Because of the depth attenuation of wave orbital velocity, wave-induced bed shear stress is much more sensitive to changes in total water depth than tidal-induced bed shear stress. The ratio between wave- and tidal-induced bed shear stress in many shelf sea regions has varied considerably over the recent geological past because of combined eustatic changes in sea level and isostatic adjustment. In order to capture the high-frequency nature of wind events, a two-dimensional spectral wave model is here applied at high temporal resolution to time slices from 12 ka BP to present using paleobathymetries of the NW European shelf seas. By contrasting paleowave climates and bed shear stress distributions with present-day conditions, the model results demonstrate that, in regions of the shelf seas that remained wet continuously over the last 12,000 years, annual root-mean-square (rms) and peak wave heights increased from 12 ka BP to present. This increase in wave height was accompanied by a large reduction in the annual rms wave- induced bed shear stress, primarily caused by a reduction in the magnitude of wave orbital velocity penetrating to the bed for increasing relative sea level. In regions of the shelf seas which remained wet over the last 12,000 years, the annual mean ratio of wave- to (M-2) tidal-induced bed shear stress decreased from 1 (at 12 ka BP) to its present-day value of 0.5. Therefore compared to present- day conditions, waves had a more important contribution to large-scale sediment transport processes in the Celtic Sea and the northwestern North Sea at 12 ka BP.
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机译:由于波浪轨道速度的深度衰减,波浪引起的床层剪切应力比潮汐引起的床层剪切应力对总水深的变化更为敏感。由于近海地质变化和等静压调整的共同作用,在最近的地质历史中,许多架子海地区波浪和潮汐引起的床层剪切应力之比发生了很大变化。为了捕获风事件的高频特性,这里使用高分辨率的二维光谱波模型将时间范围从12 ka BP应用于使用欧洲西北海的古浮游生物呈现的时间片。通过将古波气候和床剪应力分布与当前状况进行对比,模型结果表明,在过去12,000年中连续保持湿润的架子海地区,年均方根(rms)和峰值波高从12 ka BP增加到现在。浪高的增加伴随着每年均方根波诱发的床层剪切应力的大幅度降低,这主要是由于渗透到床层以增加相对海平面的波轨道速度的幅度减小所致。在过去12,000年保持湿润的大陆架地区,潮汐引起的潮汐剪切应力与(M-2)潮汐引起的床剪切应力的年平均比率从1(在12 ka BP时)下降到目前的0.5。因此,与目前的情况相比,在12 ka BP时,海浪对凯尔特海和西北北海的大规模泥沙输运过程具有更重要的作用。
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