The summer of 2022 was notable for the Svalbard archipelago due to the occurrence of several longstanding heatwaves, making it one of the warmest summers on the regional record. This study used an energy balance model forced with in situ weather observations to investigate the influence of extreme weather events on the surface energy balance of the low-elevation Aldegondabreen glacier (5.2 km2), located near Barentsburg town, with a focus on the turbulent heat exchange. The annual mass balance for 2022 (−2.13 m w.e.) was one of the most negative on record for Aldegondabreen since 2002/2003 when glaciological monitoring was first initiated. We identified four heatwaves that lasted from 9 to 19 days, the most prominent of which were observed in May and in September–October, which resulted in an anomalously prolonged melt season. In addition, several shorter, 1- to 3-day extreme melt events were identified, representing up to 75 mm w.e. day−1 of glacier-averaged melt. These events were well correlated (r = 0.87, p < 0.01), with discharge from a stream originating from the glacier terminus, and all cases were associated with significant increases in mean daily wind speeds (up to 10.3 m s−1).

An analysis of standard meteorological observations of horizontal visibility was performed, based on instrumental and visual observations at two Russian meteorological stations located on the southern coast of the Kara Sea. Horizontal visibility is an important navigation criterion for choosing safe routes and speeds along the Northern Sea Route. A decrease in horizontal visibility to less than 50 m is a dangerous weather event. The study of the conditions for the occurrence of such a dangerous phenomenon has become especially relevant when using giant ice-class tankers, the length of which reaches 300 m. The analysis showed that the frequency (probability) of unfavorable conditions for horizontal visibility has a pronounced seasonal variation. A relationship was found between the increase in frequency and changing climatic conditions, namely an increase in frequency against the background of modern global warming which is expressed both in a steady increase in surface air temperature in all seasons of the year and in a reduction of sea ice cover in the summer.

Data are presented that indicate that when the vegetation conditions of plants change, the expression levels of genes encoding chloroplast carbonic anhydrases, as well as the carbonic anhydrase activity of chloroplast compartments, change. The results of experiments with mutants in the genes of chloroplast carbonic anhydrases indicate that the activity of chloroplast carbonic anhydrases determines the nature of changes in photosynthesis reactions in response to changes in environmental conditions. Possible mechanisms of carbonic anhydrase participation in the light-dependent processes in the chloroplast are proposed. Based on the results we obtained, a hypothesis has been proposed about the interrelated functioning of carbonic anhydrases in chloroplasts.

The redox state of the plastoquinone (PQ) pool in thylakoids plays an important role in the regulation of chloroplast metabolism. In the light, the PQ pool is mostly reduced, followed by oxidation after light cessation. It has been believed for a long time that dark oxidation depends on oxygen, although the precise mechanisms of the process are still unknown and debated. In this work, we analyzed PQ pool oxidation kinetics in isolated pea (Pisum sativum) thylakoids by tracking the changes in the area above the OJIP fluorescence curve (Afl) over time intervals from 0.1 s to 10 min in the dark following illumination. Afl served as an indirect measure of the redox state of the PQ pool that enabled quantification of the rate of PQ pool oxidation. The results showed a two-phase increase in Afl. The “fast” phase appeared to be linked to electron flow from the PQ pool to downstream acceptors of the photosynthetic electron transport chain. The “slow” phase involved oxidation of PQH2 through oxygen-dependent mechanisms. Adding octyl gallate, an inhibitor of plastid terminal oxidase (PTOX), to isolated thylakoid suspensions decreased the rate of the “slow” phase of PQ pool oxidation in the dark after illumination. The addition of either H2O2 or catalase, an enzyme that decomposes H2O2, revealed that H2O2 accelerates oxidation of the PQ pool. This indicates that under conditions that favor H2O2 accumulation, H2O2 can contribute substantially to PQ pool oxidation in the dark after illumination. The contribution of PTOX and H2O2 to the modulation of the PQ pool redox state in plants in the dark after illumination is discussed.

Changes in the average annual surface air temperature (SAT) in Barentsburg (Svalbard) for the period 1899-2022 are considered. The SAT increases at an average rate of 0.34°C/10 years. The warming process is not continuous and consists of two periods of cooling and two periods of warming. Statistical methods have been used to establish the most probable position of the breaking points of the SAT trend: 1917, 1938, and 1968. The recent (“modern”) warming in the region began in the late 1960s, but since 1988, its intensity has doubled.

