ultraviolet-B Flux Research Articles

Dying in the Sun: Direct evidence for elevated UV-B radiation at the end-Permian mass extinction

Land plants can adjust the concentration of protective ultraviolet B (UV-B)-absorbing compounds (UACs) in the outer wall of their reproductive propagules in response to ambient UV-B flux. To infer changes in UV-B radiation flux at Earth's surface during the end-Permian mass extinction, we analyze UAC abundances in ca. 800 pollen grains from an independently dated Permian-Triassic boundary section in Tibet. Our data reveal an excursion in UACs that coincide with a spike in mercury concentration and a negative carbon-isotope excursion in the latest Permian deposits, suggesting a close temporal link between large-scale volcanic eruptions, global carbon and mercury cycle perturbations, and ozone layer disruption. Because enhanced UV-B radiation can exacerbate the environmental deterioration induced by massive magmatism, ozone depletion is considered a compelling ecological driver for the terrestrial mass extinction.

Proxy reconstruction of ultraviolet-B irradiance at the Earth’s surface, and its relationship with solar activity and ozone thickness

Solar ultraviolet-B (UV-B) irradiance that reaches the Earth’s surface acts as a biotic stressor and has the potential to modify ecological and environmental functioning. The challenges of reconstructing ultraviolent (UV) irradiance prior to the satellite era mean that there is uncertainty over long-term surface UV-B patterns, especially in relation to variations in solar activity over centennial and millennial timescales. Here, we reconstruct surface UV-B irradiance over the last 650 years using a novel UV-B proxy based on the chemical signature of pollen grains. We demonstrate a statistically significant positive relationship between the abundance of UV-B absorbing compounds in Pinus pollen and modelled solar UV-B irradiance. These results show that trends in surface UV-B follow the overall solar activity pattern over centennial timescales, and that variations in solar output are the dominant control on surface level UV-B flux, rather than solar modulated changes in ozone thickness. The Pinus biochemical response demonstrated here confirms the potential for solar activity driven surface UV-B variations to impact upon terrestrial biotas and environments over long timescales.

Exposure to ultraviolet-B and risk of developing rheumatoid arthritis among women in the Nurses’ Health Study

ObjectiveTo examine the association between ultraviolet-B (UV-B) light exposure and rheumatoid arthritis (RA) risk among women in two large prospective cohort studies, the Nurses’ Health Study (NHS) and the Nurses’...

Spatial Statistical Analyses of Global Trends of Ultraviolet B Fluxes in the Continental United States

Many environmental factors, such as stratospheric ozone, aerosols, and clouds, may affect ultraviolet (UV) irradiance. The aim of this study is to investigate the possible association between ultraviolet B (UVB) radiation and total cloud amount, ozone, and aerosols simultaneously, leading to the assessment of possible impacts of climate change on UVB flux variations in the continental United States (U.S.). Spatiotemporal correlation analyses were conducted, based on data collected from the Total Ozone Mapping Spectrometer (TOMS) and the International Satellite Cloud Climatology Project (ISCCP), with a geographic information system (GIS). Findings indicate that in the past 22 years, while ozone decreased and aerosols increased across the U.S., the UVB decrease in the northern states was consistent with an increase in aerosols and total cloud amount. Therefore, to some extent, the trend characteristics of UVB over the U.S. between 1980 and 2002 were simultaneously affected by such dominant factors as total ozone and by such auxiliary factors as aerosol and total cloud amount. Climate change impact resulting in higher total cloud amount in the northern states might result in lower UVB in the future.

