The following post is a paper I wrote in 2004 for EAS 10400 – (Oceanography) at Purdue University. As it says in the body of this “pasting/BlogPost” the information I had to go on at the time, was hard science, and took a fair amount of effort to turn into a readable document. At times this is fairly scientific and at others it is more Literary. I was tying to “engage” the Professor after all, and get a good grade out of this class.
Well, it must have worked as I was one of five out of 350 students for whom their Term Paper was good enough to get them out of the Semester Final. I don’t say this to brag, I say this to warn. You should UNDERSTAND that all the science/information that is in this Post is still quite valid (more so, to tell the truth) today and if you check this link <http://in.reuters.com/article/2012/03/21/climate-cost-oceans-idINDEE82K00B20120321> out you will see that the predictions of a hand full of scientists and one undergrad at Purdue University are starting to come true, Be Scared be truly afraid. If we do not get ahold of our CO2 emissions . . . . . . . . .
Sorry you will have to copy paste the link, linking feature in the WordPress Blog does not work . . . . no surprise to me.
The Thermohaline Conveyor and Our Climate: the relationship © 2004 James Longster
The Thermohaline Conveyor (THC) is a series of connected currents that move slowly around the world, moving heat from the warm parts of our world to the colder Polar Regions, and slowly doing the same in the opposite direction. The part that the Thermohaline Conveyor plays in our world climate is still very little understood . Unfortunately, the research that is being done is reported in very technical articles, published in equally technical journals which I am but poorly suited to decipher, but what I have found (and understood) I will use to show the relationship between the THC and our climate.
The THC starts as warm water flowing southward, which has slowly become more saline due to evaporation near the equator. As it travels toward the Antarctic it cools, and in cooling, becomes even denser. When the water finally reaches the southern polar icecap the Surface Sea Temperature (SST) cools even further, the water then becoming dense enough to sink to the abysmal depths. This water now becomes Bottom Water. Now because of the temperature and salinity difference, and with a little help from gravity, the newly made bottom water flows out and across the sea floor where it joins with the Antarctic Circumpolar Current. This current moves slowly and nearly circumnavigates the Antarctic continent before it begins its journey north.
These bottom waters only make up part of the THC. In fact, the THC is composed of many layers of water of differing densities and temperatures, . The depth of each of these layers of water is directly linked to that density, and the density itself tied to two things: temperature and salinity. A low salinity and warm water mass–say 80 Deg.F. and 33 or 34 % salinity –will float on top of a denser –colder and with a higher percentage of saline–water mass. What we have then is a world ocean system that is made up of discreet currents, moving at varying depths, going sometimes in different directions at different levels. There is almost no mixing that occurs between these layers, even though day to day life would lead one to expect the opposite. The difference in salinity from one layer to the next is like the difference between oil and water; they mix only if forced to. (See chart 1) Water mass chart
The THC’s deep journey is the slowest part of the journey that it makes, but for life on this world it may be the most important. While traveling through the deeps, the THC picks up the nutrients that all marine microorganisms require. When the cold, bottom water reaches those places in its journey where it rises to the surface of the sea–called upwelling points– all of these nutrients are returned into the “photic zone” (the top thirty meters or so of the ocean). There the nutrients become food for the Phytoplanktons, which in turn feed the Zooplanktons –upon which all other living things on upwards to the apex carnivores (them and us) depend for their continued existence. The success of all of this living seems, clearly, to be connected to the health of our oceans–and maybe the Thermohaline Conveyor is the heart of a healthy ocean as we now know it.
The THC, as I have said, is made up of surface currents and deeper currents, but what does all of that have to do with our climate? In what way could what is happening 4000 meters below the ocean’s surface have an effect on the weather, say, in England in February? As I have said, the THC is constantly moving heat from one region of our world to another, and as long as that continues to be so, England will have the mild winter (mild to us in Indiana) to which they are accustomed . This predictable weather pattern exists largely because the winds in February are predominately southwesterly at that time of the year and because England lies near the North Atlantic Current (NAC). The NAC, which still retains some of the heat from its earlier incarnation as the Gulf Stream, helps give them those mild winters. However, we must remember that what we see on the surface—such as the NAC–is just the wind forced aspect of a much larger system: the Thermohaline Conveyor. Even as England enjoys the mild February weather, the Arctic breeze that blows towards England cools the NAC, and it’s already more saline than the cooler water around it; it is getting more dense. The further north the NAC goes the less evaporation takes place but the colder the water gets; it is ready to go deep.
Because of its acquired density, water is constantly dropping at the North and South Poles, like the draining water from your bathtub. The water lost from the surface has got to be replaced from somewhere, so the North Atlantic Gyre (NAG) and the South Atlantic Gyre (SAG) move the water needed to replace the sinking water. It follows that the dropping of these heavy, cold and saline, waters is the energetic impetus for the flow at the depth in which the THC operates. Visualize, for instance, someone pouring water into a hose that is held up at one end with the length stretched out flat across the ground to the other end. When water is poured into the high end it flows rapidly down to the point at which the hose levels out. There, without gravity pulling the water onward, it would slow and ultimately stop. However, we did not stop pouring water in the hose, so there is still a column of water pushing on the water that is in the level part of the hose–so the flow continues. That is how the cold sinking saline water at the north and south poles works, except it is not a hose that contains this deep water and prevents it from mixing with the surrounding water but a difference in density (a temperature /salinity combination). The lighter (less dense) water above forms the top half of the “hose” which contains the bottom water, so that it, with the impetus of the water coming down behind it, flows out over the Abysmal floor on its long slow journey to whatever upwelling point is its destination.
