The North Atlantic Eastern Boundary: Observations from Moorings at Goban Spur 2016-2019

2020 ◽  
Author(s):  
Martin Moritz ◽  
Kerstin Jochumsen ◽  
Dagmar Kieke ◽  
Birgit Klein ◽  
Holger Klein ◽  
...  
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
Altimeter Data ◽  
Depth Range ◽  
The North ◽  
Eastern Boundary ◽  
The North Atlantic ◽  
Goban Spur

<p>Since 2016 a moored observatory is operated at the eastern extension of the “North Atlantic Changes (NOAC)” array at 47°/48°N. This observatory is installed across the shelf break at Goban Spur and consists of two deep-sea moorings that are separated by about 60 km.  </p><p>The aim of this ongoing monitoring program is to quantify the variability and trends in the properties and transport rates of water masses that are advected northwards along the North Atlantic Eastern Boundary and modify the adjacent regions, i.e. the Northwest European Shelf, North Sea, Nordic Seas and Arctic Ocean. Furthermore, the continuous long term time series are essential for a thorough understanding of the circulation system in the eastern North Atlantic and the underlying physical mechanisms that govern its variability.</p><p>Here, we present results of the analysis of temperature, salinity and current velocity time series from 2016 to 2019. These provide a descriptive view of the complex current structure and variability of water masses on daily to intra- and inter-annual time scales.</p><p>The most pronounced signal in the variability of temperature and salinity is caused by the presence of Mediterranean Outflow Water located at about 1000 m depth. During the observation period we find significant positive trends in temperature and salinity in the depth range of 500 to 1500 m. The velocity measurements of the onshore mooring show a northeastward directed mean flow following the topography with along-slope variations, while the flow at the offshore mooring position is more unstable with predominantly cross-slope variations. </p><p>The combination of our observations with float and altimeter data indicates that the presence of eddies and the interaction with the topography seems to play a crucial role for setting the variability of the flow in this region.</p><p>Finally, we present an approach to evaluate the volume fluxes at the eastern boundary that will add toward an integrated estimate of the strength of the Atlantic Meridional Overturning Circulation at 47°/48°N.</p>

scholarly journals Change in the North Atlantic circulation associated with the mid-Pleistocene transition

2018 ◽  
Vol 14 (11) ◽  
pp. 1639-1651 ◽  
Author(s):  
Gloria M. Martin-Garcia ◽  
Francisco J. Sierro ◽  
José A. Flores ◽  
Fátima Abrantes
Keyword(s):  
North Atlantic ◽  
Major Change ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
North Atlantic Current ◽  
The North ◽  
Oceanic Fronts ◽  
Surface Circulation ◽  
The North Atlantic

Abstract. The southwestern Iberian margin is highly sensitive to changes in the distribution of North Atlantic currents and to the position of oceanic fronts. In this work, the evolution of oceanographic parameters from 812 to 530 ka (MIS20–MIS14) is studied based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37∘34.285′ N, 10∘7.562′ W; 2585 m b.s.l.). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55∘ N, basin-wide paleoceanographic conditions are reconstructed. Variations of assemblages dwelling in different water masses indicate a major change in the general North Atlantic circulation during MIS16, coinciding with the definite establishment of the 100 ky cyclicity associated with the mid-Pleistocene transition. At the surface, this change consisted in the redistribution of water masses, with the subsequent thermal variation, and occurred linked to the northwestward migration of the Arctic Front (AF), and the increase in the North Atlantic Deep Water (NADW) formation with respect to previous glacials. During glacials prior to MIS16, the NADW formation was very weak, which drastically slowed down the surface circulation; the AF was at a southerly position and the North Atlantic Current (NAC) diverted southeastwards, developing steep south–north, and east–west, thermal gradients and blocking the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the increase in the meridional overturning circulation, in combination with the northwestward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheet growth, which could have worked as a positive feedback to prolong the glacials towards 100 ky cycles.

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.

AMOC response to changing resolution in the Finite-volumE Sea ice–Ocean Model

2020 ◽  
Author(s):  
Dmitry Sidorenko ◽  
Sergey Danilov ◽  
Nikolay Koldunov ◽  
Patrick Scholz
Keyword(s):  
Sea Ice ◽  
Finite Volume ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Ocean Model ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
Meridional Transport ◽  
The North ◽  
The North Atlantic

<p>The Atlantic meridional overturning circulation (AMOC) is the most common diagnostics of numerical simulations. Generally it is computed as a streamfunction of zonally averaged flow along the constant depth. More rarely it is computed as zonally averaged along constant isopycnals. The latter computation, however, allows one to better distinguish between water masses and physical processes contributing to the meridional transport. We analyze the AMOC in global simulations based on the Finite-volumE Sea ice–Ocean Model (FESOM 2.0) using eddy permitting to eddy resolving configurations in the North Atlantic. We (1) split the AMOC computed in density space into the constitutes induced by surface buoyancy fluxes and cross isopycnal transformations, (2) identify the water masses which contribute to the formation of the North Atlantic Deep Water and (3) study the AMOC response to the permitting or resolving eddies in the North Atlantic ocean.</p>

