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14 Causes of Hypoxia in Ocean – Effects

by Fitriani

Hypoxia simply means that there is a low oxygen supply in ocean. Oxygen is crucial to the survival of marine creatures in the same way that it’s so important for humans. However, unlike humans, most marine creatures take in oxygen in its dissolved state in water. That’s one major importance of oxygen in the ocean that you need to know so that you can understand why hypoxia is a big deal.

These 14 Causes of Hypoxia in Ocean will explain all the natural and man made contributors that deprive the ocean from its oxygen. When you become aware of all the causes and the effects of hypoxia, you can help the ocean from falling deeper into destruction.

Effects of Hypoxia in Ocean

Let’s take a quick look at what hypoxia can do to the marine ecosystem and everything that lives in it:

  • Less Reproduction in Fish: Fish do not spawn as much as they usually do and their egg counts fall below normal.
  • Mass Death of Marine Creatures: They will have less chance of survival when oxygen is low. It’s one of the biggest threats to marine biodiversity.
  • Disturbed Ecosystem: The marine ecosystem will be in chaos and does not function as its naturally supposed to do.
  • Diet Depletion: Marine creatures will have less food to rely on and it will become harder to stay alive.
  • Forced Migration: Many marine creatures will be forced to migrate somewhere else in search for food.

Now that you know the destructive effects of hypoxia in ocean, it is time to learn the numerous causes:

1. Fertilisers

One of the most concerning causes of hypoxia in ocean is fertilisers. They may be the result of farming, lawns or other agricultural activities. Fertilisers might offer us a lot of benefits but it can be deadly for the ocean. How do they end up there? Most of the time it is through runoff. Rain helps speed up the process even more. What’s even more concerning is that when agricultural lands are so close to the oceans. This will only encourage hypoxia areas to pop out more frequently.

2. Phytoplankton Blooms

Phytoplankton are great. After all, they are the primary producers in the food chain. But the fact is that too much of phytoplankton in the ocean can be fatal. What increases the production of phytoplankton is minerals. The phytoplankton will bloom and bacterias will break them down. The process will lower the availability of oxygen in the water.

3. Algae Overgrowth

Another fatal result of an algae overgrowth is that they can act like a shield that prevents sunlight from going through the surface layer. Blocking sunlight in the ocean is not something that will be helpful to the ocean. Many marine creatures need sunlight. The plants need it to photosynthesise. Meanwhile, the marine animals need those plants for their diet.

Read more: Importance of Algae in Ocean

4. Eutrophication

Eutrophication can greatly depletes oxygen in ocean, thus causing hypoxia. It’s when the water is overly loaded with a lot of minerals and nutrients. It is usually a mixture of overgrowth or death of marine creatures and also land runoff. Though eutrophication is a natural phenomenon, human activities have increased its chances of happening.

5. Geographic Nature of the Ocean

The geographic nature of the ocean matters. Hypoxia occurs in the Black Sea mainly because the water is isolated. The shallow sills are considered to also be the culprit. They cause water to be contained in one place for a very long time. When this happens, there is less chance for oxygen to be present in the water.

Read more: Effects about Layers of the Ocean

6. Low Circulation

Another factor that causes hypoxia in the ocean is low circulation. For instance, the Indian Ocean and the Pacific Ocean have areas called as OMZ. They stand for Oxygen Minimum Zones. Even from the name itself, you can tell that the zones are inevitably affected by hypoxia. The oxygen minimum zones can end up being permanent.

7. Climate Change

We know how real and terrible climate change can be to everything in this world. In fact, it can trigger more hypoxia in ocean. The unpredictable changes that climate change bring may contribute to reduce the level of oxygen in the oceans even more. This is why people need to take climate change seriously and try to care more for the environment.

8. Rising Temperature of the Ocean

The rising temperature of the ocean will make it difficult for oxygen to be evenly distributed in the ocean. According to research, troubles with oxygen concentration will start to rise once the temperature increases. It will get harder for oxygen to penetrate through the deep parts of the ocean.

9. Lack of Sea Water Mixing

This particular cause of hypoxia is a natural one. It’s important for water in the ocean to mix with one another. Most importantly, the fresh water and the heavy sea water. When there is a lack of sea water mixing, the bottom parts of the ocean don’t receive a lot of oxygen. This will make those areas to become hypoxic.

Read more: Effects of Ocean Upwelling

10. Death of Marine Creatures

The death of marine creatures can also add to the the causes of hypoxia in ocean. When there isn’t enough resources to keep any plants thriving in the ocean, the marine plants will suffer. As they all die, less and less oxygen is circulating in the ocean. It’s a deadly cycle that will only cause the ocean to experience so much loss.

Besides all the causes mentioned above, here are other reasons that also contribute to decreasing oxygen availability in ocean:

  1. Untreated sewage system
  2. Use of harmful chemical such as detergents
  3. Burning of fossil fuel
  4. Waste dumping into the ocean

See also: Future Effects of Ocean Pollution

The causes of hypoxia continue to increase and intensify in the ocean. The results are not just deadly to the marine creatures as it will affect us too. It’s important to care for the ocean and prevent hypoxia from getting worse as the year goes on.

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