The role of megatides and relative sea level in controlling the deglaciation of the British-Irish and Fennoscandinavian ice sheets

This is the final version of the article. Available from Wiley via the DOI in this record.Key external forcing factors have been proposed to explain the collapse of ice sheets, including atmospheric and ocean temperatures, subglacial topography, relative sea level and tidal amplitudes. For past ice sheets it has not hitherto been possible to separate relative sea level and tidal amplitudes from the other controls to analyse their influence on deglaciation style and rate. Here we isolate the relative sea level and tidal amplitude controls on key ice stream sectors of the last British–Irish and Fennoscandian ice sheets using published glacial isostatic adjustment models, combined with a new and previously published palaeotidal models for the NE Atlantic since the Last Glacial Maximum (22 ka BP). Relative sea level and tidal amplitude data are combined into a sea surface elevation index for each ice stream sector demonstrating that these controls were potentially important drivers of deglaciation in the western British Irish Ice Sheet ice stream sectors. In contrast, the Norwegian Channel Ice Stream was characterized by falling relative sea level and small tidal amplitudes during most of the deglaciation. As these simulations provide a basis for observational field testing we propose a means of identifying the significance of sea level and tidal amplitudes in ice sheet collapse.Funding was provided by the Natural Environment Research Council (NERC) through grant NE/I527853/1 (PhD studentship to S.L.W.). The research was supported by the Climate Change Consortium of Wales and the NERC BRITICE-CHRONO Consortium grant (NE/J007579/1). Jess Vaughan and Martyn Roberts drafted Figs 2–5

Sensitivity of palaeotidal models of the northwest European shelf seas to glacial isostatic adjustment since the Last Glacial Maximum

AbstractThe spatial and temporal distribution of relative sea-level change over the northwest European shelf seas has varied considerably since the Last Glacial Maximum, due to eustatic sea-level rise and a complex isostatic response to deglaciation of both near- and far-field ice sheets. Because of the complex pattern of relative sea level changes, the region is an ideal focus for modelling the impact of significant sea-level change on shelf sea tidal dynamics. Changes in tidal dynamics influence tidal range, the location of tidal mixing fronts, dissipation of tidal energy, shelf sea biogeochemistry and sediment transport pathways. Significant advancements in glacial isostatic adjustment (GIA) modelling of the region have been made in recent years, and earlier palaeotidal models of the northwest European shelf seas were developed using output from less well-constrained GIA models as input to generate palaeobathymetric grids. We use the most up-to-date and well-constrained GIA model for the region as palaeotopographic input for a new high resolution, three-dimensional tidal model (ROMS) of the northwest European shelf seas. With focus on model output for 1 ka time slices from the Last Glacial Maximum (taken as being 21 ka BP) to present day, we demonstrate that spatial and temporal changes in simulated tidal dynamics are very sensitive to relative sea-level distribution. The new high resolution palaeotidal model is considered a significant improvement on previous depth-averaged palaeotidal models, in particular where the outputs are to be used in sediment transport studies, where consideration of the near-bed stress is critical, and for constraining sea level index points

On the dynamics of thermohaline circulation based on the expansion in terms of diffusive vertical modes

報告番号: 乙12491 ; 学位授与年月日: 1995-09-25 ; 学位の種別: 論文博士 ; 学位の種類: 博士(理学) ; 学位記番号: 第12491号 ; 研究科・専攻: 理学系研究

拡散型鉛直モ-ド展開に基づく海洋熱塩循環の力学

University of Tokyo (東京大学

Estimating Bottom Stress on Continental Shelves from Tidal and Wave Models

A numerical model was developed to estimate bottom stresses induced by waves and tides, in order to obtain multiyear statistics on the occurrence of sediment resuspension over the continental shelf. The model consists of a tidal module which predicts tidal currents at level 1 m above the seabed by employing 20 tidal constituents, and a wave module supplying near-bottom orbital velocities averaged over a wave spectrum. Predicted waves and tides were combined to provide bottom stress estimations at the temporal interval of one hour. The model was tested at the Yellow/East China Sea and compared with observations. Tidal currents and wave heights predicted in the model was consistent with observations, and the temporal pattern of predicted bottom stress matched with that of suspended sediment concentrations observed. It was found that the temporal resolution of several hours is required to resolve extreme events which cause resuspensions and that tidal constituents other than M_2 would be necessary to reproduce tidal currents used in the bottom stress estimation

Compilation and validation of bathymetric data for the South China Sea with an emphasis on shallow region

Bathymetric data with a resolution of 5 min called gbscs5 have been compiled for a shelf region shallower than 200 m in the South China Sea by referring to paper charts, electronic charts, and trackline sounding data. Through a comparison between the new dataset and existing datasets (etopo5, etopo1, gebco08), characteristics of each dataset, including the existence of artificial features derived from erroneous sounding data or a conversion error of depth units, were documented for each dataset. It was found that small-scale bathymetric features observed along the shelf edge in gebco08 bathymetry are bounded by survey lines and were likely to be a spurious figure generated when applying a high-order interpolation scheme. Tidal simulations conducted with changing bathymetries have shown that the newly compiled dataset will produce smaller deviation from observed values than the existing bathymetries. While all four datasets analyzed in this study were found to be suitable for estimating overall tidal features of the South China Sea, a care must be taken when applying the tidal model results to a particular coastal region

Compilation and validation of bathymetric data for the South China Sea with an emphasis on shallow region

Bathymetric data with a resolution of 5 min called gbscs5 have been compiled for a shelf region shallower than 200 m in the South China Sea by referring to paper charts, electronic charts, and trackline sounding data. Through a comparison between the new dataset and existing datasets (etopo5, etopo1, gebco08), characteristics of each dataset, including the existence of artificial features derived from erroneous sounding data or a conversion error of depth units, were documented for each dataset. It was found that small-scale bathymetric features observed along the shelf edge in gebco08 bathymetry are bounded by survey lines and were likely to be a spurious figure generated when applying a high-order interpolation scheme. Tidal simulations conducted with changing bathymetries have shown that the newly compiled dataset will produce smaller deviation from observed values than the existing bathymetries. While all four datasets analyzed in this study were found to be suitable for estimating overall tidal features of the South China Sea, a care must be taken when applying the tidal model results to a particular coastal region