Tropical Pacific is major player in global ocean heat transport

Posted: May 17, 2019 by oldbrew in general circulation, Ocean dynamics, research

The Great Ocean Conveyor Belt – blue = deep cold and saltier water current, red = shallower and warmer current
[credit: NWS / NOAA]


Researchers put forward the idea that the role of the global ocean conveyor belt may be overrated in the grand scheme of ocean dynamics, and offer alternative ideas.

Far from the vast, fixed bodies of water oceanographers thought they were a century ago, oceans today are known to be interconnected, highly influential agents in Earth’s climate system, says Phys.org.

A major turning point in our understanding of ocean circulation came in the early 1980s, when research began to indicate that water flowed between remote regions, a concept later termed the “great ocean conveyor belt.”

The theory holds that warm, shallow water from the South Pacific flows to the Indian and Atlantic oceans, where, upon encountering frigid Arctic water, it cools and sinks to great depth.

This cold water then cycles back to the Pacific, where it reheats and rises to the surface, beginning the cycle again.

This migration of water has long been thought to play a vital role in circulating warm water, and thus heat, around the globe. Without it, estimates put the average winter temperatures in Europe several degrees cooler.

However, recent research indicates that these global-scale seawater pathways may play less of a role in Earth’s heat budget than traditionally thought. Instead, one region may be doing most of the heavy lifting.

A paper published in April in Nature Geoscience by Gael Forget, a research scientist in the MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS) and a member of the Program in Atmospheres, Oceans,and Climate, and David Ferreira, an associate professor in the Department of Meteorology at the University of Reading (and former EAPS postdoc), found that global ocean heat transport is dominated by heat export from the tropical Pacific.

Using a state-of-the-art ocean circulation model with nearly complete global ocean data sets, the researchers demonstrated the overwhelming predominance of the tropical Pacific in distributing heat across the globe, from the equator to the poles.

In particular, they found the region exports four times as much heat as is imported in the Atlantic and Arctic.

“We are not questioning the fact that there is a lot of water going from one basin into another,” says Forget. “What we’re saying is, the net effect of these flows on heat transport is relatively small. This result indicates that the global conveyor belt may not be the most useful framework in which to understand global ocean heat transport.”

Full article here.

Comments
  1. Phoenix44 says:

    Maybe it’s the summary that’s confusing, but how could warmer water become cooler than the cool water it comes into contact with? Surely the temperatures must equalise, at which point nothing much happens?

  2. Sid Viscous says:

    Their map is wrong. The current that flows down the west coast of North America from (Alaska) is a COLD current. If “NWS/NOAA” can’t get that right, why should I believe anything else they come up with?

  3. oldbrew says:

    Wiki says: The Alaska Current is a southwestern warm-water current alongside the west coast of the North American continent.
    https://en.wikipedia.org/wiki/Alaska_Current

    But the current Sid V mentioned could be the blue (cold) one below the Alaska current, which certainly doesn’t look like the NWS/NOAA graphic. The answer may be that the GOCB doesn’t go down the west coast of Canada/America at all, but is further out west.

  4. Graeme No.3 says:

    oldbrew:
    I am confused by the chart you posted. Where is the warm water from the tropical Pacific?
    And the Gulf Stream is shown cooling down around Iceland, and then splitting into a cold current to the Canaries and a warm current from Scotland to North Cape and beyond. What is the source of the heat for the latter (now that Scotland is relying on turbines)? Do massed ranks of Scottish politicians stand on the western isles emitting warm air?

  5. phil salmon says:

    Gael Forget and David Ferreira are foot soldiers for the Climagisterium. Anything other than CO2 in climate has to be played down.

    After all, compared to a gas making up 1/2500 of the atmosphere, what could oceans 4km deep on average covering 75% of earth with 1000x the specific heat capacity of air, holding 97% of climate heat, possibly contribute to climate??

  6. phil salmon says:

    Phoenix44
    Maybe it’s the summary that’s confusing, but how could warmer water become cooler than the cool water it comes into contact with? Surely the temperatures must equalise, at which point nothing much happens?

    Salinity is what can make this happen. Water transported from warm surface layers is more salty and thus more dense (than water of the same temperature but less saline). When salty water from low latitudes is transported to cooler regions and becomes colder, then it can become denser than surrounding water bodies having the same temperature but less salinity. So then this cooled and more saline water sinks to the ocean floor on account of its density. This process is called downwelling and “deep water formation” and is the propeller driving the global ocean deep circulation.

  7. dai davies says:

    Southern ocean surface temperatures (SST) confirm the dominance of the Thermohaline 800 year cycle.

    First, a rough attempt manually fitted in a spreadsheet.

    Next, using an algorithm optimised for extracting cycles longer than the data period.

    In both cases the ~800ycycle dominates. The extrapolated model shows about 2.5C range.

    As an interesting twist, the first model was based on a model for sunspot cycles with a little manual tweaking of parameters. A resonance between solar influence and continental movement/ocean current forcing, or just coincidence?

  8. Old Brew and Graeme3 the currents are a bit more complicated than the chart you show. I do not know around the world but for Australia, the current circulation and the meeting of cold and warm currents is where commercial fishermen know where to fish.
    Do not know how to put in an image -pity copy & paste does not as on my computer. This is the web address https://www.google.com.au/search?q=ocean+currents+around+australia&tbm=isch&source=iu&ictx=1&fir=71HFr_rWwM8R5M%253A%252Cwz4yYkGPkyEi8M%252C_&vet=1&usg=AI4_-kRCx0pG6BqdCUtQPVx252Ps3jV5fQ&sa=X&ved=2ahUKEwjfmOiGmqTiAhXk_XMBHa8UBqIQ9QEwAHoECAwQBg&biw=1366&bih=654#imgrc=oaGI7tbBfLSCOM:&vet=1 which shows up the current. Where the current is in small circles is the good fishing eg Nowra / Ulladulla NSW, Anyone surfing or swimming knows that the eastern Australian warm current only goes down to a little way past Sydney and in winter retreats a bit northward and not so strong. In Qld on the Sunshine Coast about 90 km north of Brisbane the ocean temp is gets upto 26C in summer but at the beginning of May when we last did some body boarding the temp was down to 22/23C. The waters off Victoria & Tasmania are cold. The waters off the west coast of Tasmania and New Zealand are too cold to swim as they come from Antarctica.

    [reply] image…

  9. oldbrew says:

    Ocean currents are probably a bit like the road network – primary routes, secondary routes and regional/local byways. The GOCB would consist of primary routes.

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