Oceans as a resource

The most significant biological resource humans obtain from the ocean is food, primarily fish and shellfish. Global marine catches amount to over 80 million tonnes per year. The vast majority of this harvest, over 95%, comes from the relatively shallow waters over continental shelves, which make up only 10% of the total ocean area. These zones are highly productive because their shallow depth (less than 200m) allows sunlight to penetrate to the seabed, fuelling photosynthesis in phytoplankton. Phytoplankton are the base of the marine food web. Additionally, these coastal waters are enriched with nutrients washed off the land by rivers, further boosting primary productivity. In contrast, the deep, open ocean (the abyss) is often described as a 'biological desert' due to the lack of light and lower nutrient concentrations.

Oceans are a vast storehouse of non-living resources. These can be categorised into dissolved chemicals within the seawater and solid materials on or under the seabed. Seawater itself is about 3.5% dissolved salts, with sodium chloride (common salt) being the most abundant. Salt is commercially extracted by evaporating seawater in large, shallow ponds called salt pans. Magnesium, another important chemical, is also extracted directly from seawater. The ocean floor holds valuable deposits. Sand and gravel are dredged in huge quantities for the construction industry. More valuable minerals are also mined, including diamonds off the coasts of southern Africa, tin and gold in coastal sediments, and manganese nodules from the deep-sea floor. However, mining the seabed, particularly through dredging, can cause significant environmental damage, including destroying habitats and releasing plumes of sediment that can smother organisms and block light.

The ocean's constant motion represents a huge, largely untapped source of renewable energy. The main forms are tidal energy and wave energy. Tidal energy is generated from the predictable rise and fall of sea level caused by the gravitational pull of the Moon and Sun. This can be harnessed using a tidal barrage, a large dam built across an estuary. Water is trapped at high tide and then released through turbines at low tide to generate electricity. Alternatively, underwater turbines, similar to wind turbines, can be placed in areas with strong tidal currents. Wave energy is derived from the power of wind-driven waves on the sea surface. Various devices are used to capture this energy; many float on the surface and use their bobbing or flexing motion to drive a generator. While both are renewable, tidal power is highly predictable, whereas wave power is more variable depending on wind conditions.

Beyond food and minerals, oceans provide other vital services and resources. Firstly, in a world facing water scarcity, the ocean is a potential source of fresh water through desalination. This process removes salt from seawater, typically using methods like reverse osmosis (forcing water through a fine membrane) or distillation (evaporating and then condensing water). While effective, desalination is very energy-intensive and produces a concentrated salt brine that must be disposed of carefully. Secondly, oceans are the backbone of global trade. Shipping is the most cost-effective method for transporting large quantities of bulky goods like oil, grain, and manufactured products over long distances, connecting economies worldwide. Finally, oceans are a major driver of tourism. Coastal areas provide opportunities for recreation (beaches, swimming, surfing) and generate vast revenues through hotels, restaurants, and activities like cruise shipping, sport fishing, and whale watching.