settlement until 1894 - at Angmagssalik. Even allowing for the inferior shipping of earlier times compared with

modern means of transport and communication, the ice record looks formidable. More recently, in the I ~ O S , expeditions there met with little trouble from ice but in 1968 and 1969 it has had to be taken much more into account. It will be interesting to see how the situation develops in the next few years.

ACKNOWLEDGEMENTS

My grateful thanks are due to Derek Fordhani (Leader), and Michael Tuson, members of the University of London, London Graduate Mountaineering Club, East Greenland Expedition 1968-69, for their generous help with the information concerning the ice off east Greenland in August 1969, and to Jenny Fordhain who supplied the photographs.

REFERENCES

CLARKE, P. C. JOHNSON, A. I . KRISTJANNSSON, L.

LAMB. H. H

MARSHALL, N. MURRAY, H. and

MOFFITT, €3. J .

1969 ‘The Shetland Blizzard 1968. Weather, 24 (6), p. 241 1960 The summer of 1959. Ibid., 15 (6), pp. 185-196 1969 The ice drifts back to Iceland. New Scientist, 41 (639).

1965 The winter of 1963-64. Weather, 20 (6), pp. 201-202 1967 Britain’s changing climate. Geographical Journal, 133,

1968 lcefields around Iceland. Weather, 23 (9). pp. 368-376 1969 Monthly patterns of the quasi-biennial pressure

oscillation. Ibid., 24 (10). pp. 382-389

pp. 508-509

PP. 445-466

WEATHER AND ICE OBSERVATIONS OF THE BRITISH TRANS-ARCTIC EXPEDITION 1968-9

By R. M. KOERNER Department of Energy, Mines and Resources, Ottawa

ETWEEN 21 February 1968 and 29 May 1969 four men under the leadership B of W. W. Herbert traversed the Arctic Ocean between Barrow, Alaska and a small island off the coast of Spitzbergen (Fig. I). The expedition used four sledges and dog teams and was supplied by air-drops by the U.S. Naval Arctic Research Laboratories in the early part of the journey and then by the Canadian Armed Forces. The author was glaciologist on the expedition. This article is an account of the weather conditions and scientific observations recorded on the journey. The results shown are based on a preliminary analysis of some of the data.

The Arctic Ocean is covered throughout the year by a constantly moving canopy of ice. Differential movement of the ice causes frequent fracturing. Ice forming in the fractures is forced into pressure ridges when the floes on either side come together again. As a result, ice thickness varies from a maximum of

Fig. I . Route across the Arctic Ocean. The broad arrows show the two main directions of ice drift. The Pacific Gyral lies on the U.S.-Canadian side of the North Pole and the Trans-Polar Drift Stream on the Russian side. The BTAE drifted from position A to position B between July 1968 and February 1969

about 40 m in pressure ridges to zero in open water. Ice growth in winter under the floes' that circulate undisturbed for a few years is balanced by melting in summer; the thickness of these floes is about 3 m. Ice movement depends on ocean currents, wind velocity and the roughness of the upper and lower surfaces of the ice. While the expedition was camped from July 1968 to February 1969 the camp-floe drifted from 813"N, 165.5"W to 85-5"N, 140.0'W giving a net drift of 2-4 km a day. The actual drift was greater than this as our drift path meandered a lot in the winter. Drifts of up to 10 km a day were measured in storms and daily drifts of 3 to 4 km were common.

Because of the nature of its surface the Arctic Ocean has no shipping routes across it. Commerical air routes cross it and nuclear submarines have traversed it beneath the ice, but before the British Trans-Arctic Expedition no complete surface crossing had ever been accomplished. Nansen was the first to conduct detailed scientific observations in the Arctic Ocean and his work remains a classic in the annals of scientific and geographical exploration (Nansen 1897). Nansen, sledging over the ice, travelled to a record north position and his ship, the Fram, drifted with the ice for 3 years until it broke free into the Greenland Sea. Other ships have been frozen into the ice since then, notably Amundsen's Mazld and the Russian Sedov and scientific observations have been conducted from them. Since 1937, however, when the Russians set up a drifting station at the North Pole, a large part of scientific research in the Arctic Ocean has been conducted from semi-permanent stations set up on the ice. The Russians

have supported several ice-floe stations (the British Trans-Arctic Expedition passed within 60 km of the Russian Station NP 17 in April 1969) whereas the U S A . have generally preferred the greater stability of the occasional 30 m thick ice-island. Airborne surveys, mainly by the Russians, have greatly increased the density of scientific observations on the Arctic Ocean (Fletcher 1968). Since the 1950’s nuclear submarines of the U S . Navy have recorded, among other things, ice draft and ocean bottom profiles (Lyon 1963). US. air reconnaissance flights routinely record weather and ice conditions (Wittman and Schule 1966).

