Sea-level change and superstorms; geologic evidence from the last interglacial (MIS 5e) in the Bahamas and Bermuda offers ominous prospects for a warming Earth

Geological observations from last interglacial (LIG; MIS 5e, Eemian) carbonate landscapes in the Bahamas and Bermuda reveal a turbulent climate transition at the close of the peak interglacial. The interval is associated with rapid, multi-meter shifts in sea level as major ice sheets melted and/or collapsed. Sedimentary evidence from the eastern Bahamas includes wave-transported megaboulders, lowland chevron storm ridges, and hillside runup deposits. This "trilogy" collectively provides direct geological evidence of frequent, intense storms generating sustained long-period waves from the northeast Atlantic Ocean. Penecontemporaneous with wave deposits is the subtidal production and flux of a massive volume of ooid sediments associated with amplified winds and storminess during the latter half of MIS 5e that resulted in exponential island growth. Steeper temperature and pressure gradients were evident in the North Atlantic Ocean, while the Southern Ocean appears to have had a major role in affecting atmospheric CO2, as warming of the Southern Ocean drives ventilation of the deep ocean. CO2 in turn, acts as a tight control knob on global climate. The dramatic oceanographic and island building events of late MIS 5e are unique among other interglacial periods of the past half million years. The LIG record reveals that strong climate forcing is not required to yield major impacts on the ocean and ice caps. Antarctic ice cores document that LIG atmospheric CO2 was 275 ppm, while global temperature was < 1 degrees C warmer than present. Despite only slightly warmer conditions than pre-Industrial times, relative sea level (RSL) persisted at + 2-3 m for several thousand years during the early and mid LIG. Later in the LIG, sea level abruptly rose an additional 3-5 m meters to + 6-9 m RSL. In terms of Lyellian uniformitarian principles, the trilogy of coeval deposits of MIS 5e described herein do not translate to our modern climate parameters, and further cannot be explained by coincidental megatsunami. In our industrial world, rapidly increasing atmospheric CO2 rates ( > 2 ppm/yr) have surpassed 408 ppm, levels not achieved since the Pliocene 3 Ma ago, while global temperature increased similar to 1 degrees C since the 1870s. With greatly increased CO2 forcing at unmatched rates, except perhaps during global extinction events, dramatic change is certain. In the interest of our future world, we must seek to understand the complex set of linked natural events and field observations that are revealed in the geology of past warmer climates.