The spring–neap variability and mechanisms of long-term variations in the upwelling at the tip of Liaodong Peninsula, China

Abstract

Upwelling is one of the important phenomena in oceans which plays a significant role in marine hydrology and marine ecological systems. During the summer stratified season, there are usually cold patches around the tip of Peninsula. Using the satellite sea surface temperature (SST) data from 1999 to 2018, this study showed that there was a pod-like cold water patch with two cold centers around the tip of Liaodong Peninsula, China. The range and the intensity of upwelling indicated an increasing trend during 1999–2018. We used a two-dimensional hydrodynamic model Mike21 to study the impact of the tidal current to the intra-month variations of upwelling (DHI 2009). The variability of tidal currents brought the significant spring–neap variations of the upwelling, showing that the SST of upwelling during the spring tide was lower about 1°C and the range of the cold water extended farther than that during the neap tide. The variations of upwelling area lagged behind the tide range about 4 days. The mechanisms of long-term variations of the upwelling were analyzed using the remote sensing wind data and the reanalysis ocean current data. Summer surface wind in the Bohai Sea suppressed the upwelling through the inshore Ekman transports and the effect of the wind curls could be ignored. The dispersion of geostrophic current around the Laotieshan Channel due to the bottom friction could drive the upward vertical velocities. Both of wind and current contributed to the multi-year variations of the upwelling around the tip of Liaodong Peninsula, China.