Sea of Change: How our Oceans Affect the Climate, Part 1

We are pleased to welcome guest blogger Jacob Spivey. Jacob is a senior undergraduate in Meteorology with a minor in Climatology at Penn State University. Fascinated by weather extremes as he was growing up, today he looks at possible relationships between extreme weather and climate change. Within the past few years, he has also begun looking at how these subjects are communicated to the general public, a process which he has started doing himself in his online blog, Weatherbolt.

Ask someone what they think of when they hear about climate change, and you might get a few different answers. One of the most common ones is “sea-level rise”. When it comes to the world’s oceans, this is likely the only connection – along with El Niño – that a person will generally make to climate change. That’s fine; those are really the only connections that are ever mentioned on the news. As it turns out, the oceans are actually responsible for a lot more than rising seas and warm Pacific Ocean temperatures. They can affect the warming patterns of Earth in the coming decades, and as a result, create new weather patterns in places like the Eastern U.S.

On a big scale, ocean circulations act as heat transporters. Oceans absorb over 90% of the incoming energy from the Sun, and there are circular flows on the surface of each ocean basin that move the majority of the heat, which is received at the equator, towards the poles. These types of flows are called gyres, and they are a result of large-scale wind patterns as well as the rotation of the Earth itself (the Earth’s rotation also plays a huge role in the weather that we experience every day, all over the world). The way these gyres move is the reason why California always has cold water temperatures in the summer compared to someone on the East Coast; they get water flowing from Alaska, while East Coast residents can swim in water that flows northward from Florida. However, there are other flows besides gyres that dominate the global ocean movements.

If we want to understand how the ocean moves around the globe, first we have to know about ocean properties. Sure, we all know that pure water freezes at 32°F (0°C), but the ocean isn’t just pure water. Salt is found in the oceans, and the salt level in a certain region is known as that area’s salinity. The Dead Sea, for example, is the saltiest body of water in the world and therefore has the highest salinity (337 grams of salt per kilogram of water, or 33.7% salt). That’s about 10 times as high as the average global salinity, which is just 3.5%. When salt is added to pure water, it lowers the freezing temperature; it would take a temperature of -6°F to form ice on the Dead Sea. Taking away salt, on the contrary, would raise the freezing temperature closer to its original 32°F. At the same time, higher salt content can lead to higher water density, which is why someone trying to swim in the Dead Sea would instead just float on the surface.

The different salinities of the world’s oceans drive what’s known as the global thermohaline circulation, which is a mouthful that refers to a current which transports heat through different oceans all over the world. The current takes water from the southern Atlantic Ocean, moves it towards the North Atlantic near Greenland, where it sinks because the water is very salty and dense in that region. After the water sinks, it moves back southward through the Atlantic, flows south of Africa and Australia, and rises to the surface again in the North Pacific Ocean. The global thermohaline circulation (GTC) is really important because it allows us to have the climate that we know today as normal. If all of the incoming energy from the Sun stayed near the equator and none of it was allowed to flow towards the poles, our climate would be extremely different!

thermohaline circulation
Global map of the thermohaline circulation. Red colors show where water flows on the surface, while blue indicates flow beneath the oceans. Credit: NASA Earth Observatory

I know, the flow goes in a really complex pattern, and by this point you’re probably wondering what’s the point of me giving you all of this information. Like I said, the salinity levels in the world’s oceans drive this circulation. This visualization map from NASA shows the densities of global ocean water, with dark blue meaning higher density and light blue meaning lower density; it helps you to see why water would sink in the North Atlantic and rise in the North Pacific. 

When ice melts, it is adding freshwater to the ocean around it, making that part of the ocean less salty. Greenland has been experiencing a sharp decrease in total ice over the last 10-20 years. This melting ice has led to an area in the North Atlantic Ocean that’s been colder than usual, and it's been that way for the last few years; this is especially unusual since 2014 and 2015 both broke the record for Earth’s hottest year. However, that colder ocean area is also becoming less salty, since the melting ice from Greenland is freshwater (think of it like putting ice in your lemonade; after a while, the lemonade tastes "watery" since the melting ice cubes are mitigating its artificial content).

- Jacob Spivey

Part 2 will be posted in several weeks!

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