Citation — to study
David B. Rowley, Alessandro M. Forte, Robert Moucha, Jerry X. Mitrovica, Nathan A. Simmons, and Stephen P. Grand, Dynamic Topography Change of the Eastern United States Since 3 Million Years Ago, Science Express, DOI: 10.1126/science.1229180 (16 May 2013)
Citation — to press release
Canadian Institute for Advanced Research, World’s biggest ice sheets likely more stable than previously believed, CIFAR.ca (17 May 2013)
From the abstract:
Sedimentary rocks from Virginia through Florida record marine flooding during the mid-Pliocene.
Several wave-cut scarps that at the time of deposition would have been horizontal are now draped over a warped surface with a maximum amplitude of 60 m.
We modeled dynamic topography using mantle convection simulations that predict the amplitude and broad spatial distribution of this distortion. The results imply that dynamic topography and, to a lesser extent, glacial isostatic adjustment, account for the current architecture of the coastal plain and proximal shelf.
This confounds attempts to use regional stratigraphic relations as references for longer-term sea-level determinations.
Inferences of Pliocene global sea-level heights or stability of Antarctic ice sheets therefore cannot be deciphered in the absence of an appropriate mantle dynamic reference frame.
© 2013 David B. Rowley, Alessandro M. Forte, Robert Moucha, Jerry X. Mitrovica, Nathan A. Simmons, and Stephen P. Grand, Dynamic Topography Change of the Eastern United States Since 3 Million Years Ago, Science Express, DOI: 10.1126/science.1229180 (16 May 2013) (at Abstract) (paragraph split)
Why this matters — disregarded common sense
I have always thought that the confidence some researchers placed in their calculations regarding sea level rise (or fall) and its causes was misplaced.
Common sense should indicate that — when both water and land are moving in unknown ways relative to each other — it is going to be difficult to assess what portion of the overall movement came from which source. Yet, that has not stopped claims that proportionately dramatic sea level rise (or fall) occurred in the geologically not so distant past.
When young, I presumed that these people knew something that I did not, even though what they were saying seemed scientifically questionable, at best. The results of the above cited study support my doubts:
For decades, scientists have used ancient shorelines to predict the stability of today’s largest ice sheets in Greenland and Antarctica.
Markings of a high shoreline from three million years ago, for example – when Earth was going through a warm period – were thought to be evidence of a high sea level due to ice sheet collapse at that time.
This assumption has led many scientists to think that if the world’s largest ice sheets collapsed in the past, then they may do just the same in our modern, progressively warming world.
However, a new groundbreaking study now challenges this thinking.
Using the east coast of the United States as their laboratory, a research team led by David Rowley, CIFAR Senior Fellow and professor at the University of Chicago, has found that the Earth’s hot mantle pushed up segments of ancient shorelines over millions of years, making them appear higher now than they originally were millions of years ago.
“Our findings suggest that the previous connections scientists made between ancient shoreline height and ice volumes are erroneous and that perhaps our ice sheets were more stable in the past than we originally thought,” says Rowley.
“Our study is telling scientists that they can no longer ignore the effect of Earth’s interior dynamics when predicting historic sea levels and ice volumes.”
© 2013 Canadian Institute for Advanced Research, World’s biggest ice sheets likely more stable than previously believed, CIFAR.ca (17 May 2013)
Caveat — and caveat rebutted
Certainly, the team’s computer modeling may be incorrect. And certainly the Earth’s ice sheets may be noticeably dynamic.
But neither of these potential criticisms is the point.
The take-away gist is that past claims regarding sea level change depended on minimizing the effects of vertical vector land shifts. But if we do not know (and haven’t thoroughly investigated) the magnitude, cause, or location of these — what business do we have:
(a) making seemingly precise claims about past sea level changes
(b) attributing those to alleged changes in the mass(es) of past ice sheets?
The moral? — If you are a sound and knowledgeable thinker, it is okay to be skeptical about a great many obviously invalidly supported scientific claims
Scientists are often just as likely to overlook analytical common sense, in situations in which they are motivated to say something dramatic, as anyone else is.