C H A P T E R

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Brief History of Physical OceanographySupplementary Web Site Materials for Chapter 1

This supplementary chapter contains aneclectic and necessarily truncated treatment ofthe history of physical oceanography. Numerousbooks, journal issues, and memoirs providediverse resources. Among these, the ScrippsInstitution of Oceanography’s library archiveprovides a webpage that is an excellent place tobegin searching for original materials, biogra-phies, and institutional histories (SIO, 2011).

While the ocean has been the object of manyancient science applications, the science ofoceanography is fairly young. Its origins are ina great variety of earlier studies includingsome of the earliest applications of physicsand mathematics to Earth processes. Archi-medes, the Greek physicist and mathematician,can also be considered one of the earliest phys-ical oceanographers. The familiar Archimedesprinciple describes the displacement of waterby a body placed in the water. Archimedesalso made extensive studies of harbors tofortify them against enemy attack. Pytheaswas another early physical oceanographer; hecorrectly hypothesized that the moon causesthe tides.

Many early mathematicians used their skillsto study the ocean. Sir Isaac Newton did notdirectly work on problems of the ocean, buthis principle of universal gravitation was anessential building block in understanding the

1

tides. Both Laplace and Legendre, who weremathematicians, advanced the formal theory ofthe tides (Laplace, 1790); Laplace’s equation isa fundamental element in a description of thetides. English mathematicians worked ona mathematical description of the ocean wavesthat surrounded their homeland. All of thesestudies are clearly part of what we now knowas physical oceanography.

Early charting of the ocean’s surface currentscame hand in handwith exploration of coastlinesand ocean basins and was performed by theearliest seafaring nations. Peterson, Stramma,and Kortum (1996) provided an excellent reviewof the history of ocean circulationmapping, fromthe earliest Greek times, through themiddle agesand rise of the Arabian empire, through theRenaissance and into the eighteenth and nine-teenth centuries. In the late eighteenth century,JohnHarrison’s development of the chronometerto measure longitude was a watershed, makingmore accurate mapping possible. By the nine-teenth century, descriptions of subsurface andeven deep circulation were becoming possible.

S1.1. SCIENTISTS ON SHIPS

Early charts of the ocean circulation wereproduced by mariners. Benjamin Franklin,

S1. BRIEF HISTORY OF PHYSICAL OCEANOGRAPHY2

among his many different accomplishments,was also a scientist, was one of the first tomake measurements at sea specifically to chartits features (Figure 1.1b in the textbook). Hisgoal was to decrease the time required for mailpackets to cross the Atlantic from Europe tothe United States. Another source of sea-goingphysical studies of the ocean came from studiesmade by “naturalists” who went along onBritish exploring expeditions. One examplewas Charles Darwin, who went along asthe ship’s naturalist of the HMS Beagle ona voyage to chart the southeast shore of SouthAmerica. This journey included many longvisits to the South American continent whereDarwin formulated many of his ideas aboutthe origin of species. During the cruise hetook measurements of physical ocean parame-ters such as surface temperature and surfacesalinity.

There were so many naturalists traveling onBritish vessels in the early 1800s that the RoyalSociety in London decided to design a set ofuniform measurements. Then Royal Societysecretary, Robert Hooke, was commissioned todevelop the suite of instruments that would becarried by all British government ships. Onenoteworthy device was a system to measurethe bottom depth of the deep ocean. It consistedof a wooden ball float attached to an ironweight. The pair was to be dropped from theship to descend to the ocean floor where theweight would be dropped; the wooden ballwould then ascend to the surface where itwould be spotted and collected by the ship.

S1.2. ORGANIZED EXPEDITIONSPRIOR TO THE TWENTIETH

CENTURY

In the eighteenth century, organized oceanexpeditions contributed valuable knowledge ofthe oceans. One of the most successful oceanexplorers was Captain James Cook who made

three major exploring voyages between 1768and 1780. On these cruises, British naturalistsobserved winds, currents, and subsurfacetemperatures; among other discoveries theyfound the temperature inversion in the Antarctic,with cold surface water lying over a warmersubsurface layer.

In 1838 the U.S. Congress had the Navy orga-nize and execute the United States ExploringExpedition to collect oceanographic informationfrom all over the world (see Chapman, 2004).Many of the backers of this expedition saw itas a potential economic boon, but others weremore concerned with the scientific promise ofthe expedition. In 1836, $150,000 had beenappropriated for this expedition. As originallyconceived, the expedition was to benefit naturalhistory, including geology, mineralogy, botany,vegetable chemistry, zoology, ichthyology, orni-thology, and ethnology. Some practical studiessuch as meteorology and astronomy were alsoincluded in the program. Most of the sciencewas to be done by a civilian science comple-ment; the Navy was to provide the transporta-tion and some help with the sampling. TheNavy did not like this arrangement and insistedthat a naval officer lead the entire expedition.This responsibility was given to LieutenantCharles Wilkes who had earned the reputationof being interested in and able to work on scien-tific problems. At the same time it was widelyknown that Wilkes was proud and overbearing,with his own ideas on how this expeditionshould be executed. Most of the scientificpositions were filled with naval personnel.Only nine positions were offered to civilianswho were subject to all the rules and conditionsof behavior applying to the naval staff.

