CREATING AN UNDERSTANDING OF SEA-LEVEL DYNAMICS: A. CONRAD NEUMANN’S LEGACY

I had the privilege of studying under Conrad Neumann as his first graduate student during his first years at the University of Miami. Among the many aspects of carbonate sedimentation was his efforts to better understand Holocene and late Pleistocene sea-level history. We struggled to correctly sample and analyze the thick freshwater marshes of Bermuda and elsewhere. Beyond Neumann’s resulting famous unpublished Holocene sea-level curve, were hours discussing controls on and possible rates of sea level rise and fall through the Pleistocene, how different sea-level positions on carbonate platforms would result in different sediment facies patterns; the sequence of sedimentary facies development when sea level rise slowed; and how to recognize sea level stillstands.

Recent research has made minor but very significant refinement in our understanding of periods of rising sea level and of high stands. We now know that the 120-meter post-glacial rise occurred as a series of over 15 rapid pulses of 1-10 meter rise followed by slow- or still-stands. These stillstands are recorded as sea-level markers built and commonly preserved across the world’s continental shelves: reefs , reef terraces, barrier islands, beaches, tidal- and bayhead-deltas, coastal tidal flats and wetlands, and biological erosion notches in cemented carbonate buildups. The pulses of rapid rise are each the result of rapid disintegration of some ice sheet sector.

We also now see that both the late Pleistocene and the modern sea-level highstands are in fact a composite of separate stillstands separated by small, rapid sea-level changes.

We are now entering a new rapid pulse of sea level rise triggered by a significant ocean warming as a result of additional anthropogenic greenhouse buildup 1.3 times larger and over 100 times faster than that which drove the natural post-glacial rise. Our understanding of the past is the only guide we have as to how fast and dramatic this coming rise will be.