Icebergs and Currents of the North Atlantic.
THE circumstance of icebergs and drift-ice being seldom seen in these latitudes to the eastward of the fortieth degree of west longitude, while there is an uninterrupted open ocean from Labrador to Ireland and Great Britain, is worthy of attention.
Between 42° and 43° west, is the farthest easterly position in which we have been able to trace these floating masses of ice, and this is near the meridian of the southern extreme of Greenland.
The wide opening between Cape Farewell, and the eastern extremity of Labrador, through which the Arctic currents run, faces the S.E., which would lead the flowing waters in a direct course towards the coasts of Marocco, and the Sahara, passing to the northward and eastward of the Azores, Madeiras, and Canaries. It may be presumed, however, that only a small portion, comparatively, of the body of water ejected from Arctic inland seas pursues this route, and that the stream is not continuous to the shores of North Africa.
In Davis’s Strait we find the current generally setting southerly. Those ships which were beset last year, drifted with the ice to the south, but the strength of this current seems to be very variable, and at times trifling: in October in 62° 53’ N., and 62° 52’ W. it set S. 8° W., only eight miles in twenty-four hours; a degree further south, it ran sixteen miles in the twenty-four hours.
The directions assumed by the current from Hudson’s and Baffin’s seas on escaping into the open ocean appear to be:—1. To the south towards the north coast of Newfoundland, and there being checked by the land, it winds round the east coast in the channel-deep, formed by the island and the northwest part of the Grand Bank, until it meets the flood from the gulf of St. Lawrence:—2. To the South-west through the strait of Belle Isle:—3. An off-set to the S.S.E. passing to the eastward of the Grand Bank; it is by this latter that the icebergs and drift-ice are conveyed into the Atlantic as far to the east as we have traced them; where the set, probably, becomes exhausted, or joins the Florida stream:—4. It is certain that a portion of the flowing waters from Cape Farewell, takes a direction to the E.S.E. This current was experienced by the first polar expedition under Capt. Ross, and its southern limit in 36° 21’ W. was in latitude 57° 8’ N. The direction may be correctly inferred, without farther proof, from the trial-bottles set adrift by the discovery ships, which were found on the coasts of Great Britain and Ireland. And we may reasonably conclude, that whatever ice may be carried into the open ocean by this stream, must be of small dimensions and quickly dissolved; for if this were not the case, those floating dangers would assuredly find their way to our coasts as well as the bottles. The first ice seen by Capt. Ross was near the meridian of Cape Farewell; and in July, 1812, the Hudson “Bay” ships first met with it in Hudson’s Strait. It may be presumed, also, that seasonal changes have an influence on all these streams; and consequently, that, during the summer, from the melting of the ice and the snow, their volume and velocity will be augmented; and, on the contrary, in the winter these will be diminished, and perhaps some of the off-sets be suspended. That any disarrangement in the level of the waters of Baffin’s sea takes place in consequence of the melting of ice and snow, or from pluvial discharges, we are not inclined to believe; considering that any general accumulation is prevented by the vigilance of the evaporating power, as well as by the currents which carry off the superfluous waters with a velocity regulated by the amount of the accessions. The specific gravity of the water of this easterly current in the Atlantic was found to be less than the water to the southward of it; from which it may be inferred that the fresh water does not entirely mix with that of the ocean for a considerable distance from its point of exit; this freshness was not only indicated by the less density of the water, but also its coldness, which was greater than that of the air; this was noticed as far to the eastward as 36° 21’ W.
It was long considered that sea water did not freeze, but this has been satisfactorily proved to be erroneous: Captain Sir John Ross found it seven or eight feet thick in the course of a winter; and it is clear that the increase is downwards as well, the thickness being augmented by the freezing of snow on the surface above. The water from ice taken up at sea has been found to be fresh when not in a spongy state. It has been considered that the accretions from snow upon the surface water when frozen, account for the freshness; but, although this may be true, yet it has been ascertained that water taken from the ocean and put into a bottle, having become frozen and burst the bottle, it was found to be fresh. From observations made with respect to the operation of cold on the water of a river, it is probable that the saline particles held in solution in sea-water are precipitated by the effect of extreme cold before congelation. It has been ascertained from careful and repeated observation, for several years, that the water of the Avon, which in mild weather is extremely turbid, becomes quite clear, and of a sea-green colour, whenever the temperature approaches near to the freezing point. Whether the increased density of the atmosphere may, by its pressure, have anything to do in the matter, is uncertain, but the fact is invariable.