Unlike other later and more significantsingle-ship expeditions, five naval vesselscarried out the United States Exploring Expedi-tion. Starting in Norfolk, Virginia, the expedi-tion sailed across the Atlantic to Madeira,re-crossed to Rio de Janeiro, then south aroundCape Horn and into the Pacific Ocean. By the

ORGANIZED EXPEDITIONS PRIOR TO THE TWENTIETH CENTURY 3

time the ships had sailed up the west coast ofSouth America to Callao, Peru, storms had putthree ships out of commission. What remainedof the expedition crossed the Pacific and whilethe “scientific gentlemen” were busy makingcollections in New Holland and New Zealand,two ships, the Vincennes and the Porpoise, sailedsouth into the Antarctic region where Wilkesbelieved that there was a large landmass behinda barrier of ice. In the austral summer of1839e1840, Wilkes sailed his ships south untilblocked by the northern edge of the pack ice.He then sailed west along the ice barrier andwas able to get close enough to see the land.At one point he came within a nautical mile ofthe coast of “Termination Land” as Wilkesnamed it. This was the most interesting part ofthe expedition as far as Wilkes was concerned.His alleged discovery of Antarctica was stronglycontested by the British explorer Sir James ClarkRoss, but it remains as the only well-knownbenefit of this mission. Other possible claimantsto having discovered Antarctica were CaptainNathaniel Palmer, an American sealing captainwho claimed to have sighted it in 1820, andthe Russian Fabian von Bellingshausen who cir-cumnavigated the Antarctic continent from 1819to 1821 as part of a Russian Navy expedition.

During this same period there was an impor-tant development in the United States. A Navylieutenant, Matthew Fontaine Maury, was seri-ously injured in a carriage accident and was notable to go to sea for many years. Instead he wasput in charge of a fairly obscure Navy officecalled the Depot of Charts and Instruments(1842e1861). This later became the U.S. NavalObservatory. This depot was responsible for thecare of the navigation equipment in use at thattime. In addition it received and sent out logs tobe filled out by the bridge crew ships. Maurysoon realized that the growing number of shiplogs in his keeping was an important resourcethat could be used to benefit many. His firstidea was to make use of the estimates of windsand currents from the ships to develop

a climatology of the currents and winds alongmajor shipping routes. At first most peoplewere skeptical about the utility of such maps.Luckily one of the clipper ship captains plyingthe route between the east and west coasts ofthe United States decided to see if he could usethese charts to select the best course of travelfor his next voyage. He found that this new infor-mation made it possible to cut many days off ofhis regular travel. As word got around, otherclipper ship captains wanted the same informa-tion to help to improve their travel times. Soonother route captains were doing the same andMaury’s information became a publicationknown as “sailing directions.” Even today theU.S. Coast Guard continues to publish “SailingDirections,” although the publication has littleto do with sailing and more to do with harborapproaches and changes in coastal conditions.

This publication was so successful that manyEuropean nations decided to adopt similar prac-tices. Maury was invited to advise the Europeannations onhow todevelopand implement similarsystems. In theUnited States he expanded his useof these archived data and also expanded his“depot” to include other oceanographicmeasure-ments. Itwasunderhisguidance thataLieutenantBaker developed one of the first deep-seasounding devices. Baker stuck with the age-oldconcept of measuring the ocean depth by drop-ping a line from the surface. The problem hadbeen that in 4000 m of water the line became tooheavy to retrieve from the surface, so he designeda newmetal line whose cross section varied froma very narrowgaugewire at the bottom to amuchthickerwire nearer the surface. In addition, Bakerfollowed one aspect of Hooke’s design and drop-ped the weight at the bottom, again making thesystemmuch lighter for retrieval. A later additionwas a small corer added to the end of the line tocollect a short (a few centimeters) core of the toplayer of sediment. This device led to the firstcomprehensive map of bottom topography ofthe North Atlantic. Unfortunately for Maury,when the civil war broke out he returned to his

FIGURE S1.1 Track of the HMS Challenger Expedition 1872e1876.

S1. BRIEF HISTORY OF PHYSICAL OCEANOGRAPHY4

native south and spent most of the war devel-oping explosive devices to destroy enemy shipsand to barricade harbors. An important part ofMaury’s legacy is a book, the Physical Geographyof the Sea, which remarkably is still in print(Maury, 1855).

