The crystal structure and oxygen isotopic composition of ice cores obtained from floes at the end of summer in the eastern Ross Sea, the Amundsen Sea, and the western Bellingshausen Sea were investigated to determine the ice growth processes and conditions that contribute to sea ice development in the eastern Pacific sector of the southern ocean. The isotope data indicate that a moderate amount of snow contributes to the development of the sea ice. However, even the combined use of isotopes and crystal structure analysis does not unambiguously explain the means by which all of the snow is entrained in the ice. Nevertheless, it seems clear that much of the snow is contained in granular snow-ice that results from seawater floodings of floes and the base of the snow cover. The snow cover in the Ross-Amundsen region was as much as 2 m deep and supported by 7- to 8-m-thick floes primarily composed of frazil ice. In the Bellingshausen region the snow cover and the floes were thinner than in the Ross-Amundsen region. The Bellingshausen cores were composed primarily of multiple layers of frazil and congelation ice. In addition, in both regions there were numerous tipped or inclined blocks of congelation ice and layers of rafted nilas in the cores. The data indicate that the sea ice develops by multiple mechanisms in a turbulent environment. ¿ American Geophysical Union 1994