Dynamics of planktonic foraminiferal community in the Sea of Japan during the last 2 My

Abstract

Based on the analysis of the foraminiferal assemblages in 118 sediment samples from the 210-m-long core of ODP Hole 798 drilled near Honshu Island, it is shown that the structure of their tanathocoenoses experienced three large reorganizations during the last 1.9 My, namely 0.68, 1.21, and 1.36 My B.P. The first reorganization coincides with the Matuyama-Brunhes boundary marked by the magnetic polarity reversal. The second reorganization corresponds to the sharp and progressive temperature fall caused by general climate deterioration. The third event is poorly interpretable thus far. Using the K-average method, the assemblages were differentiated into two types differing in their taxonomic structures. The replacement of one type of community with another occurred simultaneously with the cooling onset 1.21 My B.P. Spectral analysis of the variations in the integral characteristics of the taxonomic structure revealed three groups of cycles with average periods of 136, 59, and 33 ky. These estimates are one-third higher as compared to the duration of the Milankovitch climatic cycles. The species structure of the foraminiferal community is shown to be well consistent with the rank model of geometric series.