Friday, December 17, 2010

Sea Level History Refined

The huge rise in sea levels has been understood for some time though it is not yet common knowledge.  These guys went out and refined the curve as much as possible.  We are still left with averages, but the big changes are holding up.  Most important the first melt back began 19,000 years ago and I would guess that the second melt back began around 14,000 years ago, but was possibly masked by the continuation of the preceding melt back.

The unanswered question is why?  There is ample support for a directed crustal shift for the second event and I have posted extensively on this.  It is reasonable that the first melt back was triggered naturally by a less than ideal first shift as has been suggested by other commentators.  This provided confirmation of the possibility and showed what was possible if the crust was placed properly.

Otherwise we have no working theory for the ice ages that has ever stood up unless you wish to have an hundred impossibilities before breakfast.

Like the original theory of plate tectonics, the theory of Hapwood and Einstein was dismissed because of no mechanism allowing a slippery crust.  I have overcome that omission in earlier posts and articles.  The weight of outright evidence forced acceptance of the first and ample evidence is available for the second.

In the meantime this polishes the sea level data but does not pick up the fast flood brought on by Lake Agassiz.  The resolution is not so good.

Global Sea-Level Rise At The End Of The Last Ice Age
by Staff Writers

Southampton, UK (SPX) Dec 02, 2010

The researchers brought together about 400 high-quality sea-level markers from study sites around the globe, concentrating on locations far removed from the distorting effects of the past massive ice sheets.

Southampton researchers have estimated that sea-level rose by an average of about 1 metre per century at the end of the last Ice Age, interrupted by rapid 'jumps' during which it rose by up to 2.5 metres per century. The findings, published in Global and Planetary Change, will help unravel the responses of ocean circulation and climate to large inputs of ice-sheet meltwater to the world ocean.

Global sea level rose by a total of more than 120 metres as the vast ice sheets of the last Ice Age melted back. This melt-back lasted from about 19,000 to about 6,000 years ago, meaning that the average rate of sea-level rise was roughly 1 metre per century.

Previous studies of sea-level change at individual locations have suggested that the gradual rise may have been marked by abrupt 'jumps' of sea-level rise at rates that approached 5 metres per century. These estimates were based on analyses of the distribution of fossil corals around Barbados and coastal drowning along the Sunda Shelf, an extension of the continental shelf of East Asia.

However, uncertainties in fossil dating, scarcity of sea-level markers, and the specific characteristics of individual sites can make it difficult to reconstruct global sea level with a high degree of confidence using evidence from any one site.

"Rather than relying on individual sites that may not be representative, we have compared large amounts of data from many different sites, taking into account all potential sources of uncertainty," said Professor Eelco Rohling of the University of Southampton's School of Ocean and Earth Science (SOES) based at the National Oceanography Centre (NOC) in Southampton.

The researchers brought together about 400 high-quality sea-level markers from study sites around the globe, concentrating on locations far removed from the distorting effects of the past massive ice sheets.

Using an extensive series of sophisticated statistical tests, they then reconstructed sea-level history of the last 21 thousand years with a high degree of statistical confidence.

Their analyses indicate that the gradual rise at an average rate of 1 metre per century was interrupted by two periods with rates of rise up to 2.5 metres per century, between 15 and 13 thousand years ago, and between 11 and 9 thousand years ago.

The first of these jumps in the amount of ice-sheet meltwater entering the world ocean coincides with the beginning of a period of global climate warming called the Bolling-Allerod period. The second jump appears to have happened shortly after the end the 'big freeze' called the Younger Dryas that brought the Bolling-Allerod period to an abrupt end.

"Our estimates of rates of sea-level rise are lower than those estimated from individual study sites, but they are statistically robust and therefore greatly improve our understanding of loss of ice volume due to the melting of the ice sheets at the end of the last Ice Age," said lead author Dr Jennifer Stanford of SOES.

"The new findings will be used to refine models of the Earth climate system, and will thus help to improve forecasts of future sea-level responses to global climate change," added Rohling.

The researchers are Jenny Stanford, Rebecca Hemingway, Eelco Rohling and Martin Medina-Elizalde (SOES), Peter Challenor (NOC) and Adrian Lester (The Chamber of Shipping, London). Stanford, J. D., Heminway, R., Rohling E. J., Challenor, P. G., Medina-Elizalde, M. and Lester, A. J. Sea-level probability for the last deglaciation: A statistical analysis of far-field records. Global and Planetary Change (Published online, November 2010).

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