Previous Summers Research Articles

Rebound Body Mass Index Growth in Year‐Round Elementary Education Students of Largely Hispanic Descent Undergoing Obesity Interventions

Body mass index (BMI) increases when students are away on summer vacation. Evaluation of serial BMI measurements on year-round students allows new insight into the reasons children gain weight seasonally. The 206 first and second graders of 2-year-round elementary schools with obesity intervention programs were weighed and measured every 6 months from April 2011 until April 2013. BMI and BMI percentiles were recorded. Children <50th, 50th to 85th, and 85th to 95th BMI percentiles showed significant accelerated winter gains in BMI (p = 2.6 × 10(-7), p = 6.8 × 10(-10), and p = .0007, respectively) compared with the previous summers. Accelerated BMI growth of the second summer was absent when compared with the previous winter BMI changes in children <95th percentile (p = .48, p = .81, and p = .93). For children >95th percentile, BMI gain continued without significant changes year-round. School-wide interventions to induce BMI growth limitations are associated with significant rebound BMI gain with possible wintertime augmentation in nonobese children of year-round education programs. Obese children do not display rebound BMI gain, BMI seasonal change, or BMI limitations in response to school-based interventions. School weight control programs should consider off-campus sources of weight gain and be vigilant for rebound and delayed seasonal BMI gains.

Ozone and aerosol tropospheric concentrations variability analyzed using the ADRIMED measurements and the WRF and CHIMERE models

Abstract. During the months of June and July 2013, over the Euro–Mediterranean area, the ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) project was dedicated to characterize the ozone and aerosol concentrations in the troposphere. It is first shown that this period was not highly polluted compared to previous summers in this region, with a moderate ozone production, no significant vegetation fire events and several precipitation periods scavenging the aerosol. The period is modeled with the WRF (Weather Research and Forecasting) and CHIMERE models, and their ability to quantify the observed pollution transport events is presented. The CHIMERE model simulating all kinds of sources (anthropogenic, biogenic, mineral dust, vegetation fires); the aerosol speciation, not available with the measurements, is presented: during the whole period, the aerosol was mainly constituted by mineral dust, sea salt and sulfates close to the surface and mainly by mineral dust in the troposphere. Compared to the AERONET (Aerosol Robotic Network) size distribution, it is shown that the model underestimates the coarse mode near mineral dust sources and overestimates the fine mode in the Mediterranean area, highlighting the need to improve the model representation of the aerosol size distribution both during emissions, long-range transport and deposition.

The influence of masting phenomenon on growth-climate relationships in trees: explaining the influence of previous summers' climate on ring width.

Tree growth is frequently linked to weather conditions prior to the growing season but our understanding of these lagged climate signatures is still poorly developed. We investigated the influence of masting behaviour on the relationship between growth and climate in European Beech (Fagus sylvatica L.) using a rare long-term dataset of seed production and a new regional tree ring chronology. Fagus sylvatica is a masting species with synchronous variations in seed production which are strongly linked to the temperature in the previous two summers. We noted that the weather conditions associated with years of heavy seed production (mast years) were the same as commonly reported correlations between growth and climate for this species. We tested the hypothesis that a trade-off between growth and reproduction in mast years could be responsible for the observed lagged correlations between growth and previous summers' temperatures. We developed statistical models of growth based on monthly climate variables, and show that summer drought (negative correlation), temperature of the previous summer (negative) and temperature of the summer 2 years previous (positive) are significant predictors of growth. Replacing previous summers' temperature in the model with annual seed production resulted in a model with the same predictive power, explaining the same variance in growth. Masting is a common behaviour in many tree species and these findings therefore have important implications for the interpretation of general climate-growth relationships. Lagged correlations can be the result of processes occurring in the year of growth (that are determined by conditions in previous years), obviating or reducing the need for 'carry-over' processes such as carbohydrate depletion to be invoked to explain this climate signature in tree rings. Masting occurs in many tree species and these findings therefore have important implications for the interpretation of general climate-growth relationships.

