Open ocean — mean ocean temperature

The planet’s oceans are warming, and that has many implications. Changes in ocean temperature can have widespread effects on marine species and biodiversity, with direct and indirect impacts on both natural and human activities, from ecosystem services to the fishing industry. Higher ocean surface temperatures can increase water vapour in the atmosphere, which influences weather both at sea and over land. Ocean warming in coastal areas can trigger algal blooms and bacterial outbreaks, which can be dangerous to marine life, human health and industries relying on tourism, fisheries, etc.

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Open ocean — marine heatwave

Heatwaves are not confined to land areas. Marine heatwaves are defined as prolonged periods of unusually high sea surface temperatures. They pose many challenges to ocean ecosystems, whereby marine organisms living in the upper ocean layer with limited abilities to move towards colder waters are at greatest risk. Marine heatwaves also jeopardise coastal communities that depend on fishing, aquaculture and ecotourism for their livelihoods.

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Open ocean — ocean chemistry: dissolved oxygen and ocean acidity

The chemical properties of seawater, such as oxygen content, acidity and salinity, have significant impacts on the health of marine ecosystems. When carbon dioxide from the atmosphere dissolves in seawater, it forms carbonic acid, which makes the seawater more acidic. Furthermore, nutrient run-off from agricultural fertilisers can cause eutrophication of seawater and oxygen starvation, which is made worse by warming seas under climate change. Warming ocean temperatures, oxygen loss and ocean acidification have together been called climate change’s ‘deadly trio’.

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