North Atlantic Oscillation Index Research Articles

Solar Signature in Climate Indices

The influence of solar/geomagnetic activity on climate variables still remains a fully unclarified problem, although many scientific efforts have been made to better understand it. In order to bring more information to this open problem, in the present study, we analyze the connection between solar/geomagnetic activity (predictors) and climate variables (predictands) by applying elements from information theory and wavelet transform analysis. The solar activity was highlighted by the Wolf number and geomagnetic activity was quantified by the aa index. For the climate variables, we considered seven Climate Indices (CIs) that influence atmospheric circulation on regional or global scales, such as the Greenland-Balkan Oscillation Index (GBOI), North Atlantic Oscillation Index (NAOI), Arctic Oscillation (AO), Atlantic Multidecadal Oscillation (AMO), Southern Oscillation Index (SOI), Bivariate ENSO Timeseries (BEST) and Trans-Niño Index (TNI). By using the difference between synergy and redundancy, a few cases were found where the two predictors can be considered together for CIs’ estimation. Coherence analysis through the wavelet transform for three variables, both through multiple and partial analysis, provides the time intervals and bands of periods, where the two considered predictors can be used together or separately. The results differ depending on the predictand, the season and the considered lags. Significant information is brought out by using the two predictors together, namely the summer season, for GBOI and NAOI, when the predictors were taken 2 years before, and the winter season, as AMO responds to the variations of both solar and geomagnetic activity after 4 years.

Heterogeneous spatiotemporal streamflow response to large-scale climate indexes in the Eastern Alps

Analyzing temporal and spatial variability of river discharge and the impacts of large-scale climate oscillations on hydrological systems are of particular interest in Alpine catchments, which have been proved to be especially sensitive to climatic drivers. The impact of climate oscillation indexes may show a delayed response and therefore the correlation between climatic drivers and streamflow is challenging to be properly identified. For this purpose, wavelet transform (WT) is recognized as a suitable tool able to determine the crucial scales of variability. In this work, first we explore the periodicities and the coherence among several climatic indexes: North Atlantic Oscillation Index (NAO), Mediterranean Oscillation Index (MO), Greenland Blocking Index (GB), and Artic Oscillation Index (AO). This analysis shows the complementary information that different oscillation indexes provide and the need to consider their impacts on streamflow simultaneously. Previous work revealed a heterogeneous and complex response of the Inn river basin at long temporal scales, which could not be linked to analyzed anthropogenic impacts such as dams’ construction and hydropower plants operation. Therefore, the trigger of changes in streamflow variability remained unclear. In this study, we elaborate a classification based on all considered indexes’ coherence with fifty gauging stations of the Inn river catchment. We quantify similarity among stations with a focus on yearly and longer temporal scales. The results highlight the heterogeneous response of the streamflow towards changes in climatic indexes and give an overview of the possible drivers of detected long-term alterations. NAO and GB extreme phases are connected with cold winters and hot summers. We observe that from the 1980s changes detected in the streamflow behavior at yearly and longer temporal scales are in line with emerging patterns of the climatic indexes, such as the shift from constant to intermittent periodicities of the MO index. AO coherence displays a higher complexity able to capture singular hydrologic behaviors (i.e., particular hydrological regime only detected for one gauging station, often connected to high altitude small basins). From the cluster analysis we can also derive how mean catchment elevation and geographical location can contribute to the explanation of the influence and teleconnection to the oscillation indexes, while glacierized area is not identified as a dominant characteristic. Thus, this research contributes to a better understanding of streamflow variability over the Eastern Alps, and the role of teleconnection patterns on this variability. These relationships can be also used to improve hydrological forecasting and water resources management in the Alpine region.

Spatio-temporal changes of spring-summer dust AOD over the Eastern Mediterranean and the Middle East: Reversal of dust trends and associated meteorological effects