Delayed responses of an Arctic ecosystem to an extreme summer: impacts on net ecosystem exchange and vegetation functioning

Abstract. The importance and consequences of extreme events on the global carbon budget are inadequately understood. This includes the differential impact of extreme events on various ecosystem components, lag effects, recovery times, and compensatory processes. In the summer of 2007 in Barrow, Arctic Alaska, there were unusually high air temperatures (the fifth warmest summer over a 65-year period) and record low precipitation (the lowest over a 65-year period). These abnormal conditions were associated with substantial desiccation of the Sphagnum layer and a reduced net Sphagnum CO2 sink but did not affect net ecosystem exchange (NEE) from this wet-sedge arctic tundra ecosystem. Microbial biomass, NH4+ availability, gross primary production (GPP), and ecosystem respiration (Reco) were generally greater during this extreme summer. The cumulative ecosystem CO2 sink in 2007 was similar to the previous summers, suggesting that vascular plants were able to compensate for Sphagnum CO2 uptake, despite the impact on other functions and structure such as desiccation of the Sphagnum layer. Surprisingly, the lowest ecosystem CO2 sink over a five summer record (2005–2009) was observed during the 2008 summer (~70% lower), directly following the unusually warm and dry summer, rather than during the extreme summer. This sink reduction cannot solely be attributed to the potential damage to mosses, which typically contribute ~40% of the entire ecosystem CO2 sink. Importantly, the return to a substantial cumulative CO2 sink occurred two summers after the extreme event, which suggests a substantial resilience of this tundra ecosystem to at least an isolated extreme event. Overall, these results show a complex response of the CO2 sink and its sub-components to atypically warm and dry conditions. The impact of multiple extreme events requires further investigation.

Community dynamics and physiology of Symbiodinium spp. before, during, and after a coral bleaching event

Community dynamics and physiology of Symbiodinium associated with Orbicella ( = Montastraea) faveolata were examined before, during, and after a thermally induced coral bleaching event in Puerto Morelos, Mexico. We combined microsampling molecular genotyping with in situ pulse‐amplitude modulated fluorometry to correlate colony variability of Symbiodinium population identities and the phenomena of partial coral bleaching. Pigmented nonbleached portions of O. ( = M.) faveolata were compared with bleached portions of the same colony. During bleaching, maximum quantum yield of photosystem II (PSII; Fv : Fm) was significantly lower and highly variable (range 0.110 to 0.680) compared with previous summers in which coral bleaching was absent (range 0.516 to 0.661) and recovery (range 0.480 to 0.716). Differential susceptibility to environmental perturbation of Fv : Fm corresponded to distinct genetic identities of Symbiodinium. Analysis of ribosomal deoxyribonucleic acid (rDNA) internal transcribed spacer 2 (ITS2) revealed regions of the coral colonies that had phylotype A3 prior to bleaching were more resistant to the bleaching perturbation than adjacent bleaching‐prone patches that harbored phylotypes B17 and C7. During environmental perturbation, regions of the colonies containing predominantly Symbiodinium phylotypes A3 or D1a retained significantly higher Fv : Fm values than adjacent regions with phylotypes B17 and C7. Following bleaching, rapid recovery of symbiotic algal densities greatly exceeded normal seasonal oscillations. During recovery we document shifts in Symbiodinium populations and increase prevalence of Symbiodinium types A3 and D1a, phylotypes known to have enhanced thermal tolerances. Thermal tolerance of Symbiodinium spp. influences the changes of coral—Symbiodinium communities during disturbance events and the dynamics of coral—Symbiodinium repopulation.

Brief Communication: Further summer speedup of Jakobshavn Isbræ

Abstract. We have extended the record of flow speed on Jakobshavn Isbræ through the summer of 2013. These new data reveal large seasonal speedups, 30 to 50% greater than previous summers. At a point a few kilometres inland from the terminus, the mean annual speed for 2012 is nearly three times as great as that in the mid-1990s, while the peak summer speeds are more than a factor of four greater. These speeds were achieved as the glacier terminus appears to have retreated to the bottom of an over-deepened basin with a depth of ~ 1300 m below sea level. The terminus is likely to reach the deepest section of the trough within a few decades, after which it could rapidly retreat to the shallower regions ~ 50 km farther upstream, potentially by the end of this century.

