## 4 Discussion  
### Age Assignment  
Marine sediments in the Arctic Ocean, including records of paleoenvironmental change, have been studied for the purpose of reconstructing sedimentary environments using lithological, geochemical, mineralogical, and biological techniques [9; 21; 23; 27]. These various studies provide a correlation between the chronology and sediment characteristics of the core sediments in the western Arctic during the glacial/stadial and interglacial/interstadial periods of the Quaternary period [27]. In general, core sediments in the western Arctic Ocean exhibit distinct cycles in sediment color and composition, expressed as brown and gray mud and the presence of coarse grain content in several layers [2; 8; 27]. Brown-colored sediments form due to the increased supply of organic matter and large amounts of Mn flux from the continents in response to warmer climates; thus, brown units in Quaternary Arctic Ocean sediments are commonly interglacial or major interstadial deposits [30; 31]. These brown units exhibited generally high Mn content and biogenic carbonate with a vigorously bioturbated nature and sometimes included micronodules [21; 23; 27]. By contrast, glacial sediments appear gray to dark gray due to a decrease in Mn supply [21; 23; 27]. In addition, correlation tie points are provided by rare  
Figure 3: Down-core variation in mineralogical and Nd isotope data in core ARA09C-St03. The dotted lines represent the boundaries of separated units. Q/F: quartz/feldspar. K/C: kaolinite/chlorite. or unique events, such as abundant ice-rafted debris (IRD), and the PW layer expressed prominent detrital carbonate peaks [21; 23; 27]. Age assignment of ARA09C-St03 was established by comparing the lithological description, IRD content, and carbonate mineral contents with surrounding cores [21; 23] for which age had been established (Figures 2 and 3). The surficial brown B1 layer (0-5 cm) indicates the Holocene, which is corroborated by numerous AMS \({}^{14}\)C dates typically showing the age of 10-12 ka at its base in sediment cores from various regions of the Arctic Ocean [27]. The subsequent brown B2 layer (180 to 190 cm) is AMS \({}^{14}\)C/AAR dated in multiple cores from the major ridges and basins with a consistent pattern of ages around 40-45 ka for its base [23; 27]. The stratigraphically important PW layer, generally located in the upper part of B2, has an age of around 40 [23; 27]. These ages and arrangements in which PW is placed on the B2 indicate that this conspicuous brown unit in core ARA09C-St03 represents a prominent interstadial within MIS 3. Micronodules below B2 layer were also found in the adjacent core 03M03 [23], which may indicate a warm period and support the core-to-core correlation of B2. The upper gray unit between B1 and B2 could be divided into two intervals by IRD content. Core PC04 in the Chukchi Rise exhibits similar deposition [21], suggesting that IRD-rich and mud layers indicate the deglacial and glacial periods of MIS 2, respectively. Age control for Pleistocene Arctic Ocean sediment beyond the range of \({}^{14}\)C dating remains unclear [27]. The conspicuous horizon with a PW layer below B3 has been proposed to be close to either the MIS 5/4 boundary (\(\sim\)70 ka) or the MIS 4/3 boundary (\(\sim\)55 ka) based on the abundance of some foraminifers and calcareous namnofossils [27; 32; 33]. [PERSON] et al. [27] suggested that integrated stratigraphy in the western Arctic demonstrates a consistent, thick, yellowish-gray unit between brown layers B2 and B3, justifying the assignment to MIS 4/3. Accordingly, core ARA09C-St03 preserves a presumably sequential record from the late MIS 5 to the Holocene. Many cores in the western Arctic Ocean have significantly condensed sections or hiatuses between MIS 1 and MIS 3, which have been attributed to low to no sedimentation owing to a very solid sea ice cover or an ice shelf during the Last Glacial Maximum (LGM) in MIS 2 [22; 23; 32].