Earth’s Thermohaline Circulation

Here’s some background on Earth’s Thermohaline Circulation;
http://en.wikipedia.org/wiki/Thermohaline_circulation
http://www.cmar.csiro.au/currents/global/CSIRO_Conveyor_Oceans_M.wmv

NASA’s Ocean Motion page offers some good insights;
http://oceanmotion.org/html/impact/conveyor.htm

as does this page;
http://www.windows2universe.org/earth/Water/deep_ocean.html

[Lunar tidal effects mentioned toward the bottom of this lengthy informational comment, good resource as usual from just the facts]

this page;
http://www.womenoceanographers.org/Default.aspx?pid=28EF75D5-D130-46c0-947E-5CCBC627B0EE&id=AmyBower

and on this page;
http://web.deu.edu.tr/atiksu/toprak/ani4083.html

these visualizations were helpful;
http://web.deu.edu.tr/atiksu/toprak/den41.gif
http://web.deu.edu.tr/atiksu/toprak/den40.gif
http://web.deu.edu.tr/atiksu/toprak/den39.gif

This map shows where cold ocean water is sinking;
http://www.thewe.cc/thewei/&/&/bbc12/gulf_stream.gif

this one shows where heat is released to the atmosphere
http://www.windows2universe.org/earth/Water/images/thermohaline_circulation_conveyor_belt_big.gif

and this animation is helpful in visualizing the process:
http://www.whoi.edu/oceanus/viewVideo.do?fileid=46592&id=32693

In addition to temperature and salinity Earth’s rotation comes into play, especially around Antarctica;
http://en.wikipedia.org/wiki/File:Conveyor_belt.svg

which is also called the Antarctic Circumpolar Current;
http://en.wikipedia.org/wiki/Antarctic_Circumpolar_Current

and is “the largest ocean current.” “at approximately 125 Sverdrups”. Given that “The entire global input of fresh water from rivers to the ocean is equal to about 1 sverdrup.”;
http://en.wikipedia.org/wiki/Sverdrup

this circulation is of an amazing scale. Also Figure 2 about two third down this page;
http://www.waterencyclopedia.com/Mi-Oc/Ocean-Currents.html

offers another perspective. And this page offers technical insights on the Antarctic Circumpolar Current:
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter13/chapter13_04.htm

These maps seem to indicate an interesting circulation at the North Pole as well:
http://www.whoi.edu/page.do?pid=12455&tid=441&cid=47170&ct=61&article=20727
http://www.john-daly.com/polar/flows.jpg

According to this reference “The comparison suggests that the Atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004.”
http://www.nature.com/nature/journal/v438/n7068/abs/nature04385.html

In this presentation on the Atlantic Meridional overturning circulation, the chart Slide 4 seems to indicate a slight slowdown, but the alignment between data sets appears awful and the resultant divergent predictions laughable:
http://ioc-goos-oopc.org/meetings/oopc-9/presentations/monAM/Bryden_rapid4oopc.pdf

On the other hand, this article from November 29th, 2008 in Nature, is titled, “North Atlantic cold-water sink returns to life – Convective mixing resumes after a decade due to massive loss of Arctic ice.”
http://www.nature.com/news/2008/081129/full/news.2008.1262.html

The claim that it resumed “after a decade due to massive loss of Arctic ice.” seems dubious considering that there does not appear to have been a “massive loss of Arctic Ice”;
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.arctic.png

but this article from January 9, 2009;
http://www.whoi.edu/page.do?pid=12455&tid=282&cid=54347

also asserts that “One of the “pumps” that helps drive the ocean’s global circulation suddenly switched on again last winter for the first time this decade. The finding surprised scientists who had been wondering if global warming was inhibiting the pump and did not foresee any indications that it would turn back on.

The “pump” in question is in the western North Atlantic Ocean, where pools of cold, dense water form in winter and sink beneath less-dense warmer waters. The sinking water feeds into the lower limb of a global system of currents often described as the Great Ocean Conveyor (View animation (Quicktime)). To replace the down-flowing water, warm surface waters from the tropics are pulled northward along the Conveyor’s upper limb.”

These articles are based upon this paper:
http://www.nature.com/ngeo/journal/v2/n1/abs/ngeo382.html

Furthermore, “Satellite measurements of sea levels suggest the moon’s tidal pull plays a once-unrecognized role in lifting cold water from the ocean depths and influencing Earth’s climate.

Data from the U.S.-French TOPEX/POSEIDON satellite, which bounces radar off the oceans to measure sea levels precisely, also may solve the mystery of what happens to all the energy that the moon transfers to Earth by creating ocean tides.

Scientists once thought most of the energy was dissipated by friction as waves and tidal currents drag along shallow coastal sea floors. The new study indicates about three-fourths of the energy indeed is dispersed in that manner.

But the measurements also imply 25 percent to 30 percent of the energy in tides dissipates when deep-ocean tidal currents hit seamounts and mid-ocean ridges, creating turbulent “internal waves” that stir and lift cold bottom water so it mixes with warmer, shallower water. That effectively moves heat away from the sea surface, influencing climate in the overlying atmosphere.

“In the past, people thought wind was the primary agent to mix warm water down into the deep, cold part of the oceans,” said Richard Ray, a geophysicist at NASA’s Goddard Space Flight Center in Maryland. “Our work suggests tides are equally important.””
(For some reason, the article where this information is from, is no longer available at its source here:
http://www.space.com/science-astronomyplanetearth/tide_energy_000627.html

Filed under: In other online forums,Long-term Lunar Effects,Natural Processes — by Richard Holle @ 9:17 pm on September 18, 2011

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