Spring Events Research Articles

Effects of natural and anthropogenic factors and their interactions on dust events in Northern China

Aeolian dust can influence the climate, air quality, human health, and ecosystems. Dust events in Northern China are the main contributors to dust aerosols in the world, but the impacts of meteorological and anthropogenic factors and their interactions on dust events remain unclear. This study analyzed the spatial and temporal variations of dust event frequencies and quantitatively investigated the impacts of meteorological conditions, anthropogenic factors, and their interactions on dust events using the geographical detector model (GeoDetector) in Northern China. Results revealed that the dust event frequency significantly decreased by 0.006 times yr−1 per site during 1980–2007. At the regional scale, there were large seasonal variations in the effects of meteorological conditions and anthropogenic factors on dust events. Strong winds and soil surface conditions are main drivers of dust events in spring. In summer and autumn, anthropogenic factors have significant impacts on the occurrence of dust events, but the frozen period and relative humidity are major impacting factors in winter. Effects of natural and anthropogenic factors on dust events showed great spatial and seasonal disparities over different vegetation regions. Interactions between two factors enhanced their impacts on the occurrence of dust events. There are also large spatial and seasonal variations in the primary interactions on dust events over different vegetation regions. The findings could help us to better understand the relative importance of various factors on dust events, which has important implications for improving the prediction of dust emission models and developing desertification control strategies.

The Development of British Public Diplomacy in the Arab World

This paper attempts to map the major changes and developments of British public diplomacy in the Arab world. I argue here that the BBC and the British Council have greatly assisted British public diplomacy efforts and can be regarded as effective because exerting influence in an indirect way can often be more effective than the direct advocacy approach followed by the British government during the colonial periods. In the beginning, the policy was focused on spreading propaganda, while today it is related to soft power and cultural diplomacy with the active use of social media. The paper concludes with a brief reference to social media use by British embassies in the region following the major Arab Spring events, indicating little audience engagement with them.

Drought-related hot summers: A joint probability analysis in the Iberian Peninsula

Droughts and hot extremes are major sources of risk to several socio-economic activities and their impacts are expected to increase under future global warming. Moreover, the simultaneous or sequential occurrence (compound events) of different climate extremes may lead to the amplification of the associated impacts. Even though the latest efforts in assessing hot and dry extremes and their interactions, the development of models describing the joint behavior of climate extremes is still a challenge. To contribute to the understanding of these compound events, we propose to assess the probability of extremely hot summer days in the Iberian Peninsula (IP) being preceded by drought events in spring and early summer, based on their joint probability distribution through copula theory. The precursor drought hazard was characterized by the Standardized Precipitation Evaporation Index (SPEI) for the months of May, June and July for different timescales (3-, 6- and 9-months). The Number of Hot Days per month (NHD) summed over the months of July and August were considered for modelling. The dependence structure between SPEI and NHD was very well identified for the most of the IP's regions by asymmetrical copulas with upper tail dependence (except in northwestern regions), suggesting that compound hot and dry extremes are strongly associated. The results show that the transition from previous wet to dry regimes increases substantially the probability of exceeding summer NHD extreme values, depending on the region and the drought timescale and target month. The results suggest a spatial heterogeneity over the IP when characterizing the influence of water deficits on following summer extreme temperatures, whereas northeastern, western and central regions were found to be the regions more prone to summer hot extremes induced by dryness, in contrast to southwestern, northwestern and southeastern regions (depending on the month and the timescale). This study provides estimates of the probability of drought-related hot extremes in the summer of the IP for different regions, which could be an important tool for responsible authorities to mitigate the impacts magnified by the interactions between the different hazards.

