Climate Evolution Through the Onset and Intensification of Northern Hemisphere Glaciation

Abstract

The Pliocene Epoch (∼5.3–2.6 million years ago, Ma) was characterized by a warmer than present climate with smaller Northern Hemisphere ice sheets, and offers an example of a climate system in long‐term equilibrium with current or predicted near‐future atmospheric CO2 concentrations (pCO2). A long‐term trend of ice‐sheet expansion led to more pronounced glacial (cold) stages by the end of the Pliocene (∼2.6 Ma), known as the “intensification of Northern Hemisphere Glaciation” (iNHG). We assessed the spatial and temporal variability of ocean temperatures and ice‐volume indicators through the late Pliocene and early Pleistocene (from 3.3 to 2.4 Ma) to determine the character of this climate transition. We identified asynchronous shifts in long‐term means and the pacing and amplitude of shorter‐term climate variability, between regions and between climate proxies. Early changes in Antarctic glaciation and Southern Hemisphere ocean properties occurred even during the mid‐Piacenzian warm period (∼3.264–3.025 Ma) which has been used as an analog for future warming. Increased climate variability subsequently developed alongside signatures of larger Northern Hemisphere ice sheets (iNHG). Yet, some regions of the ocean felt no impact of iNHG, particularly in lower latitudes. Our analysis has demonstrated the complex, non‐uniform and globally asynchronous nature of climate changes associated with the iNHG. Shifting ocean gateways and ocean circulation changes may have pre‐conditioned the later evolution of ice sheets with falling atmospheric pCO2. Further development of high‐resolution, multi‐proxy reconstructions of climate is required so that the full potential of the rich and detailed geological records can be realized.

Biomarker Evidence for an MIS M2 Glacial‐Pluvial in the Mojave Desert Before Warming and Drying in the Late Pliocene

“…Ice sheet modeling (Berends et al., 2019) and glacial deposits (Gao et al., 2012) indicate that a substantial ice sheet was present over the modern‐day Hudson Bay and a smaller ice sheet was in place over the northern Cordillera but did not reach the Pacific coast (Sánchez‐Montes et al., 2020). Although the glacial extent and degree of cooling has been debated, the M2 glaciation is now recognized to be a major glacial, redefined as the onset of Northern Hemisphere Glaciation before the later intensification at the Pleistocene boundary (McClymont et al., 2023). The extensive Laurentide ice sheet (LIS) during MIS M2 likely affected southwest North American climate, as ice cover has been shown to affect both winter and summer hydroclimate there (Bhattacharya et al., 2018; Lora et al., 2017; Oster et al., 2015).…”

Subglacial valleys preserved in the highlands of south and east Greenland record restricted ice extent during past warmer climates

“…Records of ice-rafted debris in the North Atlantic (Bailey et al, 2013;Blake-Mizen et al, 2019;Flesche Kleiven et al, 2002;Jansen et al, 2000) and global ice volume signals extracted from marine oxygen isotope records (Mudelsee & Raymo, 2005) have been used to infer that the gradual transition towards large-scale glaciation in Greenlandreferred to as the 'onset of Northern Hemisphere Glaciation' (McClymont et al, 2023) occurred during the late Pliocene to earliest Pleistocene (ca.…”

“…CC BY 4.0 License. et al, 2002;Lisiecki & Raymo, 2005;McClymont et al, 2023). Interglacial marine sediments and terrestrial material exposed along the northern Greenland coast indicate that periods characterised by boreal forest-tundra conditions and less extensive ice cover persisted (at least intermittently) into the early Pleistocene (Bennike et al, 2010;Feyling-Hanssen et al, 1983;Funder et al, 2001).…”