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the Ice Age & the Oceans

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Carolyn Silver
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« on: February 16, 2007, 10:53:04 pm »

THE ICE AGE & THE OCEANS

Sea-level changes and the Pleistocene Ice Age


Sea-level has been close to its present level for the past 6000 years, before which it was lower and fluctuating, last achieving its present position about 120,000 years ago. About 15,000-16,000 years ago, sea-level was 130-140 m below its present position. For the past 500,000 years it has been lower than today about 90% of the time.

These major changes coincide with the Ice Age. The last 1.65 million years of geological time -- the “Quaternary” -- is split into the Pleistocene and the Holocene epochs. The latter represents the last 10,000 years when most of the icesheets had melted.

Sea-level falls coincide with periods of glaciation whereas the rises occur during interglacials -- the warmer times between ice advances, like the present day and most of the Holocene.

The onset of the Ice Age began about 40 million years when surface waters in the southern oceans suddenly cooled and the deep ocean basins quickly filled with water ~10°C cooler than before that sank because of its increased density. By about 15 million years ago, the Antarctic Icecap had formed, accelerating production of cold waters. Consequently, siliceous diatom oozes became more abundant in the southern oceans because of increased upwelling that resulted from steeper temperature, and density, gradients.

About 6–5 million years ago, Miocene Epoch, sea-level fell by as much as 50 m, probably associated with expansion of the icecap in Antarctica. Termed the Messinian Event, this might have caused the Mediterranean Sea to dry up over ~1,000 years, producing vast salt deposits, preserved in the sediments of the sea floor.

About 5 million years ago there followed a brief warming trend and sea-level rose again leaving shallow marine sediments inland of modern coastlines around much of the world. Fossil floras and faunas show that climates were generally warmer than today -- Iceland had a temperate climate; southern England was subtropical.

Between 2 and 3 million years ago, ice caps began to form in the northern hemisphere.

During times of glacier growth, areas near glaciers experienced very cold conditions. Regions away from glaciers also experienced varied climates as climatic belts shifted. Because the world ocean temperatures became cooler, there was less evaporation; consequently, much of the world was drier than today. In contrast, some areas that are arid today were much wetter during times of glacial growth. For example, the temperate, sub-tropical and tropical zones were compressed toward the equator by the expanding cold belts – rain that now falls in the Mediterranean fell on the Sahara; the southwestern U.S. was wetter during glacial times because the high-pressure zone over the northern icecap deflected Pacific winter storms southward. Many salt lakes in the western US e.g., Great Salt Lake and Death Valley, were then flooded and greatly expanded.

Information on Quaternary climates comes from many sources – e.g., glacial features and deposits, pollen and sediments on the seafloor. The evidence from terrestrial deposits suggests that Pleistocene glaciation covered 27 million km2 or about three times the present area occupied by ice. The evidence from glacial deposits, mainly tills, in North America suggests at least four main glacial episodes, separated by warmer interglacials when the ice fronts melted back or retreated. In Europe, at least seven advances have been recognized. Part of the problem is that the advancing ice commonly erodes the deposits of earlier glaciations.

In the early 1960’s, Pleistocene ocean-floor sediments were examined for the first time for evidence of ice age climates. They showed that the glacial advances and retreats were far more complex than formerly believed. The evidence from the deep-sea oozes reflects changes in ocean temperatures and ocean water chemistry that can be related to climatic conditions.

The main evidence has come from fossil planktonic foraminifera on the ocean floor. Cores are recovered of the near surface sediments, which are then washed and sieved to concentrate the foraminifera shells = calcium carbonate. Some species are sensitive to warm or cold water, so by examining their distribution in a core, one can determine whether the overlying ocean water was warm or cool. Some species migrate to warmer waters when the ocean surface cools. For example, one species, Globorotalia menardii, is only found near the equator during cool glacial periods, but is found in higher latitudes during warmer interglacial periods.

