The water masses and volumetry of the southern Agulhas Current region

Valentine, H. R.; Lütjeharms, J. R. E.; Brundrit, G. B.

doi:10.1016/0967-0637(93)90138-s

Cited by 32 publications

(10 citation statements)

References 29 publications

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“…At depth Antarctic Intermediate Water ranges from 2 to 10 o C and 34 to 34.8 psu and lies above North Atlantic Deep water. The mixture between surface and intermediate waters is called Central Water and in the vicinity of the ARC region is typically composed of South East Atlantic and South West Indian waters (Valentine et al, 1993).…”

mentioning

confidence: 99%

Current-eddy interaction in the Agulhas Return Current region from the seismic oceanography perspective

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Wood

et al. 2013

The Journal of the Acoustical Society of America

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Interleaving in the Agulhas Return Current (ARC) frontal region is commonly manifested in the form of thermohaline intrusions, as subtropical and sub-polar water masses of similar density meet. In Jan/Feb 2012, the Naval Research Laboratory and collaborators carried out a field experiment in which seismic and traditional hydrographic observations were acquired to examine frontal zone mixing processes. The high lateral resolution (10 m) of the seismic observations allowed fine-scale lateral tracking of thermal intrusions, which were corroborated with simultaneous XBT casts. Between seismic deployments both salinity and temperature data were acquired via CTD, Underway-CTD and microstructure profiles. This study focuses on analyzing seismic reflection data in a particular E-W transect where the northward flowing ARC interacted with the southward flowing portion of a large anticyclonic eddy. Strong reflectors were most prominent at the edge of a hyperbolic zone formed between the eddy and ARC, where sub-polar waters interacted with waters of sub-tropical origin on either side. Reflectors were shallow within the hyperbolic zone and extended to 1200 m below the ARC. The nature of the observed reflectors will be determined from comparison of seismic reflection and derived ∂T/∂z fields, and XBT and TS profiles from the available hydrographic data.

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confidence: 99%

Current-eddy interaction in the Agulhas Return Current region from the seismic oceanography perspective

Rice

Book

Wood

et al. 2013

The Journal of the Acoustical Society of America

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“…With a combination of observational data and numerical simulations, Bower et al (2000Bower et al ( , 2005 found that the RSOW reached neutral buoyancy at about 400-800 m in the Gulf of Aden with salinity of 37.5. Outside the Gulf of Aden, the RSOW has been observed up to 6000 km away from its source in the Agulhas retroflection region as a water mass with high salinity and low oxygen at intermediate depth (Gordon et al, 1987;Valentine et al, 1993;Beal et al, 2000). It has been observed that the primary spreading pathway of RSOW is along the African continental coast through the Mozambique Channel (Wyrtki, 1973;Beal et al, 2000).…”

Section: Introductionmentioning

confidence: 91%

“…Although the annual transport of RSOW through the Strait of Bab el Mandeb is only 0.36 Sv (Murray and Johns, 1997), its signal is observed in the Indian Ocean up to 6000 km away from its source as a salinity maximum at intermediate depth (Gordon et al, 1987;Valentine et al, 1993;Beal et al, 2000).…”

Section: Rsowmentioning

confidence: 99%

Buoyancy-driven circulation in the Red Sea

Zhai¹

2014

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This thesis explores the buoyancy-driven circulation in the Red Sea, using a combination of observations, as well as numerical modeling and analytical method.The first part of the thesis investigates the formation mechanism and spreading of Red Sea Overflow Water (RSOW) in the Red Sea. The preconditions required for open-ocean convection, which is suggested to be the formation mechanism of RSOW, are examined. The RSOW is identified and tracked as a layer with minimum potential vorticity and maximum chlorofluorocarbon-12. The pathway of the RSOW is also explored using numerical simulation. If diffusivity is not considered, the production rate of the RSOW is estimated to be 0.63 Sv using Walin's method. By comparing this 0.63 Sv to the actual RSOW transport at the Strait of Bab el Mandeb, it is implied that the vertical diffusivity is about The second part of the thesis studies buoyancy-forced circulation in an idealized Red Sea. Buoyancy-loss driven circulation in marginal seas is usually dominated by cyclonic boundary currents on f-plane, as suggested by previous observations and numerical modeling. This thesis suggests that by including β-effect and buoyancy loss that increases linearly with latitude, the resultant mean Red Sea circulation consists of an anticyclonic gyre in the south and a cyclonic gyre in the north. In mid-basin, the northward surface flow crosses from the western boundary to the eastern boundary. The observational support is also reviewed. The mechanism that controls the crossover of boundary currents is further explored using an ad hoc analytical model based on PV dynamics. This ad hoc analytical model successfully predicts the crossover latitude of boundary currents. It suggests that the competition between advection of planetary vorticity and buoyancy-loss related term determines the crossover latitude.The third part of the thesis investigates three mechanisms that might account for eddy generation in the Red Sea, by conducting a series of numerical experiments. The three mechanisms are: i) baroclinic instability; ii) meridional structure of surface buoyancy losses; iii) cross-basin wind fields.

