OBSERVATIONS ON THE PENETRATION OF DAYLIGHT INTO MID-ATLANTIC AND COASTAL WATERS

¹ From the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts; and the Laboratory of General Physiology, Harvard University, Cambridge, Massachusetts

1. Measurements of the penetration of daylight into the sea were made in the mid-Atlantic, in the Gulf of Maine, and in Woods Hole Harbor, using the photo-electric method described previously. A four-conductor insulated cable and an electrically operated internal shutter have been added to the No. 1 sea photometer.

2. All three photometers exhibit essentially the same spectral sensitivity. For purposes of standardization the range of sensitivity is considered to extend from 3460A° to 5260A° with a maximum at 4360A°.

3. The photometers have been standardized against a 1000-watt Mazda lamp, the value of the irradiation from which was limited to that occurring within the spectral range of the photometers. The results of standardization are presented in Table I.

4. The changes in emission of the photometers and other possible sources of error are discussed, particularly those not dealt with by previous investigators.

5. The observations made approximately on longitude 30° W. reveal an increasing transparency of the water, particularly of the upper 20 meters, toward the south. Toward the north, the transparency is slightly greater than that found in the Gulf of Maine (transmissive exponent, = 0.15).

6. The most transparent water encountered was in the Sargasso Sea where measurements were made down to 180 meters. In Series 12 the average exponent was = 0.031, and values of = 0.015 to = 0.010 were obtained in the upper water layers. The least transparent water was found in Woods Hole Harbor ( = 0.49).

7. Examination was made of the extent to which the altitude of the sun, the condition of the sea surface, and the vertical distribution of the zoöplankton affected the degree of penetration of light. Five series of observations under varying conditions at one station in the Gulf of Maine revealed no significant change in transparency.

8. The measurements of submarine irradiation are found to be commensurate with those of previous investigators, but certain significant differences are pointed out.