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of maps to aid navigators grew enormously. From theAtlantic in the west to the Black and Red Seas in the east,these maps of the Mediterranean depict the shape andproportions of the Mediterranean Sea quite well. Anyone familiar with reading maps will recognize Gibraltar,Italy, the Balkans, Egypt and Palestine. Many include the

British Isles and Germany, but not Scandinavia. In theearly editions of the Ptolemy atlas Scandinavia does notappear. But in 1482 Nicolaus Germanus (the Ulm atlas)drew a map in which Denmark, southern Sweden andNorway clearly appear with names of numerous regionsand towns. An updated version of this map was com-piled by Martin Waldseemller in 1513. A significantstep forward occurred in 1532 with the Jacob Zieglermap (Nordenskild, 1889) which for the first time showsthe full length of the Scandinavian peninsula (albeit con-nected with Greenland in the north). Finland alsoappears for the first time as distinct from the rest ofScandinavia.

Against this backdrop of an as yet poorly developed

cartography of the Nordic countries, Olaus Magnus in1539 published his Carta Marina, a stunningly detailedmap spanning a region from northern Germany in thesouth to the Barents Sea in the north, Greenland in thewest to Russia in the east (Figure 1). The result of manyyears of travels and note keeping, the map provided awealth of information about the Nordic countries. Themajor island groups in the North Atlantic are all repre-sented. The very long coastline of Norway stands outclearly, and the coastal regions around the Baltic Seaemerge in considerable detail. The map also includes anexplanatory key, region by region. Physically, the mapbroke new grounds in terms of size: it consists of ninewood lithographs, which fit together into a nearly seam-

less whole, 1.7 m wide and 1.25 m high. Two copies existtoday, one in Munich, Germany and the other inUppsala, Sweden. While interest in the map quite obvi-ously focuses on the geography and peoples of theNordic countries, one can also appreciate why Olausgave the map the name Carta Marina, for unlike almostall other maps that had been published by that time (orto come later) he gave extraordinary attention to theocean itself, particularly the waters west of Scandinavia.

In 1539 Olaus Magnus, an exiled Swedish priestliving in Italy, published a remarkably detailed map ofthe Nordic countries, from Iceland in the west toFinland in the east. The map, called Carta Marina,introduced a scope of information about these coun-tries that broke completely new ground in terms of

comprehensiveness and general accuracy. The geo-graphical outline of the Nordic countries is quite accu-rate and the map includes all the major island groupssuch as the Faroes, Orkneys and Shetland Islands. Inaddition to the geography and numerous ethnograph-ic sketches, the map also provides, as it name indicates,an extraordinary wealth of information about thewaters surrounding the Nordic countries.

Olaus Magnus gives the ocean striking presence bydrawing in sea monsters, some more strange than oth-ers, sailing vessels, fishing boats and kayaks. He alsogives the ocean itself unusual presence or texture inthe form of thin dotted lines drawn horizontally every-where there is water. But he departs from this lineal

pattern in one particular area: Extending east fromIceland and passing north of the Faroes but not all theway to Norway, he draws in a band of whorls ofremarkable definition. The location of these corre-sponds almost perfectly with the Iceland-Faroes Front,a major surface front. Nowhere else in the chart dowhorls appear in such a systematic fashion. This notesuggests that they were drawn deliberately to indicatethe special nature of the waters east of Iceland, and assuch would appear to be the earliest known descrip-tion of mesoscale eddies in the ocean. This is a regionof high thermal contrast where warm North Atlanticwaters from the south and very cold waters from northof Iceland come together and mix. It seems likely thatOlaus Magnus got the information from mariners ofthe Hanseatic League operating out of northernGermany cities, many of which he is known to havevisited and lived in both before and after he was exiledfrom Sweden.

IntroductionStarting in the 1400s with the rapidly expanding

exploration by the Mediterranean countries, production

Ocean Eddies in the 1539 Carta Marinaby Olaus Magnus

H. Thomas RossbyUniversity of Rhode Island Narragansett, Rhode Island USA

Peter MillerPlymouth Marine Laboratory Plymouth UK

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Figure 1. The 1539 Carta Marina by Olaus Magnus (original size 1.7 x 1.25 m). It is on display at Carolina Rediviva, thelibrary of the University of Uppsala, Uppsala, Sweden. (Reproduced with permission from Uppsala University Library.)


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The ocean teems with activity, and significantly, he givesthe ocean itself a physical presence. He does this bydrawing everywhere thin dotted lines. While stipplingof the ocean had been done before, for example thindashed lines indicate water in the 1490 Ptolemy WorldAtlas, in Carta Marina the lines are drawn with fargreater care, including an occasional wiggle or swirl tobreak the monotony. But Olaus departs from thisapproach quite conspicuously in one area: extendingeast from Iceland and passing north of the Faroes thelines are replaced by a band of whorls (circular patterns).Nowhere else in the map does one find anything likethese, it seems clear they are intended to be there. Thequestion we consider in this note is why did he draw inthese whorls and what do they represent, for he providesno explanation in his description of the map.