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“…Deep waters are primarily derived from high-salinity, oxygen-rich and nutrient-depleted NADW that is bound above and below by nutrient-rich Upper and Lower Circumpolar Deep Water (CDW) [Gordon et al, 1987]. The contribution of cold, low-salinity Antarctic Bottom Water (AABW) in the Retroflection region is very low [Valentine et al, 1993].…”

Section: Modern Hydrographymentioning

confidence: 99%

“…[7] The hydrography of the upper subsurface water column in the wider Agulhas Current region is defined by Antarctic Intermediate Water (AAIW) and Central Waters that constitute the main contributors to the water mass architecture of the upper 1500 meters water depth [Valentine et al, 1993]. Deep waters are primarily derived from high-salinity, oxygen-rich and nutrient-depleted NADW that is bound above and below by nutrient-rich Upper and Lower Circumpolar Deep Water (CDW) [Gordon et al, 1987].…”

Section: Modern Hydrographymentioning

confidence: 99%

Paleoceanography of the southern Agulhas Plateau during the last 150 ka: Inferences from benthic foraminiferal assemblages and multispecies epifaunal carbon isotopes

et al. 2007

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[1] Benthic foraminiferal assemblages and the carbon isotope composition of the epifaunal benthic foraminifera Epistominella exigua and Fontbotia wuellerstorfi have been investigated along core MD02-2589 located at the southern Agulhas Plateau (41°26.03 0 S, 25°15.30 0 E, 2660 m water depth). This study aims to evaluate changes in the benthic paleoenvironment and its influence on benthic d 13 C with a notable focus on E. exigua, a species associated with phytodetritus deposits and poorly studied in isotope paleoceanographic reconstructions. The benthic foraminiferal assemblages (>63 mm) show large fluctuations in species composition suggesting significant changes in the pattern of ocean surface productivity conceivably related to migrations of the Subtropical Convergence (STC) and Subantarctic Front (SAF). Low to moderate seasonality and relatively higher food supply to the seafloor are indicated during glacial marine isotope stages (MIS) 6, 4, and 2 and during MIS 3, probably associated with the northward migration of the SAF and confluence with the more stationary STC above the southern flank of the Agulhas Plateau. The lowest organic carbon supply to the seafloor is indicated from late MIS 5b to MIS 4 as a consequence of increased influence of the Agulhas Front (AF) and/or weakening of the influence of the STC over the region. Episodic delivery of fresh organic matter, similar to modern conditions at the core location, is indicated during MIS 5c-MIS 5e and at Termination I. Comparison of this paleoenvironmental information with the paired d 13 C records of E. exigua and F. wuellerstorfi suggests that organic carbon offsets d 13 C of E. exigua from ambient bottom water d 13 C DIC , while its d 13 C amplitude, on glacial-interglacial timescales, does not seem affected by changes of organic carbon supply to the seafloor. This suggests that this species calcifies preferentially during the short time span of the year when productivity peaks and phytodetritus is delivered to the seafloor. Therefore E. exigua, while offset from d 13 C DIC , potentially more faithfully records the amplitude of ambient bottom water d 13 C DIC changes than F. wuellerstorfi, notably in settings such as the Southern Ocean that experienced substantial changes through time in the organic carbon supply to the seafloor.Citation: Diz, P., I. R. Hall, R. Zahn, and E. G. Molyneux (2007), Paleoceanography of the southern Agulhas Plateau during the last 150 ka: Inferences from benthic foraminiferal assemblages and multispecies epifaunal carbon isotopes, Paleoceanography, 22, PA4218,

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The water masses and volumetry of the southern Agulhas Current region

Cited by 32 publications

References 29 publications

Current-eddy interaction in the Agulhas Return Current region from the seismic oceanography perspective

Current-eddy interaction in the Agulhas Return Current region from the seismic oceanography perspective

Buoyancy-driven circulation in the Red Sea

Paleoceanography of the southern Agulhas Plateau during the last 150 ka: Inferences from benthic foraminiferal assemblages and multispecies epifaunal carbon isotopes

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