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SEA-ICE NOMENCLATURE

By J. M. WORDIE, M.A. (Cantab.), Lieut. R.F.A

During the voyage of the Endurance it was soon noticed that the terms being used to describe different forms of ice were not always in agreement with those given in Markham’s and Mill’s glossary in “The Antarctic Manual,” 1901. It was the custom, of course, to follow implicitly the terminology used by those of the party whose experience of ice dated back to Captain Scott’s first voyage, so that the terms used may be said to be common to all Antarctic voyages of the present century. The principal changes, therefore, in nomenclature must date from the last quarter of the nineteenth century, when there was no one to pass on the traditional usage from the last naval Arctic Expedition in 1875 to the Discovery Expedition of 1901. On the latter ship Markham’s and Mill’s glossary was, of course, used, but apparently not slavishly; founded, as far as sea-ice went, on Scoresby’s, made in 1820, it might well have been adopted in its entirety, for no writer could have carried more weight than Scoresby the younger, combining as he did more than ten years’ whaling experience with high scientific attainments. Above all others he could be accepted both by practical seamen and also by students of ice forms.

That the old terms of Scoresby did not all survive the period of indifference to Polar work, in spite of Markham and Mill, is an indication either that their usefulness has ceased or that the original usage has changed once and for all. A restatement of terms is therefore now necessary. Where possible the actual phrases of Scoresby and of his successors, Markham and Mill, are still used. The principle adopted, however, is to give preference to the words actually used by the Polar seamen themselves.

The following authorities have been followed as closely as possible:

W. Scoresby, Jun., “An Account of the Arctic Regions,” 1820, vol. i, pp. 225–233, 238–241.

C. R. Markham and H. R. Mill in “The Antarctic Manual,” 1901, pp, xiv–xvi.

J. Payer, “New Lands within the Arctic Circle,” 1876, vol. i, pp. 3–14.

W. S. Bruce, “Polar Exploration” in Home University Library, c. 1911, pp. 54–71.

Reference should also be made to the annual publication of the Danish Meteorological Institute showing the Arctic ice conditions of the previous summer. This is published in both Danish and English, so that the terms used there are bound to have a very wide acceptance; it is hoped, therefore, that they may be the means of preventing the Antarctic terminology following a different line of evolution; for but seldom is a seaman found nowadays who knows both Polar regions. On the Danish charts six different kinds of sea-ice are marked—namely, unbroken polar ice; land-floe; great ice-fields; tight pack-ice; open ice; bay-ice and brash. With the exception of bay-ice, which is more generally known as young ice, all these terms pass current in the Antarctic.

Slush or Sludge. The initial stages in the freezing of sea-water, when its consistency becomes gluey or soupy. The term is also used (but not commonly) for brash-ice still further broken down.

Pancake-ice. Small circular floes with raised rims; due to the break-up in a gently ruffled sea of the newly formed ice into pieces which strike against each other, and so form turned-up edges.

Young Ice. Applied to all unhummocked ice up to about a foot in thickness. Owing to the fibrous or platy structure, the floes crack easily, and where the ice is not over thick a ship under steam cuts a passage without much difficulty. Young ice may originate from the coalescence of “pancakes,” where the water is slightly ruffled or else be a sheet of “black ice,” covered maybe with “ice-flowers,” formed by the freezing of a smooth sheet of sea-water.

In the Arctic it has been the custom to call this form of ice “bay-ice”; in the Antarctic, however, the latter term is wrongly used for land-floes (fast-ice, etc.), and has been so misapplied consistently for fifteen years. The term bay-ice should possibly, therefore, be dropped altogether, especially since, even in the Arctic, its meaning is not altogether a rigid one, as it may denote firstly the gluey “slush,” which forms when sea-water freezes, and secondly the firm level sheet ultimately produced.