Later, in 1555, Olaus also published a major treatisecalled HISTORIA DE GENTIBUS SEPTENTRIONAL-IBUS (History of the Nordic Peoples) which in 22 chap-ters expands upon his Carta and describes all aspects oflife and living conditions in the Nordic countries in theearly 1500s. It was a truly major piece of work, and

soon after the books publication in Latin, translationsappeared in many European languages includingGerman in 1567 and English in 1638, but not until theearly 1900s in a Scandinavian language, Swedish. Butthe book too is silent about the meaning of the whorlsin Carta Marina. In this note we attempt an oceano-graphic explanation for these, but before we go into thisin detail, we first give some background on Olaus andthe sources of information he drew upon in preparinghis map.

Olaus MagnusOlaus was born in 1490 in Linkping in Sweden and

died in Rome in 1557. He became vicar in Stockholm and(cathedral-) dean in Strngns. During the 1520s heundertook various diplomatic missions on behalf ofKing Gustav Vasa, but his relationship with the kingbecame increasingly strained after the king forcedSweden to convert to Lutheranism. Olaus remained aCatholic and after many years of travel around the con-tinent settled down in Italy where he completed hiswork on Carta Marina and his future HISTORIA. ThePope appointed him to Archbishop of Sweden in 1544(after the death of his brother who also was Archbishopin exile), but of course as a Catholic in exile he couldntassume his post in Uppsala.

Olaus was an itinerant traveler and visited many ofthe areas he was later to depict in his map. Already as a

15 year old he passed through Oslo during a trip aroundsouthern Norway. Much of his education he obtained atGerman universities during the years 1510-1517. At thebehest of the Catholic Church he spent a year (1518-1519) in northern Sweden and Norway fighting theLutheran heresy and selling indulgences. From his laterwork it is clear he was deeply impressed by the peoplehe met and landscapes he visited. Upon his return to


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older brother Johannes was elected to Archbishop ofSweden, and the following year King Gustaf Vasa sentOlaus to Rome to obtain the Popes blessing of the elec-tion. He was never to see Sweden again. During the1520s Olaus was occupied with a number of diplomat-ic assignments in Italy, Germany, the Netherlands andPoland seeking to renegotiate heavy debt burdensSweden owed the Hansa (Richter, 1967). Thus, duringthese diplomatic journeys he visited many Hanseaticports, from the Baltic in the east to the North Sea in thewest including a trip by sea from Hamburg to theNetherlands. He also resided in Danzig (Gdansk) forseveral years in the late 1520s. Given his evident curios-ity about nature and society, he no doubt acquiredmuch information about life at sea and sailing condi-tions. After Gustaf Vasa officially converted Sweden toLutheranism in 1527 relations with the firmly Catholicbrothers grew increasingly strained, and eventually theking stripped Olaus of his official positions and confis-cated his remaining belongings in Sweden.

While Olaus remained a firm Catholic his entirelife, he clearly maintained a deep love for his home

country. How else explain the love and care with whichCarta Marina was put together, including the incredi-ble richness of information about life and living condi-tions throughout the far north. Similarly, his 1555 HIS-TORIA discusses in extensive detail all aspects oflife and living, be it farming, fishing, snow ball fights,protecting homes against enemies, bird, animal andmarine life, etc in the countries of his early years.Although he gradually established a rather secure lifein Rome, one can imagine that at heart he must beenvery homesick. He died in 1557. Grape (1970) providesextensive biographical information on the life andwork of Olaus Magnus.

Carta MarinaOlaus worked on his Carta Marina over a 12-year

period, beginning in 1527, just at the time Sweden offi-cially converted to the Lutheran faith, and completing itwhile a guest of Prelate Hieronymous Quirinus inVenice in 1539 where the map was published. Later thatsame year he also published a more complete commen-tary to the map Opera breve. It is far beyond the scopeof this note to discuss Carta Marina either as a whole orin detail, but the interested reader will find consider-able biographical information about Olaus as well as acomprehensive analysis of the map in the book byRichter (1967). See also the article by Granlund (1951),which is written in English. Carta Marina is packed

with an extraordinary amount of information. It is notthe first map to show Scandinavia as a peninsula, but itis one of the first to give it, Finland and parts of Russia,roughly correct proportions. It is the first map to fullyportray the Baltic, the Finnish Gulf and Gulf of Bothniain the north. The map also covers northern Scotland, theHebrides, Orkneys, Shetlands, Faroes, Iceland andGreenland in the west. He also includes a non-existent

Stockholm, he became vicar and was in the city at thetime of the Stockholm bloodbath (November 1520)when King Christian II of Denmark took revenge on anearlier revolt against him and beheaded close to 90 peo-ple from the Swedish clergy (including a close call forOlaus himself) and nobility. In 1523 Olaus' two-year

Figure 2. A few close-ups from Carta Marina illustrat-ing life in Scandinavia. These skillfully executed wood-cuts from Olauss original show (a) a winter scene fromthe mountains including a possible self-portrait ofOlaus Magnus on his trek from Sweden to Norway win-ter 1517-1518, (b) a swimmer being defended by a ray

from a school of attacking fish, and (c) a man measuringwater depth .