On the basis of in situ weather observations and a physical-based model, verified by a glaciological method, this article investigates the surface energy balance of the Aldegondabreen glacier during the summer melt season of 2021. Aldegondabreen (5.3 km2) is a low-elevation glacier near the western shore of Spitsbergen Island. On the timescale of the whole melt season, the prevalent positive heat flux is a shortwave radiative balance (84 percent). This result is in accordance with previous studies on similar low-elevation Svalbard glaciers. However, in August and September, when the sun is low, the turbulent fluxes may outweigh the input of the shortwave balance. The study identified six events of significantly increased turbulent fluxes, which contributed to 10 percent of the total heat influx, and attributed them to the particular type of synoptic situation. All of these events are related to cyclonic activity, which drastically increased the wind speed in the study area and, consequently, both sensible and latent heat fluxes. The frequency of the extreme cyclonic events in the Svalbard region is increasing, which may potentially extend the duration of the glacier melt season in the mid- and late autumn or reduce the accumulation of solid precipitation in that time period.

Abstract Oxidation of the PQ-pool in leaves, intact chloroplasts and isolated thylakoids after its reduction by flash of light intensity 3000 µmol photons m− 2 s− 1 for 1.5 s was studied as a time-dependence in the dark of area above curve of fluorescence, Afl. The fluorescence was excited with the same flash applied after dark intervals from 0.1 s to 10 min. The samples were either dark-adapted or pre-illuminated with a continuous light. The results showed a two-phase kinetic of Afl across all samples, consistent with prior findings in thylakoids without added electron acceptors and in leaves. A comprehensive analysis of the kinetics in isolated thylakoids conducted under both aerobic and anaerobic conditions, with or without Fd and NADP+, and in the presence of catalase, enabled the proposition of mechanisms responsible for the observed two phases. Our findings suggest that the “fast” phase is likely a combination of residual electron flow from the PQ-pool to downstream acceptors and the oxidation of PQH2 by the superoxide radical, formed during illumination and preserved in thylakoid membrane. The "slow" phase involves the oxidation of the PQ-pool through slow autocatalytic reactions with molecular oxygen, and this oxidation is enhanced in the presence of hydrogen peroxide. The role of the above processes in intact chloroplasts and leaves is discussed.

Solar energy absorbed by plants can be redistributed between photosystems in the process termed "state transitions" (ST). ST represents a reversible transition of a part of the PSII light harvesting complex (L-LHCII) between photosystem II (PSII) and photosystem I (PSI) in response to the change in light spectral composition. The present work demonstrates a slower development of the state 1 to state 2 transition, i.e., L-LHCII transition from PSII to PSI, in the leaves of dicotyledonous arabidopsis (Arabidopsis thaliana) than in the leaves of monocotyledonous barley (Hordeum vulgare) plants that was assessed by the measurement of chlorophyll a fluorescence at 77 K and of chlorophyll a fluorescence at room temperature. It is known that the first step of the state 1 to state 2 transition is phosphorylation of Lhcb1 and Lhcb2 proteins; however, we detected no difference in the rate of accumulation of these phosphorylated proteins in the studied plants. Therefore, the parameters, which possibly affect the second step of this transition, i.e., the migration of L-LHCII complexes along the thylakoid membrane, were evaluated. Spin-probe EPR measurements demonstrated that the thylakoid membranes viscosity in arabidopsis was higher compared to that in barley. Moreover, confocal microscopy data evidenced the different size of chloroplasts in the leaves of the studied species being larger in arabidopsis. The obtained results suggest that the observed deference in the development of the state 1 to state 2 transition in arabidopsis and barley is caused by the slower L-LHCII migration rate in arabidopsis than in barley plants rather than by the difference in the Lhcb1 and Lhcb2 phosphorylation.

The intra-annual variability of the surface ice ablation on the 5.5 km2 Aldegondabreen glacier (Spitsbergen Island, Barentsburg area) is presented. The ice ablation was measured during five seasons (2018–2022) at the two stakes, installed in the lower part of the glacier and at the index site, where the amount of ablation numerically coincides with the glacier-averaged value with the r = 0.99 agreement. The temporal resolution of the ice ablation data is uneven and varies from 3 to 45 days. To carry out the correlation analysis, meteorological data from the automated weather station located near the glacier terminus are used. The ice ablation rates, obtained after normalization for the number of days between stake readings, have a tight correlation with both the air temperature and the downwelling shortwave radiation flux for most of the seasons, in 2018–2021 (r = 0.71–0.99). Surface air temperature and short-wave radiation are closely related; the above estimates indicate the leading role of short-wave radiation in the summer ablation of the glacier in the period 2018–2021. The year 2022 became anomalous, as the correlation with the shortwave radiation significantly decreased (r = 0.21–0.34). The European heat wave of 2022, which also affected the Svalbard archipelago, interrupted the ordinary intra-annual variability of the air temperature, causing the unprecedented ice melt on Aldegondabreen in September. The predicted increase in frequency and intensity of the future heat waves will result in an increased role of turbulent fluxes in the surface energy balance of the low-elevated Svalbard glaciers. The article demonstrates how the empirically identified dependencies can change from season to season in a non-stationary climate.