Status of Phenological Research Using Sentinel-2 Data: A Review

Remote sensing of plant phenology as an indicator of climate change and for mapping land cover has received significant scientific interest in the past two decades. The advancing of spring events, the lengthening of the growing season, the shifting of tree lines, the decreasing sensitivity to warming and the uniformity of spring across elevations are a few of the important indicators of trends in phenology. The Sentinel-2 satellite sensors launched in June 2015 (A) and March 2017 (B), with their high temporal frequency and spatial resolution for improved land mapping missions, have contributed significantly to knowledge on vegetation over the last three years. However, despite the additional red-edge and short wave infra-red (SWIR) bands available on the Sentinel-2 multispectral instruments, with improved vegetation species detection capabilities, there has been very little research on their efficacy to track vegetation cover and its phenology. For example, out of approximately every four papers that analyse normalised difference vegetation index (NDVI) or enhanced vegetation index (EVI) derived from Sentinel-2 imagery, only one mentions either SWIR or the red-edge bands. Despite the short duration that the Sentinel-2 platforms have been operational, they have proved their potential in a wide range of phenological studies of crops, forests, natural grasslands, and other vegetated areas, and in particular through fusion of the data with those from other sensors, e.g., Sentinel-1, Landsat and MODIS. This review paper discusses the current state of vegetation phenology studies based on the first five years of Sentinel-2, their advantages, limitations, and the scope for future developments.

Physiological and transcriptome analysis of Poa pratensis var. anceps cv. Qinghai in response to cold stress

BackgroundLow temperature limits the growth and development and geographical distribution of plants. Poa pratensis is a cool-season turfgrass mainly grown in urban areas. However, low winter temperature or cold events in spring and autumn may cause P.pratensis mortality, affecting the appearance of lawns. P.pratensis var. anceps cv. Qinghai (PQ) is widely distributed in the Qinghai-Tibet Plateau above 3000 m. PQ has greater cold tolerance than the commercially cultivated P.pratensis varieties. However, existing studies on the response mechanism of PQ to low temperatures have mainly focused on physiological and biochemical perspectives, while changes in the PQ transcriptome during the response to cold stress have not been reported.ResultsTo investigate the molecular mechanism of the PQ cold response and identify genes to improve the low-temperature tolerance of P.pratensis, we analyzed and compared the transcriptomes of PQ and the cold-sensitive P.pratensis cv. ‘Baron’ (PB) under cold stress using RNA sequencing. We identified 5996 and 3285 differentially expressed genes (DEGs) between the treatment vs control comparison of PQ and PB, respectively, with 5612 DEGs specific to PQ. Based on the DEGs, important Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, such as “starch and sucrose metabolism”, “protein processing in endoplasmic reticulum”, “phenylalanine metabolism” and “glycolysis/gluconeogenesis” were significantly enriched in PQ, and “starch and sucrose metabolism”, “phenylpropanoid biosynthesis”, “galactose metabolism” and “glutathione metabolism” were significantly enriched in PB. In addition, the “glycolysis” and “citrate cycle (TCA cycle)” pathways were identified as involved in cold tolerance of P.pratensis.ConclusionsAs we know, this is the first study to explore the transcriptome of P.pratensis var. anceps cv. Qinghai. Our study not noly provides important insights into the molecular mechanisms of P.pratensis var. anceps cv. Qinghai responds to cold stress, but also systematically reveals the changes of key genes and products of glycolysis and TCA cycle in response to cold stress, which is conductive to the breeding of cold-tolerance P.pratensis genotype.

Lowest drought sensitivity and decreasing growth synchrony towards the dry distribution margin of European beech

AbstractAimClimate limits the potential distribution ranges of species. Establishment and growth of individuals at range margins is assumed to be more limited by extreme events such as drought or frost events than in the centre of their range. We explore whether the growth of beech is more sensitive to drought towards the dry distribution margin and more sensitive to frost towards the cold distribution margin. Furthermore, we aim to gain insight into the adaptive potential of beech towards both the dry and cold distribution margins.LocationEuropean gradient from the dry (Spain) to the cold (Poland, Sweden) distribution margin of beech.TaxonEuropean beech (Fagus sylvatica L.).MethodsWe applied a range‐wide dendroecological study to analyse spatial and temporal trends in climate–growth relationships. We further investigated negative growth anomalies and growth synchrony towards the range margins.ResultsWe found beech to be drought sensitive across its whole range, except at the dry distribution margin. Furthermore, sensitivity to winter temperature was not found in the centre or at the cold distribution margin, but at the southern distribution margin. Growth synchrony was lower at the dry than at the cold distribution margin.Main conclusionsBeech seems to be adapted to drought at the dry distribution margin with a high adaptive potential indicated by the lowest growth synchrony along the gradient. At the cold distribution margin, cold events in winter and spring were less important for growth than drought. Still, the importance of spring frost for beech growth appears to increase in recent decades. Considering a projected north‐eastward shift of the distribution range, beech is likely facing drought stress in combination with spring frost risk at the cold margin which could lead to a hampered range expansion.

