Research challenges models of sea level change during ice-age cycles

Feb 11, 2010

Theories about the rates of ice accumulation and melting during the Quaternary Period -- the time interval ranging from 2.6 million years ago to the present -- may need to be revised, thanks to research findings published by a University of Iowa researcher and his colleagues in the 12 February issue of the journal Science.

Jeffrey Dorale, assistant professor of in the UI College of Liberal Arts and Sciences, writes that and Earth's climate are closely linked. Data he and colleagues collected on speleothem encrustations (see photo right), a type of mineral deposit, in coastal caves on the of Mallorca indicate that sea level was about one meter above present-day levels around 81,000 years ago. The finding challenges other data that indicate sea level was as low as 30 meters -- the ice equivalent of four ice sheets -- below present-day levels.

He said the sea level high stand of 81,000 years ago was preceded by rapid ice melting, on the order of 20 meters of sea level change per thousand years and the sea level drop following the high water mark, accompanied by ice formation, was equally rapid.

"Twenty meters per thousand years equates to one meter of sea level change in a 50-year period," Dorale said. "Today, over one-third of the world's population lives within 60 miles of the coastline. Many of these areas are low-lying and would be significantly altered -- devastated -- by a meter of sea level rise. Our findings demonstrate that changes of this magnitude can happen naturally on the timescale of a human lifetime. Sea level change is a very big deal."

Dorale also noted that although their findings disagree with some sea level estimates, such as those from Barbados and New Guinea that come from ancient , they are in agreement with data gathered from other sites such as the Bahamas, the U.S. Atlantic coastal plain, Bermuda, the Cayman Islands and California.

"There has been a long-standing debate on this issue, but our data is pretty robust," he said. "The key to our research is two-fold. First, the speleothem approach we employed is novel and extremely precise compared to other methods of reconstruction. Second, Mallorca appears to be particularly well suited to the task, because neither tectonics nor isostasy -- geological forces of crustal motion -- over-complicate the record. It's really close to the ideal scenario. It's also a heck of a nice place to do fieldwork."

Dorale's colleagues include Bogdan Onac of the University of South Florida, Tampa; Joan Fornos, Joaquin Gines and Angel Gines, all of the Universitat de les Illes Balears, Mallorca, Spain; Paola Tuccimei of the University of Rome III, Italy; and UI associate professor of geoscience David Peate.

The research was supported by the National Science Foundation in a grant to Dorale and Onac.

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phlipper
1.5 / 5 (2) Feb 11, 2010
I gather from the article that the natural sea level change, that is, without mankind's influence, is about one meter per 50 years. If things go as scheduled, the sea level will rise one more meter in the next 100 years then drop for the following 1000 years. That is, if the 81000 year cycle repeats itself. Kudos for not mentioning CO2. That PC stuff gets a bit tiresome.
phlipper
2 / 5 (1) Feb 11, 2010
The article said that sea level change was 20 meters per thousand years. If the high mark was 81000 years ago, when did the rising start or stop? It wasn't clear. Did it fall for 40,000 years(800 meters) then rise another 800 meters? A half mile sea level fall would be a huge thing--no?
Ronan
3 / 5 (1) Feb 11, 2010
...And goodness gracious, what CAUSED that? That's no small amount of ice melting and then re-freezing again; even if...whatever it was wasn't able to knock Earth away from its long-term slump down into the cold, that's pretty impressive.
phlipper
4 / 5 (1) Feb 11, 2010
I've tried to find other sources to learn more. The author says "The finding challenges other data that indicate sea level was as low as 30 meters" then he said "..the sea level high stand of 81,000 years ago was preceded by rapid ice melting, on the order of 20 meters of sea level change per thousand years and the sea level drop following the high water mark, accompanied by ice formation, was equally rapid."
The "20 meters" mentioned was a rate of change not a level reading. It said nothing of what the low mark was that challenged the 30 meter conjecture. Does this article beg many questions or am I having multiple senior moments? Help me here....please.
Caliban
1 / 5 (1) Feb 11, 2010
Not much is made here of the stark disagreement of his estimate with the accepted model. Was everyone else wrong, or did he overlook some factor...where is his reference median sealevel, for instance?
Ronan
2.5 / 5 (2) Feb 11, 2010
Phlipper: Well, since it was evidently thought that the sea level at that time was thirty meters below nowadays, it's probably likely that the sea level before and after this event was at least close to that figure. I'd guess, from the article, that that indicates an overall jump of ~31 meters, over a period of (yikes) 1,500 years. And Caliban, according to a summary of this paper at Watts Up With That, there are other measurements in other locations that also seem to confirm this estimate. Of course, if that's the case, I don't see why this anomaly wasn't recognized in the first place, but...
mikiwud
not rated yet Feb 12, 2010
I think that to understand what happened to sea levels we would have to read the whole paper, this is just general rundown by physorg.
feOly
5 / 5 (1) Feb 12, 2010
And I hope they have more evidence than just an island in the mediterranean sea because mediterranean sea has been several times closed and level of water decreased and increased at high speeds...