The first global oceanographic cruise wasmade on the British ship the HMS Challenger.This three-year (1872e1876) expedition (FigureS1.1) was driven primarily by the interest ofa pair of biologists (William B. Carpenter andCharles Wyville Thomson) in determiningwhether or not there is marine life in the greatdepths of the open ocean. Thomson was a Scot

educated as a botanist at the University ofEdinburgh, and in the late 1860s he wasa professor of natural history at Belfast, Ireland.He had been working with his friend Carpenter,a medical doctor, to discover if the contention byanother British naturalist (Edward Forbes) thatthere was no life below 600 m (called the azoiczone) was true. Even in the early phase of theChallenger expedition dredges of bottom mate-rial from as much as 2000 m had demonstratedthe great variety of life that exists at the oceanbottom. In addition to biological samples, thisexpedition collected a great number of physicalmeasurements of the sea such as sea-surface

SCANDINAVIAN CONTRIBUTIONS AND THE DYNAMIC METHOD 5

temperature and samples of the min-maxtemperatures at various depths.

Along with Thomson and Carpenter, theChallenger scientific staff consisted of a natu-ralist, John Murray, and a young chemist, JohnYoung Buchanan, both from the University ofEdinburgh. The youngest scientist on the staffwas 25-year-old German naturalist Rudolf vonWillemoes-Suhm who gave up a position atthe University of Munich to join the expedition.Henry Nottidge Moseley, another British natu-ralist who had also studied both medicine andscience, joined the expedition after returningfrom a Government Expedition to Ceylon.Completing the staff was the expedition’s artistand secretary, James John Wild. Much of thevisual documentation that we have from theChallenger expedition came from the able penof James Wild. The addition of John Murraywas fortuitous in that he later saw to the publi-cation of the scientific results of the expedition.Upon return, it was soon found that theChallenger expedition had exhausted the fundsavailable for the publication of the results.Fortunately Murray, who was really a studentfrom the University of Edinburgh, recognizedthe value of the phosphate formations thatdominated Christmas Island. Claiming theisland for England, Murray later set up miningoperations on the island. The income from thisoperation was later used to publish theChallenger reports.

S1.3. SCANDINAVIANCONTRIBUTIONS AND THE

DYNAMIC METHOD

In the last quarter of the nineteenth centurya group of Scandinavian scientists began toinvestigate the theoretical complexities of thesea in motion. In the late 1870s, a Swedishchemist, Gustav Ekman, began studying thephysical conditions of the Skagerrak, part ofthe waterway connecting the Baltic and the

North Sea. Motivated by fisheries problems,Ekman wanted to explain shoals of herring thathad suddenly reappeared in the Skagerrak afteran absence of 70 years. He discovered that in theSkagerrak there are layers of less-saline waterfrom the Baltic “floating” over the deeper, moresaline North Sea water. At the same time hefound that herring preferred a particular waterlayer of intermediate salinity. This shelf, orbank water, as it was called, moved in and outof the Inland Sea and with it went the fish.Ekman knew that his results would not be ofany use to the fishermen unless the shelf waterand the other layers could bemapped. He joinedforces with another Swedish chemist, OttoPettersson, and together they organized a verythorough series of hydrographic investigations.Pettersson was to emerge from this experienceas one of the first physical oceanographers. Itshould be noted that in Swedish “hydrography”translates as “physical oceanography.

Pettersson and Ekman both understood thatto obtain a useful picture of the circulationa series of expeditions involving several vesselsthat could work together at many timesthroughout each year would have to be orga-nized. This was a new approach to the studyof the sea. In the name of fisheries researchsuch a series of research cruises was begun inthe early 1890s. These were some of the firstcruises that emphasized the physical parame-ters of the ocean. For the vertical profiling ofthe ocean temperature a new device was avail-able. Since 1874, the English firm Negretti andZambra had manufactured a reversing ther-mometer that recorded accurate temperaturesat depth.

During this time, another Scandinavian brokenew ground in the rush to reach the North Pole.As a young man of 16, Norwegian FridtjofNansen was the first person to walk acrossGreenland. This exploring spirit led Nansen topropose a Norwegian effort to reach the NorthPole. After studying evidence, Nansen decidedthat there was a northwestward circulation of

S1. BRIEF HISTORY OF PHYSICAL OCEANOGRAPHY6

ice in the Arctic. Instead of mounting a largeattack on the Arctic, Nansen wanted to builda special ship that could withstand the pressuresof the sea ice when the ship was frozen into theArctic pack ice (Figure 12.7 in the textbook). Hebelieved that if he could sail as far east aspossible in summer he could then freeze hisship into the pack ice and be carried to thenorthwest. His plan was to get as close aspossible to the North Pole at which time heand a companion would use dog sleds to reachthe pole and then return to the ship. Named theFram (“forward” in Norwegian), this uniqueship was too small to carry a large crew. InsteadNansen gathered a group of nine men whowould be able to adapt to this unique experi-ence. Always a scientist, Nansen planned a largenumber of measurements to be made during theFram’s time in the ice pack.

