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  • 1
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    Quantification of the inter-ocean exchange of intermediate water masses around southern Africa (2003)
    In:  EPIC3Deep-sea research ii, 50(1), pp. 197-228, ISSN: 0967-0645
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Location Call Number Limitation Availability
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    PAPER (OA)
  • 2
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    An observed 20-year time series of Agulhas leakage (2014)
    Copernicus Publications (EGU)
    In:  Ocean Science, 10 (4). pp. 601-609.
    Details
    Publication Date: 2019-09-23
    Description: We provide a time series of Agulhas leakage anomalies over the last 20-years from satellite altimetry. Until now, measuring the interannual variability of Indo-Atlantic exchange has been the major barrier in the investigation of the dynamics and large scale impact of Agulhas leakage. We compute the difference of transport between the Agulhas Current and Agulhas Return Current, which allows us to deduce Agulhas leakage. The main difficulty is to separate the Agulhas Return Current from the southern limb of the subtropical "supergyre" south of Africa. For this purpose, an algorithm that uses absolute dynamic topography data is developed. The algorithm is applied to a state-of-the-art ocean model. The comparison with a Lagrangian method to measure the leakage allows us to validate the new method. An important result is that it is possible to measure Agulhas leakage in this model using the velocity field along a section that crosses both the Agulhas Current and the Agulhas Return Current. In the model a good correlation is found between measuring leakage using the full depth velocities and using only the surface geostrophic velocities. This allows us to extend the method to along-track absolute dynamic topography from satellites. It is shown that the accuracy of the mean dynamic topography does not allow us to determine the mean leakage but that leakage anomalies can be accurately computed.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.5194/os-10-601-2014
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Relating Agulhas leakage to the Agulhas Current retroflection location (2009)
    Copernicus Publications (EGU)
    In:  Ocean Science, 5 . pp. 511-521.
    Details
    Publication Date: 2016-10-11
    Description: The relation between the Agulhas Current retroflection location and the magnitude of Agulhas leakage, the transport of water from the Indian to the Atlantic Ocean, is investigated in a high-resolution numerical ocean model. Sudden eastward retreats of the Agulhas Current retroflection loop are linearly related to the shedding of Agulhas rings, where larger retreats generate larger rings. Using numerical Lagrangian floats a 37 year time series of the magnitude of Agulhas leakage in the model is constructed. The time series exhibits large amounts of variability, both on weekly and annual time scales. A linear relation is found between the magnitude of Agulhas leakage and the location of the Agulhas Current retroflection, both binned to three month averages. In the relation, a more westward location of the Agulhas Current retroflection corresponds to an increased transport from the Indian Ocean to the Atlantic Ocean. When this relation is used in a linear regression and applied to almost 20 years of altimetry data, it yields a best estimate of the mean magnitude of Agulhas leakage of 13.2 Sv. The early retroflection of 2000, when Agulhas leakage was probably halved, can be identified using the regression.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/os-5-511-2009
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    The Influence of the Agulhas Current on the Adjacent Coastal Ocean: Possible Impacts of Climate Change (1996)
    Elsevier
    In:  Journal of Marine Systems, 7 . pp. 321-336.
    Details
    Publication Date: 2017-06-26
    Description: The dynamics of the coastal ocean along the southeastern coast of Africa is dominated by a strong and intense western boundary current, the Agulhas Current. With a near-uniform, narrow continental shelf and a steep shelf slope that stabilizes this current, the trajectory of the Agulhas exhibits great stability. The only substantial perturbation occurs with the irregular passage of a Natal Pulse, a soliton meander. The initiation of this meander at the Natal Bight is due to a barotropic instability when the intensity of the landward border of the current exceeds a certain threshold value. This may come about with natural fluctuations in the current or with the adsorption of deep-sea eddies onto the current. Under a climate change scenario of altered wind stress curl over the South Indian Ocean it is conceivable that the threshold for the triggering of a Natal Pulse will occur more frequently. This will lead to a situation where the current axis on average lies further offshore. The possible consequences of such a situation on the rainfall of the coast, on the ecology of estuaries and the coastal ocean, and on the socio-economics of the region is discussed.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/0924-7963(95)00010-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    A weaker Agulhas Current leads to more Agulhas leakage (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L03601.
    Details
    Publication Date: 2019-09-23
    Description: Time series of transports in the Agulhas region have been constructed by simulating Lagrangian drifter trajectories in a 1/10 degree two-way nested ocean model. Using these 34 year long time series it is shown that smaller (larger) Agulhas Current transport leads to larger (smaller) Indian-Atlantic inter-ocean exchange. When transport is low, the Agulhas Current detaches farther downstream from the African continental slope. Moreover, the lower inertia suppresses generation of anti-cyclonic vorticity. These two effects cause the Agulhas retroflection to move westward and enhance Agulhas leakage. In the model a 1 Sv decrease in Agulhas Current transport at 32 degrees S results in a 0.7 +/- 0.2 Sv increase in Agulhas leakage
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008GL036614
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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