is the only natural water mass with high silicate signature spreading from the Antarctic to the North Atlantic. Due to the change of water mass properties, in this work we renamed to North East Antarctic Bottom Water NEABW north of the equator. Similarly, the distributions of Labrador Sea Water (LSW), Iceland Scotland Overflow Water (ISOW), and Denmark Strait Overflow Water (DSOW) forms upper and lower portion of NADW, respectively roughly south of the Grand Banks between ~50 and 66 °N. In the far south the distributions of Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW) are of significance to understand the formation of the AABW.

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Aegean Sea Water Masses during the Early Stages of the Eastern Mediterranean Climatic Transient (1988–90)

Journal of Physical Oceanography ◽

10.1175/jpo2940.1 ◽

2006 ◽

Vol 36 (9) ◽

pp. 1841-1859 ◽

Cited By ~ 55

Author(s):

I. Gertman ◽

N. Pinardi ◽

Y. Popov ◽

A. Hecht

Keyword(s):

Surface Water ◽

Deep Water ◽

Water Mass ◽

Sea Water ◽

Eastern Mediterranean ◽

Aegean Sea ◽

Water Masses ◽

Intermediate Water ◽

Central Basin ◽

Cretan Sea

Abstract The Aegean water masses and circulation structure are studied via two large-scale surveys performed during the late winters of 1988 and 1990 by the R/V Yakov Gakkel of the former Soviet Union. The analysis of these data sheds light on the mechanisms of water mass formation in the Aegean Sea that triggered the outflow of Cretan Deep Water (CDW) from the Cretan Sea into the abyssal basins of the eastern Mediterranean Sea (the so-called Eastern Mediterranean Transient). It is found that the central Aegean Basin is the site of the formation of Aegean Intermediate Water, which slides southward and, depending on their density, renews either the intermediate or the deep water of the Cretan Sea. During the winter of 1988, the Cretan Sea waters were renewed mainly at intermediate levels, while during the winter of 1990 it was mainly the volume of CDW that increased. This Aegean water mass redistribution and formation process in 1990 differed from that in 1988 in two major aspects: (i) during the winter of 1990 the position of the front between the Black Sea Water and the Levantine Surface Water was displaced farther north than during the winter of 1988 and (ii) heavier waters were formed in 1990 as a result of enhanced lateral advection of salty Levantine Surface Water that enriched the intermediate waters with salt. In 1990 the 29.2 isopycnal rose to the surface of the central basin and a large volume of CDW filled the Cretan Basin. It is found that, already in 1988, the 29.2 isopycnal surface, which we assume is the lowest density of the CDW, was shallower than the Kassos Strait sill and thus CDW egressed into the Eastern Mediterranean.

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Dissolved iron in the North Atlantic Ocean and Labrador Sea along the GEOVIDE section (GEOTRACES section GA01)

10.5194/bg-2018-147 ◽

2018 ◽

Cited By ~ 10

Author(s):

Manon Tonnard ◽

Hélène Planquette ◽

Andrew R. Bowie ◽

Pier van der Merwe ◽

Morgane Gallinari ◽

...

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Sea Water ◽

North Atlantic Ocean ◽

Deep Convection ◽

Labrador Sea ◽

Intermediate Water ◽

The North ◽

Irminger Sea ◽

The North Atlantic

Abstract. Dissolved Fe (DFe) samples from the GEOVIDE voyage (GEOTRACES GA01, May–June 2014) in the North Atlantic Ocean were analysed using a SeaFAST-picoTM coupled to an Element XR HR-ICP-MS and provided interesting insights on the Fe sources in this area. Overall, DFe concentrations ranged from 0.09 ± 0.01 nmol L−1 to 7.8 ± 0.5 nmol L−1. Elevated DFe concentrations were observed above the Iberian, Greenland and Newfoundland Margins likely due to riverine inputs from the Tagus River, meteoric water inputs and sedimentary inputs. Air-sea interactions were suspected to be responsible for the increase in DFe concentrations within subsurface waters of the Irminger Sea due to deep convection occurring the previous winter, that provided iron-to-nitrate ratios sufficient to sustain phytoplankton growth. Increasing DFe concentrations along the flow path of the Labrador Sea Water were attributed to sedimentary inputs from the Newfoundland Margin. Bottom waters from the Irminger Sea displayed high DFe concentrations likely due to the dissolution of Fe-rich particles from the Denmark Strait Overflow Water and the Polar Intermediate Water. Finally, the nepheloid layers were found to act as either a source or a sink of DFe depending on the nature of particles.

