Now showing 1 - 8 of 8
  • Publication
    Impacts of the EA and SCA patterns on the European twentieth century NAO-winter climate relationship
    Much of the twentieth century multidecadal variability in the relationship between North Atlantic Oscillation (NAO) and winter climate over the North Atlantic–European sector can be linked to the combined effects of the NAO and either the East Atlantic pattern (EA) or the Scandinavian pattern (SCA). Our study documents how different NAO–EA and NAO–SCA combinations influence winter climatic conditions (temperature and precipitation) as a consequence of NAO dipole migrations. Using teleconnectivity maps, we find that the zero-correlated line of the NAO–winter-climate relationship migrates southwards when the EA is in the opposite phase to the NAO, related to a southwestwards migration of the NAO dipole under these conditions. Similarly, a clockwise movement of the NAO–winter-climate correlated areas occurs when the phase of the SCA is opposite to that of the NAO, reflecting a clockwise movement of the NAO dipole under these conditions. Our study provides new insights into the causes of spatial and temporal nonstationarity in the climate–NAO relationships, particularly with respect to winter precipitation. Furthermore, interannual variability in the north–south winter precipitation gradient in the UK appears to reflect the migration of the NAO dipole linked to linear combinations of the NAO and the EA. The study also has important implications for studies of the role of the NAO in modulating the wind energy resource of the UK and Ireland, as well as for the selection of locations for terrestrial proxy archive reconstruction of past states of the NAO. Copyright © 2013 Royal Meteorological Society
      601Scopus© Citations 138
  • Publication
    A 34-year simulation of wind generation potential for Ireland and the impact of large-scale atmospheric pressure patterns
    To study climate-related aspects of power system operation with large volumes of wind generation, data with sufficiently wide temporal and spatial scope are required. The relative youth of the wind industry means that long-term data from real systems are not available. Here, a detailed aggregated wind power generation model is developed for the Republic of Ireland using MERRA reanalysis wind speed data and verified against measured wind production data for the period 2001–2014. The model is most successful in representing aggregate power output in the middle years of this period, after the total installed capacity had reached around 500 MW. Variability on scales of greater than 6 h is captured well by the model; one additional higher resolution wind dataset was found to improve the representation of higher frequency variability. Finally, the model is used to hindcast hypothetical aggregate wind production over the 34-year period 1980–2013, based on existing installed wind capacity. A relationship is found between several of the production characteristics, including capacity factor, ramping and persistence, and two large-scale atmospheric patterns – the North Atlantic Oscillation and the East Atlantic Pattern.
      354Scopus© Citations 23
  • Publication
    Data-model comparison of soil–water δ18O at a temperate site in N. Spain with implications for interpreting speleothem δ18O
    An understanding of how seasonal and longer-term δ18O signals in meteoric precipitation (δ18Op) are modified by percolation through soils is essential to link temporal changes in speleothem δ18O to surface climatic conditions. This study focuses on modifications that occur in a relatively thick soil above a temperate cave site (La Garma, N. Spain). Monthly soil–water δ18O (δ18Osw) values at a depth of 60 cm through the year are only 14% of the range in δ18Op, implying substantial homogenisation and attenuation of seasonal signals. A striking feature is that δ18Osw values at 60 cm depth are lowest in summer and highest in winter, the opposite (anti-phase) to that observed in rainfall. Soil–water residence times of up to circa 6 months in the upper 60 cm of soil, and a matrix flow, piston-type infiltration behaviour with mixing are inferred. Evaporative effects on recovered soil–water δ18O are minimal at this wet temperate site, in contrast with published results from arid and semi-arid sites. A soil–water model is presented to estimate monthly δ18Osw as a function of air temperature and δ18Op, incorporating effects such as variations in the amount of infiltrated water, changes in the ratio between evaporation and transpiration, mixing with antecedent soil moisture and small enrichments in 18O linked to evaporation and summer moisture deficits. Our model reproduces the observed δ18Osw results, and produces δ18O outputs in excellent agreement with δ18O data for two monitored drip-water sites at La Garma cave that exhibit seasonal δ18O variability. We conclude that simple evapotranspiration models that permit infiltration during months that have a positive hydrological balance only, tend to underestimate summer rainfall contributions. Overall, the study provides an improved framework for predicting δ18Osw trends at temperate sites such as La Garma that have a relatively thick soil cover, as well as for understanding seasonal ranges and trends in δ18O in cave drip-sites.
      237Scopus© Citations 16
  • Publication
    A first evaluation of the spatial gradients in δ18O recorded by European Holocene speleothems
    Oxygen isotope data for well dated Holocene speleothems from Europe have been compiled for the first time. The data were analysed at 1 ka time slices through the Holocene by taking averages of 50 year duration. After filtering the data to exclude high altitude, high latitude and sites proximal to the Mediterranean Sea, the data exhibit surprisingly tight linear correlations between speleothem O isotope values and longitude. The slope of the data on δ18O vs. longitude plots changes systematically from the early to the late Holocene, exhibiting a much steeper zonal gradient in the early Holocene. Changes in the isotope gradient through the course of the Holocene reflect both a gradual increase in δ18O in speleothems from the western margin of the transect and a simultaneous decrease in speleothem δ18O on the eastern end of the transect. These changes follow summer insolation trends through most of the Holocene, but show marked deviations from c. 4 ka to the present day. Steeper early Holocene zonal isotope gradients are attributed primarily to a combination of early Holocene warming in the west and intense convective rainfall over the European continent in summer time driven by high early Holocene summer insolation. Although the absolute δ18O values preserved in speleothems do not precisely reflect the equilibrium values with respect to the waters from which they are precipitated, the tight isotope-longitude correlations indicate that speleothems are reliable recorders of combined rainfall O isotope signals and air temperature.