(a)

(b)

(c)


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drift ice north of Iceland, including a stranded polarbear on a floe. Some creatures are recognizable includ-ing whales, sea lions, walrus, crab and lobster, but oth-ers, both to shape and size, more likely reflect a livelyreinterpretation of hearsay from fishermen and sailors.His giant sea snakes and other monsters clearlyimpressed the imagination of other mapmakers, as canbe seen for example in the Galleria delle CarteGeografiche at the Vatican (Knauer, 1981). Knauer evensuggests that some of these monsters, particularly thoseattacking vessels from protestant countries (such asGothi and Dani), are not a coincidence. The sea battle

betweenHamburgen and Scott may reflect the commer-cial tensions between the Hansa and England. On thesurface of the ocean Olaus draws ambergris, driftwoodalong the coast of Greenland and Eskimos kayaking inthe far north. The compass rose and lines indicate sail-ing directions. Recalling that 500 years ago marinerscould determine latitude and magnetic direction, butnot longitude, it was very common to sail along either

island, Tile, which some have speculated may be relat-ed to the mythical far northern community Thule.(Curiously, its location on the map puts it near St. Kilda,a small, at times inhabited island group west of theHebrides.) The list of towns, lakes, and regions is farmore comprehensive than any map either preceding itor to follow. In addition to the map information itincludes numerous small pictorials depicting farming,fishing, hunting, milking, and wolves unable to attackmoose on slippery ice (Figure 2). Little sketches illus-trate other maps of the period, such as the world mapsby Waldseemller (1516) and Ribero (1529), but in Carta

Marina they clearly serve to convey information aboutlife and living conditions. Thus it is far more than a mapor chart in the usual sense.

The oceans include a similar richness of informa-tion, indeed the presence and vitality of life at and inthe seas fully justify the maps name. A close-up ofCarta Marina between Iceland and Norway (Figure 3)reveals enormous detail about shipping, life in the sea,

Figure 3. Detail of Carta Marina between Iceland, the Faroes and Norway. Note the sea ice spreading east along the northcoast of Iceland and the many whorls in the ocean. The famous tidal whirlpool in the Lofoten Islands is clearly indicated.


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and eastern coasts during the winter months (Lamb,1977). Assuming an east- and southward flow along thenorthern coast of Iceland then as now, cold melt waterwould meet warm waters from the Atlantic on the SEcoast of Iceland, today near the town of Eystrahorn(Stefnsson, 1972). In spring the contrast in temperaturewhere these waters meet east of Iceland would havebeen enormous, presumably as large as it is today, ~5C.

Nowhere else in the Northeast Atlantic can one findwaters of such large thermal contrast so closely juxta-posed. Unquestionably shippers (and very likely theNorse Vikings some 500 years earlier) sailing to Icelandeach spring to conduct trade were well aware of thesecontrasting bodies of warm and cold water.

The HansaWe mentioned earlier that Olaus traveled exten-

sively in northern Germany visiting the major Hansatowns. This is relevant because the Hansa was respon-sible for much of the trade between Iceland and thecontinent. Until the middle 1400s trade with Icelandwas handled by Norway, but increasingly, the Hansa

bypassed its Kontor (office or hub) in Bergen and oper-ated directly between Germany and Iceland. In earliertimes the primary vessel used was the one-mastedKogge. This was gradually replaced by the larger Holkwith its rounded hull. Towards the late 1400s a majorchange in construction took place when carvel buildingreplaced the earlier klinker design, i.e. hull planks wereset up flush or next to each other instead of partiallyoverlapping. This led to a smoother (less friction) andsturdier structure allowing the vessels to operate withgreater confidence on the high seas than in the past. Theholks, typically 30 m in length, had a cargo capacity ofabout 150 tons (Figure 4). The ships transported grain,beer, wood, and textile products to Iceland. The most

important return cargo, by far, was fish, mostly driedcod but also salted. Other products included sheep-skins, butter and other fish such as salmon from themany freshwater rivers. Later in the 16th century sulfurbecame an increasingly important export item.