High dust concentrations in the Eastern Mediterranean - Middle East (EMME) region have serious effects on air quality, human health and climate. This study used long-term aerosol datasets during the main dusty season (April–July: AMJJ) over the EMME from 2000 to 2020, based on Moderate-Resolution Imaging Spectroradiometer (MODIS)/Terra-C6.1, Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2), and Copernicus Atmosphere Monitoring Service Reanalysis (CAMSRA) retrievals and analyzed the spatio-temporal variations and trends of dust, as well as the influencing factors. The dust aerosol optical depth (DAOD) experienced a significant upward trend during 2000–2010, followed by a significant decrease during 2010–2017. After 2017 and till 2020, the DAOD presented rather a stable trend. Aerosol Robotic Network (AERONET) data in the EMME region display trends compatible to those of both MERRA-2 and CAMSRA DAOD. The DAOD trends were linked to changes in regional meteorological parameters in the EMME. A significant downward trend in AMJJ sea-level pressure (SLP) during the early period (2000−2010) induced hot and dry winds from desert regions towards the EMME, which reduced relative humidity (RH) and raised temperature, thus favored soil drying and dust outbreaks through enhancing evaporation. In contrast, a significant increase in winter SLP during the late period (2010–2017), accompanying an increase in North Atlantic Oscillation index, induced cold, wet winds from northwest regions, which increased RH and lowered temperature, thus reducing dust loading in EMME. Positive anomalies in winter soil moisture persisted in the following AMJJ, and consequently suppressed dust activity. DAOD variability over the dust-prone regions was linked to various meteorological parameters via a multiple linear regression (MLR) model. The results show that climatic variability strongly affects the dust trends and contribute to better understanding of meteorological – dust dynamics in the EMME region.

Trends in hepatic cadmium concentrations in marine bird species from the Canadian Arctic

Cadmium (Cd) is a trace element of toxicological concern that has been monitored in marine birds inhabiting the Canadian Arctic since 1975. Despite nearly 50 years of monitoring, research to date has largely evaluated single species, locations, or time points, and there is as of yet no holistic overview that jointly considers all available Cd data. We addressed this information gap by combining and analyzing most of the existing data on hepatic Cd concentrations in marine birds from the Canadian Arctic. Using data collected between 1975 and 2018 from eight seabird species from 12 Arctic breeding colonies, we examined temporal, spatial, and interspecific variation in hepatic Cd levels, and we evaluated possible drivers of marine bird Cd loads. Hepatic Cd concentrations ranged from 1.6 to 124 μg/g dry weight across species, and were highest in thick-billed murres (Uria lomvia) and king eiders (Somateria spectabilis), and lowest in black guillemots (Cepphus grylle), black-legged kittiwakes (Rissa tridactyla), and long-tailed ducks (Clangula hyemalis). All sites with multiple years of data showed interannual fluctuations in Cd, which were correlated with the North Atlantic Oscillation (NAO) index and with the previous year's June sea ice coverage, where marine birds exhibited higher Cd concentrations in positive NAO years and following years with lower sea ice coverage. Climate change is likely to shift the NAO to being more negative and to reduce sea ice coverage, and our results thus identify various ways by which climate change could alter Cd concentrations in marine birds in the Canadian Arctic. Understanding variations in marine bird contaminant burdens, and how these may be alters by other stressors such as climate change, is important for long-term marine bird conservation efforts.

Insights into the population dynamics of Anastrepha obliqua and Anastrepha ludens in the neotropical limits of Mexico

AbstractAnastrepha obliqua Macquart and Anastrepha ludens Loew (Diptera: Tephritidae) represent persistent pests of quarantine significance affecting mango and citrus agroecosystems, respectively, in Mexico. We aimed to analyze the population dynamics of A. obliqua and A. ludens and the effects of endogenous and exogenous factors on the population regulation in the neotropical limits of Mexico. We explored endogenous dynamics of A. obliqua and A. ludens populations based on short sequences of time series data of adult captures from 2008 to 2010. Moreover, we analyzed the relationship between the rate of population change () and population density as an endogenous factor, and temperature, precipitation, fruit availability, and the North Atlantic Oscillation index (NAOi) as exogenous factors. Autocorrelation and partial‐rate correlation functions were used to evaluate the endogenous dynamics of populations. Generalized least square models including autoregressive–moving‐average structures were performed to assess the relationships between the and endogenous and exogenous factors. Results revealed annual patterns in the population fluctuation for both Anastrepha obliqua and A. ludens. Anastrepha obliqua and A. ludens population peaks occurred from August to September–October, and from January to July, respectively. The dynamics of the suggest persistent pest populations modulated by a first‐order feedback structure, although higher orders in feedback structures were also exhibited. Significant relationships between and population density, temperature, fruit availability, and the NAOi were observed. These findings may be a technical and ecological basis to design environmentally friendly strategies against wild populations under an area‐wide integrated pest management (AW‐IPM) approach.

