scholarly journals Occurrence and characteristics of mesoscale eddies in the tropical northeast Atlantic Ocean

2015 ◽  
Vol 12 (6) ◽  
pp. 3043-3097 ◽  
Author(s):  
F. Schütte ◽  
P. Brandt ◽  
J. Karstensen
Keyword(s):  
Current System ◽  
Coastal Region ◽  
Salt Flux ◽  
Detection Methods ◽  
Boreal Summer ◽  
Coastal Current ◽  
Mode Water ◽  
Northeast Atlantic ◽  
West African Coast ◽  
Northeast Atlantic Ocean

Abstract. Coherent mesoscale features (referred to here as eddies) in the tropical northeast Atlantic (between 12–22° N and 15–26° W) are examined and characterised. The eddies' surface signatures are investigated using 19 years of satellite derived sea level anomaly (SLA) data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo–Weiß method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST) and salinity (SSS) are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are associated with elevation/depression of SLA and enhanced/reduced SST and SSS patterns. However, about 20 % of all detected anticyclones show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs). About 146 ± 4 eddies per year are identified (52 % cyclones, 39 % anticylones, 9 % ACMEs) with rather similar mean radii of about 56 ± 12 km. Based on concurrent in-situ temperature and salinity profile data (from Argo float, shipboard and mooring data) inside of the three eddy types, their distinct differences in vertical structure is determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland region and carry South Atlantic Central Water that originates from the northward transport within the Mauretania coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d−1) is confined to distinct corridors with a small meridional deflection dependent on the eddy type (anticyclones – equatorward, cyclones – poleward, ACMEs – no deflection). Heat and salt flux out of the coastal region and across the Cap Verde Frontal Zone, which separates the shadow zone from the ventilated gyre, are calculated.

scholarly journals Occurrence and characteristics of mesoscale eddies in the tropical northeastern Atlantic Ocean

Ocean Science ◽  
2016 ◽  
Vol 12 (3) ◽  
pp. 663-685 ◽  
Author(s):  
Florian Schütte ◽  
Peter Brandt ◽  
Johannes Karstensen
Keyword(s):  
Atlantic Ocean ◽  
Current System ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Detection Methods ◽  
Boreal Summer ◽  
Coastal Current ◽  
Mode Water ◽  
Northeastern Atlantic Ocean ◽  
Northeastern Atlantic

Abstract. Coherent mesoscale features (referred to here as eddies) in the tropical northeastern Atlantic Ocean (between 12–22° N and 15–26° W) are examined and characterized. The eddies' surface signatures are investigated using 19 years of satellite-derived sea level anomaly (SLA) data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo–Weiß method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST) and sea surface salinity (SSS) anomalies are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are identified by an elevation/depression of SLA and enhanced/reduced SST and SSS in their cores. However, about 20 % of all anticyclonically rotating eddies show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs). About 146 ± 4 eddies per year with a minimum lifetime of 7 days are identified (52 % cyclones, 39 % anticyclones, 9 % ACMEs) with rather similar mean radii of about 56 ± 12 km. Based on concurrent in situ temperature and salinity profiles (from Argo float, shipboard, and mooring data) taken inside of eddies, distinct mean vertical structures of the three eddy types are determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland regions and carry South Atlantic Central Water supplied by the northward flow within the Mauretanian coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d−1) is confined to distinct zonal corridors with a small meridional deflection dependent on the eddy type (anticyclones – equatorward, cyclones – poleward, ACMEs – no deflection). Heat and salt fluxes out of the coastal region and across the Cape Verde Frontal Zone, which separates the shadow zone from the ventilated subtropical gyre, are calculated.

scholarly journals Generation mechanisms of mesoscale eddies in the Mauritanian Upwelling Region

