Paleobotanical proxies for early Eocene climates and ecosystems in northern North America from middle to high latitudes

Abstract

Abstract. Early Eocene climates were globally warm, with ice-free conditions at both poles. Early Eocene polar landmasses supported extensive forest ecosystems of a primarily temperate biota but also with abundant thermophilic elements, such as crocodilians, and mesothermic taxodioid conifers and angiosperms. The globally warm early Eocene was punctuated by geologically brief hyperthermals such as the Paleocene–Eocene Thermal Maximum (PETM), culminating in the Early Eocene Climatic Optimum (EECO), during which the range of thermophilic plants such as palms extended into the Arctic. Climate models have struggled to reproduce early Eocene Arctic warm winters and high precipitation, with models invoking a variety of mechanisms, from atmospheric CO2 levels that are unsupported by proxy evidence to the role of an enhanced hydrological cycle, to reproduce winters that experienced no direct solar energy input yet remained wet and above freezing. Here, we provide new estimates of climate and compile existing paleobotanical proxy data for upland and lowland midlatitude sites in British Columbia, Canada, and northern Washington, USA, and from high-latitude lowland sites in Alaska and the Canadian Arctic to compare climatic regimes between the middle and high latitudes of the early Eocene – spanning the PETM to the EECO – in the northern half of North America. In addition, these data are used to reevaluate the latitudinal temperature gradient in North America during the early Eocene and to provide refined biome interpretations of these ancient forests based on climate and physiognomic data.

Palynostratigraphy of the lower Paleogene Margaret Formation at Stenkul Fiord, Ellesmere Island, Nunavut, Canada

“…This study sampled mostly coals, with a few exceptions (n ¼ 7 out of 96 samples), thus limiting potential influence of lithofacies variation on the palynoflora. In the preparations from the 7 mudstone samples, the absence of dinoflagellate cysts and marine algae combined with the presence of leaf mats in several of the mudstone units at Stenkul Fiord (West et al 2019(West et al , 2020 indicate that the mudstone samples were not deposited in offshore environments; instead these rocks are interpreted as being deposited in quiescent fluvio-lacustrine and overbank deposits within a delta-plain (West et al 2019(West et al , 2020. Some sorting from riverine input in the deltaplain environment could have occurred, but would affect mostly delta-front deposits, rather than the quiescent settings where sediments accumulate in overbank and other similar fluvio-lacustrine environments.…”

African Hydroclimate During the Early Eocene From the DeepMIP Simulations

“…For this study, previously established Paleocene‐Eocene (∼41–56 Ma) paleobotanical records from Africa were compiled (see Supporting Information for age ranges for individual sites, Table S1 in Supporting Information ). The distribution of the nearest living relatives (NLR) of these taxa was then analyzed using the bioclimatic analysis approach to find the highest probability precipitation range in which all taxa could co‐occur (e.g., West et al., 2020; Willard et al., 2019).…”

Climate & Ecology in the Rocky Mountain Interior After the Early Eocene Climatic Optimum

“…The early Eocene climatic optimum (EECO) has been invoked as a climate analog for our projected future (e.g., Zhu et al, 2019). This warming during the EECO occurred 53-50 million years ago, with peak warming from 51.5-50.9 Ma; this period consisted of longterm global temperature maxima and high CO 2 levels but was tectonically comparable to today West et al, 2020). From the Paleocene to early Eocene, it has been inferred that much of North America was warm and wet, with extensive temperate forests (Smith et al, 2012;Breedlovestrout et al, 2013;Greenwood et al, 2016;West et al, 2020) up to high latitudes 65 °N (Dillhoff et al, 2013).…”