PDA

View Full Version : Discussion: Earth's Climate During the ...



Fraser
2005-Aug-25, 05:28 PM
SUMMARY: Around 251 million years ago, something happened to the Earth's climate that wiped out 90-95% of marine life and 70% of terrestrial life. Scientists at the National Center for Atmospheric Research (NCAR) have developed a computer model that demonstrates that rapid increases in carbon dioxide belched out of volcanoes did the trick. Temperatures were 10 to 30 degrees Celsius (18 to 54 degrees Fahrenheit) higher than they are today, which broke a cycle that pulled carbon dioxide out of the atmosphere.

View full article (http://www.universetoday.com/am/publish/higher_temperatures_cause_prehistoric_extinction.h tml)

What do you think about this story? Post your comments below.

StarLab
2005-Aug-25, 05:34 PM
I may be a mere layteen, but I say this is big news in Scienceland!

lswinford
2005-Aug-25, 10:57 PM
I've wondered about that "stratified" oxygen in the sea description.

In the Black Sea we have stratification in that the lower depths are oxygen poor. That permitted some ship finds in recent years because the organisms that would rot the wood couldn't live in them.

In the Gulf of Mexico the description seems different, where there are dead zones. Supposedly, fertilizer runoff carried down the Mississippi river leads to algae blooms. The algae, however, die (uneaten) and their decomposition leaves carbon dioxide in the water.

Algae are strange things, as a broad subject. Some algae are harvested as if for a flour-substitute, as a carbohydrate-type food. Some algae are being grown to produce oil, as a bio-fuel. Some algae create the killing "red tides". Some algae are hailed as a possible cure for global warming in that iron-sulfide dump experiments show great blooms of algae that grab atmospheric carbon dioxide and pump out oxygen. Obviously, as with trees it is not true that if you've seen one you've seen them all. What if a contributor to the carbon dioxide was an overabundance of the wrong kinds of algae, a sort of global "red tide" infestation?--which accounts for the sea "stratification" perhaps?

On the other hand, if vulcanism belched the carbon dioxide into the air from land volcanos, with so much of the world under the sea, the underwater vulcanism would have likely increased too, so the carbon dioxide from those eruptions would be part of the picture.

Interesting picture, thanks.

cran
2005-Aug-26, 04:19 AM
It is an interesting article, but it is also a series of conclusions based on the findings of a model...
The Permian was certainly a time of active vulcanism - it is highlighted by the formation and subsequent break-up of Pangaea - a single supercontinent criss-crossed with himalayan-style suture zones, and bounded by the most active subduction zones - most of the continent was desert... all of these factors contributed to an ice age... the evidence of which can be found in many parts of the world today...

As a result, ocean waters became stratified with little oxygen, a condition that proved deadly to marine life. This in turn accelerated the warming, since marine organisms were no longer removing carbon dioxide from the atmosphere.
This is a little misleading... oxygen levels are pretty much stratified in the oceans and seas at any time... much of the abyssal plains and many sea floor environments are relatively anoxic and are populated by anaerobic organisms.
What were killed were the upper level (aerobic) photosynthetic organisms (phytoplankton and chlorophyllic bacteria) ... the main oxygen producers, and the base of the food chain... and their aerobic predators both starved and suffocated... this is due to the ocean-atmosphere carbon balance ... an excess of CO2 and CO in the atmosphere leads to an increase in ocean uptake of CO2 and CO beyond the photosynthetic organisms' ability to cope ... as has been proven by many 'car suicides' CO will readily displace O2 in the bloodstream of aerobic life - but all of this is in the upper levels of the oceans and seas ... land plants (which were already stressed by extreme temperatures and dry conditions) have only a limited ability to cope with increases in CO2 - experiments and the fossil record show that stomata (pore) density does not continue to increase with rising atmospheric CO2, but levels off and the CO/CO2/O2 balance in the atmosphere will continue towards increasing carbon and decreasing oxygen...

