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  • 1
    Electronic Resource
    Electronic Resource
    Acoustic observations of heat content across the Mediterranean Sea (1997)
    [s.l.] : Nature Publishing Group
    Nature 385 (1997), S. 615-617 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Minimal absorption in the ocean allows low-frequency acoustic transmissions over long horizontal distances. Measuring the travel time of the sound then yields large-scale integrals of the (inverse) sound speed, which are tightly related to heat content. The most ambitious application of this ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/385615a0
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    Paper (German National Licenses)
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  • 2
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    Seasonal cycle of mixing and upward nutrient supply in the equatorial Atlantic cold tongue (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-05
    Description: The eastern equatorial Atlantic hosts a productive marine ecosystem that depends on the upward supply of nutrients. The main process that transports nutrients into the surface mixed layer is turbulent mixing induced in the shear zone between the surface mixed layer and the core of the Equatorial Undercurrent (EUC). Here we present experimental data from two trans-Atlantic cruises along the equator as well as moored observations allowing to characterize the seasonal cycle of velocity shear and turbulence. These data in combination with hydrographic data allow the analysis of the seasonal cycle of equatorial mixing and upward nitrate flux. The core of the EUC migrates vertically following an annual cycle. It reaches its shallowest position in boreal spring and its deepest position in boreal fall. The seasonal cycle of the maximum nitrate gradient instead shows a primary upward movement during boreal summer and a secondary upward movement in boreal winter bringing the nitrate gradient into the region of enhanced shear and turbulent mixing. During boreal spring, the nitrate gradient is located below the EUC core that is characterized by a minimum of turbulence. It prevents an upward supply of nitrate into the surface mixed layer and results in low productivity. The dynamic behavior of the shear zone is driven by a resonant equatorial basin mode associated with the east- and westward propagation of equatorial Kelvin and Rossby waves making the seasonal cycle of upward nutrient supply and productivity in the equatorial Atlantic distinct from that in the Pacific Ocean.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 3
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    How can coastal trapped waves and mixing explain the productivity season in the tropical Angolan upwelling system? (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-08-02
    Description: The tropical Angolan upwelling system (tAUS) is a highly productive ecosystem with a distinct seasonal variability with productivity peaking in austral winter. The tAUS is connected to equatorial dynamics via the propagation of equatorial and coastal trapped waves (CTWs). We use hydrographic, ocean turbulence and satellite data to investigate the role of CTWs in controlling the seasonal cycle of productivity in the tAUS. During austral winter associated with the passage of an upwelling CTW, the nitracline is displaced upward by about 50 m. Through this vertical advection nitrate-rich waters passes onto the shelf. Due to the elevated mixing rates on the shelf, this movement of the nitracline results an increased vertical nitrate flux into the ocean mixed layer. Our analysis further shows that interannual variability in the strength of the austral winter net primary production correlates with the amplitude of the seal level anomaly signal of the corresponding upwelling CTW. The signal of sea level depression leads the maximum productivity signal by about 40 days. It is suggested that this time lag arises, among other factors, from the vertical structure of the CTWs arriving in the tAUS. While the sea level anomaly is dominated by the faster low-baroclinic mode CTWs, the displacement of the nitracline is mainly influenced by the slower high-baroclinic mode CTWs that arrive later in the tAUS. Our results highlight the crucial role CTWs play for the productivity in the tAUS. The strong connection between equatorial dynamics and productivity further introduces a possibility for predicting interannual variability.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 4
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    On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the eastern tropical North Atlantic (2015)
    In:  EPIC3Biogeosciences, 12(2), pp. 489-512, ISSN: 1726-4189
    Details
    Publication Date: 2016-12-05
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Do submesoscale frontal processes ventilate the oxygen minimum zone off Peru? (2016)
    In:  EPIC3Geophysical Research Letters, 43(15), pp. 8133-8142, ISSN: 00948276
    Details
    Publication Date: 2016-12-05
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Indications for the Agulhas Return Current from reflections within the water column at the southern South African continental margin (2007)
    In:  EPIC310th SAGA Biennial Meeting and Exhibition, 22-26 Oct, Wild Coast Sun, South Africa.
    Details
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 7
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    Indications for the Agulhas Return Current from reflections within the water column at the southern South African continental margin (2007)
    In:  EPIC310th SAGA Biennial Meeting and Exhibition, 22-26 Oct., 1007, Wild Coast Sun, South Africa.
