2.2: Exploration and Mapping

Through most of human history, the oceans have been studied primarily to facilitate seaborne travel and transport. Hence, early studies were directed primarily toward exploring and mapping the oceans.

Prehistory

The oceans provide a food source and an important mode of transportation, but we do not know when humans first began to use the oceans for these purposes. However, humankind has used these resources for tens of thousands of years and they remain the most valuable uses of the oceans today. The bones of marine fishes discarded by Stone Age people have been found in caves in South Africa that date back to between 100,000 and 70,000 years ago. In East Timor, near Indonesia, fish hooks that date back more than 38,000 years and bones of fishes that date back as far as 42,000 years ago have been found in a limestone cave. The fish bones came from species that live both in coastal waters and the deep ocean far from shore, providing evidence that humans were using boats or rafts to fish in the open ocean. Also, humans are thought to have arrived on the island of Australia about 50,000 years ago. The first boats were probably built even earlier, perhaps for fishing on lakes or in the shallow coastal ocean, then later for transportation and colonization. The first boats or rafts may even have been made and used by Homo erectus, our immediate predecessor in the evolutionary tree. Archaeological evidence shows that some Homo erectus lived on the island of Flores, Indonesia, at least 750,000 years ago. To reach Flores, Homo erectus must have crossed a wide, deep water strait that acted as a barrier to the migration of most other species.

Early human boats were made of wood, reeds, animal skins, or tree bark. These materials do not generally survive the centuries for archaeologists to study. The oldest boat found by archaeologists is thought to be a dugout canoe found in the Netherlands that was made between 10,200 and 9600 years ago.

Ocean Exploration in Early Civilizations

Recorded history tells us that early development of ocean transportation and trade centered in the Mediterranean Sea, although the Polynesian and Micronesian cultures in the Pacific Ocean may have pursued these activities during the same period.

The Mediterranean

The Minoan civilization, which prospered on the island of Crete in the Aegean Sea from about 3000 BCE, is considered the first recorded civilization to have used boats extensively for transport, trade, defense, and conquest. The Minoans’ influence extended throughout the many islands of the Aegean, and oral and written history records that a Minoan navy fought and controlled pirates in the region. Although seafaring capability continued to develop in the Mediterranean in both the ancient Greek and Egyptian civilizations, the Phoenicians, who inhabited areas that are now parts of Israel, Lebanon, and Syria, were the greatest of all the early Mediterranean seafarers. From about 1100 to 850 BCE, the Phoenicians were a great sea power, voyaging throughout the Mediterranean to Spain, Italy, North Africa, and even the British Isles, where they traded for tin. The Phoenicians also claimed to have made a 3-year voyage around the entire continent of Africa, but that claim has not been confirmed.

Much of the information needed to navigate from one port to another was a closely held secret of the navigator’s craft. However, maps that showed the shapes and sizes of coastlines and seas were made several thousand years ago. In about 450 BCE, the Greek historian Herodotus drew a map that is a surprisingly recognizable map of the Mediterranean and Red Sea region (Fig. 2-2). The most famous of ancient mapmakers was the Greek geographer Ptolemy, who lived around 150 CE. Ptolemy’s maps, although little known until the end of the Dark Ages, about 1400 CE, were the basis of most maps until the 1500s.

Figure 2-2 Map of the known world drawn by Herodotus in approximately 450 BCE. The oceans surrounding the known landmasses were thought to extend to the edge of the world. Compare this map carefully to a current Mercator projection, and you will see that the map drawn by Herodotus somewhat distorts longitude but quite accurately reproduces latitude. (CC-BY-SA 4.0; Adapted from Bibi Saint-Pol, 2006)

Ptolemy’s maps are remarkably detailed and accurate in their reproduction of north-to-south positions (latitude). However, they are distorted by substantial errors in east-to-west positions (longitude). For example, Ptolemy shows the east-to-west length of the Mediterranean to be about 50% too long in relation to its north-to-south dimension. These errors are a consequence of the mapmaker’s inability to measure time accurately. Without precise and accurate time measurements, it was not possible to establish longitude correctly, as is discussed in Chapter 1. The east–west distortion of maps was not corrected until about the 1760s, when the first practical chronometers were developed that could keep accurate time on a ship.

In the 2000 years following the Phoenician era, ocean exploration slowed, and much of what may have been learned was lost in the turmoil of the Dark Ages. We know that philosophers did make several significant observations, especially during the early part of this period. In the sixth century BCE, Pythagoras declared the Earth to be spherical. In the fourth century BCE, Aristotle concluded that total rainfall over the Earth’s surface must be equal to total evaporation because the oceans did not fill up or dry out. In the same century, another Greek, Pytheas, sailed out of the Mediterranean to Britain, Norway, Germany, and Iceland. He developed a simple method of determining latitude by measuring the angle between the horizon and the North Star—a method still used today. Pytheas also proposed the concept that tides were caused by the moon.