On the Origin of the Solar Cycle Modulation of the Winter North Atlantic Oscillation

AbstractUsing data from recent 64 years, we found that the zonal wind signal associated with the winter‐mean North Atlantic Oscillation (NAO) tends to extend into the upper stratosphere when solar activity is high, but the vertical extension is limited when solar activity is low. To examine the physical source of this phenomenon, the momentum and wave‐energy budget are analyzed using the 63‐winter record of the Japanese Reanalysis data set from 1958 to 2021. These analyses show that (a) the zonal‐mean momentum acceleration is driven by eddies throughout the entire depth of the atmosphere around 60°N, (b) the barotropic energy conversion from eddies to zonal‐mean flow is centered in the middle stratosphere around 55°N, and (c) the baroclinic energy conversion from zonal‐mean flow to eddies from the surface to the middle stratosphere around 60°N tends to be enhanced from December to February associated with the positive winter‐mean NAO index in High Solar (HS) activity years. These energy transfers are closely related to enhanced zonal wind. These analyses suggest that the structural modulation of the NAO due to the solar cycle comes from the enhanced sensitivity of the wave‐mean flow interaction in the stratosphere in HS years, which is broadly shared with the solar cycle modulation of the late‐winter Southern Annular Mode (SAM).

Hidden Potential in Predicting Wintertime Temperature Anomalies in the Northern Hemisphere

AbstractVariability of the North Atlantic Oscillation (NAO) drives wintertime temperature anomalies in the Northern Hemisphere. Dynamical seasonal prediction systems can skilfully predict the winter NAO. However, prediction of the NAO‐dependent air temperature anomalies remains elusive, partially due to the low variability of predicted NAO. Here, we demonstrate a hidden potential of a multi‐model ensemble of operational seasonal prediction systems for predicting wintertime temperature by increasing the variability of predicted NAO. We identify and subsample those ensemble members which are close to NAO index statistically estimated from initial autumn conditions. In our novel multi‐model approach, the correlation prediction skill for wintertime Central Europe temperature is improved from 0.25 to 0.66, accompanied by an increased winter NAO prediction skill of 0.9. Thereby, temperature anomalies can be skilfully predicted for the upcoming winter over a large part of the Northern Hemisphere through increased variability and skill of predicted NAO.

The roles of climate and alternative prey in explaining 142 years of declining willow ptarmigan hunting yield

Long time series are important because they extend back to an era when animal populations were less influenced by habitat loss and climate change. Annual fluctuations in harvest yields are good proxies for large changes in population size and may reveal underlying ecological processes. From a variety of sources, we built a 142‐year long time series representing the mean daily catch (CPUE) of willow ptarmigan Lagopus lagopus in southeastern Norway. CPUE decreased over the 142 years, from approximately 35 birds shot per day in early years to around two in the last years. There were three periods in the time series: a first period with 3–5 year cycles of high peaks and low troughs (1872–1900), a short second period with similarly high peaks, variable depth of troughs and variable cyclicity (1901–1916), and a third long period with much lower peaks and faded cycles (1917–2013). Yearly variation in CPUE was best explained by an interacting effect of small rodent peak years and period, with a reduced positive effect of rodents in the last period, and a positive effect of the North Atlantic Oscillation index in spring and early summer. None of the weather variables with significant time trends explained any variation in CPUE and we could therefore not attribute the decline in CPUE directly to climate change. We postulate that a long‐term dampening of the amplitude in small rodent cycles combined with an increase in red fox numbers, have increased predation on alternative prey like ptarmigan, and prevented the populations from reaching their earlier peaks. Even though the present population of willow ptarmigan is only a fraction of what it was in former days, we recommend light hunting to motivate for monitoring and to keep public attention on the bird.

The Role of the North Atlantic Oscillation for Projections of Winter Mean Precipitation in Europe

AbstractClimate models generally project an increase in the winter North Atlantic Oscillation (NAO) index under a future high‐emissions scenario, alongside an increase in winter precipitation in northern Europe and a decrease in southern Europe. The extent to which future forced NAO trends are important for European winter precipitation trends and their uncertainty remains unclear. We show using the Multimodel Large Ensemble Archive that the NAO plays a small role in northern European mean winter precipitation projections for 2080–2099. Conversely, half of the model uncertainty in southern European mean winter precipitation projections is potentially reducible through improved understanding of the NAO projections. Extreme positive NAO winters increase in frequency in most models as a consequence of mean NAO changes. These extremes also have more severe future precipitation impacts, largely because of mean precipitation changes. This has implications for future resilience to extreme positive NAO winters, which frequently have severe societal impacts.

