Biogenic opal production changes during the Mid-Pleistocene Transition in the Bering Sea (IODP Expedition 323 Site U1343)

Abstract

Biogenic opal content and mass accumulation rate (MAR) at IODP Expedition 323 Site U1343 were found to fluctuate consistently, generally being high under warm conditions and low under cold conditions during the last 2.4Ma. Continuous wavelet transform analysis of the normalized biogenic opal content indicates that export production in the Bering Sea varied predominantly at 41-ka periodicity before 1.25Ma, and shifted to 100-ka periodicity at the onset of the Mid-Pleistocene Transition (MPT; 1.25–0.7Ma). The 100-kacycles dominated until the Holocene. Export production in the Bering Sea decreased markedly in the Bering Sea two times during the MPT: the first occurred at the beginning of the MPT (1.25Ma) and the second in the middle of the MPT (0.9Ma). These decreases coincided with both increases in the relative abundance of sea-ice diatoms and decreases in the warm-water diatom species Neodenticula seminae, indicating that reductions in export production in the Bering Sea during the MPT were associated with climate cooling. Decreases in export production in the Bering Sea during the MPT were most likely associated with the increased influence of polar/Arctic domains on the high-latitude North Pacific.