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1. Fram Strait

2. GSR Greenland Scotland Ridge

3. OSNAP Overturning in the Subpolar North Atlantic Program

4. NOAC North Atlantic Changes

5. RAPID-MOCHA-WBTS Rapid Climate Change Meridional Overturning Circulation Heat-flux Array Western Boundary Time Series

6. MOVE Meridional Overturning Variability Experiment

7. 11°S

8. SAMBA-SAMOC South Atlantic Meridional Overturning Circulation

 

11°S

11S
Contributing institutes GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
Representatives Peter Brandt, pbrandt@geomar.de
Data Representative Rebecca Hummels, rhummels@geomar.de

Scientific rationale for the TMA:

The transport mooring array at 11°S at the western boundary off Brazil captures the northward flow of warm and intermediate waters within the North Brazil Under Current (NBUC), the northward flow of Antarctic Bottom Water and the southward flow of North Atlantic Deep Water (NADW) within the Deep Western Boundary current (DWBC). The work is based on shipboard hydrographic and current observations along two zonal sections at about 5°S and 11°S as well as an array of four tall moorings on the Brazilian shelf at 11°S recording velocity with four ADCPs and additional current meters (see Fig.) as well as temperature and salinity with MicroCat sensors. The transport variability of the different branches of the western boundary current system especially the NBUC and DWBC on seasonal to decadal time scales is analyzed with respect to changes of the Atlantic meridional overturning circulation (AMOC) and/or the subtropical cell (STC).

The transport mooring array at 11°S at the eastern boundary off Angola aims at capturing the strength and variability of the Angola Current hugging the continental shelf. Ship-based hydrographic and velocity sections and the two ADCP moorings along 11°S are used to analyze the transport variability of the Angola current on intraseasonal to interannual timescales. The assessed variability at the eastern boundary is then put into context with the variability in the remote equatorial region especially focusing on the propagation of equatorial and coastally trapped waves as well as the occurrence of interannual phenomena as Benguela Nino events.

a)
Figure 1a

c)
Figure 1c
b)
Figure 1b

d)

Figure 1d


 
 

Figure 1: (a) Sketch of the circulation in the western tropical Atlantic. Schematic representation of mean currents and eddy generation at the western boundary with warm water pathways in red and cold, deep pathways in blue. Black bar and dotted black line at 11°S indicate positions of the measurement program. Current branches indicated are the south equatorial current (SEC), the north Brazil current (NBC), the north Brazil undercurrent (NBUC), the equatorial undercurrent (EUC), the north equatorial undercurrent (NEUC) merged with the north equatorial counter current (NECC) and the DWBC with alternating zonal flows marked at the Equator. Depth contours are also shown (from Dengler et al. 2004). (b) Mooring locations across the shelf with mean alongshore velocity from the 9 shipboard sections. The dashed boxes indicate cross-sections for transport calculations of the north Brazil undercurrent (NBUC) in red and of the deep western Boundary Current (DWBC) in black (update from Hummels et al. 2015). (c) Sketch of the circulation in the eastern tropical Atlantic. Schematic representation of the mean current branches indicating the EUC, the south equatorial undercurrent (SEUC), the south equatorial countercurrent (SECC), the Angola Current (AC) in orange and the Benguela Current (BC). Also indicated is the Angola Benguela Frontal Zone (ABF) in green. The red box is shown as a zoom on the right, where the positions of the moorings are indicated (red square and star). (d) Locations of the ADCP moorings with two snapshots of the alongshore velocity (July 2013 on the left and November 2015 on the right) indicating the high variability of the eastern boundary current system at 11°S, the Angola Current.

Data products: volume transport time series

a)Figure 2a b)Figure 2b

Fig. 2: Time series of volume transport at 11°S. a) The two phases of observations at the western side with NBUC showing the North Brazil Undercurrent, and DWBC showing the Deep Western Boundary Current. b) The eastern boundary current at 11°S, the Angola Current, with the observations starting in 2013.

Transport data in NetCDF can be downloaded here:
West 2000-2004,  West 2013,  East 2013

Western boundary:

Hummels, R., P. Brandt, M. Dengler, J. Fischer, M. Araujo, D. Veleda and J. V. Durgadoo (2015) Interannual to decadal changes in the western boundary circulation in the Atlantic at 11°S, Geophys. Res. Lett., 42, 18, 7615-7622, doi:10.1002/2015GL065254.

