African Hydroclimate During the Early Eocene From the DeepMIP Simulations

Abstract

The early Eocene (∼56–48 Myr ago) is characterized by high CO2 estimates (1,200–2,500 ppmv) and elevated global temperatures (∼10°C–16°C higher than modern). However, the response of the hydrological cycle during the early Eocene is poorly constrained, especially in regions with sparse data coverage (e.g., Africa). Here, we present a study of African hydroclimate during the early Eocene, as simulated by an ensemble of state‐of‐the‐art climate models in the Deep‐time Model Intercomparison Project (DeepMIP). A comparison between the DeepMIP pre‐industrial simulations and modern observations suggests that model biases are model‐ and geographically dependent, however, these biases are reduced in the model ensemble mean. A comparison between the Eocene simulations and the pre‐industrial suggests that there is no obvious wetting or drying trend as the CO2 increases. The results suggest that changes to the land sea mask (relative to modern) in the models may be responsible for the simulated increases in precipitation to the north of Eocene Africa. There is an increase in precipitation over equatorial and West Africa and associated drying over northern Africa as CO2 rises. There are also important dynamical changes, with evidence that anticyclonic low‐level circulation is replaced by increased south‐westerly flow at high CO2 levels. Lastly, a model‐data comparison using newly compiled quantitative climate estimates from paleobotanical proxy data suggests a marginally better fit with the reconstructions at lower levels of CO2.

Global and Zonal‐Mean Hydrological Response to Early Eocene Warmth

“…The new data in the compilation helps to improve geographical coverage in previously data‐poor regions, including central west coast and eastern Africa (e.g., Adeonipekun et al., 2012; Cantrill et al., 2013; Eisawi & Schrank, 2008) (also recently presented in Williams et al. (2022)); the coal and lignite bearing deposits of northeastern India and southern Pakistan (Frederiksen, 1994; Tripathi et al., 2000; Verma et al., 2019); the Tibetan plateau and sedimentary basins of southern China (e.g., Aleksandrova et al., 2015; Su et al., 2020; Xie et al., 2020); and the South American (e.g., Jaramillo et al., 2007; Pardo‐Trujillo et al., 2003; Quattrocchio & Volkheimer, 2000) and North American continent and Caribbean islands (e.g., Graham et al., 2000; Jarzen & Klug, 2010; Smith et al., 2020) (Figure 1; Supporting Information ). Most of these use the NLR approach based on palynological datasets, as plant macrofossils from the late Paleocene—early Eocene low latitudes are more rarely preserved, although some exceptions are known (Herman et al., 2017; Shukla et al., 2014; Wing et al., 2009).…”

“…For a more detailed analysis of regional hydroclimate in the DeepMIP simulations, we refer the reader to Williams et al. (2022) and Reichgelt et al. (2022), for the African and Australian continent, respectively.…”

“…For instance, whereas the 3xCO 2 experiment was performed with 7 out of 8 DeepMIP models, only 3 models (CESM, GFDL, INMCM) were used for the 6× CO 2 experiment, and only CESM ran a 9xCO 2 simulation. For a more detailed analysis of regional hydroclimate in the DeepMIP simulations, we refer the reader to Williams et al (2022) and Reichgelt et al (2022), for the African and Australian continent, respectively. In summary, our results indicate that the models with higher GMST and weaker LTGs are able to better simulate the global and regional scale hydrological cycle (Figure 12).…”