Other planktonic foraminifera change their coiling direction in response to temperature fluctuations. The Pleistocene species, Globorotalia truncatulinoides coils to the right in water temperatures >10°C, while to the left in water <8-10°. Detailed climatic curves can be reconstructed from coiling ratios.

A widely used method is to measure the ratio of the isotopes 18O to 16O in the CaCO3 of planktonic foraminifera shells. Isotopes: all atoms of an element have the same number of protons in the nucleus, but may have different numbers of neutrons. Those having different numbers of neutrons are isotopes of the element: e.g., oxygen 16, oxygen 18.

The abundance of these two oxygen isotopes is related to the amount of oxygen in seawater when the shell is formed. The exact ratio of these two isotopes reflects the amount of ocean water stored in glacier ice. When water is evaporated from the oceans and precipitated on land to form glaciers, water containing the lighter 16O isotope is more easily evaporated than water containing the heavier 18O isotope. Consequently, Pleistocene glaciers contained more of the lighter isotope, while the oceans became enriched in the heavier isotope. These changes are recorded in the shells of planktonic foraminifera, which take up oxygen in their shells as calcium carbonate = CaCO3.

When the sediments have been dated by radiometric methods - radiocarbon dating and methods that data volcanic ash falls = the chronology of glacial and interglacial periods can be interpreted. Many more glacial/interglacial phases are suggested from the oceans than the records of glacial deposits on land. About 18 glacial expansions are recognized from deep-sea cores, increasing in intensity toward the latter part of the Pleistocene. Tying the sedimentary records from the oceans and land together, correlation, has proved difficult except for the youngest glacial periods . . .


http://www.usask.ca/geology/classes/geol206/iceoceans.html
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Carolyn Silver
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« Reply #1 on: February 16, 2007, 11:05:27 pm »

Variability During the Last Ice Age: Dansgaard-Oeschger Events

Abrupt changes did not begin during the Younger Dryas. Throughout the last glacial period (60,000 to 20,000 years ago), abrupt warming and cooling events, called Dansgaard-Oeschger or D-O events occurred in the North Atlantic. Greenland ice core records reveal that during the last glacial, the climate system abruptly shifted into, and then back out of, warm, close-to-interglacial conditions 23 times. Each oscillation consisted of gradual cooling followed by an abrupt warming.

Related to some of the coldest D-O intervals were distinctive events, recorded in North Atlantic marine sediments, of changes in the delivery of icebergs to the ocean and the amount of ice-rafted sand transported southward by the icebergs.

These Heinrich events in the sediment record resulted from changes in ocean circulation and iceberg melting, and were clear indications that cold polar waters extended farther south, carrying ice-rafted material from northern regions ( Bond et al. 1992, Bond & Lotti 1995). The events may have been accompanied by an influx of freshwater into the North Atlantic, through increased melting. Scientists have hypothesized that reduced deepwater formation may have accompanied these dramatic, but temporary, shifts of the Earth's climate. This is currently an area of active research (Maslin et al. 1995).

Cariaco Basin Sediment and GISP2 Ice Core Comparisons



Figure 19a. Abrupt climate events called Dansgaard-Oeschger events are found in Greenland ice cores, and some other locations such as the Cariaco Basin in the Caribbean Sea. Warm (interstadial) events are numbered in the ice core (red). Less negative numbers in the oxygen isotope ratio indicate warmer conditions in Greenland. In the Cariaco Basin sediment cores (green), highly reflective sediment layers indicate light green mud, and signals ocean climate and circulation associated with low plankton productivity. The data are significant because they reveal ocean-wide climate changes occuring within a century or less, altering the temperatures in the far North Atlantic, and the sea surface conditions close to the equator. In both regions, conditions appear to flip back and forth between two different states.



More recently, Bond and colleagues (Bond et al. 2001) have correlated the events in the North Atlantic with changes in solar output (the latter derived from proxy records in ice cores and tree rings). Their conclusion is that small, gradual changes in solar output crossed thresholds in the climate system, and that changes in thermohaline circulation resulted in abrupt shifts in the Earth's climate system.