UV-B absorbing pigments in spores: biochemical responses to shade in a high-latitude birch forest and implications for sporopollenin-based proxies of past environmental change

Current attempts to develop a proxy for Earth’s surface ultraviolet-B (UV-B) flux focus on the organic chemistry of pollen and spores because their constituent biopolymer, sporopollenin, contains UV-B absorbing pigments whose relative abundance may respond to the ambient UV-B flux. Fourier transform infrared (FTIR) microspectroscopy provides a useful tool for rapidly determining the pigment content of spores. In this paper, we use FTIR to detect a chemical response of spore wall UV-B absorbing pigments that corresponds with levels of shade beneath the canopy of a high-latitude Swedish birch forest. A 27% reduction in UV-B flux beneath the canopy leads to a significant ( p <0.05) 7.3% reduction in concentration of UV-B absorbing compounds in sporopollenin. The field data from this natural flux gradient in UV-B further support our earlier work on sporopollenin-based proxies derived from sedimentary records and herbaria collections. Keywords: FTIR, spores, ferulic acid, p -coumaric acid, shade, sporopollenin (Published: 23 August 2011) Citation: Polar Research 2011, 30 , 8312, DOI: 10.3402/polar.v30i0.8312

Abstract 2820: Sunlight exposure, vitamin D, and risk of non-Hodgkin lymphoma in the Nurses’ Health Study

Abstract Background: Results from several recent case-control studies suggest that increased sun exposure may reduce risk of non-Hodgkin lymphoma (NHL). Vitamin D synthesis is hypothesized as one possible mechanism, since solar ultraviolet-B (UV-B) radiation exposure triggers endogenous vitamin D production in the skin. To date, no prospective studies of UV and NHL have been conducted. Methods: We identified 1057 incident cases of NHL through 2006 in the Nurses’ Health Study (NHS), a cohort study of approximately 121,700 women who have been followed since 1976. Ambient UV radiation exposure, as measured by average annual UV-B flux (in R-B counts x 10-4), was estimated for all participants based on residence at various times during life and categorized as 113. Vitamin D intake from food and supplements was calculated based on responses to food frequency questionnaires with follow-up beginning in 1980. Using plasma 25-hydroxyvitamin D (25(OH)D) measurements available for a subset of the NHS population, we developed a linear regression model to predict plasma 25(OH)D levels for the entire cohort based on multiple determinants of vitamin D status, including dietary intake and UV-B flux. Cox proportional hazards models were used to estimate incidence rate ratios (RRs) and 95% confidence intervals (CIs). The main analyses included all cases of NHL; we also performed separate analyses for the most common NHL subtypes [i.e., chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), diffuse large B-cell lymphoma (DLBCL), and follicular lymphoma (FL)]. Results: For most measures of ambient UV-B flux, the risk of NHL was increased for women in the highest category of exposure (i.e., &amp;gt; 113) compared to the lowest (i.e., 113 ranged from 1.10 (95% CI: 0.94, 1.29) for UV-B flux based on residence in 1976 to 1.21 (95% CI: 1.00, 1.47) for UV-B flux at age 15. Positive linear trends were observed for all measures. We observed stronger associations for CLL/SLL than for FL and no association for DLBCL with most measures of UV-B flux. The RR for the highest quintile of total vitamin D intake versus the lowest, after adjusting for age, body mass index, smoking, height, multivitamin use, and intake of retinol, calcium, and total calories, was 1.02 (95% CI: 0.71, 1.46). There was no association between predicted 25(OH)D score and risk of NHL. There did not appear to be differences in effect estimates for vitamin D intake by NHL subtype. Conclusions: Our findings of weak but statistically significant positive associations between UV-B flux assessed at various time points and risk of NHL in this prospective cohort study do not support the hypothesis of a protective effect of sunlight exposure. We found no association between vitamin D intake and risk of NHL, suggesting that if UV exposure is ultimately found to reduce the risk of this cancer, the effect may not act through vitamin D. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2820.

Rabbit Muscle Actin Polymerization changes by Ultraviolet –B radiation

AbstractIncrease in Ultraviolet-B flux from the Sun has the potential to alter the protein in mammals. Rabbit muscle was processed and filtered to extract G-actin, which was tested for its protein concentration before exposing to UV-B. It was found that polymerization of actin does get affected exposure of actin monomers to UV-B radiation. Inside the cell, there are many actin binding proteins which might be playing crucial role in G-actin to F-actin formation.