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.

scholarly journals The North Atlantic Oscillations: Cycle Times for the NAO, the AMO and the AMOC

Climate ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 43 ◽  
Author(s):  
Knut Lehre Seip ◽  
Øyvind Grøn ◽  
Hui Wang
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Atlantic Multidecadal Oscillation ◽  
Meridional Overturning Circulation ◽  
Cycle Times ◽  
The North ◽  
In Series ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

We show that oceanic cycle lengths persist across oceanic cyclic time-series by comparing cycles in series that come from “sister” measurements in the North Atlantic Ocean. These are the North Atlantic oscillation (NAO), the Atlantic multidecadal oscillation (AMO) and the Atlantic meridional overturning circulation (AMOC). The raw NAO series, which is an extremely noisy series in its raw format, showed cycles at 7, 13, 20, 26 and 34 years that were common with, or overlapped, the other two series, and across increasing degrees of smoothing of the NAO series. At the 1960 midpoint of the hiatus period 1943–1975, NAO was leading time-series to AMOC and AMO and AMO was a leading time-series to AMOC, but in 1975, at the end of the hiatus period, the leading relations were reversed.

scholarly journals Observed Basin-Scale Response of the North Atlantic Meridional Overturning Circulation to Wind Stress Forcing

2017 ◽  
Vol 30 (6) ◽  
pp. 2029-2054 ◽  
Author(s):  
Shane Elipot ◽  
Eleanor Frajka-Williams ◽  
Chris W. Hughes ◽  
Sofia Olhede ◽  
Matthias Lankhorst
Keyword(s):  
Time Series ◽  
Wind Stress ◽  
North Atlantic ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
The North ◽  
Basin Scale ◽  
Meridional Overturning ◽  
The North Atlantic

Abstract The response of the North Atlantic meridional overturning circulation (MOC) to wind stress forcing is investigated from an observational standpoint, using four time series of overturning transports below and relative to 1000 m, overlapping by 3.6 yr. These time series are derived from four mooring arrays located on the western boundary of the North Atlantic: the RAPID Western Atlantic Variability Experiment (WAVE) array (42.5°N), the Woods Hole Oceanographic Institution Line W array (39°N), RAPID–MOC/MOCHA (26.5°N), and the Meridional Overturning Variability Experiment (MOVE) array (16°N). Using modal decompositions of the analytic cross-correlation between transports and wind stress, the basin-scale wind stress is shown to significantly drive the MOC coherently at four latitudes, on the time scales available for this study. The dominant mode of covariance is interpreted as rapid barotropic oceanic adjustments to wind stress forcing, eventually forming two counterrotating Ekman overturning cells centered on the tropics and subtropical gyre. A second mode of covariance appears related to patterns of wind stress and wind stress curl associated with the North Atlantic Oscillation, spinning anomalous horizontal circulations that likely interact with topography to form overturning cells.

scholarly journals Role of the North Atlantic circulation in the mid-Pleistocene transition

2018 ◽  
Author(s):  
Gloria M. Martin-Garcia ◽  
Francisco J. Sierro ◽  
José A. Flores ◽  
Fátima Abrantes
Keyword(s):  
North Atlantic ◽  
Major Change ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
North Atlantic Current ◽  
The North ◽  
Oceanic Fronts ◽  
Surface Circulation ◽  
The North Atlantic

Abstract. The southwestern Iberian margin is highly sensitive to changes in the distribution of North Atlantic currents, and to the position of oceanic fronts. In this work, the evolution of oceanographic parameters from 812 to 530 ka (MIS20-MIS14) is reconstructed, based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37°34.285&amp;apos; N, 10°7.562&amp;apos; W; 2585 m bsl). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55° N, basin-wide paleoceanographic conditions are reconstructed. Variations of assemblages dwelling in different water masses indicate a major change in the general North Atlantic circulation during MIS16, coinciding with the definite establishment of the 100-ky cyclicity associated to the Mid-Pleistocene Transition. In surface, this change consisted in the re-distribution of water masses, with the subsequent thermal variation, and occurred linked to the northwestward migration of the Arctic Front (AF) and the increase in the North Atlantic Deep Water (NADW) formation. During glacials prior to MIS 16, the NADW formation was very weak, which drastically slowed down the surface circulation; the AF was at a southerly position and the North Atlantic Current (NAC) diverted southeastwards, developing steep south-north, and east-west, thermal gradients and blockading the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the important increase in the meridional overturning circulation, in combination with the north-westward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheets growth, which worked as a positive feedback to prolong the glacials towards 100-ky cycles.

Sign in / Sign up

Export Citation Format

Share Document