Tree‐ring stable isotopes record the impact of a foliar fungal pathogen onCO2assimilation and growth inDouglas‐fir

Swiss needle cast (SNC) is a fungal disease of Douglas-fir (Pseudotsuga menziesii) that has recently become prevalent in coastal areas of the Pacific Northwest. We used growth measurements and stable isotopes of carbon and oxygen in tree-rings of Douglas-fir and a non-susceptible reference species (western hemlock, Tsuga heterophylla) to evaluate their use as proxies for variation in past SNC infection, particularly in relation to potential explanatory climate factors. We sampled trees from an Oregon site where a fungicide trial took place from 1996 to 2000, which enabled the comparison of stable isotope values between trees with and without disease. Carbon stable isotope discrimination (Δ(13)C) of treated Douglas-fir tree-rings was greater than that of untreated Douglas-fir tree-rings during the fungicide treatment period. Both annual growth and tree-ring Δ(13)C increased with treatment such that treated Douglas-fir had values similar to co-occurring western hemlock during the treatment period. There was no difference in the tree-ring oxygen stable isotope ratio between treated and untreated Douglas-fir. Tree-ring Δ(13)C of diseased Douglas-fir was negatively correlated with relative humidity during the two previous summers, consistent with increased leaf colonization by SNC under high humidity conditions that leads to greater disease severity in following years.

MedStart: A Hands‐on Anatomical Experience for Middle School Students

The goal of MedStart, a medical student run, week‐long science education summer camp, is to provide East Harlem middle school students with an appreciation of cardiovascular, pulmonary, and gastrointestinal system disease pathogenesis, treatment and prevention. Introducing students to the anatomical basis of health and disease is a vital component of our program. MedStart takes an interactive approach to education, dividing the camp up into five segments—vital signs, pulmonary, gastrointestinal, cardiovascular, and CPR/first aid—with strong hands‐on components during the organ system‐based days. In the summer of 2012 our program conducted a series of activities in which campers were able to examine manually normal and pathologic human cadaveric hearts, lungs, stomachs, intestines, and livers, in small group sessions led by Mount Sinai School of Medicine medical and graduate students. Campers were given assessments before and after the camp, which, in previous summers, have demonstrated increased knowledge gains in the organ systems we focused on. Along with its other hands‐on activities, MedStart is working to increase health knowledge and empower East Harlem youth to take control of their own health.Grant Funding Source: American Association of Anatomists Educational Outreach Grant

No trespassing: using a biofence to manipulate wolf movements

Context Conserving large carnivores can be challenging because of conflicts with human land use and competition with humans for resources. Predation on domestic stock can have negative economic impacts particularly for owners of small herds, and tools for minimising carnivore depredation of livestock are needed. Canids use scent marking to establish territories and avoid intraspecific conflict. Exploiting scent-marking behaviour may provide a means for manipulating canid movements. Aims We hypothesised that human-deployed scent marks (i.e. ‘biofence’) could be used to manipulate the movements of grey wolves (Canis lupus) in Idaho, USA. Methods We deployed 65 km of biofence within three wolf-pack territories during summer 2010 and 2011 and used location data from satellite-collared wolves and sign surveys to assess the effectiveness of biofencing. Key results Location data provided by satellite-collared wolves and sign surveys in 2010 showed little to no trespass of the biofence, even though the excluded areas were used by the packs in previous summers. We also opportunistically deployed a biofence in between a rendezvous site of a resident pack and a nearby sheep grazing allotment; the pack was not implicated in any depredations in summer 2010, even though they had killed sheep every year since 2006. Location data provided by satellite-collared wolves in summer 2011 showed that wolves did trespass biofences. Conclusions Biofencing effectively manipulated the movements of wolves in the first year of our study, but not the second. Implications Our work suggests that biofencing may be most limited by the apparent necessity to maintain a continuous presence once the biofence is established. The inherent labour and costs associated with such efforts may limit the usefulness of biofencing. Our work can be improved on through further testing that maintains biofencing over a longer timeframe (&gt;3 months), samples several animals per treatment pack, and uses a treatment and control design.

