Evidence for a Northern Hemispheric trigger of the 100,000-y glacial cyclicity

Abstract

The causes of the Mid-Pleistocene Transition, the shift from ∼41-ky to 100-ky interglacial–glacial cycles and more intense ice ages, remain intensely debated, as this fundamental change occurred between ∼1,250 and 650 ka without substantial changes in astronomical climate forcings. Recent studies disagree about the relative importance of events and processes in the Northern and Southern Hemispheres, as well as whether the shift occurred gradually over several interglacial–glacial cycles or abruptly at ∼900 ka. We address these issues using a north-to-south reconstruction of the Atlantic arm of the global meridional overturning ocean circulation, a primary means for distributing heat around the globe, using neodymium (Nd) isotopes. Results reveal a period of intense erosion affecting the cratonic shields surrounding the North Atlantic between Marine Isotope Stages (MIS) 27 and 25 (∼980 and 950 ka), reflected by unusually low Nd isotope ratios in deep North Atlantic seawater. This episode preceded a major ocean circulation weakening between MIS 25 and 21 (950 and 860 ka) that coincided with the first ∼100-ky-long interglacial–glacial onset of Northern Hemisphere glaciation at around 2.4 to 2.8 Ma. The data point to a Northern Hemisphere–sourced initiation for the transition, possibly induced through regolith loss and increased exposure of the crystalline bedrock, which would lead to increased friction, enabling larger ice sheets that are characteristic of the 100-ky interglacial–glacial cycles.

North American Glaciations and Pacific Inputs in the Nd and Sr Isotope Pleistocene Record From the Western Arctic Ocean

“…1.5 Ma at P23 and ∼0.2 Ma later at the long‐term U1341B record (earlier in the point data) indicating a renewed increase in glacigenic sedimentary inputs by ∼0.9 Ma. The expansion of North American ice is consistent with a widespread cooling that changed the circulation patterns in the Pacific and North Atlantic (Khélifi & Frank, 2014) and intensified glacial erosion as revealed in increasing seawater 87 Sr/ 86 Sr isotope ratios since ∼1.5 Ma (Figures 3 and 6, blue field; Yehudai et al., 2021). However, ice sheet extent to the Arctic coastline at this time was not likely, given the lack of increase in sand content in P23 that would be indicative of iceberg transport.…”

“…(2014) (gray, see Table S2 in Supporting Information ). Dashed line in the RSL panel—Bering Strait sill depth, −50 m. Yellow field—sandy interval in P23 Unit 2; blue field—seawater 87 Sr/ 86 Sr change (Yehudai et al., 2021); rose line—authigenic εNd shift in the N Atlantic (Yehudai et al., 2021); orange line—onset of detrital Ca input in P23 (Polyak et al., 2013). Extinct benthic fauna range from Polyak et al.…”

“…Hu et al (2012) conclude that collapse of the Atlantic Meridional Overturning Circulation (AMOC) is only possible when the Bering Strait throughflow is absent or strongly reduced. It is tempting to infer that the Bering Strait closure in MIS 22-24 and subsequent prolonged closures (e.g., MIS 16 and 18) contributed to the AMOC collapses that started between MIS 25 and 21 as seen in the South and North Atlantic isotope data (Pena & Goldstein, 2014;Yehudai et al, 2021). This possibility needs to be tested by further paleoclimatic modeling and targeted proxy studies from the AMOC sensitive areas.…”

Biomarker proxy records of Arctic climate change during the Mid-Pleistocene transition from Lake El'gygytgyn (Far East Russia)

“…It could imply that the climate at the study site is not representative of the pan-Arctic region, and indeed, there is considerable spatial variability in climate change across the Arctic (Daniels et al, 2021;Tulenko et al, 2020). Alternatively, it may sug-gest that Arctic cooling was not the critical driver of intensified ice sheet growth, implicating a strong role for the regolith removal hypothesis (Clark and Pollard, 1998;Yehudai et al, 2021) or Southern Hemisphere (i.e., Antarctic) cooling and ice sheet expansion (Ford and Raymo, 2020).…”

Changes in North Atlantic deep-water oxygenation across the Middle Pleistocene Transition

“…2F) ( 47 ). This event is interpreted as a result of extensive weathering and erosion of the North American craton between MIS 27 to 25 (~980 to 950 ka) and the possible transition from terrestrial- to marine-terminating ice sheets in the Northern Hemisphere ( 64 ). MIS 26 also represents the first time the polar front shifted to a zonal position south of Site 980/981 in the Northeast Atlantic (55.5°N, 14.7°W) as inferred from an increase in the percent of the polar planktonic foraminifera Neogloboquadrina pachyderma (percent NPS), a proxy for cold surface temperatures (fig.…”