Zoospores, gametophytes, young sporophytes and discs cut from mature sporophytes of Laminaria digitata, L. hyperborea and L. saccharina were exposed in the laboratory to UV-radiation, with a spectral composition and irradiance similar to natural sunlight, for periods ranging from 15 min to 8 d, and were then returned to white light. Germination of zoospores and the growth of gametophytes were reduced after exposures to UV longer than 1 h, whereas UV had little effect on the growth of young or mature sporophytes unless exposure continued for more than 48 h. The variable fluorescence (Fv:Fm) of all stages was strongly reduced immediately after short exposures to UV, but recovered almost completely within 24 h. However, exposure of gametophytes to UV for > 4 h resulted in little or no recovery of F~:Fm, whereas > 16 h of UV were required to produce this result in young sporophytes, and > 48 h in mature sporophytes. Thus, sensitivity to UV-radiation decreased from gametophytes to sporophytes, and with increasing age of sporophytes, but, in gametophytes, growth appeared to be a more sensitive indicator of UV-damage than Fv: F,, after 24 h recovery. The responses to UV of the zoospores and gametophytes of all three species were similar, but both growth and fluorescence measurements suggested that the sporophytes ofL. saccharina were more sensitive to UV than those of the other two species.

The radiocarbon (14C) and stable isotopic (13C and D) compositions of methane and carbon dioxide from alasses (typical landforms in permafrost terrain, consisting of lakes and wetlands) were measured around Yakutsk, eastern Siberia, where few isotope studies have been done. The carbon isotopic compositions of methane and carbon dioxide were used to study the pathways of methane formation in alasses. The mean value of methane and of carbon dioxide in each alass ranged from −63.9 to −58.2‰ and from −16.7 to −0.6‰, respectively. In small alasses, where the supply of fresh organic matter from surrounding wetland ecosystems is large, methane was produced almost equally from acetate fermentation and CO2 reduction pathways. In larger alasses the CO2 reduction pathway slightly dominates over acetate fermentation, owing to a smaller supply of labile organic matter. The 13C enrichment in CO2 in large lakes indicates depletion of methane precursors. Gas‐bubble methane is depleted in deuterium (the mean δD value from lakes is −360 ± 14‰ and from shores is −380 ± 20‰), which reflects the deuterium‐depleted environmental water (from −136 to −117‰) of alasses. Lake methane relatively enriched in D is interpreted to be the result of depletion in the hydrogen pool in lake sediments. Methane in shallow lakes is somewhat enriched in 14C relative to modern biogenic methane and is produced from fresh, recently fixed organic matter. The 14C content of methane from deeper lakes is 10–20% less than that of shallow lake methane, indicating a greater contribution from older methane derived from deeper parts of the sediment. The mean 13C, D, and 14C of methane from the alasses in general are estimated to be −61.1 ± 4.4‰, −363 ± 20‰, and 104 ± 6 pMC, respectively. This corresponds to the reported mean isotopic composition of methane from wetlands for δ13C, but shows lower value for δD and 14C content.

Black carbon (BC) deposited on snow lowers its albedo, potentially contributing to warming in the Arctic. Atmospheric distributions of BC and inorganic aerosols, which contribute directly and indirectly to radiative forcing, are also greatly influenced by depositions. To quantify these effects, accurate measurement of the spatial distributions of BC and ionic species representative of inorganic aerosols (ionic species hereafter) in snowpack in various regions of the Arctic is needed, but few such measurements are available. We measured mass concentrations of size‐resolved BC (CMBC) and ionic species in snowpack by using a single‐particle soot photometer and ion chromatography, respectively, over Finland, Alaska, Siberia, Greenland, and Spitsbergen during early spring in 2012–2016. Total BC mass deposited per unit area (DEPMBC) during snow accumulation periods was derived from CMBC and snow water equivalent (SWE). Our analyses showed that the spatial distributions of anthropogenic BC emission flux, total precipitable water, and topography strongly influenced latitudinal variations of CMBC, BC size distributions, SWE, and DEPMBC. The average size distributions of BC in Arctic snowpack shifted to smaller sizes with decreasing CMBC due to an increase in the removal efficiency of larger BC particles during transport from major sources. Our measurements of CMBC were lower by a factor of ~13 than previous measurements made with an Integrating Sphere/Integrating Sandwich spectrophotometer due mainly to interference from coexisting non‐BC particles such as mineral dust. The SP2 data presented here will be useful for constraining climate models that estimate the effects of BC on the Arctic climate.

[1] The spatial isotopic distribution of the snowpack over Siberia, where winter temperatures are as cold as those of the polar regions, was observed by the Trans-Siberian Snow Survey (TSSS) and Trans-Verkhoyansk Snow Survey Expedition (TVSSE) in March 2000 and March 2001. The results show inland dD depletion and a slightly increasing deuterium excess value, d, in the snowpack over Siberia. To explore the relationship between source region variability and the isotopic composition of snow, a model simulation was performed that reproduced the observed isotopic composition of snow. Moisture sources for Siberian precipitation were estimated using the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) atmospheric general circulation model (AGCM). A simple isotopic model was used to evaluate the total isotopic changes during transport from the designated source region to the region of precipitation. The results showed that the variability of the contribution of each source to the snow results in large isotopic variability, and the fact that the model reproduced the observed inland depletion of dD in snowpack suggests that GCM-predicted source contributions were verified by observed values. However, the modeled d values did not match observed d values over Siberia. Observations of d values in precipitation show an increase during autumn toward a maximum in late autumn and then a decrease during winter; however, the modeled d value reached a maximum in early autumn and decreased toward a minimum in winter. The simple isotope model does not consider additional moisture evaporation joining an airmass moving from a source region. Therefore the disagreement between the modeled and observed d values of snow suggests that moisture supplied from the land surface during transportation significantly contributes to autumn snow. The increased d values of Siberian snow show that evaporation from open water or from the soil surface, which are accompanied by isotopic fractionation, are more important than transpiration flux, which does not change the isotopic content. The contribution of land-derived moisture that has evaporated from open water plays an important role in eastern Siberian snow.