Stratosphere–Troposphere Exchange and O3 Variability in the Lower Stratosphere and Upper Troposphere over the Irene SHADOZ Site, South Africa

This study aims to investigate the Stratosphere-Troposphere Exchange (STE) events and ozone changes over Irene (25.5° S, 28.1° E). Twelve years of ozonesondes data (2000–2007, 2012–2015) from Irene station operating in the framework of the Southern Hemisphere Additional Ozonesodes (SHADOZ) was used to study the troposphere (0–16 km) and stratosphere (17–28 km) ozone (O3) vertical profiles. Ozone profiles were grouped into three categories (2000–2003, 2004–2007 and 2012–2015) and average composites were calculated for each category. Fifteen O3 enhancement events were identified over the study period. These events were observed in all seasons (one event in summer, four events in autumn, five events in winter and five events in spring); however, they predominantly occur in winter and spring. The STE events presented here are observed to be influenced by the Southern Hemisphere polar vortex. To strengthen the investigation into STE events, advected potential vorticity maps were used, which were assimilated using Modélisation Isentrope du transport Méso–échelle de l’Ozone Stratosphérique par Advection (MIMOSA) model for the 350 K (~12–13 km) isentropic level. These maps indicated transport of high latitude air masses responsible for the reduction of the O3 mole fractions at the lower stratosphere over Irene which coincides with the enhancement of ozone in the upper troposphere. In general, the stratosphere is dominated by higher Modern Retrospective Analysis for Research Application (MERRA-2) potential vorticity (PV) values compared to the troposphere. However, during the STE events, higher PV values from the stratosphere were observed to intrude the troposphere. Ozone decline was observed from 12 km to 24 km with the highest decline occurring from 14 km to 18 km. An average decrease of 6.0% and 9.1% was calculated from 12 to 24 km in 2004–2007 and 2012–2015 respectively, when compared with 2000–2003 average composite. The observed decline occurred in the upper troposphere and lower stratosphere with winter and spring showing more decline compared with summer and autumn.

Spring Leafing Phenology Favors Younger Culms of Moso Bamboo: Aspects From Water Use Relations.

As the most widely distributed giant running bamboo species in China, Moso bamboo (Phyllostachys edulis) can accomplish both development of newly sprouted culms and leaf renewal of odd-year-old culms within a few months in spring. The two phenological events in spring may together change water distribution among culms in different age categories within a stand, which may differ from our conventional understanding of the negative age effect on bamboo water use. Therefore, to explore the effect of spring shooting and leaf phenology on age-specific water use of Moso bamboo and potential water redistribution, we monitored water use of four culm age categories (newly sprouted, 1-, 2-, and 3-year-old; namely A0, A1, A2, A3) in spring from March to June 2018. For newly sprouting culms, the spring phenological period was classified into five stages (incubation, culm-elongation, branch-development, leafing, established). Over these phenological stages, age-specific accumulated sap flux density showed different patterns. The oldest culms, A3, were not influenced by leaf renewal and kept nearly constant and less water use than the other aged culms. However, A2, which did not renew their leaves, had the most water use at the two initial stages (incubation, culm-elongation) but consumed less water than A0 and A1 after the fourth stage (leafing). At the end of June, water use of the four age categories sorted in order of A0 > A1 > A2 > A3, which confirms the conventional thought and observations, i.e., a negative age effect. The results indicate that new leaf flushing may benefit younger culms (A1 and A0) more than older culms (A2 and A3), i.e., increasing their transpiration response to radiation and share of the stand transpiration. With the underground connected rhizome system, the bamboo stand as an integration seems to balance its water use among culms of different ages to support the water use of freshly sprouted culms during their developing period.

