Swift Weathering Response on Floodplains During the Paleocene‐Eocene Thermal Maximum

Abstract

Silicate weathering is thought to increase and offset the rapid, massive input of CO2 into the atmosphere and ocean during the Paleocene‐Eocene Thermal Maximum (PETM), but few nonmarine records have been used to quantify this. We probe changes in silicate weathering intensity by measuring Li isotope ratios of bedrock and ancient floodplain deposits spanning the PETM in the Bighorn Basin, Wyoming (USA). Our results reveal a rapid increase in silicate weathering intensity during the PETM that remained high during at least the initial stage of climate recovery. Additionally, we determine that soils that formed farthest from ancient river channels underwent larger weathering changes than near‐channel soils. Alongside increased temperatures and pCO2, the simplest explanation for this response relates to increased seasonal fluctuations in water table height in the floodplain that promote dissolution and precipitation reactions. These findings newly demonstrate that weathering on floodplains, like mountain hillslopes, responds to climate change.

Strong Coupling Between Carbon Cycle, Climate, and Weathering During the Paleocene‐Eocene Thermal Maximum

“…In the Nanyang Basin, δ 7 Li in both dissolved and clays record significant negative excursions during the PETM, implying remarkable changes in weathering conditions. This observation is consistent with recent δ 7 Li records from marine and floodplain sediments (Pogge von Strandmann et al, 2021;Ramos et al, 2022). The δ 7 Li in modern rivers and riverine suspended materials has a negative relationship with the weathering intensity; the lowest δ 7 Li values correspond to the highest weathering intensity (Dellinger et al, 2015(Dellinger et al, , 2017.…”

“…The result shows that the proportion of Li in solution was almost 2.5 times as great during the peak PETM, compared to pre-PETM (Figure 3e), indicating higher silicate weathering congruency or efficiency during the PETM. The more congruent weathering is possibly linked to increased erosion and/or intensified silicate weathering due to high temperature and enhanced hydrological cycle (Pogge von Strandmann et al, 2021;Ramos et al, 2022).…”

Palynofloral Change Through the Paleocene‐Eocene Thermal Maximum in the Bighorn Basin, Wyoming

“…Changes in fluvial systems and floodplain depositional environments associated with the PETM in the BHB (e.g., Foreman, 2014; Kraus & Riggins, 2007; Kraus et al., 2015; Ramos et al., 2022; Wing et al., 2009) could have altered palynofloral composition by changing the taphonomic processes that intrude between the production of pollen by plants and pollen recovery by acid maceration. We cannot assess the full set of taphonomic processes (e.g., pollen production, dispersal, transport and preservation), but the CCA analysis above (Figure 7) shows that floral composition is less correlated with sediment grain size (related to current energy) and total organic content (related to pollen preservation), than it is with δ 13 C n ‐alkane (related to whether the sample comes from the CIE).…”

Lithospheric Flexure Controls on Geomorphology, Hydrology, and River Chemistry in the Andean Foreland Basin

“…As a result, a significant amount of silicate weathering can occur in lowland basins (e.g., Bouchez et al., 2012; Lupker et al., 2012), especially where the groundwater level is far beneath the surface. Moreover, slow and steady percolation of water in the floodplain weathering zone (Maher & Chamberlain, 2014) and seasonal water table fluctuations may promote dissolution and precipitation reactions (Ramos et al., 2022).…”