Transformation of an Agulhas eddy near the continental slope

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.

Download Full-text

Transformation of an Agulhas eddy near the continental slope

Ocean Science Discussions ◽

10.5194/osd-6-1819-2009 ◽

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.

Download Full-text

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

10.5194/egusphere-egu2020-3844 ◽

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

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.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 &#160;the coastal Henties Bay experimental site (22&#176;6&#8217; S, 14&#176;17&#8217; 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.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.

Download Full-text

The match between ocean circulation and zoogeography of epipelagic siphonophores around southern Africa

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315402006161 ◽

2002 ◽

Vol 82 (5) ◽

pp. 801-810 ◽

Cited By ~ 22

Author(s):

Mark J. Gibbons ◽

Delphine Thibault-Botha

Keyword(s):

Ocean Circulation ◽

Southern Africa ◽

Coastal Waters ◽

Water Mass ◽

Benthic Communities ◽

Internal Boundary ◽

Close Match ◽

Surface Ocean ◽

Benguela Upwelling ◽

Warm Temperate

Published and unpublished records of epipelagic calycophoran siphonophores from around southern Africa were examined for zoogeographic structure. There is a close match between prevailing patterns of surface ocean circulation and zoogeography, which while similar to previous studies of intertidal taxa and euphausiids, is different from them in some key details. Separate subtropical provinces are associated with both the Angola and Agulhas Currents, and the latter system has a marked influence on the composition of (warm-temperate) assemblages along the south coast of South Africa. The nearshore waters in the Benguela upwelling ecosystem (cold temperate) are distinct, but the Lüderitz upwelling cell does not appear to act as an internal boundary within the Benguela ecosystem, as has been previously noted for benthic communities. Species richness is greater in oceanic than coastal waters, and peaks in subtropical waters. High diversity is also noted offshore in the area between Capes Agulhas and Columbine, where water of Indian, Southern and Atlantic Ocean interact. Indicator species for each major water mass were tentatively identified.

Download Full-text

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

Geo-Marine Letters ◽

10.1007/s00367-021-00693-9 ◽

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.

Download Full-text

Atlantic transport variability at 25° N in six hydrographic sections

Ocean Science ◽

10.5194/os-8-497-2012 ◽

2012 ◽

Vol 8 (4) ◽

pp. 497-523 ◽

Cited By ~ 13

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.

Download Full-text

Direct Measurements of Ocean Currents over the Continental Slope off Sydney

Marine and Freshwater Research ◽

10.1071/mf9790833 ◽

1979 ◽

Vol 30 (6) ◽

pp. 833 ◽

Cited By ~ 1

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.

Download Full-text

On water mass exchange between the Southern Ocean and the World Ocean; emphasis on the Atlantic sector

Marine Chemistry ◽

10.1016/s0304-4203(09)90004-4 ◽

1991 ◽

Vol 35 (1-4) ◽

pp. 1-7 ◽

Cited By ~ 4

Author(s):

Worth D. Nowlin

Keyword(s):

Southern Ocean ◽

Mass Exchange ◽

Water Mass ◽

World Ocean ◽

Atlantic Sector ◽

The World ◽

Water Mass Exchange

Download Full-text

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

10.5194/egusphere-egu2020-1353 ◽

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

Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO2 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 &#948;13C 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 &#948;13C 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.

Download Full-text