What happens in the oceans doesn't stay in the oceans

As completely terrestrial beings, life in the oceans and seas seems alien to us, however, nothing in our history would exist if it weren't for the fact that millions of years ago the first molecule capable of harboring genetic material was formed in a primitive ocean. A lot has changed over those millions of years, but our dependence on the ocean has not. It may not be tangible at all, but from the oxygen we breathe to the CO2 that, if not captured, could one day completely suffocate us, the oceans, and bodies of water in general, -for now- have us covered.

Learn about these four ways in which the oceans and their organisms embrace and sustain our daily lives!

Let's start with what seems most obvious: the oxygen we breathe

I say “it seems” because breathing oxygen has involved quite a feat. From the first organisms that died when in contact with this gas, to those who revolutionized life on planet Earth and created an aerobic atmosphere that has supported more biodiversity than we could imagine.

Broadly speaking, the oceans are divided into two parts: the part that receives sunlight (photic zone), and the part that does not. Although it seems irrelevant, this column of water illuminated by the sun (no more than 600 meters, but on average, 200 meters) is indispensable for all aerobic organisms on this planet, that is, all those of us who breathe oxygen to survive. These tiny 600 meters deep (considering that one of the deepest areas of the sea is 10,000 meters) are home to the -also tiny- organisms that were busy building an atmosphere -or their families- millions of years ago, in addition to being home to most of the known marine biodiversity.

In 600 meters, more than half of the planet's oxygen is produced. In other words, we owe the fact that we are alive to a great diversity of organisms that we group into a non-taxonomic category known as phytoplankton. Phytoplankton is made up of microscopic beings, some with a single cell, such as cyanobacteria and diatoms, and others made up of several cells, such as other algae, whose photosynthetic metabolism allows them, like the terrestrial plants we know so well, to capture CO2 and expel the oxygen we breathe.

Filtration: how oysters maintain water quality

A common way to obtain food is through filtration. Oysters, among other mollusks, are animals that rely on particles or organisms suspended in the water column to survive and feed, and that is why they are also exemplary in taking care of water quality.

It is estimated that a single oyster is capable of filtering more than 100 liters of water per day. But what exactly do these bivalves filter out? Both nutrients and sediments are suspended in the water. Nutrients come from several sources: some from the decomposition of other organisms, others due to polluting landfills in agro-industry or other sectors, or simply thanks to the dissolution of atmospheric gases in water; sediments travel great distances with the help of marine currents, generating the mineralization of the oceans.

Whatever the origin of the nutrients and sediments, when these first accumulate, they cause eutrophication, and therefore, that some organisms thrive more than others, losing ecosystem balance and available oxygen. On the other hand, sedimentation along the water column prevents the passage of light and, therefore, photosynthesis, in addition to violating the way of life of the organisms that inhabit that space. These processes not only attack marine organisms, but they also pollute the waters on which terrestrial organisms subsist.

In this way, oysters act as heroines and coastal engineers, buffering and protecting the quality of the water that we all depend on by filtering and eating some particles that could endanger life and planetary livelihood.

More than just food

The oceans are closely linked to climate - and contrary to popular belief - they provide us with much more than just food, in fact, they grant us fertility, thermoregulation and rain.

Ocean currents not only move what is inside the sea, but they also participate in some internal dynamics of wind currents. Through evaporation as a result of the warming of seas and other bodies of water, it is easy to transport very small particles -such as sediments high in nutrients and minerals- from one side of the globe to the other, and with condensation and precipitation, these are able to penetrate poorly fertile soils and make them highly capable of supporting life. Something like this happens with the Amazon and the nutrients transported along the Atlantic Ocean from the Sahara, and this is also one of the reasons why the tropics of America are such productive areas.

On the other hand, in addition to generating precipitation as a result of water heating, the oceans absorb the greatest amount of solar radiation that impacts the planet. If they did not have this capacity for absorption and balance through the cooling and heating cycles of their currents, the Earth would not be a habitable planet like the one we know today. The oceans are the Earth's great thermostats.

The latter has a direct impact on climate regulation and on the dynamics of marine currents and, therefore, on the organisms that these currents harbor and transport. In a very general way, cold waters are more biodiverse than warm waters and this represents an enormous problem in the face of climate change, since the warmer the sea, the less biodiversity there is and, therefore, the less food and ecosystem services for all.

Carbon capture? Yes, the oceans capture more carbon than we thought

As we have already seen, the oceans do a great job of making this planet a very habitable one, however, they are very fragile bodies of water and sensitive to small changes. One of the biggest benefits we get from oceans, seas and coastal areas is carbon capture. In general, the oceans capture and sequester carbon in three ways: as a result of the dissolution of atmospheric CO2 in water, generating inorganic carbonates (bicarbonate and carbonate), as organic carbon (biomass) resulting from photosynthesis and as calcium carbonate (CACO3) present in organisms such as corals and mollusks.

Mangroves, algae forests, swamps and saltwater wetlands are capable of capturing and sequestering carbon for millennia. Even though they occupy just over 1% of the oceans, they capture more than half of the carbon that lies in the seabed. However, the ocean has a very well-kept secret: in the south of our planet there is an enormous mass of land, surrounded by an even more enormous mass of frozen water, the Antarctic Ocean. There is a purely physical and chemical issue that makes cold places even more capable of capturing and storing carbon than warm ones, and this is simplified by the fact that atmospheric CO2 is more soluble in cold and salty waters and more strongly dissolved in seas where the concentration gradient of atmospheric CO2 vs. Oceanic CO2 is more intense, and this, as we have seen before, happens in waters with low temperatures because they contain the greatest biodiversity of organisms, including phytoplankton (Long et al. , 2021).

The Antarctic Ocean is our planet's largest carbon sink, and its melting threatens everything we know on Earth. After these minimum four ways in which the oceans support our terrestrial life, it makes sense to state the seriousness of climate change in the face of a sink that, if heated too much, can collapse. And with it, life itself.

Today, June 8, World Oceans Day, we intend with this text to make an urgent call for the care and protection of the oceans, just as they care for and seek in truly countless ways, our existence.

References:

Long, M., Stephens, B., McKain, K., Sweeney, C., Keeling, R., & Kort, E. et al. (2021). Strong Southern Ocean carbon uptake evident in airborne observations. Science, 374(6572), 1275-1280.