On March 1895 the Fram reached 84�N, about360 miles from the pole (Figure 12.7). Nansenbelieved that this was about as far north as theFram was likely to get. In the company ofFrederik Hjalmar Johansen and a large numberof dogs, Nansen left the relative comfort of theFram and set off to drive the dog sleds to theNorth Pole. They drove slowly north over drift-ing ice until they were within 225 miles of theirgoal, farther north than any person had beenbefore. For three months they had traveledover extremely rough ice, crossing what Nansenreferred to as “congealed breakers” and theyhad lost their way. From their farthest northpoint they turned south eventually reachingFranz Josef Land where they hoped to encountera fishing boat in the short summer season.Surviving by eating their dogs, Nansen andJohansen were very fortunate to meet a Britishexpedition led by Frederick Jackson. In thesummer of 1896 they sailed home to Oslo aboardthe Windward. Meanwhile the Fram driftedfurther west and south and emerged from theice pack just north of Spitsbergen. She sailedback to Oslo and arrived just a week after Nan-sen and Johansen.

OneofNansen’sprimaryobjectives in theFramexpedition was to form a more complete idea ofthe circulations of the northern seas. This wasachieved by taking systematic measurements ofthe temperatures and salinities of the Arcticwater. Using one of Pettersson’s insulated waterbottles, Nansen had attached a reversing ther-mometer to sample the temperature and salinityprofiles. This arrangement, known as a “Nansenbottle,” is still in use.Working in the GeophysicalInstitute of the University of Bergen, Norway,Nansen tried to explain the measurements madeby the Fram. The hydrographic measurementssuggested a very complex connection betweentheNorwegianandArctic Seas.Thedailypositioninformation from the Fram was also of greatinterest for this study.As a young student, Ekmanworked on this problemwith Nansen. Both wereinterested to note that the Framdid not drift in thesame direction as the prevailing wind, instead itdiffered from the wind by about 20 to 40 degreesto the right.

Using the measurements made by the Framalong with simple tank models of the Fram,Ekman developed his theory of the wind-drivencirculation of the ocean. Published as part ofthe Fram report, Ekman (1905) postulated theresponse of the ocean to a steady wind ina uniform direction. Making some simpleassumptions about the turbulent viscosity ofthe ocean, Ekman could show how the oceancurrent response to a steady wind must havea surface current 45 degrees to the right of thewind in the Northern Hemisphere. Below thatthere is a clockwise (Northern Hemisphere)spiral of currents (called the Ekman spiral)down to a depth where the current vanishes.

In spite of these successes with the Fram data,Nansen realized that he could have done muchmore. This was motivated by the developmentof the “dynamic method” for estimating geo-strophic ocean currents (seeChapter 7 in the text-book). Developed also in Bergen, this methodmade it possible to map currents at every levelfromadetailed knowledge of the vertical density

THE METEOR EXPEDITION 7

structure. The Fram’s measurements were notdetailed enough to take advantage of this tech-nique. This theory was furthered developed byWilhelm Bjerknes, a professor of meteorologyat the University of Oslo, who coined the term“geostrophy” from the Greek geo for earth andstrophe meaning turning.

Two other Scandinavian physical oceanogra-phers of this period were Johan Sandstrom andBjorn Helland-Hansen, both of whom wereinterested in the ocean circulation and itsmeasurement. The Norwegian Board of SeaFisheries had invited Helland-Hansen, Nansen,and Johan Hjort to participate in the first cruiseof their new research vessel. They were respon-sible for the collection of hydrographic measure-ments. A new problem surfacedwhile they werecollecting their measurements. In their processof measuring salinity it was necessary to havea “reference sea water” to make the measure-ment precise, since slightly different methodsand procedures were being used. At this timea Danish physicist, Martin Knudsen, wasworking on a set of hydrographical tables thatwould clearly define the relationship betweentemperature, salinity, and density. At the 1899meeting of the International Council for theExploration of the Sea (ICES), Knudsen hadproposed that such tables be published to facil-itate the standardization of hydrographic work(Knudsen, 1901). For this same reason Knudsensuggested that a standard or normal waterbe created and distributed to oceanographiclaboratories throughout the world as a standardagainst which all salinity measurementscould be compared. Knudsen then proceededto set up the Hydrographical Laboratory forICES in Copenhagen and the standard seawaterlater became known as “Copenhagen Water.”He also published standard tables called“Knudsen Tables,” which displayed the rela-tionships between chlorinity, salinity, densities,and temperature.

