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  • 2005-2009  (8)
  • 1
    Book
    Book
    The agulhas current : with 187 figures, 8 in colour (2006)
    Berlin : Springer
    Details Availability
    Keywords: Ocean currents ; Oceanography ; Ocean currents ; Oceanography ; Agulhasstrom
    Type of Medium: Book
    Pages: XIII, 329 S. , Ill., graph. Darst., Kt.
    ISBN: 3540423923 , 9783540423928
    URL: http://www.gbv.de/dms/hbz/toc/ht014895534.pdf
    URL: https://swbplus.bsz-bw.de/bsz256170150cov.jpg
    URL: https://swbplus.bsz-bw.de/bsz256170150vlg.htm
    URL: http://www.loc.gov/catdir/enhancements/fy0817/2006926927-t.html
    DDC: 551.4615
    RVK:
    RZ 80414
    Language: English
    Note: Literaturverz. S. [241] - 293
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  • 2
    Online Resource
    Online Resource
    The Conrad Rise as an obstruction to the Antarctic Circumpolar Current (2008)
    Associated volumes
    Details Availability
    In: Geophysical research letters, Hoboken, NJ : Wiley, 1974, 35(2008), 1944-8007
    In: volume:35
    In: year:2008
    In: extent:6
    Description / Table of Contents: The Antarctic Circumpolar Current (ACC) carries water freely around the whole continent of Antarctica, but not without obstructions. Some, such as the Drake Passage, constrict its path, while others, such as mid-ocean ridges, may induce meandering in the current's cores and may cause the genesis of mesoscale turbulence. It has recently been demonstrated that some regions that are only relatively shallow may also have a major effect on the flow patterns of the ACC. This is here shown to be particularly true for the Conrad Rise. Using the trajectories of surface drifters, altimetry and the simulated velocities from a numerical model, we show that the ACC bifurcates at the western side of this Rise. In this process it forms two intense jets at the two meridional extremities of the Rise with a relatively stagnant water body over the Rise itself. Preliminary results from a recent cruise provide compelling support for this portrayal.
    Type of Medium: Online Resource
    Pages: 6 , graph. Darst
    ISSN: 1944-8007
    URL: http://onlinelibrary.wiley.com/doi/10.1029/2008GL035382/epdf
    DOI: 10.1029/2008GL035382
    Language: English
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  • 3
    Online Resource
    Online Resource
    Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies (2009)
    Associated volumes
    Details Availability
    In: Nature, London [u.a.] : Nature Publ. Group, 1869, 462(2009), 7272, Seite 495-498, 1476-4687
    In: volume:462
    In: year:2009
    In: number:7272
    In: pages:495-498
    Description / Table of Contents: The transport of warm and salty Indian Ocean waters into the Atlantic Oceanthe Agulhas leakagehas a crucial role in the global oceanic circulation1 and thus the evolution of future climate. At present these waters provide the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation (MOC)2. There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages3 and model studies4 that the amount of Agulhas leakage and its corresponding effect on the MOC has been subject to substantial change, potentially linked to latitudinal shifts in the Southern Hemisphere westerlies5. A progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing6, but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage. Here we present the results of a highresolution ocean general circulation model7,8 to show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing. The increased leakage has contributed to the observed salinification9 of South Atlantic thermocline waters. Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic, with potential implications for the future evolution of the MOC.
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1476-4687
    DOI: 10.1038/nature08519
    Language: English
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  • 4
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    Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation (2008)
    Nature Publishing Group
    In:  Nature, 456 . pp. 489-492.
    Details
    Publication Date: 2019-09-23
    Description: Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation (MOC)1. Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic2, 3 (RAPID, at latitude 26.5° N, and MOVE, at latitude 16° N) and show strong variability on intraseasonal to interannual timescales. Observational evidence of longer-term changes in MOC transport remains scarce, owing to infrequent sampling of transoceanic sections over past decades4, 5. Inferences based on long-term sea surface temperature records, however, supported by model simulations, suggest a variability with an amplitude of plusminus1.5–3 Sv (1 Sv = 106 m3 s-1) on decadal timescales in the subtropics6. Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic, particularly the renewal rate of Labrador Sea Water7. Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin: dynamic signals originating in the Agulhas leakage region at the southern tip of Africa. These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source. A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/nature07426
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  • 5
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    The Conrad Rise as an obstruction to the Antarctic Circumpolar Current (2008)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 35 (20). L20606.
