Daniel Gilford

and 5 more

Previous studies have interpreted Last Interglacial (LIG; ~129-116 ka) sea-level estimates in multiple different ways to calibrate projections of future Antarctic ice-sheet (AIS) mass loss and associated sea-level rise. This study systematically explores the extent to which LIG constraints could inform future Antarctic contributions to sea-level rise. We develop a Gaussian process emulator of an ice-sheet model to produce continuous probabilistic projections of Antarctic sea-level contributions over the LIG and a future high-emissions scenario. We use a Bayesian approach conditioning emulator projections on a set of LIG constraints to find associated likelihoods of model parameterizations. LIG estimates inform both the probability of past and future ice-sheet instabilities and projections of future sea-level rise through 2150. Although best-available LIG estimates do not meaningfully constrain Antarctic mass loss projections or physical processes until 2060, they become increasingly informative over the next 130 years. Uncertainties of up to 50 cm remain in future projections even if LIG Antarctic mass loss is precisely known (+/-5 cm), indicating there is a limit to how informative the LIG could be for ice-sheet model future projections. The efficacy of LIG constraints on Antarctic mass loss also depends on assumptions about the Greenland ice sheet and LIG sea-level chronology. However, improved field measurements and understanding of LIG sea levels still have potential to improve future sea-level projections, highlighting the importance of continued observational efforts.

Sanne Muis

and 7 more

Paul Hearty

and 5 more

Hearty, P. J., Rovere, A., Sandstrom, M. R., O’Leary, M. J., Roberts, D., & Raymo, M. E. (2020). Pliocene‐Pleistocene stratigraphy and sea‐level estimates, Republic of South Africa with implications for a 400 ppmv CO2 world. Paleoceanography and Paleoclimatology, 35, e2019PA003835. https://doi.org/10.1029/2019PA003835 The Mid-Pliocene Warm Period (MPWP, 2.9 to 3.3 Ma), along with older Pliocene (3.2 to 5.3 Ma) records, offers potential past analogues for our 400-ppmv world. The coastal geology of western and southern coasts of the Republic of South Africa expose an abundance of marine deposits of Pliocene and Pleistocene age. In this study, we report differential GPS elevations, detailed stratigraphic descriptions, standardized interpretations, and dating of relative sea-level indicators measured across ~700 km from the western and southern coasts of the Cape Provinces. Wave abrasion surfaces on bedrock, intertidal sedimentary structures, and in situ marine invertebrates including oysters and barnacles provide precise indicators of past sea levels. Multiple sea-level highstands imprinted at different elevations along South African coastlines were identified. Zone I sites average +32 ± 5 m (6 sites). A lower topographic Zone II of sea stands were measured at several sites around +17 ± 5 m. Middle and late Pleistocene sites are included in Zone III. Shoreline chronologies using 87Sr/86Sr ages on shells from these zones yield ages from Zone I at 4.6 and 3.0 Ma, and Zone II at 1.04 Ma. Our results show that polar ice sheets during the Plio-Pleistocene were dynamic and subject to significant melting under modestly warmer global temperatures. These processes occurred during a period when CO2 concentrations were comparable to our current and rapidly rising values above 400 ppmv.