The marine δ18O record overestimates continental ice volume during Marine Isotope Stage 3

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There is disagreement in the Quaternary research community in how much of the marine δ 18 O signal is driven by change in ice volume. Here, we examine this topic by bringing together empirical and modelling work for Marine Isotope Stage 3 (MIS 3; 57 ka to 29 ka), a time when the marine δ 18 O record indicates moderate continental glaciation and a global mean sea level between −60 m and −90 m. We compile and interpret geological data dating to MIS 3 to constrain the extent of major Northern Hemisphere ice sheets (Eurasian, Laurentide, Cordilleran). Many key data, especially published in the past ~15 years, argue for an ice-free core of the formerly glaciated regions that is inconsistent with inferences from the marine δ 18 O record. We compile results from prior studies of glacial isostatic adjustment to show the volume of ice inferred from the marine δ 18 O record is unable to fit within the plausible footprint of Northern Hemisphere ice sheets during MIS 3. Instead, a global mean sea level between −30 m and − 50 m is inferred from geological constraints and glacial isostatic modelling. Furthermore, limited North American ice volumes during MIS 3 are consistent with most sea-level bounds through that interval. We can find no concrete evidence of large-scale glaciation during MIS 3 that could account for the missing ~30 m of sea-level equivalent during that time, which suggests that changes in the marine δ 18 O record are driven by other variables, including water temperature. This work urges caution regarding the reliance of the marine δ 18 O record as a de facto indicator of continental ice when few geological constraints are available, which underpins many Quaternary studies. • Establishes a footprint of Northern Hemisphere ice sheets during MIS 3. • Geological data suggest an ice-free core of the formerly glaciated regions during MIS 3. • Explores inconsistencies between geological data and the marine δ 18 O record. • Identifies a ~ 30 m discrepancy in sea-level equivalent during MIS 3. • Results suggest rapid glacier growth in response to climate variability.