Ocean Deoxygenation


The oceans are changing, and more rapidly than we ever expected. Historically, changes in ecosystems have majorly been slow processes, occurring over hundreds of thousands of years. This would give ample time for the organisms living to adapt to the new challenges and opportunities created in this also evolving ecosystem.

However, a few acute points caused rapid change, and thus rapid extinctions. The K-T Extinction or K-T Boundary (K-T coming from Cretaceous and Tertiary time periods) is one such famous example where the dinosaurs could no longer survive after a hypothesised giant meteor hit the earth and changed the atmosphere and climate of the planet instantaneously. About ¾ of the plant and animal species alive at the time went extinct and everything alive to this day is a result of those ¼ plants and animals that remained. This is actually why mammals are so prolific today. Mammals were small, marsupial-like nocturnal beings that were far outcompeted by the large reptiles (AKA-dinosaurs) and probably would have remained small and inconsequential without the open niche created by the mass extinction. From there, mammals evolved in many directions and have basically taken over the globe, eventually leading to Humans which are now causing their own mass extinction event.

This brings us back to the oceans. There are so many things changing in the oceans these days, and all of them are happening more intensely and at a higher pace than we predicted. Surface temperatures have risen about 2°F or 1°C in the last century. That might not seem like much, but compare that to the 4°C temperature difference of the earth in 20th Century vs the Ice Ages (when Boston was covered under a mile of ice).

With these rising temperatures, comes ocean acidification, coral bleaching events, mass migrations to cooler waters, and something you might not have heard much about – ocean deoxygenation. Now, you may remember from biology class that all animals need oxygen to survive. Land animals and some ocean animals (sea turtles, whales, sea lions, etc.) breath in oxygen from our lungs. This is convenient because oxygen diffuses about 8,000 times more rapidly in air than in water. However, most animals must obtain their oxygen from the water.

Now since oxygen is a gas and seawater is a liquid, there are many chemical properties in play here. For the most part, gasses dissolve better in liquids that are colder. As the temperature increases, that same liquid can hold less and less oxygen. Think of the sir bubbles (gas) rising up in the kettle as you boil water for tea. That’s not entirely the same thing, but it’s close enough. This is also why we keep our carbonated drinks cold. The CO2 stays dissolved in the drink better and it will be less likely to spill everywhere when we open it and release the pressure.

So we’ve already covered the fact that the ocean temperatures are rising, this then means that the oceans can dissolve less oxygen than before. But this also means that fish – who generally (tuna are exceptions) have the same body temperature as their surroundings, are going to need more oxygen as the water temperature rises. Their metabolism will increase as the water temperature increases, so they will be more active and in need of more food. They will also need more oxygen to make up for the increased cellular activity. Except now, there is actually less oxygen in that water.

Recently, as study has been done to predict when widespread deoxygenation will occur. The answer isn’t good. By about 2030 or 2040, there will be large pockets of “dead zones” depleted of oxygen where very little can survive. These dead zones are predicted to take up most of the North Pacific, South Atlantic, and areas around Western Australia. These zones will increase rapidly as time goes on and temperatures increase. You can read more about the specifics HERE, but the gist of it is that we need to find a way, and find it rapidly, to decrease our impact on the environment. Humans are causing mass extinctions across the globe, and most of them are preventable.

‘Ocean Deoxygenation’ was written by Roya