Underwater Daylight and Moonlight Measurements in the Eastern North Atlantic

Abstract

The penetration of daylight to depths of hundreds of metres was measured in four regions of the eastern North Atlantic. At one of the stations the penetration of full moonlight was also observed. Attenuation curves for seven wavelengths are presented for each station, and spectra derived from these data indicate the colour of the light at the depths of observation. The spectral characteristics and intensities of light at equivalent depths in the four regions are compared, and the biological implications of differences in attenuation of light from sun and moon in a single area are considered. INSTRUMENTS Bathy-thermo-irradiance meterThis submersible instrument (Figs. 1, 2) records light and temperature and indicates the precise depth at which the records are made. It is supported in the water by a polythene-insulated, single-conductor cable along which commands and information are telemetered. The cable is wrapped on an electric winch; signals are transmitted to and from the deck unit by way of interconnected slip-rings on the winch. The system uses a sea return, and the circuit between underwater and deck units is completed by trailing a weighted conductor over the side.The light sensor is an RCA 6472 multiplier phototube selected from 40 such tubes

Contrast enhancement through structural variations in the rhabdoms of oplophorid shrimps

“…The downwelling irradiance measured in the North Atlantic (Kampa, 1970) had a peak transmission wavelength of 476 nm. As a result of wavelength selective backscattering, the upwelling irradiance shows a shift in λ max to around 463 nm, accompanied by a significant decrease in the amount of light above 480 nm (Fig.…”

“…The downwelling light spectrum was based on that recorded at a depth of 480 m in the North Atlantic (Kampa, 1970), close to the region where our specimens were obtained. For each wavelength, the irradiance values given in Kampa (1970) were converted from radiation flux to quanta s -1 and extrapolated to 380 nm based on the data recorded by Frank & Widder (1996) from depths in excess of 400 m. There is no recorded data for upwelling light from the depths at which mesopelagic shrimp are normally found so the downwelling data above was modified according to the irradiance reflectance properties recorded at a depth of 15 m in the Gulf Stream (Tyler & Smith, 1970). The upwelling light is approximately 0.5% of the downwelling light in typical low-scattering deep oceanic water (Denton, 1990).…”

Diel variation in the vertical distribution of deep-water scattering layers in the Gulf of Mexico

“…The depth of scattering layers has been shown to be a function of surface irradiance and/or lunar cycle (Clarke 1973;Gjøsaeter 1984;Kampa, 1970;Benoit-Bird et al, 2009), food (Gjøsaeter and Kawaguchi 1980) and thermal gradients (Tont, 1976;Yoon et al, 2007;Hazen and Johnston, 2010; Klevjer and Kaartvedt, 2011). The effect of light on the depth distribution can be rapid and occur over time periods much less than the diel cycle, as evidenced by fishes moving shallower during solar eclipses (Backus et al, 1965;Kampa 1975).…”

Light and Diurnal Vertical Migration: Photobehavior and Photophysiology of Plankton

“…Recently, with more refined equipment and a greater number of observations Kampa (l970a) reported that four layers in the eastern North Atlantic (Kampa, 1970b) and two in the Gulf of California (Kampa, 1970c) had midday depths associated with an isolume of about 3-5 X 10-5 Jl W cm-2 nm-1 at 480 nm. At most, the differences in the isolume intensity in these areas was only sixfold.…”