In a typical year, up to perhaps 25 ships wouldleave Hamburg and Bremen in late Marchearly Aprilfor Iceland (Baasch, 1889). Assuming a one-month jour-ney they would arrive in Iceland early in May when thelength of day and twilight was approaching 24 hours.Sailing over the North Sea, between the Orkneys andShetland and across the warm Shetland Current, thevessels might encounter the very cold waters on theirapproach to Iceland. In spring the winds drop in inten-

sity. Nonetheless, to avoid the strong westerlies southof Iceland and increase the chances of a tailwind, theywould benefit from passing north rather than south ofthe Faroes (the vessels often put into the Faroes alongthe way). But by assuming a more northerly route theyincrease the likelihood of encountering cold water.Even today, to avoid strong headwinds, ships en routeto western Greenland from the North Sea steer a great

lines of constant latitude or constant direction.

The scale of the chart as a whole is roughly 1:5 700000, or about one half this if we limit ourselves to theIceland, Faroes, Norway region in Figure 3. As indicatedby the number of ships, these waters were heavily traf-ficked by merchant marine vessels from Scandinavia,Germany and England. During the cold centuries of thelittle Ice Age (roughly 1300 to 1800s) Iceland often expe-rienced extensive sea ice formation along its northern

Figure 5. Simplified drawing of Figure 3 showing onlythe drift ice and whorls. The line A-A depicting theshortest distance between Iceland and the Faroes is justover 400 km.

Figure 4.Model of a Holk vessel. The model is based onpictures of vessels at the time plus records of cargocapacity (model built by Kurt Kollman, Sr., photographcourtesy of Focke-Museum, Bremen, Germany). Note

the birds nests at the top of the forward two masts. SeeEllmers (1999/2000) for an interesting survey on theorigin and evolution of the late middle-age Holk. Theword holk comes from to hollow out.


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and him the most was the remaining ice along thenorth coast in Spring and the patches of cold waters,which, we conjecture, he sought to portray as whorls inhis Carta Marina.

The WhorlsTo simplify our study we redraw Carta Marina

retaining only the eddy and ice field in relation toIceland, the Faroes and Norway (Figure 5). The whorlsseem to be an extension of the sea ice north of Icelandsuggesting that they represent pools of cold water.Given that the shortest distance (line A-A) betweenIceland and the Faroes is just over 400 km and giventhat some 3 whorls might fit in this distance, we esti-mate that the largest whorls approach an order of 100km in diameter. The whorls vary in size, some appearto swirl cyclonically (anticlockwise) and others in theopposite direction, but whether these variations in sizeand rotation are intentional we do not know. But therealism of this pattern of whorls readily matches whatwe might draw of an eddy field today. Significantly,

almost all whorls lie to the north of line A-A, the short-est distance between the Faroes and Iceland. Note alsothat they do not extend all the way over to Norway, apoint we return to below.

While we cant rule out that oceanic conditions dif-fered during the Little Ice Age 500 years ago, the factthat cod fishing was the major source of livelihood inIceland, the Faroes, and all along the Norwegian coastup to Finnmarken in the far north, it seems plausiblethat the spread of warm waters from the SubpolarFront (the northern branch of the Gulf Stream) had asimilar pattern to that of today. This in turn suggeststhat the Iceland-Faroe Front (IFF) assumed about thesame path then as now; the topography of the Iceland-

Faroe ridge almost certainly plays a major role in deter-mining its mean path. A hint at the long-term stabilityof the IFF might be found in a survey of salinity at 100m depth conducted almost 100 years ago (Helland-Hansen and Nansen, 1909), shown here in Figure 6.This early yet excellent example of the systematichydrographic survey technique developed by theNorwegians puts the IFF exactly where it is today(Hansen and sterhus, 2000). In this study the path ofthe front has a (weak) meandering pattern with a half-wavelength of about 70 km, i.e. comparable to thewhorls in Carta Marina. Figure 6 shows clearly thestriking contrast in salinity between the warm salinewaters south and cold fresh waters north of the

Iceland-Faroe ridge.Clouds cover the northeast Atlantic most of thetime, but when conditions permit satellites can meas-ure sea surface temperature (SST) with a thermal andspatial resolution of 0.1C and 1.1 km, respectively.Further, with only modest loss of small-scale detail,one can composite a number of images to removemuch of the cloud coverage. The left panel in Figure 7

circle route passing close to Iceland westbound andstraight east from Cape Farewell when eastbound.

