Posted on 01/18/2006 10:18:38 AM PST by cogitator
Scientists use deep ocean historical records to find an abrupt ocean circulation reversal
Newly published research results provide evidence that global climate change may have quickly disrupted ocean processes and lead to drastic shifts in environments around the world.
Although the events described unfolded millions of years ago and spanned thousands of years, the researchers, affiliated with the Scripps Institution of Oceanography, say they provide one of the few historical analogs for warming-induced changes in the large-scale sea circulation, and thus may help to illuminate the potential long-term impacts of today's climate warming.
Writing in this week's issue of the journal Nature, scientists Flavia Nunes and Richard Norris explain that they probed a four- to seven-degree warming period that occurred some 55 million years ago during the closing stages of the Paleocene and the beginning of the Eocene eras. The unique data set they constructed, based on the chemical makeup of tiny ancient sea creatures, uncovered for the first time evidence of a monumental reversal in the circulation of deep-ocean patterns around the world. The researchers concluded that it was triggered by the global warming the world experienced at the time.
"The earth is a system that can change very rapidly," said Nunes. "Fifty-five million years ago, when the earth was in a period of global warmth, ocean currents rapidly changed direction and this change did not reverse to original conditions for about 20,000 years."
The global warming of 55 million years ago, known as the Paleocene/Eocene Thermal Maximum (PETM), emerged in less than 5,000 years, an instantaneous blip on geological time scales. Fossil records indicate that the PETM set in motion a host of important changes around the globe, ranging from a mass extinction of deep-sea bottom-dwelling marine life to key migrations terrestrial mammal species, likely allowed by warm conditions that opened travel routes not possible under previously colder climates. For example, this period is where scientists find the earliest evidence for horses and primates in North America and Europe.
To obtain their data, Nunes and Norris analyzed carbon isotopes--chemical signatures that reveal a host of information--from the shells of single-celled animals called foraminifera, or "forams." Such organisms exist in a variety of marine environments, and their vast numbers per research sample allow scientists to uncover a range of details about the state of the seas.
"A tiny shell from a sea creature living millions of years ago can tell us so much about past ocean conditions," said Nunes. "We know approximately what the temperature was at the bottom of the ocean. We also have a measure of the nutrient content of the water the creature lived in. And, when we have information from several locations, we can infer the direction of ocean currents."
In the study, the scientists looked at a foram named Nuttalides truempyi from 14 sites around the world in deep-sea sediment cores retrieved via the Integrated Ocean Drilling Program (IODP), for which Joint Oceanographic Institutions, Inc., manages the U.S. component. The isotopes were used as nutrient "tracers" to reconstruct changes in deep-ocean circulation through the PETM period. Nutrient levels tell the researchers how long a sample has been near or isolated from the sea surface, thus giving them a way to track the age and path of deep-sea water.
The results indicate that deep-ocean circulation in the Southern Hemisphere abruptly stopped the conveyor belt-like process known as "overturning," in which cold and salty water in the depths exchanges with warm water on the surface. Even as it was virtually shutting down in the south, however, overturning apparently became active in the Northern Hemisphere. The researchers believe this shift drove unusually warm water to the deep sea, likely releasing stores of methane gas that led to further global warming and a massive die-off of deep-sea marine life.
Overturning is a fundamental component of the global climate conditions we know today, said Bil Haq, program director in the National Science Foundation (NSF)'s division of ocean sciences, which funded the research. For example, overturning in the modern North Atlantic Ocean is a primary means of drawing heat into the far north Atlantic and keeping temperatures in Europe relatively warmer than conditions in Canada, he said.
Today, "new" deep-water generation does not occur in the Pacific Ocean because of the large amount of freshwater input from the polar regions, which prevents North Pacific waters from becoming dense enough to sink to more than intermediate depths.
In the case of the Paleocene/Eocene, however, deep-water formation was possible in the Pacific Ocean because of global warming-induced changes. The Atlantic Ocean also could have been a significant generator of deep waters during this period.
Modern carbon dioxide input from fossil fuel sources to the earth's surface is approaching the same levels estimated for the PETM period, which raises concerns about future climate and changes in ocean circulation, say the scientists. Thus, they say, the Paleocene/Eocene example suggests that human-produced changes may have lasting effects not only on global climate, but on deep ocean circulation.
"Overturning is very sensitive to surface ocean temperatures and surface ocean salinity," said Norris. "The case described here may be one of the best examples of global warming triggered by the massive release of greenhouse gases. It gives us a perspective on what the long-term impact is likely to be of today's human-caused warming."
"The ocean would have much more water if it weren't for all the sponges" - 2T
This conclusion cannot be logically supported. If CO2 levels at the PETM were similar to today, then a human cause cannot be a logical assumption, since man was not present at the PETM event.
The release of frozen methane from under the ocean floor is right up there on cataclysm-meter with Everest-sized space rocks hitting the planet.
(Definitely not a good thing.)
RE: "...conclusion cannot be logically supported..."
