Well, hello there!
I know it has been a while, but with the ever warmer summers that we have been having (thanks for that, by the way) I get extremely busy this time of year. Now that we are back we shall continue our discussion on the effects of oceans on the world climate, and subsequently, the contemporary world. This post is the continuation of the effects of oceans on regional climate. If you haven’t read it already, please do so by clicking here. Caught up? Good, let us continue.
So, we saw how the climatic conditions of a region are affected by oceans by looking at two great examples- Western Europe and Peru. They both experienced somewhat opposite climatic effects due to the oceans. The factors effecting these changes, however, are the same, ocean currents.
Do you remember how Nemo’s Dad, and Dory travel the lengths of the Pacific Ocean to reach Sydney (P. Sherman, 42 Wallaby Way, Sydney, NSW, to be precise). Yes, they rode the EAC!
EAC, or East Australian Current, is one of the many, many ocean currents that together form the Global Conveyer Belt. It is a thermohaline (thermo=temperature, and haline=salinity) circulation of ocean water. Like wind, my movement is also based on the temperature and density of the surroundings. And just as there are major wind patterns, like Westerlies, trade winds, monsoon, etc , there are such patterns for oceans too. Think of them as a large river flowing through the restive oceans. The interesting thing about them is that they aren’t always on the surface. In fact, 90% of ocean water is moved by deep ocean currents.
How are currents formed?
Ocean currents can be formed by wind, gravity, earthquakes and temperature and salinity variations that cause density differences in the water mass. They can be divided into two categories; surface and deep water (thermohaline).
- Surface circulation
Like all matter, I expand when heated. So when the solar insolation heats up the oceans they expand. But since the regions near equator receive greater solar insolation than middle latitude or poles, near the equator the water is about 8 centimeters high than in middle latitudes. This cause a very slight slope and water wants to flow down the slope.
Winds blowing on the surface of the ocean aid this movement. A wind blowing for 10 hours across the ocean will cause the surface waters to flow at about 2% of the wind speed. Water will pile up in the direction the wind is blowing.
Gravity will tend to pull the water down the “hill” or pile of water against the pressure gradient. But the Coriolis Force intervenes and cause the water to move to the right (in the northern hemisphere) around the mound of water.
Coriolis Force here refers to the conservation of angular momentum in the pole ward movement of ocean water. Please click on the link to understand it better through a short and cool video.
These large mounds of water and the flow around them are called Gyres. They produce large circular currents in all the ocean basins.
For example, the North Atlantic Gyre. Note how it is separated into four distinct currents, The North Equatorial Current, the Gulf Stream, the North Atlantic Current, and the Canary Current. The Gulf Stream picks up all that warmth in the equatorial regions that North Atlantic Drift transfers to the Western Europe like we discussed in the last post.
Likewise, currents flowing from areas of high solar insolation are warm while currents coming from poles, cold regions of higher latitudes, or areas of upwelling are cold. You can notice this pattern in the global ocean current map below.
- Deep water circulation
The deep waters are “formed” where the air temperatures are cold and where the salinity of the surface waters is relatively high. The combinations of salinity and cold temperatures make the water denser and cause it to sink to the bottom. The Gulf Stream carries salt (as the evaporation due to accompanying winds leaves the interstitial salt behind) into the high latitude North Atlantic where the water cools. The cooling and the added salt cause the waters to sink in the Norwegian Sea. This is the formation of Atlantic Deep Water.
The deep water then travels southward, albeit slowly, to the areas of upwelling where it rises once again. Below are the areas where the water is cold enough and salty enough to form bottom water along with areas of upwelling.
Upwelling is a process in which deep, cold water rises toward the surface.
Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away. This process is known as “upwelling.”
Upwelling occurs in the open ocean and along coastlines. The reverse process, called “downwelling”, also occurs when wind causes surface water to build up along a coastline and the surface water eventually sinks toward the bottom.
Water that rises to the surface as a result of upwelling is typically colder and is rich in nutrients. These nutrients “fertilize” surface waters, meaning that these surface waters often have high biological productivity. Therefore, good fishing grounds typically are found where upwelling is common.
Well, there you have it. I hope you now have better understanding of the climatic variations found all around our globe. Also, if you live around the British Isles or been on holiday there, I know you’ve found a new reason to love the vast blue oceans. So that’ll be it for this post. I know it was a long one, but the topic we were covering was that much more important for me to tell you about. I’ll see you soon. Till then, it’s goodbye from the warm and sandy beaches of England.