Oceans and Seas Research Paper

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Oceans and seas comprise 98 percent of the biosphere and cover about 70 percent of the Earth’s surface. Water is circulated between the oceans and seas, the atmosphere, and the land by evaporation and precipitation, thus transporting chemicals and heat, determining the Earth’s climate, and fertilizing and eroding the land. Humans depend on ocean resources, harvesting marine life, for instance, and drilling the ocean beds for oil.

The oceans of the Earth consist of four confluent (flowing together) bodies of saltwater that are contained in enormous basins on the Earth’s surface. Seas are lesser bodies of saltwater. Oceans and seas cover 361 million square kilometers (70.8 percent of the Earth’s surface) and 98 percent of the volume of the biosphere (the part of the world in which life can exist). Saltwater comprises about 97.2 percent of the water on the planet, the remainder being freshwater. By evaporation and precipitation water is circulated between the oceans and seas, the atmosphere, and the land. The hydrological cycle (the sequence of conditions through which water passes from vapor in the atmosphere through precipitation upon land or water surfaces and ultimately back into the atmosphere as a result of evaporation and transpiration) transports and stores chemicals and heat, determines the Earth’s climate, and fertilizes and erodes the land. The average salinity of the oceans and seas is 3.5 percent, deviations being determined by evaporation and inflow of freshwater. Ocean surface temperatures around the equator may be 30°C or more, decreasing toward the poles, where seawater freezes at –2°C. Below-surface temperature is fairly constant, decreasing to around 0°C in the deep ocean.

The largest ocean is the Pacific, which has a surface area of 166 million square kilometers, almost the size of the three other oceans together: the Atlantic (84 million square kilometers), the Indian (73 million square kilometers), and the Arctic (12 million square kilometers). The Antarctic, or Southern, Ocean is sometimes counted as the fifth ocean, consisting of the waters of the southern parts of the Pacific, Indian, and Atlantic. Sections of the oceans may be described as enclosed and marginal seas. Enclosed seas—such as the Mediterranean Sea, Hudson Bay, the White Sea, the Baltic, the Red Sea, and the Mexican Gulf—cut into continental landmasses. Marginal seas—such as the Caribbean and Bering Seas, the Sea of Okhotsk, the East China Sea, the Sea of Japan, and the North Sea—are separated from the oceans by archipelagos.

The depth of the oceans increases to about 200 meters on the continental shelves, increasing further to 3,000–4,000 meters on the ocean basin floor and to 6,000–11,000 meters in the deepest areas. The ocean bed is covered by sediments of dead marine organisms, eroded soil from the continents, and red clay.

The waters of the oceans are circulated by changing winds, air pressures, and tides. The gulf current brings warm water to the North Atlantic and thus makes it possible to sustain human life at more northerly degrees in Europe than anywhere else on the globe. The upwelling areas on the margins of the Pacific and Atlantic oceans off the coasts of Chile and Peru, California, and Namibia in Africa bring cold, nutrient-rich waters to the surface of the sea, and the combination of sunlight and nutrient richness makes the relatively narrow continental shelves rich in marine life. But El Nino (an irregularly occurring flow of unusually warm surface water along the western coast of South America) may reverse ocean currents in the Pacific and cause abnormal climate effects both on land and sea.

Life began in the oceans, but science has incomplete knowledge of marine life-forms. About fifteen thousand species of marine fish are known, but it is estimated that five thousand species remain to be identified. The estimate of 200,000 ocean floor species of the North Atlantic alone may be low by a factor of three or four. Whereas the open oceans are blue deserts due to the lack of nutrients, the continental shelves are home to abundant marine life, and tropical coral reefs are habitats of large biodiversity (biological diversity as indicated by numbers of species of animals and plants).

Marine Resources

Humans utilize the oceans for transportation and trade, benefit from harvesting marine life, and drill the ocean bottoms for oil, thus creating the potential for exploitation and pollution.

