Color b* value of sediment core LV76-21

The color b* values are widely used as a paleoproductivity proxy for the NW Pacific and its marginal seas (Nürnberg and Tiedemann, 2004; Riethdorf et al., 2013). The color b* index was measured onboard after sediment core splitting at 1 cm resolution using a Konica Minolta CM-700d spectrophotometer

Size fraction >63 µm determination of sediment core LV76-21

Sediment for IRD determination was sampled from 1 cm-thick slices with steps of 2–4 cm through the core. Samples with a dry weight of approximately 10 g were wet sieved using a 150 μm and 63 μm sieves. Coarse fraction >150 μm was decarbonized using 10% HCl, washed using distilled water, and dried. The ratio of weight percentage for the decarbonized coarse fraction (150–2,000 µm) relative to the weight of the dried bulk sediment were used as IRD. This is consistent with the commonly used size fraction > 150 μm for delimiting IRD (Hemming, 2004). Data in the intervals of the visible tephra layers were excluded from the IRD record because this material was delivered into sediment through the atmosphere, rather than by ice and, therefore, is not IRD. Need to understand that the nearby Kamchatka peninsula is area of active volcanism. Therefore, the determined IRD values (wt % of decarbonated fraction 150-2,000 µm) may include as terrigenous particles as volcanic particles, which were earlier fallout of the land during explosive volcanic eruptions, captured by sea ice and icebergs from the coast and land and then transferred into core location by water currents

Carbon concentration of sediment core LV76-21

The total carbon and inorganic carbon (CaCO3) contents were measured in sediment slices of 1 cm thickness with 2 cm resolution using an AN-7529 coulometer (Gorbarenko et al., 1998). The total organic carbon (TOC) content in the sediment was calculated using the difference between the total carbon and inorganic carbon contents

Stable oxygen isotope record of Uvigerina auberiana of sediment core LV76-21

Sediments for the δ18O of planktic and benthic foraminifera analysis from core LV76-21 were sampled from 1 cm-thick slices with step of 2–5 cm along the core length. Foraminifera shells were picked from the sediment fractions of 150-250 µm in the samples where they were available. The δ18O of planktic and benthic foraminifera were measured at Tongji University (China) and at the Far Eastern Geological Institute (Russia). Isotope measurements from Tongji University were provided using a Finnigan‐MAT 252 mass spectrometer. The results were validated against a Chinese national carbonate standard (GBW04405) and NBS‐19. The standard deviation is 0.07‰ for δ18O. The isotope measurements from the Far Eastern Geological Institute were analyzed using a Finnigan-MAT 253 mass spectrometer with modification of Velivetskaya et al. (2009) without preliminary roasting. The standard deviation for the δ18O values is ± 0.05‰. All the values are reported on the Pee Dee Belemnite (PDB) scale

Results of analysis of sediment core LV76-21 from Detroit Seamount

The sediment core LV76-21 was recovered from northwest of the Detroit Seamount (51°34’N, 167°15.7’E; water depth 2,769 m) using a gravity corer on the R/V “Akademik M.A. Lavrentyev” during joint Russian–Chinese expeditions in 2016. The core sediments were predominantly gray–olive gray terrigenous silty clay–clayey silt with rare sand. The sediment was coarser in the intervals of 144–167 and 434–456 cm. The upper 17 cm of the sediment was represented by an oxidized brown–gray-brown ooze. In the intervals 0–38 cm, 76–167 cm, 356–364 cm, 407–434 cm, 456–475 cm, and 519–546 cm, the sediments were represented by grayish-olive–olive weakly diatomaceous oozes. The sediments in the intervals of 0–144 cm and 519–546 cm were enriched with foraminifera shells, and sediments were weakly enriched with foraminifera at the intervals of 407–434 cm, 456–482 cm, and 546–557 cm. The lithological description shows three visible ash layers at depths of 364–366 cm, 397–404 cm, and 467–468.5 cm, with thin ash lenses at a depth of 477–479 cm

