The North Atlantic Oscillation

International Journal of Climatology, 2013

Cold and warm temperature extremes predominantly occurring in winter gained much more attention than mean temperatures. On the basis of daily maximum and minimum surface air temperature records at 303 meteorological stations in China, the spatial and temporal distributions of five indices for winter (DJF: December, subsequent January and February) temperature extremes are analysed during 1961-2003. For the majority of stations, the frequency of cold days/nights decreases by −1.33/−2.98 and warm days/nights increases by 0.92/2.35 d/decade, respectively. Cold days/nights are significantly negatively correlated with the Arctic Oscillation (AO) index, while warm days/nights are positively correlated with the AO. The diurnal temperature range (DTR) has a declining trend with rate of −0.25°C/decade and positive correlation with the AO index. Compared with other regions in China, stations in the northern China have larger trend magnitudes and stronger correlations with the AO index, and the AO can explain more than 50% of winter temperature extreme change in China. Compared with the annual basis, the winter temperature extremes have larger trend magnitudes, which reflect the rapid warming. During strongly positive AO index years, enhanced contrast tropospheric temperature (defined as the average of air temperature vertically integrated between 200 hPa and 1000 hPa based on the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis) between the north of China and the southern China weakens the East Asian winter monsoon which in turn reduces cold outbreaks in the northern and eastern China. The composites of large-scale atmospheric circulation are consistent with the asymmetrical changes of the geopotential height, zonal and meridional winds at high and mid latitudes at troposphere. Meanwhile, the linkage between the AO and solar activity also modulates the winter temperature extremes, while the mechanism needs to be investigated.

Hydrobiologia, 2014

Winter air and spring surface water temperatures, spring epilimnetic phosphorus, and hypolimnetic oxygen in the deep lakes south of the Alps (Garda, Iseo, Como, Lugano, and Maggiore) showed a high degree of temporal coherence. The common temporal patterns were originating from the effects caused by winter climate, and from corresponding synchronisms in the interannual variations in the extent of the spring water renewal and replenishment of nutrients. In turn, the sequence of linked causal events was triggered by two atmospheric modes of variability relevant for the Mediterranean region, i.e. the East Atlantic pattern (EA) and the Eastern Mediterranean Pattern (EMP). In contrast, there were no significant relationships of air and water temperatures with the North Atlantic Oscillation. In oligotrophic lakes, which were characterised by weak vertical nutrient gradients, the spring replenishment of P was negligible and difficult to detect (Maggiore), or detectable but of minor importance (Garda and Como) compared to that measured in more enriched lakes (Iseo and Lugano). The applicability of EA and EMP in the study of the impact of climate on aquatic ecosystems will require to be tested by expanding the number, typology, and geographical location of water bodies in the Alpine and Mediterranean regions.

Journal of Avian Biology, 2011

In long-lived species, population growth rate is highly sensitive to changes in adult survival. Despite the growing concerns regarding recent climate changes, few studies have investigated the effect of climatic conditions on survival in long-lived wildlife that are either resident or breed in the Arctic. In this study, we evaluated the effect of climate across the annual life cycle (breeding, outward migration, wintering, and inward migration) on apparent annual survival of arctic-breeding peregrine falcons. From 1982 to 2008, peregrine falcons breeding near Rankin Inlet, Nunavut, Canada were monitored, in part, to assess apparent annual survival (the product of true survival and site fidelity) using re-observations of marked individuals. Our study indicated that apparent annual survival of adult peregrine falcons was correlated with indices of climatic conditions during outward migration (i.e. flight from the Arctic breeding grounds). These climatic indices (fall NAO of the current year and fall NAO with a lag of one year) explained 35% of the temporal variation in apparent annual survival of peregrine falcons. Our results suggest that this top-predator is vulnerable to weather-related environmental conditions encountered during fall migration.

Oikos, 2010

Climatic infl uences on animal populations, mediated by changes in condition-dependent survival or reproduction, have long intrigued ecologists. We analyzed links between winter North Atlantic Oscillations (NAO), a large scale climatic phenomenon aff ecting weather conditions over the North Atlantic and the Arctic, and average pre-laying body mass in common eiders. Body mass is a good proxy for condition-dependent reproductive output in this species. Time series links were assessed for two eider populations breeding at high latitudes, over a 10-and a 21-year time series. Winter NAO aff ected body mass in both populations and these eff ects were easier to detect when changes in the series rhythm were assessed using a novel method based on data discretization and information theory, rather than detection based on changes in amplitude, assessed using traditional linear models. Winter conditions aff ected body condition of eiders in both populations. Diff erent mechanisms, however, are likely to be involved in the two populations, one being presumably aff ected by direct eff ects of climate and the other by eff ects through the food chain. Th erefore, the same species can respond along diff erent pathways to the same large scale climatic pattern, an important consideration when seeking to understand or manage the response of species to present and future climate change.

International Journal of Biometeorology, 2012

Data on storm damage attributed to the two highimpact winter storms 'Wiebke ' (28 February 1990) and 'Lothar' (26 December 1999) were used for GIS-based estimation and mapping (in a 50×50 m resolution grid) of the winter storm damage probability (P DAM ) for the forests of the German federal state of Baden-Wuerttemberg (Southwest Germany). The P DAM -calculation was based on weights of evidence (WofE) methodology. A combination of information on forest type, geology, soil type, soil moisture regime, and topographic exposure, as well as maximum gust wind speed field was used to compute P DAM across the entire study area. Given the condition that maximum gust wind speed during the two storm events exceeded 35 m s -1 , the highest P DAM values computed were primarily where coniferous forest grows in severely exposed areas on temporarily moist soils on bunter sandstone formations. Such areas are found mainly in the mountainous ranges of the northern Black Forest, the eastern Forest of Odes, in the Virngrund area, and in the southwestern Alpine Foothills.