Like the Younger Dryas, these events have had a hemispheric to global footprint. They were seen in sediment cores off the coast of Africa (Zhao et al. 1995), off the coast of Venezuela (Peterson et al. 2000), in the Arabian Sea (Schulz et al. 1998), and in Hulu Cave in China (Wang et al. 2001). The magnitude of change outside the North Atlantic, and more generally the geographic extent of abrupt change in temperature and precipitation during the last glacial, are currently topics of intense research.

http://www.ncdc.noaa.gov/paleo/abrupt/data_glacial2.html
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Carolyn Silver
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« Reply #2 on: February 16, 2007, 11:21:16 pm »

Looking Farther into the Past

Most scientists believe that glacial-interglacial cycles are the result of relatively gradual, periodic changes in the Earth's orbital parameters that influence the seasonal distribution of solar radiation striking the surface of the earth. However, the record clearly shows that the transition between states was anything but gradual. The rapid climate response to the gradual changes in solar radiation is one of the most dramatic examples of abrupt climate change.

Because of its length, multiple data sets, and precision in dating, the Vostok ice core from Antarctica is one of our best records of glacial-interglacial cycling. One of the interesting perspectives from Vostok is the nearly simultaneous changes in temperature, carbon dioxide, and methane through time. The Vostok record also shows the sawtooth character of the glacial-interglacial cycle. Temperature and carbon dioxide decreased in a series of progressively cooler steps towards glacial maximum conditions. Each glacial state ended abruptly with a rapid transition to the full interglacial state marked by the warmest temperatures and highest levels of carbon dioxide in the atmosphere. Why the Antarctic region was cold during periods when southern hemisphere solar radiation was high is the subject of current investigation. The evidence suggests that the southern hemisphere cooling was driven by the reduced solar energy in the northern hemisphere. As the northern hemisphere cooled, carbon dioxide in the atmosphere dropped. The drop in concentrations of this radiatively important greenhouse gas then caused cooling in the southern hemisphere.



Figure 20. Because of its length, multiple data sets, and precision in dating, the Vostok ice core from Antarctica is one of our best records of glacial-interglacial cycling. One of the interesting perspectives from Vostok is the nearly simultaneous changes in temperature, carbon dioxide, and methane through time.

Data Links
For more on the GISP2 and GRIP ice core projects and their data, see NOAA Paleoclimatology's Greenland ice core projects page.
The Alley (2000) Greenland snow accumulation and temperature reconstructon can be found on that page as well.
Hulu cave data can be found at Wang et al. 2001
Data from the Cariaco basin off Venezuela include:
Haug et al. 2001 Cariaco Basin Trace Metal Data

Hughen et al 1996 Tropical Atlantic Deglacial Climate Change Data

Hughen et al. 2000 Synchronous Radiocarbon and Climate Shifts During the Last Deglaciation

Lea et al. 2003 Cariaco Basin Foraminiferal Mg/Ca and SST Reconstruction

Peterson et al 2000 Cariaco Basin Reflectance, Bulk Elemental Data

Data from the Vostok ice core can be found at NOAA Paleoclimatology's Vostok Data page.
The North Atlantic record of Heinrich events can be found at Bond et al 1992 Heinrich Event Data, DSDP 609.
The Arabian Sea record of Heinrich events can be found at Schulz et al. 1998 Arabian Sea Stable Isotope and TOC Data

http://www.ncdc.noaa.gov/paleo/abrupt/data_glacial3.html
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Carolyn Silver
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« Reply #3 on: February 16, 2007, 11:31:00 pm »

Abrupt Climate Change During Glacial Times
The Younger Dryas

Some of the best-documented events are dramatic, rapid rearrangements of the entire climate system as the earth shifted from glacial (ice age) to interglacial (warm) periods. These events include the prominent Younger Dryas event, as well as the numerous Dansgaard/Oeschger events.

