If you’ve heard David Attenborough start any of his documentaries relating to the ocean, you may have heard him say “Our Planet, is a Blue Planet”. If you haven’t this is a series you and your family should take the time to watch. I’ll wager it will leave you with a sense of wonder that nothing else can match.
And he is right. Our reality is, that while we - as upright bipods - walk the land, we shouldn’t call our planet ‘earth’, we should probably call it ‘ocean’. Because that is what ~71% of the globe is covered in. Seawater wraps our globe, in one continuous water body that surrounds all land masses.
In total, there is 321 million cubic miles of water on the planet. Each of those cubic miles, contains over 1 Trillion gallons, or over 4 Trillion liters!
The Oceans
For the purposes of navigation - not disconnection - seawater has been divided into a number of different seas and oceans. You may have heard of the ‘seven seas’ which is an old way of describing the ocean in the early days of exploration. Today (assuming you define a sea as an area of seawater that is partially landlocked) we recognize around 50 seas. More importantly, we recognize 5 main water masses called oceans, with stats as follows, from largest to smallest:
Pacific Ocean (Area: 60,060,700 sq. mi; 155,557,000 sq. km. Average Depth: 13,215 ft.; 4,028 m. Greatest Known Depth: Mariana Trench — 36,198 ft.; 11,033 m)
Atlantic Ocean (Area: 29,637,900 sq. mi; 76,762,000 sq. km. Average Depth: 12,880 ft.; 3,926 m. Greatest Known Depth: Puerto Rico Trench — 30,246 ft.; 9,219 m.)
Indian Ocean (Area: 26,469,500 sq. mi; 68,556,000 sq. km Average Depth: 13,002 ft.; 3,963 m.) Greatest Known Depth: Sunda Trench — 24,460 ft.; 7,455 m.)
Southern Ocean (Area: 7,848,300 sq. mi; 20,327,000 sq. km Average Depth: 10,728 ft.; 3,270 m. Greatest Known Depth: South Sandwich Trench — 23,736 ft.; 7,235 m)
Arctic Ocean (Area: 5,440,000 sq. mi; 14,090,000 sq. km. Average Depth: 3,953 ft.; 1,205 m. Greatest Known Depth: 18,456 ft.; 5,625 m)
Chemistry, Currents, and Weather Patterns
What’s in Seawater?
While variable and dependent on a range of factors including location and depth, on average seawater is made of around 96.5% water, 2.5% salts, and smaller amounts of a number of other dissolved compounds. That sounds really simple until you see the actual breakdown. Check out the list below.
Some of you may be asking the question - how does all that, get in there? Was it always in there or does it change? Great question! And, you will probably not be surprised to know, it does change. As with all things in life, the ocean absorbs and releases solids and gases, as it circulates around the globe. On top of that, the ocean contains life - 6B tonnes of C - which live, die, eat, and excrete, all of which change the chemistry of the ocean.
Slight detour - Have a listen to this…
But while the specific chemistry may not be necessary to know, the way in which this chemistry affects the oceans, and therefore us, is important for us to understand.
How the Ocean moves
If anyone has spent time by the ocean, they know it moves. There are tides, waves, and currents. But few of us are aware of oceanic movement at a global scale, nor why and how the ocean moves. Oceanic currents move in all directions. Literally. Up, down, sideways, around. The ocean is constantly in a state of flux. And there are a number of factors that drive these changes.
You’ll likely know about wind driving currents, so I’ll skip over that and jump straight to the big player you may not know about.
Thermohaline Circulation
If you have broken that word down you’ll have figured out that thermohaline circulation refers to temperature (thermo) and salinity (haline) driven circulation. Both of these factors, affect the density of water. Cold and salty water, is ‘heavy’ in oceanic terms, so it sinks; dropping down through the water column until it hits a body of water equal to or greater than its own density, or the sea floor. This is called convection.
As shown in the above illustration, while the convection occurs, replacement water is drawn into the ‘space’ left behind in the upper layers of the ocean, which then cools, and so the cycle continues. The cold water then moves away from the polar regions, until it warms, or is surfaced by shallower bathymetry.
So, while this exchange of water occurs at localized scales in both the Arctic and Antarctic regions of the globe, the currents that this exchange drives are at global scales. Commonly, the movement of oceanic water through this process is referred to as the global ‘conveyer belt’, not just because there’s a fairly consistent direction, but also because these currents are carrying all of those gases, minerals, salts, etc, with them. The below shows how the major global currents flow. You can see it ‘starts’ west of Europe where the cool water sinks. It then flows south to Antarctica in the depth of the Atlantic, before heading north under the pacific. It then lifts west of the US before warming and recirculating back south via the Indian Ocean and returning back to where it started.
What is incredible to me is how a process that operates at a localized scale in the polar regions, can be the foundation of a much larger process at a global scale. Let’s look at how that impacts us.
Weather Patterns
What is not often understood, is how the ocean, and its currents, underpin our weather (short-term changes in the atmosphere) and therefore our climate (long-term weather patterns in an area). To completely understand we can look at the ocean as a giant battery, that stores, distributes, and releases, solar radiation (heat). Just like on a stove or in the freezer, water molecules will warm or cool, when they sit adjacent to something that is hot, or cold.
This reality results in a direct link between the temperature of the ocean, and the temperature of the air above it. Essentially, like many things in nature, when the atmosphere and ocean interact, they seek equilibrium and will exchange heat in one direction or the other, to do so. This interaction occurs through evaporation - the basis of the water cycle. Water evaporates over the ocean, then rains. If it rains on land, the water flows into streams, rivers, and lakes, and is then stored as snow or ice, and eventually, the vast majority of it flows back out to the ocean. This massive process, across the entire globe, regulates our climate.
Because solar radiation from the sun is so uneven depending on the location on the globe, the seasons, and the time of day, the stability of our climate is underpinned by this massive heat exchanger. If the conveyer belt stops, it is expected there will be significant problems for us. Europe and parts of North America would stop receiving warmth and the rain cycle would be significantly disrupted.
How would that happen? Go back to the beginning - to the engine room of the global conveyer belt and reduce the fuel that feeds it; ie change the salinity. How would that happen? Add fresh water. How would that happen? Melt the ice caps. How would that happen? Warm the atmosphere…
Until next time…
Good job Dad!!😘