How exactly does this amazing ocean circulation work?
The dynamics of the ocean is a true spectacle of nature. With around 70% of the
planet’s surface covered by water, the ocean plays a key role in regulating the global
climate and distributing heat and nutrients across the globe.
Ocean circulation is made up of two main components: the surface ocean current
and the deep ocean current. The surface ocean current is driven by wind and is
faster, occurring mainly in certain ocean basins. This current is responsible for the
exchange of heat and moisture between the ocean and the atmosphere, directly
influencing the global and regional climate.
The deeper, slower current is caused by differences in the density of the water. This
current is primarily responsible for global ocean circulation, distributing heat and
energy across the Earth. Changes in this deep circulation can occur over very long
timescales and have the potential to affect local and global climate, as observed over
the last few millennia.
Water density difference is a crucial factor in understanding deep global circulation.
The density of water varies with salinity and temperature, resulting in different
densities across the ocean. Warmer water is lighter and less dense, while ice, even
at a lower temperature, is less dense than liquid water due to its crystalline structure.
This explains why ice cubes float in water.
Thus, areas of cold, salty water are denser than areas of less salty, warm water. In
the ocean, the layers of water are arranged according to their density, overlapping
like layers on a birthday cake. Denser layers lie below lighter ones, creating a
continuous flow of water around the globe.
It is important to emphasize the difference between “weather” and “climate”. Weather
refers to short-lived processes, while climate refers to the average state of nature
over longer periods. For example, a rain in a desert can be considered “rainy
weather”, but if over the years the region has little precipitation, it will have a “dry
In short, the dynamics of the ocean is a true ballet of currents, heat and nutrients.
Understanding how these processes work is essential to better understanding our
planet and how it can be affected by climate change.
Water layers are defined by temperature and salinity levels. They are known as
water masses and are fundamental to better understanding the ocean, as they allow
us to trace its origin and destination. The formation of these water masses requires a
precise combination of conditions, such as winds, solar radiation and salt availability.
These elements are only found in certain seasons and regions of the globe, such as
the North Atlantic and South Atlantic. By studying these layers, we can improve our
understanding and description of the ocean.
The ocean and its relationship with the climate: heat transport is
The formation of deep water bodies is the fuel for the transit of thermohaline
circulation. Within this circulation, the Atlantic Meridional Rollover Circulation
(CMCA) plays a crucial role in transporting heat across the Atlantic Ocean.
The CMCA starts at the surface, composed of salt water and warm coming from low
latitudes, close to the Equator. This current flows towards the North Atlantic Ocean,
where the Gulf Stream plays a key role. As it moves northward, the CMCA gradually
loses heat to the atmosphere due to the large temperature difference between the air
and the ocean.
After losing heat, the water becomes denser and sinks, returning to the south. At the
same time, winds capture warm, moist air above the CMCA. It is similar to what
happens when we forget a cup of tea: it cools down to room temperature. To achieve
equilibrium, hot tea needs to lose heat and moisture to the air around the cup.
However, this warm, humid air does not remain concentrated near the cup for very
long. On the contrary, it disperses in the environment until we can no longer perceive
The warm, humid air leaving the CMCA is captured by the winds and spreads over
long distances, reaching distant cities like London. This makes the climate in London
hotter and more humid than in other cities located at the same latitude.
Now you understand why CMCA is an essential component of the Earth’s climate
system: it plays an important role in transporting heat. The CMCA is responsible for
the relative heat of the Northern Hemisphere.
What will be the transformations in the ocean?
The ocean not only absorbs most of the solar energy that reaches Earth, but also
more than 90% of the CO2 and excess heat that humans release into the
atmosphere. But can the ocean continue absorbing heat and carbon indefinitely?
Probably not. Currently, the ocean is undergoing changes faster than scientists
expected, due to climate change and human impacts.
Every time we add something to the ocean, like heat or carbon, we change it. So
what does the future hold for the ocean?
The average temperature of the ocean is increasing, which will result in greater
stratification, with less mixing between layers of water. This will make it more difficult
for the bodies of water that currently exist to form, as they depend on mixing. These
changes in the formation of water masses will affect heat transport and,
consequently, the Earth’s climate. Also, some places will experience greater surface
heating than others. The Arctic, for example, will be more affected than any other
region, which is worrying, since it is a critical area for the formation of water bodies. If
these masses do not form quickly, ocean currents are likely to weaken. Studies have
already shown that the Atlantic Southern Overturning Circulation is weakening, and
this is attributed to climate change.
A warmer ocean could also result in the disappearance of islands and coastal cities,
due to thermal expansion. When temperature increases, liquid water expands and
occupies a larger volume, which causes sea level to rise. In addition, the melting of
the ice sheets, caused by the increase in temperature, also contributes to the
increase in the volume of the ocean and, consequently, in the sea level. In recent
years, we have seen an increase in sea levels, which requires careful study, as it can
affect countless people around the world, especially coastal communities. It is
essential to address these issues professionally and seek solutions to minimize
impacts on the ocean and society.
What can we do in the face of climate change?
Science shows us how and why the ocean will be affected if nothing is done to stop
this process. Rising ocean temperatures will have disastrous consequences for
marine organisms and for us humans. The ocean plays a key role in regulating
rainfall and producing oxygen. It provides us with food and facilitates our travels
around the world. We all depend on him! Therefore, it is essential to improve and
expand our knowledge about the ocean and the dangers it faces.
To this end, the United Nations created the Decade of Ocean Science for
Sustainable Development, which will take place between 2021 and 2030. This
initiative aims to teach people what we must do, individually and collectively, to
manage the ocean’s resources in a more sustainable way. ocean. If we don’t start to
change our habits and improve our relationship with nature, climate change will
intensify and the effects of rising ocean temperatures will get worse.
However, we have the power to change this situation! We can start to adopt more
sustainable habits in our daily lives, such as the conscious use of water and energy,
in addition to reducing the consumption of disposable plastics. Thus, we will play a
fundamental role as conscientious citizens. Children also have an important role to
play in raising awareness and building a better future. By talking about climate
change with our family and friends, we help to draw attention to the relevance of this
topic. We can discuss ways to support policies that protect the ocean and fight
climate change. In addition, we can demand that our governments and industries act
responsibly, using natural resources sustainably.
The sooner we act, the better chance we have of securing a better, brighter future for
the world’s oceans, as well as for all the animals and humans that depend on them.
It’s time to act!