scholarly journals Structure and Transport of the North Atlantic Current in the Eastern Subpolar Gyre From Sustained Glider Observations

2018 ◽  
Vol 123 (8) ◽  
pp. 6019-6038 ◽  
Author(s):  
L. Houpert ◽  
M. E. Inall ◽  
E. Dumont ◽  
S. Gary ◽  
C. Johnson ◽  
...  
Keyword(s):  
North Atlantic ◽  
Subpolar Gyre ◽  
North Atlantic Current ◽  
The North ◽  
The North Atlantic ◽  
Atlantic Current

scholarly journals The recent AMOC variability in the Subpolar Gyre: results across the OVIDE section

2020 ◽  
Author(s):  
Pascale Lherminier ◽  
Herlé Mercier ◽  
Fiz F. Perez ◽  
Marcos Fontela
Keyword(s):  
North Atlantic ◽  
Lower Limb ◽  
Deep Convection ◽  
Labrador Sea ◽  
Subpolar Gyre ◽  
North Atlantic Current ◽  
The North ◽  
Subarctic Front ◽  
The North Atlantic ◽  
Atlantic Current

<p><span>According to the subpolar AMOC index built from ARGO and altimetry, the AMOC amplitude across the OVIDE section (from Greenland to Portugal) was similar to that of the mid-1990s between 2014 and 2017, i.e. 4-5 Sv above the level of the 2000s. It then returned to average values in 2018. The same index computed independently from the biennial summer cruises over 2002-2018 confirms this statement. Interestingly, despite the concomitant cold and fresh anomaly in the subpolar Atlantic, the heat flux across OVIDE remains correlated with the AMOC amplitude. This can be explained by the paths taken by the North Atlantic Current and the transport anomalies in the subarctic front. In 2014, the OVIDE section was complemented by a section from Greenland to Newfoundland (GA01), showing how the water of the lower limb of the AMOC was densified by deep convection in the Labrador Sea. The spatial patterns of volume, heat, salt and oxygen transport anomalies after 2014 will be discussed at the light of the 2000s average.</span></p>

scholarly journals Interannual Variability in the Pathways of the North Atlantic Current over the Mid-Atlantic Ridge and the Impact of Topography

2008 ◽  
Vol 38 (1) ◽  
pp. 104-120 ◽  
Author(s):  
Amy S. Bower ◽  
Wilken-Jon von Appen
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Fracture Zone ◽  
Subpolar Gyre ◽  
North Atlantic Current ◽  
The North ◽  
Mid Atlantic Ridge ◽  
The North Atlantic ◽  
The Impact ◽  
Atlantic Current

Abstract Recent studies have indicated that the North Atlantic Ocean subpolar gyre circulation undergoes significant interannual-to-decadal changes in response to variability in atmospheric forcing. There are also observations, however, suggesting that the southern limb of the subpolar gyre, namely, the eastward-flowing North Atlantic Current (NAC), may be quasi-locked to particular latitudes in the central North Atlantic by fracture zones (gaps) in the Mid-Atlantic Ridge. This could constrain the current’s ability to respond to variability in forcing. In the present study, subsurface float trajectories at 100–1000 m collected during 1997–99 and satellite-derived surface geostrophic velocities from 1992 to 2006 are used to provide an improved description of the detailed pathways of the NAC over the ridge and their relationship to bathymetry. Both the float and satellite observations indicate that in 1997–99, the northern branch of the NAC was split into two branches as it crossed the ridge, one quasi-locked to the Charlie–Gibbs Fracture Zone (CGFZ; 52°–53°N) and the other to the Faraday Fracture Zone (50°–51°N). The longer satellite time series shows, however, that this pattern did not persist outside the float sampling period and that other branching modes persisted for one or more years, including an approximately 12-month time period in 2002–03 when the strongest eastward flow over the ridge was at ∼49°N. Schott et al. showed how northward excursions of the NAC can temporarily block the westward flow of the Iceland–Scotland Overflow Water through the CGFZ. From the 13-yr time series of surface geostrophic velocity, it is estimated that such blocking may occur on average 6% of the time, although estimates for any given 12-month period range from 0% to 35%.

scholarly journals Observed variability of the North Atlantic Current in the Rockall Trough from four years of mooring measurements.

2020 ◽  
Author(s):  
Loïc Houpert ◽  
Stuart A. Cunningham ◽  
Neil J Fraser ◽  
Clare Johnson ◽  
N. Penny Holliday ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Atlantic Current ◽  
The North ◽  
Rockall Trough ◽  
The North Atlantic ◽  
Atlantic Current

scholarly journals LONG-TERM VARIABILITY OF CURRENTS IN THE SUBARCTIC FRONT OF THE ATLANTIC OCEAN

2019 ◽  
Vol 47 (2) ◽  
pp. 246-265
Author(s):  
A. K. Ambrosimov ◽  
N. A. Diansky ◽  
A. A. Kluvitkin ◽  
V. A. Melnikov
Keyword(s):  
North Atlantic ◽  
Ocean Surface ◽  
North Atlantic Current ◽  
Reykjanes Ridge ◽  
The North ◽  
Subarctic Front ◽  
Average Water ◽  
The North Atlantic ◽  
Atlantic Current

