Potentiality of foraminifera in deciphering paleo-sea levels

Abstract

Recently, the quest for paleo-sea levels during the Holocene became intense because of their use in developing accurate predictive models in connection with the accelerated sea level rise associated with the greenhouse effect. This paper highlights the application of the foraminiferal distributional pattern in marine sediments (with special reference to the Arabian Sea), to decipher information about the paleo-sea level. Different strategies are being followed for different conditions. For example, (1) when the sea level was higher (such records are to be explored on hand), and (2) when the sea level was lower (such records are to be obtained from the sea bottom sediments). These are to be compared with the present. Foraminifera, present in the shell-bearing sediment layer in Goa and Lothal Dockyard at the head of the Gulf of Khambhat (Cambay) are discussed as case-studies of sea level rise. The results indicate the possibility of higher sea level between 4,300 and 6,000 years BP. Similarly, bottom sediments show a lower (60-90 m) sea level around 10,000 years BP. It has been discovered that Tetraclita squamosa (a barnacle) fouling on relict foraminifera provides an additional tool to decipher the paleo shoreline. Morphological variations (like the size) of the planktonic species Orbulina universa d'Orbigny in the sub-surface sediments show high temperature and low salinity (indicating fluctuation in the sea-level) conditions around 8,800, 5,500 and 2,200 years BP. With the help of percentage of planktonic foraminifera in 126 samples from the Arabian Sea a model has been developed. This model provides some paleobathymetric information on the generation of a sea level fluctuation curve