Impacts of sea ice on marine dynamics in western Laizhou Bay, Bohai Sea

Abstract

The Bohai Sea is a region with wintertime sea ice development and high levels of human economic activity, where sea ice has a powerful destructive effect on maritime transportation and ocean engineering. In the Bohai Sea, sediment resuspension caused by waves and currents has not previously been systematically studied during periods of ice cover. In the winter of 2009–2010, severe ice conditions with a recurrence period of 30 years occurred. In this study, wave, residual water level (RWL), residual current (RC), and suspended sediment concentration (SSC) data were collected by two seabed-based observation stations (QD12 and QDG2) for one continuous year during both ice-covered and ice-free conditions. The data were systematically compared and analyzed. Generally, the results showed that sea ice coverage had a clear suppressing effect on the significant wave height (Hs) and RWL. Hs decreased by almost 50%, and RWL decreased by 0.19 m and 0.10 m during ice-covered conditions at two stations. Sea ice coverage had a suppressing effect on the sediment resuspension due to a reduction in wave induced shear stress. The reduction of sea level and SSC was mainly reflected in the decrease of fluctuation amplitude and overall magnitude, and the suppression effect was more obvious in conditions of strong wind. The RC velocity varied during periods of ice cover in Laizhou Bay. Sea ice enhanced RC velocity during the destruction period. The RC velocity increased dramatically at station QD12 probably due to the long length of the destruction period, but decreased slightly at station QDG2 possibly due to a shorter destruction period and the blocking of Weifang Port. The enhanced RC in the destruction period carrying broken ice caused significant damage to coastal engineering projects. The suppressing effects of sea ice on Hs, RWL, and sediment resuspension, and the strengthening effects on RC velocity were both closely related to the wind speed and direction. This study reveals the effects of sea ice on local hydrodynamics and sediments, providing important reference values for the generation and disappearance of sea ice in mid- and high-latitude bays under the background of dramatic global climate change.