scholarly journals Transformation of an Agulhas eddy near the continental slope

2009 ◽  
Vol 6 (2) ◽  
pp. 1819-1856
Author(s):  
S. Baker-Yeboah ◽  
G. R. Flierl ◽  
G. G. Sutyrin ◽  
Y. Zhang
Keyword(s):  
South Africa ◽  
Dipole Moment ◽  
Continental Slope ◽  
Mass Exchange ◽  
Water Mass ◽  
Deep Ocean ◽  
Anticyclonic Eddy ◽  
Western Coast ◽  
Vortical Structures ◽  
Benguela Upwelling

Abstract. The transformation of Agulhas eddies near the continental slope of South Africa and their subsequent self-propagation are analyzed in both observational data and numerical simulations. Self-propagation results from a net dipole moment of a generalized heton structure consisting of a surface-intensified anticyclonic eddy and deep cyclonic pattern. Such Agulhas vortical structures can form near the retroflection region and further north along the western coast of South Africa. We analyze nonlinear topographic wave generation, vortex deformations, and filament production as an important part in water mass exchange. Self-propagating structures provide a conduit for exchange between the deep ocean and shelf regions in the Benguela upwelling system.

scholarly journals Transformation of an Agulhas eddy near the continental slope

Ocean Science ◽  
2010 ◽  
Vol 6 (1) ◽  
pp. 143-159 ◽  
Author(s):  
S. Baker-Yeboah ◽  
G. R. Flierl ◽  
G. G. Sutyrin ◽  
Y. Zhang
Keyword(s):  
Dipole Moment ◽  
Continental Slope ◽  
Southern Africa ◽  
Mass Exchange ◽  
Water Mass ◽  
Deep Ocean ◽  
Anticyclonic Eddy ◽  
Western Coast ◽  
Vortical Structures ◽  
Benguela Upwelling

Abstract. The transformation of Agulhas eddies near the continental slope of southern Africa and their subsequent self-propagation are analyzed in both observational data and numerical simulations. Self-propagation results from a net dipole moment of a generalized heton structure consisting of a surface-intensified anticyclonic eddy and deep cyclonic pattern. Such Agulhas vortical structures can form near the retroflection region and further north along the western coast of southern Africa. We analyze nonlinear topographic wave generation, vortex deformations, and filament production as an important part in water mass exchange. Self-propagating structures provide a conduit for exchange between the deep ocean and shelf regions in the Benguela upwelling system.

scholarly journals Latest Miocene restriction of the Mediterranean Outflow Water: a perspective from the Gulf of Cádiz

2021 ◽  
Vol 41 (2) ◽  
Author(s):  
Zhi Lin Ng ◽  
F. Javier Hernández-Molina ◽  
Débora Duarte ◽  
Francisco J. Sierro ◽  
Santiago Ledesma ◽  
...  
Keyword(s):  
Mass Exchange ◽  
Water Mass ◽  
Atlantic Water ◽  
Meridional Overturning Circulation ◽  
Gulf Of Cadiz ◽  
Mediterranean Outflow Water ◽  
Gulf Of Cádiz ◽  
Mediterranean Outflow ◽  
The Mediterranean ◽  
Water Mass Exchange

AbstractThe Mediterranean-Atlantic water mass exchange provides the ideal setting for deciphering the role of gateway evolution in ocean circulation. However, the dynamics of Mediterranean Outflow Water (MOW) during the closure of the Late Miocene Mediterranean-Atlantic gateways are poorly understood. Here, we define the sedimentary evolution of Neogene basins from the Gulf of Cádiz to the West Iberian margin to investigate MOW circulation during the latest Miocene. Seismic interpretation highlights a middle to upper Messinian seismic unit of transparent facies, whose base predates the onset of the Messinian salinity crisis (MSC). Its facies and distribution imply a predominantly hemipelagic environment along the Atlantic margins, suggesting an absence or intermittence of MOW preceding evaporite precipitation in the Mediterranean, simultaneous to progressive gateway restriction. The removal of MOW from the Mediterranean-Atlantic water mass exchange reorganized the Atlantic water masses and is correlated to a severe weakening of the Atlantic Meridional Overturning Circulation (AMOC) and a period of further cooling in the North Atlantic during the latest Miocene.

