Long-Term Variability of the East Sea Intermediate Water Thickness: Regime Shift of Intermediate Layer in the Mid-1990s

Abstract

The shipboard measurements over approximately 55 years in the southwestern part of the East Sea (Sea of Japan) demonstrate a remarkable basin-wide, interannual-interdecadal variability in the temperature-based thickness of the East Sea Intermediate Water (ESIW) whose temporal variability shows strong correlation with the density-based thickness (r = 0.97). Relevant to the long-term variability of the ESIW thickness, clear changes in horizonal and vertical features have been observed at the intermediate layer in the mid-1990s, such as 1) increases in vertical temperature gradient in the thermocline by shoaling of 2°C–5°C isotherms, 2) relatively high correlations among isotherms in the interdecadal timescale, 3) appearance of zonal phase difference in the ESIW thickness variability after the mid-1990s, and 4) correlation phase change between the Arctic Oscillation Index and the ESIW thickness. The ESIW thickness could be smaller when its formation is weaker and when the formation of deep-water mass below it becomes stronger. Based on the features observed, we hypothesized on the regime shift concerning the East Sea meridional overturning circulation; before the mid-1990s, active deep-water formation mainly controlled the ESIW layer variability, but after the mid-1990s, the ESIW formation rate predominantly affected its own thickness variability.

Carbon cycling in the East Sea (Japan Sea): A review

“…series of chlorophyll-a concentrations from the EJS over the period 2003-2020 and found that chlorophyll-a concentration increased in most of the EJS. Wind speed and direction, and SST, which are important physical parameters affecting the long-term trend in chlorophyll-a concentration, also showed characteristic trends and were related to Arctic Oscillation index variability (Park, 2022).…”

Climate‐Driven Fluctuations in Anthropogenic CO2 Uptake by the East Sea in the North Pacific Ocean

“…This facilitates effective ventilation in the East Sea, in response to even minor surface perturbations. The second driver is the frequent formation of cold and dense surface water associated with variations in the Arctic Oscillation (AO) (Cui & Senjyu, 2010; Nam et al., 2016; Park, 2022). These climate‐driven changes in ventilation intensity can either diminish or enhance the transfer of C ANTH ‐enriched surface water to the basin interior (Min & Warner, 2005; Park et al., 2006).…”