The inference to be drawn from the fact of ice-drifts being confined to the meridians between the fortieth degree west, and the American continent is, either that no ice proceeds from the northern regions to the east of the fortieth degree west, into the Atlantic, because icebergs which may be generated on the eastern coast of Greenland, cannot reach the open ocean on account of the fixed barrier of ice, or that, if any large masses of ice proceed from the N.E. towards the shores of Iceland, they find their way thence to the coast of Newfoundland, or otherwise are acervated upon the barrier. Something of this sort must occur, or what is to prevent them from being carried to the east or S.E. by the currents? We know of no reported or recorded instance of ice-bergs being seen on our coasts, although we recollect to have read an account of one having approached very near to Antigua. In the former case an iceberg would have to drift about 1,200 miles; in the latter about 2,100, with the increase of temperature in a double ratio; crossing the climatal parallels nearly on a meridian line.
Whatever may be the direction of the current between the north of Scotland and the Pole, we may conclude, from there being no land (except an isle or two) in that direction, that icebergs are not common to the south of the southern margin of the icy barrier; and we suspect the direction of the current is to E.S.E.
From our limited knowledge of the principles which govern the motions of the waters of the ocean, the eccentric movements of currents become very puzzling, and, with all our ingenuity, extremely difficult to be accounted for in a very satisfactory manner. The opinions of practical men drawn from experience and sober thought, although they may not always be in strict accordance with sound philosophy, may yet, if leading to no other good, serve at least to keep the subjects alive, and to draw attention towards them, besides emulating others, perhaps, to the salutary exercise of their mental powers, and spiriting up their faculty of observation. At all events, we may rest assured that the scientific theorist, although he should find little or nothing to assist him in drawing just conclusions from these opinions, yet from superior philosophical knowledge, he can never be deceived into an error from the false deductions of others.
It is quite impossible, from detached facts, to determine beyond a doubt, whether the directions of the streams we have been speaking of, are invariably held, or are merely occasional; or whether they may not even be liable to a change of course diametrically opposite.
A bottle from the Hecla, then to the southward of Greenland, was found at Teneriffe! Here we are perplexed, as it is impossible to say with certainty what course or courses this bottle followed: it may have gone direct with a S.E. drift; but this is not likely; a more probable conjecture is, that it passed close to the shore of Newfoundland, and reached the Florida stream when pressed northward; but it is just as likely to have been banded about from set to set until it finally reached the S.E. current between the Azores and Teneriffe.
In the summer, when southerly winds are occasionally felt between Newfoundland and Ireland, a drift current of about twenty miles in the twenty-four hours has been experienced, setting to the northward: the Jamaica ships in June, 1835, were exposed to its influence for several days. Whether this current may proceed from the fluent waters of the northern edge of the Florida stream being turned by the wind, or may be the S.S.E. Arctic set, altered in direction by the influence of the south wind, we cannot determine; be that as it may, it would seem at first to throw a doubt upon the generally-received opinion of the Arctic waters flowing to the southward. We conceive, however, that this northerly set can only be considered as an occasional one; and it seems to us quite within the bounds of probability, to consider that the south-east Arctic branch-current, crossing these parallels, may meet no great impediment to its course from this northerly set, but accommodate itself to the changed circumstances by dipping; or, in other words, by pursuing its original course beneath the warmer water of the other, at the depth probably, of not more than two or three fathoms.
It is perhaps this occasional current to the northward that has, in the first instance, influenced the course of the current-bottles set adrift in these latitudes, and found upon the western coasts of Britain and Ireland, as also the tropical productions, (if these really proceed from the westerly current,) such as the cocoon, the nicket or nicker, the antidote, and the horse-eye, which are said to have been picked up even as high as the western isles of Scotland occasionally. It certainly is not improbable that some of these nuts may have been carried all the way from Cuba or Florida by currents; but it is much more likely that they were thrown overboard with the sweepings of the decks from West Indiamen near our own coasts, and within the influence of the tides, on clearing out the ships in readiness for entering their respective ports of destination. The sailors pick these nuts up from the beach, and take them on board often in quantities, considering them as curious presents for their friends at home. In the rivers and ports frequented by West India ships in this country, hundreds of the husks of the cocoa-nut may be seen floating about, and lying at the high-water mark on the banks. In the Bristol channel they are common enough, together with orange-peel, pieces of sugar-cane, bamboo, &c.; but no person has attributed their presence so far from their native groves to the agency of the Florida stream. The other things being less abundant, and seen only at long intervals, have given rise to the wonder and the opinion. This latter circumstance, by-the-bye, being of rare occurrence, if it could truly be traced to the mysterious stream, would shew that the queen of currents is seldom pressed sufficiently to the north to throw her floating treasures into the lap of her herald, to be borne to our shores as a sort of tributary homage to the majesty of the greatest maritime nation the world ever knew.
