oceans top 18

Ocean coverage and volume

Oceans cover ~75% of Earth’s surface and contain ~97% of the planet’s water, forming a distinctive global feature.\n\n

Ocean basin relief

Key features include continental shelf, slope, abyssal plain, ocean ridges/rifts, trenches, and guyots; the Mariana Trench reaches ~11,000 m depth.\n\n

Horizontal and vertical variations

Salinity and temperature vary with depth and latitude: surface water ranges from ~-2°C (poles) to 35°C (equator), with deeper layers colder and more saline.\n\n

Ocean circulation

Global currents, such as the North Atlantic Thermohaline Circulation, transport heat and nutrients; deep currents move at ~1–3 km/day, influencing climate and ecosystems.\n\n

Light, nutrients, and biodiversity

Ocean ecosystems are shaped by light penetration, temperature, and nutrient supply; upwelling zones (e.g. Peru–Chile) boost productivity supporting major fisheries.\n\n

Ocean energy and mineral resources

Offshore oil (~30% of global oil) and gas (~50% of global gas), plus tidal/wave energy (<1% global electricity), are exploited with contestation over sustainability.\n\n

Renewable biological resources

Krill are managed under CCAMLR with a Total Allowable Catch of 620,000 tonnes/year (~11% of sustainable yield); biomass has declined ~80% since the 1970s.\n\n

Ocean as global commons

EEZs cover ~36% of oceans but hold ~90% of marine resources, while high seas cover ~64%; management is challenging due to weak enforcement.\n\n

Pollution sources

Oceans absorb ~30% of anthropogenic CO₂ and ~90% of excess heat, causing acidification, warming, and marine heatwaves.\n\n

Plastic pollution

~11 million tonnes of plastic enter oceans annually; the Great Pacific Garbage Patch covers ~1.6 million km², with 75–86% ghost fishing gear.\n\n

Oil spill impacts

Deepwater Horizon (2010) spilled 4.9 million barrels over 87 days, killing ~800,000 birds, stranding 1,400 marine mammals, and costing $20 billion in compensation.\n\n

Eutrophication and dead zones

Nutrient runoff causes algal blooms; dead zones occur in Gulf of Mexico, Baltic Sea, Arabian Sea, reducing oxygen as warmer water holds less dissolved O₂.\n\n

Economic and human dependence

Oceans provide ~$7 trillion annually in ecosystem services and trade, transport ~90% of global trade, and support ~50% of the global population within 100 km of coasts.\n\n

Governance frameworks

UNCLOS (1982) defines EEZs up to 200 nautical miles; MARPOL covers >99% of shipping, reducing oil spills ~90%, but only ~8% of oceans are designated MPAs with <3% strongly protected.\n\n

Sea-level rise and human risk

Global sea level rose ~10–25 cm in the last century, projected to rise ~50 cm by 2100, threatening ~680 million people in low-lying areas and ~2 billion in coastal megacities.\n\n