In 2003, a marine heat wave impacted the North Atlantic, and its effects are still felt today. Marine biologists from Germany and Norway reviewed over 100 studies and found that since then, marine heat waves (MHWs) have caused significant changes to ocean ecosystems from tiny organisms to large fish and whales.
Karl Michael Werner, a marine ecologist, notes that the events of 2003 marked the start of an unusual heating trend across the North Atlantic. After this year, numerous heat waves followed, showing ongoing changes in marine life.
During the 2003 heat wave, warm subtropical waters flooded the Norwegian Sea. The usual cold Arctic waters were weaker, causing less sea ice and drastically raising surface temperatures. For instance, the temperatures in the Norwegian Sea moved deeper into the water, hitting depths of 700 meters (about 2,300 feet).
Cold-water species struggled while those preferring warmer waters thrived. This shift affected the entire ecosystem. Species adapted to cold began to disappear, making way for warmer-water species. For example, since 2015, baleen whales returned to areas that had been blocked by ice for years, while orca sightings increased, indicating a significant ecological shift.
Conversely, species that depend on cold waters, like narwhals and hooded seals, have seen declines in their populations. These changes highlight concerns about the sustainability of marine life as food sources disappear.
One interesting detail is how bottom feeders, such as brittle stars and certain worms, flourished after feeding on excess phytoplankton blooms, which surged following the heat wave. Atlantic cod, an opportunistic predator, benefitted from this abundance of food.
The 2003 heat wave led to the decline of sandeel, a crucial prey fish for larger predators like haddock. As populations of sandeel and capelin drop, larger fish like cod are now moving north, seeking cooler waters. If temperatures continue to rise, their search for food may have limits.
This pattern resonates with a broader issue. Experts warn that marine heat waves are tied to human activity, particularly greenhouse gas emissions from burning fossil fuels. Most of the excess heat from these gases is absorbed by the oceans. As ocean temperatures rise, the warming contributes further to climate change.
A recent study emphasizes that the frequency and intensity of these heat waves may trigger unanticipated ecological changes. With warming temperatures, marine ecosystems struggle to adapt. The effects are not just local but have a wide-reaching impact, affecting the balance of life in the ocean.
Researchers urge for more understanding of the factors influencing these heat waves, as this knowledge is key to predicting future changes in marine life.
For more details, you can check the full study in Science Advances.
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