Climate and human-induced variability in Holocene Lower Meuse deposition (the Netherlands) identified from the meta-analysis of radiometric data

Abstract

The meta-analysis of riverine deposition from the Holocene provides critical knowledge on the direction and amplitude of riverine responses to climatic and human perturbations and can help to understand the severity and pacing of future changes. For the Meuse River valley in the Netherlands, a dataset of 340 radiometric dates was compiled, on which a cumulative probability density analysis was carried out to characterize the phasing in clastic and organic deposition throughout the Holocene. The results were compared with established timelines for the geomorphological and cultural changes in the valley and hinterland, and hydroclimatic records in the region and wider North Atlantic climate zone. Wavelet analysis was used to identify persistent periodicities, in an attempt to identify long-term hydroclimatic drivers of the Meuse flooding regime.

The CPDF of clastic deposition reveals limited deposition during the Early Holocene, which we link to the entrenched river setting of that time. Since c. 6 ka BP, the increase in clastic deposition closely followed the trajectory of human impact on land cover. Increased input of clastic material from upland regions led to channel aggradation, which stimulated the formation of floodplain deposits. In the last millennia clastic input increasingly became a limiting factor for the formation of organic deposits, as indicated by their strongly anti-phased correlation.

Increasing human impact during the Late Holocene seems to have created a supercharged setting where particularly during cold climate episodes the flooding regime intensified and sediment fluxes increased. Such hydroclimatic variability manifests as phasing that is superimposed on the general increase in clastic deposition owed to human impact. Although there seems to be a general correspondence between phases of clastic deposition and main drivers of the North Atlantic climate, such as variability in solar activity and the timing of volcanic eruptions, no specific systematic correlations could be established based on CPDF data. Phases of enhanced organics accumulation during the Early Holocene (anti-)correlate significantly with North Atlantic drift-ice occurrence, suggesting a hydroclimatic link between both processes. The presence of multi-centennial-scale periodicities in both organic and clastic deposition during the last four millennia further suggests a persistent climatic driver imprinting on the build-up of the fluvial archive of the Meuse valley.

It is argued that CPDFs are a useful tool to understand hydrological regime changes, particularly to identify phases and episodes of anomalous flooding in relation to the relative importance of climatic and anthropogenic forcings, and the geomorphic modulation of such signals. Such data could be considered as important baseline information for potential future flood regime changes.