Oceanic transportation is the cheapest and most important way to move goods between the continents, but it imposes severe environmental stress on marine habitats and biodiversity. Prior to the fifteenth century the oceans presented a formidable obstacle to contact between continents. Foraging (Paleolithic) era (2 million–10,000 BCE) migrants did spread from Africa and Eurasia to Australia and the Americas by crossing the straits of Torres and Bering; the Polynesian migrations into the Pacific islands around 2000 BCE and the Viking migration across the North Atlantic also testify to early maritime skills. However, the first contact between a major civilization and another continent was aborted in 1435 when the Chinese emperor decided to discontinue the explorations of the Chinese fleet to Africa across the Indian Ocean. The subsequent voyages of Columbus across the Atlantic from Spain to the Caribbean Sea, however, opened the way for a sustained exchange—causing great environmental impact—with the New World. With the development of the three-masted sailing vessel and nautical instruments, global seafaring allowed an exchange of terrestrial plants and animals that had substantial consequences for the recipient countries. Marine habitat changes followed as ports and bunker areas for loading coal were extended along shorelines and estuaries and as mud-dredgers changed tidal currents and coastal erosion. In the twentieth century tanker ships impacted marine ecosystems substantially when they discharged ballast water transported over thousands of kilometers. Ballast water is one of the most serious threats to marine biodiversity and has caused irreparable changes to ecosystems. Introduced species, which have no natural enemies in new environments, can multiply and eradicate original life-forms.

Humans have harvested inshore marine environments since earliest historical times. Whales, seals, fish, crustaceans, and algae have been fished for human consumption, and seaweeds, salt, sponges, corals, and pearls have been brought to consumers for diverse uses. Today important medicines, from anticoagulants to muscle relaxants, are derived from marine snails.

Beginning in the sixteenth century, thanks to the shipping revolution, whaling and fishing operations were taken to distant islands and continents. As marine life in these distant waters was depleted, the operations became oceanic, first in the Northern Hemisphere and later in the Southern Hemisphere. These operations extinguished some life-forms, such as the Stellar’s sea cow in the Bering Sea, the gray whale in the European and later the American Atlantic, and the Caribbean monk seal. The early human impacts on pristine ecosystems are believed to have been important not only to a few signal species but also to the whole ecosystem, which may have experienced regime shifts when top predators that controlled ecosystem dynamics were fished out. Today most of the commercially important fish species are exploited to the full or beyond sustainable levels. Because of such heavy fishing pressure, many of the most valuable fish stocks of the world are in decline, and some have become locally extinct. The most dramatic case is the Newfoundland cod fishery, which collapsed in 1991, causing not only enormous and possibly irreparable harm to the ecosystem but also the disappearance of the very means of existence for many people in Atlantic Canada.

Commercial exploitation of minerals in the ocean bed is only beginning and is expected to increase dramatically in the twenty-first century. The ocean bed contains energy in the form of oil and natural gas, and minerals such as sodium chloride (salt), manganese, titanium, phosphate, and gold are found in the oceans. People also have begun to utilize tidal power from the oceans. The development of industrialized societies has increased the discharge of sewage and other waste into the oceans and also has created the phenomenon of oil spills.

About two-thirds of the world’s population live within 60 kilometers of a coast, and almost one-half of the world’s cities with more than 1 million people are located near estuaries. This settlement pattern is a result of people choosing the oceans instead of agriculture as a source of food and employment; the oceans also have provided access to communication, transportation, and trade. However, people have had a prejudice against coastal settlement in some historical periods. The most marked instance of this prejudice occurred in many Neolithic (8000–5500 BCE) cultures with the introduction of agriculture, which increased the incentive to settle virgin inland territories. The nineteenth-century frontier movement of North America was also decidedly terrestrial, although migrants had to cross the Atlantic to pursue opportunities. In contrast, other colonizing experiences, such as the ancient Phoenician and Greek citystates, were decidedly maritime.

The French historian Fernand Braudel (1949) was the first to attempt a history of an enclosed sea—in this case, the Mediterranean—as a natural environment and a highroad for communication and cultural exchange. He argued that the common environmental conditions prevailing on the coasts of the Mediterranean provided the basis for a common culture. He showed how life in the mountains, plains, and coastal lowlands related with the sea across European and Arabic civilizations, and he stressed that the seaways were a key to the growth of the European economy. Braudel perceived of Europe as three regions: the Mediterranean, the Continent, and the Second Mediterranean of Europe; that is, the North Sea and the Baltic, or collectively the Northern Seas. Many other historians have since recognized that if the Mediterranean shores had a common culture, the same would hold true for other seas, with differences due to natural circumstances (such as enclosed or marginal character of the sea and accessibility of its shores) and historical experiences. The problem with the arguments of such historians is that they tend to list those aspects that the shores of a sea have in common but do not compare contacts inside and outside of the regional system.

Other approaches to the question of the role of oceans in human history have stressed the problems of overcoming distance. This is the dominant theme, of course, in the study of the Age of Exploration (c. 1491–1750), but it also resonates in the study of the more recent history of U.S. and European relations and most forcefully in the study of the history of Australia, which until the age of global airlines lived under the “tyranny of distance”—the fact that any visit abroad required weeks if not months of sea travel.

