EEMIAN MIS 5E: A FLASH FROM THE PAST…AND A GLIMPSE INTO THE FUTURE!

Flash! Stratigraphic and sedimentological observations among last interglacial (LIG; MIS 5e, Eemian) carbonate landscapes in the Bahamas and Bermuda reveal a rocky climate transition late in the period. Wave-transported megaboulders, hillside runup deposits, and lowland chevron ridges provide evidence of intense storms and sustained long-period waves originating in the northeast Atlantic Ocean. This turbulent period is associated with rapid, multi-meter changes in sea level as major ice sheets melted and/or collapsed.

LIG geology in the islands presents some ominous clues of potential future changes. Antarctic ice cores document that LIG atmospheric CO2 was ~280 ppm, while global temperature was less than 1°C warmer than today’s. Despite only slightly warmer conditions than pre-Industrial times, early-mid LIG sea level persisted at +2-3 m for several thousand years. Later in the LIG, sea level rose abruptly 3-5 m meters (to +6-9 m) as the cryosphere adjusted to warmer temperatures. Rapidly increasing CO2 rates (>2 ppm/yr) have surpassed 400 ppm (a Pliocene level) while global temperature increased ~1ºC since the 1870s. The Eemian reveals that major climate forcing is not required to yield major impacts on the ocean and ice caps.

Climate model simulations indicate that the flood of fresh water and ocean surface cooling in the North Atlantic as well as the Southern Ocean could have increased tropospheric meridional temperature gradients, eddy kinetic energy and baroclinicity, increasing the climatological wind field and driving more powerful storms. The Southern Ocean has a major role in affecting atmospheric CO2, as warming of the Southern Ocean drives ventilation of the deep ocean. The resulting level of CO2 in turn acts as a tight control knob on global climate. Today, ice mass losses from major global ice sheets (GIS, WAIS, and Totten/Aurora Basin (EAIS)) are growing non-linearly with doubling times on the order of 10 yr.

With few controls on GHG emissions, our global society is producing a climate system that is racing forward out of humanity’s control into an uncertain climate future. If we look back to understand the non-human-driven events of the LIG, some of the enormous consequences of our unchecked forward speed may come more clearly into focus (http://www.atmos-chem-phys-discuss.net/15/20059/2015/).