Scientists develop new coral dating method, hint at future sea-level changes

September 11, 2011

New evidence of sea-level oscillations during a warm period that started about 125,000 years ago raises the possibility of a similar scenario if the planet continues its more recent warming trend, says a research team led by the Woods Hole Oceanographic Institution (WHOI).

In a paper published online in the Sept. 11 Nature Geoscience, the researchers report data from an improved method of dating fossil coral reef skeletons in the Bahamas. By calculating more accurate ages for the coral samples than previously possible, they found that sea levels were considerably less stable than earlier believed--oscillating up and down by 4 to 6 meters (13-20 feet) over a few thousand years about 120,000 years ago during a period known as the Last Interglacial.

"This was the last time that climate was as warm as—or warmer than—today," said WHOI geochronologist William G. Thompson, lead author of the study. "If today's ice sheets continue to melt, we may be headed for a period of and sea-level change that is more dynamic than current observations of ice sheets suggest."

The polar ice caps currently are shrinking and sea level is rising at a rate of about 30 centimeters (one foot) per century. "How much sea level will rise over the next century or two is a crucial question for the significant part of the world's population that lives in coastal zones," Thompson said.

A better understanding of sea-level change in the past can help to inform predictions for the future. Historical records such as those from tide gauges extend back only a century or so. "The geological record offers a longer perspective on rates of change," Thompson said, "and sea-level changes during previous warm intervals are especially relevant to today's situation." Sea levels during the Last Interglacial are known to have been about 6 meters (20 feet) higher, on average, than they are today. "The real surprise is that sea levels were oscillating during this period."

To get more accurate age estimates from the geological record, Thompson developed an advanced way of interpreting the uranium and thorium isotope ratios that have been traditionally used as a coral dating method. Until now, scientists attempting to date Last Interglacial coral reefs concluded erroneously that sea level was relatively stable during this period. "Our analysis of Last Interglacial fossil reef ages represents a breakthrough in our understanding of U-Th coral dating, leading to improved chronologies of past sea-level change," Thompson said.

Thompson teamed up with colleagues H. Allen Curran and Brian White of Smith College, and Mark A. Wilson of the College of Wooster, experts on the key Bahamas fossil coral sites. "The geologic evidence for sea-level change at these sites is convincing," said Curran, "but we couldn't absolutely prove sea-level oscillation without more precise dating."

Because grow near the sea surface, they are accurate markers of former sea levels. Two fossil reefs are evident at the sites, separated by an erosional surface that was cut by wave action. The first reef grew when sea levels were about 4 meters (13 feet) higher than today. "The fall of sea-level is indicated by the wave-cut erosion of this first reef," said Wilson, "and the second sea-level rise was recorded by the growth of new corals on this eroded surface. The dating of fossil corals below and above this erosional surface, using our new methods, reveals important details about the timing of sea-level change that were previously obscured."

The finding of a significant sea-level oscillation 120,000 years ago is in sharp contrast to the last 5,000 years, where sea level has been relatively stable. "It appears that the smaller ice sheets of the Last Interglacial were significantly less stable than today's ice sheets," Thompson said.

Should the current continue, Thompson said, a scenario similar to that of the Last Interglacial could result. "Variable during the Last Interglacial points to instability in the polar ice sheets, which were somewhat smaller than today. If changing leads to smaller ice sheets in the future, this may provoke similar instability."

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2.1 / 5 (11) Sep 11, 2011
So sea level goes up and 6 meters WITHOUT fossil fuels.

Who knew?

Lucky for us sea level went DOWN in 2010.

1.5 / 5 (8) Sep 11, 2011
The sea level in Israel has been rising and falling over the past 2,500 years, with a one-meter difference between the highest and lowest levels, most of the time below the present-day level.
The last interglacial was NOT the last time the climate was as warm or warmer than now. There were the Medieval, Roman and Minoan Warm periods in the last few thousands years. We are now warming up after the Little Ice Age.
1.4 / 5 (10) Sep 11, 2011
sea levels were considerably less stable than earlier believed , . .

