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Staring KNGMG/NGMSO symposium

Prof. dr. G.J. van der Zwaan

Title

Experiments with fossils and fossil experiments: survival under stress

Abstract

Much of our knowledge of how the Earth functioned in the past is based on fossils, used as proxies to approximate paleoenvironmental processes. Fossils are important carriers of information, through both the skeletons and their paleoecological context. The building material of skeletons contains essential data, for example the isotope composition of carbonate that gives a quantitative estimate of climates in the past. The paleoecological index value of fossils is less precise, but nevertheless often used in reconstructing paleoenvironments.

One would expect that widely accepted reconstructions, as for instance those of the last glacial-interglacial transition, are based on well-established proxies. This is not the case. Many proxies are poorly validated and the knowledge on the paleobiology of the fossils is far too limited. Such reconstructions are further hampered because under conditions of stress organisms often do not survive. Therefore, good index fossils are those of organisms that had a high potential to survive a variety of stress types. That in itself poses an important evolutionary question: how do organisms survive stress? A good example to illustrate this is formed by the foraminifera, a group of unicellular fossils that is widely employed in paleoecology. Foraminifera are protists, which evolved in the Proterozoic and diversified significantly from the Jura onwards. Recent experiments with living planktonic and benthic foraminifera, which are very similar to their ancestral forms and in a sense "living fossils", show that the microbiology of the group is highly complex. Their role in the ecosystem is essential as far as the biogeochemistry is concerned. Benthic foraminifera survive at the aerobe-anaerobe transition and are active at redox boundaries. There, cycling and use of essential compounds are speeded up in the presence of foraminifera; they actively feed on bacteria, which are involved in biogeochemical processes.

The outcome of a number of experiments, among them one in which the role of oxygen in ecosystems is assessed, will be shown. The results will be compared with "experiments performed by nature". As a first example, the large-scale middle/late Miocene change will be discussed. Due to the closure of the Tethys, the Mediterranean became a concentration basin with important implications for the global climate. Foraminiferal patterns can be used to approximate in detail that at a certain stage the complete Mediterranean deep-water ventilation stopped, starting the onset of the salinity crisis already at 7.16 Ma. The ensuing stress is perfectly reflected by the foraminiferal patterns. As a second example, on a much smaller scale, the use of foraminifera to reconstruct the historic evolution of the Adriatic Sea will be pointed out; here, the relative importance of natural variability versus the impact of man resulting in highly polluted and stressful environments, will be discussed.

The group is extremely rich in species and occurs in almost all marine strata. Therefore, foraminifera are employed in industry and research for stratigraphic purposes, but also often used as index fossil in paleoecology. Yet, we know next to nothing of the biology, of the ecological behaviour and thus of the value of foraminifera as proxy.

Curriculum Vitae

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