Journal of Quaternary Science, 2009

The summer North Atlantic Oscillation (SNAO) is strongly associated with July-August climate variability over Europe, especially in northern regions. This association includes drought, where a positive SNAO corresponds to dry conditions over much of northern Europe and wet conditions in southern Europe, but the SNAO/climate association is weaker and less homogeneous in the south. Here we use a dendroclimatological reconstruction of the SNAO for the last 550 a to investigate the SNAO/drought relationship in the past. An association between the SNAO and a regional summer drought index from Sweden suggests that the northern European drought relationship holds back to 1700. In the last 550 a, the relationship between SNAO and drought in the Mediterranean region as a whole is weak, but over the Eastern Mediterranean the relationship is clearer and statistically significant (P < 0.05 level). The Mediterranean relationship is clearest at century scales. An association between the SNAO and Sahel rainfall can clearly be seen on interannual as well as longer timescales in the 20th century. Past droughts in the Sahel, as inferred from historical data, correspond quite well with positive phases of the SNAO on multidecadal timescales back to 1500, the phase expected from instrumental data. The physical reasons for the relationship between Sahel rainfall and the SNAO are, however, not yet understood. This research is a first step towards understanding how the atmospheric circulation over the North Atlantic region affects drought, necessary for forecast future droughts. y The contribution of C. K. Folland was written in the course of his employment at the Met Office, UK and is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland.

PLoS ONE

Weather affects the demography of animals and thus climate change will cause local changes in demographic rates. In birds numerous studies have correlated demographic factors with weather but few of those examined variation in the impacts of weather in different seasons and, in the case of migrants, in different regions. Using capture-recapture models we correlated weather with apparent survival of seven passerine bird species with different migration strategies to assess the importance of selected facets of weather throughout the year on apparent survival. Contrary to our expectations weather experienced during the breeding season did not affect apparent survival of the target species. However, measures for winter severity were associated with apparent survival of a resident species, two short-distance/partial migrants and a long-distance migrant. Apparent survival of two short distance migrants as well as two long-distance migrants was further correlated with conditions experience...

Ecography, 2015

Polar Regions are experiencing environmental changes at unprecedented rates. These changes can spread throughout entire food webs from lower trophic levels to apex predators. As many top predators forage over large areas, these indirect effects may be associated with large-scale patterns of climate variability. Using global climate indices that are known to impact the Southern Ocean ecosystem (the El Niño Southern Oscillation and Antarctic Oscillation Indices) we assessed their efficacy to predict variation in the demographic parameters of Antarctic seabirds. First, we used a long-term dataset on adult survival (estimated from capture-mark-recapture data) and reproduction of Antarctic petrel Thalassoica antarctica, from the largest known breeding colony (Svarthamaren, Dronning Maud Land) and examined whether large-scale oceanographic fluctuations impact survival and reproduction. Second, we conducted an exhaustive literature review to determine whether the effects of large-scale environmental variability on Antarctic seabirds have a coherent fingerprint across the Antarctic continent and nearby islands. We found that most of the variation in both reproductive success, timing of hatching, and survival of Antarctic petrels can be accurately modeled using the two modes of large-scale climate variability in Antarctica. The literature review, combined with the results from our field study, suggests that while the anticipated trends in the global patterns of climatic variability will generally have detrimental effects on populations of top predators in the Southwest Atlantic, these conclusions cannot be extrapolated to all seabird populations in Antarctica without additional data.

The Holocene, 2007

Millennial-scale climate variability has been increasingly recognized as one of the most prominent features of the Holocene. However, regional responses, especially in terms of moisture conditions, are poorly documented and understood. Here we present lithologic and magnetic evidence from White Lake in northern New Jersey, USA, to show that low lake levels occurred at about 1.3, 3.0, 4.4 and 6.1 ka (1 ka0/1000 cal. yr BP). The low lake levels are indicated by heterogeneous coarse calcareous sediment layers showing strong magnetic intensities. These detrital layers were likely formed during low stands when shallow-water marls were exposed, oxidized, transported and redeposited. This model is supported by laboratory experiments showing that oxidation of marls can enhance magnetic intensities. The dry periods inferred from the low lake levels of White Lake appear to occur concurrently with the cold periods recorded in the North Atlantic sediments. The correlation between millennial-scale dry/wet cycles inferred from lake-level fluctuations of White Lake and cold/warm cycles in North Atlantic sediments suggests sensitive moisture responses to Holocene millennial-scale climate variability. The dry-cold (or wetwarm) association is supported by instrumental records of the last century showing that the Mid-Atlantic region was dominated by wet conditions, while most parts of the conterminous USA experienced droughts, when the North Atlantic Ocean was warm. The consistent moisture responses of the Mid-Atlantic region to temperature changes of the North Atlantic Ocean may have persisted for the past 6000 years.

International Journal of Climatology, 2006

In this paper, a stochastic statistical forecasting methodology is employed for long-term predictions of winter precipitation over Greece. Lagged climatic indices and North Atlantic (NA) sea-level pressure (SLP) field are explored as potential predictors of the teleconnection. Rather than employing traditional stationary models, two dynamic regression-modelling schemes are analysed and validated and their parameter variation is interpreted. Dynamic regression models, in contrast to static (constant parameter) regression models, have time variable parameters (TVPs) evaluated through recursive optimisation and are suitable for analysis of non-stationary phenomena like most atmospheric processes.

Wildlife Monographs, 2013

Grancel Fitz measuring the circumference of the main beam of an Alaska-Yukon moose. Fitz and Dr. James L. Clark were key members of a committee formed by the Boone and Crockett Club to develop an equitable, objective measurement system for big game of North America. Photo courtesy Boone and Crockett Club. Monteith et al. Size of Horn-Like Structures i

Hydrobiologia, 2012

The cyanoprokaryote Planktothrix rubescens has been studied for over four decades in an alpine lake, Mondsee, Austria. We hypothesise that impacts of climate change can be distinguished from other environmental constraints controlling its population dynamics. During thermal stratification, P. rubescens formed a deep chlorophyll maximum in the metalimnion. Seasonal and diurnal depth distributions indicated that Planktothrix lived well below the euphotic zone, at low light levels and moderate temperatures. Photosynthetic parameters indicated a shade adapted population. The eutrophication and rehabilitation periods of Mondsee were characterised by fluctuations controlled by phosphorus, with periods below the P-threshold associated with low biovolumes and relatively stable populations. Positive net changes of Planktothrix biovolume occurred during the springsummer transition and in autumn. During summer, the population usually declined to an annual minimum. The standardised residuals of annual biovolumes responded positively to the climate signal of the Winter North Atlantic Oscillation and the timing of the onset of stratification. An inverse relationship existed between off-set and persistence of stratification. P. rubescens only benefits from climate warming early in the year, during late spring overturn and early summer. Longer periods of summer stratification did not favour biovolume development.

