Tropical fish have been spotted as far north as the coast of Alaska, astonishing scientists studying the effects of climate change on the world’s oceans. While the overall warming of the planet is certainly a factor in this phenomenon, ocean physics is a key player in understanding why some water ecosystems—thousands of miles from any tropical zone—are seeing temperatures rise at an alarming rate.

The most profound aspect of ocean physics affecting water temperature is the concept of ocean currents. These massive flows of water, caused by a combination of factors including the Earth’s rotation and prevailing winds, act like giant conveyor belts, transporting warm water from the equatorial regions to the poles and vice versa.

The Gulf Stream, for instance, is a powerful warm ocean current that originates near the equator and flows north along the coast of Florida. It carries immense amounts of heat from the tropics, keeping water temperatures in the North Atlantic much warmer than they would be otherwise. This is why certain regions in Northern Europe, such as Ireland and Norway, enjoy milder climates compared to areas at similar latitudes.

However, there is a downside to this natural “heating system.” When the Gulf Stream diverts water further north, it can also lead to unusually high water temperatures in the Arctic Circle. In 2020, for example, the Barents Sea—an Arctic ocean just north of Norway—experienced record-breaking temperatures that exceeded the average by almost 10 degrees Celsius. This was due to a combination of increased warm water flow from the Gulf Stream and reduced sea ice, which normally helps to insulate the Arctic.

To complicate matters further, ocean currents also influence salinity levels. As water flows from the equator to the poles, it tends to become saltier due to a process called evaporation. This is why many tropical oceans have lower salinity compared to polar regions. However, when ocean currents are altered, they can disrupt the normal salinity balance.

For instance, when the Gulf Stream carries a large volume of warm water north, it can melt sea ice and lower salinity in the Arctic. This can have consequences for marine life that are adapted to specific salinity ranges, potentially disrupting ecosystems and food chains.

In summary, ocean physics plays a crucial role in altering water temperature and salinity, even in regions far removed from the tropics. As the world grapples with climate change and its effects on ocean ecosystems, understanding these physical processes is essential for predicting and possibly mitigating future impacts on marine life.