Water masses and mesoscale circulation of North Rockall Trough waters during JASIN 1978

1983 ◽  
Vol 308 (1503) ◽  
pp. 231-252 ◽  
Keyword(s):  
North Atlantic ◽  
Atlantic Water ◽  
Water Masses ◽  
Reference Level ◽  
Intermediate Water ◽  
Norwegian Sea ◽  
The North ◽  
North Atlantic Water ◽  
Rockall Trough ◽  
North Rockall Trough

During the Joint Air-Sea Interaction Experiment (JASIN 1978) grids of temperature and salinity profiles were worked within an area of about 150 km x 150 km to obtain details of the mesoscale circulation around the location of the experiment in the North Rockall Trough. Data were also obtained from moored current meters and from research vessel observations in the surrounding waters. In the uppermost layers two water masses were present, North Atlantic Water from southern parts of the Rockall Trough and fresher Modified North Atlantic Water from the north and west. Beneath these an intermediate water formed by Atlantic Water in contact with Subarctic Intermediate Water was found and at greater depth distinctions could be drawn between water from the south, water with an admixture of Norwegian Sea Deep Water from the Scotland-Iceland ridges and, more sparse, water with a component of Arctic Intermediate Water from the Faroe-Shetland Channel. The patterns of circulation were found to change little between the lower depths and 200 m. An anticyclonic eddy of fresher, colder water moved westwards across the northern half of the grid at about 1.4 km day-1, the northern sector of a more saline meander expanded westwards across the southern part of the area, and smaller less well resolved circulations were found in the west. The eddy contained water of overflow origin and the meander appears to have been part of the main Atlantic to Norwegian Sea current. When inverse analysis was applied to two of the data sets to investigate choices of reference level, zero velocity at the bottom gave the only physically realistic solution. Although the necessary process of averaging the observations to data points 45 km apart obscured the resolution of smaller features, confidence in the reference level that satisfied the inverse analysis allowed classical geostrophic analysis to be performed on the full set of stations, supporting and quantifying the earlier analysis of patterns. The influence of the deeper circulation can be seen in the modification of the thermohaline structure in the seasonal thermocline and mixed layers. Boundaries between adjacent upper water masses were distorted by underlying convergences or fragmented by horizontal shears.

scholarly journals Declining silicate concentrations in the Norwegian and Barents Seas

2012 ◽  
Vol 69 (2) ◽  
pp. 208-212 ◽  
Author(s):  
Francisco Rey
Keyword(s):  
North Atlantic ◽  
Relative Proportion ◽  
Atlantic Water ◽  
Water Masses ◽  
Source Water ◽  
Marine Science ◽  
Norwegian Sea

Abstract Rey, F. 2012. Declining silicate concentrations in the Norwegian and Barents Seas. – ICES Journal of Marine Science, 69: 208–212. Since 1990, a decline in silicate concentrations together with increasing salinities has been observed in the Atlantic water of the Norwegian and Barents Seas. This decline in silicate has been found to be related to the relative proportion in which eastern and western source water masses from the northeastern North Atlantic enter the Norwegian Sea.

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 Paleoenvironments along the Eastern Laurentide Ice Sheet Margin and Timing of the Last Ice Maximum and Retreat

2008 ◽  
Vol 41 (2) ◽  
pp. 265-277 ◽  
Author(s):  
Anne de Vernal ◽  
Claude Hillaire-Marcel
Keyword(s):  
Late Pleistocene ◽  
North Atlantic ◽  
Environmental Changes ◽  
Atlantic Water ◽  
Polar Front ◽  
Water Masses ◽  
Labrador Sea ◽  
Eastern Canada ◽  
North Atlantic Water ◽  
Late Wisconsinan