Annals of the Association of American Geographers, 2003

Secular changes in regional storm tracking are examined as physical mechanisms for observed teleconnections between the New England hydroclimate and four predictor variables: the Southern Oscillation Index, the North Atlantic Oscillation, the Pacific Decadal Oscillation, and regional sea-surface temperatures. The main modes of New England winter precipitation, snowfall, and cyclone variability are resolved using varimax rotated principal component analysis. The first rotated principal component of regional cyclone variability defines an out-of-phase relationship between marine versus continental cyclone activity and is statistically linked with the Southern Oscillation, the Pacific Decadal Oscillation, and precipitation in northern New England. Also, El Niño winters generally accompany a slight increase in southern New England precipitation. The second cyclone rotated principal component, defining an inverse relationship between cyclone occurrences along the East Coast and cyclone occurrences along the northern boundary of the Gulf Stream, is well correlated with regional precipitation and snowfall, demonstrating the significance of marine storm tracking as a control on New England winter hydroclimatic variability.

Global Change Biology, 2003

Teleconnection patterns are large-scale atmospheric circulation systems and variation in them is often associated with impacts on climate and weather over broad areas. Arctia caja L. is a well-known, widespread and charismatic tiger moth. In recent decades, the abundance of A. caja in UK has fallen abruptly. The annual abundance of A. caja in UK is known to be affected adversely by wet winter weather and warm spring temperatures. We examined A. caja population dynamics from 1968 to 1999 for weather and climatological effects. Population growth rate displayed endogenous effects of abundance in the previous two seasons. Accounting for this, growth rate in the present season was still affected significantly by winter precipitation and spring temperature. Annual abundance of A. caja was inversely related to winter East Atlantic teleconnection pattern (winter EA index) and annual population growth rate was inversely related to winter EA in the present and previous two seasons. An index of the North Atlantic Oscillation (NAO), commonly used as an indicator of winter climate in northern Europe, did not show a significant relationship with growth rate. We noted, for the first time, that the winter EA index has increased steadily over the past five decades. The model presented here therefore implies a further decline of A. caja population growth rates and abundance in the future. This is the first demonstration of a relationship between EA and population dynamics and indicates the EA and other lesser-known teleconnection patterns may prove useful in modeling the ecological effects of climate change.

Hydrological Processes, 2014

The aim of this paper is to test the ability of neural network approaches to hindcast the spring standardized precipitation index on a 6-month time scale (SPI6) in Portugal, based on winter large-scale climatic indices. For this purpose, the linkage of the spring SPI time series with the winter North Atlantic Oscillation (NAO) and the sea surface temperature (SST) was investigated by means of maps of the correlation coefficient for the period from October 1910 to September 2004. The results indicate that the winter NAO is a good predictor for the SPI6 of the spring (SPI6 finishing in April, May and June, SPI6 April , SPI6 May and SPI6 June , respectively) for the northern, central and southern regions of Portugal. The winter SST1 (area of the Mediterranean Sea) must only be considered for the northern region, and the winter SST3 (area of the North Atlantic between Iberia and North America) only for the southern region. Spatial maps of predictive SPI6 for April, May and June were created and validated. The neural models explained more than 81% of the total variance for the SPI6 April and SPI6 May and more than 64% of the total variance for the SPI6 June . Probability maps were also developed considering the values predicted by the neural methods for the spring months and all drought categories (moderate, severe and extreme). These maps indicating the probability of droughts can provide valuable support for the integrated planning and management of water resources throughout Portugal.

Geophysical Research Letters, 2005

Journal of Geophysical Research, 2010

1] This is a study of heat fluxes and heat budget of the Mediterranean Sea using the European Centre for Medium-Range Weather Forecasts (ECMWF) 45 year reanalysis data set ERA-40. The simple use of the ERA-40 surface flux components fails to close the budget and, in particular, the shortwave radiation flux is found to be underestimated with respect to observed data by about 10%. The heat flux terms are recomputed and corrected in order to close the heat and freshwater budgets of the Mediterranean basin over the period 1958 to 2001, thus producing a corrected ERA-40 surface flux data set. Various satellite and in situ observational data are used to construct spatially varying corrections to the ERA-40 products needed to compute the air-sea fluxes. The corrected interannual and climatological net surface heat and freshwater fluxes are −7 W/m 2 and −0.64 m/yr, respectively, which are regarded as satisfactorily closing the Mediterranean heat and water budgets. It is also argued that there is an important contribution from large heat losses associated with a few severe winters over the Mediterranean Sea. This is shown to be related to wind regime anomalies, which strongly affect the latent heat of evaporation that is mainly responsible for the interannual modulation of the total heat flux. Furthermore, the surface total heat flux anomaly time series is compared with the North Atlantic Oscillation (NAO) index, and the result is a positive correlation with ocean warming for positive NAO index periods and ocean cooling associated with negative index periods.

2012

The present study examines the variability of the precipitation regime across the Ionian Islands complex, Greece (Central Mediterranean), for a period spanning more than one century. Significant negative long-term linear trends in the annual precipitation totals are observed, more pronounced in the southern parts of the studied area, while a climatic discontinuity possibly occurred during the 1970s, manifested first in the southern Ionian. Statistically significant nonlinear trends and subdecadal intermittent oscillations were detected using Monte Carlo singular spectral analysis. The correlation of the winter precipitation variability at Ionian complex with the North Atlantic Oscillation anomalies was also investigated and extended in the frequency domain. Finally, future projections were performed using an ensemble of Regional Climatic Models. Model simulations suggested a decrease of the order of ∼20% or more in the mean annual precipitation of the area by the end of the century.