The Younger Dryas was an over 1,000 year long cold period between the last ice age and modern conditions. The Earth's climate abruptly warmed at the end of the last glacial period approximately 14,500 years ago. It then cooled back to glacial conditions over the next 3,000 years. After 1,000 years of conditions comparable to the last glacial climate, the Earth's climate suddenly warmed, with much of the change happening in less than a decade.



Figure 18. Ice core reconstruction of temperature and snow accumulation from Alley 2000.

The Younger Dryas is best known from two sources. Originally, it was described from pollen data, denoting a period when the cold-loving dryas flowers were much more common across much of Europe. It was not until the 1989-1994 U.S. and European projects GISP2 and GRIP drilled their long ice cores in Greenland that scientists could understand the rapidity with which climate changed during the Younger Dryas ( Alley 2000, Cuffey and Clow 1997). As you can see from the GISP2 data (Figure 18), temperatures rapidly rose around 10° C in a very short time around 11,500 B.P. Detailed analysis of the ice cores revealed that most of the increase occurred in less than a decade.

Hulu Cave Record



Figure 19. Comparison of oxygen isotope records in a Greenland ice core (red) and a stalagmite from Hulu Cave, China (blue). The Younger Dryas event is well known as an abrupt cool event in the North Atlantic region (more negative values indicate colder conditions in Greenland). The significance of the Hulu Cave record is that a concident change occured half-way around the world in summer rainfall. More negative values for Hulu Cave are interpreted pimarily as an indicator of more summer monsoon rainfall relative to winter rainfall. Thus the east Asian summer monsoon was weaker during the Younger Dryas when the North Atlantic was cooler. The time 16,000 to 10,000 years before present spans the transition from the glacial to interglacial state.


Unlike some abrupt change events, records of the Younger Dryas can be found from around the globe. The recent stalagmite record from Hulu cave (figure 19) shows that the changes in oxygen isotopes found in Greenland ice are matched in cave deposits in eastern China (Wang et al. 2001).

Records of the Younger Dryas are prominent across most of the northern hemisphere, and some manifestations of the event may spread worldwide. The Younger Dryas has now been even more precisely dated using sediments from the tropical Atlantic off Venezuela ( Hughen et al. 1996, Hughen et al. 2000, Haug et al 2001, Lea et al. 2003).

http://www.ncdc.noaa.gov/paleo/abrupt/data_glacial.html
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George Erikson
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« Reply #4 on: February 17, 2007, 12:16:22 pm »

Evidence for Sudden Climate Change in the Americas


In Cuban Depths, Atlantis or Anomaly?
Images of Massive Stones 2,000 Feet Below Surface Fuel Scientific Speculation


Kevin Sullivan Washington Post Foreign Service 

October 10, 2002 - HAVANA -- The images appear slowly on the video screen, like ghosts from the ocean floor. The videotape, made by an unmanned submarine, shows massive stones in oddly symmetrical square and pyramid shapes in the deep-sea darkness. Sonar images taken from a research ship 2,000 feet above are even more puzzling. They show that the smooth, white stones are laid out in a geometric pattern. The images look like fragments of a city, in a place where nothing man-made should exist, spanning nearly eight square miles of a deep-ocean plain off Cuba's western tip.

"What we have here is a mystery," said Paul Weinzweig, of Advanced Digital Communications (ADC), a Canadian company that is mapping the ocean bottom of Cuba's territorial waters under contract with the government of President Fidel Castro.

"Nature couldn't have built anything so symmetrical," Weinzweig said, running his finger over sonar printouts aboard his ship, tied up at a wharf in Havana harbor. "This isn't natural, but we don't know what it is."

The company's main mission is to hunt for shipwrecks filled with gold and jewels, and to locate potentially lucrative oil and natural gas reserves in deep water that Cuba does not have the means to explore.

Treasure hunting has become a growth industry in recent years as technology has improved, allowing more precise exploration and easier recovery from deeper ocean sites. Advanced Digital operates from the Ulises, a 260-foot trawler that was converted to a research vessel for Castro's government by the late French oceanographer Jacques Cousteau.

