文摘
Speciation in foraminifera is a function of their ecology and habitat. Thus, their extreme sensitivity and specific responses to specific set of physio-chemical conditions in their environment, has led to their extensive application in palaeoclimatic studies. During the study of Recent benthic foraminiferal distribution on the Ayeyarwaddy Delta Shelf off Myanmar, the occurrence of the species Asterorotalia trispinosa was very conspicuous. Though many previous workers have reported the occurrence of the species A. trispinosa as a major constituent in foraminiferal assemblages from different regions, its ecological significance has never been studied before. The present work on the surface distribution of A. trispinosa species in the study area, establishes its preference for low salinity. The ecological preferences of A. trispinosa make the species a useful proxy for the delineation of wet and dry periods of the past. The downcore variation in the abundances of A. trispinosa, its reproductive behaviour viz. its MPS and stable isotopic values were analysed, in sediments of the core GC-5 collected at 37 m water depth on the delta front. Downcore variations in the abundance and MPS of A. trispinosa indicate two significant climatic conditions in the study area since 1513 AD; a dry climate prior to 1650 AD and warm and wet climate since 1650 to present. They also reveal that since 1650, 3 major freshwater pulses are recorded in the core at ~ 1675, 1750 and 1850 AD. The multi-proxy data also support these findings. This high-resolution palaeoclimatic data representing the past 489 years, may be the Asian signatures of the European Little Ice Age. The present work shows extreme relevance with the interest of workers around the world, trying to understand the dramatic events in global climates over the past 500 years.