Nansen and Helland-Hansen’s careful studyof the Norwegian Sea made it the most

thoroughly studied and best-known body ofwater in the world. The new method ofcomputing geostrophic currents had playeda large role in defining the circulation of theNorwegian Sea. This “dynamic method,” as itwas called, was slow to spread to other regions.Then, around 1924, a German oceanographernamed Georg Wust applied the dynamicmethod to the flows at different levels throughthe Straits of Florida. He compared the resultsto the current profiles collected in the 1880s bya Lieutenant Pillsbury in the same area witha current meter. The patterns of the currentswere essentially the same and confidence inthe dynamic method increased. Another test ofthe dynamic method arose when the Interna-tional Ice Patrol (IIP) began to compute thecirculation of the northwest Atlantic to trackthe drift of icebergs. Created after the tragicsinking of the Titanic, the IIP was chargedwith mapping the positions and drifts oficebergs released into Baffin Bay from theglaciers on Ellesmere Island.

S1.4. THE METEOR EXPEDITION

German scientists performed the real test ofthe dynamic method on the Meteor expeditionin the Atlantic from 1925 to 1927 (Spiess, 1928).This expedition was conceived by a Germannaval officer, Captain Fritz Spiess, to create anopportunity for a German navy vessel to visitforeign ports (prohibited by the treaty at theend of World War I) in the capacity of an oceanresearch vessel. Captain Spiess had served bothprior to and during the war as a hydrographerin the German navy. He realized that to besuccessful he must find a recognized Germanscientist to be the “father” of the expedition.

Spiess presented his idea to Professor AlfredMerz, then the head of the Oceanographic Insti-tute in Berlin. Merz had been educated as a phys-ical geographer, but had always worked on thephysics of the ocean. He was happy to accept

FIGURE S1.2 Overturning circulation of the Atlantic Ocean according to Merz and Wust (1923).

S1. BRIEF HISTORY OF PHYSICAL OCEANOGRAPHY8

the role of scientific leader of the future oceanexpedition. This interest included the participa-tion of his son-in-law and former student GeorgWust, who was previously mentioned withrespect to his use of the dynamic method.

Prior to the Meteor expedition, Merz andWust collected all of the German and Britishhydrographic observations and presenteda new vision of the horizontal and vertical circu-lation in the Atlantic with different watermasses in thick layers (Figure S1.2). Our presentview of the Atlantic’s “overturning circulation”is not very different from their concept. Richard-son (2008) provided an excellent overview of thehistory of charting the overturning circulationfrom these early attempts to the present.

The verification and improved resolution ofthis proposed circulation became the focus forthe expedition. Because the Meteor was nota very large ship, it was decided that the crewwould have to help out in many measurementprograms. Consequently, many crewmemberswere sent to school at the Oceanography Institutein Berlin. In addition it was decided to executea “test or shakedown cruise” to determine if allthe equipment wasworking properly. This cruise

went from Wilhelmshaven on the North Sea tothe Azores and back. This pre-cruise turned outto be a very wise move, resulting in a numberof very basic changes. The smokestack waslengthened in an effort to get the heat of theengines higher off the deck. In the tropics thelack of good ventilation on the ship becamea serious problem and a lot of work had to bedone on the deck. The unique system developedfor theMeteor to anchor in the deep ocean had tobe corrected. In addition, the forward mast wasset up to carry more sail to save coal on someof the longer sections (Figure S1.3).

There were also some interesting personnelchanges that were arranged after the pre-expedition. Most important was the fact thata chemist who was to be in charge of the salinitytitrations was found to be colorblind. (The titra-tion has a color change at the end point.) It wasthen necessary to find someone who could dothe salinity titrations. The solution was thatWust, although not originally slated to partici-pate in the expedition, was taken along totitrate the salinity samples. This later becamevery important since the expedition leader,Dr. Merz, passed away in Montevideo after the

FIGURE S1.3 Meteor after refit. Source: From Spiess (1928).

THE METEOR EXPEDITION 9

first of the Meteor’s east-west sections had beencompleted. This left the ship without a scienceleader. Although Wust was the most knowl-edgeable, he was considered too junior to takeover as expedition leader. Instead CaptainSpiess officially took over both as scientificleader and naval captain. In practice, however,it was Wust who guided the execution of themany measurements in physical oceanography.He was committed to testing the scheme that heand Merz had developed for the circulation ofthe Atlantic. He was also a careful and pains-taking collector of new measurements, makingsure that no “shortcuts” were taken in collectingor processing the measurements.

On April 16, 1925, the Meteor left Wilhelm-shaven on her way to Buenos Aires, Argentina,which was to be the starting point of the expedi-tion. Outfitted with every new instrumentpossible, the Meteor was the first ocean researchcruise to concentrate primarily on the physicalaspects of the ocean. She carried not one buttwo new echo-sounding systems, which wereto accurately measure the depth of the oceanbeneath the ship. With no computer or evenanalog storage machines it was necessary for

someone to “listen” continually to the “pings”of the unit. Crewmen were enlisted in this oper-ation and two sailors had to be in the room 24hours a day listening to pings and writingdown the travel times.

In addition the Meteor had a new system thatenabled it to anchor in the deep ocean. Becausethe Meteor was able to moor itself in the deepocean, Ekman developed a current meter thatcould be used multiple times when suspendedfrom the main hydrographic wire (FigureS1.4). Ekman had gone on the pre-expeditiontrip to the Azores, but did not go along on themain cruise. His current meter was used repeat-edly during the deep-sea anchor stations.

