If geography is the science of space, then few spaces are more important to humanity than the world-ocean. The world-ocean —the term preferred by geographers for the “seven seas,” which, in fact, constitute one unified geophysical system—covers 71% of World's surface and contains 97% of the planet's water. More than 20% of the world's petroleum derived from offshore sources and 95% of world trade by weight, or two thirds by value, carried by ship. Eighty percent of the world's fish catch comes from the ocean, supporting the livelihoods of 140 million people.
Economists have calculated that the world-ocean provides services to humanity valued at $21 trillion per year, as opposed to only $12 trillion per year provided by land. This entry reviews some of the ways in which geographers have approached the world-ocean, a space that is crucial to humanity but is all too often taken for granted as insulated from the influences of society (Lambert, 479).
The oceans of the world divided into four main water bodies: Atlantic, Pacific, Indian, and Arctic. There are no distinct geographic divisions defining where one ocean begins, and another ends.
The vast size of the oceans has hindered quantification of oceanic biogeochemical characteristics and recent environmental changes. The oceans redistribute large amounts of heat around the globe, and perturbations to ocean currents or immense ocean gyres could change regional climate patterns.
The Younger Dryas was a cooling of the Northern Hemisphere approximately 12,000 years ago, at the end of the Pleistocene. It marked by a slowdown of the global thermohaline ocean circulation (also known as the meridional overturning circulation), and a similar event expected under most climate change scenarios, as the Greenland ice cap contributes massive volumes of freshwater to the North Atlantic and disrupt this ocean current. Recent studies indicate that the sub-polar North Atlantic gyre is, in fact slowing and cooling, but future trends are uncertain.
El Niño/Southern Oscillation is a quasi-periodic reversal of equatorial winds along the equator in the Pacific. This cyclic instability disrupts precipitation patterns and fisheries across much of the world and recent decades have seen disruptions in the periodicity of the normal 3- to 5-year pattern (Steinberg, 366). Sea-level rise has been occurring for several decades as ice caps and glaciers melt globally. Sea-level rise is increasing coastal erosion and leads to greater storm impacts inland. Ecosystem and biodiversity impacts driven by fishery depletion from by-catch losses and pollution, including sewage disposal, floating trash, and oil spills.
Recent uses of high-power sonar systems for military purposes expected to have catastrophic impacts on ocean mammals. Ocean waters have become more acidic by more than 0.1 pH units, and increasing carbon dioxide atmospheric partial pressure will further acidify seawater. This leads to a reduction in aragonite saturation in seawater and weakens carbonate-secreting organisms' shell structures, including coral reefs. Ocean hypoxia is occurring in deltas and estuaries of the world, as agricultural pollutants and other chemicals reduce dissolved oxygen partial pressures in seawater to near ...