Toward New and Independent Constraints on Global Mean Sea-Level Highstands During the Last Glaciation (Marine Isotope Stage 3, 5a, and 5c)

Estimates of ice volume over the last 120 ka, from marine isotope Stage (MIS) 5d (similar to 110 ka) through MIS 3 (60-26 ka) are uncertain. Weiss et al. (2022, https://doi.org/10.1029/2021PA004361) offer an innovative new constraint on past sea level using the oxygen isotopes (delta O-18) of planktic (surface and thermocline dwelling) foraminifers to infer the salinity of the Sulu Sea in the Indo-Pacific Ocean and assess flow through the Karimata Strait (Indonesia) over the last glaciation. Based on the timing of Karimata Strait flooding, the study concludes that local relative sea level in the Karimata Strait was >-8 +/- 6 m during MIS 5c (similar to 100 ka) and >-12 +/- 6 m during MIS 5a (similar to 80 ka), relative to present. For MIS 3, a maximum possible relative sea level of -16 +/- 6 m is determined. Here, these results are placed into the context of current knowledge of last glacial sea-level change and the implications for climate forcings and feedbacks (e.g., global average surface temperature and greenhouse gases) and ice sheet growth are discussed. By tracing past ocean circulation patterns that are modulated by the depth of shallow straits such as the Karimata Strait, Weiss et al. (2022, https://doi.org/10.1029/2021PA004361) provide independent constraints on local sea level, which are essential for improving global mean sea level reconstructions on late Pleistocene glacial-interglacial cycles.