Journal of Geophysical Research, 2012

The potential impact of future climate change on methane release from oceanic gas hydrates is the subject of much debate. We analyzed World Ocean Database quality controlled data on the Norwegian-Svalbard continental margin from the past 60 years to evaluate the potential effect of ocean temperature variations on continental margin gas hydrate reservoirs. Bottom water temperatures in the Norwegian-Svalbard margin were subject to significant cooling until 1980 (by $2 C offshore NW-Svalbard and in the Barents Sea) followed by a general bottom water temperature increase until 2010 ($0.3 C in deep-water areas offshore NW-Svalbard and mid-Norwegian margin and $2 C in the shallow areas of the Barents Sea and Prins Karls Forland). Bottom water warming in the shallow outer shelf areas triggered the Gas Hydrate Stability Zone (GHSZ) retreat toward upper continental slope areas, potentially increasing methane release due to gas hydrate dissociation. GHSZ responses to temperature changes on human time scales occur exclusively in shallow water and only if near-surface gas hydrates exist. The responses are associated with a short time lag of less than 1 year. Temperatures in the bottom water column seem to be partly regulated by the North Atlantic Oscillation (NAO), with positive NAO associated with warm phases. However, cooling events in the surface water offshore NW-Svalbard might be associated with El Niño events of 1976-1977, 1986-1987 and 1997-1998 in the Pacific. Such ocean cooling, if long enough, may delay ocean temperature driven gas hydrate dissociation and potential releases of methane to the ocean.

Proceedings of the National Academy of Sciences of the United States of America, 2018

Human alteration of the global nitrogen cycle intensified over the 1900s. Model simulations suggest that large swaths of the open ocean, including the North Atlantic and the western Pacific, have already been affected by anthropogenic nitrogen through atmospheric transport and deposition. Here we report an ∼130-year-long record of the N/N of skeleton-bound organic matter in a coral from the outer reef of Bermuda, which provides a test of the hypothesis that anthropogenic atmospheric nitrogen has significantly augmented the nitrogen supply to the open North Atlantic surface ocean. The Bermuda N/N record does not show a long-term decline in the Anthropocene of the amplitude predicted by model simulations or observed in a western Pacific coral N/N record. Rather, the decadal variations in the Bermuda N/N record appear to be driven by the North Atlantic Oscillation, most likely through changes in the formation rate of Subtropical Mode Water. Given that anthropogenic nitrogen emissions h...

Theoretical and Applied Climatology, 2012

This study analyzes the mean maximum and minimum temperature trends on a monthly, seasonal, and annual timescale by applying various statistical tools to data from 476 Spanish weather stations during the period between 1961 and 2006. The magnitude of the trends was derived from the slopes of the regression lines using the least squares method, and the nonparametric Mann-Kendall test was used to determine the statistical significance of the trends. Temperature significantly increased in over 60% of the country in March, June, spring, and summer in the case of maximum temperatures and in March, May, June, August, spring, and summer for minimum temperatures. At the annual resolution, temperatures significantly increased in over 90% of Spain with a rise of around 0.3°C/decade. The maximum temperature increased at a higher rate than the minimum temperature from midsummer to early winter as well as in winter, spring, and summer and also on an annual basis.

PLOS ONE, 2016

Large-scale climate processes influence many aspects of ecology including breeding phenology, reproductive success and survival across a wide range of taxa. Some effects are direct, for example, in temperate-zone birds, ambient temperature is an important cue enabling breeding effort to coincide with maximum food availability, and earlier breeding in response to warmer springs has been documented in many species. In other cases, timelags of up to several years in ecological responses have been reported, with effects mediated through biotic mechanisms such as growth rates or abundance of food supplies. Here we use 23 years of data for a temperate woodland bird species, the great tit (Parus major), breeding in deciduous woodland in eastern England to demonstrate a time-lagged linear relationship between the onset of egg laying and the winter index of the North Atlantic Oscillation such that timing can be predicted from the winter index for the previous year. Thus the timing of bird breeding (and, by inference, the timing of spring events in general) can be predicted one year in advance. We also show that the relationship with the winter index appears to arise through an abiotic time-lag with local spring warmth in our study area. Examining this link between local conditions and larger-scale processes in the longerterm showed that, in the past, significant relationships with the immediately preceding winter index were more common than those with the time-lagged index, and especially so from the late 1930s to the early 1970s. However, from the mid 1970s onwards, the time-lagged relationship has become the most significant, suggesting a recent change in climate patterns. The strength of the current time-lagged relationship suggests that it might have relevance for other temperature-dependent ecological relationships.

Atmosphere

Extreme drought events are becoming increasingly frequent and extended, particularly in Mediterranean drought-prone regions. In this sense, atmospheric oscillations patterns, such as those represented by the North Atlantic Oscillation (NAO) index and the Westerly Index (WI) have been widely proven as reliable proxies of drought trends. Here, we used the Standardized Precipitation–Evapotranspiration Index (SPEI), as a reliable indicator of drought, to investigate the drought sensitivity of tree-ring width data (TRW) from several long-lived tree species (Abies borisii-regis, Abies cilicica, Abies pinsapo, Cedrus atlantica, Cedrus libanii, Pinus nigra, Pinus heldreichii). NAO and WI relations with TRW were also investigated in order to identify potential non-stationary responses among those drought proxies. Our temporal and spatial analyses support contrasting Mediterranean dipole patterns regarding the drought sensitivity of tree growth for each tree species. The spatial assessment of...

