Upwelling processes driven by contributions from wind and current in the Southwest East Sea (Japan Sea)

Abstract

The occurrence of coastal upwelling is influenced by the intensity and duration of sea surface wind stress and geophysical components such as vertical stratification, bottom topography, and the entrainment of water masses. In addition, strong alongshore currents can drive upwelling. Accordingly, this study analyzes how wind stress and ocean currents contribute to changing coastal upwelling along the southwest coast of the East Sea (Japan Sea), which has not yet been reported quantitatively. This study aims to estimate each geophysical factor affecting upwelling processes using the Upwelling Age index. The index assesses the major contributors to the upwelling process using the relationship between physical forcing and upwelling water fraction estimated from shipboard hydrographic data from January 1993 to October 2018. These findings reveal that wind-driven upwelling was dominant off the northern coast. In contrast, current-driven upwelling prevailed off the southern coast. These results suggest that persistent alongshore currents through the Korea Strait make the southern region a prolific upwelling area. Accordingly, it can shed light on the mechanisms of coastal upwelling in the study area, which is crucial for understanding the influence of physical forces on ocean ecosystems.

Quantification of the extremely intensified East Korea Warm Current in the summer of 2021: offshore and coastal variabilities

“…During summer, wind-driven upwelling due to monsoonal southerly winds occurs at the east coast of Korea (Park and Kim, 2010;Jung and Cho, 2020;Kim et al, 2023). We thus expect climatological northward wind stress in that area (Figure 11A).…”

“…The East/Japan Sea, a semi-closed marginal sea located in the mid-latitude region of the Northwest Pacific, serves as a natural laboratory because it mirrors characteristic processes occurring in the open ocean. Notable phenomena in this marginal sea include a meridional overturning circulation (Kim et al, 2004;Chang et al, 2016;Han et al, 2020), ventilation of subsurface cold water (Yun et al, 2004;Kim et al, 2009;Park and Lim, 2018), the western boundary current named as East Korea Warm Current (EKWC; Kim et al, 2018), the subpolar front (Park et al, 2004), eddies (Lee and Niiler, 2010a;Lee et al, 2019), and various coastal processes, such as coastal upwelling by monsoonal southerly winds (Park and Nam, 2018;Kim et al, 2023) and coastal trapped waves (Cho et al, 2014;Lee et al, 2022).…”

Morphology of Hobagella saltata n. gen. and n. sp. (Syndiniophyceae, Miozoa) infecting the marine dinoflagellate Cucumeridinium coeruleum (Dinophyceae, Miozoa) and its potential onshore advection

“…The increase in SST in the Korea Strait and near the Korean coast appeared to be associated with the increased intensity of the East Korea Warm Current (EKWC) and the Tsushima Warm Current (TWC) preceding and during the storms. For example, SST near the southeastern coast of Korea one to two weeks prior to Typhoon KROSA ranged from 18-24°C (Figures 7A, B), possibly reflecting the upwelling of cool water, as frequently occurs in that region during summer (Yoo and Park, 2009;Kim et al, 2023), while offshore water extending to the eastern side of the Korea Strait was 25-27°C. When Typhoon KROSA was positioned south of Japan (24-26°N) on 12 August, the lens of cool water adjacent to the Korean coast was replaced by water ranging from 24-26°C (Figure 7C), with temperature rising to 27-28°C by 15 August as the storm reached 35°N, crossing Japan to the East Sea (Figure 7D).…”