Last interglacial sea-level

This looks like an important new paper on interglacial isostatic adjustments, arguing that the global sea-level maximum during the Last (Ipswichian) Interglacial was not as high as many have supposed.  The work is based on detailed measurements across the Bahamas archipelago, and the authors argue that the global sea-level peak was around 1.2m higher that the sea-level of today -- and not in excess of 5m higher, as assumed in many other studies.

Unfortunately the article is behind a paywall -- but if I manage to get hold of a copy I will expand this post.

There is a popular account of the study here:

https://phys.org/news/2021-08-sea-high-thought-landmasses.html

 This is all about very subtle isostatic readjustments, hinge-lines and compensatory movements (forebulges) in the crust -- and the authors seem to be suggesting that the high (around +5m) interglacial traces found in many coastal areas are the result of crustal depressions in adjacent regions -- for example, a raised interglacial sea-level would increase the crustal loading in an ocean basis -- or even in a large lake -- and this might result in compensatory uplift on adjacent landmasses and shorelines.  Variable isostatic rebounds during and after glacial episodes also come into the frame.  These are the effects that David Sugden and I worked on in Greenland and the South Shetland Islands many years ago -- when we were amazed by the sensitivity of coasts to relatively small variations in ice mass over time.

 https://www.pnas.org/content/118/33/e2026839118

Sea-level trends across The Bahamas constrain peak last interglacial ice melt
Blake Dyer, Jacqueline Austermann, William J. D’Andrea, Roger C. Creel, Michael R. Sandstrom, Miranda Cashman, Alessio Rovere, andMaureen E. Raymo

PNAS August 17, 2021 118 (33) e2026839118; https://doi.org/10.1073/pnas.2026839118

Significance

The seas are rising as the planet warms, and reconstructions of past sea level provide critical insight into the sensitivity of ice sheets to warmer temperatures. Past sea level is reconstructed from the geologic record by measuring the elevations of fossilized marine sediments and coral reefs. However, the elevations of these features also record local uplift or subsidence due to the growth and decay of ice sheets since the time of deposition. We compare observations of paleo sea level across the Bahamian archipelago with a range of Earth deformation models to revise estimates of the last interglacial global mean sea level. Our results suggest that polar ice sheets may be less sensitive to high-latitude warming than previously thought.

Abstract

During the last interglacial (LIG) period, global mean sea level (GMSL) was higher than at present, likely driven by greater high-latitude insolation. Past sea-level estimates require elevation measurements and age determination of marine sediments that formed at or near sea level, and those elevations must be corrected for glacial isostatic adjustment (GIA). However, this GIA correction is subject to uncertainties in the GIA model inputs, namely, Earth’s rheology and past ice history, which reduces precision and accuracy in estimates of past GMSL. To better constrain the GIA process, we compare our data and existing LIG sea-level data across the Bahamian archipelago with a suite of 576 GIA model predictions. We calculated weights for each GIA model based on how well the model fits spatial trends in the regional sea-level data and then used the weighted GIA corrections to revise estimates of GMSL during the LIG. During the LIG, we find a 95% probability that global sea level peaked at least 1.2 m higher than today, and it is very unlikely (5% probability) to have exceeded 5.3 m. Estimates increase by up to 30% (decrease by up to 20%) for portions of melt that originate from the Greenland ice sheet (West Antarctic ice sheet). Altogether, this work suggests that LIG GMSL may be lower than previously assumed.