Journal of Ornithology, 2008

The effects of large-scale climatic phenomena on the timing of breeding in the Osprey Pandion haliaetus were studied during 1981-2006 in a small local population of about 20 pairs near the southern coast of Finland. The timing of breeding was estimated on the basis of the wing length of the largest young within the brood. The wing lengths were plotted against the date of the measurement to get a linear regression model characterizing the average developmental stage of broods in relation to date. This model was used when converting the measurements to correspond to the median date of all the measurements. Large-scale climatic phenomena were characterized by the winter and monthly indices of the North Atlantic oscillation (NAO). A significant positive relationship between the winter NAO index and timing of breeding in the Osprey, as indicated by the wing length of the largest young in the brood, was found. The relationship was even stronger when only the monthly value of January was considered. These relationships seemed to be linked with consequent earlier ice melting after mild winters. The results indicate prominent effects of large-scale climatic phenomena and that they can be monitored with relatively modest effort. Keywords Monitoring Á Nestling wing length Á North Atlantic oscillation Communicated by F. Bairlein.

Journal of Ornithology, 2013

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Water

Extremal dependence or independence may occur among the components of univariate or bivariate random vectors. Assessing which asymptotic regime occurs and also its extent are crucial tasks when such vectors are used as statistical models for risk assessment in the field of Climatology under climate change conditions. Motivated by the poor resolution of current global climate models in North Atlantic Small Islands, the extremal dependence between a North Atlantic Oscillation index (NAOI) and rainfall was considered at multi-year dominance of negative and positive NAOI, i.e., −NAOI and +NAOI dominance subperiods, respectively. The datasets used (from 1948–2017) were daily NAOI, and three daily weighted regionalised rainfall series computed based on factor analysis and the Voronoi polygons method from 40 rain gauges in the small island of Madeira (∼740 km2), Portugal. The extremogram technique was applied for measuring the extremal dependence within the NAOI univariate series. The cros...

Journal of Geophysical Research: Biogeosciences

The climate-vegetation coupling exerts a strong control on terrestrial carbon budgets and will affect the future evolution of global climate under continued anthropogenic forcing. Nonetheless, the effects of climatic conditions on such coupling at specific times in the growing season remain poorly understood. We quantify the climate-vegetation coupling in Europe over 1982-2014 at multiple spatial and temporal scales, by decomposing sub-seasonal anomalies of vegetation greenness using a grid-wise definition of the growing season. We base our analysis on long-term vegetation indices (Normalized Difference Vegetation Index and two-band Enhanced Vegetation Index), growing conditions (including 2m temperature, downwards surface solar radiation, and root-zone soil moisture), and multiple teleconnection indices that reflect the large-scale climatic conditions over Europe. We find that the largescale climate-vegetation coupling during the first two months of the growing season largely determines the full-year coupling. The North Atlantic Oscillation and Scandinavian Pattern phases one-to-two months before the start of the growing season are the dominant and contrasting drivers of the early growing season climate-vegetation coupling over large parts of boreal and temperate Europe. The East Atlantic Pattern several months in advance of the growing season exerts a strong control on the temperate belt and the Mediterranean region. The strong role of early growing season anomalies in vegetative activity within the growing season emphasizes the importance of a grid-wise definition of the growing season when studying the large-scale climate-vegetation coupling in Europe. Plain Language Summary Climate and terrestrial ecosystems interact and affect the global climate. Such a climate-vegetation relationship can be effectively quantified by using satellites to measure how leafy and active the vegetation is, and numerical indices reflecting large-scale climate patterns over a given region. Previous studies generally focused on changes in mean vegetation indices over the full growing season, which is usually defined by a fixed range of astronomical months for large geographical regions. This overlooks the fact that growing seasons differ in space and vegetation responds differently to the climate in different growing season periods. In this study, we explore how vegetation and climate interact within a growing season, here defined specifically for the local conditions. We find that there are strong relationships between the large-scale climate patterns and vegetation indices during the first two months of the growing season. Our findings highlight the important role of the vegetation activity during the early growing season for the year-to-year vegetation changes in Europe. Hence, for a better understanding of the climate-vegetation relationships, it is necessary to consider the spatial differences in the growing season, in particular for large geographical regions. WU ET AL.

Atmosphere, 2016

This is an overview of the results from previously published climate modeling studies reporting on projected aspects of future storminess over the North Atlantic European region (NAER) in the period 2020-2190. Changes in storminess are summarized for seven subregions in the study area and rated by a categorical evaluation scheme that takes into account emission scenarios and modeling complexity in the reviewed studies. Although many of the reviewed studies reported an increase in the intensity of high-impact wind speed and extreme cyclone frequency in the second half of the 21st century, the projections of aspects of future storminess over the NAER differed regionally. There is broad consensus that the frequency and intensity of storms, cyclones, and high-impact wind speed will increase over Central and Western Europe, and these changes will probably have the potential to produce more damage. In contrast, future extratropical storminess over Southern Europe is very likely to decrease. For Northern and Eastern Europe the results of the evaluation are inconclusive, because there is an indication of increasing as well as decreasing development of the evaluated aspects of future storminess. Concerning the storm track, we found indications of a likely north-and eastward shift in most assessed studies. Results from three studies suggest a northeastward shift of the North Atlantic Oscillation.

Journal of Paleolimnology, 2016

Carbon storage in lakes can have huge implications for the global carbon cycle, as lakes annually accumulate up to one half the amount of organic carbon buried in marine sediments. Yet little is known of the effect of recent climate change on carbon storage in lakes. We analyzed century-scale time series of climate variables (precipitation, temperature, NAO winter index) and profiles of sediment characteristics in a dated sediment core from shallow, eutrophic Lake Võrtsjärv, south Estonia. We used path analysis to evaluate the effect of climate conditions on phytoplankton biomass in the lake and accumulation of organic and inorganic carbon in the sediment. Changes in winter and spring climate influenced the lake's phytoplankton growth significantly. Carbon pathways in hard-water Lake Võrtsjärv were influenced by both hydrological (most significant in colder periods) and biogeochemical processes. Increased nutrient and water input to Lake Võrtsjärv, anticipated with projected climate warming, favours greater in-lake productivity, larger accumulation of inorganic carbon in sediments, and an increase in organic carbon mineralisation, which fuels atmospheric greenhouse gas emissions from the lake.

