Planktic foraminiferal faunal and isotope data from Deep Sea Drilling Project (DSDP) Site 214 reveal a major change in surface water properties in the eastern Indian Ocean, coinciding with the mid-Pleistocene climate transition (MPT). A comparative study of Globigerinoides sacculifer (a surface dwelling, warm water, mixed-layer tropical planktic foraminifer), Globorotalia menardii Complex (a deep dwelling, tropical species group), and Orbulina universa (an intermediate depth warm-water subtropical foraminifer) with the stable isotope record of Globigerinoides ruber suggests a warm, thick mixed layer in the eastern Indian Ocean during approximately 2000 Kyr to approximately 900 Kyr. Since approximately 900 Kyr the surface water mass stratification weakened, and the mixed layer as well as thermocline were shallow. A decrease in the population abundance of Gs. sacculifer, together with a decrease in delta (super 13) C and increase in delta (super 18) O values suggest a continuous cool climate and increased surface productivity over the last approximately 900 Kyr. This coincides with an increased variance in the 400-Kyr component of Earth's eccentricity cycle.