Ultraviolet radiation exposure of a high arctic lake in Svalbard during the Holocene

• Published in: Boreas
• Main Authors: Nevalainen, Liisa, Rantala, Marttiina V., Luoto, Tomi P., Rautio, Milla, Ojala, Antti E. K.
• Other Authors: Suomen Akatemia
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: polar desert; Svalbard
• Online Access: http://dx.doi.org/10.1111/bor.12108; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fbor.12108; https://onlinelibrary.wiley.com/doi/pdf/10.1111/bor.12108

Long‐term fluctuations in lake‐water optical properties were examined using a H olocene sediment sequence and multi‐proxy palaeolimnological approach in L ake E instaken, N ordaustlandet, S valbard. UV ‐absorbance of sedimentary cladoceran remains provided information on underwater UV exposure and changes in lake‐catchment coupling processes were inferred from sediment geochemistry. In addition, aquatic community succession was used as an indicator for lake‐water bio‐optical properties and a H olocene record of sun activity (sunspots) was utilized to evaluate long‐term solar forcing. The results indicated that the UV ‐absorbance of cladoceran remains was highest (i.e. maximum UV ‐induced pigmentation) for a short period during the early H olocene and for several millennia during the mid‐ H olocene. S un activity was high during these time intervals, probably impacting the UV intensities, but it is probable that the amount of UV ‐attenuating compounds (e.g. dissolved organic carbon ( DOC )) also significantly affected the underwater UV environment and were low during high UV exposure. Benthic autotrophic communities also responded to the millennial changes in lake‐water optical properties. UV ‐resistant N ostoc cyanobacterial colonies were established during the mid‐ H olocene, indicative of high underwater UV intensities, and F ontinalis mosses thrived during the early H olocene, indicating a highly transparent water column. The results further suggested that underwater UV exposure decreased during the late H olocene, which is probably attributable to increased DOC and decreased solar forcing. Owing to the location of L ake E instaken and its catchment in the periglacial barren landscape of the polar desert, the fluctuations of bio‐optical lake‐water properties were apparently forced by postglacial environmental processes and H olocene climate development. These factors controlled sea shoreline proximity, water discharge, ice‐cover duration and littoral‐benthic primary production and further affected the ...