      816Scopus© Citations 89
  • Publication
    Water quality perceptions and private well management: The role of perceived risks, worry and control
    Mismanagement of drinking water supplies can pose serious public health risks. There are many concerns about water source management among private well owners, as they are often solely responsible for maintaining their wells, and monitoring and testing of their own water quality. Lack of worry about contamination and a strong sense of control over risks in relation to drinking water quality have been identified as important factors that influence peoples’ perceptions and behaviour. In this paper, we investigated how worry and control moderate the influence of risk perceptions on water quality perceptions and well owners’ maintenance behaviours. We compare a sample of private well owners (N=167) with a sample of members of Group Water Schemes (GWS) (N=160) and people who are supplied via the public mains (N=195), to validate our results. We found that, in comparison to the other groups, well owners believe that water from private wells is superior and they express a high level of control over contamination risks of their drinking water. Moreover, strong feelings of control suppress their perceptions of risk in relation to water quality. However, well owners who feel largely in control also maintain their well more frequently. Our results suggest that communication strategies with well owners should aim to bring the current unrealistic levels of control perception down to more realistic levels, rather than removing all sense of control.
      111Scopus© Citations 9
  • Publication
    The coupled δ13C-radiocarbon systematics of three late Glacial/early Holocene speleothems; insights into soil and cave processes at climatic transitions
    The coupled δ13C-radiocarbon systematics of three European stalagmites deposited during the Late Glacial and early Holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions. The emphasis is on understanding how speleothems may record climate-driven changes in the proportions of biogenic (soil carbon) and limestone bedrock derived carbon. At two of the three sites, the combined δ13C and 14C data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher d13C during the cold Younger Dryas. In these stalagmites (GAR-01 from La Garma cave, N. Spain and So-1 from Sofular cave, Turkey), the combined changes in δ13C and initial 14C activities suggest enhanced decomposition of old stored, more recalcitrant, soil carbon at the onset of the warmer early Holocene. Alternative explanations involving gradual temporal changes between open- and closed-system behaviour during the Late Glacial are difficult to reconcile with observed changes in speleothem δ13C and the growth rates. In contrast, a stalagmite from Pindal cave (N. Spain) indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects, rather than climate change. For the first time, it is shown that while the initial 14C activities of all three stalagmites broadly follow the contemporaneous atmospheric 14C trends (the Younger Dryas atmospheric 14C anomaly can be clearly discerned), subtle changes in speleothem initial 14C activities are linked to climate-driven changes in soil carbon turnover at a climate transition.
      989Scopus© Citations 59
  • Publication
    Potential seasonal calibration for palaeoenvironmental reconstruction using skeletal microstructures and strontium measurements from the cold-water coral Lophelia pertusa
    Lophelia pertusa is a colonial cold-water coral species with a wide spatial distribution in recent marine waters. Analysing the chemistry of its skeleton allows reconstruction of environmental parameter variations. While numerous studies have attempted to interpret such analyses, little information is available on the microstructures of Lophelia pertusa and their temporal constraints. This study introduces newly recognized microstructures in the coral wall following growth along the radial axis. The thicknesses of these ‘micro-layers’ are correlated with strontium concentrations and can be used to estimate seasonal growth rates of single polyps from the colony. We propose that each of these micro-layers represents a period of 1 month of mineralization and can locate two decreasing periods in growth rate during a year: one caused by limited food availability during winter months and one in autumn linked to gametogenesis. High-frequency study of strontium concentrations using this interpretation shows a lunar cycle. We demonstrate that while the micro-layers are present in all L. pertusa specimens from four locations in the Atlantic Ocean and the Mediterranean Sea, growth patterns reveal a complex organization that limits their visibility. Strontium fluctuations, however, appear to be a promising mechanism by which to establish a temporal calibration.
      334Scopus© Citations 5
  • Publication
    A late-Holocene climate record in stalagmites from Modrič Cave (Croatia)
    Few terrestrial Holocene climate records exist from Southeastern Europe despite its important geographic position as a transitional climatic zone between the Mediterranean and mainland continental Europe. In this study we present new petrographic and stable isotope data for two Holocene speleothems from Modrič Cave, Croatia (44o15’N, 15o32’E), a coastal Adriatic site (120 metres inland). Modern meteorological and cave conditions have been monitored for two years to understand the links between the climate variability and the stable isotope time-series records in speleothems. Typical of a Mediterranean-type climate, a negative water balance exists between April and September, so that recharge of the aquifer is restricted to the winter months. The weighted mean δ18O of the rainfall is -5.96‰ (2σ =2.83), and the weighted mean D/H rainfall value is -36.83‰ (2σ = 19.95), slightly above the Global Meteoric Water Line (GMWL), but well below the Mediterranean Meteoric Water Line (MMWL). Modern calcite from the tops of each stalagmite exhibits δ18O values that are close to isotopic equilibrium with their respective drip water values. Unfortunately, the relatively young ages and low uranium contents (c. 50 ppb) of both stalagmites hamper the use of U-series dating. Radiocarbon dates have been used instead to constrain their chronology using a dead carbon correction. Aside from some Isotope Stage 3 material (c. 55 ka), both stalagmites were deposited during the late Holocene. Climatic conditions during the late Holocene are inferred to have been sufficiently wet to maintain stalagmite growth and any hiatuses appear to be relatively short lived. Inferred changes in the stalagmite diameters during deposition are linked to δ13C and δ18O variations, indicating alternating periods of drier and wetter conditions. Drier conditions are inferred for the late Roman Ages warm period and the mid-Medieval Warm Period (MWP). Wetter conditions are associated with the Little Ice Age period.
      893Scopus© Citations 30