GLORIA

GEOMAR Library Ocean Research Information Access

X
feed icon rss

Your email was sent successfully. Check your inbox.

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

Proceed reservation?

Export
Filter
  • AGU (American Geophysical Union)  (10)
  • 2005-2009  (10)
Document type
Publisher
Years
Year
  • 1
    facet.materialart.
    Unknown
    Uptake and spreading of anthropogenic trace gases in a eddy-permitting model of the Atlantic Ocean (2007)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 112 . C09017.
    Details
    Publication Date: 2018-04-19
    Description: An eddy-permitting circulation model of the Atlantic Ocean was used to study the effect of mesoscale processes on the uptake and spreading of anthropogenic CO2 and CFC-11. A comparison with a coarser-resolution model version shows anthropogenic tracer distributions with qualitatively similar patterns, but much more structure (e.g., stronger longitudinal gradients) in the eddy-permitting model, improving the agreement with observations. The better representation of the formation of water masses such as subpolar-mode water in the eddy-permitting model has an influence on the distribution of anthropogenic CO2 over density classes, but no influence on the total inventory taken up. In the subpolar Atlantic, the air-sea flux of CFC-11 is dominated by deep-water formation, while the air-sea flux of anthropogenic CO2 extends over a larger part of the subpolar gyre and has a clear association with North Atlantic surface currents. An in-depth analysis of the mechanisms shaping this distribution showed that the entrainment of water from below into the mixed layer determines the structure in the subpolar North Atlantic, whereas the temporal correlation between surface heat fluxes and mixed-layer depth is more important in the subtropical gyre. The northward, integrated heat and anthropogenic CO2 transports in midlatitudes are closely correlated on seasonal to interannual timescales. This has implications for using the ongoing monitoring arrays of the thermohaline circulation for estimation of the transport of anthropogenic CO2.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2006JC003966
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
    facet.materialart.
    Unknown
    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
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
    facet.materialart.
    Unknown
    Signal propagation related to the North Atlantic Overturning (2005)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 32 . L09602.
    Details
    Publication Date: 2018-03-28
    Description: Changes of the meridional overturning circulation (MOC) due to surface heat flux variability related to the North Atlantic Oscillation (NAO) are analyzed in various ocean models, i.e., eddying and non‐eddying cases. A prime signature of the forcing is variability of the winter‐time convection in the Labrador Sea. The associated changes in the strength of the MOC near the subpolar front (45°N) are closely related to the NAO‐index, leading MOC anomalies by about 2–3 years in both the eddying and non‐eddying simulation. Further south the speed of the meridional signal propagation depends on model resolution. With lower resolution (non‐eddying case, 4/3° resolution) the MOC signal propagates equatorward with a mean speed of about 0.6 cm/s, similar as spreading rates of passive tracer anomalies. Eddy‐permitting experiments (1/3°) show a significantly faster propagation, with speeds corresponding to boundary waves, thus leading to an almost in‐phase variation of the MOC transport over the subtropical to subpolar North Atlantic.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2004GL021002
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
    facet.materialart.
    Unknown
    Decadal to Multidecadal Variability of the Atlantic MOC: Mechanisms and Predictability (2007)
    AGU (American Geophysical Union)
    In:  In: Ocean Circulation: Mechanisms and Impacts - Past and Future Changes of the Ocean's Meridional Overturning. , ed. by Schmittner, A., Chiang, J. and Hemming, S. AGU Monograph, 173 . AGU (American Geophysical Union), Washington D.C., pp. 149-166. ISBN 978-0-87590-438-2
    Details
    Publication Date: 2020-07-28
    Description: The dynamics and predictability of the decadal to multidecadal Atlantic merid­ional overturning circulation (MOC) variability are described from observations and models. The investigation focuses on two modes that involve the MOC: One mode exhibits a quasi-decadal period, while the other is multidecadal. The two modes have completely different underlying dynamics, which is reflected in their rather different spatial characteristics. While the quasi-decadal mode represents a damped mode of the coupled ocean-atmosphere system, the multidecadal mode can be basically understood as the MOC response to the multidecadal forcing by the North Atlantic Oscillation (NAO). "Perfect model" predictability studies indicate a rather high predictability potential of the MOC variability on decadal timescales. Variations of the MOC are associated with variations in the meridional heat trans­port that drive sea surface temperature (SST) anomalies. SST anomalies in the North Atlantic thus exhibit a similar decadal predictability potential as the MOC. The decadal predictability carries over to the atmosphere. The probability density function of European surface air temperature anomalies, for instance, changes sig­nificantly with the state of the MOC. A reconstruction of the MOC for the 20th cen­tury from observed SSTs shows considerable variability on decadal timescales, but no strong sustained long-term trend. Furthermore, an assessment of the observed hydrographical changes in the Nordic Seas, with the aid of ocean general circula­tion model experiments and the analysis of recent scenario integrations with global climate models, indicates that the expected anthropogenic weakening of the MOC may not exceed the level of the internal variability within the next decades.
    Type: Book chapter , NonPeerReviewed
    Format: text
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Book chapter
  • 5
    facet.materialart.
    Unknown
    Decadal variability of subpolar gyre transport and its reveberation in the North Atlantic overturning. (2006)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 33 (L21S01).
    Details
    Publication Date: 2018-02-19
    Description: Analyses of sea surface height (SSH) records based on satellite altimeter data and hydrographic properties have suggested a considerable weakening of the North Atlantic subpolar gyre during the 1990s. Here we report hindcast simulations with high-resolution ocean circulation models that demonstrate a close correspondence of the SSH changes with the volume transport of the boundary current system in the Labrador Sea. The 1990s-decline, of about 15% of the long-term mean, appears as part of a decadal variability of the gyre transport driven by changes in both heat flux and wind stress associated with the North Atlantic Oscillation (NAO). The changes in the subpolar gyre, as manifested in the deep western boundary current off Labrador, reverberate in the strength of the meridional overturning circulation (MOC) in the subtropical North Atlantic, suggesting the potential of a subpolar transport index as an element of a MOC monitoring system.
