Some of the research I have seen says the sea level was down 120 meters (metres ) during the LGM. Do you think it may have been shallower at other times?
Monk, the LGM was about as severe as the earth has seen in the last million years. A drop of 120 meters appears to be the maximum. What is even more surprising is the subsidence of the continental shelves under ice could be as much as 1,100 meters in some cases. That creates for some very interesting scenarios after the ice melts and the areas begin to rebound.
I live just north of the southern glacial boundary in Ohio. People in Penna. call us flat-landers though our terrain is mainly low rolling hills, areas of marsh, peat, etc. Thirty minutes south, the terrain takes an obvious change to higher, sharp peaks as would be seen in the foothills of the ancient applachains.
Yes, Monk. I have been researching terminal ice age subsidence in the Arctic and, at the end of the Saalian (Illinoian) glaciation in Eurasia the glaciers were 4500 meters high, but 1100 of those meters were below current sea levels due to bedrock subsidence from the weight of the ice. That still leaves the above sea level glacial height at over two miles. Post glacial rebound is most rapid soon after the ice melts, achieving 50% of its total rebound within 2-3000 years.
Many sea level areas were flooded with seawater prior to rebound. In some cases, the rebounding action trapped the seawater, resulting in large brackish lakes and inland seas.
Yes, Monk. I have been researching terminal ice age subsidence in the Arctic and, at the end of the Saalian (Illinoian) glaciation in Eurasia the glaciers were 4500 meters high, but 1100 of those meters were below current sea levels due to bedrock subsidence from the weight of the ice. That still leaves the above sea level glacial height at over two miles. Post glacial rebound is most rapid soon after the ice melts, achieving 50% of its total rebound within 2-3000 years.
Many coastal areas were flooded with seawater prior to rebound. In some cases, the rebounding action trapped the seawater, resulting in large brackish lakes and inland seas.
Beagle wrote:Isostatic rebound is still happening in the northern British Isles. So little now that it's barely detectable.
Yes, though as Scotland continues to rise (I shall be off exploring raised beached etc on my holiday later this year, btw) so the south is sinking - hence the increased flood threat for London.
The original first step at the 'White Tower' in the Tower of London Essan is reputed to now be several feet below modern ground level due to the sinking.
The degree to which the bedrock is rebounding was demonstrated during the construction of the Thame's Barrier. The engineers constructed coffer dams for the foundations and started pumping and digging till they had reached bedrock.
Before they could pour concrete they found that the bedrock was expanding up inside the coffer dams and they had to reflood them to force it down again whilst they returned to the drawing board.
Apparently this problem had never been met before and caused delays and cost over runs before it was solved.
Many engineering marvels are anchored to bedrock; the golden gate bridge, skycrapers, etc. Its not supposed to be moving. I guess the old adage "solid as bedrock" only applies below a certain latitude.
Monk, concerning precession. I thought this might be of interest.
Taken in conjunction with the 26,000-year spin-axis precession, the 71,000-year orbit precession causes a 41,000-year oscillation in the tilt of the earths axis, about plus or minus 1.3 degrees from its average value of 23.3 degrees. This number is not absolutely stable - it depends on the combined positions of all the planets through time.
The tilt reached a maximum of 24.2 degrees about 9,500 years ago, and has been decreasing ever since. The tilt is now near the average value, but the rate of change of the obliquity is near a maximum.
The most startling consequence of this is that the tropics (the tropics of Cancer and Capricorn, where the most northerly or southerly vertical rays of the sun strike) are MOVING TOWARD THE EQUATOR. The rate is more than 14 meters per year! Example: the government of Taiwan erected a monument in a park marking the tropic in 1908. The actual tropic is now more than a kilometer south of this location! The arctic circles are likewise traveling toward their respective poles. The temperate zones gain 1,550 square kilometers of territory every year!
Note the dates concerning the LGM and the last sentence, need we look further for GW.
Very interesting information, Digit. I was aware of the changes in the obliquity of the ecliptic; its 41,000 year cycle. But put in the terms you expressed makes its startling clear what the effect really is.
I believe it is not known for certain what the period or amplitude of the cycle is, really. In fact it is extrapolated based on ancient observations of and estimates of the true ecliptic angle from different periods in history.
Present theory suggests the total movement is on the order of 1.5 degrees so its doubtful the arctic cirlce will ever disappear completely.
Allowing for the time I would guess that was necessary to melt vast areas of ice Monk the dates seem to correlate well with what we know about ancient climates.
Human beings who lived 500 centuries ago were fully modern, virtually indistinguishable from us in fundamental ways. Their brains and bodies were physically the same as ours. They created sophisticated art - murals, paintings, sculptures - and buried their dead in a fashion that suggests they possessed ceremonial or religious traditions. They had developed the technology and navigational skills required to travel across broad expanses of ocean.
Paleolithic hunter-gatherers did not, however, domesticate plants or animals on a large scale. Nor did they live in large, sedentary communities. No one did until about 10,000 years ago when, suddenly and in multiple locations around the globe, agriculture and cities appear in the archaeological record.
The relatively abrupt and simultaneous rise of farming and urban settlement patterns suggest that the capacity to develop such innovations had been part of humankind's intellectual and behavioral bag of tricks for a long time.
I don't know who this fellow is, but a paleolithic hunter in Europe ca50,000ya was a Neandertal. Maybe he knows that. The subject here is the importance of climate to civilization. We all know that but the article is worth reading.
From Archaeologica News.
That's the Club answer......not so sure that it is still viable.
Something is wrong here. War, disease, death, destruction, hunger, filth, poverty, torture, crime, corruption, and the Ice Capades. Something is definitely wrong. This is not good work. If this is the best God can do, I am not impressed.
Following the U.S. Senate's vote today on a global warming measure (see today's AP article: Senate Defeats Climate Change Measure,) it is an opportune time to examine the recent and quite remarkable momentum shift taking place in climate science. Many former believers in catastrophic man-made global warming have recently reversed themselves and are now climate skeptics. The names included below are just a sampling of the prominent scientists who have spoken out recently to oppose former Vice President Al Gore, the United Nations, and the media driven “consensus” on man-made global warming.
The tide of scientific opinion is swiftly turning. I think we nailed it here some time ago. Poor Al Gore.
I just read where a Prof at U of AZ has shown there was a 60 year drought in the Colorado basin that ended in 1490. I wonder where the Indians got their SUVs back then?
There are those that think myths and legends have a lot to teach us in our modern day.
Wasn't there a King in legend that tried to stop a natural occurrence by passing a law, or "Royal Edict" against it? Something about the rising tide.
Maybe A.G. will be a footnote in future textbooks when they teach that story.