Land floes. Heavy but not necessarily hummocked ice, with generally a deep snow covering, which has remained held up in the position of growth by the enclosing nature of some feature of the coast, or by grounded bergs throughout the summer season when most of the ice breaks out. Its thickness is, therefore, above the average. Has been called at various times “fast-ice,” “coast-ice,” “land-ice,” “bay-ice” by Shackleton and David and the Charcot Expedition; and possibly what Drygalski calls Schelfeis is not very different.

Floe. An area of ice, level or hummocked, whose limits are within sight. Includes all sizes between brash on the one hand and fields on the other. “Light-floes” are between one and two feet in thickness (anything thinner being “young-ice”). Those exceeding two feet in thickness are termed “heavy floes,” being generally hummocked, and in the Antarctic, at any rate, covered by fairly deep snow.

Field. A sheet of ice of such extent that its limits cannot be seen from the masthead.

Hummocking. Includes all the processes of pressure formation whereby level young ice becomes broken up and built up into Hummocky Floes. The most suitable term for what has also been called “old pack” and “screwed pack” by David and Scholleneis by German writers. In contrast to young ice, the structure is no longer fibrous, but becomes spotted or bubbly, a certain percentage of salt drains away, and the ice becomes almost translucent.

The Pack is a term very often used in a wide sense to include any area of sea-ice, no matter what form it takes or how disposed. The French term is banquise de derive.

Pack-ice. A more restricted use than the above, to include hummocky floes or close areas of young ice and light floes. Pack-ice is “close” or “tight” if the floes constituting it are in contact; “open” if, for the most part, they do not touch. In both cases it hinders, but does not necessarily check, navigation; the contrary holds for Drift-ice. Loose open ice, where the area of water exceeds that of ice. Generally drift-ice is within reach of the swell, and is a stage in the breaking down of pack-ice, the size of the floes being much smaller than in the latter. (Scoresby’s use of the term drift-ice for pieces of ice intermediate in size between floes and brash has, however, quite died out). The Antarctic or Arctic pack usually has a girdle or fringe of drift-ice.

Brash. Small fragments and roundish nodules; the wreck of other kinds of ice.

Bergy Bits. Pieces, about the size of a cottage, of glacier-ice or of hummocky pack washed clear of snow.

Growlers. Still smaller pieces of sea-ice than the above, greenish in colour, and barely showing above water-level.

Crack. Any sort of fracture or rift in the sea-ice covering.

Lead or Lane. Where a crack opens out to such a width as to be navigable. In the Antarctic it is customary to speak of these as leads, even when frozen over to constitute areas of young ice.

Pools. Any enclosed water areas in the pack, where length and breadth are about equal.

METEOROLOGY

By L. D. A. HUSSEY, B.Sc., (Lond.), Capt. R.G.A

The meteorological results of the Expedition, when properly worked out and correlated with those from other stations in the southern hemisphere, will be extremely valuable, both for their bearing on the science of meteorology in general, and for their practical and economic applications.

South America is, perhaps, more intimately concerned than any other country, but Australia, New Zealand, and South Africa are all affected by the weather conditions of the Antarctic. Researches are now being carried on which tend to show that the meteorology of the two hemispheres is more interdependent than was hitherto believed, so that a meteorological disturbance in one part of the world makes its presence felt, more or less remotely perhaps, all over the world.

It is evident, therefore, that a complete knowledge of the weather conditions in any part of the world, which it is understood carries with it the ability to make correct forecasts, can never be obtained unless the weather conditions in every other part are known. This makes the need for purely scientific Polar Expeditions so imperative, since our present knowledge of Arctic and Antarctic meteorology is very meagre, and to a certain extent unsystematic. What is wanted is a chain of observing stations well equipped with instruments and trained observers stretching across the Antarctic Continent. A series of exploring ships could supplement these observations with others made by them while cruising in the Antarctic Seas. It would pay to do this, even for the benefit accruing to farmers, sailors, and others who are so dependent on the weather.