ABSTRACT Palynological and isotopic analysis in a few deep-sea cores from the Labrador Sea reveals strong environmental changes related to the Late Pleistocene glacial fluctuations over eastern Canada. On the whole, the Labrador Sea was characterized by strong exchanges between North Atlantic water masses, Arctic outflows, and meltwater discharges from Laurentide, Greenland and lnuitian ice sheets. The penetration of temperate Atlantic waters persisted throughout most of the Late Pleistocene, with a brief interruption during the Late Wisconsinan. During this glacial substage, a slight but continuous meltwater runoff from the Laurentide ice margins grounded on the northern Labrador Shelf is indicated by relatively low 18O values and low-salinity (< 30‰) dinocyst assemblages. The calving of the ice margin, the melwater outflow and the subsequent dilution of surface waters offshore Labrador probably contributed to the dispersal of floating ice and, consequently, to a southward displacement of the polar front restraining the penetration of North Atlantic waters into the Labrador Sea. The advection of southern air masses along the Laurentide ice margins, shown by pollen assemblages, was favourable to abundant precipitation and therefore, high ice accumulation rates, especially over northern Labrador during the Late Wisconsinan. The déglaciation is marked by a brief, but significant, melting event of northern Laurentide ice shortly after 17 ka. The main glacial retreat occurred after ca. 11 ka. It allowed restoration of WSW-ENE atmospheric trajectories, increased phytoplanktonic productivity, and penetration of North Atlantic water masses into the Labrador Sea.

scholarly journals Enhancement of the North Atlantic CO<sub>2</sub> sink by Arctic Waters

2021 ◽  
Vol 18 (5) ◽  
pp. 1689-1701
Author(s):  
Jon Olafsson ◽  
Solveig R. Olafsdottir ◽  
Taro Takahashi ◽  
Magnus Danielsen ◽  
Thorarinn S. Arnarson
Keyword(s):  
North Atlantic ◽  
Thermohaline Circulation ◽  
Atlantic Water ◽  
Water Masses ◽  
The Arctic ◽  
Arctic Water ◽  
The North ◽  
The North Atlantic ◽  
Co2 Sink ◽  
The One

Abstract. The North Atlantic north of 50∘ N is one of the most intense ocean sink areas for atmospheric CO2 considering the flux per unit area, 0.27 Pg-C yr−1, equivalent to −2.5 mol C m−2 yr−1. The northwest Atlantic Ocean is a region with high anthropogenic carbon inventories. This is on account of processes which sustain CO2 air–sea fluxes, in particular strong seasonal winds, ocean heat loss, deep convective mixing, and CO2 drawdown by primary production. The region is in the northern limb of the global thermohaline circulation, a path for the long-term deep-sea sequestration of carbon dioxide. The surface water masses in the North Atlantic are of contrasting origins and character, with the northward-flowing North Atlantic Drift, a Gulf Stream offspring, on the one hand and on the other hand the cold southward-moving low-salinity Polar and Arctic waters with signatures from Arctic freshwater sources. We have studied by observation the CO2 air–sea flux of the relevant water masses in the vicinity of Iceland in all seasons and in different years. Here we show that the highest ocean CO2 influx is to the Arctic and Polar waters, respectively, -3.8±0.4 and -4.4±0.3 mol C m−2 yr−1. These waters are CO2 undersaturated in all seasons. The Atlantic Water is a weak or neutral sink, near CO2 saturation, after poleward drift from subtropical latitudes. These characteristics of the three water masses are confirmed by data from observations covering 30 years. We relate the Polar Water and Arctic Water persistent undersaturation and CO2 influx to the excess alkalinity derived from Arctic sources. Carbonate chemistry equilibrium calculations clearly indicate that the excess alkalinity may support at least 0.058 Pg-C yr−1, a significant portion of the North Atlantic CO2 sink. The Arctic contribution to the North Atlantic CO2 sink which we reveal was previously unrecognized. However, we point out that there are gaps and conflicts in the knowledge about the Arctic alkalinity and carbonate budgets and that future trends in the North Atlantic CO2 sink are connected to developments in the rapidly warming and changing Arctic. The results we present need to be taken into consideration for the following question: will the North Atlantic continue to absorb CO2 in the future as it has in the past?

scholarly journals Export of ice sheet meltwater from Upernavik Fjord, West Greenland