At the height of glaciation, CO2 is removed from the atmosphere and accumulates on/in the glacial ice (as dry ice) wherever the surface/atmospheric interface falls to -78C (at 1 atm pressure) - this happens today in parts of Antarctica and Siberia and northern Greenland during their respective winters, as well as on the highest Himalayan peaks (where atmospheric pressure is substantially lower)...

With glacial retreat, the CO2 is taken up in the meltwater and rapidly added to the continental marine margins, where a combination of chemical and biogenic processes lead to the (geologically) rapid formation of 'shelf carbonates' - a key feature of every post-glacial period.

As in many other examples, this is a case of a simplified model (with predetermined boundaries and conditions), leading to a simplistic and misleading set of conclusions.
<_<

lswinford
2005-Aug-26, 05:07 PM
Alright&#33; The cure for &#39;greenhouse gasses&#39; is a really cold winter.

I&#39;ll have to read some more on that. Thanks for the lead.

cran
2005-Aug-26, 10:25 PM
Yes, I guess so ... a really long, really cold winter&#33; :ph34r:
Which ever it goes, it&#39;s gonna really annoy anyone with beachfront property... <_<

dave_f
2005-Aug-27, 12:50 AM
Originally posted by lswinford@Aug 26 2005, 12:07 PM
Alright&#33; The cure for &#39;greenhouse gasses&#39; is a really cold winter.

I&#39;ll have to read some more on that. Thanks for the lead.
The correct term is "Ice Age". :P (just kidding... your point is quite valid).

In seriousness, this is interesting stuff. What I think though is that severe climate change is the cause of every mass extinction. Where the debate lies is what caused those climate changes. The dinosaurs didn&#39;t die when an asteroid hit the planet. They died slowly after the asteroid hit, because the Earth&#39;s ecology was altered during the ensuing distribution of dust throughout the atmosphere. Some may argue a volcano did this. Others promote a sunspot theory or something to that effect. Regardless, climate change was the effect, not the cause.

This research&#39;s conclusion is open-ended, though it does demonstrate that normal planet development defined by the current standard models can easily account for even the unexplained phenomenon that caused these extinctions.

Guest
2005-Aug-28, 01:54 AM
My understanding of this article is that the principal problem was global surface temperatures warming to a depth of 10k feet everywhere. One of the principal factors driving ocean currents is cold water at the surface sinking to lower depths at higher latitudes. What happens if it gets so warm that there is no source of cold water? Nothing sinks and everywhere there is warm stagnant ocean water. With the carbon sink lost any co2 that gets released from volcanic activity remains in the atmosphere to make it even warmer.
What is quite bothersome to me is that it seems that there is a threshold in the system beyond which just about everything dies. This threshold can be reached as it has been reached before. What should perturb many of us is that we have been artificially accelerating global warming without any significant global volcanic events. What were to happen then if there was a large scale volcanic event now?
I agree that the rate of change is likely a significant component that drives mass extinctions. I think that it will be hard if not impossible to determine just what is a safe rate of acceleration for global warming. 1 degree celcius in 50 years, 100, 200, 1000? This is a very important question to tackle as well. Most likely during large volcanic outbursts in the past such as those that produced the Deccan flats or the Siberian basalt plateau happened fairly quickly, perhaps over tens or hundreds of years.
With regards to the cretaceous mass extinction, I happen to be in the camp with those who believe it was a rapid but a more gradual process than could be explained by a single asteroid hit. Certainly there was a large asteroid/comet strike. We know this can lead to a "nuclear winter" like scenario of sudden cooling and loss of photosynthesis from a global pall of dust. If this is what casued the extinction, then everything should have died at once, a blink of an eye in the geologic record. Yet there is evidence in different locations around the world that species persisted quite a long time (although still brief with regards to the geologic record) but more likely hundreds or thousands of years rather than one or two. In regions such as North America, I believe the evidence points to a sudden extinction event all at once like one would suspect which was probably a result of a firestorm over that continent and heavy fallout in that region. So in my mind it is more likely that the dinosaurs died by fire- prolonged heavy volcanism with rising co2 and temperatures over a fairly short time period. Of course this begs the question of just what was it that cooled off the planet again to a point well below what existed before the age of the dinosaurs, but that is another story.