Because measurements show:

1. Earth's climate has changed and is changing.
2. The Sun has evolved and is evolving.
3. Life has evolved and is evolving

We are partially protected from our Sun's unstable pulsar core by:

a.) A solar mantle of mostly Fe, O, Ni, Si, S, Mg and Ca
b.) A solar photosphere of waste products (H and He)
c.) Distance from the Sun


1. "The demise of established dogmas on the Solar System formation", Nature 303 (1983) 286


2. "Is the Universe expanding?", J. Cosmology 13, 4187-4190 (2011)


3. "Origin and evolution of life", J. Modern Physics 2, 587-594 (2011)


4. "Neutron repulsion", The APEIRON J., in press (2011)

With kind regards
O K Manuel
Formerly NASA PI for Apollo
1.6 / 5 (5) Sep 11, 2011
A useful article that highlights the complexities of the Earth System response to warming events. RE Medieval Warm Period this abstract is useful
http://adsabs.har...51B..08C Extract "Temperature profiles from boreholes sufficiently deep to encompass the full millennium of time being examined exist in central Europe, northeast North America, South Africa, and central Asia. Of these regions, the central Europe borehole profiles show clearest evidence of strong LIA and MWP signals. These events, on the other hand, are either both missing, or largely cancel each other in the North American, South African, and central Asian profiles. Twentieth Century warming is dramatically apparent in all regions."
2.6 / 5 (5) Sep 12, 2011
Thank you MikPetter.

"the central Europe borehole profiles show clearest evidence of strong LIA and MWP signals. These events, on the other hand, are either both missing, or largely cancel each other in the North American, South African, and central Asian profiles"

Because the European medieval warming was a REGIONAL phenomenon caused by changes in circulation systems, and globally the temperature balance canceled out.

It is always possible to cherry pick data, which is why the whole system must be taken into consideration.
1 / 5 (2) Sep 12, 2011
Sea levels during the Last Interglacial are known to have been about 6 meters (20 feet) higher, on average, than they are today

Left unexplained here is how that could even be possible.

Recall, the greenland ice cap is allegedly what, 800k years old, with allegedly continual layers, and the antarctic ice cap is supposedly over a million.

But wait, to raise sea levels 6 meters above present levels would require melting some 95% of the greenland ice cap, or melting a significant portion of it and then melting enough of Antarctica to make up the difference.

guess that ice core science just isn't so reliable on dating after all, right? After all, these radiometric findings would require the greenland ice caps to be less than 120,000 years old to explain the alleged 6 meters higher sea levels at that alleged time.

BTW, If we had 6 meters of mean sea level rise, I think half the human population would likely die out for one reason or another.
1 / 5 (1) Sep 12, 2011
Think of all the coastal regions in the world and how all the fresh water and brakish ecosystems would be totally inundated. many regions in some countries would lose almost their entire land area.

All of the Gulf Coast states south of highway 190 would be totally submerged, and even north of 190 would be only a foot or two above salt water.

Salt domes in Lousiana woudl be submerged and dissolved back into the oceans. The sandy land left behind would quite literally dissolve and be washed away.

Tampa Bay, Galveston, NOLA, Miami, Key West, Biloxi, Gulfport, Mobile bay, all would be sunken cities. Every town, village, and city south of 190 in the central gulf would be totally submerged, and Baton Rouge would even be uninhabitable, because Salt Water would back that far up into the Mississippi basin and over-top the levees, certainly during tropical storms, if not ordinary surface lows and fronts.

Huge sections of coast in New Jersey, New York and Long Island...uninhabitable.
1 / 5 (3) Sep 13, 2011
Because the European medieval warming was a REGIONAL phenomenon caused by changes in circulation systems, and globally the temperature balance canceled out.

Or ... you could read papers that show the MWP happened elsewhere.

"most show that temperatures reached close to modern levels around 750 and then rose slowly throughout the Medieval Climate Anomaly until around 1300. Around or shortly after this time, temperatures fell rapidly, reaching levels below their modern levels early in the Little Ice Age, or about 1450. Sea-level change has proved to be a useful proxy for temperature change during the past 1,200 years along tropical Pacific coasts. Evidence shows that sea levels rose slowly during the Medieval Climate Anomaly before falling as much as 135 centimeters (typically 70-80 centimeters) during the A.D. 1300 Event"

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