In the third century BCE, Eratosthenes, a Greek studying at the library in Alexandria, Egypt, calculated the circumference of the Earth along a circle through the North and South Poles. His value of 40,000 km was very close to the 40,032 km that has been determined by extremely precise and sophisticated modern methods. Approximately 200 years later, Poseidonius incorrectly recalculated the circumference of the Earth to be about 29,000 km. Ptolemy accepted Poseidonius’s incorrect value for his maps, and the error was not corrected for centuries. In fact, this error led Christopher Columbus to believe he had reached Asia when he arrived in the Americas in 1492.

Micronesia and Polynesia

About 4500 years ago, at about the same time that ocean voyaging and trade were beginning to expand in the Mediterranean, the large islands of the far western Pacific and Micronesia were colonized. Humans traveled from mainland Asia to these islands, likely through Taiwan. The expansion may have been made possible by the development of the outrigger canoe (Fig. 2-3). After an apparent pause of about 1000 years, Polynesians colonized the islands of the western and central tropical Pacific, reaching Hawaii and Easter Island about 900 AD. Unlike Mediterranean sailors, who could follow the coastline, the Polynesians had to navigate across broad expanses of open ocean to colonize the Pacific islands. The Polynesians crossed the ocean in double-hulled sailing canoes made of wood and reeds. A larger hull provided living space for up to 80 sailors plus plants and animals; a smaller hull or outrigger stabilized the vessel. The double-hulled design is still used in much of Polynesia (Fig. 2-3).

Figure 2-3 A typical Polynesian outrigger canoe. This design has been used for centuries throughout much of Polynesia and Micronesia. This canoe was photographed in Papua New Guinea.  (©AMS; Segar, D., and E. Stamman Segar, 1997)

The Polynesians were arguably the greatest navigators in history. They successfully navigated across the open ocean using only their memorized knowledge of the stars, winds, wave patterns, clouds, and seabirds. This knowledge was passed down through generations of the families of navigators, who were justifiably venerated in Polynesian culture. Both the Polynesians and Micronesians created maps from wood sticks or rattan, but most Polynesian navigators did not use or need such maps. Some of the ancient Polynesian navigational knowledge persists today in the oral histories and experiences of just a few remaining descendants of the early navigators. Efforts have been made recently to sustain and preserve this knowledge through a series of ocean voyages across the Pacific in reconstructed replicas of ancient Polynesian boats, such as the Hokule‘a (Fig. 2-4).

Figure 2-4 The Hokule‘a. This vessel is a reproduction of the double-hulled voyaging canoes that the Polynesians used to explore and colonize the Pacific. (CC-BY 2.0; HongKongHuey, 2009 via Flickr)

The recent journeys have proved that the ancient Polynesian navigation techniques were, and still are, remarkably accurate and reliable. There is great interest in discovering and documenting all the observational clues the navigators used. Much of the Polynesian art of navigation is mysticized and undocumented, but the navigators must have known principles of wave shapes and directions, cloud formations, and other ocean phenomena that even now are not fully understood by modern scientists. For example, Polynesian navigators can deduce the location of an island hundreds of miles away by observing wave patterns created in the wake of the island. Modern science has been able to document such large-scale wave patterns around islands only since satellite observations of the sea surface became possible.

The Dark Ages and the New Era of Discovery

During the Dark Ages, when ignorance and anarchy engulfed Europe, ocean exploration by Europeans was limited. At that time, however, the Arabs were developing extensive seaborne trade with East Africa, India, and Southeast Asia. They were the first to use the monsoons to their advantage: voyaging from East Africa to Asia during the northern summer, when monsoon winds blow from the southwest, and returning in the winter, when the winds reverse and blow from the northeast. The Vikings also made great ocean voyages during the Dark Ages, reaching Iceland in the ninth century and Greenland and Newfoundland late in the tenth century.

The middle and late 1400s brought the dawn of a new era as Europeans set out on many ambitious voyages of discovery. The Canary Islands off Northwest Africa were explored in 1416, and the Azores, in the middle of the Atlantic Ocean, were discovered in about 1430. The southern tip of Africa was rounded by Vasco da Gama in 1498; Columbus rediscovered the Americas in 1492; and the world was first circumnavigated by Ferdinand Magellan’s expedition of 1519–1522, although Magellan himself was killed in the Philippines during the voyage.

