Refining Estimates of Polar Ice Volumes during the MIS11 Interglacial Using Sea Level Records from South Africa

Abstract

Peak eustatic sea level (ESL), or minimum ice volume, during the protracted marine isotope stage 11 (MIS11) interglacial at ;420 ka remains a matter of contention. A recent study of high-stand markers of MIS11 age from the tectonically stable southern coast of South Africa estimated a peak ESL of 13 m. The present study refines this estimate by taking into account both the uncertainty in the correction for glacial isostatic adjustment (GIA) and the geographic variability of sea level change following polar ice sheet collapse. In regard to the latter, the authors demonstrate, using gravitationally self-consistent numerical predictions of postglacial sea level change, that rapid melting from any of the three major polar ice sheets (West Antarctic, Greenland, or East Antarctic) will lead to a local sea level rise in southern South Africa that is 15%-20% higher than the eustatic sea level rise associated with the ice sheet collapse. Taking this amplification and a range of possible GIA corrections into account and assuming that the tectonic correction applied in the earlier study is correct, the authors revise downward the estimate of peak ESL during MIS11 to 8-11.5 m.

Sea-level rise due to polar ice-sheet mass loss during past warm periods

“…For example, when corrected for GIA, MIS 11 RSL in the Bermuda and Bahamas regions (~20 m above present) suggests a peak GMSL of only 6-13 m above present (51), a level that would require loss of the GrIS and/or sectors of the AIS. This estimate is consistent with the 8-11.5 m estimate based on paleoshorelines in South Africa that have been corrected for GIA effects and local tectonic motion (52,53). Overall, multiple lines of evidence would seem to agree that GMSL was 6-13 m higher near the end of MIS 11.…”

Disentangling interglacial sea level and global dynamic topography: Analysis of Madagascar

“…Reliable outcrops of MIS 11 are reported at uncorrected heights of 14 ± 2 m around South Africa and of 21.3 ± 1.0 m on Bermuda, which is located within the forebulge of the Laurentide Ice Sheet (Roberts et al, 2012a;Hearty et al, 1999;Olson and Hearty, 2009). Modeling of glacio-isostatic adjustment yields corrected estimates of 6-13 m and 8.0-11.5 m, respectively (Raymo and Mitrovica, 2012;Chen et al, 2014). Since the glacio-isostatic correction for South Africa is probably only a few meters, this observation alone suggests that the upper terrace of northern Madagascar could have been uplifted by at least 10-20 m (Chen et al, 2014).…”

“…Modeling of glacio-isostatic adjustment yields corrected estimates of 6-13 m and 8.0-11.5 m, respectively (Raymo and Mitrovica, 2012;Chen et al, 2014). Since the glacio-isostatic correction for South Africa is probably only a few meters, this observation alone suggests that the upper terrace of northern Madagascar could have been uplifted by at least 10-20 m (Chen et al, 2014). We note in passing that there is a peneplain above the upper terrace at a height of ∼ 50 m, which may represent Middle Pliocene sea level that is reported elsewhere at heights of 30 ± 18 m (Dowsett and Cronin, 1990;Rovere et al, 2014).…”

The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future

“…Sea level estimates for MIS 11 have been debated, with a suggested highstand of ~20 m higher than today (Hearty et al, 1999; McMurtry et al, 2007; Olson & Hearty, 2009; van Hengstum et al, 2009), which would require collapse of the Greenland and WAIS, in addition to significant contributions from the EAIS. This initial estimate was revised downward between 6–13 m after taking into account the influence of GIA (Raymo & Mitrovica, 2012), and refined further to 8–11.5 m (Chen et al, 2014). Raymo and Mitrovica (2012) argued that these revised estimates would require meltwater contributions most of Greenland and West Antarctica but without significant contribution from the EAIS.…”