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

Abstract

Long‐term fluctuations in lake‐water optical properties were examined using a Holocene sediment sequence and multi‐proxy palaeolimnological approach in Lake Einstaken, Nordaustlandet, Svalbard. 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 Holocene 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 Holocene and for several millennia during the mid‐Holocene. Sun 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 Nostoc cyanobacterial colonies were established during the mid‐Holocene, indicative of high underwater UV intensities, and Fontinalis mosses thrived during the early Holocene, indicating a highly transparent water column. The results further suggested that underwater UV exposure decreased during the late Holocene, which is probably attributable to increased DOC and decreased solar forcing. Owing to the location of Lake Einstaken 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 Holocene climate development. These factors controlled sea shoreline proximity, water discharge, ice‐cover duration and littoral‐benthic primary production and further affected the underwater UV environment. Although the role of solar forcing cannot be underestimated, the current record emphasizes the role of climate‐mediated lake‐catchment interactions in impacting bio‐optical properties and UV exposure of high arctic aquatic systems.

Spatio‐temporal cladoceran (Branchiopoda) responses to climate change and UV radiation in subarctic ecotonal lakes

“…In addition, lake depth is relevant for underwater UV exposure of mobile organisms, which can mitigate UV through horizontal or vertical migration to search for deep‐water UV refugia (Sommaruga, ). In previous high arctic Holocene and late Holocene records, solar activity has been shown to be positively related to lakes’ UV exposure (Nevalainen, Rantala, et al., ; Nevalainen et al., ) suggesting that solar forcing has an important role in aquatic UV exposure of such regions. Although the long‐term trends of Námmájávri's ABS UV and solar intensity were synchronous, exhibiting gradual increases from 1700 C.E.…”

Role of terrestrial carbon in aquatic UV exposure and photoprotective pigmentation of meiofauna in subarctic lakes

“…) were highly similar than those measured for synthetic melanin (Rautio & Nevalainen, ), suggesting that the carapaces contained melanin pigments. The absorbance spectra also closely follow those published previously from cladoceran carapaces extracted from lake sediments (Rautio & Nevalainen, ; Nevalainen & Rautio, ; Nevalainen et al ., ).…”

“…The ongoing climate change adds to the challenge in climate‐sensitive lakes (Williamson et al ., ; Häder et al ., ), causing significant reorganisation of aquatic communities and ecosystem structure (Smol et al ., ; Thienpont et al ., ). It also significantly alters bio‐optical lake‐water properties and underwater UV doses by impacting, for example, ice break‐up time, catchment vegetation and surface run‐off (Pienitz & Vincent, ; Saulnier‐Talbot et al ., ; Clark et al ., ; Nevalainen et al ., , ). It has been shown in palaeolimnological studies that cladoceran meiobenthos responds to centennial–millennial scale changes in underwater UV exposure through changing the degree of melanin pigmentation (Nevalainen & Rautio, ; Nevalainen et al ., ).…”

“…Thus, cladoceran melanisation seems to be dependent on site‐specific underwater UV exposure that is controlled by UV‐screening DOC concentration of the lake water and ultimately by catchment characteristics and climate. This has also been recorded using long‐term palaeolimnological approach, as climate dynamics and catchment succession through the past centuries and millennia are known to have influenced cladoceran carapace melanisation in fossil specimens preserved in lake sediments (Nevalainen & Rautio, ; Nevalainen et al ., ). Understanding of spatial and temporal patterns in UV‐protective pigmentation and its connections to the lake–catchment coupling and climate conditions is important, since increasing UV doses and accelerating climate warming in future may create unique and unexpected aquatic environmental settings in underwater UV regimes for the aquatic organisms to adapt.…”

Invertebrate communities of the High Arctic ponds in Hornsund

“…Species distribution models for Svalbard−nesting pink−footed geese (Anser brachyrhyn− chus) suggests that climate warming may lead to a further growth in geese popula− tions (Jensen et al 2008), and therefore enhance the eutrophication of Arctic freshwaters. Lakes and ponds in Svalbard are extremely sensitive to climate changes and when combined with superimposed stressors, they have cascading ef− fects Guilizzoni et al 2006;Luoto et al 2014a;Nevalainen et al 2015), such as increasing lake productivity and warming of surface waters.…”