COVID-19 Scratch Models To Support Local Decisions

This article is based on modeling studies conducted in response to requests from Yale University, the Yale New Haven Hospital and the State of Connecticut during the early weeks of the SARS-CoV-2 outbreak. Much of this work relied on scratch modeling, that is, models created from scratch in real time. Applications included recommending event crowd-size restrictions, hospital surge planning, timing decisions (when to stop and possibly restart university activities), and scenario analyses to assess the impacts of alternative interventions, among other problems. This paper documents the problems faced, models developed, and advice offered during real-time response to the COVID-19 crisis at the local level. Results include a simple formula for the maximum size of an event that ensures no infected persons are present with 99% probability; the determination that existing ICU capacity was insufficient for COVID-19 arrivals which led to creating a large dedicated COVID-19 negative pressure ICU; and a new epidemic model that showed the infeasibility of the university hosting normal spring and summer events, that lockdown-like stay-at-home and social distancing restrictions without additional public health action would only delay transmission and enable a rebound after restrictions are lifted, and that aggressive community screening to rapidly detect and isolate infected persons could end the outbreak.

Climatology of Iraqi dust events during 1980–2015

Mesopotamia in Iraq is exposed to dust events of different intensity because of adjacent extended desert or semi-desert areas. This study investigates the spatial–temporal distributions of dust events (including suspended dust, rising dust and dust storms) in Iraq by analysing dust observations based on visibility from seven meteorological stations supplied by the Iraqi Meteorological Organization (IMO) during 1980–2015. The annual and seasonal evaluation of all dust event frequencies is examined. The findings show that Iraq has been exposed to the maximum number of dust events in spring and summer seasons over the past 35 years. The dust was more active in summer compared with other seasons for the northern region of Iraq, while the south and central parts of Iraq are exposed to the largest frequency of dust storms in spring and summer. The cities near desert areas (e.g. Nasiriya, Basra and Baghdad) suffer from the greatest frequency of dust storms compared to the northern and eastern regions. According to the annual average during 1980–2015, the frequency of major dust storm activity in Nasiriya was 7.8 days, in Baghdad 3.1 days) and in Basra 2.3 days. Suspended dust is more frequent in Iraq compared with rising dust or dust storms. There was a greater frequency of dust events associated with high temperatures and wind speeds in the central and southern areas during summer. All three types of dust events show similar time trend distributions with three periods: increased frequency of dust between 1980 and 1993, decreased frequency during 1993–2001 and increased again from 2001.

Phenological responses in a sycamore-aphid-parasitoid system and consequences for aphid population dynamics: A 20year case study.

Species interactions have a spatiotemporal component driven by environmental cues, which if altered by climate change can drive shifts in community dynamics. There is insufficient understanding of the precise time windows during which inter-annual variation in weather drives phenological shifts and the consequences for mismatches between interacting species and resultant population dynamics-particularly for insects. We use a 20year study on a tri-trophic system: sycamore Acer pseudoplatanus, two associated aphid species Drepanosiphum platanoidis and Periphyllus testudinaceus and their hymenopteran parasitoids. Using a sliding window approach, we assess climatic drivers of phenology in all three trophic levels. We quantify the magnitude of resultant trophic mismatches between aphids and their plant hosts and parasitoids, and then model the impacts of these mismatches, direct weather effects and density dependence on local-scale aphid population dynamics. Warmer temperatures in mid-March to late-April were associated with advanced sycamore budburst, parasitoid attack and (marginally) D. platanoidis emergence. The precise time window during which spring weather advances phenology varies considerably across each species. Crucially, warmer temperatures in late winter delayed the emergence of both aphid species. Seasonal variation in warming rates thus generates marked shifts in the relative timing of spring events across trophic levels and mismatches in the phenology of interacting species. Despite this, we found no evidence that aphid population growth rates were adversely impacted by the magnitude of mismatch with their host plants or parasitoids, or direct impacts of temperature and precipitation. Strong density dependence effects occurred in both aphid species and probably buffered populations, through density-dependent compensation, from adverse impacts of the marked inter-annual climatic variation that occurred during the study period. These findings explain the resilience of aphid populations to climate change and uncover a key mechanism, warmer winter temperatures delaying insect phenology, by which climate change drives asynchronous shifts between interacting species.