Pan-Arctic melt pond fraction trend, variability, and contribution to sea ice changes

Because the Pan-Arctic melt pond significantly influences the mass balance of sea ice, analyzing changes in the Pan-Arctic melt pond can offer insights into the Arctic sea ice and environment. In this study, the MODIS level 2 surface reflectance product (MOD09A1) was used to calculate variability and trends in the Pan-Arctic melt pond fraction (MPF) from May 9 to August 29 during the period 2000–2019, along with its relationship with September sea ice extent (SIE). The results showed that as a result of advances in Arctic ice melt onset and the extension of the melting period, the MPF as a whole showed an insignificant upward trend but that the MPF in the multiyear ice area increased significantly. Melt pond distribution is closely related to atmospheric circulation over the Arctic. Significant positive and negative geopotential height anomalies at different locations in the Arctic will cause poleward winds from different directions, bringing warm, humid air and leading to an increase in MPF in different regions of the Arctic. There is a strong negative correlation between integrated MPF and September SIE, concentrated in the northern part of the Beaufort Sea. On June 18, the integrated MPF had the strongest correlation with September SIE, at −0.96. The use of linear regression and support vector machine combined with integrated MPF and 850-hpa average wind, Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) indexes to forecast September SIE shows that the support vector machine is more suitable for forecasting September SIE. When the forecast factor is only the integrated MPF, the MPF is integrated from May 9 to June 10 has the forecast accuracy is the highest, with a considerable forecast skill. When the average May–June AO is combined with the integrated MPF, the forecast skill will be further improved.

Decadal variability in the austral summer precipitation over the Central Andes: Observations and the empirical‐statistical downscaling model

AbstractThe decadal variability in summer precipitation over the Central Andes (10°–30°S) is investigated from 1921 to 2010 using low‐pass filtered time series of the central and eastern El Niño–Southern Oscillation (ENSO) Pacific (C and E) indices, the South Pacific Convergence Zone (SPCZ) index, the Atlantic SST indices, Atlantic Multidecadal Oscillation (AMO) index, North Atlantic Oscillation (NAO) index, and ERA‐20C reanalysis. Additionally, an empirical‐statistical downscaling (ESD) model was built. A rotated empirical orthogonal function (REOF) analysis shows that the first leading mode of precipitation (RPC1) represents 38.2% of the total decadal variance. RPC2, RCP3, and RPC4 represent 18.8, 12.8, and 9.7% of the total decadal variance, respectively. Furthermore, RPC1 features highest loadings over most of the region. RPC2 features a dipole of highest loadings over the southernmost Bolivian Altiplano and lowest loadings over the northwestern Argentinian Andes. Conversely, RPC3 presents highest loadings over the eastern‐central Bolivian Altiplano and northwestern Argentinian Andes. RPC4 features highest loadings over the southern Bolivian Andes. RPC1 and RPC3 wet summers are associated with moisture transport from the Amazon basin, but RPC1 features the strengthening upper‐level Bolivian high‐Nordeste low system over South America. Conversely, RPC2 and RPC4 wet summers are associated with local processes induced by southward displacement of the South Atlantic Convergence Zone and warm sea surface temperature (SST) anomalies over the Indian Ocean, respectively. According to the ESD model, the decadal variability in the central and eastern Pacific (CP and EP) and Atlantic Ocean reproduces the decadal component of the DJF precipitation over most of the Central Andes.

Trends and Interdependence of Solar Radiation and Air Temperature—A Case Study from Germany

This study characterizes the spatiotemporal solar radiation and air temperature patterns and their dependence on the general atmospheric circulation characterized by the North Atlantic Oscillation (NAO) Index in Germany from 1991 to 2015. Germany was selected as the study area because it can be subdivided into three climatologically different regions: the North German lowlands are under the maritime influence of the North and Baltic Seas. Several low mountain ranges dominate Germany’s center. In the south, the highest low mountain ranges and the Alps govern solar radiation and air temperature differently. Solar radiation and air temperature patterns were studied in the context of the NAO index using daily values from satellite and ground measurements. The most significant long-term solar radiation increase was observed in spring, mainly due to seasonal changes in cloud cover. Air temperature shows a noticeable increase in spring and autumn. Solar radiation and air temperature were significantly correlated in spring and autumn, with correlation coefficient values up to 0.93. In addition, a significant dependence of solar radiation and air temperature on the NAO index was revealed, with correlation coefficient values greater than 0.66. The results obtained are important not only for studies on the climate of the study area but also for photovoltaic system operators to design their systems. They need to be massively expanded to support Germany’s climate neutrality ambitions until 2045.

