On the Penetration of Light into Sea Water.

Abstract

1. A description is given of some measurements of the penetration of light into sea-water carried out near Plymouth in the autumn of 1925 by means of photo-electric cells, the current through the cell being, measured by a method, previously described, which is not affected by the motion of the ship.2. The absorption coefficients found for off-shore waters down to 30 metres are smaller than the average of those found by several recent observers in various localities, but considerably larger than those found by Shelford and Gail for the deeper waters of Puget Sound. The coefficients tend.to increase with increase of depth, and are generally larger for in-shore waters. The clearest water, 20 miles out in the English Channel, gave an absorption coefficient 0-110 for the upper 10 metres, 0-117 for the second, and 0-133 for the third. This water, with glassy surface, transmitted 0-54% of the vertical illumination to 34-8 metres, 28-3% to 8-9 metres, at which depth a white disc was just visible, and 71-2% to 1-5 metres.

Vertical light attenuation and phytoplankton development in Lake Zürich1

“…The validity of this approximation has been shown in many ecological investigations (e.g. Poole and Atkins 1926;Aberg and Rodhe 1942;Kuroiwa et al 1983). Narrow spectral bands should be used and measurements must be made at various depths (Smith 1968;Dubinsky and Berman 1979).…”

Effects of algae on the Secchi transparency of the southeastern Mediterranean Sea

“…There is uncertainty about the light levels where 1640 a disk disappears and also about the underlying theory of the Secchi disk. Poole andAtkins (1926, 1929), who were the first to compare measurements of underwater light with transparency measurements, assumed that transparency is inversely proportional to the vertical attenuation coefficient for diffuse underwater sunlight, as predicted by the Lambert-Bouguer law. Many subsequent workers have adopted this assumption, but others (Tyler 1968;Holmes 1970) assumed that transparency depends on the sum of diffuse attenuation and beam attenuation, as proposed by Duntley (1963) and Preisendorfer ( 19 8 6).…”

Seasonal Variations in the Phosphate and Silicate Content of Sea Water during 1926 and 1927 in Relation to the Phytoplankton Crop

“…They consider the length of the day, rather than the amount of sunshine, to be the most important factor. Working with a muffed glass receiving surface mounted over a photoelectric cell, Poole and Atkins (1926) found that in September-which may be considered as more or less comparable to April~the ratio of the reading with the cell exposed horizontally to full sunlight to that obtained when the direct rays of the sun were cut off, so that the cell received diffuse light only, was about 3.5 under clear conditions, falling to about two with weak sunlight and hazy or cloudy sky, so that the diffused light was high. These figures are not accurate measures of the ratio of total light to diffuse light, since the average obliquity of the diffuse light was not identical with that of the sun's rays, but it serves well as a comparison.…”