cran
2005-Aug-28, 07:19 AM
The CCSM indicated that ocean waters warmed significantly at higher latitudes because of rising atmospheric levels of carbon dioxide (CO2), a greenhouse gas. The warming reached a depth of about 10,000 feet (4,000 meters), interfering with the normal circulation process in which colder surface water descends, taking oxygen and nutrients deep into the ocean.
As a result, ocean waters became stratified with little oxygen, a condition that proved deadly to marine life. This in turn accelerated the warming, since marine organisms were no longer removing carbon dioxide from the atmosphere.
Hi Guest,
you were referring to the above paragraphs, which is one set of results of a model based on preset boundary conditions and estimated consequences, into which one set of variables were entered... the conclusions drawn from them are not borne out in the geological record.
Further, the presentation of the conclusions are over-simplified and misleading ... the oceans are always stratified in general terms, and very little free or dissolved oxygen makes it into the Deep Water masses or the Bottom Water masses at any time ... and the unusually high heat capacity of water makes mixing and current flows very slow ...
surface and upper current warming can indeed alter convection regimes, but will not shut them down entirely - higher water temperatures mean stronger horizontal currents and greater evaporation rates and higher upper level salinities, the pressure gradients then induce the more saline (therefore denser) water to form downward &#39;diapiric&#39; flows until a density equivalence is reached and the warmer water, if not part of the integrated current will form a thermohaline lens - as it cools, its density increases and it falls further - as far as currents and convection are concerned, it is the density differences that drive them, not the absolute temperatures ...
under the conditions described by the model, oxygen levels will be less in the upper layers (above the thermocline) due to the increase in molecular motion (leading to evaporation at the surface) and due to preferential displacement of oxygen by increasing levels of CO2 - records in sediment- and ice- cores indicate when in the past such warmer waters (and by proxy warmer global climates) have prevailed by showing increases in CO2 ratios, and by higher 18O ratios (because 18O is more likely to be retained and 16O is more likely to be lost during evaporation)...
marine organisms do not "remove CO2 from the atmosphere" ... the CO2 and water do that by preferentially displacing oxygen ... it is known as the &#39;ocean/atmosphere carbon balance&#39; ... the marine organisms which rely on dissolved oxygen die by suffocation ... the marine organisms which normally take up CO2 (from the water) and release oxygen (blue-green algae and other phytoplankton) die off where there has been a sudden or extended increase in CO2 because the water becomes too acidic (like the erroneously-called &#39;soda water&#39; or the more accurately labelled &#39;carbonated water&#39;) and attacks cellular structures - life in the deep oceans seems immune to these changes in the upper layers.

With regards to the cretaceous mass extinction, I happen to be in the camp with those who believe it was a rapid but a more gradual process than could be explained by a single asteroid hit. Certainly there was a large asteroid/comet strike. We know this can lead to a "nuclear winter" like scenario of sudden cooling and loss of photosynthesis from a global pall of dust. If this is what casued the extinction, then everything should have died at once, a blink of an eye in the geologic record. Yet there is evidence in different locations around the world that species persisted quite a long time (although still brief with regards to the geologic record) but more likely hundreds or thousands of years rather than one or two. This is very interesting news&#33; Guest, can you please indicate where such discoveries have been made? The K/T boundary is quite distinct in the geological record, and is found in outcrop in many parts of the world, and also in drill cores; the boundary is quite thin and comprises compressed ash, char and a distinctive anomalous iridium content; of the species said to have gone extinct in this mass extinction event, numerous fossils are found below and at the K/T boundary layer... not one has been found above it, as far as I am aware - so again, can you please indicate where and when such discoveries have been made? The record does show that, among the dinosaurs, speciation was trending towards more bizarre forms (rapid mutations) and that species were dying out for some millenia prior to the K/T event ... perhaps that is the extended time you were thinking of?

