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

Published and unpublished records of epipelagic calycophoran siphonophores from around southern Africa were examined for zoogeographic structure.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.

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Transformation of an Agulhas eddy near the continental slope

Ocean Science ◽

10.5194/os-6-143-2010 ◽

2010 ◽

Vol 6 (1) ◽

pp. 143-159 ◽

Cited By ~ 15

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.

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Relative timing of precipitation and ocean circulation changes in the western equatorial Atlantic over the last 45 kyr

Climate of the Past ◽

10.5194/cp-14-1315-2018 ◽

2018 ◽

Vol 14 (9) ◽

pp. 1315-1330 ◽

Cited By ~ 6

Author(s):

Claire Waelbroeck ◽

Sylvain Pichat ◽

Evelyn Böhm ◽

Bryan C. Lougheed ◽

Davide Faranda ◽

...

Keyword(s):

Mass Transport ◽

Ocean Circulation ◽

North Atlantic ◽

Wavelet Transforms ◽

Water Mass ◽

Sediment Cores ◽

Equatorial Atlantic ◽

The North ◽

Atmospheric Changes ◽

Circulation Changes

Abstract. Thanks to its optimal location on the northern Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e., Greenland stadials). These rainfall events are recorded in MD09-3257 as peaks in ln(Ti ∕ Ca). New sedimentary Pa ∕ Th data indicate that mid-depth western equatorial water mass transport decreased during all of the Greenland stadials of the last 40 kyr. Using cross-wavelet transforms and spectrogram analysis, we assess the relative phase between the MD09-3257 sedimentary Pa ∕ Th and ln(Ti ∕ Ca) signals. We show that decreased water mass transport between a depth of ∼1300 and 2300 m in the western equatorial Atlantic preceded increased rainfall over the adjacent continent by 120 to 400 yr at Dansgaard–Oeschger (D–O) frequencies, and by 280 to 980 yr at Heinrich-like frequencies. We suggest that the large lead of ocean circulation changes with respect to changes in tropical South American precipitation at Heinrich-like frequencies is related to the effect of a positive feedback involving iceberg discharges in the North Atlantic. In contrast, the absence of widespread ice rafted detrital layers in North Atlantic cores during D–O stadials supports the hypothesis that a feedback such as this was not triggered in the case of D–O stadials, with circulation slowdowns and subsequent changes remaining more limited during D–O stadials than Heinrich stadials.

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Ocean Convection

Fluids ◽

10.3390/fluids6100360 ◽

2021 ◽

Vol 6 (10) ◽

pp. 360

Author(s):

Catherine Vreugdenhil ◽

Bishakhdatta Gayen

Keyword(s):

Climate Change ◽

Ocean Circulation ◽

Mixed Layer ◽

Water Mass ◽

Current Knowledge ◽

Open Ocean ◽

Meridional Overturning Circulation ◽

Ocean Dynamics ◽

Global Circulation Models ◽

Ocean Convection

Ocean convection is a key mechanism that regulates heat uptake, water-mass transformation, CO2 exchange, and nutrient transport with crucial implications for ocean dynamics and climate change. Both cooling to the atmosphere and salinification, from evaporation or sea-ice formation, cause surface waters to become dense and down-well as turbulent convective plumes. The upper mixed layer in the ocean is significantly deepened and sustained by convection. In the tropics and subtropics, night-time cooling is a main driver of mixed layer convection, while in the mid- and high-latitude regions, winter cooling is key to mixed layer convection. Additionally, at higher latitudes, and particularly in the sub-polar North Atlantic Ocean, the extensive surface heat loss during winter drives open-ocean convection that can reach thousands of meters in depth. On the Antarctic continental shelf, polynya convection regulates the formation of dense bottom slope currents. These strong convection events help to drive the immense water-mass transport of the globally-spanning meridional overturning circulation (MOC). However, convection is often highly localised in time and space, making it extremely difficult to accurately measure in field observations. Ocean models such as global circulation models (GCMs) are unable to resolve convection and turbulence and, instead, rely on simple convective parameterizations that result in a poor representation of convective processes and their impact on ocean circulation, air–sea exchange, and ocean biology. In the past few decades there has been markedly more observations, advancements in high-resolution numerical simulations, continued innovation in laboratory experiments and improvement of theory for ocean convection. The impacts of anthropogenic climate change on ocean convection are beginning to be observed, but key questions remain regarding future climate scenarios. Here, we review the current knowledge and future direction of ocean convection arising from sea–surface interactions, with a focus on mixed layer, open-ocean, and polynya convection.

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<i>Brief communication</i> "The 2013 Erebus Glacier tongue calving event"

The Cryosphere Discussions ◽

10.5194/tcd-7-1749-2013 ◽

2013 ◽

Vol 7 (2) ◽

pp. 1749-1760

Author(s):

C. L. Stevens ◽

P. Sirguey ◽

G. H. Leonard ◽

T. G. Haskell

Keyword(s):

Ocean Circulation ◽

Ocean Currents ◽

Mcmurdo Sound ◽

Glacier Tongue ◽

Surface Ocean ◽

Fast Ice

Abstract. The Erebus Glacier Tongue, a~small floating glacier in southern McMurdo Sound, is one of the best-studied ice tongues in Antarctica. Despite this, its calving on the 27 February 2013 (UTC) was around 10 yr earlier than previously predicted. The calving was likely a result of ocean currents and the absence of fast ice. The subsequent trajectory of the newly-created iceberg supports previous descriptions of the surface ocean circulation in southern McMurdo Sound.

