IMIS | Flanders Marine Institute
 

Flanders Marine Institute

Platform for marine research

IMIS

Publications | Institutes | Persons | Datasets | Projects | Maps
[ report an error in this record ]basket (0): add | show Printer-friendly version

Long-term observations of the East Madagascar Undercurrent
Ponsoni, L.; Aguiar-Gonzáles, B.; Maas, L.R.M.; van Aken, H.M.; Ridderinkhof, H. (2015). Long-term observations of the East Madagascar Undercurrent. Deep-Sea Res., Part 1, Oceanogr. Res. Pap. 100: 64-78. dx.doi.org/10.1016/j.dsr.2015.02.004
In: Deep-Sea Research, Part I. Oceanographic Research Papers. Elsevier: Oxford. ISSN 0967-0637, more
Peer reviewed article  

Available in  Authors 

Author keywords
    East Madagascar Undercurrent; East Madagascar Current; Indian Ocean; Western boundary current; Bi-monthly variability; Semi-annual variability

Authors  Top 
  • Ponsoni, L., more
  • Aguiar-Gonzáles, B., more
  • Maas, L.R.M., more
  • van Aken, H.M., more
  • Ridderinkhof, H., more

Abstract
    An array of five moorings was deployed at 23°S off eastern Madagascar and maintained for about 2.5 years as part of the “INdian-ATlantic EXchange in present and past climate” (INATEX) experiment. The observations reveal a recurrent equatorward undercurrent (during 692 of 888 days), the East Madagascar Undercurrent (EMUC), flowing below the poleward surface East Madagascar Current (EMC). The average core of the undercurrent was found near the continental slope, at a depth of 1260 m and at an approximate distance of 29 km from the coast, with mean velocities of 6.4 (±4.8) cm s-1. Maximum speeds reach 20 cm s-1. The mean equatorward volume transport is estimated to be 1.33 (±1.41) Sv with maxima up to 6 Sv. The baroclinic/barotropic partitioning of the geostrophic flow shows a persistent equatorward baroclinic velocity in the undercurrent core, which is sometimes inhibited by a stronger poleward barotropic contribution. The wavelet spectrum analysis of the transport time series displays two dominant frequency bands: (i) nearly bi-monthly (46–79 days), previously observed in the surface EMC, and attributed to the forcing of barotropic waves generated in the Mascarene Basin; and (ii) nearly semi-annual (132–187 days), which seems to be related to the semi-annual cycle in the equatorial winds near the Indian Ocean eastern boundary. A historical dataset of temperature–salinity Argo profiles was used to investigate the spatial variability of the thermohaline properties at intermediate levels. Lastly, Argo-derived velocities suggest an undercurrent flowing upstream until approximately 17°S.

All data in IMIS is subject to the VLIZ privacy policy Top | Authors