Summary of Abstract Submission

Abstract Submission No. IO50-09-0002PresentationOral


T Lamont*1

1 Oceans & Coastal Research: Department of Environmental Affairs, South Africa


A research cruise was undertaken in a cyclonic eddy located between Madagascar and South Africa. Stations were occupied across the eddy to investigate hydrographic conditions and phytoplankton adaptation. Absorption, HPLC and CHEMTAX analyses were used to characterise phytoplankton communities. There was upliftment of isotherms between 800 m and 200 m in the core of the eddy, but the upper 100 m appeared to be relatively well mixed. Phytoplankton communities at the eddy centre and on the NE boundary were dominated by diatoms and haptophytes at both the surface and deep chlorophyll maximum (DCM), with pelagophytes and prasinophytes being of secondary importance. The waters on the eastern approach to the NE boundary were dominated by haptophytes, although Prochlorococcus, pelagophytes and prasinophytes were present. The SW boundary was also dominated by haptophytes, although prasinophytes, cryptophytes and pelagophytes were also present. Beyond the SW boundary, Prochlorococcus was most prominent together with haptophytes. Absorption characteristics indicated that chlorophyll a and photosynthetic carotenoids absorbed 65-70% of the irradiance at both the surface and DCM across the central and NE boundary sectors of the eddy. Outside the SW boundary, the photosynthetic carotenoid absorption decreased due to increased absorption by the photoprotective carotenoids at the surface and by chlorophyll b at the DCM. Unusually, the similar surface and DCM population structures and absorption characteristics were indicative of well-mixed communities in the upper 100 m of this cyclonic eddy.