2021 ◽  
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
North Atlantic Ocean ◽  
Atlantic Water ◽  
Water Masses ◽  
Buoyant Plume ◽  
Freshwater Input ◽  
The North ◽  
Freshwater Source ◽  
Lateral Mixing

Abstract Meltwater from Greenland is an important freshwater source for the North Atlantic Ocean, released into the ocean at the head of fjords in the form of runoff, submarine melt and icebergs. The meltwater release gives rise to complex in-fjord transformations that result in its dilution through mixing with other water masses. The transformed waters, which contain the meltwater, are exported from the fjords as a new water mass “Glacially Modified Water” (GMW). Here we use summer hydrographic data collected from 2013 to 2019 in Upernavik, a major glacial fjord in northwest Greenland, to describe the water masses that flow into the fjord from the shelf and the exported GMWs. Using an Optimum Multi-Parameter technique across multiple years we then show that GMW is composed of 57.8 ±8.1% Atlantic Water, 41.0 ±8.3% Polar Water, 1.0 ±0.1% subglacial discharge and 0.2 ±0.2% submarine meltwater. We show that the GMW fractional composition cannot be described by buoyant plume theory alone since it includes lateral mixing within the upper layers of the fjord not accounted for by buoyant plume dynamics. Consistent with its composition, we find that changes in GMW properties reflect changes in the AW and PW source waters. Using the obtained dilution ratios, this study suggests that the exchange across the fjord mouth during summer is on the order of 50 mSv (compared to a freshwater input of 0.5 mSv). This study provides a first order parameterization for the exchange at the mouth of glacial fjords for large-scale ocean models.

scholarly journals Observed trends of anthropogenic acidification in North Atlantic water masses

2012 ◽  
Vol 9 (3) ◽  
pp. 3003-3030
Author(s):  
M. Vázquez-Rodríguez ◽  
F. F. Pérez ◽  
A. Velo ◽  
A. F. Ríos ◽  
H. Mercier
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Deep Convection ◽  
Temporal Trends ◽  
Atlantic Water ◽  
Water Masses ◽  
The North ◽  
Iceland Basin ◽  
The North Atlantic ◽  
Atmospheric Co2 Concentrations

Abstract. The lack of observational pH data has made difficult assessing recent rates of ocean acidification, particularly in the high latitudes. Here we present a time series of high-quality carbon system measurements in the North Atlantic, comprising fourteen cruises spanning over 27 yr (1981–2008) and covering important water mass formation areas like the Irminger and Iceland basins. We provide direct quantification of anthropogenic acidification rates in upper and intermediate North Atlantic waters by removing the natural variability of pH from the observations. Bottle data were normalised to basin-average conditions using climatological data and further condensed into averages per water mass and year to examine the temporal trends. The highest acidification rates of all inspected water masses were associated with surface waters in the Irminger Sea (−0.0018 ± 0.0001 yr−1) and the Iceland Basin (−0.0012 ± 0.0002 yr−1) and, unexpectedly, with Labrador Seawater (LSW) which experienced an unprecedented pH drop of −0.0015 ± 0.001 yr−1. The latter stems from the formation by deep convection and the rapid propagation in the North Atlantic subpolar gyre of this well-ventilated water mass. The high concentrations of anthropogenic CO2 are effectively transported from the surface into intermediate waters faster than via downward diffusion, thus accelerating the acidification rates of LSW. An extrapolation of the observed lineal trends of acidification suggests that the pH of LSW could drop 0.45 units with respect to pre-industrial levels by the time atmospheric CO2 concentrations double the present ones.