Freeze-thaw events delay spring budburst and leaf expansion while longer photoperiods have opposite effect under different [CO2] in white birch: Advance it under elevated but delay it under ambient [CO2

Past studies indicate that narrower conduits such as those in diffuse-porous species are less vulnerable to freeze-thaw (FT) induced embolism and also facilitate the refilling of embolized xylem conduits early in the spring, resulting in an earlier bud break. In this study, we investigated if a novel environmental condition associated with climate change-induced northward migration will affect the vulnerability to FT-induced embolism and spring phenology in white birch. Seedlings were grown under ambient (400 μmol mol−1) or elevated CO2 concentration (1000 μmol mol−1), and four photoperiod regimes corresponding to 48 (seed origin), 52, 55, and 58 °N latitude. We found that the longest photoperiod (corresponding to 58 °N latitude) significantly increased the maximum specific hydraulic conductivity of the stem. CO2 concentration ([CO2]) and photoperiod had no significant impact on the vulnerability to FT-induced embolism. The treatment of 5 freeze-thaw cycles (+5 to −20 °C) led to an 11 % loss of hydraulic conductivity in dormant seedlings that had been stored at −4 °C for 3 months while the effect of such a treatment in the fall was much smaller. This result suggests that freeze-thaw events in late winter or spring can impair the hydraulic conductivity of the xylem which in turn may negatively affect the physiology of the trees. Indeed, the FT treatment in this study delayed budburst and leaf expansion in the spring. It is interesting to note that photoperiods had the opposite effect on budburst under different [CO2]: longer photoperiods led to earlier budburst in the spring under elevated [CO2], but delayed budburst under ambient [CO2]. The synergistic effect of longer photoperiods and CO2 elevation suggests that the growing season for white birch may be longer than what we predict from either factor alone at a migration site in the future when [CO2] will be much higher.

Spatiotemporal variations of nitrogen and phosphorus in a clay plain hydrological system in the Great Lakes Basin

Nutrient imbalance in groundwater and surface water resources can have severe implications on human and aquatic life, including contamination of drinking water sources and the degradation of ecosystems. A field-based watershed-scale study was completed to investigate nutrient dynamics and hydrologic processes in an agriculturally-dominant clay plain system within the Great Lakes Basin. Spatial and temporal variations of nitrogen and phosphorus were examined by sampling groundwater and surface water regularly over a period of one year (June 2017 to July 2018) for nutrients including nitrate, soluble reactive phosphorus, total dissolved phosphorus and total reactive phosphorus. Nitrate transport from surrounding agricultural land to surface water was intensified with an increase in precipitation events in spring and early winter and phosphorus transport to surface water was increased during freeze-thaw cycles in the winter. The results are pertinent to the improvement of current nutrient and water management policies in clay plain systems where nutrient imbalances in surface water are a concern.

Meteorological and hydrological drought from 1987 to 2017 in Doce River Basin, Southeastern Brazil

ABSTRACT Meteorological drought is a natural hazard characterized as below-average precipitation from expected or normal that can affect various economic sectors, and lead to period with inadequate streamflow for established uses of the water (hydrological drought). We aimed to apply the Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSI) to identify the occurrence and the intensity of droughts in Doce River Basin (DRB), Southeastern Brazil. For this purpose, 71 rain gauge stations and one streamflow station were selected with 30-year monthly historical series (1987 to 2017). The SPI and SSI were calculated for the hydrological year (October-September) and the seasons (Spring, Summer, Fall, and Winter). SPI mapping was performed by geostatistical procedures. Pearson's coefficient was calculated to analyze the influence of meteorological on hydrological drought. The main meteorological drought events, observed in the hydrological years of 1994/95, 2000/01, and a recent and consecutive period of four hydrological years (2013-2017), were mainly influenced by events in spring and summer and, to a lesser extent, in fall. It was observed the influence of the meteorological drought on the hydrological drought on an annual and seasonal scale, except winter, where low precipitation does not influence in the streamflow.

