Registration of abrupt climate changes within fluvial systems: insights from numerical modelling experiments

Potential effects of both gradual and abrupt (within 1 ka) climate changes on fluvial longitudinal profile dynamics were explored by means of numerical modelling experiments. A calibrated model version was used to simulate dynamics in the Meuse fluvial system for the last 250 ka. Simulations indicate that climatic control of fluvial dynamics appears most profound in the uplifting upper reaches (above the hinge line). This straightforward relationship between climate change and fluvial response magnitudes diminishes owing to complex-response dynamics and increasing sea-level control as further one migrates downstream. The results for the hinge zone indicate that climatic change events of small magnitude and short duration are progressively 'filtered out'. Despite this threshold effect, long-lasting and intensive stadials and interstadials still have a clear traceable impact on fluvial dynamics in both upper and lower-reaches. The best reach to study direct climate impacts on fluvial dynamics is in the terraces found between the apex and hinge line. Here, terrace stratigraphy can be directly related to climate dynamics including abrupt changes (within 1 ka), Downstream of the hinge line in the subsiding basin, the sediments have a higher preservation potential. However, because of the increasing importance of sea-level control, these sediments can only be indirectly and qualitatively matched to climate change. This wiggle matching can still be a useful correlation tool, but our simulation exercises indicate that the lower-reach record is unsuitable to track and/or reconstruct abrupt (< 1 ka) climate changes on a one-to-one basis. (C) 2001 Elsevier Science B.V. All rights reserved.