Variability of Remotely Sensed Solar-Induced Chlorophyll Fluorescence in Relation to Climate Indices

Global remote sensing of solar-induced fluorescence (SIF), a proxy for plant photosynthetic activity, represents a breakthrough in the systematic observation of global-scale gross primary production and other ecosystem functions. Here, we hypothesize that all earth ecosystem variabilities, including SIF, are affected by climate variations. The main contribution of this study is to apply a global empirical orthogonal function (EOF) analysis of SIF to quantify the relations between the large-scale GPP variability and climate variations. We used 2007–2019 SIF data derived from the Global Ozone Monitoring Experiment-2 (GOME-2) satellite sensor observations and a rotated empirical orthogonal function (EOF) analysis to explore global SIF variability over years and decades. The first leading EOF mode captures the well-known ENSO pattern, with most of the variance over continents in the tropical Pacific and Indian Oceans. The second and third leading EOF modes in SIF variability are significantly related to the NAO and PDO climate indices, respectively. Our analysis also shows that the 2011 La Niña (2015 El Niño) elevated (decreased) global SIF.

Trends in the abundance of Celtic Sea demersal fish: Identifying the relative importance of fishing and environmental drivers

The Celtic Sea is a productive fishing ground, therefore identifying the relative importance of fishing and environmental factors on fish stock dynamics is crucial for developing our understanding of sustainable yields and to operationalize Ecosystem Based Fisheries Management (EBFM). We investigated the effect of environmental variables and fishing on the relative abundance inferred from catch-per-unit-effort (CPUE), of twelve demersal stocks (i.e., cod, haddock, whiting, anglerfish, hake, megrim, plaice, sole, lesser-spotted dogfish, spurdog, Trisopterus spp., skates and rays) in the Celtic Sea from 1997 to 2019 (23 years). Annualized time series (1997-2019) of net primary production, bottom temperature, copepod abundance (Calanus finmarchicus and Calanus helgolandicus) and North Atlantic Oscillation index were used to characterize key environmental variables. Fishing exploitation rates (F/FMSY) were used to represent fishing pressure and CPUE trends derived from an International Bottom Trawl Survey (IBTS) were used to infer abundance. We used redundancy analysis to identify key explanatory variables and then dynamic factor analysis to assess their relationships with the CPUE series and identify underlying patterns in the unexplained temporal variation. Our results show that for the majority of demersal fish species, the CPUE trends were strongly influenced by fishing exploitation rates. The gradual reduction in exploitation rates observed throughout the study period most likely led to the partial recovery of cod, spurdog, hake, megrim, plaice, whiting, Trisopterus spp., and the skates and rays. In addition, exploitation patterns on one stock influenced CPUE trends of other demersal stocks (e.g., hake, megrim, plaice, lesser-spotted dogfish, sole). We also observed that the CPUE of whiting, hake and plaice increased when C. finmarchicus were abundant in the plankton. We infer from our findings in the investigated time series that the recovery of cod, spurdog, hake, megrim, plaice, whiting, Trisopterus spp., and the skates and rays in the Celtic Sea remains dependent on controlling fishing mortality, and this would not, at least for now, be confounded by the environmental conditions.