The primary navigational tools in the late 1400s toearly 1500s consisted of the compass for direction andthe cross-staff to determine solar elevation. Thus ves-sels preferred to sail at constant heading or along aconstant latitude. They used the sounding line to meas-ure water depth, but the log line used to estimate speedthrough the water (and hence distance) had not yetcome into widespread use (Ellmers, 1999/2000). So faras is known, charts like the portolan charts of the

Mediterranean did not yet exist for these Nordicwaters, but the shippers (from shep-her, i.e. shipsmaster) had detailed notes about coastlines in theirrutter as these books were called in England (Waters,1958) or Seebuch in German (Ellmers, 2002). On deckmuch of the time the mariners must have been verykeen observers. They would notice changes in watertemperature, currents, wind direction, waves andswell. They would notice differences in the color ofwater and marine life between warm waters from theNorth Atlantic Current and cold waters from north ofIceland. These observations of sea conditions becamepart of the knowledge base to help ensure that theywould reach their destinations safely.

It seems plausible that Olaus learned about theremarkable waters east of Iceland while visitingHanseatic ports, and perhaps especially on hisHamburg-Netherlands trip (Richter, 1967). Themariners may have told him about ice conditions,pools of cold water, winds and sea conditions, andabout the marine life; and given his evident curiosityhe would be one to ask. Perhaps what struck mariners

Figure 6. Salinity at 100 m depth. The sharp gradient insalinity east of Iceland indicates the path of the Iceland-Faroe Front at the time of the survey (Helland-Hansenand Nansen, 1909).


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seems fairly simple as in the left panel of Figure 7, atother times rather messy as in the right panel. Further,as Figure 6 indicates, the IFF extends below the surface,and in fact it extends to the bottom all along the north-ern slope of the Iceland-Faroe ridge. We might addhere that the difference in water properties across thefront (dense, cold water north, light, warm watersouth) leads to a substantial pressure difference across

the front that maintains a large transport of warmwater, ~3 to 4x106 m3s-1, along it from the North Atlanticinto the Norwegian Sea. The interested reader will finda very comprehensive discussion of the IFF in thepaper by Hansen and sterhus (2000).

The images of sea surface temperature also allowus to determine where surface fronts are most likely tobe found. From an analysis of twelve years of satellitedata, Belkin et al. (2003) show that the IFF leaves theeast Iceland coast near Eystrahorn at 6430N firsttowards the northeast and then southeast along thenorthern slope of the ridge between Iceland and theFaroes (Figure 8). This accords with Stefnsson (1972)who wrote that the front demarking the warm and coldwaters just offshore of Iceland migrates seasonally nomore than about 35 nautical miles (nm). From a navi-gational point of view the stability of the front mayhave been quite useful. Returning to Carta Marina, itseems that the mariners knew where to find the regionof contrasting waters, as indicated by the mean path ofthe whorls. But they also knew that they likely wouldbe traversing a variable field of warm and cold pockets

shows a one-week composite from May 2002, at thetime our seafarers would be approaching Iceland. Thecontrasting waters to either side of the IFF show upclearly at all times, and in spring can exceed 5C intemperature. Sometimes the temperature contrast canappear very sharp, suggesting a narrow front, at othertimes the front appears to be rather broad. In thisimage the IFF shows up as a well-defined meandering

front, not unlike the salinity front in Figure 6. The rightpanel shows SST on April 18 2003, in early spring. Onlyvery rarely does one get such a clear view of the NEAtlantic in a single snapshot. The IFF close to Icelandheads almost straight NE, but after turning SE becomeshighly convoluted, breaking up into numerous eddiesincluding a very cold but elongated one halfwaybetween the Faroes and Iceland. The SST images indi-cate that shippers approaching Iceland will experiencelarge variations in temperature, on scales of severaltens to a hundred kilometers. After crossing the warmShetland Current in the lower right of Figure 7, contactwith the cold waters would seem quite bracing to sea-farers from the continent!

A detailed analysis of the front and its meanderingstatistics lies beyond the scope of this study, and weshould be careful not to inter-compare observationswith the whorls in Carta Marina too closely. But theSST images give us an insight to what sailors 500 yearsago might have experienced. They reveal striking con-trasts in temperature across the IFF and warm and coldeddies north and south of the front. At times the region

Figure 7. Two satellite images of sea surface temperature. The left panel shows a 7-day composite (May 5-12, 2002) ofonce/day high resolution AVHRR images with 1.1 km spatial resolution. Black areas without a white border have no data dueto persistent cloud coverage. The right image shows a single snapshot of SST from April 18, 2003. The expanded color rangeemphasizes the temperature variations in the frontal region.


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waiting for suitable winds. (By way of comparison,Columbus made his 3100 nm transit from the Canariesto San Salvador in only 33 days, a mean speed of 4knots, but then he had the benefit of the very steadyNE trade winds.)

