Greetings, caring viewers, to today’s episode of Planet Earth: Our Loving Home, the first of a two-part series, focusing on the deep interconnection between our oceans and the world’s climate.

The experts featured today are Dr. Steve Rintoul, an oceanographer from Australia’s national scientific research body, the Commonwealth Scientific and Industrial Research Organisation and Professor Anders Levermann, a senior researcher at the Potsdam Institute of Climate Impact Research in Germany and the lead author of the Sea Level Change chapter for the coming 5th Assessment Report of the United Nations Intergovernmental Panel on Climate Change.

Oceans cover 71% of the Earth’s surface, contain approximately 97 % of the world’s water, sustain a diverse array of sea life and play a vital role in regulating our planet’s climate in a multitude of ways – including through thermohaline circulation, also known as the Great Ocean Conveyor.

If you think about the globe and what this overturning circulation really looks like, it’s probably easiest to start in the northern part of the Atlantic (Ocean) up near Greenland and Iceland. Water sinks at the surface there and flows southward through the whole Atlantic basin, until it reaches the Southern Ocean.

And then very strong currents in the Southern Ocean redistribute that water, (and) carry it around the globe, spinning around Antarctica. That water then passes through the Indian and Pacific Oceans, ultimately returns to the Southern Ocean and gradually warms and becomes lighter again. And then (it) flows back in, northward through the Atlantic Basin in the upper part of the ocean, and that closes the loop.

The oceans help stabilize Earth’s temperature by absorbing heat, with approximately a thousand times greater heat absorption capacity than that of the atmosphere.

The thermohaline circulation transports a lot of heat from low latitudes in the Atlantic (Ocean), near the equator, to high latitudes near the North Pole in the Atlantic (Ocean). The entire climate system is in tune with this thermohaline circulation operating.

The oceans influence climate mostly because they can store and transport vast amounts of heat and carbon dioxide. So, the upper few meters of the ocean, for example, can store more heat than the entire atmosphere. So when we talk about global warming over the last 50 years, what we’re really talking about is heating up of the ocean.

Because about 80 or 90% of the extra heat that’s been stored by the Earth’s system over the last 50 years has gone into the oceans. And so the oceans influence climate and it also means that observations of the oceans are an important way for us to track climate change because that’s where the heat is accumulating.

Scientists estimate that the oceans currently absorb a third to 40% of the CO2 emitted from human activity. However recent research by Dr. Jeffrey Park of Yale University, USA’s Institute for Biospheric Studies concludes that in recent decades there has been a reduction in capacity because the oceans are warming.

If the oceans did not serve as a carbon sink, atmospheric CO2 levels would be much higher than the current 392 parts per million, perhaps reaching a highly dangerous 500-600 parts per million.

The other important aspect is that the ocean stores lots of carbon dioxide that we’re emitting into Earth’s atmosphere by burning fossil fuels and by clearing land. About a third of that is ending up in the ocean. If the ocean removes that carbon dioxide, that tends to slow down the rate of climate change. They’re helping to slow down or moderate the rate of climate change that would otherwise occur if all the carbon dioxide remained in the atmosphere.

What would happen if thermohaline circulation substantially slowed or even shut down due to the effects of climate change? Professor Levermann believes such an event would produce huge instability in the planet’s climate system, such as global sea levels rising 10 to 20 times faster than the current rate.

If you put additional fresh water into the North Atlantic (Ocean) by melting Greenland or by having more discharge from rivers, from Siberian rivers, which flows into the Arctic, and then eventually into the North Atlantic (Ocean) or, change in precipitation patterns in the Atlantic (Ocean) can freshen the North Atlantic (Ocean) so strongly that there won’t be any sinking of water anymore, that would disrupt this thermohaline circulation, and could make it stop.

If you shut it down in climate models, the temperature in the North Atlantic (Ocean) decreases by up to eight degrees (Celsius). That’s on top of global warming. It’s not a contradiction to global warming, because it’s just a re-organization of heat. So the Southern Oceans get warmer, the entire Southern Hemisphere gets warmer, while the North Atlantic (Ocean) gets colder.

The problem is that this would already influence agriculture in Europe quite significantly, but of course, also the ecosystems and the Arctic sea ice cover. But it’s because there’s so much heat associated with this thermohaline circulation, it’s going to disturb the entire climate system.

And that means two things: First, global warming would increase or would accelerate slightly in this period. And there would be less CO2 uptake, which would further increase global warming too. Then the rain belt in the tropics would shift.