Seasonal Variations and Long‐Term Trend of Dust Particle Number Concentration Over the Northeastern United States

AbstractMineral dust is known to affect cloud and precipitation by serving as ice nuclei, and an increasing number of modeling studies have explicitly related ice nucleation with the dust number concentrations. We examine the seasonal variations and the long‐term trend of dust number concentrations over the northeastern United States (NEUS) during 2000–2017, based on results from a global chemical transport model with size‐resolved particle microphysics (GEOS‐Chem/APM). Comparisons with observations show that GEOS‐Chem/APM can capture most of the strong dust events in the NEUS. The model results indicate that mineral dusts over the NEUS are dominated by dust transported in the lower and middle troposphere (from 2 to 6 km). The number concentrations of dust larger than 500 nm (ND,d > 500nm) vary by over 2 orders of magnitude from nondust‐transport days to event days, and ND,d > 500nm in different seasons can vary by 1 order of magnitude. The frequencies of dust events also show seasonal variation, with most annually top 50% dust events in spring and early summer (March–June) and in fall and early winter (September–December), and stronger dust events mainly in March–June. From 2000 to 2017, the springtime dust event days decrease by about 50% (above‐average dust events), 76% (top 10% events), and 85% (top 5% events), and ND,d > 500nm of strong events decreases by about 50%. Our analysis indicates that these decrease trends are caused by the declining Asian dust loading. The frequencies of dust events in summer have a weaker decreasing trend, and there is no obvious tendency in other seasons.

Relative Deprivation as a Factor of Sociopolitical Destabilization: Toward a Quantitative Comparative Analysis of the Arab Spring Events

The article analyzes relative deprivation as a possible factor of sociopolitical instability during the Arab Spring events using the methods of correlation and multiple regression analysis. In this case, relative deprivation is operationalized in two ways: (a) through the indicator of subjective feeling of happiness on the eve of the events of the Arab Spring, and (b) through the scale of decrease of the subjective feeling of happiness on the eve of the events of Arab Spring. It is shown that the change in the level of subjective feeling of happiness between 2009 and 2010 is a powerful, statistically significant predictor of the level of destabilization in Arab countries in 2011. The next most powerful predictor is the mean value of the subjective feeling of happiness in the corresponding country for 2010. At the same time, the fundamental economic indicators we tested, while controlling for them, have turned out to be extremely weak and at the same time statistically insignificant predictors of the level of sociopolitical instability in the Arab countries in 2011.

Digital media and the acceleration of resistance


 
 
 
 This article is concerned with providing empirical evidence relating to the use of digital media and resistance during the so-called Arab Spring events. These events have been widely acknowledged as a case where digital media significantly contributed to the successful attainment of movements’ objectives. The use of such innovative technologies has been tied to the characteristics and, ultimately, the ends of these movements, with their ‘youthful’, ‘leaderless’ and ‘spontaneous’ nature reflecting Western-orientated practices. However, the analysis presented here utilises interview data obtained from participants in the 2010/11 Tunisian Revolution, detailing their perspectives and explanations of digital media’s role. The data and analysis show that while such technologies were a useful tool, their prominence has been exaggerated and offers a flawed understanding of the events. Rather, the social change being pursued during the Tunisian revolution was profound. Therefore, the deeper implications of the common emphasis on digital media in the literature is explored, with Rosa’s (2015) assessment of social acceleration being informative for elaborating on the nuances of these technologies’ use during the 2010/11 events.
 
