Glacial isostatic adjustment driven by asymmetric ice sheet melt during the Last Interglacial causes multiple local sea-level peaks

Global mean sea-level (GMSL) change during the Last Interglacial (LIG, 129−116 ka) gives perspective on how ice sheets respond to warming. Observations of multiple peaks in LIG relative sea level (RSL) records, combined with an assumption that the Laurentide Ice Sheet (LIS) collapsed prior to the LIG, have been used to infer Greenland and Antarctic ice sheet melt histories as well as oscillations in LIG GMSL. However, evidence for an LIS outburst flood at ca. 125 ka and extensive early-LIG Antarctic melt suggests that Laurentide remnants may have persisted longer into the LIG than typically thought even as Antarctic melt accelerated. Here, we explore the effect of concurrent early-Holocene Laurentide persistence and Antarctic collapse on glacial isostatic adjustment and sea level. In our models, we hold GMSL constant at present levels (i.e., GMSL = 0) from 128 ka to 117 ka by balancing excess Laurentide ice with early-LIG Antarctic melt. We find that due to glacial isostatic adjustment, this synchronous but asymmetric ice change causes multiple RSL peaks, separated by ∼4.2 ± 2.5 m of RSL fall near North America and ∼1.3 ± 0.7 m around the Indian Ocean. This spatial pattern resembles observations. These results show that multiple peaks in LIG RSL could have occurred with asymmetric ice changes between the Northern and Southern Hemisphere that sum to little, if any, change in GMSL. Our work highlights the need for LIG modeling studies to consider that dynamic cryospheric changes can occur even with near-constant GMSL.