2021 ◽  
Author(s):  
Ahmad Fehmi Dilmahamod ◽  
Johannes Karstensen ◽  
Heiner Dietze ◽  
Ulrike Löptien ◽  
Katja Fennel
Keyword(s):  
Current System ◽  
Ekman Transport ◽  
Boreal Summer ◽  
Unstable State ◽  
Coastal Current ◽  
Boundary Current ◽  
Mode Water ◽  
Buoyancy Forcing ◽  
Surface Buoyancy ◽  
Anticyclonic Eddies

AbstractThe physical processes driving the genesis of surface- and subsurface-intensified cyclonic and anticyclonic eddies originating from the coastal current system of the Mauritanian Upwelling Region are investigated using a high-resolution (~1.5 km) configuration of GFDL’s Modular Ocean Model. Estimating an energy budget for the boundary current reveals a baroclinically unstable state during its intensification phase in boreal summer and which is driving eddy generation within the near-coastal region. The mean poleward coastal flow’s interaction with the sloping topography induces enhanced anticyclonic vorticity, with potential vorticity close to zero generated in the bottom boundary layer. Flow separation at sharp topographic bends intensifies the anticyclonic vorticity, and submesoscale structures of low PV coalesce to form anticyclonic vortices. A combination of offshore Ekman transport and horizontal advection determined the amount of SACW in an anticyclonic eddy. A vortex with a relatively dense and low PV core will form an anticyclonic mode-water eddy, which will subduct along isopycnals while propagating offshore and hence be shielded from surface buoyancy forcing. Less contribution of dense SACW promotes the generation of surface anticyclonic eddies as the core is composed of a lighter water mass, which causes the eddy to stay closer to the surface and hence be exposed to surface buoyancy forcing. Simulated cyclonic eddies are formed between the rotational flow of an offshore anticyclonic vortex and a poleward flowing boundary current, with eddy potential energy being the dominant source of eddy kinetic energy. All three types of eddies play a key role in the exchange between the Mauritanian Coastal currents system and the adjacent eastern boundary shadow zone region.

scholarly journals A Long-Lasting Mode Water Vortex in the Northeast Atlantic Ocean

2009 ◽  
Vol 39 (3) ◽  
pp. 536-558 ◽  
Author(s):  
Gilles Reverdin ◽  
Jean-Claude Gascard ◽  
Bernard Le Cann ◽  
Louis Prieur ◽  
Michel Assenbaum ◽  
...  
Keyword(s):  
Inner Core ◽  
Azimuthal Velocity ◽  
Relative Vorticity ◽  
Sea Surface ◽  
Mode Water ◽  
Northeast Atlantic ◽  
The Core ◽  
Long Time ◽  
Northeast Atlantic Ocean ◽  
Neutrally Buoyant

Abstract An anticyclonic mode water vortex and its environment were investigated from November 2000 to September 2001 in the northeast Atlantic (near 43.5°N, 15°–19°W) with neutrally buoyant drifting floats, moored current meters, satellite altimetric sea surface height, and several hydrological surveys and sections. These observations reveal a coherent inner core (∼30 km in diameter) made of very oxygenated northeast Atlantic central waters (11°–12.7°C and 35.5–35.7 on the 1978 practical salinity scale) from 150 m down to about 750-m depth. The core presents high relative vorticity (up to approximately −0.5 times the Coriolis frequency f ) within at least 10 km of its center, near 400–700 m. Peak velocity along the core rim is located deeper than 600 m bordering the deepest and densest (σθ = 27.175 kg m−3) northeast Atlantic mode water found during the Programme Océan Multidisciplinaire Méso Echelle (POMME) project. This water likely originates north of 47°N, where it could have been in contact with the sea surface in early 1999. Below the core, large near-inertial internal waves are found. At least during spring and summer 2001, the core was embedded in a much larger anticyclonic eddy that extends to 100 km from its center, with azimuthal velocity decreasing from the sea surface to 1500 m. This eddy does not trap floats for a long time and is associated with a sea level anomaly on the order of 10 cm. From January through August 2001, both the core and the larger eddy moved anticyclonically around a shallow part of the Azores–Biscay ridge. The core trajectory also exhibits smaller anticyclonic loops on shorter time scales, suggesting that at least at times it is not located at the center of the larger eddy.

