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<p>Sortable silt (SS), defined as the 10–63&#xa0;μm grain size fraction, responds sensitively to variations in deep-sea bottom current speeds. The mean size of sortable silt (SS_Mz) has been widely used as a proxy for reconstructing relative changes in past bottom current strength. Although a quantitative relationship between SS_Mz and bottom current speed was recently proposed for the Atlantic Ocean, its broader application is limited due to differences in sediment size composition and bottom circulation patterns in other oceanic regions. This study aims to develop a new regional calibration applicable to the East Sea (Japan Sea) by comparing SS_Mz values from surface sediments on the continental slope with bottom current speeds derived from GLORYS ocean reanalysis data. Preliminary results show that SS_Mz correlates strongly with modeled bottom current speeds, particularly at sites with pronounced changes in bottom velocity associated with steep seafloor morphology. The sensitivity of current speed change to SS_Mz variation, derived from the resulting calibration, is 0.19&#xa0;cm s⁻¹ µm⁻¹, which is significantly lower than the 1.36&#xa0;cm s⁻¹ µm⁻¹ previously reported for the Atlantic. This discrepancy is mainly attributed to the generally weaker bottom current regime of the East Sea. Further calibration efforts across diverse depositional settings, together with higher resolution current models and in situ measurements, are needed to enhance the applicability of SS_Mz as a quantitative current speed proxy in this region.</p>

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Calibration of sortable silt mean size to bottom current speeds in the East Sea (Japan Sea): challenges and prospects

  • 期刊论文

  • 发表日期：

    2025年12月6日

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  • Jang-Jun Bahk,
  • Gyutae Sim,
  • Haedo Baek,
  • Dong Eun Lee,
  • In-Kwon Um

摘要

Sortable silt (SS), defined as the 10–63 μm grain size fraction, responds sensitively to variations in deep-sea bottom current speeds. The mean size of sortable silt (SS_Mz) has been widely used as a proxy for reconstructing relative changes in past bottom current strength. Although a quantitative relationship between SS_Mz and bottom current speed was recently proposed for the Atlantic Ocean, its broader application is limited due to differences in sediment size composition and bottom circulation patterns in other oceanic regions. This study aims to develop a new regional calibration applicable to the East Sea (Japan Sea) by comparing SS_Mz values from surface sediments on the continental slope with bottom current speeds derived from GLORYS ocean reanalysis data. Preliminary results show that SS_Mz correlates strongly with modeled bottom current speeds, particularly at sites with pronounced changes in bottom velocity associated with steep seafloor morphology. The sensitivity of current speed change to SS_Mz variation, derived from the resulting calibration, is 0.19 cm s⁻¹ µm⁻¹, which is significantly lower than the 1.36 cm s⁻¹ µm⁻¹ previously reported for the Atlantic. This discrepancy is mainly attributed to the generally weaker bottom current regime of the East Sea. Further calibration efforts across diverse depositional settings, together with higher resolution current models and in situ measurements, are needed to enhance the applicability of SS_Mz as a quantitative current speed proxy in this region.