As the British Trans-Arctic Expedition aimed to cross the entire Arctic Ocean the glaciological programme was designed to take advantage of such a long transect by measuring changes in the ice cover in both space and time.

Fig. 2 . New pressure ridge

WE AT H E R

Synoptic weather observations were made throughout the expedition and each day one observation was transmitted by radio to Barrow, Alaska. From there the expedition radio operator transmitted the observation to the British Meteor- ological Office where it entered the world meteorological circuit.

In addition to these observations, a micro-meteorological programme was conducted during the expedition’s static period from July 1968 to February 1969. Wind, temperature and humidity profiles were measured between the surface and 5 m. All-wave radiation was measured on a Packard-Bell radio- meter, and short-wave radiation on two Lintronic dome solarimeters. Tem- peratures in the ice were measured with thermistors.

Continuous cold and darkness in winter increased the difficulty of taking scientific observations. Ordinary electric cable breaks at low temperatures and special low-temperature materials had to be used. Hoar frost frequently formed

220

Fig. 4. Old hummock: the rule is z& m long

on sensing elements of instruments and could not be brushed off. Drifting snow also penetrated some instruments and filled them with hard-packed snow. Instru- ments therefore required frequent attention. The radiometer transducer plate was especially susceptible as it had to remain exposed continuously. Hoar frost deposit could not be safely brushed off the transducer plate so the whole instru- ment had to be brought inside to melt and evaporate the deposit. The cups

221

Fig. 6 . Old floe in the Trans-Polar Drift Stream

on the aneiiioiiieters occasionally filled with drift snow and recorded anomalously low wind speeds. On occasions when the ice fractured near the camp, water vapour from the open water sublimed on to the instruments. Finally, one problem, peculiar perhaps to the expedition, was that any dogs getting free from the dog-spans showed a very low regard for scientific equipment!

222

THE MELT SEASON

The ' warm-season' effect on the ice lags behind the return and rise of the sun. Cloud cover increased in May (Table I, p. 224) when white-outs became common. These develop under overcast conditions and are situations where all contrast disappears from the landscape; with no horizon there is a dimensionless view where not a single feature can be seen. In conditions like these one can drive over isolated hummocks, half-way up huge pressure ridges and into impassable areas without being aware of their existence until the sledge jars to a halt.

In May, with rising temperatures and increasing elevation of the sun, open water exposed by fracturing no longer freezes over but there is no sudden, dramatic summer break-up of the ice-cover in the central Arctic Ocean. As far as could be determined by casual observations, fracturing continued at the same rate from spring into summer but, as ice no longer formed in the fractures, the percentage of open water gradually increased. Surface travel was therefore slowed down and in late June, after the snow-cover had been reduced to slush and melt pools formed, camp was made for the summer.

The snow cover had completely melted, except in a few deep drifts, by the second week in July and for the rest of July and most of August ice melted froin both the upper and lower surfaces of the floes. The surface of the entire central Arctic Ocean is a t 0°C for most of July and August and the weather over this period is remarkably uniform. In July 1968, the absolute range of tem- perature was only 4 deg C and often the temperature varied less than 2 deg C for periods of several days. There were no strong temperature inversions between the surface and a height of 4 m and the gradient was usually less than 0.25 deg C per metre. The relative humidity a t I m was generally above go per cent and visibility for 45 per cent of the observations in July was less than 800 m. In July and August, cloud cover, which averaged 7 oktas, was usually in the form of very low stratus. Rain and drizzle were common (Table I) and a total of 4-0 cm of rain fell.

THE FREEZING SEASON

Ice did not begin to grow under thick floes until December, but freezing of the exposed ocean surface continued from September until early May. During September cloud-cover began to decrease and visibility to improve. The temperature dropped from September to March, the coldest month. By December, however, a characteristic winter weather pattern of clear skies, good visibility and low temperatures had set in. During the winter, the weather was clear enough for travelling around the local area on all except 7 or 8 days. The expedition records (Table I) show no significant seasonal variation of wind speed, and storms occurred in every month. Wind speeds, even in storms, were low and the highest recorded wind speed was 40mph in July. As a result, blowing snow was uncommon although low drifting snow occurred on an average of one day in five.