scholarly journals Elevated iron to nitrogen recycling by mesozooplankton in the Northeast Atlantic Ocean

2012 ◽  
Vol 39 (12) ◽  
pp. n/a-n/a ◽  
Author(s):  
Sarah L. C. Giering ◽  
Sebastian Steigenberger ◽  
Eric P. Achterberg ◽  
Richard Sanders ◽  
Daniel J. Mayor
Keyword(s):  
Atlantic Ocean ◽  
Nitrogen Recycling ◽  
Northeast Atlantic ◽  
Northeast Atlantic Ocean

scholarly journals Availability of iron and major nutrients for phytoplankton in the northeast Atlantic Ocean

2004 ◽  
Vol 49 (6) ◽  
pp. 2095-2104 ◽  
Author(s):  
Stèphane Blain ◽  
Cècile Guieu ◽  
Hervè Claustre ◽  
Karine Leblanc ◽  
Thierry Moutin ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Northeast Atlantic ◽  
Northeast Atlantic Ocean ◽  
Major Nutrients

Seismic‐stratigraphic constraints on the age of the Faroe Islands Basalt Group, Faroe–Shetland region, Northeast Atlantic Ocean

2019 ◽  
Vol 31 (5) ◽  
pp. 841-865
Author(s):  
Jana Ólavsdóttir ◽  
Martyn S. Stoker ◽  
Lars O. Boldreel ◽  
Morten Sparre Andersen ◽  
Óluva R. Eidesgaard
Keyword(s):  
Atlantic Ocean ◽  
Faroe Islands ◽  
Northeast Atlantic ◽  
Northeast Atlantic Ocean

scholarly journals The uptake of silica during the spring bloom in the Northeast Atlantic Ocean

2003 ◽  
Vol 48 (5) ◽  
pp. 1831-1845 ◽  
Author(s):  
Louise Brown ◽  
Richard Sanders ◽  
Graham Savidge ◽  
Cathy H. Lucas
Keyword(s):  
Atlantic Ocean ◽  
Spring Bloom ◽  
Northeast Atlantic ◽  
Northeast Atlantic Ocean

Evidence for thermally mediated settlement in lobster larvae (Homarus americanus)

2013 ◽  
Vol 70 (11) ◽  
pp. 1641-1649 ◽  
Author(s):  
Eric R. Annis ◽  
Carl J. Wilson ◽  
Robert Russell ◽  
Philip O. Yund
Keyword(s):  
Water Temperature ◽  
Settlement Patterns ◽  
Coastal Region ◽  
Homarus Americanus ◽  
Size Increase ◽  
Coastal Current ◽  
Bottom Temperature ◽  
Degree Days ◽  
Successful Recruitment ◽  
Behavioral Avoidance

We examined the potential for bottom temperatures ≤12 °C to inhibit successful recruitment of planktonic lobster postlarvae to the benthos. In laboratory trials, postlarvae held at 11 °C exhibited higher mortality, slower development, and reduced size increase at molt relative to postlarvae held at 13 °C. We sampled at field sites within Machias Bay, Maine (mean bottom temperature 12.39 °C, 46.1 degree-days ≥12 °C) and at the mouth of the bay (mean bottom temperature 11.57 °C, 5.1 degree-days ≥12 °C), where temperature was influenced by the cold Eastern Maine Coastal Current (EMCC). We found significantly higher settlement at the warm inshore site but, the abundance of competent planktonic postlarvae was not significantly different between sites, indicating a disconnect between postlarval abundance and settlement. Regional sampling of newly settled lobsters revealed a pattern of higher settlement at inshore sites extending across a broader coastal region impacted by the EMCC. Our results suggest that small differences in water temperature may shape settlement patterns through either behavioral avoidance of colder settlement sites or elevated postsettlement mortality of postlarvae settling at colder sites.

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