Systematic mapping of the oceans began during the middle of the second millennium. After the mid-1400s, exploration of the oceans was incessant, and maps improved rapidly. However, most exploration was undertaken only to discover and colonize lands that could be reached by crossing the oceans. Systematic study of the oceans themselves is generally not considered to have begun until 1768, when Captain James Cook began the first of three voyages to explore and map the Pacific Ocean (Fig. 2-5). Captain Cook was the first navigator to carry an accurate chronometer to sea, so he was the first navigator able to measure longitude precisely, enabling dramatic improvement of existing maps. On his voyages, Cook made many measurements of water depth, or soundings, which he accomplished with a lead weight attached to a rope. He measured depths to 200 fathoms (366 m). He also made many accurate measurements of water temperature, currents, and wind speed and direction, and he documented the occurrence and general characteristics of coral reefs. On his final voyage, Captain Cook died at the hands of Polynesian natives at Kealakekua Bay, Hawaii.

Figure 2-5 Routes of the three voyages of Captain Cook: 1768–1771, 1772–1775, and 1776–1780. Cook visited all the major oceans, traveling south into the waters near Antarctica and as far north as the Bering Sea. Places named after Captain Cook include Cook Inlet, Alaska; Cook Strait between the North and South Islands of New Zealand; and a group of Polynesian islands in the tropical Pacific near Tahiti. (©AMS; Adapted from Franklin, B., 1770 via Central Library)

At the same time that Cook was exploring the Pacific, Benjamin Franklin, then deputy postmaster for the American colonies, learned that it took 2 weeks longer for mail ships to sail the northerly route from Europe to the colonies than to sail the longer southerly route. Franklin’s interest in that phenomenon led him to have many discussions with ships’ navigators, from which he concluded that ships coming from the north were sailing against a great ocean current. From his observations, he and his cousin Timothy Folger were able to develop a remarkably accurate map of the Gulf Stream current in 1770 (Fig. 2-6).

Figure 2-6 Map of the Gulf Stream originally drawn by Benjamin Franklin and Timothy Folger in 1770. (Public Domain; Franklin, B., 1770 via NOAA)

The Birth of Oceanography 

By 1800, several seafaring nations had established government offices with primary responsibility for producing charts that could be used by mariners to navigate safely and avoid reefs and shoals. Matthew Fontaine Maury, a U.S. Navy officer in charge of the Depot of Naval Charts, made a particularly significant contribution to the intensive ocean mapping efforts of the nineteenth century. Maury gathered data on wind and current patterns from numerous ships’ logbooks, and he published his detailed findings in 1855 in a volume entitled The Physical Geography of the Sea. Maury also initiated cooperative efforts among seafaring nations to standardize the means by which meteorological and ocean current observations were made. Because of his many contributions, Maury has often been called the “Father of Oceanography.”

The Beagle

In 1831, the HMS Beagle started a 5-year epic voyage of discovery that forever changed the way humans view their world (Fig. 2-7). The major objective of this voyage was to complete a hydrographic survey of the Patagonia and Tierra del Fuego coastal regions to improve maps used by English ships sailing between the Pacific and Atlantic Oceans around the tip of South America. The Beagle also visited the Galápagos Islands off the coast of Peru, crossed the Pacific to New Zealand and Australia, and returned to England across the Indian Ocean and around the southern tip of Africa.

Figure 2-7 The voyage of HMS Beagle and Charles Darwin, 1831–1836. More than half the voyage was spent near South America

The Beagle expedition has become famous primarily because of the young naturalist who traveled on the ship, observing the plant and animal life of the many places where the Beagle touched land. This naturalist was, of course, Charles Darwin. Darwin’s observations on the Beagle expedition were part of the basis for his book Origin of Species, in which he proposed the revolutionary theory of natural selection. 

Although the observations that led to the theory of evolution were the most famous of his findings on the Beagle expedition, Darwin also made several other major discoveries. For example, he proposed a theory to explain the formation of coral atolls that is still accepted (Chap. 4). In addition, he made a startling observation on one of his land excursions during the voyage: Darwin climbed high into the Andes Mountains, which run along the west coast of South America. At the top of these mountains, he found fossils in the rocks that were undeniably the remains of marine creatures. Darwin concluded correctly that the rocks had originated beneath the sea. Thus, he deduced that continents were not permanent and unchanging, as was widely accepted at the time, but that they must move, at least vertically. That observation remained almost unnoticed among Darwin’s works until the twentieth century, when the theories of continental drift and plate tectonics were developed (Chaps. 4, 5).

The Challenger

During the 1860s, British vessels investigating the seafloor prior to laying a transatlantic telegraph cable brought up living creatures in mud samples from the bottom of the deep sea. At the time, the prevailing scientific opinion was that the deep ocean was devoid of life, because of the high pressures and low temperatures. Thus, the discovery of life on the deep-ocean floor was perhaps as dramatic a finding as the discovery of life on Mars would be if it were to occur today. The discovery of life in the deep sea led to the true birth of oceanography as a modern science, an event that can be precisely dated to 1872 through 1876. It was during these years that HMS Challenger sailed the world’s oceans as the first vessel outfitted specifically so that its crew could study the physics, chemistry, geology, and biology of the oceans (Fig. 2-8). The Challenger was a sail-powered navy corvette with an auxiliary steam engine. For its scientific expedition, sponsored by the Royal Society of London, the corvette’s guns were removed and replaced with laboratories and scientific gear. Included was equipment for measuring the ocean depths, collecting rocks and sediment from the ocean floor, and collecting seawater and organisms from depths between the ocean surface and the seafloor. The scientific additions crowded the vessel and left only spartan living quarters for the crew and the six scientists.

