Summary of Abstract Submission

Abstract Submission No. IO50-04-0035PresentationPoster


Dilmahamod Fehmi*1

1 University of Cape Town , South Africa


The biological variability of the upwelling region of the Seychelles-Chagos Thermocline Ridge (SCTR), both at surface and subsurface levels, is investigated using a coupled biophysical model. Owing to its large spatial distribution and sensitivity to climate variability, the SCTR was studied as three distinct regions namely sub-region 1 (western; 5S-12S, 55E-65E), 2 (central; 5S-12S, 65E-75E) and 3 (eastern; 5S-12S, 75E-90E). Surface and subsurface chlorophyll-a (Chl-a) exhibit completely different response mechanisms in sub-region 3 compared to sub-regions 1 and 2 during El Nio Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) phenomena. During the intense 1997/1998 ENSO-IOD event, the high Chl-a tongue observed in the eastern Indian Oceans basin induce a slight increase in surface concentration in sub-region 3, whose subsurface variability is also substantially less (more) impacted by downwelling (upwelling) Rossby waves generated by El Nio (La Nia) forcing. Wavelet analysis of surface Chl-a (with annual cycle filtered out) revealed a significant 6 month periodicity in sub-regions 1 and 2 but a 5-year signal in sub-region 3, establishing it as more prone to different ENSO/IOD influences, due to its proximity to the eastern Indian Ocean. Subsurface Chl-a in sub-region 3 exhibits a very significant 1 year band, with sub-regions 1 and 2 having a pronounced 6-year and 5-year signals respectively, without any signal filtered out. These analysis show that this sensitive region cannot be investigated as a single homogeneous region due to its large spatial distribution and different response mechanisms to climate modes.