The oceans are a vast and mysterious world, and their depths are home to a number of fascinating phenomena. One of these is the global system of ocean currents, which flow at the speed of a few centimetres per second.
These currents are driven by a variety of factors, including temperature, salinity and water pressure. Colder, saltier waters are denser and thus sink towards the ocean floor. While warmer, less salty waters rise to the surface. This circulation of water creates a global system of currents that transport heat, nutrients and other substances from one area of the planet to another.
Recently, however, there has been a change and these currents now seem to be slowing down. As was to be expected, climate change is responsible for this situation. To complicate matters further, the decrease in these ocean currents could accelerate the climate crisis. And at the same time reducing the productivity of fisheries. Which are a source of sustenance for numerous organisms, including humans.
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The role of the oceans in climate change
In 1990, the UN’s Intergovernmental Panel on Climate Change (IPCC) published a groundbreaking first report on climate change. In which the complex interaction between climate and ocean was barely hinted at.
Projections at that time were still basic and simplistic. Although it was already known that the oceans were absorbing carbon dioxide (CO2) and heat.
Science has come a long way since then. And today we have a detailed view of the key role the oceans play in shaping climate.
Ocean currents and climate change
According to coastal oceanographer Ruth Reef, of Monash University in Melbourne, Australia, water moves through three-dimensional space in a wind-like manner. There are currents that flow from left to right and currents that rise and fall. The horizontal movement of the water is caused by wind resistance. While the vertical movement is determined by changes in the density of the water.
During the freezing process of salty seawater at the poles, the remaining water increases its salt concentration, becoming denser and thus sinking. This phenomenon is fundamental to the functioning of the ocean conveyor belt. Huge quantities of cold, dense water move towards the depths of the polar regions and then head towards the tropics.
Here, the water heats up and warmer currents, such as the Gulf Stream that crosses the North Atlantic from west to east, spread into the Pacific, Indian and Atlantic oceans. During this process, they emit heat, oxygen and nutrients and absorb carbon dioxide. Finally, the currents return to the poles and the cycle begins again.
Antarctica is in trouble: thermohaline circulation is slowing down
Antarctica is the main driving force behind the change in ocean circulation. This, due to the formation of the Antarctic Ocean floor water. However, this driving force is currently facing difficulties.
“We found that a deep part of the circulation is slowing down and the amount of oxygen reaching the ocean depths is decreasing,” says Kathryn Gunn, oceanographer and climatologist at the University of Southampton in the UK.
Gunn and other scientists conducted research on changes in the formation of Antarctic bottom waters. In a study the scientists analysed a specific area of the Antarctic shelf bordering the Ross Sea and the Antarctic-Australian Basin.
The results show that the volume of this cold, saline, oxygen-rich water moving towards the ocean floor decreased by 28% between 1994 and 2017.
An alarm for our planet
The current slowdown is allegedly caused by global climate change, which is causing Antarctic ice to melt rapidly. According to Gunn’s explanations, the water from the melting makes the waters less salty, less dense and consequently less prone to sinking.
This slows down the process of reversing the circulation of ocean currents. The impact of this slowdown on regional climatology, however, is not always fully evident. In Australia, for example, it is plausible that the climate is more affected by phenomena such as El Niño and La Niña. Which are predicted to intensify as a result of climate change, causing droughts, heat waves and more extensive flooding.
Although the problem is complicated, the solution seems to be simple. Namely, stop global warming. However, the period during which we can act to reverse these changes is rapidly shrinking.