The IFF delineates the boundary between thewarm salty waters of the North Atlantic and the coldwaters flowing east along the north coast of Iceland.Such a strong temperature contrast can only be main-tained by means of a persistent flow towards and alongthe front. It seems likely that navigators of the timewere aware of such mean flows. First, the distributionof the whorls point to an eastward spreading. Second,given the large size of the merchant fleet approachingIceland each year, it seems likely that they wouldnotice which routes tended to require the least transittime. Keeping in mind the number of vessels that visit-

ed Iceland each year, century after century, it seemsself-evident that the seafarers had extensive knowl-edge about the best ways to sail to Iceland. Even a 13th

century text, Konungs skuggsj (Anon., 1976), discuss-es in detail when not to head out on the high seas andwhy, the presence of maelstroms (whorls?), and exis-tence of wind-accelerated surface currents.

Navigational CluesGiven the limited navigational capabilities 500

years ago, vessels were not likely to notice changes incourse made good unless the currents were strongenough for long enough that a change in latitudecould be detected. On the other hand changes incourse might be easier to detect between Iceland andthe Faroes, and especially close to Iceland where thesnow-covered 1000 m high eastern mountain range onclear days might be visible 50 nm out to sea. Theymight also have noticed that as they left Iceland thefront stayed in about the same place close to shore,but farther to east it could vary in position such that

on their journey to Iceland, hence the whorls with ascale of roughly 100 km. We should not make too muchof the size comparison; nonetheless, given the similar-ity of scale, the agreement in location, Olaus evidentdesire to be informative, and the fact that he calls the

map Carta Marina all suggest that he drew the whorlsthere for a specific reason. Further, the band of whorlsextends only to a point north or northeast of the Faroes,they do not continue east towards Norway nor northinto the Norwegian Sea. This may be significantbecause the Iceland-Faroe Front turns northeast andweakens in thermal contrast. And perhaps just asimportant, Olaus does not draw whorls like these any-where else in Carta Marina.

Coherent structures such as an eddy or meanderrequire a circulation or flow to maintain their structurefor any length of time. This means our mariners alsoshould have observed currents or changes in currentsas they sailed towards Iceland. How large are thesecurrents, and could the mariners have detected them?This seems likely. First, as mentioned earlier, theKogge and the larger Holk were unlikely to exceed 5knot speeds and then only with a favorable tailwind.The 1000 nm transit from Germany to Iceland tookroughly one month according to Baasch (1889). Thistranslates into a mean speed of 1.5 knots, not a verylarge speed, and only twice this if hove to half the time

Figure 8. Long-term (1985-1996) frequency of occur-rence of SST fronts in spring (April-June) in the Iceland-Faroe-Shetland region, based on twice-daily 9-km resolu-

tion AVHRR SST images from the NOAA satellitesprocessed with the Cayula-Cornillon algorithms forcloud screening and front detection. The color scaleshows the percentage of the total cloud-free time that a

given 9 km x 9 km pixel contained a front. This picturewas kindly provided by Igor Belkin (see Belkin et al.,2003 for further information).

Figure 9. An example of a surface front as might be seenby a mariner. The bright and dark bands reflect varia-tions in surface wave roughness due to converging anddiverging bands of water.


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will cause the vessel to rotate and point in a differentdirection as it passes through the shear zone, as indicat-ed in the lower panel. The heading change will dependupon the velocity difference across the shear zoneand the time required to traverse it. Typical maximumsurface currents in the IFF and eddies can range up to 2knots. This is not insignificant for a slow-moving ves-sel. Given a front where the velocity changes linearly,dv/dx, and that it takes a vessel T (seconds) to traverseit, the change in the vessels heading in degrees due tothe shear will be dv/dx x T x 57.3 (/rad). Assuming avelocity change of 0.5 ms-1 over 100 m (dv/dx = 0.005s-1) and a vessel speed of 2 knots such that it takes100 sto cross the front, the change in heading would be 0.005x 100 x 57.3 = 29 or almost three points on the 32 pointcompass rose in common use in those times. Thiswould be very apparent to the helmsman. As ourancient sailors crossed through what they perceived tobe pools of cold water, sometimes bounded by regionsof sharp change in velocity, the step to representingthese as whorls in Carta Marina does not seem far-fetched. That some are larger than others would also

not surprise, hence the variation in size of the whorls inFigure 5.

Ocean color varies with water type. Generallyspeaking the warm waters from the North Atlanticwould have a somewhat deeper blue color than thosefrom the cold East Iceland Current. Stefnsson (1972)mentions that the frontal zone southeast of Iceland isoften very sharply defined. Marine life would alsohave a different character and might be particularlyactive along the front itself due to upwelling of nutri-ent-rich waters from below. Such waters can support ahigh production of phytoplankton, grazing zooplank-ton, and so on up the food chain. On a cruise to the IFFregion this summer, we saw numerous slick lines due

to organic material that reduces the surface tension andhence the roughness of the surface. Also, on one occa-sion we passed through an assembly of pilot whaleseasily numbered in the hundreds, a truly extraordinarysight. The frolicking whales around us made themarine fauna in Carta Marina seem very believable.We have no information on how our ancient marinersexperienced and recorded their observations of cur-rents and marine life, but we can be sure they woulduse everything they saw as best they could to improvetheir navigational capability and safety at sea. The inci-dences where a vessel did not find Iceland appear tohave been few (Baasch, 1889).