Inhibitory analysis is a useful tool for studying cytochrome b 6 f complex in the photosynthetic electron transport chain. Here, we examine the inhibitory efficiency of two widely used inhibitors of the plastoquinol oxidation in the cytochrome b 6 f complex, namely 2,4-dinitrophenyl ether of 2-iodo-4-nitrothymol (DNP-INT) and 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB). Using isolated thylakoids from pea and arabidopsis, we demonstrate that inhibitory activity of DNP-INT and DBMIB is enhanced by increasing irradiance, and this effect is due to the increase in the rate of electron transport. However, the accumulation of protons in the thylakoid lumen at low light intensity has opposite effects on the inhibitory activity of DNP-INT and DBMIB, namely increasing the activity of DNP-INT and restricting the activity of DBMIB. These results allow for the refinement of the conditions under which the use of these inhibitors leads to the complete inhibition of plastoquinol oxidation in the cytochrome b 6 f complex, thereby broadening our understanding of the operation of the cytochrome b 6 f complex under conditions of steady-state electron transport.

The knockout of the At2g28210 gene encoding α-carbonic anhydrase 2 (α-CA2) in Arabidopsis thaliana (Columbia) led to alterations in photosynthetic processes. The effective quantum yields of both photosystem II (PSII) and photosystem I (PSI) were higher in α-carbonic anhydrase 2 knockout plants (α-CA2-KO), and the reduction state of plastoquinone pool was lower than in wild type (WT). The electron transport rate in the isolated thylakoids measured with methyl viologen was higher in α-CA2-KO plants. The amounts of reaction centers of PSII and PSI were similar in WT and α-CA2-KO plants. The non-photochemical quenching of chlorophyll a fluorescence in α-CA2-KO leaves was lower at the beginning of illumination, but became slightly higher than in WT leaves when the steady state was achieved. The degree of state transitions in the leaves was lower in α-CA2-KO than in WT plants. Measurements of the electrochromic carotenoid absorbance shift (ECS) revealed that the light-dependent pH gradient (ΔpH) across the thylakoid membrane was lower in the leaves of α-CA2-KO plants than in WT plants. The starch content in α-CA2-KO leaves was lower than in WT plants. The expression levels of the genes encoding chloroplast CAs in α-CA2-KO changed noticeably, whereas the expression levels of genes of cytoplasmic CAs remained almost the same. It is proposed that α-CA2 may be situated in the chloroplasts.

The article is devoted to the analysis of interannual and seasonal variability of sea ice extent in the waters of the Svalbard and Franz Josef Land archipelagos for the period of 1979–2020. Quantitative results are based on the analysis of trends in surface air temperature, sea surface temperature and sea ice extent in the water areas of both archipelagos are obtained, indicating the current climate warming. In the course of the study, global warming trends were confirmed and evaluated, which are expressed in the reduction of ice cover, increase in surface air temperature and surface sea temperature in the investigated region.

This review analyzes data available in the literature on the rates, characteristics, and mechanisms of oxygen reduction to a superoxide anion radical at the sites of photosynthetic electron transport chain where this reduction has been established. The existing assumptions about the role of the components of these sites in this process are critically examined using thermodynamic approaches and results of the recent studies. The process of O-2 reduction at the acceptor side of PSI, which is considered the main site of this process taking place in the photosynthetic chain, is described in detail. Evolution of photosynthetic apparatus in the context of controlling the leakage of electrons to O-2 is explored. The reasons limiting application of the results obtained with the isolated segments of the photosynthetic chain to estimate the rates of O-2 reduction at the corresponding sites in the intact thylakoid membrane are discussed.

New ways to improve the original technique for assessing the albedo of snow–ice surfaces with the use of ground measurements of incoming solar radiation, photogrammetric information, and metadata on shooting parameters (Zhuravskiy et al., 2018) are considered. The first version of the technique was used to assess the albedo of natural and artificial snow–ice surfaces (fast ice, glacial-crack zones, ice-airfield runways) in the region of the Russian Antarctic station Progress (Zhuravskiy et al., 2020). However, that technique did not always allow assessment of the albedo under strong changing illumination of the surface and with limited source data. The new technique makes more correct estimation of the albedo under extreme conditions possible.