As an instance of the value of a knowledge of Antarctic weather conditions, it may be mentioned that, as the result of observations and researches carried out at the South Orkneys—a group of sub-Antarctic islands at the entrance to the Weddell Sea—it has been found that a cold winter in that sea is a sure precursor of a drought over the maize and cereal bearing area of Argentina three and a half years later. To the farmers, the value of this knowledge so far in advance is enormous, and since England has some three hundred million pounds sterling invested in Argentine interests, Antarctic Expeditions have proved, and will prove, their worth even from a purely commercial point of view.

I have given just this one instance to satisfy those who question the utility of Polar Expeditions, but many more could be cited.

As soon as it was apparent that no landing could be made, and that we should have to spend a winter in the ship drifting round with the pack, instruments were set up and observations taken just as if we had been ashore.

A meteorological screen or box was erected on a platform over the stern, right away from the living quarters, and in it were placed the maximum and minimum thermometers, the recording barograph, and thermograph—an instrument which writes every variation of the temperature and pressure on a sheet of paper on a revolving drum—and the standard thermometer, a very carefully manufactured thermometer, with all its errors determined and tabulated. The other thermometers were all checked from this one. On top of the screen a Robinson’s anemometer was screwed. This consisted of an upright rod, to the top of which were pivoted four arms free to revolve in a plane at right angles to it. At the end of these arms hemispherical cups were screwed. These were caught by the wind and the arms revolved at a speed varying with the force of the wind. The speed of the wind could be read off on a dial below the arms.

In addition there was an instrument called a Dines anemometer which supplied interesting tracings of the force, duration, and direction of the wind. There was an added advantage in the fact that the drum on which these results were recorded was comfortably housed down below, so that one could sit in a comparatively warm room and follow all the varying phases of the blizzard which was raging without. The barometer used was of the Kew Standard pattern. When the ship was crushed, all the monthly records were saved, but the detailed tracings, which had been packed up in the hold, were lost. Though interesting they were not really essential. Continuous observations were made during the long drift on the floe and while on Elephant Island the temperature was taken at midday each day as long as the thermometers lasted. The mortality amongst these instruments, especially those which were tied to string and swung round, was very high.

A few extracts from the observations taken during 1915—the series for that year being practically complete—may be of interest. January was dull and overcast, only 7 per cent. of the observations recording a clear blue sky, 71 per cent. being completely overcast.

The percentage of clear sky increased steadily up till June and July, these months showing respectively 42 per cent. and 45.7 per cent. In August 40 per cent. of the observations were clear sky, while September showed a sudden drop to 27 per cent. October weather was much the same, and November was practically overcast the whole time, clear sky showing at only 8 per cent. of the observations. In December the sky was completely overcast for nearly 90 per cent. of the time.

Temperatures on the whole were fairly high, though a sudden unexpected drop in February, after a series of heavy north-easterly gales, caused the ship to be frozen in, and effectually put an end to any hopes of landing that year. The lowest temperature experienced was in July, when —35° Fahr., i.e. 67° below freezing, was reached. Fortunately, as the sea was one mass of consolidated pack, the air was dry, and many days of fine bright sunshine occurred. Later on, as the pack drifted northwards and broke up, wide lanes of water were formed, causing fogs and mist and dull overcast weather generally. In short, it may be said that in the Weddell Sea the best weather comes in winter. Unfortunately during that season the sun also disappears, so that one cannot enjoy it as much as one would like.

As a rule, too, southerly winds brought fine clear weather, with marked fall in the temperature, and those from the north were accompanied by mist, fog, and overcast skies, with comparatively high temperatures. In the Antarctic a temperature of 30°, i.e. 2° below freezing, is considered unbearably hot.

