Oxygen isotope analysis of skeletal remains of planktonic foraminifers is being successfully used to solve paleoclimatic and stratigraphic problems. At middle latitudes, where considerable seasonal variations in environmental conditions of habitat are found, one has to use for analysis shells of an entire complex of planktonic foraminifera rather than those of individual species. At the same time, one must take into account to what average depths correspond obtained results. A study of variations of O18/O16 ratio in ocean water and in shells of recent foraminifera has made it possible to establish the average depth of habitat of their complexes. This depth is equal to about 200 m at middle, subtropical and tropical latitudes and 100-150 m in equatorial regions. These figures are confirmed by results of determination of average habitat depths by other methods.

Supplement to: Nikolaev, Vladimir I; Blyum, Natalia S; Nikolayev, Sergey D (1979): Average depth of habitat of planktonic foraminifera, according to oxygen isotope analysis. Oceanology, 19(6), 712-715