Holocene Critical Zone dynamics in an Alpine catchment inferred from a speleothem multiproxy record: disentangling climate and human influences

Eleonora Regattieri,John C Hellstrom,Luca Lanci,Emanuele Costa,Ilaria Isola,Giovanni Zanchetta,Elena Zanella,Andrea Zerboni,Federico Magrì,Russell N Drysdale,Luigi Dallai,Evdokia Tema

doi:10.1038/s41598-019-53583-7

Abstract

Disentangling the effects of climate and human impact on the long-term evolution of the Earth Critical Zone is crucial to understand the array of its potential responses to the ongoing Global Change. This task requires natural archives from which local information about soil and vegetation can be linked directly to climate parameters. Here we present a high-resolution, well-dated, speleothem multiproxy record from the SW Italian Alps, spanning the last ~10,000 years of the present interglacial (Holocene). We correlate magnetic properties and the carbon stable isotope ratio to soil stability and pedogenesis, whereas the oxygen isotope composition is interpreted as primarily related to precipitation amount, modulated at different timescales by changes in precipitation source and seasonality. During the 9.7-2.8 ka period, when anthropic pressure over the catchment was scarce, intervals of enhanced soil erosion are related to climate-driven vegetation contractions and occurred during drier periods. Immediately following the onset of the Iron Age (ca. 2.8 ka), by contrast, periods of enhanced soil erosion coincided with a wetter climate. We propose that the observed changes in the soil response to climate forcing were related to early anthropogenic manipulations of Earth’s surface, which made the ECZ more sensitive to climate oscillations.

Highlights

Disentangling the effects of climate and human impact on the long-term evolution of the Earth Critical Zone is crucial to understand the array of its potential responses to the ongoing Global Change
Speleothems are formed by meteoric water and receive inputs from bedrock, soil, vegetation and the atmosphere[7]. Geochemical properties of these deposits track environmental processes operating at the catchment scale[8], as well as climatic changes acting at the regional scale in response to global or hemispheric climate patterns[9]. Rarely exploited in this sense, speleothems are well suited to reconstruct past soil dynamics and their relationship with climate, allowing us to disentangle the array of potential Earth’s Critical Zone (ECZ) responses to climatic and land use changes
The stable isotope composition can provide information on paleo-precipitation, temperature patterns and/or soil-vegetation dynamics at the surface[7], complementing the surficial processes recorded by the magnetic properties and linking local evolution to climate changes at the regional and extra-regional scale

Summary

Introduction

Human impact on the local ECZ dynamics should have been almost negligible (especially if compared with nearby lowlands), and the arboreal cover over the cave catchment would have limited soil erosion and the transport of detrital material, dampening the influence on soil of centennial-scale precipitation (and temperature) variability, as well as reducing the impact of extreme rain events.

Results

Conclusion