So in my mind it is more likely that the dinosaurs died by fire- prolonged heavy volcanism with rising co2 and temperatures over a fairly short time period. Of course this begs the question of just what was it that cooled off the planet again to a point well below what existed before the age of the dinosaurs, but that is another story. There is no indication in the geological record that temperatures increased after the K/T event - the Mesozoic (from the Triassic to the Cretaceous; ie the Age of the Dinosaurs) is distinguished by much higher global temperatures, higher CO2 levels and lower O2 levels when compared with theTertiary and Quaternary -
in fact, the indications are the opposite; a distinct cooling marks the beginning of the Tertiary - the Palaeocene - followed by mild warming and cooling cycles throughout the Eocene and Miocene (and are matched with stranded beach lines and &#39;transgression/regression&#39; stratigraphic profiles, meaning rising and falling sea levels) - the Pliocene marks the beginning of the Last/Recent (or Pliocene/Pleistocene) Ice Age.
Earlier in this post, I mentioned sediment cores as records of global temperature; results from Antarctica and the Deep Sea Drilling Project (published in Shackleton and Kennett, 1975, and Kennett 1977) showed that, with only minor variations during the Eocene/Miocene, the temperature of Antarctic Bottom Water has fallen from a high above 15C in the early Palaeocene to where it is now at less than 0C&#33;
Following the K/T event &#39;recovery&#39; period (typically post mass extinction recoveries take ~5-10Ma) life in the oceans, and on land, flourished, until the last series of glacial advances and retreats (coinciding with the emergence of homo saps) <_<

Guest
2005-Aug-29, 06:08 AM
Yes, you are correct in that I was referring to those passages in my previous post. I have not yet learned how to cut and paste from previous posts. In my mind, the mechanism described by the authors of the study in question is the best explanation I have yet heard for what may have caused the Permian mass extinction.
I appreciate your explanation of thermohaline convection and this most certianly applies on a local and regional scale in the oceans, lakes, and seas. My line of thinking was more along that global convection currents (ie that which drives the gulf stream)would be disrupted by the loss of cold water intrusion from arctic sources once glacial and ice cap melt slows or stops. With no mass movement of cold water from north to south there would no longer be inversion layers in the oceans that generate upwelling of nutrients such as nitrates that are critical raw materials to photoplankton blooms. There was a recent article that I read about the devastating effect of such a failure to bring up nutrients had on fish populations off the northwest US coast (although this event was thought to be part of a normal cycle there.) Regarding a reference for this, I most likely read this from the newscientist website or periodical within the last month (since I am on vacation I do not have access to all of my sources.)
I agree that the effects of increasing O2 displacement and increasing acidity as a result of increasing atmospheric and then ocean CO2 are potentially harmful effects to marine organisms by themselves and there have been at least one article or two citing these effects on a large scale as potential precipitating factors for mass extinctions.
Regarding the K-T mass extinction, I was referring to a couple of sources that I have read withing the last month or two. One is Newscientist, Aug 20-26, p. 11 which summarizes a presentation by Anne Chenet of the Paris Geophysical Institute presented at the Earth Systems Processes Conference in Calgary this month. She and her colleagues concluded from their fieldwork that the Deccan Traps eruptions occured in less than a 30k year period at the K-T boundary and may have been responsible for the K-T extinction (via a sudden outburst of co2 over that timeframe). I do agree that if the above authors conclusions are correct, then a brief period of warming should be supported by other evidence form that era, and I do not know if this was addressed.
My main point regarding the geologic record is that the radioisotope dating is not precise enough to determine whether the mass extinction took place over 2 years, 20, 200, 2000, or perhaps more years. If it were that precise and the margin of error that low, then there would be no doubt whatsoever that the asteroid/comet strike was responsible if it were to show that it took only 3 years for the mass extinction to occur rather than 500 or even 5000 years. So in a period of active global warming, I would think it wise to keep this line of reasoning (that global warming might cause mass extinctions if it goes too far and at too quick a pace) in mind while trying to assess the potential harm it could cause in the next few hundred years.
With regards to the Antarctic and Greenland ice cores, I believe that the longest only goes back about a million years. I have similar doubts about how accurate ocean sediment data is if you are talking about going back 65 million years. I would be more comfortable with data from the last 10 or 20 myrs. What exactly triggered the extended periods of cooling (ice ages) since the K-T boundary is something everyone would like to know, and about which a number of plausible theories exist. I think it is safe to say that a comet strike did not usher in each and every ice age and it is not plausible to think that the K-T bondary strike initiated the extended period of cyclic warming and cooling that has followed unless you can find major impacts coinciding with the onset of each cooling period.