Of mast and mean: differential‐temperature cue makes mast seeding insensitive to climate change

Mast-seeding plants often produce high seed crops the year after a warm spring or summer, but the warm-temperature model has inconsistent predictive ability. Here, we show for 26 long-term data sets from five plant families that the temperature difference between the two previous summers (ΔT) better predicts seed crops. This discovery explains how masting species tailor their flowering patterns to sites across altitudinal temperature gradients; predicts that masting will be unaffected by increasing mean temperatures under climate change; improves prediction of impacts on seed consumers; demonstrates that strongly masting species are hypersensitive to climate; explains the rarity of consecutive high-seed years without invoking resource constraints; and generates hypotheses about physiological mechanisms in plants and insect seed predators. For plants, ΔT has many attributes of an ideal cue. This temperature-difference model clarifies our understanding of mast seeding under environmental change, and could also be applied to other cues, such as rainfall.

West Nile Virus in North‐Eastern Italy, 2011: Entomological and Equine IgM‐Based Surveillance to Detect Active Virus Circulation

Since 2008, West Nile Virus (WNV) has expanded its range in several Italian regions, and its yearly recurrence suggests the virus may have become endemic in some areas. In 2011, a new plan based also on the detection of IgM antibodies was implemented in the north-eastern Italian regions of Veneto and Friuli Venezia Giulia, aiming to early detect WNV infections in areas where the virus had already circulated during the previous summers, and in adjacent zones. From July to November 2011, 1880 sera from 521 equine premises were screened by a commercial IgM capture ELISA. Mosquitoes were captured by CDC-CO2 traps at 61 locations in the two regions. Collected mosquitoes were identified, pooled by species/date/location and examined by real-time RT-PCR and sequencing. Passive surveillance was carried out on clinically affected horses and non-migratory wild birds found dead. IgM sero-positive equines were detected in 19 holdings, five in the area with WNV circulation (AWC) and 14 in the surveillance area (SA); 10 more horse premises tested positive to further serological controls within 4 km of the positive holdings. A total of 85,398 mosquitoes of 15 species were collected and 2732 pools examined. Five Culex pipiens pools tested positive for the presence of WNV. Passive surveillance on non-migratory wild birds allowed detection of the virus only in one found dead collared dove (Streptopelia decaocto), of 82 birds sampled. The WNV belonged to the lineage 2, which had been isolated for the first time in Italy earlier in 2011. By the first week of October, nine human cases had been confirmed in the same area. The implementation of a protocol combining IgM screening of horses with surveillance on mosquito vectors proved to be valuable for early detecting WNV circulation.

Neonatal mortality of elk driven by climate, predator phenology and predator community composition

1. Understanding the interaction among predators and between predation and climate is critical to understanding the mechanisms for compensatory mortality. We used data from 1999 radio-marked neonatal elk (Cervus elaphus) calves from 12 populations in the north-western United States to test for effects of predation on neonatal survival, and whether predation interacted with climate to render mortality compensatory. 2. Weibull survival models with a random effect for each population were fit as a function of the number of predator species in a community (3-5), seven indices of climatic variability, sex, birth date, birth weight, and all interactions between climate and predators. Cumulative incidence functions (CIF) were used to test whether the effects of individual species of predators were additive or compensatory. 3. Neonatal elk survival to 3 months declined following hotter previous summers and increased with higher May precipitation, especially in areas with wolves and/or grizzly bears. Mortality hazards were significantly lower in systems with only coyotes (Canis latrans), cougars (Puma concolor) and black bears (Ursus americanus) compared to higher mortality hazards experienced with gray wolves (Canis lupus) and grizzly bears (Ursus horribilis). 4. In systems with wolves and grizzly bears, mortality by cougars decreased, and predation by bears was the dominant cause of neonatal mortality. Only bear predation appeared additive and occurred earlier than other predators, which may render later mortality by other predators compensatory as calves age. Wolf predation was low and most likely a compensatory source of mortality for neonatal elk calves. 5. Functional redundancy and interspecific competition among predators may combine with the effects of climate on vulnerability to predation to drive compensatory mortality of neonatal elk calves. The exception was the evidence for additive bear predation. These results suggest that effects of predation by recovering wolves on neonatal elk survival, a contentious issue for management of elk populations, may be less important than the composition of the predator community. Future studies would benefit by synthesizing overwinter calf and adult-survival data sets, ideally from experimental studies, to test the roles of predation in annual compensatory and additive mortality of elk.