It really doesn't matter what the source of the CO2 was. In this case, since the climate change took place after the extinction of the dinosaurs, it's a 100% certainty that flatulence from sauropods had nothing to do with the warm up, either.
I'm sure that that's a huge comfort to the departed dinosaurs, as they continue to graze, ruminate and poot Big Ones, in the Elysian Aalanian Fields.
It does when you're using the argument to justify reducing CO2 output of human activity.
The "proof" of the causation of the current atmospheric CO2 levels as being primarily due to human activities is not reliant on the PETM. The main thing that the PETM does is show in the Earth system that greenhouse gases can force temperature changes (and apparently then cause some "downstream" effects).
My point is not that the event won't happen as before, but that mankind may have absolutely nothing to do with it.
Leni
Another point: The PETM does not establish the cause/effect relationship of CO2 to climate change. Just that the CO2 levels were elevated at the time of the "overturning". CO2 levels as a cause of that event, rather than an effect of it, or spuriously related to a different overriding cause, cannot be established.
I've read some other articles about the PETM. The cause of the methane release appears to have been a fairly rapid decrease in sea level (cause unknown, as far as I can tell), leading to destablization of the sea floor methane deposits, which released into the atmosphere, and apparently were then converted to CO2, prolonging the initial warming caused by the methane. This process wasn't an all-at-once event, either.
Under current conditions, thought methane was increasing a bit in the atmosphere, the main gas on the rise is CO2. IF (big if) CO2 can induce the same temperature effect as the methane --> CO2 did in the PETM, it's possible that there could be ocean circulation changes, as other research has indicated. The main question is how much temperature change the increasing CO2 in the atmosphere will cause.
Bush's fault!
Although the events described unfolded millions of years ago and spanned thousands of years, the researchers, affiliated with the Scripps Institution of Oceanography, say they provide one of the few historical analogs for warming-induced changes in the large-scale sea circulation, and thus may help to illuminate the potential long-term impacts of today's climate warming.Since the climate change today is natural, just as it was then, Scripps demagogues can join the long list of global warming demagogues who can dine on my feces.
I like that closing sentence -- "future decision-making could be made based on scientific data and not on political expediency". I wouldn't count on it, but that would be great.Caves reveal clues to UK weatherAt Pooles Cavern in Derbyshire, it was discovered that the stalagmites grow faster in the winter months when it rains more. Alan Walker, who guides visitors through the caves, says the changes in rainfall are recorded in the stalactites and stalagmites like the growth rings in trees. Stalagmites from a number of caves have now been analysed by Dr Andy Baker at Newcastle University. After splitting and polishing the rock, he can measure its growth precisely and has built up a precipitation history going back thousands of years. His study suggests this autumn's rainfall is not at all unusual when looked at over such a timescale but is well within historic variations. He believes politicians find it expedient to blame a man-made change in our weather rather than addressing the complex scientific picture... He said he wanted greater awareness to ensure "future decision-making could be made based on scientific data and not on political expediency".
by Tom Heap
Saturday, 2 December, 2000
I can understand that such phenomenon are complex, but much is left unexplained and unconvincing here.
If you have warm water at the top and cold water at the bottom, especially when the cold water stretches down a couple of miles, there will be no natural circulation. The cold water will stay at the bottom and the warm water will stay at the top. The warm water would rise to the top if it wasn't already there.
Therefore, what does the fresh water content got to do with anything?
And have these people never heard of osmosis? Yes, the ocean is huge. But with so many other forces, currents, circulations, and eddies going on in the complex ocean, why would you make rash assumptions about fresh water content being the cause of anything?
If you could magically take all of the salt out of the top 1/2 mile of the ocean's depth vertically, so that the top 1/2 mile were fresh water and the lower 1/2 mile (say) were salt water, what would happen? Even without any vertical circulation of the actual water itself on the basis of temperature, the salt would -- by the power of osmosis (which is an actual force) -- be DRAWN up into the fresh water, so that the salt would be equally diffused throughout the entire ocean. It would be very hard to prevent this from occurring. The absence of salt suspended in the fresh water would ATTRACT salt molecules from the depths, and the salt would move from suspension in the salty water toward the fresh water, even if the water itself did not actually move.
Meanwhile, it will take an unusual pattern of circulation to stir the water high to low. Most likely, a circulatory pattern may create a mild cyclone effect drawing water up from the depths.
Similarly, imperfections in the movement of the currents may create eddies and tangential consequences creating up-down movement of water.
Also, the vertical circulation of sea water may be most affected by volcanic eruptions under the ocean. Cold water will naturally stay at the bottom. However, a volcanic event or heat source at the ocean's floor would heat the water, causing it to rise, thus setting up a whole series of circulatory actions that would stir the ocean vertically, top to bottom.
Furthermore, do these people not know that the shape of the oceans has been CHANGING over time as the continents drift?
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Some climatologists view carbon dioxide as a SYMPTOM rather than a CAUSE of [paleoclimatic episodes of] global warming. Warmer climates with adequate moisture enable various life forms to flourish (with greater biomass per unit land area) than cooler (or drier) climates permit.
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