A Sensor Designed to Record Underwater Irradiance with Concern for a Shark’s Spectral Sensitivity

To ascertain how scalloped hammerhead sharks make nightly migrations to their feeding grounds as many as 20 km from their daytime abode, a seamount, a sensor was developed that measured irradiance intensity within the spectral range and sensitivity of the vision of the species. Could the sharks guide their movements by sensing the polarity of irradiation energy radiated from the sun or moon that penetrated into the oceanic depths? Two sensory receptors, cones and rods, are present in the retina of sharks to enable them to see both during daytime and nighttime. The peak sensitivity of the cones is red-shifted due to the presence of these wavelengths during the former period, while their response is linear under the range of the high light levels also present at this time; the peak sensitivity of rods is blue-shifted due to the presence of these wavelengths during dawn, dusk, and nighttime and is linear over the complementary range of low light levels. Spectral response curves for these two receptors were determined for sharks, and an attempt was made to match those of the sensors to the shark’s wavelength perception. The first sensor was matched to the photopic range using a photocell covered with a red-shifted gel filter; the second was matched to the scotopic range using a blue-shifted gel filter.

The improved representation of underwater radiances and its impact on simulated physics and biogeochemistry in the North Sea

<p>In the presented work we advanced our modelling of in-water optics on the North-West European (NWE) Shelf, with important implications for how we model stratification of the water column, primary productivity, and the underwater radiances. We implement a stand-alone bio-optical module into the existing coupled physical-biogeochemical model configuration. The advantage of the bio-optical module, when compared to the pre-existing light scheme is that it resolves the underwater irradiance spectrally and distinguishes between direct and diffuse downwelling streams. The changed underwater irradiance compares better with both satellite and in-situ observations. We show that both underwater irradiance and model biogeochemistry can be further improved by assimilating suitable ocean-color derived satellite products into the model. We use the light module to introduce feedback from biogeochemistry to physics and demonstrate that the two-way coupled model tends to outperform the one-way coupled model in both physics and biogeochemistry. We discuss the implications of our developments for future modelling of the NWE Shelf.</p>

VLADIMIR ALEXANDROVICH ARTEMIEV - MORE THAN 60 SEA EXPEDITIONS FROM ARCTIC TO ANTARCTIC

The article is dedicated to the 70th birthday of Vladimir Aleksandrovich Artemiev, senior researcher at the Ocean Optics Laboratory of the IO RAS. This is a unique electronics specialist who directly performs scientific research and provides this opportunity to others. V.A. Artemyev has been developing and improving optical equipment for marine expeditionary research for over 40 years; Among the devices he developed are an underwater irradiance meter (Alfamer device), three types of submersible transparent meters (PUM, PUM-A, PUM-200). Member of more than 60 sea expeditions from the Arctic to the Antarctic and about two dozen coastal marine. Conducted measurements of the underwater brightness of solar radiation at depths of up to 300 m in the Philippine Sea, diving on the Pysis underwater manned vehicle (PA), and in the Black Sea on the Argus PA. Vladimir Aleksandrovich is an irreplaceable expeditionary employee both in terms of his business and human qualities: contact, benevolent, always ready to help, creating a friendly atmosphere in the team. Coauthor of over 80 scientific publications and one invention patent. Has state awards.

On the influence of wind and waves on underwater irradiance fluctuations

The influence of various wind and wave conditions on the variability of downwelling irradiance Ed (490 nm) in water is subject of this study. The work is based on a two-dimensional Monte Carlo radiative transfer model with high spatial resolution. The model assumes conditions that are ideal for wave focusing, thus simulation results reveal the upper limit for light fluctuations. Local wind primarily determines the steepness of capillary-gravity waves which in turn dominate the irradiance variability near the surface. Down to 3 m depth, maximum irradiance peaks that exceed the mean irradiance Ed by a factor of more than 7 can be observed at low wind speeds up to 5 m s−1. The strength of irradiance fluctuations can be even amplified under the influence of higher ultra-gravity waves; thereby peaks can exceed 11 Ed. Sea states influence the light field much deeper; gravity waves can cause considerable irradiance variability even at 100 m depth. The simulation results show that under realistic conditions 50% radiative enhancements compared to the mean can still occur at 30 m depth. At greater depths, the underwater light variability depends on the wave steepness of the characteristic wave of a sea state; steeper waves cause stronger light fluctuations.

Attenuation coefficients of ultraviolet and photosynthetically active wavelengths in the waters of Heron Reef, Great Barrier Reef, Australia

Variation in subsurface solar radiation has been identified as a second-order factor in coral bleaching. This study examines transmission of radiation at Heron Reef (southern Great Barrier Reef, Australia) testing the hypotheses that spectral transmission is independent of location, season and solar zenith angle. In June and December 2004, 132 underwater irradiance profiles were collected at six ultraviolet wavelengths (305, 313, 320, 340, 380, 395 nm) and photosynthetically-active radiation (PAR) to estimate spectral diffuse attenuation coefficients Kd(λ). Mean Kd(λ) decreased through the ultraviolet spectrum (0.435 m–1 at 305 nm to 0.115 m–1 at 395 nm) whereas mean Kd(PAR) was 0.129 m–1. Ultraviolet Kd(λ) values were highly correlated with each other, but less well correlated with Kd(PAR). Kd(λ) values were larger inside than outside Heron Lagoon, both across all wavelengths and at individual wavelengths. Similarly, Kd(λ) values were significantly larger in December than June. These results are consistent with greater resuspension and transport of particulates in Heron Lagoon at higher wind speeds. Kd(λ) values were not dependent on solar zenith angle. The implications are that location and season must be accounted for when setting Kd(λ) values to calculate spectral irradiances affecting corals at Heron Reef.