Since they began exploration three years ago with sophisticated side-scan sonar and computerized global-positioning equipment, Weinzweig said they have mapped several large oil and gas deposits and about 20 shipwrecks sitting beneath ancient shipping lanes where hundreds of old wrecks are believed to be resting. The most historically important so far has been the USS Maine, which exploded and sank in Havana harbor in 1898, an event that ignited the Spanish-American War.

In 1912, the ship was raised from the harbor floor by the U.S. Army Corps of Engineers and towed out into deeper water four miles from the Cuban shore, where it was scuttled. Strong currents carried the Maine away from the site, and its precise location remained unknown until Ulises's sonar spotted it two years ago.

Then, by sheer serendipity, on a summer day in 2000, as the Ulises was towing its sonar back and forth across the ocean like someone mowing a lawn, the unexpected rock formations appeared on the sonar readouts. That startled Weinzweig and his partner and wife, Paulina Zelitsky, a Russian-born engineer who has designed submarine bases for the Soviet military.

"We have looked at enormous amounts of ocean bottom, and we have never seen anything like this," Weinzweig said.

The discovery immediately sparked speculation about Atlantis, the fabled lost city first described by Plato in 360 B.C.. Weinzweig and Zelitsky were careful not to use the A word and said that much more study was needed before such a conclusion could be reached.

But that has not stopped a boomlet of speculation, most of it on the Internet. Atlantis-hunters have long argued their competing theories that the lost city was off Cuba, off the Greek island of Crete, off Gibraltar or elsewhere. Several Web sites have touted the ADC images as a possible first sighting.

Among those who suspect the site may be Atlantis is George Erikson, a Prescott, Arizona, anthropologist who co-authored a book in which he predicted that the lost city would be found offshore in the tropical Americas.

"I have always disagreed with all the archaeologists who dismiss myth," said Erikson, who said he had been shunned by many scientists since publishing his book about Atlantis. He said the story has too many historical roots to be dismissed as sheer fantasy and that if the Cuban site proves to be Atlantis, he hopes "to be the first to say, 'I told you so.' "

Manuel Iturralde, one of Cuba's leading geologists, said it was too soon to know what the images prove. He has examined the evidence and concluded that, "It's strange, it's weird; we've never seen something like this before, and we don't have an explanation for it."

Iturralde said volcanic rocks recovered at the site strongly suggest that the undersea plain was once above water, despite its extreme depth. He said the existence of those rocks was difficult to explain, especially because there are no volcanoes in Cuba.

He also said that if the symmetrical stones are determined to be the ruins of buildings, it could have taken 50,000 years or more for tectonic shifting to carry them so deep into the ocean. The ancient Great Pyramid of Giza in Egypt is only about 5,000 years old, which means the Cuba site "wouldn't fit with what we know about human architectural evolution," he said.

"It's an amazing question that we would like to solve," he said.

But Iturralde stressed that the evidence is inconclusive. He said that no first-hand exploration in a mini-submarine had been conducted, which would provide a much more comprehensive assessment. He said a remote-operated video camera provides only a limited perspective, like someone looking at a close-up image of an elephant's toe and trying to describe the whole animal.

The National Geographic Society has expressed interest and is considering an expedition in manned submarines next summer, according to Sylvia Earl, a famed American oceanographer and explorer-in-residence at the society.

"It's intriguing," Earl said in an interview from her Oakland, Calif., home. "It is so compelling that I think we need to go check it out."

Earl said a planned expedition this past summer was canceled because of funding problems. But she said National Geographic hopes to explore the site next summer as part of its Sustainable Seas research program.

Earl has visited Cuba and described the preliminary evidence as "fantastic" and "extraordinary." But she stressed that as a "skeptical scientist," she would assume that the unusual stones were formed naturally until scientific evidence proved otherwise.

"There is so much speculation about ancient civilizations," she said. "I'm in tune with the reality and the science, not the myths or stories or fantasies."

