I don't know about you, but those three things together sound very uncomfortable. Unfortunately, this is the reality that many marine organisms are dealing with today.
Worldwide, oceans are becoming hotter, less oxygenated and more acidic -- the biggest contributor to these changes are CO2 (carbon dioxide) emissions from human beings. Not that human beings themselves are giving off more CO2 to the atmosphere, but the things that we do: using transportation vehicles, increased agriculture, burning oil and gas and even deforestation (cutting down large areas of trees) are the driving forces behind an increase in carbon in the air.
Why the ocean?
Water covers 2/3 of the earth's surface (fresh and salt), and while there are seven "defined" oceans, it's all connected. The ocean (I'm going to generally refer to all oceans as one "ocean" for this blog post), is actually the biggest continuous ecosystem on the planet (IPCC Report 2019). Animals are able to move freely through the water, up and down the coasts, some migrating from the tropics to the arctic circle every year (i.e., the humpback whale).
Image 1: Australian Humpback Whale with young calf. (Off the Map Travel; https://www.offthemap.travel/news/understanding-whale-migration/)
Image 2: Migration Routes of Humpback Whales over the course of feeding, breeding and migration. (WWF Australia; https://www.wwf.org.au/news/blogs/australian-humpback-highways)
This also means that if something is happening in one part of the ocean then it is likely going to impact other parts of the ocean as well.
When the earth receives light from the sun, some of the light is reflected back, and some becomes heat. Essentially, heat is "trapped" within the atmosphere, which is how we are able to live on earth in the first place; we need heat. However, when there is more CO2 in the atmosphere, less and less can be released back into space and more is trapped in the atmosphere, meaning our atmosphere gets warmer. This is called the Greenhouse Effect. The ocean can compensate for some of this "extra heat" and takes it in, but this process also warms the ocean. The more that the atmosphere warms, the more heat that the ocean has to take in to compensate.
Image 3: Simplified version of the Greenhouse Effect. (Wikipedia: Greenhouse Effect; https://en.wikipedia.org/wiki/Greenhouse_effect#/media/File:Climate_Change_Schematic.svg)
Another thing the ocean is good at is storing carbon. A system that stores carbon is called a "carbon sink," while a system that releases carbon is a "source." Excess CO2 in the atmosphere is stored in the ocean just like heat. Chemically, CO2 is acidic (think sour -- like lemons, limes, etc.), and while the ocean can compensate for some acidity, it cannot compensate for all of it. This means that the more CO2 in the ocean, the more acidic it becomes -- it doesn't exactly taste more sour, but it does change the chemical composition of the water. If you've every tested the pH of your pool, the water you are swimming in should have a pH of around 7.4. If it's not, you usually add an acid or a base to the water to either decrease or increase the pH, so it's safe to swim in. A base will increase the pH of the water and an acid will lower the pH. The same thing happens in the ocean; except the ocean has a pH of about 8.1 (EPA 2022), which many organisms are used to and have adapted to. There are animals with skeletons, like crabs, corals, clams, mussels, etc., that will begin to dissolve or become weaker if the water becomes more acidic. As the ocean becomes more acidic, these organisms find it more and more difficult to survive.
Examples of Organisms sensitive to ocean acidification.
Image 5: Giant clam (Shutterstock; https://www.shutterstock.com/search/giant-clam)
Image 6: Crab (PxHere; https://pxhere.com/en/photo/980453)
Image 7: Coral on the Great Barrier Reef (Westend61; https://www.westend61.de/en/imageView/KIJF02257/australia-queensland-great-barrier-reef-corals-close-up)
In combination with the ocean warming and becoming more acidic, the ocean is becoming more deoxygenated. As water warms, it holds less and less oxygen, limiting the amount of oxygen that is available for marine organisms. The scientific jargon for oxygen deoxygenation is hypoxia.
The biggest concerns in the tropics right now are warming and hypoxia.
Image 4: Map defining the geographical zones of the world. (Wikepedia: Temperate Zone; https://en.wikipedia.org/wiki/Temperate_climate)
Because the tropics receive a consistent amount of sunlight year round and year-round temperatures tend not to fluctuate as much as areas above and below the tropics, organisms that live in the tropics are acclimated to a specific range of environmental variables (i.e, temperature and oxygen levels).