TAULC I Summary of the nleteorologlcal log of the Britlsh Trans-Arctlc ~ _ _ ~- . -~ ~~

Temp ("C) wind vis (miles) incan max in111 direction speed <24 24710 > I 0

(knots) yo total ~ - _ ~ _ - _ _ _ - - _ _

Feb* -3.2 -23 -41 EN E 6 0 0 I00

April -e7 -16 -41 E 7 3 6 91

June - 3 + 2 - 9 wsw 8 41 46 I3 July

Sept - 8 0 - 2 2 ESE & 7 55 31 11

Oct -18 - 6 -34 SSE 9 38 28 33 No\ -31 -17 -39 W 8 4 33 63 Dec -36 -15 -44 WNW 9 7 37 56 Jan -37 -25 -44 ESE 7 a 16 76 Fch -36 - 2 1 -47 WNW 7 4 27 69 March -39 -29 -47 SSE 6 I 2 6 $2

May - 9 0 - 2 1 8 45 18 37 June* - 4 - 1 - 9

Maich -26 - 9 -42 ESE 7 I 2 26 62

1May - I 0 0 - 2 8 ssw I0 31 40 29

+ I + 3 - 1 ssw 8 75 10 I5 2 2 1 i 2 - 5 ssw 8 61 I7 - Aug

WNW

April -26 - 7 -39 - 8 26 6 6# -

7 - -- ~ _~ _ _ __ _ _ _ _ _ _ _ ~ _ _ _ _

*lhe avcragcs for February 1968 and June 1969 are based on observatrons on 7 days and 8 days

PRECIPITAlION

Between latitudes 72'" and ~ I " N , snow accumulation on the floes was measured a t 31 locations by probing to the underlying ice surface. Snow densities were measured to determine the water equivalent. Between latitudes 72"N and 77'N, the mean snow cover (corrected to include precipitation along the traverse) was 11 g/cm2 and between 77"N and 81"N was 8 g/cm2, while the mean snow density was 0.301 g,"cnP. This decrease in thickness of the snow- cover north of 77"N is significant a t the 0.1 per cent level. As wind removes snow from the floes and deposits it in open water or in badly broken areas these figures do not represent the total precipitation fm the September to June period. After adding the 4 g/cm2 of rain that fell in July and August 1968 it can be seen that precipitation in the central Arctic Ocean for the period September 1967 to August 1968 was greater than 12 g,'cm2.

The snow depth increased again between 84"N, 3o'E and Spitzbergen; between 84"N and 82"N along longitude 30"E the snow-cover was 12 to 13 g,/cin2 while off the shore of Spitzbergen it was greater than 15 g/cm2. The deeper snow-cover at each end of the traverse is probably related to greater cyclonic activity there, for depressions generally follow tracks around the periphery of the Arctic Ocean (Wilson 1963, pp. 268-9).

During the winter, snow accumulation was measured every month showing that 75 per cent of the winter snow-cover accumulated between the beginning of September and the middle of October. Deflation of the snow-cover occurred in storms when snow was moved into new fractures around the station area. Although snow fell on inore than one day in two during the winter, 75 per cent was in the form of minute columns or bullets (where the volume of each column

Expedition February 1968 to June 19%

cloud precip. drifting total 1 m h (days) snow (oktas) yo total (days)

3 36 14 50 ? ? Feb* 4 64 9 27 '3 7 March 3 14 2 84 14 6 April 6 69 9 22 25 5 May 6 76 11 13 9 3 June 7 74 I7 9 16 I July . 7 66 25 9 23 2 Aug 7 74 15 1" 19 I4 Sept

6 76 13 11 4 69 3 28 5 54 13 33 4 30 33 37 4 53 16 31 2 6 44 50 4 56 7 37

7 85 5 10

6 81 7 12

16 I3 Oct

21 5 Jan

15 7 Nov 22 I1 Dec

14 6 Feb

I 3 6 April 6 4 March

I4 2 May June*

respectively.

was about 3 x I O - ~ mm3) and they added very little depth to the snow-cover. Most of the snow-cover accumulated in September when 75 per cent of the snow consisted of stellar crystals. Precipitation of the latter type occurred in May and June also.