Benjamin Leigh Smith's third Arctic expedition: Svalbard, 1873

ABSTRACTIn 1873, the British explorer Benjamin Leigh Smith concluded the private oceanographic and geographical explorations in the seas around Svalbard that he had begun in 1871 and continued in 1872. The logistics of the 1873 expedition, however, were far more complicated than those of the first two voyages. Rather than using a single ship as he had done with the sailing vessel Samson the previous summers, Leigh Smith chartered James Lamont's Arctic steamer Diana and employed Samson as a reserve supply tender. With the added supplies Samson afforded, Leigh Smith planned to round the northeast limit of Svalbard, which he had discovered in 1871, and survey Kong Karls Land. Among those invited to join to expedition was a twenty-three-year-old member of the Royal Engineers, Lieutenant Herbert C. Chermside, who would visit the Arctic for the first and last time in a long life of military service. It was to Chermside that Leigh Smith entrusted the keeping of the expedition's logbooks. These three unpublished journals, along with a log kept by Samson's captain, William Walker, provide details of an expedition that, while it failed in its primary objective to round Nordaustlandet, did succeed in relieving Adolf Erik Nordenskiöld's Swedish polar expedition beset near Mosselbukta. It also maintained an array of contacts with whalers and sealers, for example the Peterhead whaler David Gray and the Norwegian skipper Frederick Christian Mack, regarding local conditions around Svalbard. At Augustabukta, Chermside's observations of uplifted skeletons of remotely harvested whales give estimated death ranges of between 1569–1691 and 1764–1807. The expedition would end with a major island in Svalbard being named for Chermside.

Possible relationship between nonvolcanic tremor and the 1998–2001 slow slip event, south central Alaska

We document the occurrence of nonvolcanic tremor (NVT) in south central Alaska for 3 months of each year between 1999 and 2001 to provide a first‐order attempt to understand the relationship between NVT and a large slow slip event that occurred over a 2 to 3 year period between 1998 and 2001. The majority of the NVT signals observed after the onset of the slow slip event are bursts lasting between 10 and 15 min with frequencies ranging from 1 to 6 Hz. By the summer of 2001 the quantity of NVT has decreased dramatically from the previous summers, and episodes rarely last up to 10 min. The decrease in NVT activity in the summer of 2001 is coincident with the end of the slow slip event. There is a clear spatial correlation between the observed NVT and the slow slip event, with most of the NVT events located on the downdip edge of the region of highest slip. Depth estimates range widely over the region, with approximately half concentrated near the interpreted North America‐Yakutat/Pacific plate interface and the remainder located above the plate interface. However, owing to inadequate station coverage and poor knowledge of the local structure, determining accurate depths is difficult and thus the relationship between the NVT and the plate interface is problematic. This is the first study giving evidence that the relationship between slow slip events and NVT seen in Cascadia and southwest Japan may also exist in Alaska.