As they search for answers, Weinzweig and Zelitsky have suddenly become involved in a new mystery -- the discovery of a potential blockbuster shipwreck. They said that on Aug. 15, their remotely operated vehicle came across what appears to be a 500-year-old Spanish galleon that they had been searching for.

They declined to name the ship, fearful of other treasure hunters, but they said it carried a priceless cargo of emeralds, diamonds and ancient artifacts. By contract, they said they can keep 40 percent of the value of whatever they recover. They said the value of findings at the newly discovered wreck could far exceed the nearly $4 million that their private backers have so far invested in their operations.

Weinzweig said a closer examination is needed to prove the ship's identity. He said that in treasure hunting, as in the search for Atlantis, there is no substitute for science.

"One thing is legend," he said, sitting on Ulises's bridge. "Another is the hard evidence you find on the ocean floor."

Contact:  George Erikson,   Coauthor of  Atlantis In America: Navigators of the Ancient World

Italian Edition:  Le Strade Di Atlantide (Piemme)

             760 251-9342
             Eriksongd@aol.com
             www.AtlantisInAmerica.com

Erikson runs tours to Ancient sites in Belize, Guatemala and the Yucatan. For 2006 Tour Info contact via email at Eriksongd@aol.com
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Carolyn Silver
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« Reply #5 on: March 23, 2007, 11:32:10 pm »

Meltwater pulse 1A



Image showing sea level change during the end of the last glacial period. Meltwater pulse 1A is indicated.

Description
 
Sea level rise since the last glacial episode in meters
Sea level rise from direct measurements during the last 120 years in centimetersThis figure shows changes in sea level during the Holocene, the time following the end of the most recent glacial period, based on data from Fleming et al. 1998, Fleming 2000, & Milne et al. 2005. These papers collected data from various reports and adjusted them for subsequent vertical geologic motions, primarily those associated with post-glacial continental and hydroisostatic rebound. The first refers to deformations caused by the weight of continental ice sheets pressing down on the land, the latter refers to uplift in coastal areas resulting from the increased weight of water associated with rising sea levels. It should be noted that because of the latter effect and associated uplift, many islands, especially in the Pacific, exhibited higher local sea levels in the mid Holocene than they do today. Uncertainty about the magnitude of these corrections is the dominant uncertainty in many measurements of Holocene scale sea level change.

The black curve is based on minimizing the sum of squares error weighted distance between this curve and the plotted data. It was constructed by adjusting a number of specified tie points, typically placed every 1 kyr and forced to go to 0 at the modern day. A small number of extreme outliers were dropped. It should be noted that some authors propose the existence of significant short-term fluctuations in sea level such that the sea level curve might oscillate up and down about this ~1 kyr mean state. Others dispute this and argue that sea level change has been a smooth and gradual process for essentially the entire length of the Holocene. Regardless of such putative fluctuations, evidence such as presented by Morhange et al. (2001) suggests that in the last 10 kyr sea level has never been higher than it is at present.

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« Reply #6 on: March 23, 2007, 11:34:12 pm »





Description
 
Expansion of the most recent 9 kyrThis figure shows sea level rise since the end of the last glacial episode based on data from Fleming et al. 1998, Fleming 2000, & Milne et al. 2005. These papers collected data from various reports and adjusted them for subsequent vertical geologic motions, primarily those associated with post-glacial continental and hydroisostatic rebound. The first refers to deformations caused by the weight of continental ice sheets pressing down on the land, the latter refers to uplift in coastal areas resulting from the increased weight of water associated with rising sea levels. It should be noted that because of the latter effect and associated uplift, many islands, especially in the Pacific, exhibited higher local sea levels in the mid Holocene than they do today. Uncertainty about the magnitude of these corrections is the dominant uncertainty in many measurements of sea level change.

