Light in the Polar Night

How much light isa vailable for biological processes during Polar Night? This question appears simple enough. But the reality is that conventional light sen- sors for measuring visible light (~350 to ~700 nm) have not been sensitive enough to answer it. Beyond this technical challenge, “light” is a general term that must be qualified in terms of “light climate” before it has meaning for biological systems. In this chapter, we provide an answer to the question posed above and explore aspects of light climate during Polar Night with relevance to biology, specifically, how Polar Night is defined by solar elevation, atmospheric light in Polar Night and its propaga- tion underwater, bioluminescence in Polar Night and the concept of Polar Night as a deep-sea analogue, light pollution, and future perspectives. This chapter focuses on the quantity and quality of light present during Polar Night, while subsequent chapters in this volume focus on specific biological effects of this light for algae (Chap. “Marine Micro- and Macroalgae in the Polar Night”), zooplankton (Chaps.“Zooplankton in the Polar Night” and “Biological Clocks and Rhythms in Polar Organisms”), and fish (Chap. “Fish Ecology in the Polar Night”)

accurate and self-consistent ocean color algorithm:simultaneous retrieval of aerosol optical properties and chlorphyll concentrations

A new algorithm has been developed for simultaneous retrieval of aerosol optical properties and chlorophyll concentrations in case I waters. This algorithm is based on an improved complete model for the inherent optical properties and accurate simulations of the radiative transfer process in the coupled atmosphere-ocean system. It has been tested against synthetic radiances generated for the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) channels and has been shown to be robust and accurate. A unique feature of this algorithm is that it uses the measured radiances in both near-IR and visible channels to find that combination of chlorophyll concentration and aerosol optical properties that minimizes the error across the spectrum. Thus the error in the retrieved quantities can be quantified

The specific inherent optical properties of three sub-tropical and tropical water reservoirs in Queensland, Australia

The underwater light climate, which is a major influence on the ecology of aquatic systems, is affected by the absorption and scattering processes that take place within the water column. Knowledge of the Specific Inherent Optical Properties (SIOPs) of water quality parameters and their spatial variation is essential for the modelling of underwater light fields and remote sensing applications. We measured the SIOPs and water quality parameter concentrations of three large inland water impoundments in Queensland, Australia. The measurements ranged from 0.9–42.7 μgl/1 for chlorophyll a concentration, 0.9–170.4 mgl/1 for tripton concentration, 0.36–1.59 m/1 for aCDOM(440) and 0.15–2.5 m for Secchi depth. The SIOP measurements showed that there is sufficient intra-impoundment variation in the specific absorption and specific scattering of phytoplankton and tripton to require a well distributed network of measurement stations to fully characterise the SIOPs of the optical water quality parameters. While significantly different SIOP sets were measured for each of the study sites the measurements were consistent with published values in other inland waters. The multiple measurement stations were allocated into optical domains as a necessary step to parameterise a semi-analytical inversion remote sensing algorithm. This paper also addresses the paucity of published global inland water SIOP sets by contributing Australian SIOP sets to allow international and national comparison

Colourful niches of phototrophic microorganisms shaped by vibrations of the water molecule

The photosynthetic pigments of phototrophic microorganisms cover different regions of the solar light spectrum. Utilization of the light spectrum can be interpreted in terms of classical niche theory, as the light spectrum offers opportunities for niche differentiation and allows coexistence of species absorbing different colors of light. However, which spectral niches are available for phototrophic microorganisms? Here, we show that the answer is hidden in the vibrations of the water molecule. Water molecules absorb light at specific wavebands that match the energy required for their stretching and bending vibrations. Although light absorption at these specific wavelengths appears only as subtle shoulders in the absorption spectrum of pure water, these subtle shoulders create large gaps in the underwater light spectrum due to the exponential nature of light attenuation. Model calculations show that the wavebands between these gaps define a series of distinct niches in the underwater light spectrum. Strikingly, these distinct spectral niches match the light absorption spectra of the major photosynthetic pigments. This suggests that vibrations of the water molecule have played