Plant spore walls as a record of long-term changes in ultraviolet-B radiation

Determining stratospheric ozone levels from before instrumental records began has proved difficult. Measurements of the chemical composition of plant spore walls suggest that ultraviolet-B-absorbing compounds have the potential to act as a proxy for past changes in ultraviolet-B radiation and stratospheric ozone. Stratospheric ozone screens the Earth’s surface from harmful ultraviolet-B radiation. Concentrations of stratospheric ozone are governed by a variety of natural and anthropogenic factors, including solar cycles1, volcanic aerosols2, ozone-depleting substances3 and climate change4. However, assessing this variability before instrumental records has proved difficult owing to the lack of a well-constrained proxy5. Here, we use microspectroscopy to analyse the chemical composition of herbarium samples of clubmoss (Lycophyta) spores originating from high- and low-latitude localities, where they were exposed to different ultraviolet-B histories. We show that the concentration of two ultraviolet-B-absorbing compounds in the walls of high-northern- and southern-latitude spores is strongly regulated by historical variations in ultraviolet-B radiation. Conversely, we find little change in the concentration of these compounds in spores originating from tropical Ecuador, where ultraviolet levels have remained relatively stable. Using spores from Greenland, we reconstruct past (1907–1993) changes in ozone concentration and ultraviolet-B flux; we reveal strong similarities between spore-wall reconstructions, and independent instrumental records6 and model results7. Our findings suggest that ultraviolet-B-absorbing compounds in plant spore walls have the potential to act as a proxy for past changes in terrestrial ultraviolet-B radiation and stratospheric ozone. The chemical signature of plant spore walls in herbaria, and possibly also in sedimentary and ice-core archives, may therefore prove valuable for reconstructing past variations in stratospheric ozone and their connections with changes in solar radiation and climate.

Ultraviolet-B-induced oxidative stress and responses of the ascorbate–glutathione cycle in a marine macroalga Ulva fasciata

The regulation of the antioxidant defence system by ultraviolet-B (UV-B) was determined in a marine macroalga Ulva fasciata Delile exposed to low (0.5, 1 W m(-2)), medium (2.5, 5 W m(-2)), and high (10, 20 W m(-2)) UV-B irradiance. UV-B > or =2.5 W m(-2) increased H2O2 contents that are positively correlated with lipid peroxidation and total peroxide contents. Inhibition of the UV-B-induced H2O2 increase by a specific O2.- scavenger, 1,2-dihydroxy-benzene-3,5-disulphonic acid, shows that O2.- is the primary source of H2O2. Superoxide dismutase activity was increased by UV-B with a peak at 2.5 W m(-2), which did not match the H2O2 pattern. Alleviation of UV-B-induced oxidative damage by a H2O2 scavenger, dimethylthiourea, and a free radical scavenger, sodium benzoate, which inhibited UV-B-induced H2O2 accumulation, suggests that oxidative damage caused by UV-B > or = 2.5 W m(-2) is ascribed to accumulated H2O2. However, a decrease in growth rate and TTC reduction ability only at high UV-B doses indicates that the defence and repairing systems operate at low and medium UV-B doses. H2O2 not only can be excreted but can also be detoxified via the ascorbate-glutathione cycle. Increases in catalase, peroxidase, ascorbate peroxidase, and glutathione reductase activities and ascorbate (AsA) and glutathione pools, as well as AsA regeneration ability, function to keep the balance of cellular H2O2 under low UV-B doses. Dehydroascorbate reductase and monodehydroascorbate reductase are responsible for AsA regeneration under low and medium UV-B radiation, respectively. The appearance of oxidative damage in medium and high UV-B flux is attributable to a lower induction of the ascorbate-glutathione cycle as an antioxidant defence system. Overall, the availability of antioxidants and the induction of antioxidant enzyme activities for detoxifying reactive oxygen species (ROS) are regulated in U. fasciata against UV-B-induced oxidative stress, and experiments using ROS scavengers demonstrate that the antioxidant defence system is modulated by O2.- or H2O2.

