2019 was the warmest year on record for the global ocean, continuing a trend that has scientists worried about the health of marine ecosystems worldwide.
According to a recent study published in the journal Advances in Atmospheric Science, the past five years have been the top five warmest in the ocean since 1955.
The findings indicate that unless greenhouse gas emissions are reduced globally, ocean temperatures will continue to rise, with significant consequences for marine life.
Brian Hunt, a biological oceanographer and professor at the University of British Columbia, says short-term warming events may have a greater impact on the ocean and its inhabitants than the long-term warming that is occurring gradually across the globe — but the severity and frequency of these short-term events are connected to a long-term increase in ocean and atmospheric temperatures.
For example, in 2013, an area of warmer-than-normal water — which scientists called “The Blob” — developed in the northeastern Pacific and lingered until 2016. During that marine heatwave, starfish were affected by an outbreak of sea star wasting disease and plankton decreased in size, which had cascading effects up the food chain.
“Long-term trends are changing conditions gradually. In a given location they can push the conditions towards thresholds for an organism. When you have a short-term event on top of that, it can be more dramatic because the animal might already be closer to its threshold,” says Hunt.
Not just a surface issue
Rising temperatures in the deepest waters of the ocean are also of increasing concern for scientists studying the effects of climate change in Canada’s oceans. When heat is trapped in deep waters it is harder to disperse because there is no contact with the atmosphere.
“Deep waters tend to be much more stable. They are much less variable. When you see the warming in the deep waters, you can be more confident that yes, this is actually a climate signal,” says Lisa Miller, a climate geochemist who is studying and monitoring Canada’s oceans for Fisheries and Oceans Canada.
Normally, nutrients are cycled from the surface of the ocean to the deep waters and back. When there is a significant difference in temperature between the two, it hinders the transportation of nutrients and oxygen within the water column.
“The warmer, thinner layers cannot absorb as much oxygen and the reduced mixing with deeper waters prevents that oxygen from getting down below the surface to support all of the organisms in the subsurface ocean,” says Miller.
An increase in temperature in Canada’s oceans is not the only threat to marine species. According to Kumiko Azetsu-Scott, a chemical oceanographer with Fisheries and Oceans Canada, the world’s oceans are expected to increase in acidity by 170 per cent by the end of the century.
“The ocean provides a great service to the planet by taking up excess carbon, but it is paying the price for it right now,” she says.
As more carbon dioxide from the atmosphere is dissolved into the ocean, it becomes more acidic. A decreased pH in the ocean can make it more difficult for organisms that grow shells to build and maintain those shells.
“The pH of the ocean determines how easily calcium is available to animals in the ocean and calcium is important for species that grow shells, like lobster, mussels, clams, and many small phytoplankton,” says Sean Brilliant, manager of marine programs at the Canadian Wildlife Federation. “If the pH regime changes so that calcium becomes less available, it is possible that this may become a limiting factor for productivity in some areas.”
The Arctic Ocean was the first to see the effects of ocean acidification because cold water can hold more gases than warm water can. The melting of sea ice has allowed for increased exposure to and absorption of carbon dioxide, which in turn has made the Arctic Ocean more acidic.
The future for marine life
As oceanic environments rapidly change, scientists are now asking whether organisms will be able to adapt.
The west coast of North America could see another “Blob” within the next year, says Hunt, and while some organisms will be able to move away from the warming conditions, others cannot. And any form of movement will disrupt ecosystems and food webs.
The federal government had set a target to protect 10 per cent of Canada’s marine and coastal areas by this year, but Brilliant says any effort to establish sanctuaries for wildlife must take into account how they might move as they adapt to climate change.
“It’s about preparing to live in a world with an altered climate and acknowledging that animals and plants don’t stay in the same place. We need to make sure we give them more space. If we are establishing marine refuges in the ocean, we need to make sure that the refuge is large enough to accommodate changes in distribution of the animals that we are trying to protect, and the connection between these areas needs to be well understood so that we can prepare for the future.”
Understanding the science of climate change is just one step that must be taken to prevent a worst-case scenario of rising temperatures and ocean acidity, adds Brilliant. We must also recognize our responsibility to protect our oceans.
“We are quickly realizing that we need to take on the role of stewards and use the knowledge we have about how ecosystems are connected to make sure we plan for this. We cannot allow ourselves to be surprised by these changes anymore.”