scholarly journals Atlantic transport variability at 25° N in six hydrographic sections

Ocean Science ◽  
2012 ◽  
Vol 8 (4) ◽  
pp. 497-523 ◽  
Author(s):  
C. P. Atkinson ◽  
H. L. Bryden ◽  
S. A. Cunningham ◽  
B. A. King
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Decadal Variability ◽  
Potential Temperature ◽  
Deep Ocean ◽  
Velocity Shear ◽  
Western Boundary ◽  
Boundary Current ◽  
Annual Average ◽  
Deep Western Boundary Current

Abstract. In January and February 2010, a sixth transatlantic hydrographic section was completed across 25° N, extending the hydrographic record at this latitude to over half a century. In combination with continuous transport measurements made since 2004 at 26.5° N by the Rapid-WATCH project, we reassess transport variability in the 25° N hydrographic record. Past studies of transport variability at this latitude have assumed transport estimates from each hydrographic section to represent annual average conditions. In this study the uncertainty in this assumption is assessed through use of Rapid-WATCH observations to quantify sub-seasonal and seasonal transport variability. Whilst in the upper-ocean no significant interannual or decadal transport variability are identified in the hydrographic record, in the deep ocean transport variability in both depth and potential temperature classes suggests some interannual or decadal variability may have occurred. This is particularly striking in the lower North Atlantic Deep Water where southward transports prior to 1998 were greater than recent transports by several Sverdrups. Whilst a cooling and freshening of Denmark Straits Overflow Water has occurred which is coincident with these transport changes, these water mass changes appear to be density compensated. Transport changes are the result of changing velocity shear in the vicinity of the Deep Western Boundary Current.

There are three species of Chrysaora (Scyphozoa: Discomedusae) in the Benguela upwelling ecosystem, not two

Zootaxa ◽  
2020 ◽  
Vol 4778 (3) ◽  
pp. 401-438
Author(s):  
V. RAS ◽  
S. NEETHLING ◽  
A. ENGELBRECHT ◽  
A.C. MORANDINI ◽  
K.M. BAYHA ◽  
...  
Keyword(s):  
South Africa ◽  
Valid Species ◽  
Gulf Of Guinea ◽  
Geographical Patterns ◽  
Dna Evidence ◽  
South West ◽  
Benguela Upwelling ◽  
Colour Patterns ◽  
A New Species ◽  
Meristic Data

Chrysaora (Pèron & Lesueur 1810) is the most diverse genus within Discomedusae, and 15 valid species are currently recognised, with many others not formally described. Since Chrysaora fulgida (Reynaud 1830) was first recognised as occurring off the south west (SW) coast off South Africa, the species has been variously synonymised with Chrysaora hysoscella (Linnaeus 1767) and Chrysaora africana (Vanhöffen 1902). Using DNA evidence alongside multivariate tools to analyse quantitative morphometric and meristic data, as well as information from the cnidome, we unambiguously separate C. fulgida from C. hysoscella; we resurrect C. africana as a valid species and recognise a new species, Chrysaora agulhensis sp. nov. Full descriptions of C. fulgida, C. africana and C. agulhensis sp. nov. are provided. The species have different geographical patterns of distribution around the region, with restricted areas of overlap: C. agulhensis sp. nov. is found along the southern coast of South Africa and over the Agulhas Bank, C. fulgida extends from Cape Point in South Africa to southern Angola, and C. africana can be found from southern Namibia northwards to the Gulf of Guinea. The species can be readily separated in the field by a combination of tentacle/lappet number and shape, colour patterns and the form of the oral arms. 

Direct Measurements of Ocean Currents over the Continental Slope off Sydney

1979 ◽  
Vol 30 (6) ◽  
pp. 833 ◽  
Author(s):  
BV Hamon
Keyword(s):  
Continental Slope ◽  
Deep Ocean ◽  
Surface Current ◽  
Ocean Currents ◽  
North East ◽  
Direct Measurements ◽  
Deep Ocean Currents ◽  
Neutrally Buoyant ◽  
Tracking Period

The results of measurements of deep ocean currents over the continental slope off Sydney in May 1979 are presented and discussed. The measurements were made using neutrally buoyant floats. Four floats were used, at mean depths of 766, 1251, 1519 and 1886 m. All four floats moved towards north-north-east, approximately parallel to the depth contours, with mean speeds, over the 34-day tracking period, in the range 5-9 cm s-1. The surface current, estimated from ship's set, was towards north-east, at 25 cm s-1.