Before returning to Germany in the spring of1927, the Meteor made 14 sections across theAtlantic, traveled 67,000 miles, made 9 deep-seaanchor stations, and occupied a total of 310hydro-graphic stations. In addition over 33,000 depthsoundings had been made in an area where onlyabout 3000 depth soundings already existed.During this voyage she encountered more thanone hurricane that greatly challenged her seawor-thiness. She had also suffered due to the problemof storing sufficient coal for the crossings.

FIGURE S1.4 Ekman repeating current meter. Source:

From Spiess (1928).

S1. BRIEF HISTORY OF PHYSICAL OCEANOGRAPHY10

It was indeed fortunate that Wust waspresent on the cruise to take over the scientificleadership. He worked on later analyses of theMeteor results with Albert Defant of the Ocean-ographic Institute in Berlin (Wust, 1935; Defant,1936). Defant joined the Meteor for the lastsection across the Atlantic.

S1.5. WORLD WAR II AND MID-TWENTIETH CENTURY PHYSICAL

OCEANOGRAPHY

Before World War II a number of oceano-graphic institutions were founded in variousparts of the world. In the United States twovery notable institutions were created. InCalifornia, the San Diego Marine BiologicalAssociation was founded in 1903, becoming the

Scripps Institution for Biological Research in1912 and renamed Scripps Institution of Ocean-ography (SIO) in 1925 (Shor, Day, Hardy, &Dalton, 2003), while in Massachusetts theMarine Biological Laboratory (MBL) located inWoods Hole spun off the Woods Hole Oceano-graphic Institution (WHOI) in January of 1930.Both organizations became and continue to beleading American institutions for the study ofthe ocean. At WHOI Henry Bigelow was madethe first director in spite of his genuine distastefor administrative duties. Originally WHOIwas only to be operated in the summer leavingBigelow the rest of the year for his scientificresearch and hobbies (fishing). Bigelow was soconvinced of the importance of having a fine,seaworthy vessel capable of making longvoyages in the stormy North Atlantic that hedodged the efforts of many to donate old plea-sure yachts or tired fishing vessels. Instead heagreed to spend $175,000 on the largest steel-hulled ketch in the world. A sailing ship witha powerful auxiliary engine was chosen overa steamship because of the inability to carrysufficient coal for long distance cruising. Thecontract was awarded to a Danish shipbuildingcompany and included two laboratories, twowinches, and quarters for 6 scientists and 17crewmembers. After delivery in the summerof 1931 Bigelow hired his former student,Columbus O’Donnel Iselin, as master of theresearch vessel named Atlantis. Iselin laterbecame the director of WHOI and left a legacyof important developments in the study of thewater masses of the ocean.

At SIO, Harald Sverdrup was hired as thenew director in 1936, bringing from the Bergenschool an emphasis on physical oceanography.Within a year of his arrival, SIO purchaseda movie star’s pleasure yacht and convertedher into the research vessel E.W. Scripps.Sverdrup had earlier been involved with aninternational effort to sail a submarine underthe North Polar ice cap. During a test it wasdiscovered that the submarine, named the

WORLD WAR II AND MID-TWENTIETH CENTURY PHYSICAL OCEANOGRAPHY 11

Nautilus, had lost a diving rudder and wouldnot be able to cruise beneath the ice. (It wasnot until 1957 that another submarine namedNautilus cruised beneath the North polar icecap and surfaced in one of the larger leads inthe ice pack.)

As is usually the case, war prompted somenew developments in physical oceanography.At WHOI, a naval Lieutenant William Pryorcame looking for an explanation as to why thedestroyer he was working on as a soundmancould not find the “target” submarine in theafternoon after being able to do it well in themorning. At WHOI, Bigelow and Iselin werehappy to collaborate with the navy and anexperiment was set up in the Atlantic and inGuantanamo Bay where for two weeks twoships “pinged” on each other. From the Atlantis,closely spaced water bottles and thermometerswere let down into the water. As Iselin expected,the results showed that Pryor’s assumption thatbubbles created by plankton were not the causeof the acoustic problems; instead the verticaltemperature profile was found to alter dramati-cally during the day. The change of the verticaltemperature distribution caused the soundpulses to be refracted away from the targetlocation making it impossible to detect thesubmarine. What was needed was a detailedknowledge of the vertical temperature profilein the shallow upper layers of the ocean.

Detailed studies of the generation and propa-gation of ocean waves led by Harald Sverdrupandhis studentWalterMunk at SIObeganduringWorld War II, driven by the importance of fore-casting wave conditions for military operations,including beachhead assaults (Sverdrup &Munk, 1947; Nierenberg, 1996; Inman, 2003).