The greatest difficulty that was experienced was due to the accumulation of rime on the instruments. In low temperatures everything became covered with ice-crystals, deposited from the air, which eventually grew into huge blocks. Sometimes these blocks became dislodged and fell, making it dangerous to walk along the decks. The rime collected on the thermometers, the glass bowl of the sunshine recorder, and the bearings of the anemometer, necessitating the frequent use of a brush to remove it, and sometimes effectively preventing the instruments from recording at all.

One of our worst blizzards occurred on August 1, 1915, which was, for the ship, the beginning of the end. It lasted for four days, with cloudy and overcast weather for the three following days, and from that time onwards we enjoyed very little sun.

The weather that we experienced on Elephant Island can only be described as appalling. Situated as we were at the mouth of a gully, down which a huge glacier was slowly moving, with the open sea in front and to the left, and towering, snow-covered mountains on our right, the air was hardly ever free from snowdrift, and the winds increased to terrific violence through being forced over the glacier and through the narrow gully. Huge blocks of ice were hurled about like pebbles, and cases of clothing and cooking utensils were whisked out of our hands and carried away to sea. For the first fortnight after our landing there, the gale blew, at times, at over one hundred miles an hour. Fortunately it never again quite reached that intensity, but on several occasions violent squalls made us very fearful for the safety of our hut. The island was almost continuously covered with a pall of fog and snow, clear weather obtaining occasionally when pack-ice surrounded us. Fortunately a series of south-westerly gales had blown all the ice away to the north-east two days before the rescue ship arrived, leaving a comparatively clear sea for her to approach the island.

Being one solitary moving station in the vast expanse of the Weddell Sea, with no knowledge of what was happening anywhere around us, forecasting was very difficult and at times impossible.

Great assistance in this direction was afforded by copies of Mr. R. C. Mossmann’s researches and papers on Antarctic meteorology, which he kindly supplied to us.

I have tried to make this very brief account of the meteorological side of the Expedition rather more “popular” than scientific, since the publication and scientific discussion of the observations will be carried out elsewhere; but if, while showing the difficulties under which we had to work, it emphasizes the value of Antarctic Expeditions from a purely utilitarian point of view, and the need for further continuous research into the conditions obtaining in the immediate neighbourhood of the Pole, it will have achieved its object.

PHYSICS

By R. W. JAMES, M.A. (Cantab.), B.Sc. (Lond.), Capt. R.E

Owing to the continued drift of the ship with the ice, the programme of physical observations originally made out had to be considerably modified. It had been intended to set up recording magnetic instruments at the base, and to take a continuous series of records throughout the whole period of residence there, absolute measurements of the earth’s horizontal magnetic force, of the dip and declination being taken at frequent intervals for purposes of calibration. With the ice continually drifting, and the possibility of the floe cracking at any time, it proved impracticable to set up the recording instruments, and the magnetic observations were confined to a series of absolute measurements taken whenever opportunity occurred. These measurements, owing to the drift of the ship, extend over a considerable distance, and give a chain of values along a line stretching, roughly from 77° S. lat. to 69° S. lat. This is not the place to give the actual results; it is quite enough to state that, as might have been expected from the position of the magnetic pole, the values obtained correspond to a comparatively low magnetic latitude, the value of the dip ranging from 63° to 68°.

So far as possible, continuous records of the electric potential gradient in the atmosphere were taken, a form of quadrant electrometer with a boom and ink recorder, made by the Cambridge Scientific Instrument Company, being employed. Here again, the somewhat peculiar conditions made work difficult, as the instrument was very susceptible to small changes of level, such as occurred from time to time owing to the pressure of the ice on the ship. An ionium collector, for which the radioactive material was kindly supplied by Mr. F. H. Glew, was used. The chief difficulty to contend with was the constant formation of thick deposits of rime, which either grew over the insulation and spoiled it, or covered up the collector so that it could no longer act. Nevertheless, a considerable number of good records were obtained, which have not yet been properly worked out. Conditions during the Expedition were very favourable for observations on the physical properties and natural history of sea-ice, and a considerable number of results were obtained, which are, however, discussed elsewhere, mention of them being made here since they really come under the heading of physics.