ICE PRODUCTION AND DECAY

During July and August 1968,40 to 45 g/cm2 of ice melted from the surface of the multi-year floe on which the expedition was camped, and about 10 g/cma from its base. More ice than this melted from younger floes nearby where several holes, up to about 30 m in diameter, were melted through the ice. These holes, covered by thin ice and snow in the autumn, form dangers to the surface traveller. In multi-year floes, most of the salt has been removed from the ice during the process of solidification from sea water. Thus, the ice and snow on melting produce fresh-water which drains into fractures. The fresh-water (0.2 parts per thousand of salt) is less dense than sea-water (29 parts per thousand) and stays at the surface to provide a ready supply of drinking water. This surface water froze in late August and early September to form a cover very similar in structure to lake ice. Fracturing and pressuring of the ice in September mixed the surface fresh-water with the saline water underneath to bring the surface water back to a salinity of 28 to 29 parts per thousand by early October.

Althdugh ice formed in open water in September, growth at the base of multi-year floes was not detected until late December. Amounts too small to be detected by drilling may have grown under the non-ponded parts of the multi- year floes. However, ice accretion under floes where there were extensive ponds on the surface was inhibited by the isothermal layer of pond water. Sur-

face ponds were completely frozen by mid-December but penetration of these ponds by drilling in November released considerable pressure which forced water up through the drill-hole to a height 2 m above the ice surface. Water in the ponds, initially suitable for drinking (0.2 parts per thousand) increased in salinity to 10 parts per thousand due to the freezing process, when fresh-ice forms and leaves behind an increased concentration of salt in the water. Ice growth in the early months of winter was therefore restricted to open water exposed by fracturing, and to the underside of thin floes and in ponds.

1 ABLL 2 . ~. ICC growth (in cm) in the central Arctic Ocean, September 1968 to February 1969

Month Sept Oct Nov Dec Jan Feb

from open water, 10-18 21 ? ? 26-36 32

from open water, 54 56 GZ ? 54 71

zoo to 300 cin thick -5 0 0 5 I 0 ?

first 5 days

first 30 days

floe, monthly rate __

The rate of ice growth in new fractures is shown in Table 2. In January, ice growth in open water for the first five days after exposure to the atmosphere is 16 to 22 times greater per unit area than under floes 2 to 4 ni thick. Therefore, if during the winter months only 0.5 per cent of the ocean cover is open water 10 per cent of the ocean's ice growth will occur there. Ice growth in open fractures can form 1-5 in of' ice before the melt season begins, even if the fracture opens as late as January. Over the same period ice growth under a multi-year floe would be of the order of 0.4 in (Untersteiner 1964). As fracturing plays such an important part in the process of ice production in the Arctic Ocean it means, in terms of climatic change, that increased atmospheric cir- culation associated with a northward migration of cyclone paths, while it might slightly lower the growth rate under floes, could, a t the same time, increase ice production by causing more fracturing in winter.

During the winter of 1968 to 1969, the local area around the hut was traversed daily to estimate the amount of fracturing and ice production. Some differential movement was observed on approximately one day in four. In late December 196S, fracturing and divergent movement created immense polynyas so that 20 per cent of a local area measuring 10 kni by 5 ltm was open water. By late February the ice in these formerly open areas was over I ni thick. Even if they closed a few days after the camp was abandoned, ice growth in the polynyas would have contributed at least a third of the winter ice growth in the local area.

CHANGE OF TOPOGRAPHY I N TIME A N D SPACE

During the summer, melting smooths the landscape, so to determine the magnitude of this effect on ice-forms a profile was levelled across a floe in July and again in August. Ridges and hummocks formed the previous winter (Figs. 2

and 3 p. 220) were found to have undergone the greatest change due to melting (Table 3 ) . Old hummocks (Fig. 4) melted less than level areas due to a higher

226

albedo on the higher, better-drained ice (Table 4). The highest melting rate was in ice under ponds but as the pond-water refroze the following winter the change of surface level there was small and similar to that of old hummocks (Table 3) . The measurements suggest that surface irregularities may be self- perpetuating. If this is so then as a floe ages it will become more hummocked simply because hummocks and ridges may form any time the floe fractures and

TABLE 3. Ice ablation, lowering of the surface on a multi-year floe. Measurements are expressed as percentages of lowering of level areas where surface ablation of ice July, August 1969 was 40-45 g/cm2.

new ridge 2 60 old hummocks 69 level areas I 0 0 ponds, ice surface 146 ponds, water surface 57

