MARINE ISOTOPE STAGE (MIS) 11: EVIDENCE OF DYNAMIC BEHAVIOR OF ICE SHEETS -- REALITIES, REASSESSMENT, AND ‘THE NOTCH’

MIS 11 stands out among Quaternary interglacials and offers a potential analogue for our present warming interglacial. Proxy deep-sea δ¹⁸O records indicate MIS 11 was one of the longest (423 to 362 ka) and perhaps warmest interglacials of the past 1 Ma. The highest geologic and geomorphic imprints of MIS sea level (SL) are generally above 10 m, reaching over +20 m at some localities. The most complete records are found in Bermuda, Bahamas, Curacao, Oahu, and South Africa. But field studies reveal a complex MIS 11 morphostratigraphic sequence where multiple stable intervals are punctuated by episodes of rapidly shifting SL. The highest and latest SL stand indicates a brief pause and fall of SL that is manifest by bioerosional notches, rubble benches, and/or phreatic caves systems situated well above lower, broader terrace features. Significant misinterpretation of MIS 11 SL history could result if all components of this complex succession are not considered.

Other factors complicate the precise calculation of paleo-eustatic-SL during MIS 11. These include geochronology, variable depositional environments, and post-depositional effects. Because of the middle Pleistocene age of the sediments and fossils, dating by U/Th or luminescence methods has traditionally been problematic. Whereas coral reefs optimally respond to stable or slowly rising seas, shorter SL excursions during MIS 11 may not be recorded in reef geology. And further, many SL imprints on coastlines have experienced significant post-depositional movements due to tectonics, glacio-isostatic adjustment, and dynamic topography, which all involve some important, yet elusive assumptions.

This presentation will review the current evidence regarding MIS 11 SL. Regardless of various research and scientific obstacles, even minimum estimates of SL implicate Greenland (GIS), West Antarctica (WAIS), and possibly East Antarctic (EAIS) ice sheets if maximum SL indicators are examined and ultimately verified.