“WE'RE BURNING DAYLIGHT!” A TRIBUTE TO STAN RIGGS' AMAZIN' CAREER OF THINKING BIG—SOME LESSONS OF SEA LEVEL CHANGES AND COASTAL RESPONSE FROM A CARBONATE RAMP--THE WEST FLORIDA MARGIN

Sea-level rise models, projected out to the year 2100, presented in the 2007 IPCC report and by more recent studies predict a global sea-level rise from 23—180 cm thus yielding a maximum rate of 200 cm/100 yrs. The newer studies favor the higher elevations with increased sea-level rise rates occurring towards the latter part of the 21^st century. Rates of ~200 cm/100 yrs are indeed ominous indicating wholesale changes in placement and geometry of coastal landscapes thus requiring significant disruption in human infrastructure. However, we point out that rates of up to 540 cm/100 yrs of sea-level rise have occurred during the disintegration of the northern hemisphere ice sheets shown by ¹⁴C measurements from drowned carbonate paleo-shorelines.

Carbonate depositional systems, by being “born and not made” and by being chemically reactive on short time scales, provide information about high-frequency sea-level changes not seen in siliciclastic systems. And, ramped, non-rimmed carbonate systems provide a horizontally-extended playing field over which minor sea-level fluctuations create recognizable lateral shifts in shallow-marine, carbonate depositional systems. Our work has indicated that “tipping points” or thresholds may exist whereby coastal systems remain relatively stable and then undergo rapid translation and transformation. Additionally, large open-marine, coastal marsh systems seem to suggest similar behavior. Along Florida’s Big Bend coast, for example, marsh islands appear unchanged for decades then rapidly disappear, again suggesting a non-linear (and non storm-related) behavior.

These observations provide added difficulties in predicting coastal response based on sea-level rise models that do not include pulses and episodic events. Future coastal landscape reconstructions need to recognize the possibility of periods of stability followed by brief periods of wholesale translation, re-organization, and re-establishment of coastal depositional environments and ecosystems driven by episodic sea-level behavior and/or inherent tipping points in depositional systems that exist independent of sea-level rates of change.