Drought Monitoring Using MOWCATL Data Mining Algorithm in Aras Basin, Turkey

Drought is a natural phenomenon that occurs frequently and has some adverse effects on the ecosystem and humanity. Determination of drought beforehand is vital for optimal management of water resources. Many different methods have been developed to detect drought. Sequential association analysis is used for the data series analysis containing time information and is one of the methods used to determine the drought. A correlation can be established between the values taken by the data at different times when determining association rules with this method. The primary purpose of this study is to determine the sequential association patterns between precipitation and climate oscillation index for Aras Basin. The Aras basin is a region where irrigation and animal husbandry are common. Today, many dams and hydroelectric power plants, together with the increasing population, meet the water and energy needs. A possible drought event in this region will adversely affect the living things in the basin. Therefore, the study focused on this basin. Finding sequential associations between precipitation and climate oscillation index can determine the temporal correlations between these parameters and specifically detect drought. The MOWCATL (Minimal Occurrences with Constraints and Time Lags) algorithm was used to detect sequential associations, and the J-measure was used to evaluate the patterns in the study. Sequential association patterns were determined by applying this method to the precipitation data obtained from 6 meteorology stations in the Aras basin. AO (Arctic Oscillation) Index, MEI (Multivariate ENSO) Index, NAO (North Atlantic Oscillation) Index, Oceanic Niño Index (ONI), PDO (Pacific Decadal Oscillation) Index, PNA (Pacific/North American), and SOI (Southern Oscillation Index), followed by the 1, 3, 6 and 12-month Agricultural Standardized Precipitation Index (a-SPI) were used in sequential association. The study results revealed that the antecedent parameters were ineffective in detecting arid conditions in Ardahan and Doğubeyazıt stations, and they were influential on drought conditions, especially in a-SPI-3 and a-SPI-12 month periods at other stations. Although the altitude and geographical features are different, similar climatic patterns have been detected in some stations. As a result, it has been determined that climatic oscillations generally bring about typical situations in terms of drought for the Aras Basin.

Characteristics of the Greenland Ice Sheet Mass Variations Revealed by GRACE/GRACE Follow-On Gravimetry

As a major contributor to global mean sea-level rise, the Greenland ice sheet (GrIS) and the patterns of its mass change have attracted wide attention. Based on Gravity Recovery and Climate Experiment (GRACE)/GRACE Follow-On (GRACE-FO) gravimetry data, we computed monthly non-cumulative mass change time series of the GrIS, which agree with those from the mass budget method confirming the reliability of GRACE-FO-derived mass change. Over the GrIS, mass was mainly gained in winter, followed by spring. It primarily lost mass in summer, with the percentage of summer mass loss versus the corresponding annual mass loss ranging from 61% to 96%. We report that spring mass loss has become more frequent since 2015, and autumn mass gain occurred more frequently after 2014. By separating mass gain from mass loss at the annual timescale, we find that both the mass gain and mass loss showed a slightly increasing trend during 2003–2020, which might be a response to the ongoing Arctic warming. Summer mass variations highly correlated with the summer North Atlantic Oscillation index are dominated by temperature-associated precipitation and meltwater runoff. This study suggests that long-term observations would be necessary to better understand patterns of the GrIS mass variations in future.

Compound Extremes of Air Temperature and Precipitation in Eastern Europe

The spatial distribution of compound extremes of air temperature and precipitation was studied over the territory of Eastern Europe for the period 1950–2018. Using daily data on air temperature and precipitation, we calculated the frequency and trends of the four indices—cold/dry (CD), cold/wet (CW), warm/dry (WD) and warm/wet (WW). The connection between these indices and large-scale patterns in the ocean–atmosphere system, such as the North Atlantic Oscillation (NAO), the East Atlantic (EA) and Scandinavia (SCAND) patterns, was also studied. The positive and statistically significant trends in the region were observed for the warm extremes (especially the WW index) in all seasons, with maximum values in the winter season, while negative trends were obtained for the cold extremes. The NAO index has a strong positive and statistically significant correlation with the warm compound indices (WD and WW) in the northern part of Eastern Europe in winter like the EA pattern, but with smaller values. The spatial distribution of the correlation coefficients between compound extremes and the SCAND index in the winter season is opposite to the correlation coefficients with the NAO index.

Having a better home range does not reduce the cost of reproduction in Soay sheep.

A cost of reproduction may not be observable in the presence of environmental or individual heterogeneity because they affect the resources available to individuals. Individual space use is critical in determining both the resources available to individuals and the exposure to factors that mediate the value of these resources (e.g. competition and parasitism). Despite this, there has, to our knowledge, been little research to understand how between-individual differences in resource acquisition, caused by variation in space use, interact with environmental variation occurring at the population scale to influence estimates of the cost of reproduction in natural populations. We used long-term data from the St. Kilda Soay sheep population to understand how differences in age, relative home range quality, and average adult body mass, interacted with annual variation in population density and winter North Atlantic Oscillation index to influence over-winter survival and reproduction in the subsequent year, for females that had invested into reproduction to varying degrees. Our results suggest that Soay sheep females experience costs both in terms of future survival and future reproduction. However, we found little evidence that estimated costs of reproduction vary depending on relative home range quality. There are several possible causes for the lack of a relationship between relative home range quality and our estimate of the costs experienced by females. These include the potential for a correlation between relative home range quality and reproductive allocation to mask a relationship between home range quality and reproductive costs, as well as the potential for the benefit of higher quality home ranges being offset by higher densities. Nevertheless, our results raise questions regarding the presence or context-dependence of relationships between resource access and the estimated cost of reproduction.