Attenuation of ultraviolet radiation in streams of northern Michigan

AbstractWe measured the attenuation of ultraviolet B (UVB) and ultraviolet A (UVA) radiation in 32 streams located within the Ontonagon River watershed on the Upper Peninsula of Michigan, USA. Attenuation coefficients (Kd) of UVB and UVA ranged widely among these streams, but generally translated into relatively shallow 1% transmission depths into the water column (2–45 cm for UVB and 6–103 cm for UVA). Both Kd UVB and Kd UVA were positively correlated with stream dissolved organic C concentration (DOC, range 2–35 mg C/L). Absorbance coefficients of dissolved matter (ad) of UVB and UVA also were strongly correlated with DOC. Kd UVA (but not Kd UVB) was weakly related to the concentration of particulate organic C and DOC molar absorptivity. DOC-specific Kd UVB was, on average, higher in streams of our study compared to previously published values from lakes and wetlands. We developed a statistical model that predicts UVB flux to benthic organisms. The model incorporates information on water depth, DOC conc...

VARIABLE BREEDING PHENOLOGY AFFECTS THE EXPOSURE OF AMPHIBIAN EMBRYOS TO ULTRAVIOLET RADIATION

Reduced water depth in dry years has been proposed to interact with ultra- violet-B (UV-B) radiation and a pathogenic fungus to cause episodes of high mortality of amphibian embryos. Observations of breeding phenology of boreal chorus frogs (Pseudacris maculata) in Colorado from 1986 to 2001 show that dry years result in earlier breeding. The earliest and latest dates of maximum calling activity by males were 20 May and 16 June, and the date of maximum calling was strongly related to the amount of snow accu- mulation during the winter. Surface UV-B flux, estimated from satellite-based measure- ments, was positively related to date of maximum calling. In dry years, surface UV-B during calling was reduced by an amount similar to that attributed to reduced depth. Al- though there was a significant trend of increasing UV-B from 1978 to 2001 on the average date (2 June) of maximum calling activity, there was no relationship between year and surface UV-B at actual dates of maximum calling. Exposure to extreme temperatures is an alternative explanation for increased mortality of amphibian embryos in shallow water.

Solar ultraviolet-B detectors using Eu 2+ doped alkali halide crystals

The continuous depletion of the ozone layer causes an increase in the ultraviolet-B (UV-B) reaching the Earth’s surface. In this paper the behaviour of the KCl:Eu 2+ under solar UV irradiation has been investigated. Considering the thermoluminescence (TL) excitation spectra, the geometrical solar radiation parameters (solar zenith angle related to the light path) and the atmosphere characteristics (ozone content, Rayleigh scattering and aerosols’ concentration), the solar UV irradiation flux registered by the dosimeter has been simulated throughout the day. This modelled hourly signal agrees with the measured TL signal at different hours. Moreover, these curves throughout the day are compared to the convoluted signal obtained from a gaussian curve centred at different UV-C wavelengths and the same solar spectrum. This comparison supports the idea that the KCl:Eu 2+ crystal behaves under the sun as a narrow band gaussian detector centred at about 265 nm, but with the main registered solar UV-B signal at 285 nm. On the other hand, a comparison of the KCl:Eu 2+ system with commercially available broad band UV-B biological sensors (biometers), shows that the europium doped crystals are more sensitive to minor changes of the solar UV-B flux and therefore, it is a good instrument for the study of small ozone layer depletions.

