TRACER DYNAMICS IN OCEAN SEDIMENTS AND THE DECIPHERING OF PAST CLIMATES

An analysis of tracer dynamics in ocean sediments taking into account the disordered, fractal, character of geological materials is performe d. The complexity of the medium is modeled by augmenting the equation of motion of the tracer through the addition of a stochastic forcing. In the one-dimensional version of the model, it is found both analytic ally and numerically that the dynamics is characterized by a large dis persion of arrival times at a given depth of the sediment as deduced f rom the first passage time probability distribution of the tracer. Mor eover, the trajectories of two initially close tracer particles deviat e at later times according to a power law, thereby raising the questio n of reliability of climatic trends deduced from geological data. Nume rical simulations in a more realistic, two-dimensional setting show th at this uncertainty becomes even more pronounced entailing the formati on of a fractal precipitation front whose width increases with time. T he implications of the results on the interpretation of geological rec ords are discussed.