The black curve is based on minimizing the sum of squares error weighted distance between this curve and the plotted data. It was constructed by adjusting a number of specified tie points, typically placed every 1 kyr but at times adjusted for sparse or rapidly varying data. A small number of extreme outliers were dropped. It should be noted that some authors propose the existence of significant short-term fluctuations in sea level such that the sea level curve might oscillate up and down about this ~1 kyr mean state. Others dispute this and argue that sea level change has largely been a smooth and gradual process. However, at least one episode of rapid deglaciation, known as meltwater pulse 1A, is agreed upon and indicated on the plot. A variety of other accelerated periods of deglaciation have been proposed (i.e. MWP-1B, 2, 3, 4), but it unclear if these actually occurred or merely reflect misinterpretation of difficult measurements. No other events are evident in the data presented above.

The lowest point of sea level during the last glaciation is not well constrained by observations (shown here as a dashed curve), but is generally argued to be approximately 130 +/- 10 m below present sea level and to have occurred at approximately 22 +/- 3 thousand years ago. The time of lowest sea level is more or less equivalent to the last glacial maximum. Prior to this time, ice sheets were still increasing in size so that sea level was decreasing semi-continuously over a period of approximately 100,000 years.

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« Reply #7 on: March 23, 2007, 11:36:43 pm »



Sea level rise from direct measurements during the last 120 years in centimeters
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« Reply #8 on: March 23, 2007, 11:38:02 pm »

Description
 
Sea level rise since the last glacial episode in meters


Sea level rise from direct measurements during the last 120 years in centimetersThis figure shows changes in sea level during the Holocene, the time following the end of the most recent glacial period, based on data from Fleming et al. 1998, Fleming 2000, & Milne et al. 2005. These papers collected data from various reports and adjusted them for subsequent vertical geologic motions, primarily those associated with post-glacial continental and hydroisostatic rebound. The first refers to deformations caused by the weight of continental ice sheets pressing down on the land, the latter refers to uplift in coastal areas resulting from the increased weight of water associated with rising sea levels. It should be noted that because of the latter effect and associated uplift, many islands, especially in the Pacific, exhibited higher local sea levels in the mid Holocene than they do today. Uncertainty about the magnitude of these corrections is the dominant uncertainty in many measurements of Holocene scale sea level change.

The black curve is based on minimizing the sum of squares error weighted distance between this curve and the plotted data. It was constructed by adjusting a number of specified tie points, typically placed every 1 kyr and forced to go to 0 at the modern day. A small number of extreme outliers were dropped. It should be noted that some authors propose the existence of significant short-term fluctuations in sea level such that the sea level curve might oscillate up and down about this ~1 kyr mean state. Others dispute this and argue that sea level change has been a smooth and gradual process for essentially the entire length of the Holocene. Regardless of such putative fluctuations, evidence such as presented by Morhange et al. (2001) suggests that in the last 10 kyr sea level has never been higher than it is at present.

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« Reply #9 on: March 23, 2007, 11:42:41 pm »



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« Reply #10 on: March 23, 2007, 11:45:26 pm »

Tethys Ocean

The Tethys Ocean was a Mesozoic era ocean that existed between the continents of Gondwana and Laurasia before the opening of the Indian Ocean.



Historical theory

In 1893, using fossil records from the Alps and Africa, Eduard Suess proposed the theory that a shallow inland sea had once existed between Laurasia and Gondwana. He named it the 'Tethys Sea' after the Greek sea goddess Tethys. The theory of plate tectonics later disproved or overrode many parts of Suess's theory, even determining the existence of an earlier body of water called the Tethys Ocean. However, Suess's overall concept was still relatively accurate and remarkably imaginative for its day, so he generally is credited with the discovery of both the Tethys Sea and the Tethys Ocean.


Modern theory

About 250 million years ago, during the late Permian Era, a new ocean began forming in the southern end of the Paleo-Tethys Ocean. A rift formed along the northern continental shelf of Southern Pangaea (Gondwana). Over the next 60 million years, that piece of shelf, known as Cimmeria, traveled north, pushing the floor of the Paleo-Tethys Ocean under the eastern end of Northern Pangaea (Laurasia). The Tethys Ocean formed between Cimmeria and Gondwana, directly over where the Paleo-Tethys used to be.