There exists one other map (that we know of) that

possibly portrays thermal patterns or whorls in theocean. It is located at the Bibliotheque Royale inBrussels, Belgium (Codex Ms 14887). Most likely drawnby a Jan van Kriekenborch (or someone in his work-shop) in 1485, it is based on a map of Scandinaviaincluded in a production of Ptolemys Geography pub-lished by Nicolaus Germanus in Ulm in 1482. SincePtolemy did not know the northern limits of the old

sailing along a constant heading the temperaturescould vary widely. Keen observers as they undoubted-ly were, they would also notice changes in surfacewave structure and perhaps velocity as they crossedsurface fronts.

Slick lines signify a surface front and often wavepatterns will have a different character to either side,shiny on one side and rough on the other. Figure 9shows a picture of such a front near the Laurentianchannel across the continental shelf east of Nova Scotia.At a distance the difference in surface roughness showsup clearly (the dark and shiny zones) whereas close upone can see concentrations of surface flotsam due toconvergent flows at the surface. Such fronts may sepa-

rate waters with different properties such as tempera-ture and color. Figure 10 (top) shows the wake from aresearch vessel after crossing the North Wall of the GulfStream. Notice how the wake does not continue straightback but is cut off and shifted to the left by the jump invelocity at the surface. A slow moving holk would notleave a long wake, but it very likely would be affectedby the shear as it crosses a front. Specifically, the shear

Figure 10. Top panel shows a ships wake being cut off bya velocity front at the surface. Bottom panel shows how aslow-moving ship might behave in such a front: the shearwould cause the vessel to turn to port, but this would benoticed by the helmsman who would then put the rudderto starboard to recover the original heading.


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SummaryCarta Marina and the companion HISTORIA by

Olaus Magnus brought the northern countries to theattention of Europe at a time of rapid development from

a medieval, rather provincial frame of mind to a keenawareness of worlds far beyond the Mediterranean. Hebrought to Europe a vivid and detailed description ofthe geography and peoples of the Nordic countries.Thus his Carta Marina can be studied on many levels.Its fascinating to discover how the more you probe themap the greater the wealth of information to emerge.

The whorls drawn in the ocean exemplify thisrichness of information embedded in the map. Theirlocation, size and spacing seem too deliberate to be apurely artistic expression. Instead, we suggest that theyrepresent what we today call the Iceland-Faroe Front, ameandering front that separates the warm waters flow-ing north between Iceland and the Faroes from the cold

waters flowing east and south around the northerncoast of Iceland. The 5C temperature differencebetween these two waters can often appear as sharpchanges in sea surface temperature along the meander-ing front. Unquestionably mariners were keenly awareof these variations in temperature, and likely noticedvariations in surface currents as well. However, in thosedays they had neither the instruments to quantify these

hemisphere (Scandinavia is limited to two islands,Scandia and Thule), geographers composed new mapsto correct those of Ptolemy. This particular map ofScandinavia, which is the last of four additional maps inthe Ptolemy Geography in The Library of Raphael de

Marcatellis (Derolez, 1979), clearly shows Scandinaviaas a peninsula although not yet fully developed in thenorth-south direction. But what interests us here is thefact that the map gives the ocean a physical presence inthe form of gently waving blue lines. This, in itself, israther unusual, but what is even more remarkable, thelines turn into whorls in the north, to the right of Icelandin the upper left corner (Figure 11). Unquestionably thebright blue lines and whorls have enormous estheticappeal, but it is tempting to think that the whorls have amore than decorative purpose, for here, as in CartaMarina, they do not populate the map as a whole, butcluster in a particular area corresponding to that of theIFF. We do not know if the original map by Nicolaus

Germanus included these whorls. Living in themonastery of Reichenbach near Regensburg in southernGermany before moving to Italy, he may not have hadmuch contact with the Hanseatic League, but vanKriekenborch, living in Ghent, a port and manufactur-ing city in Belgium, could very well have had contactwith mariners and heard their descriptions of sailingconditions in the northern North Atlantic.

Figure 11.Map (original size 0.651 x 0.450 m) of Scandinavia in Ms 14887, Bibliotheque Royale, Brussels, Belgium. From anno-tations in Ms 14887 a likely date for the map is 1485 (Reproduced with permission from Bibliotheque Royale, Brussels, Belgium.)


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Scandinavia in Figure 11. Most likely from 1485.Derolez, A., 1979: The library of Raphael de Marcatellis,

Abbot of St. Bavons, Ghent, 14371508. E. Story-Scientia Ltd. Ghent, 335, 4853.

