PULSES OF RAPID SEA LEVEL RISE: THEIR EFFECT ON PAST, PRESENT AND FUTURE COASTAL ENVIRONMENTS AND SEQUENCES

The 120 meter sea level rise following the last glacial maximum is commonly graphed as a relatively smooth accelerating and then decelarating curve. This is incorrect. Sea level rise over the past 18,000 years was dominated by a repetitive series of very rapid pulses of rise alternating with periods of relative stability. This is based on preserved peri-tidal beach, barrier island, tidal delta, reef, and coastal wetland deposits that remain stranded at various levels across the continental shelves. Pulses of rise, from 1 to 10 meters, drowned out these environments stranding them on the sea floor. Most of these pulses appear the result of collapse of portions of continental ice sheets in response to climatic warming.

Even the overall slowed sea level rise towards the end of the post-glacial rise contains small pulses of accelerated rise at about 4,300-4,000, 3,500-3,200, 2,500-2,400 years before present, and during the past 80 years. Each one of these resulted in a transgression of previous coastal deposits, rapid recycling of coastal sedimentation, coastal turbidity/nutrient stress, and generation of new shallowing upwards sediment sequences. As these pulses of rise are each less than 2 meters, they have generated multiple shallowing-upwards sediment cycles within the ‘high-stand’ coastal system. Each of these ‘intra-interglacial’ sedimentary depositional cycles (stacked or offset) may be quite different, being controlled by the nature and pattern of pre-existing sedimentary environments, sediment supply, and the nature and extent of the sea level rise. A more careful examination of ancient sequences will undoubtedly reveal that a composite sets of more rapidly formed sedimentary sequences is a common feature of an overall sea level high stand.

As rapid steps or pulses of rapid sea-level rise followed by pauses are how sea level responded to warming at the end of the last glacial period, we must expect that this is be how sea level will respond to the warming from the buildup of anthropogenic green house gasses. Recent accelerated ice melt of Greenland and Antarctica may well be the onset of a significant rapid pulse of anthropogenic-induced sea level rise. None of the current forecast models for sea level rise include the feedback parameters needed to consider such a response.