1,720,964 research outputs found
The North Atlantic Ocean and climate change in the UK and northern Europe
No full textThis article considers the changes in the North Atlantic Ocean since the commencement of the RAPID array in 2004, which measures the Meridional Overturning Circulation. Emphasis is placed on the heat and freshwater transports associated with this circulation and its influence on the climate of the UK
Bioenergetic modelling of the marine phase of Atlantic salmon (Salmo salar L.)
Full text linkA bioenergetic model of marine phase, wild Atlantic salmon was constructed to investigate the potential effects on post-smolt growth of predicted changes in oceanic conditions. Short-term estimates of growth in weight were similar to measurements in captivity and simulated growth varied with water temperature and swimming speed as expected. Longer-term estimates of growth in length were less than that achieved by wild salmon, particularly with constant swimming assumed. The model was sensitive to parameters relating to maximum daily food consumption, respiration and the relationships between body energy content, length and weight. Some of the sensitive parameters were based on substantive information on Atlantic salmon and their realistic ranges are likely to be much narrower than those tested. However, other parameter values were based on scant data, farmed Atlantic salmon or other salmonid species, and are therefore less certain and indicate where future empirical research should be focussed.<br/
Global secular changes in different tidal high water, low water and range levels
No full textTides exert a major control on the coastal zone by influencing high sea levels and coastal flooding, navigation, sediment dynamics, and ecology. Therefore, any changes to tides have wide ranging and important implications. In this paper, we uniquely assess secular changes in 15 regularly used tidal levels (five high water, five low water and five tidal ranges), which have direct practical applications. Using sea level data from 220 tide gauge sites, we found changes have occurred in all analyzed tidal levels in many parts of the world. For the tidal levels assessed, between 36% and 63% of sites had trends significantly different (at 95% confidence level) from zero. At certain locations, the magnitude of the trends in tidal levels were similar to trends in mean sea level over the last century, with observed changes in tidal range and high water levels of over 5 mm/yr and 2 mm/yr, respectively. More positive than negative trends were observed in tidal ranges and high water levels, and vice versa for low water levels. However we found no significant correlation between trends in mean sea level (MSL) and any tidal levels. Spatially coherent trends were observed in some regions, including the north-east Pacific, German Bight and Australasia, and we also found that differences in trends occur between different tidal levels. This implies that analyzing different tidal levels is important. Because changes in the tide are widespread and of similar magnitude to MSL rise at a number sites, changes in tides should be considered in coastal risk assessments
Modelling of tide and surge elevations in the Solent and surrounding waters: the importance of tide–surge interactions
No full textA regional two-dimensional hydrodynamic model using the MIKE-21 software and data from a pre-operational forecasting system of the English Channel is described and applied to the Solent–Southampton Water estuarine system. The regional model was able to predict surge heights with a root mean squared error (RMSE) accuracy of 0.09 m during a three month hindcast in the winter of 2009, comparing closely with accuracy assessments from other independent systems. However, consistent underprediction of tidal harmonic constituent amplitudes was present throughout the region leading to errors in the prediction of the total water level elevations. Despite the complex nature of the Solent tidal regime, interpolation of tidal elevations from harmonic analysis at fixed tide gauge locations was shown to be effective in reducing this uncertainty at gauged and un-gauged sites. The degree to which tide–surge interactions were taking place was examined. Of particular interest was the quantification of the sensitivity of the predicted surge to the levels of uncertainty expected in the prediction of the tide within a complex nearshore region such as the Solent. The tide–surge interaction during three surge events was shown to be greatest in the Western Solent and Southampton Waters regions, where the tidal uncertainty was greatest. Interaction between the tide and surge resulted in a change of up to 0.3 m (11%) in the predicted total peak water level when the surge was added to the harmonic analysis-based tidal prediction. Despite the significant effect of removing the tide–surge interactions, tests indicated that the error in tidal range expected in the regional models tidal prediction altered the prediction of the surge only enough to induce changes in peak total water elevations by up to 0.03 m during an event on 10th March 2008. The findings suggest that the current tidal predictions in complex estuarine systems, such as the Solent, are of high enough quality to reproduce the majority of the tide–surge interactions taking place and that the error in the surge due to uncertainties in the predicted tide are expected to be relatively small
Re-emerging ocean temperature anomalies in late-2010 associated with a repeat negative NAO
Full text linkNorthern Europe was influenced by consecutive episodes of extreme winter weather at the start and end of the 2010 calendar year. A tripole pattern in North Atlantic sea surface temperature anomalies (SSTAs), associated with an exceptionally negative phase of the North Atlantic Oscillation (NAO), characterized both winter periods. This pattern was largely absent at the surface during the 2010 summer season; however equivalent sub-surface temperature anomalies were preserved within the seasonal thermocline throughout the year. Here, we present evidence for the re-emergence of late-winter 2009/10 SSTAs during the following early winter season of 2010/11. The observed re-emergence contributes toward the winter-to-winter persistence of the anomalous tripole pattern. Considering the active influence of the oceans upon leading modes of atmospheric circulation over seasonal timescales, associated with the memory of large-scale sea surface temperature anomaly patterns, the re-emergence of remnant temperature anomalies may have also contributed toward the persistence of a negative winter NAO, and the recurrence of extreme wintry conditions over the initial 2010/11 winter season
High-frequency sea level variations and implications for coastal flooding: A case study of the Solent, UK
No full textThis study examines the occurrence and characteristics of high-frequency (<6 h) sea level variations in the Solent, UK – a mesotidal estuarine strait located in the central English Channel. A 14-year time series (2000–2013) of sea level observations sampled at 15-min intervals from the Southampton tide gauge was analyzed. The 8 highest-energy events have a mean amplitude of approximately 0.6 m and a dominant period of around 4 h. These events correspond with periods of enhanced meteorological activity, namely a marked reduction in air pressure and onset of strong southwesterly-southeasterly winds. Sea level observations from tide gauges around the Solent and the wider English Channel region (23 in total) were used to assess the spatial characteristics of these events. Analysis of time series and phase information indicates the occurrence of standing waves oscillating across the English Channel between southern England and northern France. This study provides a unique example of standing waves generated by extra-tropical cyclones over a large basin (the English Channel) with implications for flood inundation. The event of 28th October 2013 – the highest-amplitude (1.16 m) event in the record – was associated with minor coastal flooding at Yarmouth, Isle of Wight. This flood occurred during a neap tide, when such events are widely thought to be impossible. Hence, our findings emphasize the relevance of high-frequency sea level variability for regional sea level forecasting and flood risk management
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