During the Jurassic Period (150 mya), Cimmeria finally collided with Laurasia. There it stalled, the ocean floor behind it buckling under, forming the Tethyan Trench. Water levels rose and the western Tethys came to shallowly cover significant portions of Europe. Around the same time, Laurasia and Gondwana began drifting apart, leaving the Atlantic Ocean between them. Between the Jurassic and the Cretaceous (100 mya), even Gondwana began breaking up, pushing Africa and India north, across the Tethys. As these land masses pushed in on it from all sides, up until as recently as the Late Miocene (15 mya), the Tethys ocean continued to shrink, becoming the Tethys Seaway or 'Tethys Sea'.

Today, India, Indonesia and the Indian Ocean cover the area once occupied by the Tethys Ocean, and Turkey, Iraq, and Tibet sit on Cimmeria. What was once the Tethys Sea has become the Black, Caspian and Aral Seas. Most of the floor of the Tethys Ocean disappeared under Cimmeria and Laurasia. We only know the Tethys existed because geologists like Suess found fossils of ocean creatures in rocks in the Himalayas. So, we know those rocks were underwater, before the Indian continental shelf began pushing upward as it smashed into Cimmeria. We can see similar geologic evidence in the Alpine orogeny of Europe, where the movement of the African plate raised the Alps.

Paleontologists also find the Tethys Ocean particularly important because much of the world's sea shelves were found around its margins for such an extensive period of time. Marine, marsh-dwelling, and estuarian fossils from these shelves are of considerable paleontological interest.


Terminology and subdivisions

Like every science, geology is a continuously evolving system of theories, and the terms used to describe various pre-historic formations have fluctuated as more accurate theories have emerged. For example, many internet sources use "Tethys Ocean" to refer to the "Tethys Sea" and vice versa. Some even appear to erroneously refer to the growing Atlantic Ocean during the Jurassic as the Tethys Sea.

The western end of the Tethys Ocean is called Tethys Sea, Western Tethys Ocean or Alpine Tethys Ocean. The Black, Caspian and Aral Seas are thought to be its crustal remains. However, this "Western Tethys" was not simply a single open ocean. It covered many small plates, Cretaceous island arcs and microcontinents. Many small oceanic basins (Valais Ocean, Piemont-Liguria Ocean) were separated from each other by continental terranes on the Alboran, Iberian, and Apulian plates. The high sealevel in the Mesozoic age flooded most of these continental domains forming shallow seas.

The eastern part of the Tethys Ocean is likewise sometimes referred to as Eastern Tethys.

As theories have improved, scientists have extended the "Tethys" name to refer to similar oceans that preceded it. The Paleo-Tethys Ocean, mentioned above, existed from the Silurian (440 mya) through the Jurassic eras, between the Hunic terranes and Gondwana (later the Cimmerian terranes). Before that, the Proto-Tethys Ocean existed from the Ediacaran (600 mya) into the Devonian (360 mya), and was situated between Baltica and Laurentia to the north and Gondwana to the south. Neither of these should be confused with the Rheic Ocean, which existed to the west of them in the Silurian era.

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Mark of Australia
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« Reply #11 on: March 24, 2007, 11:51:38 am »

I can't help but cringe when I see those maps of Pangaea ..The continents all bunched together on an Earth with the same diameter as it has at present ....It just looks so out of date ,so wrong.   Like the Earth is flat and their are only four elements ,Earth ,Air ,Fire and Water.   Tongue   

Expanding Earth .



I admit there is a lot to cringe about in that video aswell   .lol             ...   I ripped it of an AR thread   Roll Eyes

But I agree the Earth did expand .that's all I'll agree to.

Why should the Earth have a stable diameter ?  It's just one of those lazy assumptions of permanency.
« Last Edit: March 24, 2007, 11:56:16 am by Mark Ponta » Report Spam   Logged
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