Water

Medjerda is a key transboundary watershed in the Maghreb region, crossing from the Algerian mountains through northern Tunisia. Therefore, the analysis of the rainfall regime in this basin is of paramount importance for water resources management and regional economic development, notably concerning agriculture. This study examines the rainfall trends over the Medjerda watershed on multi-temporal scales (monthly, seasonally and annually) with a database of monthly rainfall observed in 60 stations evenly spread over the watershed. After filling gaps and homogenizing data, the Mann–Kendall test for trend detection was applied to rainfall series and the Sen’s slope method was adopted to estimate the trend’s magnitude, interpolated over the sub-catchments, to analyze the spatial distribution of rainfall changes within the watershed. Results showed the absence of significant trends at the annual scale for the entire catchment. However, rainfall redistribution was observed throughout the ...

Journal of Geophysical Research: Atmospheres

 Associations between seasonal occurrences of compound drought and heatwave (CDHW) events and the major natural modes of climate variability are investigated.  ENSO is the most influential natural mode of variability associated with the seasonal occurrences of CDHW events over tropical regions in the Southern Hemisphere.  Anomalies in seasonal composites of pertinent variables explain most of these associations except for few regions.

European Journal of Phycology, 2015

In this study we combine field demographic surveys with controlled culture experiments, to understand if temperature might be the factor leading to differences in life expectancy and seasonality across different latitudinal ranges in the kelp Saccorhiza polyschides. This species overwinters as a macroscopic sporophyte in geographically central populations, like Brittany (northwestern France), while in northern Portugal, the southern range of its distribution, only microscopic forms are present in winter. Our results did not support temperature as the cause of the different life histories observed in central and southern ranges. We found that sporophyte recruitment occurs year-round in Brittany while farther south it is limited to spring. Our results show that this seasonal recruitment is not due to winter temperature, as zoospores were able to develop between 5 and 20°C with an optimum at 10-15°C, placing the Portuguese winter temperatures within the optimum range. In addition, we showed that the synchronized release of zoospores in early autumn in the southern range does not explain the absence of recruits throughout winter, as these took a maximum of 62 days, at 5°C, to develop into a sporophyte visible in the field (5 cm) and only 20 days at 10°C. An alternative hypothesis that could explain the different life histories is the seasonality of high seawater nutrient levels occurring in the southern but not in the central-northern range, where permanently higher nutrient concentrations might allow sporophytes to occur in any season. This hypothesis is supported by the coincidence of macroscopic sporophytes with the seasonal upwelling period in the southern range, but it requires further testing.

Journal of Geophysical Research: Solid Earth, 2016

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Fisheries Oceanography, 2004

We tested whether synchronous, long-term fluctuations in Atlantic bluefin tuna (Thunnus thynnus) trap catches, collected from the ancestral Mediterranean and Atlantic trap fishery, might be related to large-scale environmental change. Nine time series of trap catches of more than 80 yr long were compared with long time series of three preselected environmental variables, i.e. the North Atlantic Oscillation (NAO), the Length of the Day Index (LOD, a proxy of the atmospheric circulation index) and the temperature. Spectral analyses of trap catches, LOD and temperature displayed similar spectra with peaks at low frequencies, whereas those of the NAO exhibited a broad band spectrum. Regression analyses and tests of correlation did not reveal any clear relationship between trap catches on the one hand and NAO and LOD on the other hand. In contrast, longterm fluctuations in trap catches appear to be closely and negatively related to long-term trends in temperature. Underlying processes that could explain such a relationship are discussed, with special focus on changes in migration patterns of the Atlantic bluefin tuna.

PLoS ONE, 2013

Climate influences the dynamics of natural populations by direct effects over habitat quality but also modulating the phenotypic responses of organisms' life-history traits. These responses may be different in males and females, particularly in dimorphic species, due to sex-specific requirements or constraints. Here, in a coastal seabird, the European shag (Phalacrocorax aristotelis), we studied the influence of climate (North Atlantic Oscillation, NAO; Sea Surface Temperature, SST) on two sex-related population parameters: fledgling sex ratio and sex-specific dispersal. We found that fledgling sex ratio was female skewed in NAO-positive years and male skewed in NAO-negative years. Accordingly, females dispersed a longer distance in NAO-positive years when females were overproduced, and on the contrary, males dispersed more in NAO-negative years. Overall, our findings provide rare evidence on vertebrates with genetic sex determination that climate conditions may govern population dynamics by affecting sex-specific density and dispersal.

Atmospheric Science Letters, 2001

Monthly (1659±1995) and seasonal (1500±1658) North Atlantic Oscillation (NAO) indices were estimated using instrumental and documentary proxy predictors from Eurasia. Uncertainty estimates were calculated for the reconstructions, and the variability of the 500-year winter NAO has been assessed. The late twentieth century NAO extremes are within the range of variability during earlier centuries.

Remote Sensing, 2020

Based on 26 years of satellite altimetry, this study reveals the presence of a persistent east–west pattern in the sea level of the Red Sea, which is visible throughout the years when considering the east–west difference in sea level. This eastern–western (EW) difference is positive during winter when a higher sea level is observed at the eastern coast of the Red Sea and the opposite occurs during summer. May and October are transition months that show a mixed pattern in the sea level difference. The EW difference in the southern Red Sea has a slightly higher range compared to that of the northern region during summer, by an average of 0.2 cm. Wavelet analysis shows a significant annual cycle along with other signals of lower magnitude for both the northern and southern Red Sea. Removing the annual cycle reveals two energy peaks with periodicities of &lt;12 months and 3–7 years, representing the intraseasonal and El Nino—Southern Oscillation (ENSO) signals, respectively. Empirical O...