In the age before modern transport systems, sea transport was generally cheaper than land transport but not faster. Ship movements had many natural and unpredictable constraints. Delays of weeks occurred frequently because of unfavorable winds, and although some skippers would travel day and night because of a good knowledge of local waters, most dared sail only in daytime. Calculations of actual distances traveled by ships indicate that in spite of good winds sometimes bringing a ship’s speed to 10 knots per hour (18 kilometers per hour), the distance covered during full trips, including the time spent waiting at anchor, seldom averaged more than 1 or 2 nautical miles (1.85–3.7 kilometers) per hour spent at sea. The distance covered per day thus works out to 45–90 kilometers. This calculation corresponds with actual travel distances on land. Whereas one cartload normally contained only twelve to eighteen barrels of grain or fish, even a small shipload might contain many times more. A typical ship of two hundred tonnes required a maximum crew of only ten men. The person-to-ton ratio would thus be 1:10 for the ship as against 1:1 for the cart, whereas distance traveled per day would be the same. Thus coastal urban markets received supplies by sea at a rate competitive with supplies from inland. A recent study of medieval England showed a ratio 1:4:8 for transport costs by sea, river, and road. Because the efficiency of land transport did not develop to the same pace as productivity increased in other trades such as agriculture, land transport costs grew relative to other costs until the eighteenth century.

The sea did not necessarily facilitate cultural impulses, such as aesthetic, dietary, or religious preferences, in the same way. The transportation of information and cultural impulses was not related to bulk freight rates but rather relied as much on individual travel patterns, most often by foot or horseback. Although enclosed and marginal seas may often have contained a well-developed trade and transport infrastructure, cultural relations do not necessarily mirror this and indeed may show quite different patterns of communication. Nevertheless, during the age of sail, roughly from 1500 to 1850, maritime regions played a decisive role in many parts of the world. Coastal stretches of enclosed or marginal seas had an unusual concentration of maritime capital and labor that made possible the development of a distinctively maritime culture. This concentration was often based on the availability of timber for shipbuilding, although lack of forests did not preclude some regions rising to maritime preeminence.

The industrial transport revolution of the nineteenth century greatly enhanced long-distance and even global travel, but it lessened the importance of regional transport economics. Improved roads, railways, and steam shipping created a world market for many more goods than before, and regional markets gave way to the global market. Most small maritime communities were not able to raise the capital needed to participate in the global transport market, and as a result the coastal landscape changed from a string of human settlements to a few port towns with a concentration of maritime capital. In the industrial age, therefore, the age of regional seascapes came to an end.

Port towns are the nodes of the maritime transport system. The first port towns were well developed in the Mediterranean three thousand years ago. A port town may have its own home fleet, the crucial characteristic being that the town is a hub of inland and seaborne trade. Port towns tend therefore to utilize natural assets such as ease of multimodal transportation (land, river, and sea transport), access to a productive hinterland and a market, and strategic advantages such as control of waterways. Port towns provide access to the economic arteries of a country and therefore have historically been keenly regulated both for fiscal and military purposes. Occasionally they have gained full or partial sovereignty, as did the Italian city-states and the towns of the Hanseatic League, or have dominated a territorial state, such as the Netherlands in the sixteenth to eighteenth centuries, but most often they have been controlled by larger territorial powers. With the increased demands of shipping in the nineteenth century came the need for a larger workforce, and port towns became densely populated with laborers. The towns themselves sprawled along wharves and quays to become unwieldy entities, congested and heavily polluted. As a result of the spread of coal-fired steamer traffic in the second half of the nineteenth century, however, adhering to strict time schedules became possible and of utmost importance. Thus new infrastructures of bunker ports and dedicated quays sprang up along the coasts to facilitate the steamers. Wind-powered ships continued to defeat the steam ships as long as a line of bunker ports did not dot the margins of the seas, but eventually the steam ships took possession of more and more sea routes so that by the early twentieth century the slow windjammers to Australia were the last to give in.

By that time diesel engines were being introduced, and by the 1950s coal was all but given up. At that point, passenger ships lost their edge in the oceanic transportation of people to the airlines, but a new era for the shipping of goods more than compensated for the loss to ship owners. In the first half of the twentieth century ships were designed to provide optimum cargo facilities and quicker turn-around times in ports. The Argentine meat industry and the Canary Island banana trade demanded refrigerated ships, and the oil industry gave rise to tanker ships. By the 1960s a design revolution took place, introducing the all-purpose shipping container, a metal box that could be refrigerated or otherwise modified and that conformed to standard measures and therefore allowed for convenient storage on board. The container ship became the vehicle for the globalization of trade, which severed the links between origin of resource, modification and packaging, and consumption.

