ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    facet.materialart.
    In:  [Talk] In: IAPSO Assembly, 28.08.-21.09.2017, Cape Town, South Africa .
    Publication Date: 2017-11-27
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2017-11-27
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2017-11-27
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2019-02-25
    Description: We analyze the contribution of the Agulhas Current on the central water masses of the Benguela upwelling system (BUS) over the last decades in a high-resolution ocean simulation driven by atmospheric reanalysis. The BUS is an Eastern Boundary Upwelling System where upwelling of cold nutrient-rich water favors biomass growth. The two distinct subregions, North and South Benguela, differ in nutrient and oxygen properties of the upwelling water mass. Our analysis indicates that the contribution of Agulhas water to the upwelling is very strong in both subregions. Although the water masses feeding the upwelling have a common origin, their pathways are distinct in both regions. Whereas for the central waters of South Benguela the path is rather direct from where it is formed, the central waters of North Benguela takes a longer route through the equatorial current system. Not only the travel time from the Agulhas Current to the BUS is longer but also the central water mass is twice as old for the northern part when compared to the southern. Our analysis traces the pathways, history, and origin of the central water masses feeding upwelling in the BUS and emphasizes the direct impact of the Agulhas Current on the upwelling region. The variability of that link between the Indian Ocean and the South Atlantic is likely to change the nutrient and oxygen content, as well as temperature and salinity of the water masses in the upwelling region.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    facet.materialart.
    facet.materialart.
    American Meteorological Society
    In:  Journal of Physical Oceanography, 49 (5). pp. 1141-1157.
    Publication Date: 2019-05-02
    Description: To model tracer spreading in the ocean, Lagrangian simulations in an offline framework are a practical and efficient alternative to solving the advective–diffusive tracer equations online. Differences in both approaches raise the question of whether both methods are comparable. Lagrangian simulations usually use model output averaged in time, and trajectories are not subject to parameterized subgrid diffusion, which is included in the advection–diffusion equations of ocean models. Previous studies focused on diffusivity estimates in idealized models but could show that both methods yield similar results as long as the deformations-scale dynamics are resolved and a sufficient amount of Lagrangian particles is used. This study compares spreading of an Eulerian tracer simulated online and a cloud of Lagrangian particles simulated offline with velocities from the same ocean model. We use a global, eddy-resolving ocean model featuring 1/20° horizontal resolution in the Agulhas region around South Africa. Tracer and particles were released at one time step in the Cape Basin and below the mixed layer and integrated for 3 years. Large-scale diagnostics, like mean pathways of floats and tracer, are almost identical and 1D horizontal distributions show no significant differences. Differences in vertical distributions, seen in a reduced vertical spreading and downward displacement of particles, are due to the combined effect of unresolved subdaily variability of the vertical velocities and the spatial variation of vertical diffusivity. This, in turn, has a small impact on the horizontal spreading behavior. The estimates of eddy diffusivity from particles and tracer yield comparable results of about 4000 m2 s−1 in the Cape Basin.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2019-05-10
    Description: The northward flow of the upper limb of the Atlantic Meridional Overturning Circulation (AMOC) is fed by waters entering the South Atlantic from the Indian Ocean mainly via the Agulhas Current (AC) system and by waters entering from the Pacific through Drake Passage (DP), commonly referred to as the “warm” and “cold” water routes, respectively. However, there is no final consensus on the relative importance of these two routes for the upper limb's volume transport and thermohaline properties. In this study we revisited the AC and DP contributions by performing Lagrangian analyses between the two source regions and the North Brazil Current (NBC) at 6∘ S in a realistically forced high-resolution (1∕20∘) ocean model. Our results agree with the prevailing conception that the AC contribution is the major source for the upper limb transport of the AMOC in the tropical South Atlantic. However, they also suggest a non-negligible DP contribution of around 40 %, which is substantially higher than estimates from previous Lagrangian studies with coarser-resolution models but now better matches estimates from Lagrangian observations. Moreover, idealized analyses of decadal changes in the DP and AC contributions indicate that the ongoing increase in Agulhas leakage indeed may have induced an increase in the AC contribution to the upper limb of the AMOC in the tropics, while the DP contribution decreased. In terms of thermohaline properties, our study highlights the fact that the AC and DP contributions cannot be unambiguously distinguished by their temperature, as the commonly adopted terminology may imply, but rather by their salinity when entering the South Atlantic. During their transit towards the NBC the bulk of DP waters experiences a net density loss through a net warming, whereas the bulk of AC waters experiences a slight net density gain through a net increase in salinity. Notably, these density changes are nearly completely captured by Lagrangian particle trajectories that reach the surface mixed layer at least once during their transit, which amount to 66 % and 49 % for DP and AC waters, respectively. This implies that more than half of the water masses supplying the upper limb of the AMOC are actually formed within the South Atlantic and do not get their characteristic properties in the Pacific and Indian Oceans.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    facet.materialart.