In addition to these main lines of work, many observations of a miscellaneous character were made, including those on the occurrence and nature of parhelia or “mock suns,” which were very common, and generally finely developed, and observations of the auroral displays, which were few and rather poor owing to the comparatively low magnetic latitude. Since most of the observations made are of little value without a knowledge of the place where they were made, and since a very complete set of soundings were also taken, the daily determination of the ship’s position was a matter of some importance. The drift of the ship throws considerable light on at least one geographical problem, that of the existence of Morrell Land. The remainder of this appendix will therefore be devoted to a discussion of the methods used to determine the positions of the ship from day to day.

The latitude and longitude were determined astronomically every day when the sun or stars were visible, the position thus determined serving as the fixed points between which the position on days when the sky was overcast could be interpolated by the process known as “dead reckoning,” that is to say, by estimating the speed and course of the ship, taking into account the various causes affecting it. The sky was often overcast for several days at a stretch, and it was worth while to take a certain amount of care in the matter. Captain Worsley constructed an apparatus which gave a good idea of the direction of drift at any time. This consisted of an iron rod, which passed through an iron tube, frozen vertically into the ice, into the water below. At the lower end of the rod, in the water, was a vane. The rod being free to turn, the vane took up the direction of the current, the direction being shown by an indicator attached to the top of the rod. The direction shown depended, of course, on the drift of the ice relative to the water, and did not take into account any actual current which may have been carrying the ice with it, but the true current seems never to have been large, and the direction of the vane probably gave fairly accurately the direction of the drift of the ice. No exact idea of the rate of drift could be obtained from the apparatus, although one could get an estimate of it by displacing the vane from its position of rest and noticing how quickly it returned to it, the speed of return being greater the more rapid the drift. Another means of estimating the speed and direction of the drift was from the trend of the wire when a sounding was being taken. The rate and direction of drift appeared to depend almost entirely on the wind-velocity and direction at the time. If any true current-effect existed, it is not obvious from a rough comparison of the drift with the prevailing wind, but a closer investigation of the figures may show some outstanding effect due to current.¹

The drift was always to the left of the actual wind-direction. This effect is due to the rotation of the earth, a corresponding deviation to the right of the wind direction being noted by Nansen during the drift of the Fram. A change in the direction of the wind was often preceded by some hours by a change in the reading of the drift vane. This is no doubt due to the ice to windward being set in motion, the resulting disturbance travelling through the ice more rapidly than the approaching wind.

For the astronomical observations either the sextant or a theodolite was used. The theodolite employed was a light 3´´ Vernier instrument by Carey Porter, intended for sledging work. This instrument was fairly satisfactory, although possibly rigidity had been sacrificed to lightness to rather too great an extent. Another point which appears worth mentioning is the following: The foot-screws were of brass, the tribrach, into which they fitted, was made of aluminium for the sake of lightness. The two metals have a different coefficient of expansion, and while the feet fitted the tribrach at ordinary temperatures, they were quite loose at temperatures in the region of 20° Fahr. below zero. In any instrument designed for use at low temperatures, care should be taken that parts which have to fit together are made of the same material.

