Transparency of Antarctic ice‐covered lakes to solar UV radiation

• Published in: Limnology and Oceanography
• Main Authors: Vincent, Warwick F., Rae, Rowena, Laurion, Isabelle, Howard‐Williams, Clive, Priscu, John C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1998
• Subjects: Antarctic; Four Lakes; Lake Vanda; McMurdo Dry Valleys; Vanda; Antarc*; polar desert; Tundra
• Online Access: http://dx.doi.org/10.4319/lo.1998.43.4.0618; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.4319%2Flo.1998.43.4.0618; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1998.43.4.0618

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 μg Chl a liter −1 ) but receive little input of chromophoric dissolved organic matter (CDOM) from their barren, polar desert catchments. The diffuse attenuation coefficients for downwelling radiation ( K d ) 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 −1 . The attenuation lengths (l/ K d ) 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 2 ≥ 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 over the polar regions.