What is Ocean Circulation and how does it work?

During your last read you have found out that Ocean Circulation may answer your question of how rapid climate changes can occur.In the next few sessions an important and famous scientist will help us understand how Ocean Circulation and Climate are interconnected.

Nothing in nature is static. Everything moves, forms and reforms constantly throughout the geological timescale. Constant movement is also found in the world’s oceans. Due to wind, rain and evaporation (e.g. Richter & Xie, 2010; Clark et al., 2002) water is being moved in, out and within each large mass of water. In certain location this movement becomes directed and forms large ocean currents flowing past landmasses and through continent openings. This whole system consisting of many directed flows of current is referred to as ocean circulation.

In 1982, a scientist by the name of W.S. Broecker published his first idea of what the global ocean circulation may be like. He thought of ocean circulation as a conveyor belt transporting water along a route through all world oceans and back to its original position. This means that oceans throughout the earth are interconnected. Thus, changing the climate in one place will automatically influence the whole Earth.

The Great Ocean Conveyor Belt, taken from W.S. Broecker's "The biggest chill" (1982)

However, as young critical scientists you have to ask Mr. Broecker one particular question to verify his hypothesis: what are the important factors that drive and influence the ocean conveyor belt?

If you have an idea, post your answer below.

Here is the Answer: Abrupt Climate Changes

Last posted question:

What is the difference between warming phases and cooling phases?

Here is the answer:

During cooling phases, the Earth tends to gradually cool down over a period of thousands of years. In contrast, warming phases happen over a few centuries! 

This discovery has put scientists infront of a difficult question: Slow climate changes are explainable with extraterrestrial forcing through the Milankovich cycles, but how do we explain those observed rapid climate changes?

When reconstructing climate, it is important to look not only at one component (eg the atmosphere) or one resource (eg ice cores), but many possible variables.
Thus, let’s have a look at a different climate record that highlights another component: coral reefs in the ocean:

Sea level fluctuation time series reconstructed from coral reef terraces, taken from Siddall et al. (2003)

When looking at past sea level stands we see almost identical fluctuation structures in the ocean compared to the fluctuations of temperature or greenhouse gases in the atmosphere.

Thus, mechanisms for changing climates may not only be found in the atmosphere, but also in the oceans.

And here is the big clue: Ocean Circulation is believed to be one possible mechanism that may trigger these otherwise unexplainable abrupt climate changes!

Why are we interested in ocean circulation? A short trip to the Earth's past.

Many people today are worried about the future of the earth when thinking of climate change. To most humans, climate and natural settings were considered the one stable concept in their otherwise unstable life. Hence, the thought of a 4˚C warmer Earth, as it is postulated by the IPCC and many newspapers often triggers communal fears of mass extinction that may even include the human race.

You may panic.

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However! Here is the interesting bit. During the last century, climate scientists have found evidence for long term climate changes throughout the earth’s history (e.g. Daansgard et al., 1982; Daansgard et al., 1993). Proxy data (eg by converting information found through biological and abiological indicators into climate variables) or even direct measurements (eg trapped air bubbles in ice cores) in geological records have shown that Earth has went through climates much more aggressive than the one we know.

-          Precambrian (600-3500 Ma): Snowball Earth: The whole of the earth’s surface was covered in ice (Hydeet al., 2000; Donnadieu et al., 2004)

-          Cretaceous (65-144 Ma): Greenhouse Earth: Ice did not exist. Fun fact: CO₂ pressure was above 1000 ppm vs today at 400 ppm (Barron et al., 1981; Barron,1983; Kuypers et al., 1999)

This shows that the Earth has a much greater climate span than we would have initially believed. Since our climate today includes ice on Earth (glaciers and permafrost) we are actually closer to the snowball earth climate than the Cretaceous version; meaning, we are stuck in an Icehouse Climate, while an ice free earth represents a Greenhouse Climate.

To get a more accurate understanding of our current climate situation, we should take a closer look at the recent past of our climate.

Vostok Ice core time series and Insolation, taken from Petit et al. (1999)

Petit et al. (1999) have managed to characterize climate for the last 400,000 years. We see that temperature (line b) has fluctuated strongly between cold glacial and warm interglacial periods. The Insolation curve (line e) suggests that those fluctuations are initiated by changes in solar energy on earth. Thanks to Milankovitch, we know today that climate over the last ice ages was indeed forced by three external variables (Eccentricity, Obliquity and Precession) with different oscillations (Zachos et al., 2001).

Now put yourself in the shoes of a climate change scientist and try to answer the following question using the graph above:

What is the difference between warming phases and cooling phases?

Post your answer if you like and see whether you were right next time J

the treasure hunt begins

So put on your diving gear, and don't forget a flashlight! It might be dark down there...

Now what?

Ok now what? 

Have you ever wondered about the actual scientific consensus on the doom stories known about climate change and ocean circulation?

Well you have found the right place! Together with me and many other people, you will find out about the scientific base that lies underneath the ocean circulation theory.

Come by each week and learn about ocean circulation, the conveyor belt model, the threshold hypothesis, future projections and ways of doing climate research.

You have stumbled upon Sophie's ocean circulation blog

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I am glad you have found my humble blog in the midst of all those blogs out there.
Feel free to make a cup of tea, roam around and learn new things. Comments, thoughts and link suggestions are much apprechiated!