For determining the position in drifting pack-ice, the theodolite proved to be a more generally useful instrument than the sextant. The ice-floes are quite steady in really thick pack-ice, and the theodolite can be set up and levelled as well as on dry land. The observations, both for latitude and longitude, consist in measuring altitude of the sun or of a star. The chief uncertainty in this measurement is that introduced by the refraction of light by the air. At very low temperatures, the correction to be applied on this account is uncertain, and, if possible, observations should always be made in pairs with a north star and a south star for a latitude, and an east star and a west star for a longitude. The refraction error will then usually mean out. This error affects observations both with the theodolite and the sextant, but in the case of the sextant another cause of error occurs. In using the sextant, the angle between the heavenly body and the visible horizon is measured directly. Even in dense pack-ice, if the observations are taken from the deck of the ship or from a hummock or a low berg, the apparent horizon is usually sharp enough for the purpose. In very cold weather, however, and particularly if there are open leads and pools between the observer and the horizon, there is frequently a great deal of mirage, and the visible horizon may be miraged up several minutes. This will reduce the altitude observed, and corrections on this account are practically impossible to apply. This error may be counterbalanced to some extent by pairing observations as described above, but it by no means follows that the mirage effect will be the same in the two directions. Then again, during the summer months, no stars will be visible, and observations for latitude will have to depend on a single noon sight of the sun. If the sun is visible at midnight its altitude will be too low for accurate observations, and in any case atmospheric conditions will be quite different from those prevailing at noon. In the Antarctic, therefore, conditions are peculiarly difficult for getting really accurate observations, and it is necessary to reduce the probability of error in a single observation as much as possible. When possible, observations of the altitude of a star or of the sun should be taken with the theodolite, since the altitude is referred to the spirit-level of the instrument, and is independent of any apparent horizon. During the drift of the Endurance both means of observation were generally employed. A comparison of the results showed an agreement between sextant and theodolite, within the errors of the instrument if the temperature was above about 20° Fahr. At lower temperatures there were frequently discrepancies which could generally be attributed to the mirage effects described above.

As the Endurance was carried by the ice-drift well to the west of the Weddell Sea, towards the position of the supposed Morrell Land, the accurate determination of longitude became a matter of moment in view of the controversy as to the existence of this land. During a long voyage latitude can always be determined with about the same accuracy, the accuracy merely depending on the closeness with which altitudes can be measured. In the case of longitude matters are rather different. The usual method employed consists in the determination of the local time by astronomical observations, and the comparison of this time with Greenwich time, as shown by the ship’s chronometer, an accurate knowledge of the errors and rate of the chronometer being required. During the voyage of the Endurance about fifteen months elapsed during which no check on the chronometers could be obtained by the observation of known land, and had no other check been applied there would have been the probability of large errors in the longitudes. For the purpose of checking the chronometers a number of observations of occultations were observed during the winter of 1915. An occultation is really the eclipse of a star by the moon. A number of such eclipses occur monthly, and are tabulated in the “Nautical Almanac.” From the data given there it is possible to compute the Greenwich time at which the phenomenon ought to occur for an observer situated at any place on the earth, provided his position is known within a few miles, which will always be the case. The time of disappearance of the star by the chronometer to be corrected is noted. The actual Greenwich time of the occurrence is calculated, and the error of the chronometer is thus determined. With ordinary care the chronometer error can be determined in this way to within a few seconds, which is accurate enough for purposes of navigation. The principal difficulties of this method lie in the fact that comparatively few occultations occur, and those which do occur are usually of stars of the fifth magnitude or lower. In the Antarctic, conditions for observing occultation are rather favourable during the winter, since, fifth-magnitude stars can be seen with a small telescope at any time during the twenty-four hours if the sky is clear, and the moon is also often above the horizon for a large fraction of the time. In the summer, however, the method is quite impossible, since, for some months, stars are not to be seen.

No chronometer check could be applied until June 1915. On June 24 a series of four occultations were observed; and the results of the observations showed an error in longitude of a whole degree. In July, August, and September further occultations were observed, and a fairly reliable rate was worked out for the chronometers and watches. After the crushing of the ship on October 27, 1915, no further occultations were observed, but the calculated rates for the watches were employed, and the longitude deduced, using these rates on March 23, 1916, was only about 10´ of arc in error, judging by the observations of Joinville Land made on that day. It is thus fairly certain that no large error can have been made in the determination of the position of the Endurance at any time during the drift, and her course can be taken as known with greater certainty than is usually the case in a voyage of such length.