Early to middle Holocene development of the Tsushima Warm Current based on benthic and planktonic foraminifera in the Nakdong River delta (southeast Korea)

Fossil benthic and planktonic foraminifera from a part of core ND-02 and the published data of core ND-01 from the Nakdong River delta, southeast Korea were analyzed to evaluate the impact of the Tsushima Warm Current on coastal environments in the Korea/Tsushima Strait between Korea and Japan during the early to middle Holocene. Based on cluster analysis, four sample clusters (A, B, C, and D), suggestive of a landward–seaward gradient of environmental conditions, can be defined. According to the spatio-temporal and cluster distributions of benthic foraminifera in faunal compositions, the landward occurrence of benthic foraminifera was delimited in the inner part of the Nakdong River delta at ∼8–7 ka. The common occurrence of warm-water planktonic foraminifera suggests that this maximum landward expansion of benthic foraminifera within the delta was caused by the intensification of the Tsushima Warm Current in addition to sea level rise during the early to middle Holocene. Changes in both marine biota and sedimentation were reported in the coastal areas of southwestern Japan in that period. They were also caused by a precursor of the enhanced Tsushima Warm Current at ∼8 ka. Thus, the evolution of the Tsushima Warm Current during the early to middle Holocene is important for understanding various phenomena in the coastal environments of the Korea/Tsushima Strait.