In the 1940s and 1950s, Sverdrup and Munkat SIO were also studying the dynamics ofwind-driven currents. AtWHOI, Henry Stommelwas also involved in these studies. Basic modelsof the wind-driven circulation emerged fromthese studies starting with Sverdrup’s model,which explained the basic balance between the

major currents and the pressure gradients,followed by Stommel’s model and its explana-tion of the westward intensification that closedthe major ocean gyres at the western end(Section 7.8 in the textbook). Munk’s model,with a slightly different explanation for thewestward intensification, put it all together,presenting a realistic circulation in response toa simplification of the meridional wind profile.These models were the basis for future morecomplex and eventually numerical models ofthe ocean circulation.

Continuations of basin-scalemeasurements oftemperature, salinity, and other properties fromresearch ships continued in the 1950s with theInternational Geophysical Year (IGY). In the1960s, the international Indian Ocean Experi-ment completed the global scale observationsbegun in the IGY. In the 1970s, the InternationalSouthern Ocean Study (ISOS) concentrated onmore restricted regions and involved manydifferent countries.

Meanwhile, understanding of the shortertime and space scales in the ocean began toemerge thanks to development of reliablemoored current meters, with studies of eddiesin the 1970s beginning with a Russian experi-ment, Polygon 70, which established theimportance of large-scale “synoptic” eddies inthe ocean. Considered the “weather” of theocean, these mesoscale features carry heat,momentum, and other properties as they moveabout the ocean. The work was definitivelyexpanded by the U.S. Mid Ocean DynamicsExperiment of the early 1970s and the subse-quent joint U.S.-Russian Polymode Experiment,which began to reveal the rich variability thatoccupies much of the ocean (Munk, 2000). Inthe 1970s in the North Pacific, an ambitiousprogramof temperatureprofiling frommerchantships began to define the time and space vari-ability of a large swath of ocean.

There has been a dramatic shift in emphasis ofresearch inphysical oceanographynear the endofthe twentieth century. A global survey of ocean

S1. BRIEF HISTORY OF PHYSICAL OCEANOGRAPHY12

circulation (WOCE), whose main purpose was toassist through careful observations; the develop-ment of numerical ocean circulation modelsused for climate modeling; and an intensiveocean-atmosphere study of processes governingEl Nino in the tropical Pacific (Tropical OceanGlobal Atmosphere; TOGA) were completed.Many of the programs that have continuedbeyond these studies focus on the relationshipbetween ocean physics and the climate. At thesame time the practical importance of oceanphysics in the coastal ocean is emerging. Theneed for military operations in the ocean hasshifted to the coasts largely in support of otherland operations. Oil operations are primarilyrestricted to the shallow water of the coastalregionswhere tensionwith the local environmentrequires even greater study of the coastal ocean.

The most dramatic shifts in physical oceano-graphic methods at the turn of the twenty-firstcentury are to extensive remote sensing, in theform of both satellite and more automatedin situ observations, and to ever-growing relianceon complex computer models. Satellitesmeasuring sea-surface height, surface tempera-ture, and most of the components of forcing forthe oceans are now in place. Broad observationalnetworks measuring tides and sea level andupper ocean temperatures in the mid-to-latetwentieth century have been greatly expanded.These networks now include continuous currentand temperature monitoring in regions wherethe ocean’s conditions strongly affect climate,such as the tropical Pacific and Atlantic, andgrowing monitoring of coastal regions. Globalarrays of drifters measuring surface currentsand temperature, and subsurface floatsmeasuring deeper currents and ocean propertiesbetween the surface and about 2000 m depth arenow expanding. Meanwhile the enormousgrowth in available computational power andnumbers of scientists engaged in oceanmodelingis expanding our modeling capability and abilityto simulate ocean conditions and studyparticularocean processes. With increasing amounts of

globally distributed data available in near realtime, numerical ocean modelers are now begin-ning to combine data and models to improveocean analysis and possibly prediction of oceancirculation changes in a development similar tothat for numerical weather prediction in thetwentieth century. Full climatemodeling includesocean modeling, and many oceanographers arebeginning to focus on the ocean component ofclimate modeling. These trends are likely tocontinue for some time.

S1.6. A BRIEF HISTORY OFNUMERICAL MODELING INPHYSICAL OCEANOGRAPHY

Numerical modeling is a major componentof contemporary ocean science, alongwith theoryand observation. Models are quantitative expres-sions of our understanding of the ocean and itsinteractions with the atmosphere, solid earth,and biosphere. They provide a virtual laboratorythat allows us to test hypotheses about particularprocesses, predict future changes in the ocean,and toestimate the responseof theocean topertur-bations inexternal conditions.Thecomplexityandnonlinearity of the physical laws governing thesystem preclude solution by analytical methodsin all but the most idealized models. The mostcomprehensive models, known as ocean generalcirculation models, are solved by numericalmethods, often on the most powerful computersavailable. Blending of models and observationsto provide comprehensive descriptions of theactual state of the ocean, through a process ofdata assimilation similar to that used in numericalweather forecasting, has become a reality in thepast decade, due to advances in observingsystems, increases in computer power, and dedi-cation of scientific effort.

