On April 20, Gao Huiwang, professor of College of Environmental Science and Engineering of Chinese Marine University delivered a lecture on the impact of atmospheric forcing on the marine ecosystem. Professor Gao gave a general introduction to the background and model of typhoon research, and the impacts and regularity of typhoon events. Professor Zheng Mei was the host of this seminar.

Professor Gao Huiwang

Professor Zheng Mei

Research background and model introduction:

The typhoon is a strong weather system in the ocean and the most intuitive form of air-sea interaction, which causes a strong mixing process, having a significant impact on the exchange between the upper ocean and the deep-sea water heat, energy and material. The typhoon-induced upwelling and vertical mixing bring nutrient form the lower ocean into the upper ocean and results in the increase in chlorophyll concentration, which affects the level of the primary productivity of the ocean.

The influence of typhoon on the ocean is mainly reflected in two aspects--the marine physical environment and the ecological environment. To the marine physical environment, it can reduce the temperature of the sea surface, make the mixed layer of the ocean deepened, and produce near inertial oscillation. To the marine ecological environment, it can increase the concentration of chlorophyll in the sea surface, increase the primary productivity and change the structure of plankton.

At present, the impact of typhoon on the upper ocean has been reported based on satellite remote sensing data, but these reports only focus on the surface of the sea, and little attention is paid to the influence of typhoon in the sub surface or deep sea. Therefore, there are many problems to be discussed about the effect of typhoon on the ocean, such as the influence of typhoon on the physical and ecological factors of marine subsurface and deep layer, the contribution of nutrients to vertical transport and primary productivity in the oligotrophic sea area, and the influence of various factors on the marine ecosystem.

The impact of a typhoon event:

Professor Gao takes Typhoon Damrey (0518) as an example to describe the impact of the tropical cyclone.

Using the vertical one-dimensional marine ecological dynamics model, it is found that the impact of the typhoon on the ocean is mainly reflected in three aspects. The first is the change in temperature. After Typhoon Damrey, the temperature of the upper 50m layer decreases with the maximum temperature drop of 4 degrees, the temperature of the 50-150m layer rises with the maximum increase of 1.3 degrees, and the mixing layer depth increases to 85m. The second is the effect on the nutrients in sea water. The nutrient concentration of the upper layer first rises and then falls in response to the passing by of the typhoon. The third is the effect on phytoplankton.

The reasons of changes of chlorophyll concentration in the ocean after typhoon's passage can be attributed to the following points:

First, the rapid increase of surface chlorophyll concentration and the rapid reduction of subsurface chlorophyll concentration are mainly controlled by physical processes (vertical turbulent mixing).

Second, the slow increase of chlorophyll in the surface and subsurface is is caused by the fact that the biological process plays a leading role. In addition, the increase of chlorophyll concentration in the subsurface is longer than that in the surface layer.

In addition, he compared the influence of two different typhoons and discussed the regularity of typhoon influence as well. The results show that ocean responses to typhoons depending on their intensity and transit speed. At the same time, the seawater stratification and nutrient level before typhoon passing are also important factors that cannot be ignored.

The Q&A Session