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Progress in Earth and Planetary Science
Fig. 2 | Progress in Earth and Planetary Science

Fig. 2

From: Climatic reconstruction at the Sannai-Maruyama site between Bond events 4 and 3—implication for the collapse of the society at 4.2 ka event

Fig. 2

Time series records of a alkenone SSTs and estimated ATs in Mutsu Bay with age-controlling points represented in solid reversed triangles (Kawahata et al. 2009b); b alkenone SSTs and ATs at St. 5 Funka Bay (Kawahata 2017); c content of hematite-stained grains as drift ice indices in the north Atlantic with the number of Bond events (Bond et al. 1997); d relative abundances of Emiliania huxleyi and Gephyrocapsa oceanica; e the first factor (VF1) of ostracods (Irizuki et al. 2015); f δ18O values of benthic foraminifera (Nonionella stella (Cushman) and Nonionellina labradorica (Dawson)); g δ 13C values of benthic foraminifera (N. stella (Cushman) and N. labradorica (Dawson)); h relative abundances of Castanea, Picea, and Abies (Kawahata et al. 2009b); i Gini-Simpson index for pollen (upper: including Castenea, lower: excluding Castenea); and j accumulation rate of alkenone (Kawahata et al. 2009b). In the upper column, periods are classified based on the SST: periods 8 (8.3–7.9 cal. kyr B.P.), 6 (7.0–5.9 cal. kyr B.P.), 4 (5.1–4.1 cal. kyr B.P.), and 2 (2.3–1.4 cal. kyr B.P.) were characterized by warm alkenone SSTs with mean values of 23.4, 23.4, 23.8, and 23.5 °C, respectively. In contrast, periods 7 (7.9–7.0 cal. kyr B.P.), 5 (5.9–5.1 cal. kyr B.P.), and 3 (4.1–2.3 cal. kyr B.P.) were characterized by cold alkenone SSTs with mean values of 21.6, 22.8, 22.9, and 22.7 °C, respectively (Kawahata et al. 2009b). Orange and yellow shadings represent very and relatively warm environments, respectively, after the sea level was stabilized around 6.2 cal. kyr BP. The water-column structure of the Tsugaru Strait as reconstructed by Kuroyanagi et al. (2006) is shown in the second column. During 9.0–6.2 cal. kyr BP, the intensity of the Tsugaru Warm Current (TWC) was weak and the subsurface water remained under the influence of the cold Oyashio Current. The modern oceanographic regime was established at 6.2 cal. kyr BP, when the subsurface waters began to warm as a result of the enhanced flow rate of the TWC. Only TWC flows along the Tsugaru Straight since 3.4 cal. kyr BP. Light gray shading represents water influenced by warm currents

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