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Surface Ocean Circulation and Variability Determined from Satellite Altimetry

The Ocean Surface ◽

10.1007/978-94-015-7717-5_46 ◽

1985 ◽

pp. 345-350 ◽

Cited By ~ 1

Author(s):

Richard Coleman

Keyword(s):

Ocean Circulation ◽

Satellite Altimetry ◽

Surface Ocean

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Taxonomic Review of the perciform fish genus Acanthistius from the east coast of southern Africa, with description of a new species and designation of a neotype for Serranus sebastoides Castelnau, 1861

Zootaxa ◽

10.11646/zootaxa.2352.1.4 ◽

2010 ◽

Vol 2352 (1) ◽

pp. 59 ◽

Cited By ~ 1

Author(s):

PHILLIP C. HEEMSTRA

Keyword(s):

South Africa ◽

New Species ◽

South America ◽

Southern Africa ◽

East Coast ◽

Valid Species ◽

Shallow Waters ◽

Single Specimen ◽

Warm Temperate ◽

A New Species

The genus Acanthistius Gill, 1862 comprises ten putative valid species occurring in shallow warm-temperate waters of the Southern Hemisphere: South America (coasts of Ecuador, Peru, Chile, Brazil, and Argentina) southern Africa (Namibia and South Africa), southern Australia, New Zealand, Lord Howe, Norfolk, Kermadec and Easter, and Sala y Gómez islands. Two species: Acanthistius sebastoides (Castelnau, 1861) and Acanthistius sp are known from shallow waters of the east coast of South Africa (Heemstra and Randall, 1986). The latter taxon, previously known from a brief description of a single specimen, is here described from 23 specimens and named Acanthistius joanae. Acanthistius sebastoides is redescribed from 13 specimens and compared with A. joanae and species of Acanthistius known from South America and Australia. A neotype is designated for Serranus sebastoides Castelnau, 1861, as the two syntypes are apparently lost.

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The marine algae of Hluleka (Transkei) and the warm temperate/sub-tropical transition on the east coast of southern Africa

Helgoländer Meeresuntersuchungen ◽

10.1007/bf02364698 ◽

1987 ◽

Vol 41 (2) ◽

pp. 165-183 ◽

Cited By ~ 23

Author(s):

J. J. Bolton ◽

H. Stegenga

Keyword(s):

Southern Africa ◽

Marine Algae ◽

East Coast ◽

Warm Temperate

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Water-mass formation and potential vorticity balance in an abyssal ocean circulation

Journal of Marine Research ◽

10.1357/002224000321358918 ◽

2000 ◽

Vol 58 (5) ◽

pp. 789-808 ◽

Cited By ~ 26

Author(s):

Jiayan Yang ◽

James F. Price

Keyword(s):

Ocean Circulation ◽

Potential Vorticity ◽

Water Mass ◽

Water Mass Formation ◽

Vorticity Balance ◽

Mass Formation

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Recent density decline in wild-collected subarctic crustose coralline algae reveals climate change signature

Geology ◽

10.1130/g46804.1 ◽

2019 ◽

Vol 48 (3) ◽

pp. 226-230 ◽

Cited By ~ 3

Author(s):

P.T.W. Chan ◽

J. Halfar ◽

W.H. Adey ◽

P.A. Lebednik ◽

R. Steneck ◽

...

Keyword(s):

Structural Integrity ◽

Benthic Communities ◽

Crustose Coralline Alga ◽

Coralline Algae ◽

Co2 Uptake ◽

Strong Correlations ◽

Crustose Coralline Algae ◽

Skeletal Density ◽

Surface Ocean

Abstract Warming surface ocean temperatures combined with the continued diffusion of atmospheric CO2 into seawater have been shown to have detrimental impacts on calcareous marine organisms in tropical and temperate localities. However, greater oceanic CO2 uptake in higher latitudes may present a higher oceanic acidification risk to carbonate organisms residing in Arctic and subarctic habitats. This is especially true for crustose coralline algae that build their skeletons using high-Mg calcite, which is among the least stable and most soluble of the carbonate minerals. Here we present a century-long annually resolved growth, density, and calcification rate record from the crustose coralline alga Clathromorphum nereostratum, a dominant calcifier in Pacific Arctic and subarctic benthic communities. Specimens were collected from the Aleutian Islands, Alaska (USA), a region that has undergone a long-term decline of 0.08 ± 0.01 pH units since the late 19th century. Growth and calcification rates remain relatively stable throughout the record, but skeletal densities have declined substantially since A.D. 1983. Strong correlations to warming sea-surface temperatures indicate that temperature stress may play a significant role in influencing the ability of corallines to calcify. Decreasing algal skeletal density may offset the benefits of continued growth and calcification due to a weakening in structural integrity, which could have detrimental consequences for the diverse reef-like communities associated with algal structures in mid-to-high latitudes.

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