Sharing facts, thoughts and stories to make climate change accessible

At the turning of the tide; our oceans and us (part 1/3)

We are tied to the ocean. And when we go back to the sea, whether it is to sail or to watch – we are going back from whence we came…

John. F. Kennedy

Oceans are kind of a big deal. 71% of our planet’s surface is covered by them. They give Earth its distinct identity in the solar system, a vivid blue spec floating around amongst the other less colourful specs. They contribute enormously to meteorology (weather), coastal events and erosion, livelihoods like fishery and tourism, and of course, balancing out carbon parts per million (ppm) in the atmosphere by acting as an absorber of CO2. For these reasons we are deeply connected with our oceans; a symbiosis that, until lately, has existed in balance.  

Now, I won’t cover the obvious (i.e. that they’re getting hotter and are sadly full of microplastics) but this 3 part blog ‘searies’ starts with a foundation of how the ocean works and what the lesser reported and understood oceanic changes are. Next I’ll talk to the impacts of these changes on marine ecosystems and finally, on us, as humans. They play a huge part in many lives and, whether you’re like me and well up at every Blue Planet episode, or are more concerned about the impacts they will have on our own living conditions, there’s hopefully something in this series to demonstrate how crucial seas are and why we need to reduce greenhouse gas (GHG) emissions. If not to protect them, then to protect ourselves.

Photo by Philip Graves on Unsplash. Sunset over Laguna Beach, USA.

Starting with circulation

The ocean is full of complex and surprising circulation processes, forwards, backwards, up, down (it’s a bit of a hokey cokey as you observe the patterns of how ocean water moves). Oceans have two main layers – surface ocean (c. 10%) and deep ocean (remaining 90%) – and what things move these two layers around are different.

 A large contributing factor for surface ocean movement is wind. Air pressures are formed by the Earth’s rotation and hot and cold air rising and falling between the poles and the equator (the Coriolis effect if you want the sciencey term here). It’s why ocean surface currents move in rotating ‘gyres’, going clockwise in the northern hemisphere and anti-clockwise in the southern (and no, before you say it, this isn’t why a loo flushes differently in Australia than in the UK despite the common myth!). You’ll have likely seen storms take on similar rotating patterns. 


Although the above does contribute to moving the deep ocean somewhat, the main influence for deeper water is the Thermohaline Effect. As water becomes colder it also gets more ‘salty’ and dense, causing it to sink and be replaced by warmer water. So when this plays out across the planet it makes up the global conveyor belt of moving deep sea water (or as I like to call it for the Lion King fans out there, the oceanic circle of life). The ocean water moves in a single loop due to it becoming hotter in the tropics and colder as it nears the poles. The belt acts as a brilliant balancer, controlling salinity and freshwater levels, ocean temperatures and rich water nutrient levels (the deep ocean contains the ‘good stuff’ because all dead organisms sink to it and decompose)

So what’s changing about circulation?

Well, evidence is showing this movement of water is slowing down, and certain other oceanic circulations (like the AMOC) at risk of collapsing completely. Because of temperature increase and ice cap melting it reduces the driving factor of the Thermohaline effect since there is more freshwater and less dense salty water. This has monumental impacts for all living things in and out of oceans, as you’ll read in the rest of the series.

El Niño and La Niña

I’d heard of these weather patterns before but never really understood them until now, so here’s a very quick definition of what they are and how they slosh water about round the world!

Trade winds, caused by the planet’s rotation, move eastward from the Americas towards Asia, taking warm water with them which is replaced by that lovely rich stuff in the deep ocean (known as upwelling). But, these winds aren’t consistent, and cause the phenomena El Niño or La Niña depending on how they change in a given year:

El Niño – The trade winds weaken, and so the warm water flows back towards the Americas. This therefore reduces upwelling – essentially a bad time for most marine species in the Pacific coast. It also leads to drought conditions for North America & Canada as well as Australia, but very wet tropical storms for the US Gulf and South America due to the hotter waters evaporating.

La Niña – Take the above, but put it in reverse. The trade winds are stronger than usual so more warm water is driven towards Asia. Largely this means more biodiversity off the coasts in the Americas, drought in the southern US and heavy rains/ flooding in northern US, Canada and Australia.

Who’d have thought all that ay?

Photo by Michael Olsen on Unsplash. Surf waves of Haleiwa, US.

How are these both changing?

Even now, it’s impossible to predict what type of year we’ll have until it’s happening, but looking back things are clearer – El niño patterns are getting more extreme and more frequent. 3 out of the 5 extreme El niño events since 20th century happened after the 1970s (Luo, W.B.X. et. al, 2019) when global warming started really ramping up, but not (yet) proven to be down to human impact. Regardless, the results were significant in showing El niños become more intense with warmer temperatures. 

So, if we take some examples from the above, extreme weather events like droughts and monsoons will be more intense along with storms and wind speeds. Given a lot of natural defences have been removed by human activity (sea grass, wetlands, mangroves) this means populations may be doubly exposed to these extremes. Biodiversity will be reduced (much more on this in episode 2!) and of course, with rainfall being little or large, this brings with it food and water shortages.

Acidity and oxygenation

This part is a bit easier to wrap your head around. The PH levels  in our oceans depend on the amount of CO2 being absorbed from the atmosphere. The ocean is an awesome carbon sink, absorbing ⅓ of atmospheric carbon. The more CO2, the more acidity. 

With oxygenation, this depends on three things:

  1. temperature; the warmer a liquid is, the less gas it can retain (now I know why my fizzy drinks lose their fizz in the sun). 
  2. Back to that lesser circulation of deep ocean and surface ocean covered earlier. Oxygen enters the ocean from the surface either from the atmosphere or from organisms during photosynthesis, so less mixing equals less oxygen in the depths. 
  3. Chemical runoff from human waste in the ocean causing ‘eutrophication’. Oceans that have a lot of other matter like phosphorus and nitrogen means there is ‘less space’ to absorb other things. So a chemically full ocean may have no room at the inn for oxygen, vital for most marine life.

What’s changing about these levels?

Put simply, acidity is on the up, and oxygen is going down for our seas. Carbon levels in our atmosphere have been increasing for hundreds of years, but not at the rate as we are seeing now, currently at 420 parts per million (PPM). The ocean is dissolving more carbon, getting more acidic and deadly for its inhabitants. 

Oxygen is both escaping as sea temperatures increase and not being replenished due to reduced mixing and chemical concentrations from human waste. This has lead to less oxygen, and in certain areas specifically, ‘dead zones’ of little to no oxygen where no marine life can survive (but do note a few dead zones occur naturally without climate change as a cause). The Baltic Sea has 7 out of the 10 largest dead zones as a result of sewage and agricultural fertiliser leakages.

Photo by Eugene Chystiakov on Unsplash. Dead fish carcass, Kyiv, Ukraine.

Wrapping up…

So we know that ocean water is moving less, both in its mixing layers and in its quest around the global conveyor belt. We also know that the intrinsic patterns between oceans and weather is changing, growing in intensity and frequency, which cause extreme conditions experienced on land as well as for coastal marine life. And finally we learned about the changes in oceanic chemical make up, getting more acidic and less oxygenated. But what do these changes really signify for ocean ecosystems? Are marine species able to adapt? And how will those changes affect us? Stay tuned for episodes 2 and 3 of this series sports fans!

References:

sophieroseteddy

Leave a comment