The growth and evolution of ocean modelingis paced, to a certain degree, by the growth incomputing power over time. The computationalcost of a model is determined by its resolution,

A BRIEF HISTORY OF NUMERICAL MODELING IN PHYSICAL OCEANOGRAPHY 13

that is, the range of scales represented; the size ofthe domain (basin or global, upper ocean or fulldepth); and the comprehensiveness andcomplexity of the processes, both resolved andparameterized, that are to be represented. Anoceanmodel is typically first formulated in termsof the differential equations of fluid mechanics,often applying approximations that eliminateprocesses that are of no interest to the study athand. For example, in the study of large-scaleocean dynamics, sound wave propagationthrough the ocean is not of great importance, soseawater is approximated as an incompressiblefluid filtering sound waves out of the equations.

The continuous differential equations mustthen be discretized, that is, approximated bya finite set of algebraic equations that can besolved on a computer. In ocean models this stepis most often done with finite-difference orfinite-volume methods, although finite-elementmethods have also been employed. In additionto the choice of numerical method, a major pointof diversity among ocean general circulationmodels is the choice of vertical coordinate. Inthe upper ocean, where vertical mixing is strong,a discretization based on surfaces of constant geo-potential ordepth is themostnatural. In the oceaninterior, where transport and mixing occurprimarilyalongneutraldensitysurfaces,averticaldiscretization based on layers of constant density,or isopycnal coordinates, is the most natural.Near the ocean bottom, a terrain-following coor-dinate provides a natural and accurate frame-work for representing topography and applyingthe boundary conditions for the flow.

The earliest three-dimensional ocean generalcirculation models, originally developed in the1960s by Kirk Bryan and colleagues at theNOAAGeophysical Fluid Dynamics Laboratory,were based on finite-difference methods usingdepth as the vertical coordinate (Bryan & Cox,1968; Bryan, 1969). Models descended from thisformulation still comprise the most widely usedclass of ocean general circulation models, partic-ularly in the climate system modeling

community. The first global ocean simulationscarried out with this type of model were limitedby the then available computational resources toresolutions of several hundred kilometers, insuf-ficient to represent the hydrodynamic instabilityprocesses responsible for generating mesoscaleeddies.

In the 1970s observational technologyemerged that showed the predominance ofmesoscale eddies in the ocean. A new class ofnumerical models with simplifications to thephysics, such as using the quasi-geostrophicrather than the primitive equations and limiteddomain sizes with resolutions of a few tens ofkilometers, was developed by Bill Holland, JimMcWilliams, and colleagues at the NationalCenter for Atmospheric Research (NCAR).Models of this class have contributed greatly tothe development of our understanding of theinteraction of mesoscale eddies and the large-scale ocean circulation, and to the developmentof parameterizations of eddy-mixing processesfor use in coarser resolution models, such asthose used in climate simulations. Initiallydeveloped as a generalization to the quasi-geostrophic eddy-resolving models, isopycnalcoordinate models such as that developed byBleck and co-workers at the University of Miami(Bleck & Boudra, 1981) became increasinglypopular for ocean simulation through the 1980sand 1990s. Today global eddy-resolving modelshave spatial resolution of less than 10 km, withregional models achieving much higher spatialresolution. A recent overview of progress waspublished in Hecht and Hasumi (2008) bymany of the principal groups.

Terrain-following coordinate models, alsoknown as “sigma coordinate” models initiallydeveloped primarily in the coastal oceanmodeling community by Mellor and co-workersat Princeton University, were used in basin- toglobal-scale ocean studies throughout the1980s and 1990s. A model of this type widelyused at present in regional studies is theRegional Ocean Modeling System (ROMS).

S1. BRIEF HISTORY OF PHYSICAL OCEANOGRAPHY14

Ocean general circulation models are impor-tant in coupled climate modeling, althoughthey must be run in much coarser spatial config-urations than the eddy-resolving versions toattain the many decades of integration required.Many of the major international modelinggroups have participated in the Intergovern-mental Panel on Climate Change assessments,which included more than 20 coupled modelsin its summaries (Meehl et al., 2007).

In the twenty-first century we are witnessingboth a tighter integration of modeling withobservational oceanography, for example,through the use of data assimilation techniques,and significant merging and cross-fertilizationof the various approaches to ocean modelingdescribed earlier. Computer power has reacheda level where the ocean components of fullycoupled climate system models have sufficientresolution to permit mesoscale eddies, blurringthe distinction between ocean models used forclimate applications and those used to studymesoscale processes. Several new models haveemerged with hybrid vertical coordinates,bringing the best features of depth, isopycnal,and terrain-following coordinates into a singlemodel framework.

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