Element concentrations of sediment core LV76-21

Nearly 30 mg of sediment was sampled with steps of 1 cm through the core depth for element content analyses. The sediment was compressed into tablets of 5 mm in diameter and 0.13 g×cm^−2 in the surface density following the methods of Phedorin et al. (2007). The concentrations of elements were measured using the method of X-ray fluorescence analysis using synchrotron radiation at the collective station VEPP 3 (Institute of Nuclear Physics, Novosibirsk, Russia) following the method of Piminov et al. (2016). The concentration of Rb and Ti in the sediment is used as an indicator of terrigenous material accumulation in the sediments and V content as proxy of the redox condition at the bottom (Bodin et al., 2007; Colman et al., 1995; Goldberg et al., 2007). Ratio Y/Rb is used as indicator of volcanic material input (Gorbarenko et al., 2014)

Benthic foraminifera abundances of sediment core LV76-21

Benthic foraminifera were studied in the core LV76-21 sediments sampled in 1 cm-thick slices. All the samples were dried, weighted, and wet sieved using a 63 μm sieve. The benthic foraminifera shells were picked and counted from the 63–250 μm sediment fraction. In total, 222 samples were analyzed at an average resolution of 2.5 cm (range 1–5 cm). Almost all the samples had enough microfossils for representative evaluation, except for intervals 365 cm, 398–408 cm, 435–440 cm, 444–465 cm, and 490–510 cm, where foraminifera were rare or absent. The total benthic foraminifera abundance (BFA) expressed as the number of shells per 1 g of dry sediment (shells x g^−1)

Stable oxygen isotope record of Cibicidoides spp. of sediment core LV76-21

Sediments for the δ18O of planktic and benthic foraminifera analysis from core LV76-21 were sampled from 1 cm-thick slices with step of 2–5 cm along the core length. Foraminifera shells were picked from the sediment fractions of 150-250 µm in the samples where they were available. The δ18O of planktic and benthic foraminifera were measured at Tongji University (China) and at the Far Eastern Geological Institute (Russia). Isotope measurements from Tongji University were provided using a Finnigan‐MAT 252 mass spectrometer. The results were validated against a Chinese national carbonate standard (GBW04405) and NBS‐19. The standard deviation is 0.07‰ for δ18O. The isotope measurements from the Far Eastern Geological Institute were analyzed using a Finnigan-MAT 253 mass spectrometer with modification of Velivetskaya et al. (2009) without preliminary roasting. The standard deviation for the δ18O values is ± 0.05‰. All the values are reported on the Pee Dee Belemnite (PDB) scale

Age determination of sediment core LV76-21

Eight samples of monospecific planktic foraminifera of Neogloboquadrina pachyderma (sin.) with a weight of 4–6 mg were picked from the >125‐μm size fraction and measured in the Beta Analytic Radiocarbon Dating Laboratory. Conventional accelerator mass spectrometer (AMS) 14C ages were calibrated to calendar ages using Calib 8.20 with the Marine20 calibration curve (Heaton et al., 2020) and the ΔR of 350 ± 40 years according to the reservoir age of the far NW Pacific equal to 900 years (Max et al., 2012). The resultant AMS 14C data along with other time points were used for age model construction

Size fraction >150 µm determination of sediment core LV76-21

Sediment for IRD determination was sampled from 1 cm-thick slices with steps of 2–4 cm through the core. Samples with a dry weight of approximately 10 g were wet sieved using a 150 μm and 63 μm sieves. Coarse fraction >150 μm was decarbonized using 10% HCl, washed using distilled water, and dried. The ratio of weight percentage for the decarbonized coarse fraction (150–2,000 µm) relative to the weight of the dried bulk sediment were used as IRD. This is consistent with the commonly used size fraction > 150 μm for delimiting IRD (Hemming, 2004). Data in the intervals of the visible tephra layers were excluded from the IRD record because this material was delivered into sediment through the atmosphere, rather than by ice and, therefore, is not IRD. Need to understand that the nearby Kamchatka peninsula is area of active volcanism. Therefore, the determined IRD values (wt % of decarbonated fraction 150-2,000 µm) may include as terrigenous particles as volcanic particles, which were earlier fallout of the land during explosive volcanic eruptions, captured by sea ice and icebergs from the coast and land and then transferred into core location by water currents