At the moment, the rain belt, which follows the equator quite nicely, is slightly dislocated over the Atlantic Basin because of this heat transport to the north, because this rain belt doesn’t really want to follow the equator, it wants to follow the thermal equator, the warmest place.

When we return, we’ll continue examining our oceans and their effect on global climate. Please stay tuned to Supreme Master Television.

Welcome back to today’s Planet Earth: Our Loving Home on Supreme Master Television where we are focusing on how the oceans affect the world’s climate. Recently scientists have discovered a fast-moving, deep ocean current around Antarctica that transports massive volumes of water annually and is a major component of the Great Ocean Conveyor.

An important part of this overturning circulation are these very strong, deep currents that we find mostly on the western sides of the ocean basins. They’re pretty well studied in the Atlantic (Ocean), but we know very little about them in the Southern Ocean. So, there’s a huge plateau, a submarine mountain range, which is more than 2,000 kilometers long, that sits in the Indian Ocean sector of the Southern Ocean.

On the flanks of that we had some reasons to expect there might be a current there, but no one had ever measured it. So we really didn’t know just how strong the current was and whether it was an important part of the overturning circulation or not.

A few years ago, in a joint experiment with Japanese scientists and Australian scientists, we deployed some instruments along the flanks of this plateau to measure the deep ocean currents there. What we found were some surprises. The first surprise was that the ocean currents were quite strong; the average speed over two years was about 20 centimeters per second at a depth of 4,000 meters.

Twenty centimeters per second doesn’t sound very fast, but for the deep ocean it’s very unusual. In fact they’re the strongest, the quickest deep currents that we’ve measured in the ocean at those depths. It sits about 4,000 meters below the sea surface and runs along the sea floor. But it extends for thousands of meters up through the water column. So, it occupies a lot of the depth of the ocean, but it’s quite narrow. It’s only about 50 kilometers across.

So we’ve used those current speed measurements, and measurements of temperature and salinity of the water to calculate how much water is moving northward, away from Antarctica, in this deep current system. We found that it’s about 10 million cubic meters of water per second. That’s a pretty tough number to get your head around. If we add up the flow of all the world’s rivers combined we get about one-million cubic meters per second.

This deep river of cold water flowing away from Antarctica is about 10 times the size of all the world’s rivers combined. So what that tells us is that this is indeed an important branch of this overturning circulation and it’s one aspect of the ocean currents that we need to understand and be able to simulate if we’re going to project how climate might change in the future.

Little research has been done on the oceans of the Southern Hemisphere compared to those of the Northern Hemisphere. However, over the years, measurements of Southern Ocean currents have been improved through the use of innovative satellite systems.

So what’s changed in the last few years is, first of all, much better satellite instruments. We have satellites that can now measure the height of the sea surface to within a millimeter or two. So we’re able to study ocean currents from space now in a way that we couldn’t do before. It works a little bit like a speed gun that police might use on the highway to determine how fast your car is moving. It sends down a radar pulse from the satellite, it bounces off the surface of the ocean and returns to the satellite.

“Argo,” a robotic instrument that collects regular information on the status of ocean currents, is a collaborative international project in which 23 countries contribute floats and many others help in implementation.

It’s an instrument that drifts with the ocean currents at a depth of one- or two-thousand meters below the sea surface. It’s carried by the ocean currents, and every 10 days it inflates a small balloon that’s part of the instrument. That changes the buoyancy. It makes the float a little bit lighter in the water column. It rises through the ocean from 2,000 meters up to the surface.

And it measures temperature, salinity and sometimes oxygen levels as it goes. When it reaches the surface, it can transmit that data to us by satellite and then sinks back down again and drifts for another 10 days. We now have more than 3,000 of these instruments deployed throughout the world’s oceans.

We sincerely thank you Dr. Steven Rintoul and Professor Anders Levermann for taking time from your busy schedules to speak with us about the oceans and their relation to our planet’s climate system. From your significant research, it is apparent that the functioning of the Great Ocean Conveyor is highly important in controlling how much carbon and heat our oceans can absorb and thus plays a very significant role in determining the extent of future climate change.

For more details on the scientists featured on today’s program, please visit the following websites:
Professor Anders Levermann www.PIK-Potsdam.de
Dr. Steven Rintoul www.CSIRO.au

Eco-conscious viewers, thank you for joining us on today’s program. Please join us again next Wednesday on Planet Earth: Our Loving Home for the final part of this two-part series. Coming up next is Enlightening Entertainment, after Noteworthy News. May the guidance of the Providence always be with us.