Ecography, 2008

In the light of the predicted changes in climate as a consequence of global warming, it is a major concern how animal species will respond to altered meteorological and oceanographic conditions. Seabirds constitute a diverse group of marine top predators which have relatively low fecundity and high annual survival rates. In order to predict effects of climate change, it is a necessary precondition to first understand responses to naturally occurring climatic fluctuations. While the ecological effects of different large-scale climatic phenomena have received much attention in the recent past, the factors determining the responses of seabirds are still little understood. We analyze more than a hundred previously published time series of seabird offspring production and adult survival rates in the North Atlantic in order to detect climatic signals in this data base. As our analyses are phylogenetic-comparative, we are able to search for patterns across species. Using the correlation of these parameters with the North Atlantic Oscillation (NAO) as a measure of responsiveness to climatic variability, we find that effects of climate on either parameters considered are not more common than expected by chance. The magnitudes of the responsivenesses were not entirely randomly distributed throughout the seabird phylogeny, but were not strongly related to the explanatory variables considered. However, some tendencies indicate that both life-history traits and feeding ecology may influence how seabirds respond to climatic variability. An explanation of those patterns based on life-history theory is given.

International Journal of Climatology, 2015

International Journal of Climatology-For peer review only on frequency 29 f , and the Hurst and Hausdorff exponents suggest fractional Gaussian noise, fGn, as a right 30 simulation of empiric WeMOi. Comparisons are made with monthly North-Atlantic Oscillation, 31 NAO, and Atlantic Multidecadal Oscillation, AMO, indices. The analysis is complemented with 32 an ARIMA(p,1,0) autoregressive process, which yields a more accurate prediction of WeMOi 33 than that derived from fGn simulations. 34 35 36

The Handbook of Environmental Chemistry, 2020

The trajectory of the Seine basin water resources is rebuilt from the early 1900s to the 2000s before being projected to the end of the twenty-first century. In the first part, the long-term hydrological data of the Paris gauging stations are analysed beginning in 1885, highlighting the effect of anthropogenic water management on the Seine River discharge. Then a detailed water budget of the Seine basin is proposed. It quantifies for the first time the water exchanges between aquifer units and the effect of water withdrawals on river–aquifer exchanges. Using this model, the trajectory of the system is evaluated based on a downscaled climate reanalysis of the twentieth century and a reconstruction of the land use in the early 1900s, as well as the choice of a climate projection which favours the model that best reproduces the low frequency of precipitation. The trajectory is synthesised as average regimes, revealing a relative stability of the hydrosystem up to the present, and drast...

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 2017

Observational estimates and numerical models both indicate a significant overall decline in marine oxygen levels over the past few decades. Spatial patterns of oxygen change, however, differ considerably between observed and modelled estimates. Particularly in the tropical thermocline that hosts open-ocean oxygen minimum zones, observations indicate a general oxygen decline, whereas most of the state-of-the-art models simulate increasing oxygen levels. Possible reasons for the apparent model-data discrepancies are examined. In order to attribute observed historical variations in oxygen levels, we here study mechanisms of changes in oxygen supply and consumption with sensitivity model simulations. Specifically, the role of equatorial jets, of lateral and diapycnal mixing processes, of changes in the wind-driven circulation and atmospheric nutrient supply, and of some poorly constrained biogeochemical processes are investigated. Predominantly wind-driven changes in the low-latitude oc...

Proceedings of the National Academy of Sciences of the United States of America, 2011

Despite the importance of the nitrogen (N) cycle on marine productivity, little is known about variability in N sources and cycling in the ocean in relation to natural and anthropogenic climate change. Beyond the last few decades of scientific observation, knowledge depends largely on proxy records derived from nitrogen stable isotopes (δ(15)N) preserved in sediments and other bioarchives. Traditional bulk δ(15)N measurements, however, represent the combined influence of N source and subsequent trophic transfers, often confounding environmental interpretation. Recently, compound-specific analysis of individual amino acids (δ(15)N-AA) has been shown as a means to deconvolve trophic level versus N source effects on the δ(15)N variability of bulk organic matter. Here, we demonstrate the first use of δ(15)N-AA in a paleoceanographic study, through analysis of annually secreted growth rings preserved in the organic endoskeletons of deep-sea gorgonian corals. In the Northwest Atlantic off...

Climate of The Past, 2017

Previous studies suggested that short-term freshening events in the subpolar gyre can be counterbalanced by advection of saline waters from the subtropical gyre and thus stabilize the Atlantic Meridional Overturning Circulation (AMOC). However, little is known about the inter-gyre transport pathways. Here, we infer changes in surface and subsurface transport between the subtropical and polar North Atlantic during the last 11 000 years, by combining new temperature and salinity reconstructions obtained from combined δ 18 O and Mg / Ca measurements on surface and subsurface dwelling foraminifera with published foraminiferal abundance data from the subtropical North Atlantic, and with salinity and temperature data from the tropical and subpolar North Atlantic. This compilation implies an overall stable subtropical warm surface water transport since 10 ka BP. In contrast, subsurface warm water transport started at about 8 ka but still with subsurface heat storage in the subtropical gyre. The full strength of intergyre exchange was probably reached only after the onset of northward transport of warm saline subsurface waters at about 7 ka BP, associated with the onset of the modern AMOC mode. A critical evaluation of different potential forcing mechanisms leads to the assumption that freshwater supply from the Laurentide Ice Sheet was the main control on subtropical to subpolar ocean transport at surface and subsurface levels.

