Record-Breaking Slow Temperature Evolution of Spring Water During 2020 and Its Impacts on Spring Bloom in the Yellow Sea

Abstract

Unprecedented retardation of spring water temperature rising during the 2020 pandemic year was identified in the Socheongcho Ocean Research Station within the northeastern basin of the Yellow Sea: an exceptionally high water temperature anomaly in March and a contrasted low-temperature anomaly in May. The slowest temperature evolution was principally caused by the significant increase in latent heat releases in April (117% higher than the climatology of 1982–2019). Strong northwesterly winds generated these exceptional heat fluxes associated with the dipole-like atmospheric circulation pattern over Siberia and the East Sea (Japan Sea). Besides, warm winter water facilitated the enhanced release of latent heat fluxes as a precondition. The oceanic heat redistribution partially supported the cold anomaly in the surface layer up to the middle of May through positive feedback between the low surface temperature and the active entrainment associated with tidal turbulent mixing. The resultant low temperature at the surface weakened the vertical stratification, both impeding the activation of phytoplankton’s photosynthesis albeit under the eutrophic surface layer, consequently resulting in the delayed and suppressed spring bloom during 2020. Since such extreme events are anticipated to occur more frequently under global warming, our results highlight the importance of continuously monitoring multi-disciplinary environmental conditions, climate extremes, and their impact on the Yellow Sea marine ecosystem.

Causes for an extreme cold condition over Northeast Asia during April 2020

“…Our study highlights that extreme Siberian blocking and strong EAWR pattern influenced the dipole atmospheric circulation causing the cold condition in Northeast Asia during April 2020. This cold condition seriously harmed agricultural and marine ecosystems, such as fruit tree blossoms, farm sprouts, and phytoplankton spring blooms 7 , during the peak growth period over northeastern Asia, resulting in great economic losses throughout this region ( www.cma.gov.cn and www.mafra.go.kr ). Therefore, the current results will provide a better understanding of the extreme weather or climate conditions over northeastern Asia in April and may aid in decreasing the associated damage to land–ocean ecosystems.…”

“…Our study highlights that extreme Siberian blocking and strong EAWR pattern influenced the dipole atmospheric circulation causing the cold condition in Northeast Asia during April 2020. This cold condition seriously harmed agricultural and marine ecosystems, such as fruit tree blossoms, farm sprouts, and phytoplankton spring blooms 7 , during the peak growth period over northeastern Asia, resulting in great economic losses throughout this region (www. cma.…”

“…The severe cold environment in April 2020 had a negative influence on not only the land in North China and Korea but also the marine ecosystem of the Yellow Sea. Kim et al 7 identified the slowest water temperature evolution over the northeastern basin of the Yellow Sea for spring 2020 in the last four decades. This record-breaking evolution from March to May was principally attributed to the exceptional latent heat release in April 2020 via robust northwesterly wind and high sea surface temperature that was partially caused by warm winter water.…”

“…Interestingly, such a cold winter environment occurred during April 2020 in Northeast Asia. Previous studies have proposed that the anomalous anticyclonic circulation was located over Siberia, accompanying the cyclonic circulation anomaly over the East Sea (also referred to as the Japan Sea) in April 2020 6 , 7 . This dipole circulation led to the strong northerly flow resulting in the cold condition in Northeast Asia 6 , 7 .…”

“…Previous studies have proposed that the anomalous anticyclonic circulation was located over Siberia, accompanying the cyclonic circulation anomaly over the East Sea (also referred to as the Japan Sea) in April 2020 6 , 7 . This dipole circulation led to the strong northerly flow resulting in the cold condition in Northeast Asia 6 , 7 . However, the specific cause of the atmospheric dipole structure in April 2020 remains unknown.…”