The oceans have four main roles in the context of the environment:
- Carbon storage – Carbon is sequestered very efficiently in mangrove swamps and salt marshes – more efficiently than forests. Any degradation of these ecosystems results in a significant increase in the amount of carbon dioxide released into the atmosphere or the oceans.
- Oxygen generation – Microalgae and macroalgae in the oceans generate much of the oxygen in the atmosphere,
- Food production – The catching of fish, fish farming (aquaculture) and the use of many other aquatic animals and plants plays an important role in food supply to many millions of people.
- Income – The above food-related activities employ millions of people world wide.
The oceans play a central role in the regulation of the Earth’s climate. It has been calculated (5th Assessment Report, IPCC, 2013) that the oceans have absorbed 93% of the additional energy produced by the greenhouse gas effect. This warming has been recorded down to a depth of 1,000 m.
This absorption of extra heat has had a number of effects on the oceans:
- Increased stratification of the oceans (limiting water mixing)
- changes on ocean currents
- increase of zones of water with depletion of oxygen
- changes in growing seasons for animals and plants
- changes in the geographical distribution of species
- changes in the diversity of species
- changes in abundance of species
Warming of the atmosphere has resulted in the melting of glaciers and ice resulting in rising sea levels. This causes coastal erosion and intrusion of saltwater inland.
The production of increasing amounts of carbon dioxide has resulted in an acidification of the oceans affecting many species and habitats. In particular, corals, shellfish and some plankton are limited in their ability to produce their calcareous shells. The effect of changes in the oceans on corals has been particularly well studied.
Next, the land mass ecosystem