cran
2005-Aug-29, 12:24 PM
Okay, there are a lot of points you&#39;ve made, Guest... (I can&#39;t keep calling you Guest... please include a name by which you&#39;d like to be addressed... Hi, I&#39;m Cran) ... and I may miss one or two as I go back through your post...

In my mind, the mechanism described by the authors of the study in question is the best explanation I have yet heard for what may have caused the Permian mass extinction. That&#39;s fine, you have an opinion, and it may well be valid, and you are most certainly entitled to it ... my opinion is formed from studying this period, and global ocean/atmospheric circulation, and mass extinctions and &#39;Snowball Earth&#39; theories; neither you nor the article you&#39;ve cited have convinced me to alter my opinion... <_<

I appreciate your explanation of thermohaline convection and this most certianly applies on a local and regional scale in the oceans, lakes, and seas. My line of thinking was more along that global convection currents (ie that which drives the gulf stream)would be disrupted by the loss of cold water intrusion from arctic sources once glacial and ice cap melt slows or stops. It also applies to global current regimes ... including the Gulf Stream System, which is currently being &#39;disrupted&#39; and weakened by an increasing influx of fresh colder meltwater from the Labrador Current, derived from accelerated melting of the Greenland and Baffin ice sheets... not from any warm water sources... once again, your line of thinking is your right to hold and express, but I&#39;ll stick with what I&#39;ve learned from oceanographers about that... <_<

With no mass movement of cold water from north to south there would no longer be inversion layers in the oceans that generate upwelling of nutrients such as nitrates that are critical raw materials to photoplankton blooms. How do you arrive at that conclusion, Guest? :huh:

There was a recent article that I read about the devastating effect of such a failure to bring up nutrients had on fish populations off the northwest US coast (although this event was thought to be part of a normal cycle there.) Yes, it is called the ENSO cycle (El Nino-Southern Oscillation). :)

