A CATASTROPHIC CONSEQUENCE OF GLOBAL WARMING? SEA-LEVEL FLUCTUATIONS DURING THE LAST INTERGLACIATION (MIS 5E) AND THE MELTING/COLLAPSE OF POLAR ICE SHEETS

The sedimentary systems of the Bahamas and other global sites reveal the relative movements of sea level during marine isotope stage (MIS) 5e (~130 to 119 ka). Shoreline deposits and morphological features are widespread on most coastlines in these areas and are datable by multiple methods (e.g., amino acids and U/Th). Direct reading of the rocks, soils, and fossils on the coastline facilitate reconstruction of past events and environments. The bulk of morphological evidence of early-mid MIS 5e sea-level position is manifest in broad terraces and reef tracts at +2 to +3 m on stable coastlines. However, rounded and flat-topped sea-level curves constructed only from these conspicuous features are incomplete, as sea level later in the interglacial shows evidence of multiple erratic shifts of short duration. After a brief period of sea level lowering, sea level late in the period (~122 to 120ka) was characterized by rapid upward shifts between +6 and +9 m during which multiple notches and benches were imprinted on older rocks. During the same interval, the Bahamas suffered severe storms and high seas that transported massive boulders and flooded vast, lowland areas forming chevron ridges. The descent of sea level into MIS 5d after 119 ka was also apparently rapid, implying a rapid buildup of glacial ice across polar landscapes.

The geological evidence documents significant climate and oceanographic shifts throughout the later half of MIS 5e. Fluctuating sea levels and a catastrophic termination of MIS 5e are linked to the instability of grounded and marine-based ice sheets, with the Greenland (GIS) and West Antarctic (WAIS) ice sheets being the major contributors to sea-level rise – most likely in that order. The recent unusual glacial activity in the GIS and WAIS ice shelves may offer an ominous bellwether for a greenhouse world, perhaps leading to a succession of extreme events including oceanographic reorganization, global ecological shifts, and rapid sea level changes.