To achieve optimum handling the once-prolific system of ocean ports has been minimized to a system of a few world ports that are the nodes of a few big container lines. Servicing the system are a number of feeder lines from lesser ports and a prolific number of trucking services that ensure that the individual container is brought to its final destination.

The environmental impact of the globalized container system is enormous. Although the system undoubtedly brings rationalization of the economic system, it is dependent on the availability of abundant and cheap energy, which will marginalize, for example, the costs of moving east Asian tiger prawns to Morocco to be peeled by cheap labor before they are moved to Germany to be packaged before they are eventually consumed in, for example, a restaurant in Paris.

Sea Law and Sea Powers

The oceans and seas have long been governed by law. Hugo Grotius, a Dutch lawyer, historian, and theologian laid down the first principles for an international law of the seas his 1609 treatise Mare Liberum (The Free Sea). He observed that the sea is an inexhaustible, common property and that all should have open access to it. These principles were adhered to in theory by all major European naval states and eventually were introduced as the guiding principles for access to all oceans and seas. Most states claimed dominion over territorial or coastal waters, but commercial ships were allowed free passage. The most important exception to this principle was the Danish Sound, providing access between the North Sea and the Baltic. The Danish government in 1857 lifted its toll on the sound and the right of inspection only after international treaty and compensation. The shooting range of a cannon originally defined the width of territorial waters, but during the nineteenth century a 3-nautical-mile (5.5 kilometers) limit was increasingly accepted and laid down in international treaties. After World War II, U.S. President Harry Truman claimed wider rights to economic interests on the North American continental shelf against Japan, and Chile and Peru claimed a 200-nautical-mile (370 kilometers) exclusive fishing zone off the coasts against U.S. tuna fishers. Iceland followed soon after with claims to exclude British fishers from Icelandic waters. Oil and fisheries were the main economic motives for these claims. In 1958 the United Nations called the first International Conference on the Law of the Sea to establish a new consensus on sea law. The conference extended territorial limits to 12 nautical miles (22 kilometers) but failed to settle the issue. A second conference in 1960 made little progress. During the 1960s and 1970s positions changed dramatically. It became much more evident that the supplies of fish stocks were limited and that depletion was becoming more prevalent. Attempts to manage resources through international bodies were proving to be largely ineffective. Many coastal states, both developed and developing, felt increasingly threatened by the large fleets of distant-water states off their coasts. Simultaneously, the issue of control over the mineral resources in the deep ocean beds raised the demands of developing states for a more equitable distribution of ocean wealth. The third international conference, which lasted from 1974 to 1982, resulted in a convention that is internationally recognized. The main innovation was the declaration of the right of coastal states to a 200-nautical mile “extended economic zone” (EEZ), which may be claimed by a coastal state for all mineral and living resources. The convention was signed by 157 states, while the United States, United Kingdom, and Germany took exception to the stipulations on seabed mineral resources. The EEZs represent the largest redistribution of territorial jurisdiction sine nineteenth century colonialism.

The choice of 200 nautical miles as a limit for jurisdiction has no relevance to ecosystems or indeed to the distribution of mineral wealth but is simply a result of international negotiations. Whatever the imperfections of the convention, it has, however, provided coastal states with the authority to manage the resources within their zone. The short history of EEZs shows that they may be implemented to promote conservation interests in addition to the national economic interests for which they were designed.

Management and Protection

Whereas the law of the sea provides only a broad framework for international regulation of matters relating to oceans and seas, nation-states have developed intricate policies and institutions that impact the oceans. Two policies for the marine environment have been developed in recent years: integrated coastal zone management (ICZM) and marine protected areas (MPA). The specific policies that deal with issues such as watersheds and coastal development to seabed utilization by their very nature fail to take issue with the complete set of challenges that confronts people when they seek to manage, preserve, and develop the marine environment. This is the justification for the development of integrated coastal zone management. ICZM has developed as a cross-cutting policy for coastal and inshore management concerns since the 1980s, but it is implemented only to a limited degree in most countries. Marine protected areas have been designated throughout the world as areas where human access is restricted in order to conserve marine habitats. Coral reefs, fragile spawning areas, and hot spots of marine biodiversity have often been selected, but by 2000 only about 1 percent of the oceans were protected even by limited restrictions. The oceans and seas are still subject to open access and unrestricted human practices in most regions of the world, and the underwater world remains the last frontier, still to a large degree unexplored by humans.


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