It appears yet undetermined how far to the eastward the Florida stream ranges—a point that really seems worth a little care to settle. Some perplexity would probably attend an investigation of this matter, from the stream towards its eastern bounds becoming feeble and spreading wide, as also being subject, we may presume, to be diverted from its course by northerly and southerly winds; yet, it would still be an object of interest and importance to the mariner; and the best information from competent authority thus gained, could not fail of becoming highly valuable to him. The waters of that part of the Atlantic from America to Europe, between the fortieth and sixtieth degrees north, we may properly consider as being constantly in motion, acted upon by various causes. The consequence is, that, during the prevalence of the strong winds between south-west and north-west, the waters already in streams, (at least those, the velocity of which is not too powerful, or the volume of which is not very deep,) acquire by the force of these winds, sets respectively towards the points to which these winds blow; and this may satisfactorily account for the general tendency of the waters between these parallels to the eastward. But it is a question, whether a space of sea in a quiescent state, would be acted upon by the agency alone of any wind, so as to flow in a stream or current.
There is no doubt that a certain degree of fluency is imparted to the sea by the action of the wind, when harrowing up the waters during strong gales; this, however, does not constitute a current, but what may be termed a drift.
The plain reason for such a doubt is so well known to seamen, that none will perhaps question its propriety, although it does not appear to have been advanced before by writers: it is, that all strong winds do not induce a current, and therefore such cannot be urged as a general principle.
Upon this datum it seems, that as surface currents only occasionally flow during the prevalence of gales, we must conclude that wind, unaided by any other principle in nature, has not the power of setting in motion in a stream water which had previously been in a quiescent state; that either the water itself, or the atmosphere incumbent over it, or both, as being necessary to the end, should be in a peculiar state, hitherto unsuspected, to receive or impart a flowing motion. The wind, when that has been acquired by the water, then becoming a directing power, as well as a propelling one. This, at first, may appear to some persons as a fanciful surmise; it has not, however, been lightly considered, but the result of much thought and reflection; and until it can be proved that a current is produced by every strong or stormy wind that blows, perhaps most seamen will consider the doubt as justified. The north-east trade-wind, which is perennial, gives to the waters a set amounting only to from nine to eighteen miles in the twenty-four hours. The Florida stream runs stronger with an opposing wind in the strait. And the discovery ships near Melville Island found a strong current running to the west, whilst a gale was blowing from that quarter. The drift of ships too during hurricanes has been comparatively trifling, compared to the strength and pressure of the wind.
Very careful observations by competent persons must take place, ere we can expect to have this matter elucidated. The electric fluid which pervades all nature may have great influence in this respect; when we are told that it gives pulsation to the heart, what cannot we expect of it? Sudden differences of temperature between the air and the water may be taken into consideration. From analogy, too, we may not unreasonably infer, that, as vallies, from their particular situation with respect to certain winds, act as conductors to the aerial fluid, oceanic permanent currents may be guided in their courses by the disposition of the submarine mountain chains.
The following points appear evident:—1. Water already in motion, especially in narrow channels, may have its velocity augmented by a brisk gale blowing in the same direction that the stream flows. 2. A strong wind may turn a weak or superficial current from its original course. 3. Water in a trough, or canal, or aqueduct, may be raised on the leeward side, and proportionally depressed on the windward side, or end, by a strong wind causing pressure; common sense dictates, however, that what may take place on so small a scale is inapplicable to the open ocean.
An interesting question remains to be clearly and satisfactorily answered, namely, what becomes of the vast influx of water thrown into the Atlantic, from the Arctic region to the westward of the fiftieth degree? This can only be resolved from yet careful investigation. At present we know little or nothing of the matter. It appears evident, however, on a mere inspection of the chart, that the mighty Florida stream is a boundary to the southward that it cannot pass over. There can be no doubt that much of the supply runs in the line of coast to the south-west, perhaps even as low as the peninsula of Florida, where, having acquired a high degree of temperature, it may serve to augment the great stream itself; it is probable, too, that a portion escapes round the end of the great bank running to north-east, until spread abroad, and, that under-currents dispose of the rest, so as to maintain a proper level, an operation which nature will accomplish to a certainty, in some way or other.
Perhaps these remarks may be appropriately concluded by observing, that if there were not a general circulation of the waters most actively carried on by means or under-currents, as well as those of the surface, we should find all the level shores overflowed.
It is well known that the general movement of the waters at the portals of the Atlantic is inclined towards it. Independent, however, of under-currents, the disarrangement of its level is prevented by counter-streams, which are a consequence of every great movement of the waters of the ocean, and which, with the under-currents, carry back an equal quantity to that drawn off from other parts by main streams, as well as distributing and spreading abroad the fluid, by which means the level of all oceans and seas are preserved alike. And this most admirable operation, although we may in our limited perceptions but imperfectly understand it, is as certain and perfect, notwithstanding all its various complicated, and to us in some cases inexplicable, movements, for the attainment of the ends designed, as that the blood circulates through the veins and arteries of the human body.
E. F. G.
 One of the ships caught in the ice lately, drifted 600 miles with it.