Thus, any changes, even if they are not dramatic, can be devastating for many tropical organisms, especially if they cannot move, like corals. They are not able to escape hotter waters or low-oxygen zones. Many reefs are also closer to the surface than deep-sea life and are grouped in with other coastal ecosystems such as kelp underwater forests, seagrass meadows, mangrove forests, and sandy beaches.
Light is largely unable to penetrate deep into the ocean, so shallower waters receive the majority of the sunlight and heat, warming them faster than the deep ocean. The level of oxygen in shallow waters is primarily controlled by photosynthesis (the amount of oxygen being produced by plants when converting sunlight into energy), temperature and oxygen exchange between the atmosphere and the ocean. As less and less oxygen is available because of warming temperatures, this can become a major problem for reefs especially at night. During the night, plants are not producing oxygen, but everything is still breathing. In order for organisms to function, they must have oxygen in order for their cells to operate properly, just like you an me, although many marine organisms don't have lungs like you and I.
Between 1970 - 2010, worldwide ocean oxygen levels between the surface and a depth of 1000 meters (~3280 ft for all my imperial system people) declined between 0.5 - 3.3%. While that doesn't seem like a lot, that is a 0.5 - 3.3% decrease for 361,000 kilometers cubed (139,000 miles cubed) of water that is losing that amount of oxygen (IPCC Report 2019); that is 953,661,100,000,000 gallons of water.
Considering that 80% of plant and animal biodiversity (different species within an are) is concentrated in the tropics and most marine species live in shallower waters, these changes will continue to severely impact tropical ecosystems (STRI Resources).
According to an Intergovernmental Panel on Climate Change (IPCC) Report from 2019, warm water corals are the coastal ecosystems that are at the highest risk of added impacts of current and future climate change. Meaning that if temperature continues to increase, there is an increased risk of losing a large portion of the world's coral reef, as we are already starting to see in the Great Barrier Reef, Australia.
This is one of the many reasons that I am studying and learning about corals in the tropics. Currently, I am trying to understand how corals breathe under different conditions, such as higher temperatures and under hypoxia (low-oxygen). More on the specifics of that next week, as this week acts as the ground work of why conservation and marine research is so important and some of the changes that are impacting oceans today.
Overall, this blog seems like a lot of doom and gloom, but I promise you, that is not all there is to the story. There are stories of some coral resilience, conservation efforts and people taking steps forward to change the current narrative, and hopefully, those stories will be shared on this platform in the coming weeks. The truth is that our world is changing, and I believe that we have an obligation to become aware, learn from our mistakes, take responsibility where it is due and move forward in a way that is honoring to the world around us.
Scientifically yours,
The *miss* in miss-adventures.
Fun fact: The volume of the ocean is 352 quintillion gallons (that's 352 with 16 zeros after it). (Nautiluslive.org)
Animal of the week: This is honestly one of my favorite animals to snorkel with! While it is under the family "Comb jelly," (Ctenophora -- Tee-no-phora) it's not actually a jelly because it does not have stinging cells. Personally, I enjoy it's colloquial name because I usually call it a "Sea walnut." This animal essentially looks like a jiggly, gelatinous floating walnut, and it is awesome. Sea walnuts also bio luminesce, which means it can give off light due to chemical reactions in it's tissue -- HOW COOL IS THAT!?
Sea Walnut (Mnemiopsis leidyi)
(Source: Smithsonian; https://ocean.si.edu/ocean-life/invertebrates/sea-walnut-mnemiopsis-leidyi)
Sources:
[1] IPCC Report 2019, Bindoff, N.L., W.W.L. Cheung, J.G. Kairo, J. Arístegui, V.A. Guinder, R. Hallberg, N. Hilmi, N. Jiao, M.S. Karim, L. Levin, S. O’Donoghue, S.R. Purca Cuicapusa, B. Rinkevich, T. Suga, A. Tagliabue, and P. Williamson, 2019: Changing Ocean, Marine Ecosystems, and Dependent Communities. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 447-587. https://doi.org/10.1017/9781009157964.007
[3] STRI Resources
As always, a thank you to Elizabeth Zerrien on her blog design skills!