 
 
 

A Climatology of Rain-on-Snow Events for Norway

Abstract Rain-on-snow (ROS) events are multivariate hydrometeorological phenomena that require a combination of rain and snowpack, with complex processes occurring on and within the snowpack. Impacts include floods and landslides, and rain may freeze within the snowpack or on bare ground, potentially affecting vegetation, wildlife, and permafrost. ROS events occur mainly in high-latitude and mountainous areas, where sparse observational networks hinder accurate quantification—as does a scale mismatch between coarse-resolution (50–100 km) reanalysis products and localized events. Variability in the rain–snow temperature threshold and temperature sensitivity of snowmelt adds additional uncertainty. Here the high-resolution (1 km) seNorge hydrometeorological dataset, capturing complex topography and drainage networks, is utilized to produce the first large-scale climatology of ROS events for mainland Norway. For daily data spanning 1957–2016, suitable rain and snowpack thresholds for defining ROS events are applied to construct ROS climatologies for 1961–90 and 1981–2010 and to investigate trends. Differing ROS characteristics are found, reflecting Norway’s diverse climates. Relative to 1961–90, events in the 1981–2010 period decrease most in the southwest low elevations in winter, southeast in spring, and north in summer (consistent with less snow cover in a warming climate) and increase most in the southwest high elevations, central mountains, and north in winter–spring (consistent with increased precipitation and/or more snow falling as rain in a warming climate). Winter–spring events also broadly correlate with the North Atlantic Oscillation, and the Scandinavia pattern—and more so with the Arctic Oscillation, particularly in the southern mountain region where long-term ROS trends are significant (+0.50 and +0.33 daily ROS counts per kilometer squared per decade for winter and spring).

Centennial decline in North Sea water clarity causes strong delay in phytoplankton bloom timing.

With climate warming, a widespread expectation is that events in spring, such as flowering, bird migrations, and insect bursts, will occur earlier because of increasing temperature. At high latitudes, increased ocean temperature is suggested to advance the spring phytoplankton bloom due to earlier stabilization of the water column. However, climate warming is also expected to cause browning in lakes and rivers due to increases in terrestrial greening, ultimately reducing water clarity in coastal areas where freshwater drain. In shallow areas, decreased retention of sediments on the seabed will add to this effect. Both browning and resuspension of sediments imply a reduction of the euphotic zone and Sverdrup's critical depth leading to a delay in the spring bloom, counteracting the effect of increasing temperature. Here, we provide evidence that such a transparency reduction has already taken place in both the deep and shallow areas of the North Sea during the 20th century. A sensitivity analysis using a water column model suggests that the reduced transparency might have caused up to 3weeks delay in the spring bloom over the last century. This delay stands in contrast to the earlier bloom onset expected from global warming, thus highlighting the importance of including changing water transparency in analyses of phytoplankton phenology and primary production. This appears to be of particular relevance for coastal waters, where increased concentrations of absorbing and scattering substances (sediments, dissolved organic matter) have been suggested to lead to coastal darkening.

On the contribution of chemical oscillations to ozone depletion events in the polar spring

Abstract. This paper presents a numerical study of the oscillations (or recurrences) of tropospheric ozone depletion events (ODEs) using the further-developed one-dimensional KInetic aNALysis of reaction mechanics with Transport (KINAL-T) chemistry transport model. Reactive bromine is the major contributor to the occurrence of ODEs. After the termination of an ODE, the reactive bromine in the air is deposited onto aerosols or on the snow surface, and the ozone may regenerate via NOx-catalyzed photochemistry or by turbulent transport from the free troposphere into the boundary layer. The replenished ozone then is available for the next cycle of autocatalytic bromine release (bromine explosion) leading to another ODE. The oscillation periods are found to be as short as 5 d for the purely chemically NOx-driven oscillation and 30 d for a diffusion-driven oscillation. An important requirement for oscillation of ODEs to occur is found to be a sufficiently strong inversion layer. In a parameter study, the dependence of the oscillation period on the nitrogen oxides' concentration, the inversion layer strength, the ambient temperature, the aerosol density, and the solar radiation is investigated. Parameters controlling the oscillation of ODEs are discussed.