    Type: Article , PeerReviewed
    DOI: 10.1029/2006GL026906
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
    facet.materialart.
    Unknown
    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
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
    facet.materialart.
    Unknown
    Seasonal and interannual variations of upper ocean heat balance off the west coast of Australia (2008)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 113 . C12025.
    Details
    Publication Date: 2019-09-23
    Description: The Leeuwin Current, a warm, poleward flowing eastern boundary current, dominates the surface circulation off the west coast of Australia and has profound influence on regional marine ecosystem and fisheries recruitment. In this study, the seasonal and interannual variations of upper ocean heat balance in the Leeuwin Current region are analyzed by using an eddy-resolving numerical model simulation, as a first step to quantify the climate impacts on regional ocean thermodynamics and marine ecosystem. The volume transport and heat advection of the Leeuwin Current are stronger during the austral winter on the seasonal cycle and are stronger during a La Nina event on the interannual scale. On both seasonal and interannual timescales, the mixed layer heat budget off the west coast of Australia is predominantly balanced between the variations of the Leeuwin Current heat advection and heat flux across the air-sea interface. On the interannual timescale, the variation of the Leeuwin Current heat advection tends to lead that of the air-sea (latent) heat flux by two months, which is likely a reflection of advection timescales of the Leeuwin Current and its eddy field. The interannual variation of the average February–April sea surface temperature off the west coast of Australia, which is crucial for the larval settlement of western rock lobster, is mostly influenced by the Leeuwin Current heat advection as well as the ocean memory from the previous austral winter, with the air-sea heat exchange playing a buffering role.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008JC004908
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
    facet.materialart.
    Unknown
    Changes of anthropogenic CO〈sub〉2〈/sub〉 and CFCs in the North Atlantic between 1981 and 2004 (2006)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 20 (4). GB4017.
    Details
    Publication Date: 2019-09-23
    Description: We compare total dissolved inorganic carbon (DIC) and chlorofluorocarbon (CFC) measurements in the northwest Atlantic made during the Transient Tracers in the Ocean, North Atlantic Study (TTO‐NAS) in 1981 with modern measurements from a cruise in 2004. The observed changes in the DIC and CFC fields are compared to those predicted from an eddy‐permitting ocean circulation model. The rapid, but time‐variable, atmospheric CFC increase in relation to the relatively steady anthropogenic CO2 increase influences the relationship between the observed uptake of DIC and CFC. We demonstrate the importance of ocean mixing in the calculation of anthropogenic CO2 (Cant) based on transient tracer data by comparing our observations to a “no‐mixing” scenario. We further find that the Cant is in transient steady state in the North Atlantic; that is, the Cant concentration increases proportionally over time through the whole water column in a manner that is directly related to the time‐dependent surface concentration.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2006GB002695
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
    facet.materialart.
    Unknown
    Modes of the southern extension of the East Madagascar Current (2009)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 114 . C01005.
    Details
    Publication Date: 2019-09-23
    Description: Data sets from satellite observations and a nested high-resolution model are used to study a source region of the Agulhas Current. Altimeter-derived geostrophic surface currents are averaged over varying periods, providing evidence of the persistence of flow patterns in the extension of the southern branch of the East Madagascar Current (SEMC). South of Madagascar, the SEMC separates into one branch toward the Agulhas Current and into a second branch retroflecting and connecting to the Subtropical Indian Ocean Countercurrent (SICC). Good agreement is found between long-term mean patterns of observational and model dynamic heights. Two basic modes are identified in the SEMC extension, with anticyclonic motion favoring retroflection in the northern Mozambique Basin when the extension is in a southwestward direction and cyclonic motion occurring in the case of the SEMC flowing westward along the southern Madagascar slope. A cross-correlation sequence between model SEMC transports and the modal changes in the extension region displays a correlation at about 1-month lag which agrees with eddy propagation time from the SEMC to the outflow region. Mean model SEMC transports are determined using floats released at 21 degrees S, and the contribution of the SEMC to the SICC is obtained using floats injected at 55 degrees E with the model running backward. Almost half of the SEMC volume transport contributes to the Agulhas system, and about 40% of SICC water originates from the SEMC.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008JC004921
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
    facet.materialart.
    Unknown
    Mesoscale perturbations control inter-ocean exchange south of Africa (2008)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 35 (L20602).
    Details
    Publication Date: 2017-11-08
    Description: The quantification of inter-ocean leakage from the South Indian to the South Atlantic Ocean is an important measure for the role of the Agulhas system in the global thermohaline circulation. To explore the specific role of mesoscale variability (such as Agulhas rings and Mozambique eddies) in this process a high-resolution model (based on NEMO-ORCA) for the Agulhas region has been set up. It is nested into a global coarse-resolution model. The high-resolution nest captures all salient features of the greater Agulhas region, including the upstream perturbations of the Agulhas Current and Natal Pulses along the African coast. A comparison of the inter-ocean exchange in the high-resolution nest with its coarse resolution counterpart reveals that the latter significantly over-estimates the amount of water flowing into the Atlantic Ocean, demonstrating the need to explicitly simulate the mesoscale features. A sensitivity experiment that excludes the upstream perturbations revealed no difference in the amount of inter-ocean exchange. However, the realistic representation of Agulhas rings and their drift path into the South Atlantic depends on the simulation of those upstream perturbations.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: image
    Format: video
    DOI: 10.1029/2008GL035132
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...