TABLE 4. The albedo of Arctic Ocean pack-ice, measurements taken on the British Trans- Arctic Expedition, July and August 1968

Multi-year floe old hummock old, drained pond-area recently drained pond-area pond level, clean area dissected, dirty area

pond (almost through to sea) lead (open water)

first-year floe pond

0.74 0.57 0.51 0.41 0.65 0.62 0.24

0.08 0 '20

will accumulate with time. Many floes with large, smooth, old hummocks were seen in the Pacific Gyral (Fig. 5 , p. 222) where floes may circulate for over 20 years. In the Trans-Polar Drift Stream, however, where most of the ice drifts out of the Arctic Ocean within 5 years of its formation, hummocks were usually slightly angular, indicating that the floes of which they were part were only a few years old (Fig. 6) . The change in topography indicated that the expedition entered the Trans-Polar Drift Stream at approximately 88"N, 150"W.

Ridging of ice is usually caused by a sequence of three processes: I. fracturing, 2.

3. underneath the floes on either side (Fig. 2).

ice forming on the open water, closure of the fracture, thus building up the new ice both on top of and

After fracturing, the floes on either side of the fracture move relative to each other so that the irregularities are offset (fracturing always produces a very jagged break). If the fracture closes before very much new ice has formed the sharp, protruding irregularities bear all the force of the pressure and break to form isolated hummocks (Fig. 3) . Approximately 5 to 10 ridges a mile were crossed between the North Pole and Spitzbergen where a ridge count was made. Most of the ridges in the central Arctic Ocean were I to 2 m high and the slabs of ice forming them were usually less than 40 cm thick. From this, and the growth rates given in Table 2, we can see that most fractures close within about a week of forming.

Pressure ridges, hummocked ice and new ice must all be included in any calculation of the average thickness of the ice-cover. The modal value of the

thickness measurements taken mostly through ponded areas on multi-year floes was between 2 and 3 m (Fig. 7), whereas an average thickness based on a preliminary analysis of a small part of the ice log data was 4.17 m. The 2 to 3 m figure may be useful, if similar measurements are repeated some time in the future, to detect any climatic changes. However, the figure of average thickness is more important in ice-budget considerations (Wittman and Schule 1966).

I'ig. 7. Ice thickness measurements taken on the British Trans-Arctic Expedition, mainly through pontled ;irciis of multi-ycar floes

e

. .~ 200

ICE rt4lCINE85 I L M I

Ridges, although often a problem to cross, cost the expedition less time than fractures which were usually skirted as boating across them took at least 8 hours. Generally, high ridges and wide fractures were sufficiently discontinuous to make it worthwhile following along them to find an easy route across or around.

ACKNOWLEDGEMENTS

The observations in this paper were collected while the author was a Lever- hulme Research Fellow. The author would like to acknowledge the cooperation of the Canadian Armed Forces, the U.S. Naval Arctic Research Laboratories in Barrow, Alaska, and the expedition radio-operator and coordinator in Barrow, Sq. Ldr. 17. Church. Meteorological equipment was loaned by the U S . Weather Bureau, The Canadian Department of Transport, and the British Meteorological Office. The data are now being analysed at the Polar Continental Shelf Project, Department of Energy, Mines and Resources, Canada.

REFERENCES

I"LETCHER, J. 0. I908

L Y O N , W. K. 196.3

NANSEN, F. 7897

UNTERSTEINER, N. 1964

WILSO~Y, H. I963

WITTMAN, W. I. and 1966 J . J. SCHULE Jr.

Origin and early utilization of aircraft-supported drifting stations. I n Arctic Drifting Stations, (Ed. Sater, J . E.) pp. 1-13

The submarine and the Arctic Ocean. Polar Record, 1963, 11 (751, pp. 699-705

Scientzfic Results of the Norwegian North Polar Expe- dition, Christiania, Norway

Calculations of temperature regime and heat budget of sea ice in the Central Arctic. J,. Geophys. Res.,

The atmosphere and above. In Proceedings of the Arctic Basin Symposium, October 1962. Arctic Institute of North America, June 1963, pp. 256-270

Commcnts on the mass budget of Arctic pack ice. In Proceedings of the symposium on the Arctic heat budget and atmospheric circulation (Ed. Fletcher, J. 0.) Santa Monica, Calif., The Rand Corporation. pp. 215-240

69 ( 2 4 , PP. 4755-4766

228