"The Escalating Heat of Our Oceans" by June Kim

Climate change causes massive impacts on the marine ecosystem. Global warming causes warmer average temperatures of the oceans, and it has been known that the ocean has absorbed more than 93% of heat released from greenhouse gas emissions since the 1970s. In addition, it disrupts ocean currents, which may cause unpredicted and serious weather events. These are the ways warmer oceans may impact marine life:

Marine life has its own specific water temperatures in which it can thrive. Due to rising temperatures of the oceans, animals will migrate in search of the oceans that suit the specific temperature. One study revealed that more than 100 species living on the coast of the northern U.S. has moved 10 miles northward and 20 feet deeper since 1982. Moreover, lobsters have moved north 119 miles since the 1960s. These findings highlight the dynamic responses of aquatic organisms to changing ocean temperatures.

The rising sea temperature poses a significant threat to the future of aquatic organisms, affecting their mating behaviours and the viability of their egg. For example, experts from the Alfred Wegener Institute and Helmholtz Centre for Polar and Marine research have revealed that fish embryos are at higher risk as they are particularly sensitive to increased water temperatures, as they lack gills that would allow intake of more oxygen. Moreover, fish is less tolerant of heat during mating, due to the additional body mass created by the egg and sperm cells that need to be supplied with oxygen. Due to these impacts, temperature is an important factor that determines the success rate of reproduction; thus increased temperature can be detrimental. The researchers analysed that rising water temperatures may negatively impact reproduction up to 60 percent regardless of the fish species.

Coral bleaching and ocean acidification are also climate-related impacts on oceans. Increased water temperatures may stress the coral polyps, which then lose the algae - or zooxanthellae that they harboured. This is called “coral bleaching”, as without algae, the coral turns completely white. Coral bleaching also deprives the coral polyps of food, which was previously provided by the algae. Although corals can still survive coral bleaching, it puts them in greater stress, and they lose resistance to other threats including disease, being at higher risk of death. Moreover, as the ocean absorbs more than one-third of the excess carbon dioxide in the atmosphere, the ocean is acidified. Ocean acidification slows the rate of corals generating calcium carbonate, which should be produced at a faster rate than the erosion rate of reefs, in order to grow coral skeletons.

Lastly, a shift in ocean currents may be caused. It has been unveiled that global ocean circulation is slowing down. It is because if the water at the poles is not as cold and dense as before, it will not be able to circulate as well. Moreover, when the greenland ice sheet melts, freshwater is poured into the salty ocean, which alters the density of the water again. Differences in water density arose, promoting stratification, which causes boundaries between the water. The boundaries then make the transfer of dissolved compounds, including oxygen and carbon dioxide, much more challenging. Some areas won’t be able to receive oxygen, creating oxygen depleted zones, where organisms cannot thrive. Moreover, carbon dioxide circulation slows down as well, causing surface waters and atmosphere to keep more of them, leading to ocean acidification, which is very harmful to marine ecosystem as demonstrated previously.