Palaeoceanography and numerical modelling: the Mediterranean Sea at times of sapropel formation
E. J. Rohling, S. De Rijk, P. G. Myers, K. Haines, 2000. "Palaeoceanography and numerical modelling: the Mediterranean Sea at times of sapropel formation", Climates: Past and Present, Malcolm B. Hart
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Palaeo-circulation concepts based on (micro-)palaeontological records are compared with results of a general circulation model (GCM), in a review of the eastern Mediterranean conditions during sapropel S1 deposition (7–8 ka bp). We discuss two conceptual models, based on proxy data, which integrate bottom water anoxia and high productivity during sapropel formation. One infers a weakened version of the present-day anti-estuarine circulation, whereas the other invokes a reversal of the circulation to an estuarine type. Although both seem reasonable, in view of the available palaeoceanographic proxy data, they imply completely different states of the Mediterranean fresh-water budget. Numerical modelling has been based on three available reconstructions of changes in the west–east salinity gradient compared with present-day conditions (small decrease, intermediate decrease and reversing). The three scenarios give surprisingly similar results. The interface between the surface and intermediate water has shoaled significantly compared with the present, which fuels a deep chlorophyll maximum. All three simulations show stagnant deep waters, which could cause bottom water anoxia. Reversal of circulation is not observed, not even in the reconstruction of most extreme salinity changes. The combined approach of palaeoceanographic and numerical modelling reviewed in this paper shows that modelling provides an indispensable feedback on the viability of the various proxy-based conceptual models.
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The climate of the early Earth was probably very warm and has, in general, reduced since the Archean. However, it now seems that the world is about 0.6°C warmer than it was 100 years ago and estimates of the rate of global warming over the next century range from 0.16°C to 0.35°C per decade. Concurrently, global sea-level is predicted to rise from 2.4 to 10 cm per decade. These rates of change are much faster than those normally associated with the geological record, causing geologists and palaeontologists to reassess their data and their forecasts on rates of future change.
With the current interest in global climatic change and, more specifically, with global warming, it is clear that palaeontologists have valuable information to provide on the impacts of past climatic change. This volume contains papers from an international array of such geologists and palaeontologists, showing how studies of micro- and macrofossils, plant and vertebrate fossils from a range of geological ages have contributed to our understanding of how climate affects both local and more widespread areas. The contributions are arranged in geological order, ranging from the Permo-Carboniferous to the post-glacial recovery of the last 18,000 years, with an emphasis on climate change during the last two million years, particularly in NW Europe.
Climates: Past and Present will be of interest to palaeontologists, geologists and palaeoclimatologists who specialize in climatic reconstructions and any professionals enagaged in research into the geological aspects of climate change.