Ultraviolet-B and photosynthetically active radiation environment of inclined leaf surfaces in a maize canopy and implications for modeling

The potential increase in ultraviolet-B (UVB) flux density and potential decrease in productivity of agricultural crops due to stratospheric ozone loss requires knowledge of the characteristics of UVB flux density above and within crops. Measurements of the photosynthetically active (PAR) and UVB radiation on inclined surfaces above and within a maize ( Zea mays L.) canopy were made in 1990. Sunlit surfaces within the canopy had similar UVB and PAR relative flux density levels to that above the canopy. Shaded surfaces within the canopy had very different relative flux density in the UVB and PAR as a result of differences in sky view, diffuse fraction, and orientation. These differences can be expected to result in canopy transmittance estimation errors of the order of 0.1 in the UVB and 0.05 in the PAR when one assumes an invariant diffuse radiation of leaves with differing aspect. The diffuse fraction of global radiant flux density influenced the radiation regimes present in the canopy. Two distinct radiation regimes were found for surfaces throughout the canopy in the relatively low diffuse fraction PAR waveband; a sunlit regime and a deep shade regime. Three distinct radiation regimes were evident for the relatively high diffuse fraction UVB waveband for surfaces at a height with cumulative leaf area index (LAI) of 1; a sunlit regime, a deep shade regime, and a light shade regime. At greater cumulative LAI, this additional light shade regime in the UVB was absent. Therefore, the bi-modal approach of modeling sunlit or shaded radiation regimes is adequate to estimate the photosynthetically active photon flux density throughout the canopy as well as to estimate the UVB radiant flux density when the cumulative canopy LAI was 2. At lower LAI, the UVB radiant flux density should be modeled using either a three-dimensional model or a model partitioning the gap probability into large and small gaps in the canopy. The necessity for two shade sub-models to model the UVB radiation environment apparently depends on the size distribution of gaps in the canopy.

Biologically Active Radiation in the Vicinity of a Single Tree

ABSTRACTThe horizontal photon flux density of photosynthetically active radiation (PAR) and flux density of ultraviolet A (UVA) and ultraviolet B (UVB) radiation were measured in the vicinity of isolated single trees during the summer of 1996. Measurements were made under shade and sunlit conditions along a transect aligned with the solar disk and the tree trunk. Flux density measurements were normalized by the flux density at a reference location away from the tree. Results showed (1) a more rapid decline in the flux density of UVA and UVB radiation than PAR with decreasing distance to the tree trunk on both the sunlit and shaded side of a tree and (2) more rapid changes in the flux density of UVB radiation UVA radiation, and PAR with distance from the tree on the sunlit side of the tree than the shaded side of the tree. The UVB/PAR ratio was found to increase in the shadow of a tree with increasing distance from the tree to between 4 and 6 for the conditions of the study. The potential for detrimental effects by UVB flux density under conditions of the high ratio may be mitigated by sunflecks at a given location over the course of a day.

Potential effects of UV-B on the chemical environment of marine organisms: A review

An increase in ultraviolet-B (UV-B) due to depletion of stratospheric ozone may affect growth of marine phytoplankton by altering the chemistry of their environment. Production of bioactive free radicals, photodecomposition of organic matter, and availability of trace metals are likely to be altered by increased UV-B flux. Such changes to the chemical environment may be both deleterious and beneficial to marine phytoplankton. Extracellular free radicals such as OH, Br 2 −, and CO 3 − are predicted to have a negligible impact, but superoxide and its decomposition product hydrogen peroxide may react rapidly with cell surfaces and destroy membrane function and integrity. Increased UV-B will enhance the bioavailability of the redox active trace metals Fe and Cu. Thus, in the Fe-limited high latitude ocean, increased Fe availability may promote phytoplankton production, while in other parts of the ocean increased Cu availability may be toxic. Overall, the interdependent direct and indirect effects of UV-B on phytoplankton may compensate for each other and account for the ability of marine ecosystems to be subjected to widely variable UV-B flux without apparent damage.