Without the THC operating as it does now, Eastern Europe and other places that have relatively warm current breezes blowing over them would go into something like a miniature Ice Age, at least during the winter months. But it is not just winter that would be distorted. All seasons would be affected, all over the world. The air you breathe today, was over an ocean just a few days ago. If it was a warm water mass then the air that passes over it will bring moisture and warm breezes, if it was an Arctic or Antarctic mass , the air will bring cold, mostly dry, skin-ripping, Alberta-clipper-like winds. The wind patterns would undoubtedly be affected if the THC shut down, because ocean masses would not have the benefit of the cooling effect of the upwellings. No upwelling, no flow; no flow, stagnation; stagnation, then finally, the overheating of our ocean waters.
Think about it; the ocean’s coral is under temperature stress already, dying in places, in fact. Just a few more degrees of added heat would be disastrous. The question is: could global warming also have the effect of shutting down the THC completely, or at the least reducing it to virtual ineffectiveness?
An increase above the norm of the level of fresh water in the southern or northern latitudes, resulting from excess rain or polar ice melt, has the most potential to disrupt the THC. During this potential warm up, the far northern and southern winds would have a much greater capacity to carry water, and thus the potential to drop a much larger than normal quantity of fresh water in the northern and southern seas, and the land masses which feed those seas, where the deep water of the THC normally forms. The effects of this level of Global warming (a.k.a. “greenhouse warming”), is being studied even as we sleep. The early results returned from such studies are both alarming and reassuring.
Modeling studies of the response of the Antarctic ice sheet to greenhouse warming suggest that for temperature increase of up to 5.3C. from present-day temperatures, the increased accumulation still dominates the increase in ablation (Huybrechts and Oerlemans 1990). The Greenland ice sheet seems more sensitive to global warming, but for climates colder than today’s, the precipitation-temperature feedback is expected to work there as well [Huybrechts, et al. 1991, Fig. 31]. Other studies suggest that this feedback may also work in the context of global future warming due to CO2 increase (Miller and DeBernal 1992; Ledley and Chu 1994) (Tziperman and Gildor, 2002).
Tziperman and Gildor’s research dealt with the THC as a model in colder climate situations, glacial or near glacial periods. They concluded that during these periods of colder weather the THC would remains stable and properly functioning. (Tziperman and Gildor, 2002). While citing the work of the above researchers, they state, however, that this stability would most likely not be the case in a climate undergoing a global warming period. The words used were “The out come of global warming is a collapse or a significant weakening of the THC, in spite of the weakened meridional temperature gradient in the atmosphere (Kattenberg et. al. 1996: Cubasch et. al. 2001)” (Tziperman and Gildor, 2002).
Tziperman and Gildor’s research is centered around the idea that during colder periods less moisture was available in the far northern and southern latitudes to precipitate onto the ice sheets, land masses, or surrounding oceans. This of course would have prevented a rapid influx of fresh water into what is now known to be a balanced system, the down welling points. Fresh water in above-average quantities (a.k.a. the Global Warming Scenario) at above freezing would most likely bring the THC’s down welling to a rapid halt. How long it would take the rest of the THC’s circulation to shut down, I don’t know, and haven’t found any one person (or group of people) who is ready to put a time frame on it.
In another research scenario it has been proposed that evidence may support the possibility that the Arctic and Antarctic did not each warm equally during the last deglaciation (Broecker, W. S. et. al. 1999). There may be evidence that the deep-water formation may have alternated between the north Atlantic and the south Atlantic oceans (Broecker, W. S. et. al. 1999). This may have allowed for a partial shutdown of the THC in whichever hemisphere was not creating the most deep water at the time. To study this possibility, researchers created models that studied the PO4 versus O2 ratio (see fig3.).
Along with this research, other research was conducted into the relationship between CFC-11 concentrations as a function of PO4 in waters south of 40deg. This was an attempt on the part of the researchers to determine whether the known Antarctic source locations for deep water formation have contributed enough to set up the amount needed for proper production of deep water, or whether the polynyas or other open ocean convective cells have been necessary to make up the difference.(see fig.1)
Well, as a junior at Purdue University I have now read many articles from some of the most prestigious and respected Journals this country and the rest of the world has to offer on the subject of the Thermohaline Conveyor, and all that reading has brought me to several major conclusions:
1.That most of all the THC is and has always been inextricably connected to the climatic wellbeing of the Holocene and that, though this is the case, the exact methodology of this relationship is still but dimly understood. Research continues on this subject by many scientists affiliated with many organizations or individually looking for pieces of this far reaching question, with as many avenues of research as man can dream. And the answers may scare us all!
2.Most of the researchers that have mentioned Global Warming have said that it will have an effect, most likely a major effect, on the deep circulation of our oceans. Just exactly what that effect will be is not yet known. The THC has a range of potential reactions to this. It seems to me, it can completely shut down, and that will likely kill the oceans almost completely, or there could be just a partial shut down. That would be best because only the unhappy half of the world would go to WAR over the lack of food and the fact that the normal movement of air and water no longer follows the age old formulas. You think Bluefin is expensive now?
3.the BIG question in my mind is not : is there going to be a major effect due to partial or full shutdown of the THC, or is that effect going to be a bad one? I don’t doubt that both are true. The question is: can YOU guys scare the politicians or the average Joe on the street into believing that something has to be done to lower greenhouse gasses in time to prevent a collapse of the THC? Maybe it is already too late, and we are all riding on a Hell-bound train, and the boiler has already been over stoked.
I’m waiting for the hiss of leaking steam.
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