Oxygen reduction in chloroplasts in the light was discovered by (Mehler Arch Biochem Biophys 33:65-77, 1951) as production of hydrogen peroxide. Later, it was shown that the primary product of the oxygen reduction is superoxide radical produced in thylakoids by one-electron transfer from reduced components of photosynthetic electron transport chain to O2 molecule. For a long time, the formation of hydrogen peroxide was considered to be a result of disproportionation of superoxide radicals in chloroplast stroma. Here, we overview a growing number of evidence indicating on another one, additional to disproportionation, pathway of hydrogen peroxide formation in chloroplasts, namely its formation in thylakoid membrane due to reaction of superoxide radical generated in the membrane with the reduced plastoquinone molecule, plastohydroquinone. Since various components of photosynthetic electron transport chain (primarily photosystem I) can supply superoxide radicals to this reaction, we refer this two-step O2 photoreduction to H2O2 as a cooperative process. The significance of hydrogen peroxide production via this pathway for redox signaling and scavenging of reactive oxygen species is discussed.

Experiments related to the use of unmanned aerial vehicle (UAV) for assessing the albedo of Svalbard glaciers is described. Study area - Esmark Glacier (Isfjord Bay) and Aldegonda Glacier (Greenfjord Bay). The main purpose of the experiments is to estimate the surface albedo in the zone of the edge cracks of the outlet glacier (Esmark), where standard ground-based observations are impossible due to safety conditions, as well as to obtain spatial albedo estimates (Aldegonda) when satellite data cannot be used (overcast). The UAV (DJI Phantom 4 Pro) was retrofitted with a sensor that measures reflected solar radiation. The data on the incoming solar radiation at the surface level, measured by a similar sensor, were used to calculate the albedo. The albedo measurements were carried out along several profiles across the Aldegonda Glacier and along one profile above the Esmark Glacier, which was laid from a flat plateau (ice dome) through a zone of cracks to the open water surface of the fiord. For the first time, estimates of the surface albedo of the outlet glacier in the zone of edge cracks were obtained. Ground-based verification observations carried out on the Aldegonda glacier confirmed the results obtained by the UAV.

Inhibitory analysis is a useful tool for studying reactions in the photosynthetic apparatus. After introducing by Aachim Trebst in 1978, dinitrophenylether of iodonitrothymol (DNP-INT), a competitive inhibitor of plastoquinol oxidation at the cytochrome (cyt.) b6f complex, has been widely applied to study reactions occurring in the plastoquinone pool and the cyt. b6f complex. Here we examine the inhibitory efficiency of DNP-INT by implementing three approaches to estimate the extent of blockage of electron flow from the plastoquinone pool to photosystem I in isolated thylakoids from spinach (Spinacia oleracea). We confirm that DNP-INT is a potent inhibitor of electron flow to photosystem I and demonstrate that inhibitory action of DNP-INT depends on irradiance and H+ uptake by thylakoid membranes. Based on these findings, we infer that affinity of the quinol-oxidizing site of the cyt. b6f complex to DNP-INT is increased in the light due to hydrogen bonding between DNP-INT molecules and acidic amino acid residue(s), which is (are) protonated in the light.

Light harvesting is finetuned through two main strategies controlling energy transfer to the reaction centers of photosystems: i) regulating the amount of light energy at the absorption level, ii) regulating the amount of the absorbed energy at the utilization level. The first strategy is ensured by changes in the cross-section, i.e., the size of the photosynthetic antenna. These changes can occur in a short-term (state transitions) or long-term way (changes in antenna protein biosynthesis) depending on the light conditions. The interrelation of these two ways is still underexplored. Regulating light absorption through the long-term modulation of photosystem II antenna size has been mostly considered as an acclimatory mechanism to light conditions. The present review highlights that this mechanism represents one of the most versatile mechanisms of higher plant acclimation to various conditions including drought, salinity, temperature changes, and even biotic factors. We suggest that H2O2 is the universal signaling agent providing the switch from the short-term to long-term modulation of photosystem II antenna size under these factors. The second strategy of light harvesting is represented by redirecting energy to waste mainly via thermal energy dissipation in the photosystem II antenna in high light through PsbS protein and xanthophyll cycle. In the latter case, H2O2 also plays a considerable role. This circumstance may explain the maintenance of the appropriate level of zeaxanthin not only upon high light but also upon other stress factors. Thus, the review emphasizes the significance of both strategies for ensuring plant sustainability under various environmental conditions.