A new global ice sheet reconstruction for the past 80 000 years

Abstract

The evolution of past global ice sheets is highly uncertain. One example is the missing ice problem during the Last Glacial Maximum (LGM, 26 000-19 000 years before present) – an apparent 8-28 m discrepancy between far-field sea level indicators and modelled sea level from ice sheet reconstructions. In the absence of ice sheet reconstructions, researchers often use marine δ18O proxy records to infer ice volume prior to the LGM. We present a global ice sheet reconstruction for the past 80 000 years, called PaleoMIST 1.0, constructed independently of far-field sea level and δ18O proxy records. Our reconstruction is compatible with LGM far-field sea-level records without requiring extra ice volume, thus solving the missing ice problem. However, for Marine Isotope Stage 3 (57 000-29 000 years before present) - a pre-LGM period - our reconstruction does not match proxy-based sea level reconstructions, indicating the relationship between marine δ18O and sea level may be more complex than assumed.

New Evidence of MIS 3 Relative Sea Level Changes from the Messina Strait, Calabria (Italy)

“…Therefore, we support the contention that a reduction of global ice sheets volumes across the MIS 3, and specifically at the MIS 3.1 and 3.3, is needed. Our results confirm previous evaluations by Pico et al [101] and Gowan et al [98].…”

“…Published global information coupled with new field data from southern Calabria suggest that the quantity of melted ice during MIS 3 could have been underestimated in the global curves [5,6] to the global curves. To note, an agreement exists between predicted sea-level and observed markers with Gowan et al [98] for MIS 5.3, 5.1 and 3.1.…”

“…The uplift rate estimated for Middle-Late Pleistocene terraces supports our reconstruction of the eustatic elevation of the MIS 3.1 deposits. For this estimation, we used the sea level curve of Gowan et al [98] (Figure 7) where the average between PaleoMIST problematic due to the lack of unquestionable sea level markers. Therefore, we choose a conservative approach not adopting a bathymetric correction for Cannitello 1 but an error of ± 10 m. The resulting uplift rate ranges between 1.2 and 1.4 mm/yrs, in agreement with estimation from older terraces.…”

“…PaleoMIST 1.0[98]: this model stems from the combination of simplified 2-Dimensional ice flow modelling and geological data that constrain the ice-sheets boundaries in space and time (2,500 years temporal snapshots). The reconstructed ice sheets margins, once combined with the topography, allow for the calculation of the basal sheat stress that, for a prescribed ice flow law, yields the 2-Dimensional, steady state ice thickness variations within the ice sheets margins.…”

Capturing the Interactions Between Ice Sheets, Sea Level and the Solid Earth on a Range of Timescales: A new "time window" algorithm

“…There is a need to overcome this challenge in order to understand ice sheets and sea-level changes over a wider range of timescales and in greater detail, especially as the spatiotemporal resolution and extent of paleo records improves (e. g., Khan et al, 2019;Rovere et al, 2020;Gowan et al, 2021). Motivations include running simulations over longer time periods in the past (e.g., from the warm mid-Pliocene to the modern), or in higher spatiotemporal resolutions in order to accurately capture rapid paleo ice-sheet variability and sea-level rise events observed in geological records (e.g., Ice Rafted Debris events -Weber et al, 2014;Meltwater Pulse 1A event -Fairbanks, 1989;Deschamps et al, 2012;Brendryen et al, 2019).…”