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  • 1
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    Seasonal Changes in the North Atlantic Subtropical Gyre (1988)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 93 (C7). pp. 8111-8118.
    Details
    Publication Date: 2017-09-26
    Description: The eastern part of the North Atlantic subtropical gyre is found in the region between the Azores and the Cape Verde Islands. A study of the gyre structure in the area east of 35°W between 8°N and 41°N is presented. The geostrophic flow field determined from historical temperature-salinity data sets by objective analysis indicates seasonal variations in shape but no significant changes in the magnitude of volume transports. The eastern part of the gyre has a larger east-west and smaller north-south extension in summer compared with the winter season. The center shifts by about 2° latitude to the south from winter to summer. Long-term temperature time series (6.5 years) from a mooring near the Azores are consistent with these results, showing always a consistent temperature increase at the beginning of the year which is apparently due to the displacement of the northeastern part of the gyre. A comparison between the mean flow fields and fields obtained from individual zonal sections indicates large deviations north and south of the gyre but small deviations within the gyre.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/JC093iC07p08111
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    On the Origin of the Azores Current (1989)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 94 (C5). pp. 6159-6168.
    Details
    Publication Date: 2017-09-26
    Description: The Azores Current, south of the Azores Archipelago, is part of the subtropical North Atlantic gyre. Using an international hydrographic data set, we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the Azores Current in the western basin and seasonal changes in the related flow. Geostrophic currents are obtained by using the method applied by Stramma (1984) in the eastern basin. The Azores Current is found to originate in the area of the Southwest Newfoundland Rise (Figure 10). In winter an almost uniform current connects this region of origin with the Azores Current, while a branching into two current bands is observed in summer, with the southern band forming a marked cyclonic loop. Within the upper 800 m, all of the transport in the northern band and about 70% of the transport in the southern band recirculates in the eastern basin. Additionally, expendable bathythermograph data from the Azores Current region indicate an increase of eddy potential energy from winter to summer.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/JC094iC05p06159
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Energy conversion in the Cape Verde Frontal Zone (1998)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 103 (C10). 21,469-21,479.
    Details
    Publication Date: 2018-04-30
    Description: Mechanical energy terms are calculated from moored current meter data in the Cape Verde Frontal Zone (about 20°N, 25°W) and compared with those derived from a mesoscale model of this frontal region. The model is of the Bleck and Boudra [1981] type with isopycnal coordinates. An initially zonal jet, representing the Canary Current, is allowed to develop under the influence of baroclinic and barotropic instability processes. We find reasonable agreement in magnitudes, somewhat smaller in the model, and similar distributions in the vertical. This leads to the conclusion that the energy transfer terms from the model can be expected to be sufficiently close to reality. Determination of the transfer terms confirms that the energy transfer in the zone is dominated by baroclinic instability processes while barotropic instability is of minor importance. Average baroclinic instability energy transfer terms reach values of 2–3 μW m−3 in the pycnocline. Peak layer mean values are of the order 10 μW m−3. It is shown that the spatial distribution of active transfer regions is closely related to the structure of the transient eddy field in the frontal zone and that strong instability processes are restricted to the pycnocline.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/98JC01887
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Path of the North Atlantic Deep Water in the Brazil Basin (1998)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 103 (C3). pp. 5419-5428.
    Details
    Publication Date: 2018-04-30
    Description: Recent hydrographic sections and high-quality historical data sets are used to determine geostrophic currents at subtropical latitudes in the western basin of the South Atlantic. Levels of no motion are determined from water mass information and a mass balance constraint to obtain the transport field of North Atlantic Deep Water (NADW) in this region. The incoming NADW transport of about 20 Sv from the north at 19 degrees S appears to be balanced by only one third of this transport leaving in the south and two thirds leaving to the east or northeast at the Mid-Atlantic Ridge. A simple model is proposed to determine the cause of the NADW branching. It is shown that potential vorticity preservation in the presence of topographic changes leads to a similar flow pattern as observed, with branching near the Vitoria-Trindade-Ridge and also an eastward turning of the southward western boundary current at about 28 degrees S, the latitude where a balance of planetary vorticity change and stretching can be expected.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/97JC03287
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    On the Variability of Southern Ocean Front Locations Between Southern Brazil and the Antarctic Peninsula (1989)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 94 (C4). pp. 4757-4762.
    Details
    Publication Date: 2019-02-27
    Description: A 4-year expendable bathythermograph data set (1984–1987) from the area between southern Brazil and the Antarctic Peninsula provides information on the interannual variability of front locations. Two boundaries of subtropical water at different depths are identified north and south of the Brazil Current-Falkland (Malvinas) Current confluence zone. The northern Subtropical Front is displaced over a large part of the Argentine Basin from one observational period to the other. The shallow southern Subtropical Front appears fixed to the Falkland Escarpment. The Polar Front and Subantarctic Front locations do not vary much, except for one case where a cold core eddy in the Polar Frontal Zone causes a large northward displacement of the Subantarctic Front.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/JC094iC04p04757
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Meridional transport of dissolved inorganic carbon in the South Atlantic Ocean (1998)
    AGU (American Geophysical Union)
    In:  Global Biogeochemical Cycles, 12 (3). pp. 479-499.
    Details
    Publication Date: 2018-03-15
    Description: The meridional oceanic transports of dissolved inorganic carbon and oxygen were calculated using six transoceanic sections occupied in the South Atlantic between 11 degrees S and 30 degrees S. The total dissolved inorganic carbon (TCO2) data were interpolated onto conductivity-temperature-depth data to obtain a high-resolution data set, and Ekman, depth-dependent and depth-independent components of the transport were estimated. Uncertainties in the depth-independent velocity distribution were reduced using an inverse model. The inorganic carbon transport between 11 degrees S and 30 degrees S was southward, decreased slightly toward the south, and was -2150 +/- 200 kmol s(-1) (-0.81 +/- 0.08 Gt C yr(-1)) at 20 degrees S. This estimate includes the contribution of net mass transport required to balance the salt transport through Bering Strait. Anthropogenic CO2 concentrations were estimated for the sections. The meridional transport of anthropogenic CO2 was northward, increased toward the north, and was 430 kmol s(-1) (0.16 Gt C yr(-1)) at 20 degrees S. The calculations imply net southward inorganic carbon transport of 2580 kmol s(-1) (1 Gt C yr(-1)) during preindustrial times. The slight contemporary convergence of inorganic carbon between 10 degrees S and 30 degrees S is balanced by storage of anthropogenic CO2 and a sea-to-air flux implying little local divergence of the organic carbon transport. During the preindustrial era, there was significant regional convergence of both inorganic carbon and oxygen, consistent with a sea-to-air gas flux driven by warming. The northward transport of anthropogenic CO2 carried by the meridional overturning circulation represents an important source for anthropogenic CO2 currently being stored within the North Atlantic Ocean.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1029/98GB01533
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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