Water and energy exchange in East Siberian forest: A synthesis

This paper summarizes and synthesises the results obtained in several recent studies on water and energy exchange of East Siberian forests located on permafrost. It is found that annual evaporation of these forests shows relatively small inter-annual variation (147–196 mm). The availability of stored water in the permafrost probably functions as a buffering resource that is only used occasionally in very dry years. Surface soil water content shows a 1-year memory to precipitation in Eastern Siberia because the precipitation conditions in previous summers carry over in a frozen condition to the next spring. Modelling shows that evaporation was larger for southern forests than for northern forests. Compared to tundra, taiga forest shows a relatively small Bowen ratio. In an alas system, observations show considerable impact of the distribution of lakes in the vicinity on the observed evaporation fluxes. There appeared to be little difference in the observed Bowen ratio between a young and old larch forest. Surface conductance modelling and upscaling studies note that leaf area index (LAI) was a controlling factor in evaporation. With the permafrost area under strong pressure from climate warming, the need to understand the ecophysiological controls of these forests in East Siberia is paramount. With the data and analysis presented in this special issue becoming available we are now in a better position to model the effects of permafrost degradation on water and energy balances.

Oak seedling survival and growth along resource gradients in Mediterranean forests: implications for regeneration in current and future environmental scenarios

Understanding seedling performance across resource gradients is crucial for defining the regeneration niche of plant species under current environmental conditions and for predicting potential changes under a global change scenario. A 2‐year field experiment was conducted to determine how seedling survival and growth of two evergreen and two deciduous Quercus species vary along gradients of light and soil properties in two Mediterranean forests with contrasting soils and climatic conditions. Half the seedlings were subjected to an irrigation treatment during the first year to quantify the effects on performance of an alteration in the summer drought intensity. Linear and non‐linear models were parameterized and compared to identify major resources controlling seedling performance. We found both site‐specific and general patterns of regeneration. Strong site‐specificity was found in the identity of the best predictors of seedling survival: survival decreased linearly with increasing light (i.e. increasing desiccation risk) in the drier site, whereas it decreased logistically with increasing spring soil water content (i.e. increasing waterlogging risk) in the wetter site. We found strong empirical support for multiple resource limitation at the drier site, the response to light being modulated by the availability of soil resources (water and P). Evidence for regeneration niche partitioning among Quercus species was only found at the wetter site. However, at both sites Quercus species shared the same response to summer drought alleviation through water addition: increased first‐year survival but not final survival (i.e. after two years). This suggests that extremely dry summers (i.e. the second summer in the experiment) can cancel out the positive effects of previous wetter summers. Therefore, an increase in the intensity and frequency of summer drought with climate change might cause a double negative impact on Quercus regeneration, due to a general reduction in survival probability and the annulment of the positive effects of (infrequent) ‘wet’ years. Overall, results presented in this study are a major step towards the development of a mechanistic model of Mediterranean forest dynamics that incorporates the idiosyncrasies and generalities of tree regeneration in these systems, and that allow simulation and prediction of the ecological consequences of resource level alterations due to global change.

Modelling the sensitivity of coastal winds over the Southern Benguela upwelling system to different SST forcing

Regional atmospheric modeling has been utilised in an attempt to resolve mesoscale spatial variations in wind stress forcing over the southern Benguela. The regional atmospheric model MM5 was used to simulate low-level coastal winds at high resolution (3 km) over the southern Benguela upwelling system for the March 2001 period and to assess the sensitivity to different resolution sea surface temperature (SST) forcing. The ability of a regional atmospheric model to resolve the mesoscale spatial variability in the local wind field which results from the adjustment of the large scale flow to regional topography and thermal gradients is demonstrated. The model output has been validated quantitatively through comparison with limited observations and qualitatively through comparison with wind fields observed in aircraft surveys conducted during previous summers. The regional model was capable of reproducing the qualitative effect of topographic forcing and thermal gradients on the equatorward flow. Local enhancement of low-level wind speed due to the interaction of the synoptic equatorward flow with both the Cape Peninsula and Cape Columbine was reproduced with associated bands of wind maxima, while lighter winds were seen in the lee of these capes. Increasing the spatial resolution of SST forcing to resolve cold SST's induced by upwelling is seen to enhance the mean response of low-level winds to coastal topography during the March 2001 event. These wind variations have important implications for coastal ocean dynamics and the development of extreme events in the region such as harmful algal blooms.