Regarding the K-T mass extinction, I was referring to a couple of sources that I have read withing the last month or two. One is Newscientist, Aug 20-26, p. 11 which summarizes a presentation by Anne Chenet of the Paris Geophysical Institute presented at the Earth Systems Processes Conference in Calgary this month. She and her colleagues concluded from their fieldwork that the Deccan Traps eruptions occured in less than a 30k year period at the K-T boundary and may have been responsible for the K-T extinction (via a sudden outburst of co2 over that timeframe). I do agree that if the above authors conclusions are correct, then a brief period of warming should be supported by other evidence form that era, and I do not know if this was addressed. Yes, the massive low viscosity basaltic flows of the Deccan Traps are quite well known, and have been studied for dating of individual flows (duration and interval), and are indeed a leading contributor to the catastrophic global changes that were taking place at the K/T transition (as are the Siberian Traps for the P/T transition) ... and yes the total outpouring can be confidently constrained to <30Kyr (last I heard was the largest flows seemed to be constrained to <~18Kyr with some minor late flows) ... I would be surprised if Anne Chenet claims that the extinction was due to a sudden outpouring of CO2, or any link or evidence of global warming arising from the Deccan Traps - because the evidence and field obs all point to exactly the opposite, ie that the Deccan Traps contributed to an &#39;extended nuclear winter&#39; scenario of global cooling and dimming, as should be expected from extensive vulcanism ... but what does any of that have to do with species linked to the K/T mass extinction event lingering on for tens of thousands of years? :huh:
My main point regarding the geologic record is that the radioisotope dating is not precise enough to determine whether the mass extinction took place over 2 years, 20, 200, 2000, or perhaps more years. If it were that precise and the margin of error that low, then there would be no doubt whatsoever that the asteroid/comet strike was responsible if it were to show that it took only 3 years for the mass extinction to occur rather than 500 or even 5000 years. Fair enough, and one of the reasons why it is difficult to determine whether the Yucatan Bolide Event preceded, or coincided with the Deccan Traps outpouring, and made even more difficult to constrain because the global evidence is based on particle settling, which from &#39;global&#39; events (such as the Deccan Traps vulcanism or the Yucatan Bolide impact) can persist for decades, if not centuries... :)
So in a period of active global warming, I would think it wise to keep this line of reasoning (that global warming might cause mass extinctions if it goes too far and at too quick a pace) in mind while trying to assess the potential harm it could cause in the next few hundred years. Yes, it might... but how is global warming linked to the K/T mass extinction event? The Cretaceous ecosystems were adapted to climates and CO2 levels much higher than ours... indeed higher than any of the estimates for climate and CO2 levels predicted... ? :huh:
With regards to the Antarctic and Greenland ice cores, I believe that the longest only goes back about a million years. I have similar doubts about how accurate ocean sediment data is if you are talking about going back 65 million years. I would be more comfortable with data from the last 10 or 20 myrs. With regards to ice cores, the oldest are ~745Kyr; and reliable deep ocean sediments ~8Ma, which is the Pliocene (the period I referred to in this regard)... climate proxy data going back to 65Ma (and indeed much earlier) are based on other records - palynological, carbonate reefs, sedimentary rocks and other deposits, peat sediments, fossil tree rings, and distinct biota indicators - these are independent lines of investigation which give consistent results... I would be more inclined to trust expert opinions in these fields, than to ignore them and simply form my own opinion... <_<

What exactly triggered the extended periods of cooling (ice ages) since the K-T boundary is something everyone would like to know, and about which a number of plausible theories exist. I think it is safe to say that a comet strike did not usher in each and every ice age and it is not plausible to think that the K-T bondary strike initiated the extended period of cyclic warming and cooling that has followed unless you can find major impacts coinciding with the onset of each cooling period.
There is extensive literature on ice ages and the conditions under which they can occur - a google search will turn up plenty, and a visit to any large library will provide even more detailed information. Who said anything about a &#39;comet strike&#39;?
For information about warm/cool cycles, the previously mentioned search and library will provide quite a lot of background, if that&#39;s not sufficient, try natural or climate feedback and rebound cycles, and you will find that not one is claimed to be linked specifically to any boloidal cause... :)

lswinford
2005-Aug-29, 04:15 PM
with no mass movement of cold water from north to south there would no longer be inversion layers in the oceans

Just a quick note, there will always be currents and differentiation zones. Just like warm air rises and displaces denser colder air, there are density differentiations with water. The currents may change, inversions occur, etc., but until the oceans boil away there will still be denser matter sinking and more diffuse rising to its equilibrium.

When Eric the Red moved people to Greenland, there really was land that had green things growing on it. Climate changes, land lifts and erodes, and even if we were the most benign of lifeforms infesting a supposedly pristine earth, there would be still be changes.

cran
2005-Aug-29, 06:31 PM
Thank you, Iswinford :)

...but until the oceans boil away there will still be...
"...or freeze solid..." but that&#39;s much less likely... :lol:

Greg
2005-Aug-30, 06:03 AM
I have been posting from a different computer as I am away from home. I also have not had much time to research the topic in more detail before posting (for various reasons) as I usually do, so I am not answering with as much depth as usual.
With regards to the K-T extinction event topic, the article I read summarizes Chenet&#39;s position a little too briefly. After reading it more closely, it seems she invokes the method of extinction as "suffocation" which I presume means loss of oxygen due to really excessive outporings of volatile gasses reacting with it and depleting it. With regards to marine extinctions, an excess of Co2 would result in this, but with regards to land organisms neither warming or cooling applies to her putative mechanism of extinction. I am sure more information on her presentation would be helpful if anyone in the audience attended the conference. If not, then I guess we shall await publication of her findings. With regards to the carbonate reef findings and peat bog findings, I am not well read. Perhaps I should take a closer look at few of them (as well as the counterview.) Mind posting a few links or references?
Perhaps my understanding of of how the Atlantic and Pacific ocean currents work is overly simplistic, so I will try to explain better. As I see it, colder water is more dense than warmer water (ie ice will sink mostly below the surface of warmer water.) Warm water moving north should be limited and driven further south(and east) when it encounters colder denser water in arctic regions (assuming salinity is equal for the moment.) Such an effect is being seen now as arctic runoff increases. As this more dense water moves southeast along the ocean current it will sink. Warmer and less dense water full of nutrients will replace it from below resulting in an upwelling of nutrients needed for surface marine organisms (Again assuming salinity is in equilibrium and temperature is not.)
I take from your argument that lower salinity is the determining factor that keeps the colder water from sinking, but if so, why would the less dense water sink at all, even after it warms up? To which the answer I guess would be until it evaporates enough to become more dense than the water below.
A good portion of what I was trying to say is that it does matter what the temperature difference is. Consider what the average ocean temperature is in the Gulf of Mexico and near Greenland presently. 90 degrees F versus 30 degrees F. With advanced global warming what might it look like in 100 years? 98 F versus say 65 F. The difference is far less, and I would argue that it this difference would effect the mass movement of ocean currents globally. Add to this that the current heading southeast from Greenland will be less dense to start with due to far less freshwater input yearly from arctic melt, and I do not see how this will not effect these currents as both the starting (from Greenland and moving southeast) temperature and salinity will be far different than it is today.
Thanks for the feedback, this conversation has proven worthwhile in getting me to think more about these processes and understand them more clearly.

cran
2005-Aug-30, 08:39 AM
Greg, hi,

With regards to the carbonate reef findings and peat bog findings, I am not well read. Perhaps I should take a closer look at few of them (as well as the counterview.) Mind posting a few links or references? Normally Greg, that would be no problem... but I&#39;m not moved into my new home yet, and all of my hardcopy files are now packed in storage waiting for Thursday... I had a quick look on my computer &#39;bookmarks&#39; and in my &#39;articles archives&#39;, and they are enormous (&#33;&#33;) and the titles aren&#39;t always clear about the content... the fastest and surest way I can suggest is a google search for keywords ... for a narrower search of peer-reviewed items, do you have links to science organisations or universities, so you can use their internal search engines?; if you have access to a good public library (or better yet, a university library), you&#39;ll get all of that plus good reference books with all of the background that journal articles assume as &#39;prior knowledge&#39;.


I take from your argument that lower salinity is the determining factor that keeps the colder water from sinking, but if so, why would the less dense water sink at all, even after it warms up? To which the answer I guess would be until it evaporates enough to become more dense than the water below. Got in one&#33; :D

In the case of warm current systems, in particular the Gulf Stream System, this warmer water mass is already much more saline than the Labrador and Arctic Water Masses, and it begins to sink below these water masses as it gives up its heat to the atmosphere and surrounding waters (this also includes some marginal mixing of waters)


A good portion of what I was trying to say is that it does matter what the temperature difference is. Again, you are spot on, Greg. In this, and all thermodynamic flow, the differences in values are far more important than the absolute values; the differences determine the strength of the pressure gradient and therefore the strength and persistence of flow, which is always from higher potential to lower potential (2nd law); conversely a reduced difference means a weaker pressure gradient and a weaker flow.