Oecologia, 2018

Evaluating long-term drivers of foraging ecology and population productivity is crucial for providing ecological baselines and forecasting species responses to future environmental conditions. Here, we examine the trophic ecology and habitat use of North Atlantic leatherback turtles (St. Croix nesting population) and investigate the effects of large-scale oceanographic conditions on leatherback foraging dynamics. We used bulk and compound-specific nitrogen isotope analysis of amino acids (CSIA-AA) to estimate leatherback trophic position (TP) over an 18-year period, compare these estimates with TP estimates from a Pacific leatherback population, and elucidate the pre-nesting habitat use patterns of leatherbacks. Our secondary objective was to use oceanographic indices and nesting information from St. Croix leatherbacks to evaluate relationships between trophic ecology, nesting parameters, and regional environmental conditions measured by the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation. We found no change in leatherback TP over time and no difference in TP between Atlantic and Pacific leatherbacks, indicating that differences in trophic ecology between populations are an unlikely driver of the population dichotomy between Pacific and Atlantic leatherbacks. Isotope data suggested that St. Croix leatherbacks inhabit multiple oceanic regions prior to nesting, although, like their conspecifics in the Pacific, individuals exhibit fidelity to specific foraging regions. Leatherback nesting parameters were weakly related to the NAO, which may suggest that positive NAO phases benefit St. Croix leatherbacks, potentially through increases in resource availability in their foraging areas. Our data contribute to the understanding of leatherback turtle ecology and potential mechanistic drivers of the dichotomy between populations of this protected species.

Trudy Zoologičeskogo instituta, 2017

На Куршской косе Балтийского моря сотрудниками биологической станции «Рыбачий» с 1957 г. ведется мониторинг сроков весенней и осенней миграции, времени гнездования и послегнездовой дисперсии, динамики численности гнездовых и транзитных популяций птиц с помощью больших ловушек «рыбачинского» типа. Данные мониторинга показывают, что существуют долговременные колебания сроков миграции и гнездования птиц, а также численности их гнездовых и пролетных популяций в Балтийском регионе. Эти колебания в первую очередь связаны с изменениями климата, которые происходят в настоящее время на нашей планете. Потепление климата в северном полушарии в зимний и весенний периоды ведет к более раннему прилету птиц в гнездовой район не только у видов, зимующих в Европе, но и в Африке. Похолодание, наоборот, задерживает прилет птиц на 15-30 дней. Изменение климата может приводить не только к флуктуациям сроков прилета птиц в гнездовой район, но и к срокам отлета их с зимовок (как европейских, так и африканских). Климат в меньшей степени влияет на сроки осенней миграции, они в первую очередь зависят от времени гнездования популяции. Ранний прилет, как правило, приводит к более раннему гнездованию птиц на Куршской косе, что, в свою очередь, способствует более успешному размножению и росту численности гнездовых и транзитных популяций за счет молодых особей. Благодаря долговременному мониторингу местных и пролетных популяций птиц с помощью больших ловушек удалось оценить не только состояние популяций у целого ряда видов в Балтийском регионе, но и выявить влияние современного изменения климата на годовой цикл и динамику численности птиц.

npj Climate and Atmospheric Science

The Tropical Western-Central Indian Ocean (WCIO) precipitation anomalies play an important role in modulating the anomalous climate conditions in the North Atlantic and European (NAE) region during the early boreal winter (November–December; ND) season. In this study, we analyzed the forcing mechanism and predictability for the early winter tropical WCIO precipitation anomalies and its teleconnections to the North Atlantic region. The two main forcing mechanisms emerging are the autumn Indian Ocean Dipole (IOD) and a direct atmospheric teleconnection from El Niño-Southern Oscillation (ENSO). Since the autumn IOD is partially forced by ENSO, their independent contributions are also investigated. We found the IOD dominates over the ENSO contribution. The ECMWF-SEAS5 seasonal re-forecast reproduces these forcing mechanisms well and shows a substantial prediction skill for early winter WCIO precipitation. Moreover, the North Atlantic response to the positive WCIO phase projects spatiall...

Journal of Geophysical Research, 2007

A new documentary source of data for wind, atmospheric pressure and air temperature for the city of Cádiz (southern Spain) has been abstracted, analyzed and compared with present-day data. Wind records cover the period 1806-1852 with three observations per day. Instrumental pressure and temperature cover the period 1825-1852. While the historical pressure series shows average values very close to that found for the period 1971-2000, temperature shows a large asymmetric seasonal warming, with increments in the order of 2°C for the winter months and almost no change for summer. Wind measurements have been transformed into their numerical equivalents and then compared with present-day values. The analysis shows that the numerical estimation of ancient wind forces observed at Cádiz, while providing a robust climatic signal, has a strong bias to larger values than their instrumental equivalents. Despite the uncertainties involved in the interpretation of early wind series, this effect could be related to the recording of ''average wind gusts'' rather than average winds as measured by today's anemometers. In consequence, wind climatologies based on historical data, which recently are becoming available to the scientific community, should be used carefully.

Geophysical Research Letters, 2006

Katrina is a grim reminder of the serious social and economic threat that hurricanes pose to the United States. Recent advances in hurricane climate science provide skillful forecasts of the U.S. hurricane threat at (or near) the start of the season. Predictions of hurricane landfalls at longer lead times (forecast horizons) for the complete hurricane season would greatly benefit risk managers and others interested in acting on these forecasts. Here we show a model that provides a 6-month forecast horizon for annual hurricane counts along the U.S. coastline during the June through November hurricane season using the North Atlantic Oscillation (NAO) and Atlantic sea-surface temperature (SST) as predictors. Forecast skill exceeds that of climatology. The long-lead skill is linked to the persistence of Atlantic SST and to teleconnections between North Atlantic sea-level pressures and precipitation variability over North America and Europe. The model is developed using Bayesian regression and therefore incorporates the full set of Atlantic hurricane data extending back to 1851.

Hydrological Processes, 2016

The mountain headwater Bow River at Banff, Alberta, Canada, was subject to a large flood in June 2013, over which considerable debate has ensued regarding its probability of occurrence. It is therefore instructive to consider what information long‐term streamflow discharge records provide about environmental change in the Upper Bow River basin above Banff. Though protected as part of Banff National Park, since 1885, the basin has experienced considerable climate and land cover changes, each of which has the potential to impact observations, and hence the interpretations of flood probability. The Bow River at Banff hydrometric station is one of Canada&#39;s longest‐operating reference hydrological basin network stations and so has great value for assessing changes in flow regime over time. Furthermore, the station measures a river that provides an extremely important water supply for Calgary and irrigation district downstream and so is of great interest for assessing regional water s...