Ellmers, Detlev, 1999/2000: Zur Herkunft des sptmitte-lalterlichen Schiffstyps Holk. Zeitschrift fr

Archologie des Mittelalters, 27/28, 119128.Ellmers, Detlev, 2002: English summary of Old Sea

Book from the 14th century, (Personal communica-tion).

Granlund, John, 1951: The Carta Marina of OlausMagnus. Imago Mundi 8, 3543.

Grape, Hjalmar, 1970: Olaus Magnus forskare moralistkonstnr. Propius Frlag, Stockholm, 245 p.

Helland-Hansen, B. and F. Nansen, 1909: TheNorwegian Sea: its physical oceanography basedupon the Norwegian researchers 19001904. Reporton Norwegian Fishery and Marine Investigations, 2(2),390 p.

Hansen, B. and S. sterhus, 2000: North Atlantic-NordicSeas exchanges. Prog. Oceanogr., 45, 109208.

Knauer, Elfriede Regina, 1981: Die Carta Marina des OlausMagnus von 1539. Ein kartographisches Meisterwerkund seine Wirkung. Gttingen Gratia-Verlag Heft10, 151 p.

Lamb, H.H., 1977: Climate, present, past and future.Volume 2: Climatic history and the future. Methuen &Co. Ltd., 835 p.

Magnus, Olaus, 1555: HISTORIA DE GENTIBUSSEPTENTRIONALIBUS. ROMA. Translated into theSwedish 19091925. Reissued in 1976 and in pocket2001. Gidlunds Frlag, 1087 p.

Nordenskild, A.E., 1889: Facsimile Atlas to the earlyhistory of cartography. Stockholm, Sweden.Reissued by Dover Publications in 1973.

Richter, Herman, 1967: Olaus Magnus Carta Marina 1539.

Lund (Lychnos-Bibliotek 11,2). Almquist & Wiksell.Stockholm, 195 p.

Stefnsson, U., 1972: Near-shore fluctuations of thefrontal zone southeast of Iceland. ICES Rapp. P.-v.,162, 201205.

Waters, D.W., 1958: The Art of NAVIGATION in Englandin Elizabethan and Early Stuart Times. Yale UniversityPress, New Haven, 696 p.

observations nor the means to express them. Againstthis backdrop or lack of tools of expression, the whorlsin Carta Marina appear to be a surprisingly accuraterepresentation of todays meandering front and theintermittent formation of warm and cold eddies toeither side. The fact that the eddies appear as an east-ward extension of sea ice north of Iceland could alsoindicate that Olaus envisioned his whorls as pools of

melted ice. Sailing very close to the waters, these ther-mal contrasts must have been well known to earliergenerations of Iceland farers including Norse Vikings,the first major settlers of Iceland. The whorls in theBrussels map might possibly be interpreted in a similarlight. But at present we do not know how to developthis conjecture further. Our reading of the Carta Marinaliterature has not brought us any information thatmight give insight or substantiation to the meaningof the whorls. Indeed, the significance of the whorlsapparently got lost rather quickly. When the mapwas reissued as a copper print in 1572 by AntoineLafrre, everything in it, including the ships and marinefauna, was faithfully reproduced, but the whorls were

omitted!

AcknowledgementsWe thank Prof. Teddy Brunius and Map Curator

sa Henningsson, both at the University of Uppsala,for enlightening discussions and helpful commentsabout Carta Marina. Special thanks are due Dr.Charlotta Scheich at the Catholic University ofLouvain, Belgium for help in researching the BrusselsMs 14887. Drs. Elke Burkhardt and Olaf Boebel at theAlfred Wegener Institute provided generous assistancein locating several books and references. Dr. JohanBlindheim at the Marine Research Institute in Bergenbrought the book Konungs skuggsj to our attention.

The comments from reviewers Igor Belgin and BogiHansen were very much appreciated.A colored version of Carta Marina can be viewed at

http://bell.lib.umn.edu/map/OLAUS/carta.html.

ReferencesAnon, 1976: Kongspegelen. Norwegian translation of

Konungs skuggsj, a 13th century book of good man-ners and conduct written in the form of a dialoguebetween a king and his son. Det Norske Samlaget,Oslo. 228 p. The book is also available in English asThe Kings Mirror, 1917. American-ScandinavianFoundation.

Baasch, Ernst, 1889: Forschungen zur hamburgischenHandelsgeschichte. 1. Die Islandsfahrt der Deutschen.Hamburg, 140 p.

Belkin, I.M., P. Cornillon, D. Ullman, and Z. Shan, 2003:Global pattern of ocean fronts from Pathfinder SSTdata: I. Atlantic Ocean. To be submitted toJ. Geophys.Res.

Codex Ms 14887. Manuscript from the library ofRaphael de Marcatellis which includes the map of

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