Proloculus size variation in recent benthic Foraminifera: Implications for paleoclimatic studies

Ratios of dimorphic (microspheric/megalosperic) forms of Foraminifera are affected by temperature and hence are useful in paleoclimatic studies. In some cases, however, it is not possible to distinguish between the dimorphic forms and, therefore, mean proloculus size is useful: a higher ratio means more microspheric forms and thus a lower mean size of the proloculus. To test this possibility, the mean proloculus size of Cavarotalia annectens (Parker & Jones) was measured in 14 surface sediment samples from the near-shore region along the west coast of India (Bombay to Kannyakumari), covering a stretch of 10° latitude. In this region, temperature varies from 27·5 to 29·25°C and salinity from 33·7 to 36·0‰. The results show that mean proloculus size varies from 0·045 to 0·103 mm, and is inversely proportional to temperature ( r = -0·78) and salinity ( r = -0·71) variations. It is proposed, therefore, that this parameter (mean proloculus size of Foraminifera) can be used as an additional tool in paleoclimatic studies.