Table 1 The results of principal component analysis (PCA) on the Chiba composite section records. The percentage of the total variance explained and correlation coefficient (loading) for each mode are presented according to taxa

PC1

PC2

PC3

PC4

PC5

PC6

36.3

15.4

9.7

8.2

6.5

5.1

Microfossil group

Taxa

Radiolarians

Tetrapyle spp.

-0.14

0.14

0.34

0.15

0.49

0.12

Spongodiscus resurgens

0.07

0.25

0.42

-0.05

0.16

0.33

Lithomelissa setosa

0.27

-0.35

-0.07

-0.08

0.19

-0.43

Didymocyrtis spp.

-0.21

0.01

-0.16

0.25

-0.36

-0.28

Dictyocoryne spp.

-0.17

0.43

-0.01

0.13

-0.01

0.01

Cycladophora davisiana

0.00

-0.16

-0.22

-0.34

-0.32

0.59

Calcareous nannofossils

Calcidiscus leptoporus

-0.20

-0.16

-0.25

0.50

0.06

0.19

Coccolithus pelagicus braarudii

0.34

0.11

-0.09

-0.23

-0.10

-0.04

Coccolithus pelagicus pelagicus

0.05

0.24

0.02

-0.47

0.04

-0.18

Umbilicosphaera spp.

-0.35

0.10

0.08

0.00

-0.14

-0.06

Helicosphaera spp.

-0.20

-0.37

0.16

0.08

0.02

0.02

Florisphaera profunda

-0.33

-0.04

0.11

-0.28

0.11

-0.21

Geochemical proxies

G. bulloides δ¹³C

-0.26

-0.16

-0.33

-0.23

0.37

0.01

G. bulloides δ¹⁸O

0.32

-0.08

-0.04

0.15

0.30

0.03

G. inflata δ¹³C

-0.27

-0.35

0.21

-0.20

0.05

-0.09

G. inflata δ¹⁸O

0.39

-0.15

0.14

0.20

0.00

-0.01

G. inflata Mg/Ca

-0.02

0.35

-0.09

0.09

-0.05

-0.35

δ¹³C difference (Δδ¹³C_inf-bul)

-0.01

-0.19

0.54

0.03

-0.32

-0.09

δ¹⁸O difference (Δδ¹⁸O_inf-bul)

0.08

-0.07

0.18

0.04

-0.30

-0.04