Dimethylsulfide production in Sargasso Sea eddies

Abstract Lagrangian time series of dimethylsulfide (DMS) concentrations from a cyclonic and an anticyclonic eddy in the Sargasso Sea were used in conjunction with measured DMS loss rates and a model of vertical mixing to estimate gross DMS production in the upper 60 m during summer 2004. Loss terms included biological consumption, photolysis, and ventilation to the atmosphere. The time- and depth (0–60 m)-averaged gross DMS production was estimated to be 0.73±0.09 nM d −1 in the cyclonic eddy and 0.90±0.15 nM d −1 in the anticyclonic eddy, with respective DMS replacement times of 5±1 and 6±1 d. The higher estimated rate of gross production and lower measured loss rate constants in the anticyclonic eddy were equally responsible for this eddy's 50% higher DMS inventory (0–60 m). When normalized to chlorophyll and total dimethylsulfoniopropionate (DMSP), estimated gross production in the anticyclonic eddy was about twice that in the cyclonic eddy, consistent with the greater fraction of phytoplankton that were DMSP producers in the anticyclonic eddy. Higher rates of gross production were estimated below the mixed layer, contributing to the subsurface DMS maximum found in both eddies. In both eddies, gas exchange, microbial consumption, and photolysis were roughly equal DMS loss terms in the surface mixed layer (0.2–0.4 nM d −1 ). Vertical mixing was a substantial source of DMS to the surface mixed layer in both eddies (0.2–0.3 nM d −1 ) owing to the relatively high DMS concentrations below the mixed layer. Estimated net biological DMS production rates (gross production minus microbial consumption) in the mixed layer were substantially lower (by almost a factor of 3) than those estimated in a previous study of the Sargasso Sea, which may explain the relatively low mixed-layer DMS concentrations found here during July 2004 (∼3 nM) compared to previous summers (∼4–6 nM).

Atmospheric water-soluble organic carbon measurements at Summit, Greenland

The recently discovered active photochemistry in the surface layers of polar snow may complicate the interpretation of organic compounds found in ice cores. In order to better understand the transformation and cycling of organic species in Arctic surface snow, measurements of water-soluble organic carbon (WSOC) in the gas (WSOC G) and particle (WSOC P) phases were made during the 2006 summer season at Summit, Greenland. These samples represent the first direct, simultaneous measurements of both WSOC G and WSOC P at Summit. From early June to early July, WSOC G and WSOC P concentrations at 150 cm above the snow averaged 667 and 194 ng C m −3, respectively. This value for WSOC G is very similar in magnitude to the sum of acetic and formic acid gas concentrations measured during previous summers at Summit, suggesting that these two monocarboxylic acids constitute a significant fraction of the mass of measured WSOC G. Firn air measurements of WSOC G revealed concentrations within the snowpack nearly an order of magnitude greater than those in the air just above the snow. During one period, four out of five consecutive nights showed concurrent decreases in WSOC G and increases in WSOC P, likely resulting from temperature-dependent gas-to-particle partitioning, as these episodes occurred during the coldest part of the early morning.

Photoprotective responses of Mediterranean and Atlantic trees to the extreme heat-wave of summer 2003 in Southwestern Europe

Summer 2003 was extremely hot in Europe. High light in combination with heat and drought exacerbates the generation of photo-oxidative stress. Under these conditions photoprotective responses can be critical for plant survival. Photoprotection was analysed in 2003 in several Mediterranean and Atlantic woody species. These data were compared with previous summers (1998, 1999 and 2001) to evaluate the potential acclimation for each species. A pattern of changes consisting on a decrease in chlorophyll, ascorbate and Fv/Fm and an increase in tocopherol, xanthophyll cycle pigments (VAZ) and de-epoxidation index was regularly observed. Acclimation potential was measured by the use of the plasticity index for each parameter. Mediterranean species were more plastic than Atlantic ones. The latter were unable to increase antioxidant pools to the same extent or to down-regulate the efficiency of light energy conversion. These results indicate that most Mediterranean species are able to perform an efficient acclimation to heat stress, whilst Atlantic species will be more affected by climate warming.