Landscape sensitivity to global warming and signal propagation from source to sink: An integrative study of the PETM in the Southern Pyrenees (Spain)

Sedimentary systems are affected by environmental conditions. Given current global warming, accurate predictions of the sensitivity of Earth surface processes to climate are urgently needed. To do so, the geological record provides various climate events from which we must read the narratives of how surface processes have adjusted.

Here, we take the example of the Paleocene-Eocene Thermal Maximum (PETM, ~ 56 Ma), the Cenozoic's most rapid and intense global warming. This event was caused by a massive release of carbon into the atmosphere, which led to global temperature rises of 5-8°C and hydroclimate disruptions. In turn, increased erosion rates and sediment transport are hypothesized from worldwide observations of siliciclastic progradation in the oceans and coarser sediments recorded in the alluvial plains. We need to quantify the increases in sediment flux and track the propagation of this Qs response signal from mountainous catchments to the oceans.

The PETM is well-recorded in the South Pyrenean Foreland Basin, from alluvial to oceanic depositional environments. These settings allow an integrative study of the response of sedimentary systems to the PETM from source to sink. First, a doubling of the sediment fluxes from the hinterland catchment is calculated from sedimentary volumes deposited and preserved in the Tremp basin, located at the foothill of the Pyrenees. Erosion models indicate that this doubling in sediment flux likely resulted from a doubling of the intensity of extreme rainfall events, with a minor impact from mean annual precipitation rates and temperatures.

The propagation of the hinterland Qs response signal to the alluvial plain is studied from fluvial channels in three localities in the Tremp Basin. The adjustment of the morphology of fluvial channels to the PETM varies from the Claret axial system to the Esplugafreda and Serraduy transverse systems. However, the total channel belt of all three systems widened by a factor of 8 during the PETM global warming. Moreover, paleohydraulic reconstructions indicate a 1.8-fold increase in flood-related bedload sediment flux. Therefore, the Qs signal of coarse sediments is slightly buffered downstream. On the contrary, enhanced channel mobility led to a 3-fold increase in the delivery of fine-grained sediments to the ocean during the warming event (Prieur et al., 2024). Therefore, the propagation of the PETM-related Qs signal along the South Pyrenean sedimentary system was enhanced due to increased dynamics of fluvial systems.

This integrative study shows the global response of a sedimentary system to a climatic perturbation from source to sink. Extreme rainfall events mainly drive the sensitivity of hinterland erosion, and this signal propagates to the alluvial plain and the ocean, implying modifications of the sedimentary systems' morphology and dynamics. Analog quantitative studies focusing on various climate changes worldwide are needed to frame the sensitivity of sedimentary systems to global warming.

This research was funded by the S2S-FUTURE European Marie Skłodowska-Curie ITN (grant agreement No 860383).

Prieur et al. (2024) Fingerprinting enhanced floodplain reworking during the Paleocene-Eocene Thermal Maximum in the Southern Pyrenees (Spain): Implications for channel dynamics and carbon burial. Geology, 52(9), 651-655. doi: 10.1130/G52180.1