An article I read today pointed out what was aggravating me a bit about this simulation business, and a tendency to fix &#39;universal&#39; causes to similar events- eg, what caused the P/T mass extinction event applied equally to the K/T mass extinction event. While there are similarities (eg, both are mass extinction events; both seem to coincide with massive continental basaltic flows), there are some striking differences before, during, and after the transitions...

The P/T transition is marked by the greatest temperature spike in the Phanerozoic Eon >thinks< it is &#39;eon&#39;, isn&#39;t it ... damn wall chart is packed away&#33;
Pangaea was breaking up, and the climate was quite rapidly pulling out of an Ice Age, which means that there was a double dose of CO2 being added to the atmosphere and ocean (both from the vulcanism, and from the meltwater); what actually caused the &#39;spike&#39; is still debated, but I tend to favour the idea of a massive release of methane from methane-ice under the ocean ... with higher CO2 levels and reduced free oxygen, methane would last longer in the atmosphere and, as a greenhouse gas, is 4 times more effective than CO2.

The K/T transition came during an already extended period of much warmer climate and higher CO2 levels... there is no evidence of a temperature &#39;spike&#39;; in fact, a cooling trend begins in the Tertiary, with milder fluctuations, but descending into the Pliocene Ice Age.

I tend to think that the two events had quite different direct causes, despite the similarities I mentioned above ... as to whether there is a common underlying cause to these (and other) major transitions ... well, that&#39;s another story :D (My studies have indicated &#39;yes&#39;, but it&#39;s not relevant to this particular thread).

So, I apologise, Greg if I came across too harsh or critical of the various reports of findings, or if I seemed too dismissive of your views ... I can understand (only too well right now) what it&#39;s like not to have all of your data and background info right at hand... in fact, I even have to break down my computer tomorrow evening for the big move on Thursday >sniff&#33;< ... guess what I&#39;ll be setting up first in my new home&#33; :lol:

Greg
2005-Aug-31, 08:09 AM
No problem on my end. I enjoy bandying ideas about in a generalized way. Usually I am trying to synthesize different articles from different fields of interest and try to find generalized truths that may apply to all of them. This tendency comes from working in a field focused on the application of science rather than basic research (thus I do not need to know any one field of basic science in great detail.) As a result I am somewhat ecclectic and broad in knowledge, but sometimes I do not go into enough detail and not a thorough as I should be. I enjoy feedback and debate since it forces me to focus in on a topic extend my thought process, and as a result I learn alot more about the topic by the time I am finished discussing it.
As far as the K-T boundary being more of a devil&#39;s advocate. As far as I knew there was not solid evidence that pinpoints the extinction event precisely enough to say an asteroid/comet hit was the sole cause. I believe there is a margin for error regarding the dating accuracy that allows for mechanisms of extinction (which can take longer to occur than an intestellar body strike) to still be considered as responsible, such as Chenet&#39;s proposed suffocation mechanism by gasses released by the Deccan traps eruption. I agree that the proponderence of evidence favors the prevailing theory.
The discussion of this topic stimulated my thinking along similar lines to yours. The effects of a massive volcanic eruption could lead to depletion of oxygen on the surface, deoxygenation of marine organisms indirectly by C02 absorbtion, acidification of the oceans by the same mechanism, massive particulate emissions blocking photosynthesis with a selective loss of marine and plant life dependent on it, or a global winter scenario due to excessive particulates in the stratoshphere. Certainly there could be some or all of these mechanisms responsible for mass extinction events that have occured in the past, so this is not so simple a topic as it appeared to be initially. To actually answer the complexities of the question of what happened, you would need a sufficient accumulation accurate hard data from the field which is an ongoing process.
I do agree with your reservations about making specific conclusions about models. They are inherently biased by the starting conditions that you put into them and how accurately the computer can simulate real world conditions. I think that they are useful in the absence of observational data if they can accurately predict current conditions from an earlier timepoint before they go on to predict future endpoints, and of course how many of their earlier predictions have come true now.