The Arctic region, with magnificent ice cover on the surface of the Arctic Ocean and adjacent seas, is not only extremely sensitive to but also has strong amplification effects on climate change. Observations during the past decades have documented substantial retreat and thinning of the Arctic sea-ice cover, a process that is accelerating. Its feedback and impact on the global climate has become an important subject of current climate change research. Calcite tests of planktonic foraminifers are major constituents in pelagic sediments, and they provide valuable materials for the reconstruction of past oceanographic conditions. However, research is still sparse in the Arctic sea area because of limited availability of the materials for investigation. Here, we present a study of modern foraminifers from the plankton tow samples taken in the Makarov Basin of the Arctic Ocean during the fourth Arctic expedition of China. We have analyzed ecological information stored in the modern planktonic foraminifers and in their stable isotope signals, and established a relationship between the distribution of the main taxa and the environment. Our main observations are as follows: (1) in the Makarov Basin, the polar species Neogloboquadrina pachyderma (sinistral coiling) dominates the > 150 mu m planktonic foraminiferal assemblages. (2) The planktonic foraminifers live mainly in the upper halocline at a water depth of 50-100 m and less in the depth interval of 100-200 m. (3) Temperature change in the halocline can affect the absolute abundance of planktonic foraminifers and their distribution in the water column. The warmer halocline is more favorable to the development of planktonic foraminifers. (4) A lighter delta O-18 value (2.11 aEuro degrees) of N. pachyderma (sin.) is recorded in the depth interval of 100-200 m, which is likely related to the isotopically light brines separated out during sea ice freezing. The relatively heavy delta O-18 value (1.68 aEuro degrees aEuro"2.68 aEuro degrees, average 2.27 aEuro degrees) in the depth interval of 50-100 m may be influenced by the low salinity water with the relatively heavy delta O-18 value formed during the sea-ice melting in the surface layer.