This paper is the result of coastal geological survey engineering.

Objective More and more high resolution paleoclimatic records confirm that a number of subcentennial climate abrupt change events were exit in the Holocene. Such abrupt climate change events had a very close relationship with the social and economic development of human. 4.2 ka BP event are recorded in Asia, North America, the Mediterranean, Southern Europe and other places which indicated that this event were global in extent. However, the record of this evnent has not been adequently substantiated in the coastal zone, especially in northern China muddy coastal zones.

Methods This paper focuses on three buried oyster reefs and their overlying mud layers located 1−6 km apart on the northwest coast of Bohai Bay, namely Lingtou, Zengkouhe and the sourthern part of Biaokou. Through diatom analysis (83 samples), AMS ¹⁴C dating (32 data) and sedimentological research, the environmental information recorded by the reefs and overlying mud layers was reconstructed, and the possible imprints of the ‘4.2 ka BP event’ in the coastal zone were discussed.

Results The study area experienced a transgression−regression environment evolution from upper tidal salt marsh to intertidal zone in the Early Holocene→subtidal zone to lower and middle part of intertidal zone to middle and upper part of intertidal zone in the Mid−Holocene→salt marsh lowlands in the Late Holocene. At about 7 ka cal BP ago, three reefs appeared one after another, and as the reefs build up, the influence of the seawater become weakened. At about 5−4.3 ka cal BP, the three reefs entered the lower and middle part of the intertidal zone, the climate became colder and lead the three reefs be buried at the same time of 4.2−4 ka cal BP and covered by the overlying mud immediately.

Conclusions A climate fluctuation process occurred during 5−4 ka cal BP in the study area. The climate became colder during 5−4.3 ka cal BP, and gradually warmed after 4.3 ka cal BP. The turning point of the climate change occurred at about 4.3 ka cal BP. We speculate that this climate fluctuation was probably a response to the ‘4.2 ka BP event’ in the north muddy coast of China.