Geochemical methods to infer landscape response to Quaternary climate change and land use in depositional archives: A review

Abstract

Understanding and quantifying the processes and geochemical cycles associated with catchment erosion, the development of soils and weathering horizons, and terrestrial habitat change beyond the scales of modern observations remain challenging. Such research, however, has become increasingly important to help predict future landscape change in light of increasing land use and rapid global warming. We herein review organic and inorganic geochemical tools applied to depositional archives to better understand various aspects of landscape evolution on geological time scales. We highlight the potentials and limitations of inorganic geochemical analytical methods, such as major element geochemistry, metal and radiogenic isotopes, and in-situ cosmogenic nuclides, as qualitative, semi-quantitative, and quantitative proxies for the transformation of bedrock material via regolith and soils to sediments. We also show how stable isotope geochemistry applied to lacustrine endogenic carbonates can be used to infer rock-water interactions, vegetation change, and soil development in limestone-rich catchments. Proxies focusing on the silicilastic element of sediment formation, transport and deposition are also ideally combined with organic geochemical proxies for vegetation change and soil organic matter evolution in a catchment to gain a comprehensive picture of the Critical Zone's evolution over time. Multi-proxy and multidisciplinary research combining organic and inorganic geochemical techniques from several sedimentary archives in the same catchment have high potential to provide comprehensive information on Quaternary landscape evolution and thus improve the robustness of associated forecasting models.

Catchment vegetation and erosion controlled soil carbon cycling in south-eastern Australia during the last two glacial-interglacial cycles

“…Palaeo-sediment residence times are a measure of catchment erosion, which depends on catchment size and morphology, bedrock geology, chemical weathering, vegetation, and climate Francke et al, 2020a;Thollon et al, 2020). Of these factors, catchment size, morphology, and geology were effectively constant over the time interval investigated herein.…”

“…However, there is little information on the fate of SOC during soil erosion, introducing large uncertainties into national carbon flux estimates, Earth System Models (ESM), and General Circulation Models (GCM, Doetterl et al, 2016;Lugato et al, 2018;Francke et al, 2020a). Reanalysis of national greenhouse gas emissions in Australia, for example, has suggested that not considering cropland soil erosion overestimated the nation's net carbon flux into the atmosphere by 40% (Chappell et al, 2015), explained by SOC lost by erosion and subsequently buried in sedimentary sinks rather than being re-oxidised (Chappell et al, 2015).…”

“…Direct vegetation modelling, which accounts for different pollen production and accumulation processes (e.g. LOVE, REVEALS, Sugita, 2007a;Sugita, 2007b;Trondman et al, 2015;Li et al, 2020) combined with quantitative estimates about catchment erosion, landscape change, and carbon cycling over time are still challenging to obtain (Francke et al, 2020a). Detailed multiproxy studies on erosion, vegetation, climate, and terrestrial-aquatic carbon cycling on geological timescales are one of the few approaches that can investigate these interactions simultaneously.…”

“…2). The conceptual model introduced by DePaolo et al ( 2006) is based on a-recoil induced depletion of the intermediate radioactive nuclide 234 Th from fine-grained detritus in the weathering profile, during transportation, temporary storage, and after final deposition (reviewed in Francke et al, 2020a). Recent research has further substantiated the approach via detailed assessments of uranium mobility before and after final deposition (Martin et al, 2019;Francke et al, 2020b), and by comprehensive statistical analyses of lithologic, weathering, climatic, and morphologic controls on ( 234 U/ 238 U) activity ratios in modern stream sediments (Thollon et al, 2020).…”

Desertification and Degradation Risks vs Poverty: A Key Topic in Mediterranean Europe

“…In the past, LD was considered to be a specific issue of some territories due to particular sequences of natural drivers (Francke et al, 2020;Larrey et al, 2020). LD is generally associated to biophysical conditions (soil characteristics, steep slopes, lack of vegetation cover, (e.g.…”