    Details
    Publication Date: 2019-07-16
    Description: Seismic oceanography comprises a new field within Geophysics where reflections within the water column are investigated. It was shown that those reflections correspond to thin layers with strong vertical temperature gradients. Those reflections hence represent a chance to trace those temperature gradients over large distances.Weak seismic reflections within the water column south of South Africa gave rise to the question whether here traces of the Agulhas Current or Agulhas Retroflection can be observed. A careful reprocessing of the data led to the imaging of fields of reflections pointing towards a 135 km broad and about 1000 m deep reaching well stratified area with strong reflection amplitudes and several weaker reflections extending down to at least 1500 m water depth over the whole area of investigation.To image both the boundaries between the water masses as reflections and the different properties of the long wavelength velocity variations in depth special imaging technigues like prestack depth migration analysis were performed. Further, the temperature gradients from the short wavelength properties as velocity and density contrasts were determind by a two step inversion of acoustic amplitude versus angle analysis to better quantify the variations of the water masses of the Agulhas Current.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 8
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    Indications for the Agulhas Return Current from reflections within the Water column at the southern South African continental margin (2007)
    In:  EPIC310th SAGA Biennial Meeting and Exhibition, 24-26 Oct, 1007, Wild Coast Sun, South Africa.
    Details
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 9
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    Seismic reflections within the water column south of South Africa: indications for the Agulhas Retroflection (2008)
    In:  EPIC3EGU General Assembly 2008, 13. - 18. Apr, Vienna.
    Details
    Publication Date: 2019-07-16
    Description: The gateway south of South Africa allows the exchange of water masses between the Indian/Pacific Oceans (warm surface water masses) and the Atlantic (cold deep and bottom water masses). This heat transfers maintains the global conveyor belt. Hence the South African continental margin represents an important gateway, whose detailed evolution is not yet fully understood. A compilation of the evolution of the oceanic circulation within the South African gateway since the Early Eocene on the basis of seismic reflection data is put forward and discussed. The effect of a proto-AABW can be found in the southern Cape Basin and south of South Africa as early as Early Eocene-Early Oligocene. In the period Early Oligocene-Middle Miocene a current equivalent to AAIW/Agulhas Retroflection leaves its oldest traces identifiable on the eastern Agulhas Plateau. Indications for the Benguela Current can be found in the Cape Basin in Middle Miocene times. With the onset of NADW in the period Middle Miocene-Early Pliocene the branch of AABW flowing through the Agulhas Passage is weakened and finally deflected to the south in Early Pliocene-Holocene times.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 10
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    Seismic reflections within the water column south of South Africa: indications for the Agulhas Retroflection (2008)
    In:  EPIC31st ESF Exploratory Workshop on Seismic Oceanography, Barcelona.-21.11., 19
    Details
    Publication Date: 2019-07-16
    Description: With the publication of Holbrook et al. (2003) the field of seismic oceanography experienced a major momentum. Several authors since then (Nandi et al., 2004; Holbrook and Fer, 2005; Paramo and Holbrook, 2005) could show that those reflections within the water column correspond to thin layers with strong vertical temperature gradients. Those reflections hence represent a chance to trace those temperature gradients over large distances.Weak seismic reflections within the water column south of South Africa gave rise to the question whether here traces of the Agulhas Current or Agulhas Retroflection can be observed. A careful reprocessing of the data led to the imaging of fields of reflections pointing towards a 135 km broad and about 1000 m deep reaching well stratified area with strong reflection amplitudes and several weaker reflections extending down to at least 1500 m water depth over the whole area of investigation.To image both the boundaries between the water masses as reflections and the different properties of the long wavelength velocity variations in depth special imaging technigues like prestack depth migration analysis were performed. Further, the temperature gradients from the short wavelength properties as velocity and density contrasts were determind by a two step inversion of acoustic amplitude versus angle analysis to better quantify the variations of the water masses of the Agulhas Current. References:Holbrook, W.S., and I. Fer, Ocean internal wave spectra inferred from seismic reflection transects, 2005, Geophys. Res. Lett., 32, L15604, doi:10.1029/2005GL023733.Nandi, P., W.S. Holbrook, S. Pearse, P. Paramo, and R.W. Schmitt, 2004, Seismic reflection imaging of Norwegian Sea water mass boundaries, Geophys. Res. Lett., 31, L23311, doi:10.1029/2004GL021325.Páramo, P., and W. S. Holbrook, 2005, Temperature contrasts in the water column inferred from amplitude-versus-offset analysis of acoustic reflections, Geophys. Res. Lett., v. 32, L24611, doi:10.1029/2005GL024533.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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