Figure 2-8 The Challenger expedition. (a) A painting of HMS Challenger. (b) Route of the voyage of the Challenger, 1872–1876, which sailed through all the major oceans, but not into the high-latitude regions.

The Challenger sailed 127,500 km across the oceans during its 5-year expedition to study the North and South Atlantic Ocean, the North and South Pacific Ocean, and the southern part of the Indian Ocean. The expedition made hundreds of depth soundings using a lead weight on a hemp line that was hauled in by hand over a steam capstan. With this equipment, a single deep sounding required an entire day. Despite the extreme difficulty and tedium of obtaining deep soundings, the Challenger expedition was able to measure a depth of 8185 m in the Mariana Trench east of the Philippines.

The Challenger also conducted

• Hundreds of observations of ocean water temperature, both near the surface and at depth
• More than 100 dredge samples of rocks and sediment from the seafloor
• One hundred and fifty open-water net trawls for fishes and other organisms
• Numerous samples of seawater
• Many readings of ocean current velocity and meteorological conditions
• Countless visual observations of fishes, marine mammals, and birds

The expedition brought back a wealth of samples and new scientific information about the oceans, including the identification and classification of almost 5000 previously unknown species of marine organisms. The quantity of data and samples obtained was so great that a special government commission was established to analyze the information. Indeed, the 50 volumes of research reports generated by the expedition were not completed until decades after the ship returned to England. The volumes contained so much information that they provided the foundation on which almost all major disciplines of oceanography were later built.

The Modern Era

In the 150 years since the Challenger expedition, oceanographers have traveled the seas in research ships with increasing frequency, and with observation and sampling equipment of ever-increasing sophistication. A significant proportion of ocean research is still performed from research vessels in much the same way that it was in 1872. However, during the twentieth century, oceanographic research expanded to include exploration and study using scuba and manned submersibles, as well as unmanned observation using robotic vehicles and instrument packages either free-floating or attached to cables moored to the seafloor. Many of these instruments now report their data by acoustic links to the surface, and by radio signals sent through satellites to land-based facilities. In addition, oceanographers make many observations from aircraft and satellites using remote sensing techniques. The introduction in 1978 of satellites specifically designed to look at ocean processes was an important milestone because it allowed almost simultaneous observations to be made across an entire ocean basin for the first time. Satellites are now among the most important observing platforms used by oceanographers (Chap. 3).

The detailed history of oceanography since the Challenger expedition is too voluminous to include in this text. However, some of the important events are summarized in Appendix 4, and subsequent chapters review many of the more important findings of ocean study and exploration in the modern era. Among the most important events or discoveries during this author’s lifetime have been:

• The 1959 publication by Heezen and Tharp of the first comprehensive map of the ocean floor topography (Chap. 3).
• The discovery in 1964 and 1965 of hot, high-salinity brines and unusual black ooze-like sediments at the bottom of the Red Sea. This was the first observation of hydrothermal vents, although that was not recognized at the time.
• The first visit to a hydrothermal vent by the submarine Alvin in 1977, where a previously unknown type of ecosystem, based on chemosynthesis and sustaining hundreds of previously unknown species was discovered.
• The steady accumulation of evidence that led to the acceptance of Wegener’s 1912 theory of continental drift (Chap. 5). Much of the crucial evidence supporting this theory was gathered by the Deep Sea Drilling Program, which obtained samples from deep within ocean sediments for the first time.
• Satellite observations of the world ocean provided the first comprehensive snapshot view of the oceans. This view did not have to rely on many individual observations from ships and enabled the observation of large-scale dynamic processes as never before.
• The development of autonomous robotic measuring devices, including Argo floats, allow the gathering of data of unprecedented detail about processes that occur below the surface layer and that cannot be observed by satellite sensors.
• The discovery of the horizontal gene transfer mechanism in the mid-1950s.
• The finding, at the end of the 20th century (based on DNA analysis) that ocean life is dominated by microbial organisms.
• The finding that microbial life exists deep within ocean sediments and even deep within the Earth’s crust below these sediments.

Each of these can arguably be claimed to be as important a breakthrough or advancement for ocean sciences as, for example, Darwin’s observations on the voyage of the Beagle were to biology. We live in an age of discovery for ocean sciences and many more surprises, advancements, and revelations are to come.