NIFS said the East Sea has seen a long-term decrease in primary production*, and the reason for the decrease is ocean-warming drived reduction in nutrients supply.

*Primary production refers to the process where phytoplanktons convert inorganic substances into organic matter using energy from sunlight (photosynthesis), forming the base of the food web, providing energy and nutrients for other organisms. 

Based on the long-term observation results from satellite and NIFS research vessels (R/Vs), NIFS confirmed that the reason behind the decreased primary production in the East Sea was the increasing temperature gap between sea surface and bottom water, which increased stratification*, resulting in reduced nutrients supply by weak vertical mixing of materials between water layers. 

*Ocean stratification refers to the natural layering of ocean. The waters into distinct horizontal layers based on density. Stronger ocean stratification intensifies the separation of ocean layers and reduces vertical mixing, impacting the exchange of nutrients, salinity, oxygen, carbon, etc. 

The recent analysis on 22-year satellite* data(MODIS-aqua/2003–2024) confirmed that primary production in the East Sea showed the distinct long-term decrease (0.3%/year). 

The R/Vs observation results also showed that primary production in 2024 was decreased by 13% compared to the average of recent six years (2018-2023). Moreover, distribution range of macro- and megaplankton decreased by 1.1% per year(1,630㎢/year), confirming that the structure of marine ecosystem is changing clearly. 

The stratification in the East Sea had been stronger around 1.83% a year on average from 1990 to 2023. Since 2015, in particular, it increased by 13.8% compared to the average of the past 25 years, which was more than 2.5 times the global increase average rate (around 4.9%). 

The main factors of the stronger stratification is aggressive ocean warming, which takes on a complex tenor including △increasing heat energy from atmosphere, △stronger inflow of the East Korea Warm current, which enters the Korea Strait from the East China Sea.

Such physical and chemical changes, in turn, lead to the decrease of primary production in the East Sea.