Based on time series of near-bottom current velocities and temperatures obtained in the period June, 2016 to July, 2017, at three points in the Atlantic Subarctic Front, along with the use of multi-year (since 1993 up to now) satellite ocean surface sounding data, multi-scale fluctuations of ocean surface and near-bottom flows over the western and eastern flanks of the Reykjanes ridge, as well as near Hatton Rise, on the Rokoll plateau, are studied. Hydrological profiles were carried out from the ocean surface to the bottom with readings every 10 m, when setting and retrieving the buoy stations. Using data from the Bank of hydrological stations (WOD13), SST satellite arrays (Pathfinder), long-term sea level and geostrophic velocities time series (AVISO), and bottom topography (model ETOPO-1), features of longterm cyclical fluctuations of SST, sea level, geostrophic currents on the ocean surface were defined in the sub-polar North Atlantic. It is shown that, in accordance with the large-scale thermohaline structure of the Subarctic front, two branches of the North Atlantic Current are detected on the ocean surface.One is directed from the Hatton towards the Icelandic-Faroese Rise, and the other – alomg the western flank of the Reykjanes Ridge toward Iceland. For the first branch, which is the main continuation of the North Atlantic Current, the average (for 25 years) water drift at a speed of 9.1±0.1 cm/s is determined to the northeast. The second branch, which forms the eastern part of the Subarctic cyclonic gyre, has the average water drift at a speed of 4.0±0.1 cm/s is directed north-northeast, along the western flank of the Reykjanes Ridge. In the intermediate waters of the frontal zone, an average water flow is observed at a speed of 2.7±0.1 cm/s to the north-northeast, along the eastern slope of the Reykjanes ridge.Due to the multy-scale components of the total variability, the average kinetic energy densities(KED) of total currents (109, 45, 97, (±3) erg/cm3, at station points from east to west) are much greater than the mean drift KED. The near-bottom flows on the Reykjanes ridge flanks are opposite to the direction of the North Atlantic Current. Outside the Subarctic gyre, the direction of average transport is maintained from the ocean surface to the bottom. The average (per year) KED of near-bottom currents are 31, 143, 27 (±3 erg/cm3), for three stations from east to west, respectively. In the intermediate waters of the frontal zone, above the eastern slope of the Reykjanes Ridge, there is a powerful reverse (relative to the North Atlantic Current) near-bottom water flow to the south-west, with a high average speed of ~ 15 cm/s. The KED of the currents during the year varies widely from zero to ~ 600 erg/cm3. The overall variability is due to cyclical variations and intermittency (“flashes”) of currents. Perennial cycles, seasonal variations, synoptic fluctuations with periods in the range of 30–300 days, as well as inertial oscillations and semi-diurnal tidal waves are distinguished. The intermittency of oscillations is partly due to changes in low-frequency flows, which can lead to a dopler frequency shift in the cyclic components of the spectrum. The amplitude of temperature fluctuations in the bottom layer for the year was (0.07–0.10) ± 0.01°C by the standard deviation. The seasonal changes of the bottom temperature are not detected. However, a linear trend with a warming of ~ (0.10–0.15) ± 0.01°С per year is noticeable.

scholarly journals A Eurasian Ice-Sheet Study Using A Combined Ice-Sheet/ Ice-Shelf Numerical Model

1990 ◽  
Vol 14 ◽  
pp. 345-345
Author(s):  
Dean R. Lindstrom
Keyword(s):  
Numerical Model ◽  
Mass Loss ◽  
North Atlantic ◽  
Ice Sheet ◽  
The Arctic ◽  
North Atlantic Current ◽  
Ice Shelf ◽  
The North ◽  
The North Atlantic ◽  
Atlantic Current

A numerical model which simultaneously computes grounded and ice-shelf flow was used to develop an equilibrium ice-sheet–ice-shelf system over Eurasia and the Arctic region. Present-day net accumulation rates and mean annual and July temperature values were used as base values for climatic variable specifications. The values were adjusted during the model run to account for changes in the ice-surface elevation and atmospheric CO2 concentration. The model-determined equilibrium ice-sheet configuration was used as input for additional runs to observe what effect removing the Arctic ice shelf and increasing the CO2 concentration from glacial to present-day values has on the ice sheet.At equilibrium, an ice shelf formed over the Arctic Ocean and Greenland and Norwegian seas. Ice easily grounded over the Barents, Kara, East Siberian, and Laptev seas. The grounded ice-sheet profile differs in Europe from most glacial geological reconstructions because the North Atlantic Current effect was not removed from the climatic adjustments. As a result, ice did not extend over the North Sea and onto the British Isles because of the North Atlantic Current's warming effect. Also, the precipitation rate over Europe was too high because of the moisture source the North Atlantic Current carries, and the ice sheet expanded beyond the field-determined ice-sheet margins in the region south-east of Finland.Removing most of the Arctic region's ice-shelf cover had little effect on the grounded ice sheet unless it rested upon a deformable sediment layer. The ice sheet was able to collapse within 10 000 years, however, when the CO2 concentration was gradually increased toward present-day values using the Vostok ice core's CO2 record from the last 18 000 years. Initially, most mass loss resulted from surface melting. Once the thickness decreased enough over some regions for the grounded ice to become ungrounded, however, most mass loss resulted from the ice shelf rapidly transporting the ice to the ice-shelf front and discharging it to the sea.

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