    facet.materialart.
    In:  (Bachelor thesis), Christian-Albrechts-Universität, Kiel, Germany, 50 pp
    Publication Date: 2013-12-19
    Description: To investigate the advective propagation of Agulhas Leakage into the Atlantic Ocean this study evaluates results of the hindcast experiment K326 of the global eddy-permitting ocean model ORCA025. Using the software ARIANE a lagrangian analysis of virtual floats is realized that provides information about the pathways and advective timescales of Indian Ocean water entering the Atlantic. In the period from 1965 to 1974 the modeled mean volume transport is 68,6 Sv for the Agulhas Current and 15,1 Sv for Agulhas Leakage. In general floats of the Agulhas leakage are first advected with the South Equatorial Current. Some of them circulate in the subtropical gyre of the southern hemisphere, but most of them do not reach the North Atlantic during the integration period of 86 years. The majority of the floats that end up in the North Atlantic directly follow the North Brasil Current to equatorial latitudes after their advection with the South Equatorial Current. A large portion of Agulhas Leakage reaches the subtropical North Atlantic in about one decade and accounts for the thermohaline circulation in a non-negligible way. On average there are 10 Sv of Agulhas Leakage passing 6° South and 6 Sv passing 26° North. The most likely timescales associated with the advection up to those latitudes are 6 and 14 years respectively. Agulhas Leakage even penetrates far higher latitudes but it takes several more decades for Leakage floats to get there. During their way into the North Atlantic Floats of the Agulhas Leakage are likely to be affected by the intricate zonal equatorial circulation. Moreover there is a high probability for recirculation in the subtropical gyre of the northern hemisphere. The identified advective timescales become especially relevant under consideration of the latest IPCC results. Based on model simulations, that poorly represent the dynamics of Agulhas Leakage, the IPCC states that a weakening of the MOC during the 21. century is most likely. Keeping in mind previous surveys, the current findings support the assumption, that the increased transport of salt into the Atlantic Ocean, linked to an intensification of the Agulhas Leakage in the course of anthropogenic climate change, might have a stabilizing effect on the MOC.
    Keywords: Course of study: BSc Physics of the Earth System
    Type: Thesis , NonPeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    facet.materialart.
    facet.materialart.
    AGU
    In:  Geophysical Research Letters, 40 (15). pp. 3997-4000.
    Publication Date: 2017-06-20
    Description: Current research indicates an increase in Agulhas leakage for the past and coming decades. This change potentially alters the strength of the Atlantic meridional overturning circulation, in particular, through advection of positive density anomalies into the North Atlantic. To explore the fate of Agulhas leakage, results from a Lagrangian analysis were evaluated, with virtual floats advected within an eddy-permitting ocean model (ORCA025). A considerable fraction of Agulhas leakage reached the subtropical North Atlantic: of a mean Agulhas leakage transport of 15.3 Sv entering the South Atlantic, 9.7, 7.7, and 6.1 Sv crossed sections at 6 degrees S, 6 degrees N, and 26 degrees N, respectively. The most probable transit time of leakage to reach the respective latitudes is one to two decades. We suggest that changes in Agulhas leakage could manifest in the Gulf Stream regime most probably within two decades. These results were supported by an eddy-resolving implementation of the ocean model (INALT01)
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    facet.materialart.
    facet.materialart.
    In:  [Talk] In: AGU Ocean Sciences Meeting, 23.-28.2.2014, Honolulu, USA .
    Publication Date: 2014-12-19
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    facet.materialart.
    facet.materialart.
    In:  (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 49 pp
    Publication Date: 2015-01-05
    Keywords: Course of study: MSc Climate Physics
    Type: Thesis , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...