Eastern boundary:

Kopte, R., P. Brandt, M. Dengler, P.C.M. Tchipalanga, M. Macuéria, M. Ostrowski (2017) The Angola Current: Flow and hydrographic characteristics as observed at 11°S, J. Geophys. Res., 122, 2, 1177-1189, doi:10.1002/2016JC012374.


The array instrument data are available at:

Western boundary:

kpo_0884: https://doi.pangaea.de/10.1594/PANGAEA.886415
kpo_0885: https://doi.pangaea.de/10.1594/PANGAEA.886416
kpo_0886: https://doi.pangaea.de/10.1594/PANGAEA.886417
kpo_0887: https://doi.pangaea.de/10.1594/PANGAEA.886419
kpo_0888: https://doi.pangaea.de/10.1594/PANGAEA.886420
kpo_0905: https://doi.pangaea.de/10.1594/PANGAEA.886426
kpo_0906: https://doi.pangaea.de/10.1594/PANGAEA.886428
kpo_0929: https://doi.pangaea.de/10.1594/PANGAEA.886430
kpo_0930: https://doi.pangaea.de/10.1594/PANGAEA.886434
kpo_0931: https://doi.pangaea.de/10.1594/PANGAEA.886435
kpo_0958: https://doi.pangaea.de/10.1594/PANGAEA.886448
kpo_0959: https://doi.pangaea.de/10.1594/PANGAEA.886449
kpo_0960: https://doi.pangaea.de/10.1594/PANGAEA.886450
kpo_0961: https://doi.pangaea.de/10.1594/PANGAEA.886451

Eastern boundary:

https://doi.org/10.1594/PANGAEA.870917

And at ftp://ftp.ifremer.fr/ifremer/oceansites/DATA/
and ftp://data.ndbc.noaa.gov/data/oceansites/DATA/ under subdirectory "11S".



Western boundary
Observation Period 2000 - 2004, 2013 - ongoing
Observed quantities Temperature, salinity, velocity
Current funding source / end of funding BMBF RACE II / 2018

Eastern boundary
Observation Period 2013 – ongoing
Observed quantities Velocity
Current funding source / end of funding BMBF SACUS/PREFACE / 2018

Publications

Dengler, M., F. Schott, C. Eden, P. Brandt, J. Fischer, and R. Zantopp (2004), Break-up of the Atlantic deep western boundary current at 8°S. Nature, 432, 1018-1020.

Herrford, J., P. Brandt, and W. Zenk (2017) Property changes of deep and bottom waters in the Western Tropical Atlantic, Deep Sea Research Part I: Oceanographic Research Papers, 124, 103-125.

Hummels, R., P. Brandt, M. Dengler, J. Fischer, M. Araujo, D. Veleda and J. V. Durgadoo (2015) Interannual to decadal changes in the western boundary circulation in the Atlantic at 11°S, Geophys. Res. Lett., 42, 18, 7615-7622, doi:10.1002/2015GL065254.

Kopte, R., P. Brandt, M. Dengler, P.C.M. Tchipalanga, M. Macuéria, M. Ostrowski (2017) The Angola Current: Flow and hydrographic characteristics as observed at 11°S, J. Geophys. Res., 122, 2, 1177-1189, doi:10.1002/2016JC012374.

Kopte, R., P. Brandt, M. Claus, R. J. Greatbatch, and M. Dengler (2017) Role of Equatorial Basin-Mode Resonance for the Seasonal Variability of the Angola Current at 11°S, J. Phys. Oceanogr., resubmitted Sep. 20, 2017.

Schott, F., Brandt, P., Hamann, M., Fischer, J. und Stramma, L. (2002) On the boundary flow off Brazil at 5-10°S and its conncetion to the interior tropical Atlantic. Geophysical Research Letters, 29 (17). DOI 10.1029/2002GL014786.

Schott, F., M. Dengler, R. J. Zantopp, L. Stramma, J. Fischer and P. Brandt (2005), The shallow and deep western boundary circulation of the South Atlantic at 5°-11°S, J. Phys. Oceanogr., 35, 2031-2053.