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A series of opinion pieces on, mostly climate change and related subjects to do with New Zealand.

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Ocean conveyer circulation time.

2/5/2014

4 Comments

 
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The Great Ocean Conveyor is a huge mover in the worlds climate and yet we know very little about its deeper workings. 
As the Gulf stream travels from the Caribbean to the Arctic circle it cools and as it does so it soaks up vast quantities of CO2  and when the cold water disappears into the deeps it takes this CO2 with it. This CO2 load has the capability to make the sea more acidic when it eventually resurfaces  which would be very bad for phytoplankton, the base of the marine food chain, . The water going into the depths, although cold, is not as cold as it used to be and is consequently carrying heat into the depths of the ocean which is one way the oceans absorb 93% of the world’s heat.

Now this is the question. The Gulf Stream travels at 6.4 kilometres an hour and if the world has a circumference of 40,075 kilometres it would take 260 days to make a full circumnavigation. Clearly it does not do this but how long does it take? We know almost nothing about the current flow in the deep oceans even though we have a map of the thermohaline circulation flow.


NOAA states that it takes 1000 years for a full circumnavigation but I was under the impression it was only 14 years from sinking in the North Atlantic to surfacing in the Southern Ocean. That’s a huge disparity for a physical process that has a monumental effect on the temperature of the atmosphere and the acidity of the oceans.

It’s a question of how the water circulates. Does it stay as a current moving down valleys on the sea bed like a river or does it disperse and spread its heat and acidity throughout the oceans.

It’s not for the author. Bob Bingham to disagree with NOAA but I think it would be more like the faster option with the water surfacing after about twenty or thirty years bringing its heat and acidity back into circulation. Research is gathering pace and I suspect we will not have long to wait for more answers but at this stage your informed speculation is as good as anyone else
.


4 Comments
John ONeill
2/5/2014 06:58:04 pm

If water was resurfacing after only thirty years or so it would already be showing the isotope signature of the atom bomb tests from the fifties and sixties. The carbon 14 tests, which rely on the steady accumulation and disintigration of carbon 14 produced from nitrogen in the ionosphere by cosmic rays, don't work later than that as the ratios to carbon 12 and 13 are skewed. That works for anything breathing air, but in seawater there would be other isotopes showing up as well. For example, the first seawater with radioactive traces from Fukushima has just been detected off the west coast of the US. The amount of cesium was tiny, even compared to what was left over from the sixties bomb tests, but it could be distinguished from that signal as it was a shorter-lived isotope. According to wikipedia
'Deep waters have their own chemical signature, formed from the breakdown of particulate matter falling into them over the course of their long journey at depth. A number of scientists have tried to use these tracers to infer where the upwelling occurs.' If they're still arguing about it, it's presumably because it's hard to find, therefore diffuse, and so necessarily slow.

Reply
Bob Bingham
4/5/2014 02:14:58 am

Thanks for the input John. Probably the fastest point at which deep ocean water would resurface is between South America and West Antarctica and I am not sure anyone is monitoring it. The measurements were taken in the North East Pacific because the Oysters in that region have too much acidity in the sea and are no longer breeding the way they used to.

Reply
Bob Bristow
7/5/2014 03:38:18 am

Thanks an interesting post on Ocean currents, my understanding is that it takes around 1000 years for surface waters to go through the whole cycle, that is to move to the Oceans bottom and then rise to the surface again, while moving around the globe. Deep water currents move very slowly (as low as 1 -2 meters a day), when compared with surface waters. Carbon used to be in balance, before man's industrial efforts, and carbon atoms would be absorbed by living things like plankton and go into the shells of marine life. Eventually finding it's way to the bottom to form sedimentary rock. Over a few million years it may be subducted and heated and the CO2 gas set free to join the atmosphere again.

We are talking of huge long cycles in time to cope with CO2 naturally, yet man is pumping it out much faster than the natural chemical processes can handle. We are lucky the Ocean is acting as a sink today and creating a negative feedback effect, but in palaeoclimatology it can also turn to positive feedback releasing in vast store of Carbon into the atmosphere.

I attach a Potsdam paper on the time it takes for some of the processes which I found of interest.

regards
Bob

http://www.pik-potsdam.de/~victor/archer.subm.clim.change.pdf

Reply
Bob Bingham
7/5/2014 09:38:48 am

Thanks for the post to the research I read it though and got some good information from it. We know so little about the deep oceans that it is still a closed book. I get the point about the 1000 years for the water to circulate but the Gulf Stream flows at 6.4 Klm and hour and when it sinks it has much of that speed. There are deep canyons which are copletely unknown and I believe that water could flow along the bottom at a modest speed of say 2Klm per hour and that would give a much faster circulation speed. A lot of people want to know so I suspect we wont have to wait long for the answer.

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    Bob Bingham 

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