Abstract. Mixing states of soot-containing aerosol particles are important information for the simulation of climatic effects of black carbon aerosols in the atmosphere. To elucidate the mixing states and morphological features of soot-containing particles in remote ocean areas, we conducted onboard observations over the southern Indian Ocean and the Southern Ocean during the TR/V Umitaka-maru UM-08-09 cruise, which started from Benoa, Indonesia on 1 December 2008 via Cape Town, South Africa and which terminated in Fremantle, Australia on 6 February 2009. The light absorption coefficients of size-segregated particles (