The impact of climate oscillations on the surface energy budget over the Greenland Ice Sheet in a changing climate

Abstract. Climate change is particularly strong in Greenland, primarily as a result of changes in the transport of heat and moisture from lower latitudes. The atmospheric structures involved influence the surface mass balance (SMB) of the Greenland Ice Sheet (GrIS), and their patterns are largely explained by climate oscillations, which describe the internal climate variability. By using k-means clustering, we name the combination of the Greenland Blocking Index, the North Atlantic Oscillation index and the vertically integrated water vapor as NAG (North Atlantic influence on Greenland) with the optimal solution of three clusters (positive, neutral and negative phase). With the support of a polar-adapted regional climate model, typical climate features marked under certain NAG phases are inter-seasonally and regionally analyzed in order to assess the impact of large-scale systems from the North Atlantic on the surface energy budget (SEB) components over the GrIS. Given the pronounced summer mass loss in recent decades (1991–2020), we investigate spatio-temporal changes in SEB components within NAG phases in comparison to the reference period 1959–1990. We report significant atmospheric warming and moistening across all NAG phases. The pronounced atmospheric warming in conjunction with the increase in tropospheric water vapor enhance incoming longwave radiation and thus contribute to surface warming. Surface warming is most evident in winter, although its magnitude and spatial extent depend on the NAG phase. In summer, increases in net shortwave radiation are mainly connected to blocking systems (+ NAG), and their drivers are regionally different. In the southern part of Greenland, the atmosphere has become optically thinner due to the decrease in water vapor, thus allowing more incoming shortwave radiation to reach the surface. However, we find evidence that, in the southern regions, changes in net longwave radiation balance changes in net shortwave radiation, suggesting that the turbulent fluxes control the recent SEB changes. In contrast to South Greenland under + NAG, the moistening of North Greenland has contributed to decreases in surface albedo and has enhanced solar radiation absorption. Regardless of the NAG phase, increases in multiple atmospheric variables (e.g., integrated water vapor and net longwave radiation) are found across the northern parts of Greenland, suggesting that atmospheric drivers beyond heat and moisture originated from the North Atlantic. Especially in the northern ablation zone, sensible heat flux has significantly increased in summer due to larger vertical and horizontal temperature gradients combined with stronger near-surface winds. We attribute the near-surface wind intensification to the emerging open-water feedback, whereby surface pressure gradients between the ice/snow-covered surface and adjacent open seas are intensified.

Relationship between plankton dynamics and growth of the long-lived clam Arctica islandica on the Faroe shelf

Marine ecosystem dynamics can vary on timescales ranging from months to centuries, but many observational data are limited to just a few decades. The bivalve Arctica islandica may live up to five centuries depositing annual growth increments in its shells which can serve as an indicator for ecosystem productivity. In the present study, 154 specimens of A. islandica were collected on the Faroe Shelf and standardised annual growth increments for 143 of them – 44 from coastal stations and 99 from shelf stations – were compared with climatic, oceanographic and biological variables. A. islandica growth from coastal and shelf stations was not correlated with basin-scale climate indices (the AMO index, the NAO index, the AO index or the subpolar gyre index) or, more locally, with windspeed or sea surface temperature on the Faroe Shelf. For the shelf stations there was a significant negative correlation between A. islandica growth and the volume transport of the Faroe Current flowing just north of Faroe Islands (r = -0.62). There was a weak nonsignificant positive correlation with an index of primary production on the Faroe Shelf (r = 0.31) and a strong negative correlation with a zooplankton biomass index in mid-summer (r = -0.76). There was also a strong positive correlation between A. islandica growth and the biomass of the bottom-feeding fish species Melanogrammus aeglefinus two years later (r = 0.62). These results seem to suggest that A. islandica growth may represent the amount of fresh phytoplankton that reaches the near-bottom water layers and could probably be regarded as a proxy for the strength of pelagic-benthic coupling that is modulated through phytoplankton-zooplankton interactions in the overlying water. Our results highlight the potential for A. islandica to serve as a long-term proxy for linking variability in pelagic ecosystem dynamics to demersal fish stocks.