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

2019 ◽  
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.

scholarly journals Trends of anthropogenic CO<sub>2</sub> storage in North Atlantic water masses

2010 ◽  
Vol 7 (5) ◽  
pp. 1789-1807 ◽  
Author(s):  
F. F. Pérez ◽  
M. Vázquez-Rodríguez ◽  
H. Mercier ◽  
A. Velo ◽  
P. Lherminier ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Atlantic Water ◽  
Average Concentration ◽  
Rate Of Change ◽  
Point Of View ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
The North ◽  
The North Atlantic

Abstract. A high-quality inorganic carbon system database, spanning over three decades (1981–2006) and comprising of 13 cruises, has allowed the applying of the φC°T method and coming up with estimates of the anthropogenic CO2 (Cant) stored in the main water masses of the North Atlantic. In the studied region, strong convective processes convey surface properties, like Cant, into deeper ocean layers and grants this region an added oceanographic interest from the point of view of air-sea CO2 exchanges. Generally, a tendency for decreasing Cant storage rates towards the deep layers has been observed. In the Iberian Basin, the North Atlantic Deep Water has low Cant concentrations and negligible storage rates, while the North Atlantic Central Water in the upper layers shows the largest Cant values and the largest annual increase of its average concentration (1.13 ± 0.14 μmol kg−1 yr−1). This unmatched rate of change in the Cant concentration of the warm upper limb of the Meridional Overturning Circulation decreases towards the Irminger basin (0.68 ± 0.06 μmol kg−1 yr−1) due to the lowering of the buffering capacity. The mid and deep waters in the Irminger Sea show rather similar Cant concentration rates of increase (between 0.33 and 0.45 μmol kg−1 yr−1), whereas in the Iceland basin these layers seem to have been less affected by Cant. Overall, the Cant storage rates in the North Atlantic subpolar gyre during the first half of the 1990s, when a high North Atlantic Oscillation (NAO) phase was dominant, are ~48% higher than during the 1997–2006 low NAO phase that followed. This result suggests that a net decrease in the strength of the North Atlantic sink of atmospheric CO2 has taken place during the present decade. The changes in deep-water ventilation are the main driving processes causing this weakening of the North Atlantic CO2 sink.

Éléments d'une climatostratigraphie du Pléistocène moyen et tardif dans l'est du Canada par l'analyse palynologique et isotopique du forage 84-030-003, mer du Labrador

1987 ◽  
Vol 24 (9) ◽  
pp. 1886-1902 ◽  
Author(s):  
A. de Vernal ◽  
C. Hillaire-Marcel
Keyword(s):  
North Atlantic ◽  
Strong Relationship ◽  
Atlantic Water ◽  
Water Masses ◽  
Labrador Sea ◽  
Aeolian Transport ◽  
Eastern Canada ◽  
The North ◽  
Labrador Current ◽  
Isotopic Analyses

The piston and gravity cores 84-030-003, collected in the southern Labrador Sea, have been sampled for detailed palynological and isotopic analyses. The δ18O record on foraminifera (Neogloboquadrina pachyderma, left-coiling) indicates a stratigraphy spanning isotopic stages 8 to 1, i.e., over ca. 300 000 years. The isotopic record allows the calculation of a mean sedimentation rate of approximately 5 cm/ka.The pollen and spore contents of the sediments are low. The low pollen influxes (generally less than 1 grain/cm2 per year) and the dominance of Pinus suggest aeolian transport over long distances with southwest–northeast to south-southwest–north-northeast trends. Dinoflagellate cyst concentrations are relatively low, indicating a low regional phytoplanktonic productivity. The assemblages are, however, diversified. They reflect influences from the North Atlantic Drift and from the Labrador Current. The occurrence of warm-temperate to tropical Impagidinium species in deposits suggests an almost permanent penetration of North Atlantic water masses into the Labrador Sea during the middle and Late Pleistocene. This divergence was apparently interrupted during the last glacial maximum of isotopic stage 2. Increases in the concentration of dinocysts such as Operculodinium centrocarpum, Nematosphaeropsis labyrinthea, and Bitectatodinium tepikiense were recorded during interglacial maxima of stages 7, 5, and 1. These dinocyst peaks indicate a high primary productivity and cool-temperate to subarctic conditions in surficial water masses offshore eastern Canada. In addition, they are probably related to a strong hydrodynamic regime of the Labrador Current. Fluctuations in the dinocyst concentrations are in most cases synchronous with the δ18O changes of foraminifera, indicating a strong relationship between the paleo-oceanography of the Labrador Sea and the Quaternary glaciations.

Sign in / Sign up

Export Citation Format

Share Document