## 2 Materials and Methods  
Gravity core ARA09C-St03 (475 cm long, 75.9174\({}^{\circ}\) N, 170.31887\({}^{\circ}\) W) was collected from the slope of the Chukchi Rise at a water depth of approximately 820 m by [PERSON] of KOPRI during the ARA09C cruise in 2018. The cores were subsampled at intervals of approximately 10 cm for mineralogical and Nd isotope analyses.  
For bulk sediment mineralogy, subsamples were dried and crushed using a ball mill, and then 4 g aliquot from the homogenized material. X-ray diffraction analysis was performed using a D8 Advanced A25/Bruker at the Department of Geology at Gyeongsang National University, and the analysis conditions were set to 40 Kv/40 mA, a step size of 0.02\({}^{\circ}\) 20 in the range of 4-70\({}^{\circ}\) 20 and a counting time of 0.4 s per step. Quantitative analysis of bulk minerals was performed using TOPAS software. The weighted profile R-factor (Rwp) was 20 or less, and the goodness of fit (GOF) was 3 or less to ensure adequate reliability.  
Clay mineral compositions were obtained using semi-quantitative results of oriented samples separated into <2 \(\upmu\)m particles. The organic matter of bulk sediment was removed using a 6% hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) solution. After they were sieved through a 63 \(\upmu\)m mesh, the clay particles were extracted using a settling technique based on Stoke's Law. To optimize the orientation of the specimens for XRD analyses, lumps of clay were smeared onto glass slides to minimize the grain-size effect. To identify each clay mineral, oriented samples were taken from both air-dried and ethylene glycol (EG)-treated samples. Relative abundances of four major clay minerals--illite, smectite, kaolinite, and chlorite--were estimated using a semi-quantitative calculation [28], which was used to weight integrated peak areas of characteristic basal reflections in the glycolated state using Eva 3.0 software with the empirical factor.  
Sand portions (>64 \(\upmu\)m) were calculated as a weight ratio using the weight of particles separated through sieving for the 4 g of dried subsamples. Particles >250 \(\upmu\)m were counted by separating through a 250 \(\upmu\)m mesh sieve. The micronodules in the separated IRD particles were analyzed for verification based on chemical composition using a field-emission electron probe micro analyzer (FE-EPMA), JXA-8530F PLUS/JEOL at Gyeongsang National University's Center of Research Facilities. Energy-dispersive spectroscopy (EDS) patterns and backscatter electron (BSE) images were obtained under the conditions of 15 keV, 10 nA, and a beam diameter of 5-10 \(\upmu\)m.  
Fourteen clay fraction samples were selected for Nd isotopic analysis. \({}^{143}\)Nd/\({}^{144}\)Nd analysis, including chemical separation and multicollector thermal ionization mass spectrometry (VG54-30, Isoprobe-T) analyses, were performed at the Korea Basic Science Institute. To correct isotope fractionation during the analysis, Nd isotope ratio was normalized to \({}^{146}\)Nd/\({}^{144}\)Nd = 0.7219 [29]. Analysis of the Nd standard JNdi-1 resulted in \({}^{143}\)Nd/\({}^{144}\)Nd = 0.512115 \(\pm\) 6. For convenience, the \(\varepsilon\)Nd parameter was calculated using a \({}^{143}\)Nd/\({}^{144}\)Nd value of 0.512638 for the Chondritic Uniform Reservoir (cNd = [(\({}^{143}\)Nd/\({}^{144}\)Nd)/0.512638 \(-\) 1] \(\times\) 10\({}^{4}\)).