Foraminifera: Indicators of past environment; key to future: A review

Abstract

In the very long history of the Earth, it has undergone through cyclic stage of warming and cooling which are geologically well documented. Foraminifera have emerged as in important tool to not only provide details of past climate and environment but also give an insight to what the future climate and environment holds forth. The morphology of the foraminifer tests along with their oxygen isotope ratio, the proportion of the planktic specimens, species diversity and different shell type ratios are closely related to physico-chemical characteristics of ambient seawater. These characteristics of foraminifera, especially the capacity of equilibrium fractionation of oxygen, are extensively used in paleo-oceanographic studies, specifically paleosea surface temperature and pale salinity estimations based on whole test ICP-MS oxygen isotope analysis of planktic foraminifera. A few species of foraminifera are unique in that their tests' coiling are a function of ocean temperature. Left handed coiled tests live in colder water while right handed coiled tests in warmer water. Paleo-environmental interpretations are made possible by recognizing several kinds of patterns in foraminiferal assemblages. Rise in sea-level and changes in monsoonal rainfall pattern are the significant consequences of warming due to greenhouse effect. Present-day responses of planktic foraminifera to anthropogenic change should provide a "living laboratory" for interpreting past responses that have been recorded in the sediments over geological times-scales. Understanding the drivers of the changes in foraminifer species assemblages, abundances, distributions and shell chemistry should lead to improved reconstructions of past climates. It has been observed that assemblages characterized by high proportions of agglutinated taxa dominate in intertidal marshes whereas those largely made up of porcelaneous species characterize shallow tropical environments. It can be thus concluded that a decrease in temperature in most cases results in size increase. Historical changes in foraminifer abundance have been shown to reflect anthropogenic climate change. Foraminifera are established proxies of past climatic change and, by corollary, should "record" future climate change.