Northern Sourced Water dominated the Atlantic Ocean during the Last Glacial Maximum

2020 ◽  
Author(s):  
Frerk Pöppelmeier ◽  
Patrick Blaser ◽  
Marcus Gutjahr ◽  
Samuel Jaccard ◽  
Martin Frank ◽  
...  
Keyword(s):  
Carbon Storage ◽  
Last Glacial Maximum ◽  
Water Mass ◽  
Stable Carbon Isotope ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Ice Age ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO<sub>2</sub> concentrations. This carbon must have been stored away from the atmosphere for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Here we present new sediment derived bottom water neodymium isotope data that allow fingerprinting of water masses and their mixtures and provide a more complete picture of the Atlantic overturning circulation geometry during the Last Glacial Maximums. These results suggest that the vertical and meridional structure of the Atlantic deep water mass distribution only experienced minor changes since the last ice age. In particular, we find no compelling evidence supporting glacial southern sourced water substantially expanding to shallower depths and farther into the northern hemisphere than today, which has been inferred from stable carbon isotope reconstructions. We argue that depleted δ<sup>13</sup>C values observed in the deep Northwest Atlantic do not necessarily indicate the presence of southern sourced water. Instead, these values may represent a northern sourced water mass with lower than modern preformed δ<sup>13</sup>C values that were further modified downstream by increased sequestration of remineralized carbon, facilitated by a more sluggish glacial deep circulation. If proven to be correct, the glacial water mass structure inferred from Nd isotopes has profound implications on our understanding of the deep ocean carbon storage during the Last Glacial Maximum.</p>

Chemical composition and characterization of aerosols off Namibia: results from the AEROCLO-sA project

2020 ◽  
Author(s):  
Paola Formenti ◽  
Danitza Klopper ◽  
Servanne Chevaillier ◽  
Barbara D’Anna ◽  
Karine Desboeufs ◽  
...  
Keyword(s):  
Southern Africa ◽  
Climate Models ◽  
Biogenic Emissions ◽  
Western Coast ◽  
Anthropogenic Aerosols ◽  
Physico Chemical ◽  
Benguela Upwelling ◽  
Coastal Fog ◽  
Online Measurements

<p>The western coast of southern Africa off Namibia is characterized by a semi-permanent and widespread stratocumulus (Sc) cloud deck, very frequent coastal fog, and the oceanic northern Benguela upwelling system (nBUS). It is also the crossroad of large quantities of natural and anthropogenic aerosols of distant and local origins (biogenic, anthropogenic, biomass burning, sea salt and mineral dust) from continental and marine sources, with significant differences in terms of physico-chemical and optical properties, water affinity, scale and height of transport, which are not well represented in climate models.</p><p>In this presentation we will illustrate the results of the first extensive chemical and microphysical characterisation of aerosol particles in the area that has been conducted since 2016 at  the coastal Henties Bay experimental site (22°6’ S, 14°17’ E) in the framework of the AErosol, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) and the Atmospheric Research in the Southern Africa and Indian Ocean (ARSAIO) projects.</p><p>Synergetic filter sampling and online measurements provide examples of the numerous new particle formation in link with marine biogenic emissions and the apportionment of maritime sulfate aerosols, including their biogenic component.</p>

Water mass exchange and diapycnal mixing at Bussol’ Strait revealed by water mass properties

2007 ◽  
Vol 63 (2) ◽  
pp. 281-291 ◽  
Author(s):  
Kazuya Ono ◽  
Kay I. Ohshima ◽  
Tokihiro Kono ◽  
Motoyo Itoh ◽  
Katsuro Katsumata ◽  
...  
Keyword(s):  
Mass Exchange ◽  
Water Mass ◽  
Diapycnal Mixing ◽  
Mass Properties ◽  
Water Mass Exchange
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