Role of oceanic fronts in promoting productivity in the Southern Indian Ocean

Abstract

The role of oceanic fronts as highly productive areas are discussed. Using hydrographic data, the mean positions of fronts have been delineated. Surface chlorophyll a data were used to study productivity. From 16 crossings, the mean positions of the Subtropical Front (STF) and the Antarctic Polar Front (APF) in the western region are found to be at 41 degrees 9'S and 50 degrees 43'S, respectively, whereas it is observed that the mean positions of the STF, the Subantarctic Front (SAF), and APF from 20 crossings in the eastern region are at 38 degrees 57'S, 47 degrees 9'S, and 51 degrees 6'S, respectively. As the morphology of the fronts varies in the study area, the area has been divided into two regions, western and eastern. Although all fronts are highly productive in nature, the productivity varies. In the western region, the concentration of chlorophyll a at the STF is comparable with that at the APF, 0.5 and 0.6 mg/m3, respectively. Similarly, in the eastern region, the chlorophyll a concentration at the STF is 0.15 mg/m3 and at the SAF and APF are 0.6 and 0.9 mg/m3, respectively. The incidence of high chlorophyll a values at the frontal zones has been discussed, and it is observed that among the different factors affecting the biota stability plays a major role.