Short biography:
My name is Juliano Ramanantsoa. I come from Madagascar, but I am currently residing in Cape Town, South Africa. I am currently holding a postdoctoral research position at the Department of Oceanography, University of Cape Town.
I have a Master in Applied Oceanology from the University of Toliara in Madagascar, and a Master in Remote Sensing and Signal Treatment from the University of La Reunion, France. I did my PhD at the University of Cape Town in South Africa.
My research focuses on the variability of ocean circulation and its interactions with the continental shelf around Madagascar.
For my current post-doctoral position, my main focus is to investigate the mechanisms of the shelf-circulation around Madagascar, particularly for the south of the island.
Abstract:
Madagascar’s southern coastal marine zone is a region of high biological productivity which supports a wide range of marine ecosystems, including fisheries. This high biological productivity is attributed to the coastal upwelling.
Number of different data sets, such as satellite remote sensing, in-situ observations, and an ocean numerical model was used to characterise the structure, variability and drivers of the coastal upwelling at the south of Madagascar.
The study provides new insights on the seasonal cycle of the coastal upwelling and the drivers dominating this seasonality. Results reveal the presence of two well-defined upwelling cells: Core 1 and Core 2. The cores are characterized by different seasonal variability, different intensities, different upwelled water mass origins, and distinct forcing mechanisms. Core 1 is associated with a dynamical upwelling forced by the detachment of the East Madagascar Current (EMC), which is reinforced by upwelling favourable winds. Core 2 appears to be primarily forced by upwelling favourable winds, but it is also influenced by a poleward eastern boundary flow coming from the Mozambique Channel.
This intrusion of Mozambique Channel warm waters was identified as a coastal surface poleward flow in the south-west of Madagascar: the South-west MAdagascar Coastal Current (SMACC). The SMACC is a relatively shallow (<300 m) and narrow (<100 km wide) warm and salty coastal surface current, which flows along the southwestern coast of Madagascar toward the south, opposite to the dominant winds. The SMACC exhibits a seasonal variability: intense in summer and reduced in winter. It is forced by a strong cyclonic wind stress curl associated with the bending of the trade winds along the southern tip of Madagascar. The SMACC directly influences the coastal upwelling regions south of Madagascar. The intrusion of SMACC’s warm waters could result in asynchronicity seen in the seasonality between upwelling surface signature and upwelling favourable winds.
Core 1 and Core 2 have a different inter-annual variabilities. Core 1 inter-annual variability is a ssociated with East Madagascar Current (EMC) inter-annual changes, while Core 2 is primarily influenced by the South-west MAdagascar Coastal Current (SMACC). The inter-annual variability of EMC is significantly linked with the South Equatorial Current (SEC) bifurcation off Madagascar, while the inter-annual incidence of SMACC is influenced by the inter-annual variation of the wind stress curl. This suggests that the Indian Ocean large-scale circulation has a downstream impact at the coastal upwelling level. It is also found that the contribution from mesoscale eddies (cyclonic and anticyclonic) enhances and/or reduces the volume transport of both currents which induce significant irregularities in their inter-annual modulations.
The inter-annual variation of the upwelling is also linked with global/regional climate oscillation mode, as well as, the Indian Ocean Dipole (IOD) and the El-Ni ̃no Southern Oscillation (ENSO).
Arranged date for the seminar talk: Apr 08, 2019 at 14:15, BCCR Seminar Room 4020