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

Biogeosciences ◽

10.5194/bg-15-2075-2018 ◽

2018 ◽

Vol 15 (7) ◽

pp. 2075-2090 ◽

Cited By ~ 21

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.

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Assessment of the structure and variability of Weddell Sea water masses in distinct ocean reanalysis products

Ocean Science ◽

10.5194/os-10-523-2014 ◽

2014 ◽

Vol 10 (3) ◽

pp. 523-546 ◽

Cited By ~ 10

Author(s):

T. S. Dotto ◽

R. Kerr ◽

M. M. Mata ◽

M. Azaneu ◽

I. Wainer ◽

...

Keyword(s):

Deep Water ◽

Sea Water ◽

Horizontal Resolution ◽

Weddell Sea ◽

Water Masses ◽

Ocean Reanalysis ◽

In Situ Data ◽

Ocean Data Assimilation ◽

Sea Bottom ◽

Warm Deep Water

Abstract. We assessed and evaluated the performance of five ocean reanalysis products in reproducing essential hydrographic properties and their associated temporal variability for the Weddell Sea, Antarctica. The products used in this assessment were ECMWF ORAS4 (European Centre for Medium-Range Weather Forecasts Ocean Reanalysis System 4), CFSR (Climate Forecast System Reanalysis), MyOcean UR025.4 (University of Reading), ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) and SODA (Simple Ocean Data Assimilation). The present study focuses on the Weddell Sea deep layer, which is composed of the following three main water masses: Warm Deep Water (WDW), Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW). The MyOcean UR025.4 product provided the most accurate representation of the structure and thermohaline properties of the Weddell Sea water masses when compared with observations. All the ocean reanalysis products analyzed exhibited limited capabilities in representing the surface water masses in the Weddell Sea. The CFSR and ECCO2 products were not able to represent deep water masses with a neutral density ≥ 28.40 kg m−3, which was considered the WSBW's upper limit throughout the simulation period. The expected WDW warming was only reproduced by the SODA product, whereas the ECCO2 product was able to represent the trends in the WSDW's hydrographic properties. All the assessed ocean reanalyses were able to represent the decrease in the WSBW's density, except the SODA product in the inner Weddell Sea. Improvements in parameterization may have as much impact on the reanalyses assessed as improvements in horizontal resolution primarily because the Southern Ocean lacks in situ data, and the data that are currently available are summer-biased. The choice of the reanalysis product should be made carefully, taking into account the performance, the parameters of interest, and the type of physical processes to be evaluated.

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Hydrology of the Indian Ocean. III. Water masses of the upper 500 metres of the South-east Indian Ocean

Marine and Freshwater Research ◽

10.1071/mf9640025 ◽

1964 ◽

Vol 15 (1) ◽

pp. 25 ◽

Cited By ~ 7

Author(s):

DJ Rochford

Keyword(s):

Indian Ocean ◽

Persian Gulf ◽

Water Mass ◽

Sea Water ◽

Core Layer ◽

Water Masses ◽

Intermediate Water ◽

Surface Currents ◽

North West ◽

East Indian

The following seven water masses have been identified, and their distribution traced during several seasons of the year: Red Sea mass, with the same distribution and properties in 1962 as the north-west Indian Intermediate described in 1959-60; Persian Gulf mass, which is confined to the region south of Indonesia and is limited in extent of easterly flow by the opposing flow of Banda Intermediate water; upper salinity minimum mass, entering via Lombok Strait and moving zonally in the direction of the prevailing surface currents, a secondary movement of this water mass towards north-west Australia is limited by the northern boundary of a south-east Indian high salinity water mass. This latter water mass occurs as three separate core layers north of 22-23� S. The deep core layer mixes with waters of the oxygen maximum below it, the mid-depth core layer mixes with Persian Gulf and upper salinity minimum water masses, and the upper core layer mixes with the Arabian Sea water mass. The latter water mass spreads eastwards to about 120� E. and southwards to north-west Australia, in conformity with surface currents. A sixth water mass enters with the counter-current and is found as a salinity maximum within the thermocline to about 20� S. A seventh water mass characterized by a salinity maximum around temperatures of 28-29�C has a limited distribution and an unknown origin. Both of these water masses move in the direction of surface currents.

