The salinity and temperature of the Irish Channel and the waters south of Ireland / by Donald J. Matthews.

  • Matthews, Donald John, 1873-1956.
Date:
1914
Catalogue details

Licence: In copyright

Credit: The salinity and temperature of the Irish Channel and the waters south of Ireland / by Donald J. Matthews. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    and prevents any such direct current. This fresh area is really the diluted remnant of this same salt warm current, so that a portion of the water here circulates in a closed curve. Gehrke1 has shown on theoretical grounds that more water enters the English Channel from the westward than escapes through the Straits of Dover*, after allowance has been made for the addi- tion of fresh water from the land, and that a portion must therefore turn back and escape in a north-westerly direction. This salt warm current gives rise to the peculiar cyclonic circulation which takes place in the southern entrance of the Irish Channel and which leads to some rather unusual physical conditions, such for instance as the fact that as we travel sea- wards from the north-west Cornish coast the salinity begins to fall at a comparatively short distance from the shore and may reach its lowest value in midchannel. The proof of this circulation depends on the combined Irish and Plymouth observations, and as it happens the stations have been so placed that the isohalines may be drawn in two ways. The inset charts on the section plates show a small area of triangular shape immediately south of section V in which there are no stations, and it is this lack of stations which give rise to the uncertainty. One way of drawing the isohalines, which would fit the mean results perfectly, has not been followed as it would necessitate the assumption of a strong current of low salinity flowing from St. George’s Channel to far south of 50° N. Lat. Such a current would be inherently improbable, and there is no reason to suppose that it exists when there is a much simpler explanation to hand. This explanation is to be found in the cyclonic or counter-clockwise circulation which has already been described in detail in the discussion of the mean conditions for August. It is more extensive than the charts show, and the Plymouth observations have proved that it reaches at times as far south as 48|-° N. Lat. Its cause is to be found in great measure in the configuration of the coast, which forces the stream to turn to the left of its direction ; but at the same time it would be always striving to turn to the right under the influence of the earth’s rotation. While in the narrow waters it would not be able to do so to any extent, but once clear of the south coast of Ireland on the western edge of the circulation it might be expected that part at least should turn to the right. At times indeed this seems to occur ; a branch is thrown off westwards which is able to travel as far as the Fastnet before it is turned to the left and southwards by the west wind drift of the ocean. The first hint of such a cyclonic circulation is to be found, as far as the writer knows, in a suggestion by 1 J. Gehrke : The mean velocity of the Atlantic currents running north of Scotland and through the English Channel. “Pub. de C ire on stance,” of the International Council for the Exploration of the Sea, No. 50 Copenhagen.
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