Transparency of Antarctic ice‐covered lakes to solar UV radiation

Abstract

Depth profiles of solar ultraviolet radiation (UVR), photosynthetically available radiation (PAR), and related variables were measured beneath the thick, permanent ice cover of four lakes in the McMurdo Dry Valleys (77'S, 162"E). These lakes span a range of phytoplankton concentrations (0.1-10 pg Chl a liter-l) but receive little input of chromophoric dissolved organic matter (CDOM) from their barren, polar desert catchments. The diffuse attenuation coefficients for downwelling radiation (K,) in the upper water column of the lakes were at or below those for clear natural waters elsewhere, with minimum values in Lake Vanda of 0.080 (305 nm), 0.055 (320 nm), 0.036 (340 nm), 0.023 (380 nm) and 0.034 (PAR) m-l. The attenuation lengths (l/K,) for these lakes and for a set of high latitude lakes in the northern hemisphere (tundra and boreal forest catchments) showed a close log-log relationship with dissolved organic carbon (DOC) concentrations (r* L 0.90; n = 20); dry valley lakes were at the high transparency end of this polar-subpolar continuum. Phytoplankton exposure to UVR relative to PAR is known to rise steeply with decreasing DOC in the concentration range 2-4 g m-3; the addition of the dry valley lakes data shows the continuation of this upward, markedly nonlinear trend at lower DOC concentrations. Calculation of the biologically effective UVR dosage rate for the upper phytoplankton community of Lake Vanda indicated that sufficient UVR penetrates through the 3.5-m-thick lake ice to cause inhibition of algal growth. These results show that polar desert lakes are optical extremes in terms of their water-column transparency to UVR, and that their dilute, mostly autochthonous CDOM offers little protection against the ultraviolet-B radiation flux that is continuing to increase dver the polar regions.

A search for polycyclic aromatic hydrocarbons over the Martian South Polar Residual Cap

“…Dartnell et al (2012) propose that PAHs might be protected from the deleterious effects of UV radiation and oxidization chemistry if they were within the subsurface of Mars, inside rock, or in areas of permanent shadow. Additionally, ice can act as a barrier to solar radiation ( Vincent et al, 1998 ;Cockell et al, 20 0 0 ), and allow organic compounds to become more complex where partial shielding of UV radiation occurs ( Herbst and van Dishoek, 2009;Oberg et al, 2009 ). In situ astrobiological detection of the subsurface will be carried out in the future, for example on the ESA ExoMars Rover mission scheduled for launch in 2020, which will carry with it a drill unit capable of penetrating down to 2 m in depth ( ESA, 2014 ).…”

Diversity of RuBisCO gene responsible for CO2 fixation in an Antarctic moss pillar

“…Lizotte 2008). These oligotrophic lakes are covered with ice for the majority of the year, leading to variation in the light environment depending on the ice thickness and snow cover (Vincent et al 1998). Moreover, biologically harmful levels of solar radiation may penetrate through the ice cover and shallow water column (Vincent et al 1998) because of low concentrations of UV-absorbing material (Morris et al 1995).…”

“…These oligotrophic lakes are covered with ice for the majority of the year, leading to variation in the light environment depending on the ice thickness and snow cover (Vincent et al 1998). Moreover, biologically harmful levels of solar radiation may penetrate through the ice cover and shallow water column (Vincent et al 1998) because of low concentrations of UV-absorbing material (Morris et al 1995). Benthic microbial communities in the lake produce carotenoids, xanthophyll, scytonemin, and mycosporine-like amino acids (Vincent et al 1993a;Quesada et al 1999;Hodgson et al 2004;Tanabe et al 2010), presumably to protect against intense light conditions (Kudoh et al 2009).…”

Field calibrations of a long-term UV dosimeter for aquatic UVB exposures

“…Bracchini et al [2] in shallow lake water; Conde, Aubriot & Sommaruga [3] in lagoon waters within the Southern Atlantic Ocean; Crump et al [4] in shallow pond water; Vincent et al [5] in Antarctic ice covered lakes; and Sommaruga & Psenner [6] in a high altitude mountain lake in Austria. Most recently, Belmont et al [7] analysed diffuse attenuation factors for river water in both the laboratory and field environments using radiometric instrumentation set to multiple wavelength channels.…”