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Water Mass Characteristics and Distribution Adjacent to Larsen C Ice Shelf, Antarctica

10.5194/egusphere-egu2020-112 ◽

2020 ◽

Author(s):

Katherine Hutchinson ◽

Julie Deshayes ◽

Jean-Baptiste Sallee ◽

Julian Dowdeswell ◽

Casimir de Lavergne ◽

...

Keyword(s):

Continental Shelf ◽

Ocean Circulation ◽

Deep Water ◽

Water Mass ◽

Heat Content ◽

Weddell Sea ◽

Global Ocean ◽

Spatial And Temporal Variability ◽

Ice Shelf ◽

Shed Light

<p>The physical oceanographic environment, water mass mixing and transformation in the area adjacent to Larsen C Ice Shelf (LCIS) are investigated using hydrographic data collected during the Weddell Sea Expedition 2019. The results shed light on the ocean conditions adjacent to a thinning LCIS, on a continental shelf that is a source region for the globally important water mass, Weddell Sea Deep Water (WSDW). Modified Weddell Deep Water (MWDW), a comparatively warmer water mass of circumpolar origin, is identified on the continental shelf and is observed to mix with local shelf waters, such as Ice Shelf Water (ISW), which is a precursor of WSDW. Oxygen measurements enable the use of a linear mixing model to quantify contributions from source waters revealing high levels of mixing in the area, with much spatial and temporal variability. Heat content anomalies indicate an introduction of heat, presumed to be associated with MWDW, into the area via Jason Trough. Furthermore, candidate parent sources for ISW are identified in the region, indicating the potential for the circulation of continental shelf waters into the ice shelf cavity. This highlights the possibility that offshore climate signals are conveyed under LCIS. ISW is observed within Jason Trough, likely exiting the sub-ice shelf cavity en route to the Slope Current. This onshore-offshore flux of water masses links the region of the Weddell Sea adjacent to northern LCIS to global ocean circulation and Bottom Water characteristics via its contribution to ISW and hence WSDW properties.&#160;</p><p>What remains to be clarified is whether MWDW found in Jason Trough has a direct impact on basal melting and thus thinning of LCIS. More observations are required to investigate this, in particular direct observations of ocean circulation in Jason Trough and underneath LCIS. Modelling experiments could also shed light on this, and so preliminary results based on NEMO global simulations explicitly representing the circulation in under-ice shelf seas, will be presented.&#160;</p>

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Oxygen export to the deep ocean following Labrador Sea Water formation

10.5194/bg-2021-185 ◽

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.

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Late Quaternary paleoceanography of deep and intermediate water masses off Gaspé Peninsula, Gulf of St. Lawrence: foraminiferal evidence

Canadian Journal of Earth Sciences ◽

10.1139/e93-120 ◽

1993 ◽

Vol 30 (7) ◽

pp. 1390-1403 ◽

Cited By ~ 23

Author(s):

Cyril G. Rodrigues ◽

James A. Ceman ◽

Gustavs Vilks

Keyword(s):

Deep Water ◽

Water Mass ◽

Late Quaternary ◽

Water Masses ◽

Intermediate Water ◽

Low Salinity ◽

New Information ◽

Intermediate Water Mass ◽

Gaspe Peninsula ◽

Gaspé Peninsula

Radiocarbon-dated benthonic foraminiferal zones in three cores provide new information on the evolution of the deep and intermediate water masses off Gaspé Peninsula. The deglacial phase in the deep Laurentian Channel began before 14 000 BP and was characterized by low-salinity (<20‰) or alternating low-salinity and saline (~35‰) water. This was followed by a cold saline phase, which ended ca. 13 500 BP, and a salinity minimum (30–33.5‰), which began ca. 12 100 BP. Between 8700 and 7900 BP, the temperature and salinity of the deep water mass increased, resulting in the modern deep water mass (temperature 4–6 °C, salinity 34.5–34.9‰) at the end of the Goldthwait Sea episode. The salinity of the deep water was apparently controlled by the meltwater flux from the ice front during the deglacial phase. After the deglacial phase the characteristics of the deep water mass were determined by the composition of offshore water entering the Laurentian Channel. Runoff from the Lake Agassiz – Great Lakes system does not appear to have mixed with the deep water of the Goldthwait Sea. The deglacial phase in Chaleur Trough, which is within the intermediate water mass, began before 12 200 BP. The temperature of the intermediate water mass has remained close to 0 °C after deglaciation; however, the salinity has increased from 25–30‰ at 12 200 BP to about 33.5‰ by 5900 BP.

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