    Details
    Publication Date: 2017-11-08
    Description: The Antarctic Circumpolar Current (ACC) carries water freely around the whole continent of Antarctica, but not without obstructions. Some, such as the Drake Passage, constrict its path, while others, such as mid-ocean ridges, may induce meandering in the current's cores and may cause the genesis of mesoscale turbulence. It has recently been demonstrated that some regions that are only relatively shallow may also have a major effect on the flow patterns of the ACC. This is here shown to be particularly true for the Conrad Rise. Using the trajectories of surface drifters, altimetry and the simulated velocities from a numerical model, we show that the ACC bifurcates at the western side of this Rise. In this process it forms two intense jets at the two meridional extremities of the Rise with a relatively stagnant water body over the Rise itself. Preliminary results from a recent cruise provide compelling support for this portrayal.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008GL035382
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
    facet.materialart.
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    Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies (2009)
    Nature Publishing Group
    In:  Nature, 462 . pp. 495-498.
    Details
    Publication Date: 2019-09-23
    Description: The transport of warm and salty Indian Ocean waters into the Atlantic Ocean—the Agulhas leakage—has a crucial role in the global oceanic circulation1 and thus the evolution of future climate. At present these waters provide the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation (MOC)2. There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages3 and model studies4 that the amount of Agulhas leakage and its corresponding effect on the MOC has been subject to substantial change, potentially linked to latitudinal shifts in the Southern Hemisphere westerlies5. A progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing6, but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage. Here we present the results of a high-resolution ocean general circulation model7, 8 to show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing. The increased leakage has contributed to the observed salinification9 of South Atlantic thermocline waters. Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic, with potential implications for the future evolution of the MOC.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/nature08519
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
    facet.materialart.
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    Phytoplankton distribution in the Agulhas system from a coupled physical-biological model (2005)
    Elsevier
    In:  Deep Sea Research Part I: Oceanographic Research Papers, 52 (7). pp. 1300-1318.
    Details
    Publication Date: 2016-11-01
    Description: The greater Agulhas Current system has several components with high mesoscale turbulence. The phytoplankton distribution in the southwest Indian Ocean reflects this activity. We have used a regional eddy-permitting, coupled physical–biological model to study the physical–biological interactions and to address the main processes responsible for phytoplankton distribution in three different biogeochemical provinces: the southwest Subtropical Indian Gyre (SWSIG), the subtropical convergence zone (SCZ) and the subantarctic waters (SAW) south of South Africa. The biological model with four compartments (Nitrate–Phytoplankton–Zooplankton–Detritus) adequately reproduces the observed field of chlorophyll a. The phase of the strong modelled seasonality in the SWSIG is opposite to that of the SCZ that forms the southern boundary of the subtropical gyre. Phytoplankton concentrations are governed by the source-minus-sink terms, which are one order of magnitude greater than the dynamical diffusion and advection terms. North of 35°S, in the SWSIG, phytoplankton growth is limited by nutrients supply throughout the year. However, deeper stratification, enhanced cross-frontal transport and higher detritus remineralization explain the simulated higher concentrations of phytoplankton found in winter in the SWSIG. The region between 35° and 40°S constitutes a transition zone between the SCZ and the oligotrophic subtropical province. Horizontal advection is the main process bringing nutrients for phytoplankton growth. The front at 34°S represents a dynamical barrier to an extension further to the north of this advection of nutrients. Within the SCZ, primary production is high during spring and summer. This high productivity depletes the nutrient standing stock built up during winter time. In winter, nutrients supply in the convergence zone is indeed large, but the deep mixing removes phytoplankton from the euphotic zone and inhibits photosynthesis, yielding lower surface chlorophyll a concentrations. Waters south of the Subantarctic Front have a summer biomass close to that of frontal waters and higher than for subtropical waters. However, these simulated concentrations are slightly higher than the observed ones suggesting that limitation by iron and/or silica may play a role
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.dsr.2004.12.008
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  • 8
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    Walter Zenk: a distinguished ocean observer (2005)
    In:  EPIC3Deep-Sea Research II, 52(3), pp. 375-382
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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